How many mpg do u get?
12-13-06, 04:07 PM
#26
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I dunno about recommending illegal acts like popping the cats myself...at least try to clean up the exhaust a bit instead of going full hog eco-terrorist...115 rwhp with a bone stock Nikki that will pass TX standards is possible....
12-13-06, 05:51 PM
#27
Old [Sch|F]ool
33mpg with STOCK type paper element, STOCK ignition system, and 4,78 gears.
Only use a K&N if you like spending (A LOT OF) money on junk that doesn't filter very well or appreciably work better than a new paper filter. Do the grease test and see for yourself.
Only use a K&N if you like spending (A LOT OF) money on junk that doesn't filter very well or appreciably work better than a new paper filter. Do the grease test and see for yourself.
12-13-06, 05:55 PM
#28
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Ahhh, but several independent dyno tests have shown the K&N filter to flow more CFM through its grid and other independent studies have documented horsepower gains on the dyno with a K&N filter over paper filters...
12-13-06, 06:48 PM
#32
Old [Sch|F]ool
Originally Posted by aws140
peejay. id say youre speedo/odometer HAD to be off.
There's two ways you can do the math.
One, I ran an odo check one time, and I get 47.7 miles indicated to 40 miles actual. 40/47.7 = .8386 correction factor. 40mpg indicated times the correction factor is 33.544. (Never minding that 245/6.1 is actually 40.16, so true would be 33.67, but now we're splitting hairs
)Or you an math out the difference between 3.909 gears and a 5/17 speedometer drive (what the speedo is designed to read) and 4.778 gears and a 6/21 speedometer drive (what I have in the car). Tire size is still 185/70-13 for highway driving so that is a given. Since I have the calculator handy, and I am curious is to how far off theoretical correction factor is from actual, I'll math it out now.
3.909/4.778 = .8181247
3.5/3.4 = 1.0291176
Multiply the two and we get .842187, which is "close enough", eh?
Incidentally, judging speed on the road with this combo is easy. Just take the speed in MPH, convert it as from inches to feet, and multiply by ten.
Or: 72mph = 60mph. (72 times the correction factor above is 60.61, damend close enough eh?)
But of course, I'm totally way off base and there is no way an RX-7 could possibly get more than 12mpg....
12-13-06, 06:56 PM
#34
Old [Sch|F]ool
Originally Posted by wackyracer
He drives it like a senior citizen OR running it very very lean. Those are the things I CANT DO!!
And no, I don't drive like a senior citizen, unless maybe you're thinking of Paul Newman.
On one weekend trip from Cleveland to Dayton (appx. 210mi) to Convoy (appx, what, 150-180mi?) to Cleveland (250mi), I knocked down 27mpg for both days. Including racing, which usually uses a quarter tank in itself from all of the idling, oh and the WOT action but mostly the idling. I was NOT driving slowly, in fact that was the trip that destroyed by 5th gear synchro (dumb FC trans) because of all of the fun WOT/snapshifting action on the highways. Tranquil was with me taking video, there's some funny shots of it pouring down rain, some sort of soothing metal on the radio, speedo pointing at 110mph...
12-13-06, 07:08 PM
#35
Old [Sch|F]ool
Originally Posted by rx7doctor
Peejay, what is your tach reading at 65mph?
Shifting by feel, in city traffic I usually change up around 2k. That's in fourth before crossing the intersection. I love 4.78's and Shockproof gear oil
Oh and my crowbar shift lever that lets me power past the non-synchros...I used to have an Autometer Sport-Comp tach. Very nice unit. It stopped working over 5500rpm, for some reason. What is the point of it then? It's sitting on a shelf because I can't bear to throw such an expensive unit away.
The video shows the Sport-Comp reading around 4000rpm at 105ish indicated, which is, what, 85-90 actual? That is with the FC trans with the stupidly wide 4-5 drop, the reason why they eat 5th gear synchros. I noticed no MPG change good or bad between it and a proper SA/early FB trans with a .825 ratio. Noticed a huge change in RPM on the highway
I much prefer the early trans because the shift spacing is a lot nicer, and my engine is a lot quieter on the highway if it is spinning and lightly loaded versus loading it down at a lower speed. I hate noise.(*) After installing the Accel 300+ ignition box, fuel economy dropped to the 20-25mpg range. I was super-pissed. But, better poor MPG than a blown engine.
