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I doubt his dyno sheets are backward, the file # looks to be sequential with the lower rating being an older file. However, you are right, the secondaries are not fully opening, which means there could be some top end power left on the table. Based on the size of the ports, it may not matter though, and sometimes leaving them tilted helps with atomization.
Walk me through this, so I understand.
So the springs hold the secondaries closed. They can be pulled open with the vacuum actuator. There is a vacuum solenoid inline with the vacuum source which is controlled by the ECU. When the solenoid is closed, the actuator is released and sees no vacuum, the springs pull the secondaries shut. When the solenoid is opened, the actuator pulls vacuum which over powers the springs. What is the source of the vacuum? Normally vacuum secondaries pull from venturi vacuum which increases with RPM, but I'm guessing there isn't a venturi on this throttle body. Is it from a reservoir that stores vacuum instead? I bet it's a real kick in the butt when the ECU releases that solenoid on the street....but I wonder how the throttle response is when all you have is an on-off switch for those secondaries.
Anyway, really cool video and I bet it's a hoot to drive. I've been able to get my 4 48mm throttle bodies to work on my 13b after much headache, but in the end, it still has a very sensitive throttle with huge difference between 3-10% throttle for cruising. If they weren't paired in a manner that prevents me from doing this, I would certainly find a way to incorporate something similar.
from the original post: " Here's the throttle staging in action. (It has since been adjusted so the secondaries open fully) "
Not sure what is meant by backwards. 116 was the first dyno with carb. 162 was second dyno with EFI and fully opening secondaries.
chuyler1, your description is exactly how I understand it. I haven't seen the car myself, yet, so I can't elaborate any further. There is a vacuum reservoir in the system and I'd guess it takes its vacuum source from the same place the brake booster does. Probably from a port in the manifold, or under the primary throttles on the TB itself. As you know, at idle, there's plenty of vacuum below the throttles.
I asked for the secondary 'switching' point to be dependent on A) a full throttle condition and B) the rpm at which dyno testing shows either i) primaries-only power starts to fall off, or ii) secondaries-open power exceeds primaries-only power-- Whichever came first. That means I figured it was possible that the point at which open-secondaries began to make better torque might actually be higher than the point at which primaries-only began to fall off, which would create a step in the dyno plot. That doesn't appear to be the case, although you can see there is a tiny dip at 3900rpm. I don't know if that is the secondaries-open point, or what. It could be that there is about 100rpm where the either the engine needs more air and isn't getting it during the time it takes for the primaries to open, or conversely during that 100rpm there is more air than the engine needs. Or maybe it is tuning related, the tuner did say that the Haltech Sprint RE is 'somewhat limited' in what it can do. I've so many questions, but busy guys are hard to pin down.
I can't wait to try it myself, but it'll be a few months yet. I'll take some pics and vids and put descriptions on here for any who are interested.
The manager of the shop doing the work on the car (and long-time friend of mine) says the car is totally different and way better. I believe him unreservedly. Very excited!
Can you send me a pic of your throttle bodies and their linkages? I might have an idea that could help you.
Thanks for the explanation. I think the only concern I'd have with your setup would be with Autocross or circuit racing. Let's say you are keeping the car above 4,000RPM, which is above the point where you'd be running just primaries. You're exiting a turn and you ease into the throttle, going from 50% all the way to 100% over the course of a few seconds controlling your speed and grip. However, the moment you reach 100% throttle the secondaries snap open all the way, you break traction and spin out. This doesn't happen with typical carburetor secondaries because they would already be trying to open in sync with the primaries through a linkage that will lock them together when there is enough vacuum pressure. I don't see that in your linkage, in fact, when you lift off the throttle it takes a moment for the secondaries to actually close.
