21 replies to this topic

[William Bonsell]

There was some discussion earlier on this forum about what appeared to be a pretty high RPM rev limiter on a 1.6...Not sure if that motor was "pro" or not. But, I have been watching a bit of video and noticed on a car, which is supposed to be a non-pro motor based upon class designation, where HD video clearly shows and you also can clearly hear the fuel cutoff coming on around 7700-7800 rpm according to the stock tach. So i am left to ask a couple of questions...

1. How is it possible for a stock 1.6 to begin fuel cutoff at 7700-7800...I appear to hit the limiter at around 7300rmp. Can the stock tach be that far off from car to car. And remember, this is supposed to be a stock OEM motor. Would a freshened head provide this much rpm gain?

2. And if it is not possible, then how could I get my rpm's to 7700-7800 before fuel cutoff and still be SM legal regardless of cost. If I were to make the investment in a pro motor, does this provide that 7700-7800 cutoff? Or do you need compression outside the legal SM numbers?

Thanks....

Bill-

[davew]

Couple issues with your post

1. The engine can be built pro or not, with any compression etc. but that does not effect the rev limiter. The rev limiter is built into the ECU

2. Yes the stock tachs can be off that much. The stock rev limit is 7200, but I have seen tachs read 7700 when the engine is actually at 7200. The rev limiters are accurate, the stock tachs are not.

3. Unless some pretty illegal head work and cams have been done, raising the revlimiter will not make the car faster. You are so far above the torque curve, of a legal engine, that this will slow you down.

Dave

[Todd Green]

3. Unless some pretty illegal head work and cams have been done, raising the revlimiter will not make the car faster. You are so far above the torque curve, of a legal engine, that this will slow you down.

Caveat it can make you faster where you would run out of 3rd and have to shift to 4th for a very short period of time. (or 2nd -> 3rd etc.) The loss of acceration during the shift, plus the lower mechanical advantage of the higher gear usually outweighs any loss in power in upper rpms in my experience.

[William Bonsell]

Couple issues with your post

1. The engine can be built pro or not, with any compression etc. but that does not effect the rev limiter. The rev limiter is built into the ECU

2. Yes the stock tachs can be off that much. The stock rev limit is 7200, but I have seen tachs read 7700 when the engine is actually at 7200. The rev limiters are accurate, the stock tachs are not.

3. Unless some pretty illegal head work and cams have been done, raising the revlimiter will not make the car faster. You are so far above the torque curve, of a legal engine, that this will slow you down.

Dave

Thanks Dave...really appreciate your expertise in this. I understand that once you are approaching the rev limiter, the numbers begin to fall off pretty quick, but in this case, the car I am looking at consistently runs near the front with extremely fast times rivaling those times posted by pro engined cars with very good drivers. And I know this specific car does not have a pro motor. I would not even be questioning this for myself, except for the visual of a tach in the 7700-7800 rpm range starting to bounce off the limiter. I guess I can accept that the stock tach might be off 500 rpm's or so, but the times sort of cause me to pause and ask if something else might be going on.

If you manipulate (illegally I am sure) the ECU are you not only raising the rev limiter but also extending the hp and torque curve to a competitive advantage? As a newer racer and a non-mechanical type, I am just trying to understand how I can be seeing what I am seeing on video and everything still be within class rules. Thanks.

Bill-

[davew]

Raising the rev limiter simply raises the rev limiter, it does not effect anyting else.

A 1.6 should be shifted at 6800, if you go to 7300 with your massaged rev limiter, you will go slower than shifting up and down at the correct rpm. The rev limite is NOT the shift point.

Dave

[William Bonsell]

Raising the rev limiter simply raises the rev limiter, it does not effect anyting else.

A 1.6 should be shifted at 6800, if you go to 7300 with your massaged rev limiter, you will go slower than shifting up and down at the correct rpm. The rev limite is NOT the shift point.

Dave

Sooooo, the stock tach being off by 500 or so is just that...and it really is banging off the limiter at 7200...ok...but wicked fast times for a stock 1.6....must be the Stig!