12-13-06, 07:26 PM
#36
Obeying the interstate speed limit, I pulled 23-24 out of my 12A-1/2bp coming back from CO after Christmas last Dec. On the flipside, with cold weather warmups and in town driving, I've had it drop as low as 8.5.
After I rebuilt kgrays carb on his SA, he regularly gets 28-30 mpg on the highway. He is also a very conservative driver to achieve that.
If you want good fuel mileage, pick up a Honda HF or something similiar. Keep in mind that to get great gas mileage, you will need to purchase a newer vehicle, for more money. The idea is to balance initial capital costs, interest of a newer more expensive vehicle, against a cheaper vehicle that gets less gas mileage. The fun factor has no real measureable dollar value, that you have to decide and assign yourself.
Maintinance costs are another factor. While an older vehicle usually needs more repairs, a 1st gen is fairly simple and can be kept up by most shadetree mechanics at a minimal cost for parts. The newer ones usually require shop time for engine repairs/diagnostics and that can become quite pricey.
After I rebuilt kgrays carb on his SA, he regularly gets 28-30 mpg on the highway. He is also a very conservative driver to achieve that.
If you want good fuel mileage, pick up a Honda HF or something similiar. Keep in mind that to get great gas mileage, you will need to purchase a newer vehicle, for more money. The idea is to balance initial capital costs, interest of a newer more expensive vehicle, against a cheaper vehicle that gets less gas mileage. The fun factor has no real measureable dollar value, that you have to decide and assign yourself.
Maintinance costs are another factor. While an older vehicle usually needs more repairs, a 1st gen is fairly simple and can be kept up by most shadetree mechanics at a minimal cost for parts. The newer ones usually require shop time for engine repairs/diagnostics and that can become quite pricey.
12-13-06, 08:29 PM
#37
Old [Sch|F]ool
I get 40mpg with my '89 Golf. The PO is mystified since he normally got about 32mpg.
Of course, I run 93 octane and not the 89 he was running. That particular car is factory- tuned for 93 and has a knock sensor to tame things back down, so it gets much better fuel economy on the good stuff. That, and I tend to WOT it around winding the gears out, and apparently the fuel system on this car runs lean over 5k, so it's actually using less fuel at full throttle at near the revlimit than less throttle in the meat of the powerband...
ANYWAY. Yes the 33mpg claim is NO JOKE and I can tell you how I did it but I can't make it exact for your car since a lot of it was trial and error tuning: make a change, drive a statistically significant distance (100-150 miles, usually), make another small change based on those findings, so on and so forth.
First the stuff that is a given. Stock size/type tires. No fat hoops, no bling huge wheels with rubberband tires, and no gumball rubber. Cheap S-rated all-seasons. Run them at about 45psi front, 40psi rear. Get an alignment if you haven't had one in the last six months. Alignments aren't for tire wear, they are for handling and economy!
Run a good fuel pump and regulate it down to about 2psi. I can't explain it, but when I went from the Purolator rattlebox pump to a Holley unit, fuel economy went up. I haven't done drag testing on this car with an O2 hooked up, but my memory served that about 2psi was the sweet spot for good power, and a nice dead-lean on cruise. Note: This will induce a bit of a flat-spot between about 1/4 throttle and when the secondaries start to open. It's great for cruising on the highway at about 80-85mph, which in my car takes just a bit less pedal than the secondary opening point. Push through to the secondaries and the power comes on nicely...
Headers and a free flowing exhaust system. I noticed no economy or performace difference between running with a converter or not. I do not have a converter, simply because I don't want to set any fires. Plus, I use the space for an additional muffler. My exhaust system is headers (Pacesetter, i know, but I spent a lot of time porting the collector), perforated-core absorption mufflers, and short pieces of pipe to connect the two. I also have a homemade "silencer" that cuts the noise down dramatically. It's still loud, but quieter tham most non-RB performance exhaust setups. I am also going to repalce the homemade silencer with another 2.5" perf-core muffler mounted under the back where the rear bumper will have used to be...