As for my setup, this photo should explain things. The two twin throttle bodies are linked in the center, but there is no way to separate them. I suppose I could attach a separate throttle body above the current ones that is controlled separately, or I could start over and put the throttle bodies in front of one another. But anyway, I do have it running, it's just very sensitive. Attachment 737596
Thanks for the explanation. I think the only concern I'd have with your setup would be with Autocross or circuit racing. Let's say you are keeping the car above 4,000RPM, which is above the point where you'd be running just primaries. You're exiting a turn and you ease into the throttle, going from 50% all the way to 100% over the course of a few seconds controlling your speed and grip. However, the moment you reach 100% throttle the secondaries snap open all the way, you break traction and spin out. This doesn't happen with typical carburetor secondaries because they would already be trying to open in sync with the primaries through a linkage that will lock them together when there is enough vacuum pressure. I don't see that in your linkage, in fact, when you lift off the throttle it takes a moment for the secondaries to actually close.
As for my setup, this photo should explain things. The two twin throttle bodies are linked in the center, but there is no way to separate them. I suppose I could attach a separate throttle body above the current ones that is controlled separately, or I could start over and put the throttle bodies in front of one another. But anyway, I do have it running, it's just very sensitive. Attachment 737596
Yes, I see you’re saying. My gut feeling is that it’s not going to be a problem. And I base that strictly on the flatness of the torque curve on the dyno plot. If there was a huge spike in it like how some turbo cars have, It might be difficult to control, especially in the corners as how you describe. Because the torque curve is so flat, I think maybe they got the operation of the system “bang on“. I do have many questions, and originally I did ask for a dyno plot of primaries only as well as a separate plot for all four open from the get-go. I don’t know if I have that or not, I don’t want to pester busy dudes until I know it’s not an inconvenient time. I have a couple ideas that might prove interesting to play with. The first and easiest is changing the RPM point at which the switch occurs. The next is putting a restrictor in the vacuum line to slow down the actuation of the secondaries. Again, these are just random ideas because I have not driven the car. It could very well be that it’s really really good the way it is and it does not need any fiddling. Time will tell!
I get an attachment link for the picture in your response, and click it and it says it’s invalid. Maybe this is another Apple phone problem, I’m gonna try it on my Samsung tablet
Yes, I see you’re saying. My gut feeling is that it’s not going to be a problem. And I base that strictly on the flatness of the torque curve on the dyno plot. If there was a huge spike in it like how some turbo cars have, It might be difficult to control, especially in the corners as how you describe. Because the torque curve is so flat, I think maybe they got the operation of the system “bang on“. I do have many questions, and originally I did ask for a dyno plot of primaries only as well as a separate plot for all four open from the get-go. I don’t know if I have that or not, I don’t want to pester busy dudes until I know it’s not an inconvenient time. I have a couple ideas that might prove interesting to play with. The first and easiest is changing the RPM point at which the switch occurs. The next is putting a restrictor in the vacuum line to slow down the actuation of the secondaries. Again, these are just random ideas because I have not driven the car. It could very well be that it’s really really good the way it is and it does not need any fiddling. Time will tell!
I get an attachment link for the picture in your response, and click it and it says it’s invalid. Maybe this is another Apple phone problem, I’m gonna try it on my Samsung tablet
i see it! Ok, good. Yes, I think we can reduce/eliminate your twitchy/on-off throttle response fairly easily. I’ll need my desktop computer to illustrate, which won’t be for a few more days.
In the meantime, what is that system, (looks great!) and do you have anymore closeup pics of the linkage?
The only thing I could think of was a second set of throttle plates above or below, Jenvey makes them, and remove the primary plates from each pair and have them open the secondaries via similar connection to yours.
Hi,
Ok, here's what I'd do to reduce or eliminate the twitchy-ness of the throttle. I did the same once in the past with an old VW Rabbit that had a large, single-butterfly throttle body replacing its much more intelligent double butterfly (one big one small-- guess which one opened first and when the second one opened?) throttle body.
Ok, the left half of the above sketch (don't dis the microsoft paint! haha) represents what you currently have for a 'throttle arm'-- the part which the throttle cable end attaches to and wraps around. Linkage connects this arm to the throttle shafts. Distance A and Distance B are close enough to being equal that it doesn't matter. Even if that were not true, it appears as though the arc along which the throttle cable rests is 1/4 of a perfect circle. This gives a 1:1 'pull ratio' (my term. engineers laugh if you want-- then shut up when realize you monkeys designed a throttle to give a twitchy on/off response when you didn't have to ) meaning for every millimeter of cable pull you get an equal millimeter of linkage pull. For ease in visualizing this (necessary for the likes of me) you can relate it to a bicycle where the crank gear is the same size as the sprocket gear on the wheel. Think of A as the radius of the sprocket gear and B as the radius of the crank gear. One turn of the crank equals one turn of the wheel. One mm of throttle cable pull equals one mm of linkage pull.