Bill

[Ron Alan]

Our stock tach reads about 7400 at the rev limiter in a 95(which is actually at 6900 at the rev limiter). Post up the video in question and see if the vultures start circling...unless of course it's your pit mate and you want food or not at the next event

[Keith Novak]

Caveat it can make you faster where you would run out of 3rd and have to shift to 4th for a very short period of time. (or 2nd -> 3rd etc.) The loss of acceration during the shift, plus the lower mechanical advantage of the higher gear usually outweighs any loss in power in upper rpms in my experience.

Agreed. The one other advantage is that you aren't as likely to run out of gear in tight low speed corners.

[BrianPDX]

Bill,

Interesting post. My tach shows 7800 when the rev limiter kicks in, and I found that to be odd. I tried multiple ECU's and still had the same results. My conclusion is that the tach is off. I also have a shift light that has an RPM dial on the back. I currently have it set to 7100, and when it lights up my tach reads about 7600-7700. Very confusing, so I have stopped looking at the tach, and now rely only on the light. If I use the tach, I am either way to early or too late.

Eventually I am going to get data, and just mount the digital readout over the stock cluster. (I do have a Rebello motor with a head that was refreshed over the winter, same exact RPM readings before & after).

Hope that helps.

-Brian

[William Bonsell]

Bill,

Interesting post. My tach shows 7800 when the rev limiter kicks in, and I found that to be odd. I tried multiple ECU's and still had the same results. My conclusion is that the tach is off. I also have a shift light that has an RPM dial on the back. I currently have it set to 7100, and when it lights up my tach reads about 7600-7700. Very confusing, so I have stopped looking at the tach, and now rely only on the light. If I use the tach, I am either way to early or too late.

Eventually I am going to get data, and just mount the digital readout over the stock cluster. (I do have a Rebello motor with a head that was refreshed over the winter, same exact RPM readings before & after).

Hope that helps.

-Brian

Yes that helps a great deal Brian...if it was my car with my lap times, I'd just cross it off to a tach not reading accurately. But, damn it's fast....has a non-pro motor...and often runs faster qualifying times than the pro motored guys. I'm not looking to get anyone in trouble...I just am trying to make sense of the data I am seeing in video and the times I can see on mylaps.....

Bill-

[trimless]

Could it be the driver and set up that makes this non-pro motor car so fast? Or maybe he changes the wheel bearing grease every weekend
You can get very similiar power on a do it yourself build with a lot of knowledge and a little luck. Most pro builders can get you more power than you can on your own but driver skill and set up are more important IMO.

[Caveman-kwebb99]

Everyone who says they don't have a Pro-Motor, arent always telling the truth either... I don't know about this situation, but I think it is just part of racing that people tell little white lies about how little hp they have, or how bad their motor is running etc. I just tell the truth abotu my hp #, if someone beats me then he knows he outdrove me. It is a little like a story I heard about this driver that everytime your lap times where a little better than his, he used to say wow That is some Motor you have there, in some ways that could be interpreted as insulting the others guys driving ability, even if it was meant as a compliment, which I am pretty sure it was.

This car in question, from what I have thus far read, nothing seems out of place, I have not seen a video of him closing or pulling a 7 car gap in .2 seconds on someone he has seemingly been running a very close race with lap after lap. Now I am a bit of a one track wonder, but last year I was able to take a p2 and p3 in the same weekend, I knew the car was not right all weekend, so when I got home i went to dyno and I was off 6hp. I was in the hunt the entire race weekend against some of the most tallented guys in the area at this particular track, I even took the pole on day one. I felt really good about how well I had driven it and almost overcame the 6hp with driving. The car and more importantly the driver you are questioning in this thread may be just simply outdriving people. I can certainly think of one competitor I race against regularly, I know he is and has been off on power for some time, he is still a threat a win everytime out. All because the man can flat drive the car! He podiums in that hundred year old used up SM all the time, I often wonder what he could do in my car? One day we may just find out...

