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I posted this in my build thread but I'm sure I'll get more eyes here....
Got an Apexi solenoid wired up to the PFC to use to control boost( @arghx old posts are so helpful). Turbo is a Borg S300-SXE 8380 with a 40mm Turbosmart WG with a 7psi spring (I have a second 7psi spring as well). My final target boost for this car is 14psi
In my first run, I set the target boost in the PFC at .5 kg/cm^2 (7.1 psi so pretty much equal to my 7psi spring) with a 65% duty cycle and I was able to do a 1/2 throttle 1st gear and then 2nd gear WOT and you can see from the chart that boost was flat at .52!
Now when I tried to up the boost to .85 (~13psi) with 65%, what I saw that it held steady around .8, I shifted gears, went hard on gas, and it went above to 1.1 and hit the fuel cutoff. I guess what I need to understand now is why the solenoid didn't bleed off boost to stop me from overshooting after I shifted gears?
What I'm also noticing is that it seems like by the time I'm able to spool to .85 boost, I'm pretty high up in the RPM (~6000) and I get pretty close to hitting the rev limiter so there isn't a lot of time for the boost controller to hold that boost. Is the just how my (big) turbo behaves in terms of spooling? A function of wastegate spring? Would I be better off putting a 14psi spring it it? Do I need be progressive on the gas vs just mashing the crap out of it?
.50 kg/cm^2 @65% duty -- holds flat in second gear at .52!
.85 kg/cm^2 @65% duty -- holds flat but as soon as I change gears, it doesn't hold and I spike and hit the fuel cutoff
Unplug the boost solenoid electrical connector (NOT the vacuum hoses) and do a WOT pull and then post the log. That's your base boost curve on spring pressure. A good base boost curve naturally tapers off slightly at high rpm in higher gears.
I bet it's creeping at higher gears, at least in colder weather. I bet your spring isn't stiff enough or your wastegate is too small. 7psi spring is asking a lot. The lower the spring pressure the harder it is to tune. Try a 10psi spring.
Unplug the boost solenoid electrical connector (NOT the vacuum hoses) and do a WOT pull and then post the log. That's your base boost curve on spring pressure. A good base boost curve naturally tapers off slightly at high rpm in higher gears.
I bet it's creeping at higher gears, at least in colder weather. I bet your spring isn't stiff enough or your wastegate is too small. 7psi spring is asking a lot. The lower the spring pressure the harder it is to tune. Try a 10psi spring.
I'll try a run with the sol disconnected. Any specific gear(s) I should pull in? Also, I know you use PIM even though there is a boost metric. Any reason why? Switching the spring is kind a pain only because I don't have a vice grip, drill press, etc. to hold the hat down to open and replace. I'll have to check with some friends.My garage doesn't current;y have a place to mount one otherwise I'd just buy one. You think moving to 14psi is too drastic since I already have a second 7psi spring to go in it?
@arghx I did some runs tonight, all in 3rd gear. I did a baseline run (7psi spring), then I did a .50@70%, and tried a .90@70%. Just based on the fact that when I'm at .50, it's controlling the boost, it tells that the solenoid is working. I just don't know if it's working right. It wasn't capture in these charts but if I get on it in certain gears, I'm still overshooting and hitting fuel cutoff
The .90 at 70% (double my spring rate), doesn't look the least bit right and I noticed my Wideband crept into the 12+ range so I won't do that again. I spoke to Bryan at Rotorsports and he said to back off anytime I get into 12s. Once I know my boost controller is working and that I have the right WG, we can get in the dyno and tune it properly. My brain hurts from staring at these so maybe your eyes see something I don't. I can't tell if what I see is good or bad for the baseline vs. the non baseline. I still feel like my WG isn't holding shut long enough and to your point, it could just be this spring rate is too small. Do the charts point to anything else before I try that?
Baseline (no connected solenoid) - 7psi spring at .50@70% duty
boost setting opens and closes the solenoid. The duty cycle is what determines if you can hold that PSI.
You can manipulate the boost through the duty cycle to be beneficial to you if you want a certain boost characteristic.
for instance, if you want 12PSI in lower gears you open the gate at 12PSI and have a higher duty cycle, in the upper gears with more load and time, the boost can creep another 2PSI without getting fuel cut.
The opposite can also happen. You can open the spring at 12PSI, put a much lower duty cycle and the boost tapers off with rpm. depends on what you want.
Well the Power FC's boost settings aren't the most precise. You give it a boost and a duty cycle and then it decides when to open the wastegate and how to handle the feedback.
In this case, OP's boost control is creeping pretty bad. 7psi spring is about 0.50 as he said, and with the wastegate solenoid disconnected it's hitting about 0.80 . Basically you have no boost control, and it will vary with the weather and the gear. It's not safe. You probably need a 14psi spring honestly before it will consistently control boost, or you need a bigger wastegate. Safest thing to do is get a bigger wastegate because 40mm is widely known to be too small for a single turbo conversion car.