Anyone who has taken a good look at OE throttle bodies (and carbs, too) will see there's a certain amount of engineering put into making an engine not twitchy in its throttle response. The staged, 1-big-1-small butterflies in the old wabbit TBs, for example. Later VWs used a larger single butterfly, but riveted a wedge on the back side of the butterfly that acted as a restriction during he first 15 degrees (or so) of throttle movement, dulling throttle response until the user pushed the pedal down far enough to indicate that rapid acceleration was desired. Unfortunately, it would also act as a restriction at full throttle, but at least the manufacturing cost of a simple single butterfly was lower than the cool, older double units. (boo)
chuyler1, your TBs are gorgeous and undoubtedly do an excellent job of helping the engine make max power. They dropped the ball on driveability, however. Take a look at the right half of the above diagram. Same setup as your throttle arm but with a variable ratio. Like a CVT bicycle. Ok, never mind that analogy. Call it.... (I'm digging deep here) a 'fixed variable-ratio pull throttle arm'. It is displayed in the idle position. B2 is (let's just say) twice as long as A2. That gives a 1:2 ratio which means the throttle cable needs to be pulled 2mm to effect 1mm of linkage travel. To visualize this, I imagine an admittedly odd bicycle that has a crank gear half the size of wheel sprocket gear. Two turns of the crank equals one turn of the wheel. Good for hill climbing. Good for slowing down throttle response in relationship to pedal travel.
Now, we can't keep a 1:2 ratio from idle to WOT, otherwise you'd need 2x the pedal travel. So the arc along which the cable travels diminishes from 1:2 to 1:1 along the exact span (in degrees) of throttle arm rotation in both cases. C represents the change in pull ratios between the original arc (hard-to-see orange) and the F.V.R.P.T.A. (sigh... ok, engineers, permission to laugh) arc in blue. As you can see, the distance changes smoothly for the first 2/3rds of the pedal travel, then quickly meets 1:1 in the last 1/3rd. This gives your right foot the mechanical advantage to operate the throttle butterflies at a much more controllable rate for most of the normal driving (unless you're cop-bait like me) throttle positions, and gives a big, more sudden bump in the last bit where clearly all we want is to get a ticket (more likely for noise than speed, in my case)
You could design the throttle arm to have a 2.5 or 3-to-one pull ratio for 90% of it's travel, and then give a big whallop in the last (say) 10mm of pedal travel. My WANKTEC just kicked in, yo! (ummm. I mean, Wankel, of course... right? Never mind...)
The ratio and its variation along the arc could be anything, as long as the number of degrees of arm travel remains the same, and the free (exposed) length of throttle cable is long enough to clear the arm itself. 10:1 for 95% falling off a cliff to 1:1 in the last 5%... It would work. That is just an example, as it would likely be quite excessive. I could see 3:1 for 75% with a smooth curve to 1:1 in the last 25% being reasonable.
The only issue here is that you have a rigidly-clamped throttle cable housing. In the existing setup, the cable is always 'straight' out of the housing. With a variable ratio throttle arm, the cable would angle sideways somewhat as it interacted with the different ratios along the throttle arm arc. I expect there would be a certain amount of leeway where this simply wouldn't matter. But there would likely be a point (in increasing ratios) where the cable would start to rub against the ferrule at the end of the cable housing through which it exits. One way to combat this would be to increase the length of free, exposed cable by shortening the cable housing and clamping it further away from the throttle arm. This would reduce the total angle traveled side-to-side. Another way would be to have the cable mounted in a clamp that was free to flex (like how the hollow ball in a 'heim joint' rod end can move). Another thing you could do is replace the ferrule on the end of the cable (might require some cable surgery) with something that looks like the bell on the loud end of a trumpet.