Of course, I run 93 octane and not the 89 he was running. That particular car is factory- tuned for 93 and has a knock sensor to tame things back down, so it gets much better fuel economy on the good stuff. That, and I tend to WOT it around winding the gears out, and apparently the fuel system on this car runs lean over 5k, so it's actually using less fuel at full throttle at near the revlimit than less throttle in the meat of the powerband...
ANYWAY. Yes the 33mpg claim is NO JOKE and I can tell you how I did it but I can't make it exact for your car since a lot of it was trial and error tuning: make a change, drive a statistically significant distance (100-150 miles, usually), make another small change based on those findings, so on and so forth.
First the stuff that is a given. Stock size/type tires. No fat hoops, no bling huge wheels with rubberband tires, and no gumball rubber. Cheap S-rated all-seasons. Run them at about 45psi front, 40psi rear. Get an alignment if you haven't had one in the last six months. Alignments aren't for tire wear, they are for handling and economy!
Run a good fuel pump and regulate it down to about 2psi. I can't explain it, but when I went from the Purolator rattlebox pump to a Holley unit, fuel economy went up. I haven't done drag testing on this car with an O2 hooked up, but my memory served that about 2psi was the sweet spot for good power, and a nice dead-lean on cruise. Note: This will induce a bit of a flat-spot between about 1/4 throttle and when the secondaries start to open. It's great for cruising on the highway at about 80-85mph, which in my car takes just a bit less pedal than the secondary opening point. Push through to the secondaries and the power comes on nicely...
Headers and a free flowing exhaust system. I noticed no economy or performace difference between running with a converter or not. I do not have a converter, simply because I don't want to set any fires. Plus, I use the space for an additional muffler. My exhaust system is headers (Pacesetter, i know, but I spent a lot of time porting the collector), perforated-core absorption mufflers, and short pieces of pipe to connect the two. I also have a homemade "silencer" that cuts the noise down dramatically. It's still loud, but quieter tham most non-RB performance exhaust setups. I am also going to repalce the homemade silencer with another 2.5" perf-core muffler mounted under the back where the rear bumper will have used to be...
12-13-06, 08:59 PM
#39
Old [Sch|F]ool
Next is the stuff that requires fiddling... TIMING!
A little backtracking, though. There are two interesting tidbits that can provide some insight:
A stock 12A has its torque peak at 4000rpm.
A stock 12A distributor does not see full mechanical advance until 4000rpm.
Now this may seem to be a coincidence, until you read up on your tuning and find that you are supposed to RETARD timing at the torque peak, and ADVANCE it off of torque peak, or in a nutshell make the advance curve look like an upside-down representation of the torque curve. This is beacause peak torque coincides with peak combustion pressures, so you need/want less timing at that point, but off peak torque the combustion pressures are lower, so you can crank in some more timing.
"WTF does this have to do with anything" you are asking.
If the 12A isn't making peak combustion pressures below 4000, how come it doesn't have very much timing below 4000?
The answer is that in order to idle well (low HC emissions) the factory wants a minimal amount of timing. Because of the limitations of a mechanical distributor, the only way they can do that is to have a slowish advance curve. They have it nice and slow so it runs nice and smooth and clean for the parts of the rev range for the Federal emissions test, then above that point it is allowed to finally get up to levels where the party can sort-of get started.
We're enthusiasts. We're different, and we have a different set of priorities. We don't mind a rough idle, but we do want good power, and good power at all revs.
The cheap and easy thing to do is to just lock the distributor advance mechanism and run it at full advance all of the time, in our case 20 degrees before top dead center, leading (20BTDC) and TDC trailing. Note, with a siamese distributor (everything after 1974), there is only one mechanical advance mechanism, so the split is fixed, until you start playing with the vqacuum advance. More on that later.