Either way there is no boost controller out there that can control this consistently. You don't have enough wastegate flow. Your gate is basically for like a sub 2 liter 4 cylinder (think 90s Honda) and a rotary is more like a large 6 cylinder in exhaust flow.
With solenoid plug disconnected it should hit the rated wastegate pressure and then taper off when it's cold outside and you floor it in 4th or 5th gear (worst case scenario). If it can't do that you will be chasing your tail.
The only other workaround is using electronic throttle to help control boost, which is not an option here but is common on modern cars.
One final option is to restrict the exhaust and keep the wastegate and manifold the same. A quieter exhaust system and/or cat(s) will do that. Run a Racing Beat catback and a high flow cat and you might be ok. You'll have to run richer to keep the cat from burning up, probably staying in the 10's.
I don't recommend an actual restricter plate as it is a very crude approach.
@arghx - thanks for the feedback! Any recommendation on size for a WG? As for exhaust, I've got a TurboTuff Exhaust that @DaleClark gave me. Not sure how much restriction it has, but its got a muffler on there. It was still pretty loud though so I had a Magna-Flow inline resonator put on as well but it doesn't restrict flow. I think the short term solution is a WG. I know when Rotorsports put 14psi in the WG, they saw boost creep into the 20psi range. Sounds like I got sized wrong...
Assuming a fixed turbo and manifold, the wastegate sizing depends on how low you want your boost to go at a given level of restriction, and whether you are willing to put up with occasional spikes and fuel cuts. The lower you want the boost to go on an open exhaust, the harder it is to get a consistent boost curve.
If the turbo, manifold, and wastegate are fixed, you need to try progressively stiffer springs (10psi, then a 14psi, then a 16psi) and/or progressively more exhaust restriction. Put a cat in there, put some kind of additional in line muffler or change the catback, etc.
Or keep it like it is, accept somewhat inconsistent boost control (unpredictable with gear and weather), and set the boost target setting in the PFC (which is used to calculate overboost fuel cut) low enough so that fuel cut hits easily. So in your case you'd want to set your boost setting to no higher than about .70 (which will then fuel cut at about 1.05 if i remember correctly which is about 15psi). Then adjust your duty up and down and whatever boost you get is what you get. You can get an external controller too but all these controllers do is send a duty signal to a solenoid. It can't lower boost to less than what it wants to do with an unplugged solenoid.
Without hardware changes the boost can't get any better than your "unplugged solenoid" chart (unless you're in a different gear or the weather changes). I mean maybe if you moved the pressure source around for the gate or something it could help slightly. Whether the boost is "in control" depends on how you define it.
So the exhaust manifold it probably one of the few parts I don’t know anything about on my car. My car was one of the latter cars that was worked on by Peter Farrell Supercars (according to the previous owner) which we now know got a little shady at the end of their run. As I took my car apart, I saw all sorts of cheap knockoff parts that were not what he thought was on there. I couldn’t stomach a new exhaust manifold when the one I had wasn’t broken. As such, it’s a mystery.
I tried to snap a photo from the engine bay looking down near the ABS system. I have no idea what it is, who makes it, or how it flows. I remember when Bryan put in the 14psi spring, it was hitting like 20+psi so he went to 7psi spring. That was with no boost controller. Would putting a 14psi spring with the boost controller working allow for better control so as to not spike to like 20 and risk detonation? The original plan was to drive the car as is for a while, figure out what I liked and didn't like, make some DIY mods, and then go back for a dyno tune.
Depending on the cost, I guess I may be forced to just live with a 7psi that can "overboost" to .7 and then hit fuel cut if it spools to fast, but that seems like a bandaid that I dont want to take to the dyno and the end goal was to dyno tune this, and then finally have a tuned running car I could enjoy for a while vs. pump more and more money into...
quick solution that costs more than zero dollars but isn't too expensive is to weld a high flow cat into it. you have a lot of unknowns and considering the economic situation, overhauling your whole setup is probably not a good idea.
OR unplug the wastegate solenoid and leave it that way (no boost controller). It boosts what it boosts with the 7psi spring, and you set a fuel cut again to something like .60 or .70 boost setting (which would make it cut fuel around 14psi. From a safety perspective I think keeping a controller plugged in is risky. I say that because this is not your area of expertise and you're not likely wanting to risk breaking anything in a time like this.
quick solution that costs more than zero dollars but isn't too expensive is to weld a high flow cat into it. you have a lot of unknowns and considering the economic situation, overhauling your whole setup is probably not a good idea.
OR unplug the wastegate solenoid and leave it that way (no boost controller). It boosts what it boosts with the 7psi spring, and you set a fuel cut again to something like .60 or .70 boost setting (which would make it cut fuel around 14psi. From a safety perspective I think keeping a controller plugged in is risky. I say that because this is not your area of expertise and you're not likely wanting to risk breaking anything in a time like this.
Very true. I know hitting the fuel cut is designed to protect the engine so but is it going to do any long term damage? I suppose if I do this, I'll need to make sure my Wideband stays below 12 at this setting. I also assume it means a dyno tune is out the question?
03-14-20, 09:37 PM