To effect and test this, I would build a new throttle arm out of modeler's plywood (high grade stuff in hobby shops), or out of a little block of polypropylene plastic or similar. Something that can be sculpted easily with hand tools. A drill and a hacksaw could be used to get a chunk of plastic into a usable shape, then a length of old throttle cable or steel wire heated with a propane torch could melt a groove into the edge for the throttle cable to rest in. It only needs to last several minutes to test the chosen ratio and arc variation's effectiveness. Chances are it would last many months, but let's face it-- when you find your ideal throttle arm design, you'll want it made of metal. If you have some half-decent equipment and patience, you could make one of metal yourself. Most anything a CNC machine can make can also be made by hand, given enough (skill and equipment and) patience. Or, you could farm it out to a machine shop. (I may be of some assistance in that regard)
Just to really quickly test the effect, you could find something to space the cable out of its groove about 15mm, for the first 2/3rds of the travel. The tricky part here would be preventing it from slipping off the arm (like a bike chain falling off the crank gear). Clay might be effective here. remove the cable from the arm, and shape a piece of clay to fit into the existing cable groove in the arm, and that smoothly spreads wider from 1/3 back of where the cable end attaches to the rear end of the throttle arm. Be sure to have the clay form over the top and bottom surfaces of the arm for stability. then use an appropriate diameter piece of wire, or a drill bit or maybe the cable itself to press a groove into the clay for the cable to rest in. I bet if you worked a bunch of 2cm-long snippings of regular sewing thread into the clay beforehand, it would be more crack-resistant when being tugged on by the throttle cable once installed. Let it harden (bake in the oven?), glue it in place with some silicone and take if for a drive up the street and back. Keep in mind you will probably have to adjust the position of the throttle cable housing in its clamp, likely moving it a little closer to the throttle arm. Don't worry too much about displacement angle of the cable itself, it'll just be a couple-minute drive, and if it looks long-term problematic, you can apply one of the aforementioned solutions.
So, there you have it. By changing the pull ratio, and forming a custom arc that suits your 'how much and when' needs, you can dampen the throttle butterfly response to gas pedal travel, while still having WOT at 'pedal to the metal'. That should improve driveablility significantly. Like many things, some time invested in fiddling to sort it all out, but a long lasting and satisfying solution once complete.
Or not. After just re-reading all that, I suddenly feel quite lazy. Maybe I wouldn't bother. haha
That was a very long winded explanation. Let's say I start with a circle diameter of 8cm. The circumference of 1/4 of that circle is 6.25cm which we will consider the full length of wire required to go from 0% to 100%. I can create an oval with a long diameter of 10 and short diameter of 5.25 which has the same length over 1/4 the circumference of the above circle. If I go more "oval" than that it would probably make it too difficult to reach the final throttle opening, and I need to maintain that same circumference or else I need more pedal travel.
On the circle, the first and last cm of travel will result in a 14.4 degree change of both the input and output. On the oval, the first cm of travel will result in roughly 11.5 degree change while the last will result in 20.83 degree change.
Doing some rounding, here is the translation of throttle position to actual throttle opening...
Pedal: 1cm 2cm 3cm 4cm 5cm 6cm
Original:
14.4% 28.8% 43.2% 57.6% 72% 86.4% 100%
New:
11.5% ---.-% ---.-% ---.-% ---.-% 79.17% 100%
Given that most of my cruising is under 15% this isn't all that much of an improvement. Compare that to your setup. Initial tip in only opens the primaries which are smaller. I'd roughly say that's about 5-7% total potential.
Now I do have my setup running and driving. I have issues, but I can get the adaptronic 440d to dump enough fuel for me to rev the motor. I'm having issues changing gears if I lift off completely, but I think it's just a matter of fine tuning the transient table a little better. I'm not sure I'll be able to get there without a day at the dyno, but I'm going to keep trying.