The cheap and easy way to lock the distributor is to remove the advance weights' springs. Timing will go to max advance as soon as the engine fires. No need for welding, and it is reversible if you need to. (You WILL not pass an emissions test) It is very easy to damage the springs, so it may be a good idea to do this to a spare distributor. Not a good idea if you have a converter, the increase in HC output will have it working overtime.
What happens? You get a rougher idle, and you get stump-pulling torque. You don't need to rev the gears out anymore just to keep up with traffic. You don't need to use as much throttle opening for a given amount of power. You can cruise at 3k all day long if you want, no need to downshift to Fourth for mild passing or hills. This is all because the engine is making more power with the same amount of air/fuel at lower engine speeds, or conversely, you can make the same amount of power with less air and importantly less fuel!
That is why I say, I don't NEED to rev over 2k/go over 1/4 throttle opening in the city. It pulls just fine with just a little tickle of the throttle pedal, no big gulps needed.
We still haven't connected the vacuum advance back up, though, which is in the Next Part...
A little backtracking, though. There are two interesting tidbits that can provide some insight:
A stock 12A has its torque peak at 4000rpm.
A stock 12A distributor does not see full mechanical advance until 4000rpm.
Now this may seem to be a coincidence, until you read up on your tuning and find that you are supposed to RETARD timing at the torque peak, and ADVANCE it off of torque peak, or in a nutshell make the advance curve look like an upside-down representation of the torque curve. This is beacause peak torque coincides with peak combustion pressures, so you need/want less timing at that point, but off peak torque the combustion pressures are lower, so you can crank in some more timing.
"WTF does this have to do with anything" you are asking.
If the 12A isn't making peak combustion pressures below 4000, how come it doesn't have very much timing below 4000?
The answer is that in order to idle well (low HC emissions) the factory wants a minimal amount of timing. Because of the limitations of a mechanical distributor, the only way they can do that is to have a slowish advance curve. They have it nice and slow so it runs nice and smooth and clean for the parts of the rev range for the Federal emissions test, then above that point it is allowed to finally get up to levels where the party can sort-of get started.
We're enthusiasts. We're different, and we have a different set of priorities. We don't mind a rough idle, but we do want good power, and good power at all revs.
The cheap and easy thing to do is to just lock the distributor advance mechanism and run it at full advance all of the time, in our case 20 degrees before top dead center, leading (20BTDC) and TDC trailing. Note, with a siamese distributor (everything after 1974), there is only one mechanical advance mechanism, so the split is fixed, until you start playing with the vqacuum advance. More on that later.
The cheap and easy way to lock the distributor is to remove the advance weights' springs. Timing will go to max advance as soon as the engine fires. No need for welding, and it is reversible if you need to. (You WILL not pass an emissions test) It is very easy to damage the springs, so it may be a good idea to do this to a spare distributor. Not a good idea if you have a converter, the increase in HC output will have it working overtime.
What happens? You get a rougher idle, and you get stump-pulling torque. You don't need to rev the gears out anymore just to keep up with traffic. You don't need to use as much throttle opening for a given amount of power. You can cruise at 3k all day long if you want, no need to downshift to Fourth for mild passing or hills. This is all because the engine is making more power with the same amount of air/fuel at lower engine speeds, or conversely, you can make the same amount of power with less air and importantly less fuel!
That is why I say, I don't NEED to rev over 2k/go over 1/4 throttle opening in the city. It pulls just fine with just a little tickle of the throttle pedal, no big gulps needed.
We still haven't connected the vacuum advance back up, though, which is in the Next Part...
12-13-06, 09:49 PM
#40
Old [Sch|F]ool
VACUUM ADVANCE
"I on't want that crap, vacuum hoses are bad!"
Yes you do want that crap, if you care about drivability and economy.
Remember, in my last post, I mentioned that we generically want to run less advance at higher chamber pressures and vice-versa. That was in the context of the torque curve versus "mechanical" advance. But what about when you are at part-throttle? That also has a big change on the chamber pressures!