Another thing I considered was adjusting the throttle so the gas pedal will only open the plates about 20-30% mechanically, then having an actuator like you have open them the rest of the way. I'd need a secondary switch on the gas pedal itself to disengage the actuator when I lift off though. But it sounds dangerous unless I can mechanically pull back on them when I release the gas pedal. It's the same issue I see with your setup. If that actuator sticks open for any reason, you are stuck with your primaries open and no mechanical way for them to close short of cutting power.
Yeah, my wind is often long in the attempt to be clear. Apologies!
I like the oval idea. It reminds me of a very long duration cam lobe-- very purposeful. Using that idea, yes perhaps the oval's 1st cm of pedal travel would only be a 2.9% difference vs the 8cm circle, but the second and third centimeters of pedal travel would give a difference of 17.3% and 31.7% difference respectively. 46.1% for the 4th.
Are you sure you're only using the first 1cm of pedal travel during normal driving? Thinking about my own car (pre-EFI, at least), the 1st cm of pedal travel was ok for lazily raising the engine speed to upper-mid RPM in neutral, but not good for much more than tortoise-like acceleration up to 30-40km/h through a couple or three gears. Holding a steady highway speed would take a few centimeters of pedal travel at least. Add a stern headwind or a bit of an uphill slope, add another cm of pedal travel. If the proposed 15% of pedal travel required for cruising is a little on the lean side of reality (It's one of those things that might be easy to underestimate when thinking about it) and cruising might actually be more like 30-40% throttle opening during calm city acceleration and holding highway speeds, your oval idea might actually be quite beneficial.
What would be an interesting test would be to put a temporary mechanical stop under the accelerator pedal to prevent more than 15% movement, and go for a drive. That might be quite telling. Then again, if your TBs let a LOT of air in quite early, it might be a bit of a misleading test in that it would indicate that indeed your cruising is done in 15% of the pedal travel (with these throttle bodies). This would be confirmation of the... eagerness of your TBs, but not of what pedal travel:twitchiness ratio is comfortable. Such a test should be performed on a car with a stock carb, let's say, to give and idea of what 'normal' pedal travel is required to do what, and use that as a benchmark. The whole premise being (I guess) that you'd prefer to have OEM 'soft' throttle response in the first 4-ish cms of pedal travel, then all the high-flow goodness of the throttle bodies up in the higher spectrum.
Either way, after doing a pedal travel test during calm driving in your car or a stock car (or both), if it was discovered that cruise driving required more pedal travel than expected, such a mod to your throttle arm might cause things to slow down enough during various tip-in points to make it easier to dial in the perfect tune.
Maybe!
I love this stuff! I wish I had access to my car to try it out and give you some comparative data.
Food for thought.
Regarding the secondaries-disengage issue, I've also thought about this. Something would have to go pretty darned wrong for them to remain open. A freakish glitch in the EFI programming, the heavily return-sprung pneumatic actuator not springing back when vacuum was cut off, not to mention the two hefty external return springs on the throttle shaft arm itself... Maybe the vacuum solenoid sticking and either continuing to apply vacuum or not releasing it. All of it seems very low probability, but like Murphy says, if something can go wrong it eventually will. I will have to double-check with the tuner, but given that this system will only open the secondaries at WOT on the primaries and above X rpm, it would seem to me that even if the secondaries managed to stick open, as soon as the primaries closed a little bit,( < WOT) the secondaries' injectors should be cut off. I imagine it would immediately become very obvious something was not right which would lead to an instinctive letting-off the throttle entirely. In both cases-- partial or complete closing of the primaries-- with the secondaries stuck open the engine would be subjected to an incredibly lean condition, probably to the point of being unable to support useful combustion, at least until the engine rpm dropped to the point of the decel-cutoff giving way to idle quantity. Then we'd have an idle-quantity of fuel trying to burn in a 50% of WOT air environment. Probably not too exciting.
In short, I'm not REALLY worried about it, but what I will do is simulate that condition on the dyno and see what happens. I'll report the results on here. My expectation is there won't be anything crazy and it'll seem like the engine stalled. Another EFI-vs-carb advantage: electricity = fuel, not air = fuel as in carbs, which is quite beneficial in this case.
In your setup, all four throttle butterflies open equally and at the same time, as do all four injectors firing equally and simultaneously?