So we can definitely stand to have more advance at part throttle. Vacuum advance is by its very nature load-dependent, so we can have as much of our cake as the simple technology allows, and eat it too. Plus, it's already there.
I've talked at length on the subject before as regards to drivability and the various ways of connecting it up, but in a nutshell, you will always want PORTED vacuum for the advance. A "ported" vacuum source is one just above the throttle plate, so that it sees no vacuum at closed throttle, but after you open the throttle past idle, the throttle plate crosses the port and it gets manifold vacuum. Easy to check with a vacuum gauge, just connect it to one of the nipples on the carb spacer (the one with like five or six vacuum caps on it after you took the solenoid rack off of your engine) and check for vacuum at idle. No vacuum? Step 2: Snap throttle open. Did you see something happen on your gauge? Good to go. Use that one!
Now we're getting to the part where you fiddle around a lot. How much split, and do you run vacuum advance on leading, trailing, or both?
This is something that I am STILL not happy with I go around a lot fiddling around. I like to maintain a 10 degree split in the distributor for simplicity's sake, plus I know it works! I adjusted the timing back and forth and found that, for me, leading at 22BTDC gave the best power/fuel economy. Higher than that destroyed power! I have also experimented with vacuum advance with leading-only, trailing-only (which gives you a BIG negative split under cruise), and both (which will give you a slight negative split under cruise; the leading can has less advance than the trailing can, and it totals a bit more than the 10deg "static split" I was running) It was all so long ago that I've FORGOTTEN what the results all were, especially as I tried playing with timing at the same time as playing with L/T/L+T, probably two or three thousand miles' worth of experimenting just with the timing like this, but I'll tell you what: Currently, the car has BOTH hooked up. So that is what I'm running!
I also found that the spark plugs are important. I have been running cut-down (sidefire-converted) Autolite 3923 plugs, mainly because they are cheap, which is good because I'm cheap! I recently ran out of pre-made plugs and had to use some FC plugs lying around. HOLY CRAP. Fuel economy took a nosedive (like, got 25% worse!) and the power felt so strangled that I thought someone had replaced my air filter with some extra-soggy French toast. It sucked so bad that I put some worn-out Autolites back in as an IMPROVEMENT.
"I on't want that crap, vacuum hoses are bad!"
Yes you do want that crap, if you care about drivability and economy.
Remember, in my last post, I mentioned that we generically want to run less advance at higher chamber pressures and vice-versa. That was in the context of the torque curve versus "mechanical" advance. But what about when you are at part-throttle? That also has a big change on the chamber pressures!
So we can definitely stand to have more advance at part throttle. Vacuum advance is by its very nature load-dependent, so we can have as much of our cake as the simple technology allows, and eat it too. Plus, it's already there.
I've talked at length on the subject before as regards to drivability and the various ways of connecting it up, but in a nutshell, you will always want PORTED vacuum for the advance. A "ported" vacuum source is one just above the throttle plate, so that it sees no vacuum at closed throttle, but after you open the throttle past idle, the throttle plate crosses the port and it gets manifold vacuum. Easy to check with a vacuum gauge, just connect it to one of the nipples on the carb spacer (the one with like five or six vacuum caps on it after you took the solenoid rack off of your engine) and check for vacuum at idle. No vacuum? Step 2: Snap throttle open. Did you see something happen on your gauge? Good to go. Use that one!
Now we're getting to the part where you fiddle around a lot. How much split, and do you run vacuum advance on leading, trailing, or both?
This is something that I am STILL not happy with
I go around a lot fiddling around. I like to maintain a 10 degree split in the distributor for simplicity's sake, plus I know it works! I adjusted the timing back and forth and found that, for me, leading at 22BTDC gave the best power/fuel economy. Higher than that destroyed power! I have also experimented with vacuum advance with leading-only, trailing-only (which gives you a BIG negative split under cruise), and both (which will give you a slight negative split under cruise; the leading can has less advance than the trailing can, and it totals a bit more than the 10deg "static split" I was running) It was all so long ago that I've FORGOTTEN what the results all were, especially as I tried playing with timing at the same time as playing with L/T/L+T, probably two or three thousand miles' worth of experimenting just with the timing like this, but I'll tell you what: Currently, the car has BOTH hooked up. So that is what I'm running!I also found that the spark plugs are important. I have been running cut-down (sidefire-converted) Autolite 3923 plugs, mainly because they are cheap, which is good because I'm cheap! I recently ran out of pre-made plugs and had to use some FC plugs lying around. HOLY CRAP. Fuel economy took a nosedive (like, got 25% worse!) and the power felt so strangled that I thought someone had replaced my air filter with some extra-soggy French toast. It sucked so bad that I put some worn-out Autolites back in as an IMPROVEMENT.