OP - Did you try the TB without the secondary "progressive mod"? If so, what exactly did you guys noticed? Any dyno charts from the unmodified TB?
Apparently with primaries only, the power curve fell off too rapidly and early to bother with a full dyno plot. With all four barrels opening from the get-go, it was apparently way too boggy in the lower half of the rpm spectrum to bother. I can't say for sure that this wasn't an initial tuning thing that couldn't have been sorted out with enough time. I expect an engine would run with no intake manifold or throttles at all if you could get the right amount of fuel inside per intake 'stroke'. Probably it could have been tuned to run all four barrels open right off idle, but we know it wouldn't be as good having just the primaries only doing the work in the lower revs, so that path was not explored.
I expect they took the point at which 'all four' ran smoothly and used that as a switching point, and tuned from there. Could be there's more to squeeze out of the old honey. When I get my hands on it, I'll play with it and see if anything seems like it could be bettered.
I was using cm as a basic example of the cable travel, which through a series of levers, including the pedal itself doesn't quite reflect perfectly pedal position. But anyway, I have a TPS sensor obviously, and logs show I need between 5-10% of the total throttle travel for cruising at 40-50 mph, maybe like 15% for highway speeds, I'd have to check. It is definitely a lot less than the pedal travel needed on the stock motor. Once the motor is in gear and cruising, let's say 2,000 RPM, I can go from say 7% cruising to 25% throttle to accelerate. The remaining 75% of travel at low RPMs does nothing. Velocity is tapped out by what the ports can suck in. Over 4,000RPM most of the travel will yield a change in acceleration, maybe above 75-80% does nothing. With that in mind, there are some adjustments on the linkage to change total travel. I used the smallest setting which means the throttle plates, at full throttle, don't open perpendicular to the throttle body. This was an attempt to chill it out a little. I have no idea if I'm losing power, but slight tip in, even at full throttle, probably helps atomization a little. I could always drill another hole to reduce total travel even more. There is no reason a stock port motor needs 48mm quads.
As for your setup, I'm sure the shop could add a bracket onto the primary linkage which adds a cross bar to pull the secondaries closed (but won't be directly attached to open them). This is how the stock linkages work on the various carburetors. It would solve all my concerns with your setup. A partial throttle pull, say 50% will limit the secondaries to opening only 50% as well, even though the vacuum solenoid is pulling hard on them. Likewise, if you are at 100% throttle and back off to 50% it will pull both primary and secondary plates closed.
It's so obvious now. TPS. haha! This is my first programmable EFI car ever, and I haven't even touched it yet since install. Before this it has only been mechanically injected gas and diesel engines, and vehicles not requiring OEM EFI fiddling. Need to drag my thinking out of the cave and into the computer.
Very interesting, so if your SP engine doesn't even need to open the throttles all the way, you could divert some of that 'wasted' cable length used to pull the throttles from (for example) the unneeded 75-100% range to instead accommodating a much larger throttle arm radius. It could still be a useful plan.
Yes, a mechanical pull from the primaries to the secondaries in only the closed-direction would kill 99% of the stick-open fail modes. (the last "1%" being the linkage/throttle shafts themselves) But only if the return springs can overpower the pneumatic actuator. I'm guessing it's pretty strong to already be working against the secondary shaft's return spring plus the two external springs. Maybe the addition of the primary shaft's spring plus (i guess) the gas pedal's spring might be enough to overpower it. I'll definitely be looking into that in parallel to whether the engine would actually run with the secondaries open and the primaries at < WOT.
I just had another thought for you. Look up how Toyota's T-VIS system worked. 2 ports per cylinder, a throttle body that would close one of the two ports per cylinder. A spring holds the plates in the open position. Vacuum will CLOSE them. They can also be locked closed via solenoid. I think this is essentially what i need to do...but it will cost me $600-700 I don't want to spend on a separate set of throttle bodies.
this doesn't solve your throttle off issue...you still need to make sure closing the primaries also closes the secondaries. But using vacuum to close them instead of open them means they can remain closed at any RPM when you are at partial throttle. Only when you are at full throttle (no vacuum) and the solenoid releases, will the secondaries open and move in sync with the primaries.