12-13-06, 09:50 PM
#41
peejay, glad to see you posting more lately. You're experience and knowledge is most welcome.
So, now the question, before you get to Part 2. Since I'm running a 1/2sp-1/2bp, and as we all know, they are dogs for low rpm torque, will your full mechanical advance help in my case also? I'm running stock ignition and timing without the vacuum advance hooked up to the Mikuni.
So, now the question, before you get to Part 2. Since I'm running a 1/2sp-1/2bp, and as we all know, they are dogs for low rpm torque, will your full mechanical advance help in my case also? I'm running stock ignition and timing without the vacuum advance hooked up to the Mikuni.
12-13-06, 09:55 PM
#42
Old [Sch|F]ool
HeckifIknow. I know my P-port loved as much timing as it could get down low and more. It wasn't quite a dog at low RPM, though.
I even ran the vacuum advance to manifold vacuum, mainly because any time the throttle was open, there was no vacuum. It sucked that way, because the idle would hang up at 1800-2000rpm because the hgher advance raised the engine speed and manifold vacuum, which kept the vacuum advance up... It would either slowly sag back down to 1200-1400ish or I'd have to jerk it down with a quick clutch-jerk. It was never happy.
I am slowly but surely aquiring the bits needed to have EFI. The Shotgun will brap again
I even ran the vacuum advance to manifold vacuum, mainly because any time the throttle was open, there was no vacuum. It sucked that way, because the idle would hang up at 1800-2000rpm because the hgher advance raised the engine speed and manifold vacuum, which kept the vacuum advance up... It would either slowly sag back down to 1200-1400ish or I'd have to jerk it down with a quick clutch-jerk. It was never happy.
I am slowly but surely aquiring the bits needed to have EFI. The Shotgun will brap again
12-13-06, 10:06 PM
#43
Well, I don't see any point in having vacuum advance on mine for 2 reasons, my idle is 1200-1300 rpm, where the mechanical is already kicking in and my vacuum at idle runs 8-9 hg. Since I have spare dizzys, I'll try one without springs and see how it works.
Very interesting info btw, thank you.
Very interesting info btw, thank you.
12-13-06, 11:18 PM
#45
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Originally Posted by trochoid
Well, I don't see any point in having vacuum advance on mine for 2 reasons, my idle is 1200-1300 rpm, where the mechanical is already kicking in and my vacuum at idle runs 8-9 hg. Since I have spare dizzys, I'll try one without springs and see how it works.
Very interesting info btw, thank you.
Very interesting info btw, thank you.
so it runs max vacuum advance @light load
12-15-06, 09:11 AM
#48
peejay--PLEASE make a whole new thread about your solution. maybe even a write up format. some pics would help. id REALLY like to do this but i just cant seem to fully understand parts of it for some odd reason. also, all the specs on your drivetrain please. i know you have the 4.78, stock wheels/tires, 207(?)m stock engine, and FC tranny. what carb? thanks.
12-15-06, 10:15 AM
#49
Terrified.
Originally Posted by wackyracer
For some reason, I thought it was Paul Yaw. Then I realized it is Peejay. Very interesting. For once, I have to say, sticky sticky instead of archive.
Either that or move his posts into a thread of his own.
Just my two cents, anyway.
12-15-06, 01:09 PM
#50
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I have to agree with AWS140. It will help with people who want to do this and are not as familiar with this model rx7, like me. I am happy this thread has been so Informative.