Impessive numbers! Thank you for taking the time to post your Dyno results. Too often most people just post their seat of pants impressions so it is nice to see actual results.
I just had another thought for you. Look up how Toyota's T-VIS system worked. 2 ports per cylinder, a throttle body that would close one of the two ports per cylinder. A spring holds the plates in the open position. Vacuum will CLOSE them. They can also be locked closed via solenoid. I think this is essentially what i need to do...but it will cost me $600-700 I don't want to spend on a separate set of throttle bodies.
this doesn't solve your throttle off issue...you still need to make sure closing the primaries also closes the secondaries. But using vacuum to close them instead of open them means they can remain closed at any RPM when you are at partial throttle. Only when you are at full throttle (no vacuum) and the solenoid releases, will the secondaries open and move in sync with the primaries.
I read up on the T-VIS after seeing your post. Interesting system. Sort of plays along the same idea as staging the throttles on my setup. If there is any possible chance that stuck open secondaries will result in any power generation, 'foot off the pedal', I think I'll go with a mechanical pull from the primary throttle linkage. Should be easy to set up, as you said.
Maybe the best thing for you would be a BIG street port, put those 4 big stacks to use!
hello again, friends!
I thought I would post a video of an autocross racie last weekend, which I think does a pretty good job of illustrating how well the engine runs with this EFI 4 barrel throttlebody configuration.
As you can see, it remains in second gear throughout the entire course, pulling smoothly out of even tight corners.
One thing I noticed was that during the rush to put this all together, the fact that the throttlebody bores are 1 cm larger in diameter than the manifold holes was ignored. There is a huge flat step in the interface between throttlebody and manifold. Disgusting! I liken it to three people standing abreast, shoulder to shoulder, running full speed through a regular doorway… They'll all get through, but it's not going to be pretty. I can only imagine that with bore-matching and blending 2-3 inches down the manifold runners will net even more power from this configuration.
The one thing that I would change with this particular installation is he addition of another vacuum reservoir. Under certain rare conditions, I think I deplete the vacuum and the secondaries don't open.
Other than that, it works really well, considering it's simplicity.
Rather than add more vacuum reservoirs, I'm going to begin experimenting with using a PLC reading a map sensor to drive the secondaries open with an electronic servo. This way, it won't be "on-off", And there will be no guesswork as to when and how far to open the secondaries. They will only open when needed, and only far enough to keep the engine producing the maximum torque possible for that particular RPM.
Continuing from earlier in this thread, I've verified with the tuner that when the throttle pedal is anything less than 100%, if the secondaries were to remain open, no additional fuel would be provided, and it would at best make little more power than what it would based on the primary throttle position, but most likely be in a "stalling-lean condition".
To be continued…
Sounds good, is that a Racing Beat Exhaust because it sounds nearly identical to my car, can't really hear any intake noise over it.
The problem with using a servo is that you still need them to close immediately when you lift off the throttle, and I'm not sure an electronic servo will be as easy to do that.
Maybe just try mechanical secondaries. Give yourself about 50% pedal travel before they start to open, and then make sure they open fully at 100%. It shouldn't be hard to creat a linkage that does this. Certainly a lot easier than a complex servo or vacuum system, and people swear by it with their Nikki's.
Good ear! Yes, the racing beat street port system. I wear earplugs pretty much all the time. Haha
i get what you’re saying. Maybe there aren’t any servos or other electrical actuators that move fast enough to match the speed of mechanically linked primaries and secondaries.
The good news is that the secondary fuel injectors only operate when the TPS (measuring the pedal-controlled primary throttle movement) reads 100%. Fuel to the secondary ports is chopped as fast as I can lift my foot from 100% throttle to <100%. Power is not more that what the primaries can provide for their given (decreasing) throttle position, and for the split second it takes for an actuator to catch up, probably less due to a momentary lean condition.
Actually, the pneumatic actuator I’m using now isn’t an instantaneous thing either. I’m pretty pleased with the way it works nonetheless. Before getting the car on the road, I was considering mechanical secondaries. Now I feel that would be a step backward.. The system is that good. It is, however, an on-off device though. Having the secondaries begin to open a little before 4000rpm is good on this engine, but full open half a moment later... Maybe a bit too much, too soon in the upper gears. Easing them open only as needed, (possibly even earlier than now without ‘ over-airing’ the engine) I think that is the hot ticket. Beyond that, I’m really keen to learn and play with a plc. It can manage the secondaries, control nitrous and rad fans and an exhaust dump valve and a seat cushion fart vent valve all at the same time, all shown and adjusted and indicated on a touchscreen. Pretty powerful stuff. I’m a bit giddy thinking about it.
Of course it might not work, but I’m determined to find out one way or another.
If it works, I’m going to peripheral port the engine, block off the secondary side intake ports and use the throttle body’s secondaries to operate the peripherals on top of the pedal-operated side port primaries. See if I can overlay a peripheral port emgine’s top-end power curve onto a side port engine’s low and mid range power curve.
Wishful thinking?
Let’s find out!
Originally Posted by chuyler1
Sounds good, is that a Racing Beat Exhaust because it sounds nearly identical to my car, can't really hear any intake noise over it.
The problem with using a servo is that you still need them to close immediately when you lift off the throttle, and I'm not sure an electronic servo will be as easy to do that.
Maybe just try mechanical secondaries. Give yourself about 50% pedal travel before they start to open, and then make sure they open fully at 100%. It shouldn't be hard to creat a linkage that does this. Certainly a lot easier than a complex servo or vacuum system, and people swear by it with their Nikki's.
I don't know, that setup doesn't sound ideal to me but it seems to be working for you on the autox course. I would just prefer full control of all 4 ports once the motor makes it over 4,000RPM. That's essentially how a properly functioning Nikki works. I'm opening and closing all my ports in sync right now and idle is a little rough, and throttle is a little sensitive at low RPMs, but once i get moving I have total control.
I mulled over that too, prior to driving the car.
what I’ve since found is that I do 95% of my driving on just the primary ports. Even highway passing doesn’t always require full jam. When I want full power I floor it and the secondaries open (if over 3800rpm). They only open when I hit 100% on the TPS. In that sense, I have full control over when they open and close. I just don’t have any control over how fast they open. They do what they do. However, the system has been tuned such that when i want full power, the secondaries do not open up until the engine is above the ‘bogging threshold’.
if we consider wide open primaries as 50% of full throttle, and the addition of wide open secondaries as 100% wide-open throttle, 50% is more than enough for 95% of my driving needs. When I want to pass, or take off in a hurry, I don’t want 65% or 83%, I want 100%. Over the last three weeks of driving, I did not come across a single situation where I wished I had something between 50 and 100. In all cases, 50 or below was adequate and 100% was Not too much.. There is no need for anything in between 50 and 100.
an interesting point of note--much like your car, it turns out that my secondary throttles have been rigged not to open fully. If they go all the way wide open, the engine bogs. So when I’m describing “100%“ wide open secondaries, I actually mean open fully to their set stop point, which is actually around 65%. I find this to be good news, as this idea of having the secondaries control a couple peripheral intake ports is floating around in my head. Clearly, the secondaries have more capacity for flow than the engine currently needs. I take that to mean there’s a very good chance that they can handle a pair of peripheral intake ports without presenting any significant restriction to flow.
I wish you could come and drive this thing, to see for yourself.
I think what you describe for around town driving is perfectly fine, and with low power on an autox course it is fine as well, but what worries me would be mid corner on a track when you lift slightly to set up the car. It sounds like it will close the secondaries, which is too much and could easily cause snap oversteer.
03-22-18, 02:50 PM
) meaning for every millimeter of cable pull you get an equal millimeter of linkage pull. For ease in visualizing this (necessary for the likes of me) you can relate it to a bicycle where the crank gear is the same size as the sprocket gear on the wheel. Think of A as the radius of the sprocket gear and B as the radius of the crank gear. One turn of the crank equals one turn of the wheel. One mm of throttle cable pull equals one mm of linkage pull.