I tend to agree with Gale I guess that a driver can really make a huge difference. I sometimes race PT class with NASA, most recently running in PTD, I really need to get my head checked for that one, but I did finish p2 and was in the hunt the whole race against guys that had 15+mph on me on the straight aways, now clearly the PTD crowd does not have the driving tallent of SM, but my point here is the only way I took p2 was driving ability, it sure wasnt my car, or my hp #! Who knows its possible those guys are mumbling about how does a 2000 Miata hang with us all race, what has he done that is illegal?

[FTodaro]

Could it be the driver and set up that makes this non-pro motor car so fast? Or maybe he changes the wheel bearing grease every weekend
You can get very similiar power on a do it yourself build with a lot of knowledge and a little luck. Most pro builders can get you more power than you can on your own but driver skill and set up are more important IMO.

I agree with your point Gale that sometimes the "driver" can make up the difference of a well prepped car. We have some guys in our region that do not have pro built, top prep equipment, but boy they sure can drive the wheels off of them and around ME.

[Michael Colangelo]

Bill, Brian said he has a Rebello (pro-build) motor.

[William Bonsell]

Bill, Brian said he has a Rebello (pro-build) motor.

Funny Michael...the driver and car in question is not my son...but he may be motoring by me sometime this summer for sure. Won't that be a father/son moment! CYA in May at Pacific.

Bill-

[DES4]

... Unless some pretty illegal head work and cams have been done, raising the revlimiter will not make the car faster. You are so far above the torque curve, of a legal engine, that this will slow you down.

Doesn't it also have to do with where in the powerband the revs are after the upshift? To clarify; if a normal rev-limited upshift drops the engine speed below the sweet spot in the torque curve after a gearchange, wouldn't revving beyond the point where the engine is making its most power help the car pull better in the higher gears?

Just asking; this is something I've wondered...

[Danny Steyn]

If you are not quite sure if someone has a cheated ECU with raised limiter, the easiest way to find out is to have a spotter see where his shift points are on the track. A certain primate had his spotter report back each race!

There are absolute maximum speeds in each gear for the standard gear ratios and the standard ECU's.

Also if you are running next to the driver in question, and you are banging against the rev limiter but he somehow manages to delay his shit, then I would have a nice whisper in his ear about the situation.

This weekend at VIR there were a few cars that ran from T2 to T3 without needing to shift. Unusual to say the least.

However sometimes it can be deceiving so be careful.

ALSO This weekend in R1 at VIR many of us did not hit the rev limiter before starting the uphill esses (you normally have to shift at the bottom of the esses). The ambient air was that bad - hot and humid. Lots of us felt our engines had laid down, but it was true for all.

If you do find someone that is playing with the rules, best way is to chat to them personally. Most will react positively to a sincere request to clean up their act.

[High Chair]

If you are not quite sure if someone has a cheated ECU with raised limiter, the easiest way to find out is to have a spotter see where his shift points are on the track. A certain primate had his spotter report back each race!

There are absolute maximum speeds in each gear for the standard gear ratios and the standard ECU's.

Also if you are running next to the driver in question, and you are banging against the rev limiter but he somehow manages to delay his shit, then I would have a nice whisper in his ear about the situation.

This weekend at VIR there were a few cars that ran from T2 to T3 without needing to shift. Unusual to say the least.

However sometimes it can be deceiving so be careful.

ALSO This weekend in R1 at VIR many of us did not hit the rev limiter before starting the uphill esses (you normally have to shift at the bottom of the esses). The ambient air was that bad - hot and humid. Lots of us felt our engines had laid down, but it was true for all.

If you do find someone that is playing with the rules, best way is to chat to them personally. Most will react positively to a sincere request to clean up their act.

I know there were a few of us that did not shift between turns 2 and 3 but instead just lifted short of the rev limiter as to not screw up the 4th 3rd downshift while turning. Same thing in the back section. Some used 4th while other used 3rd coming onto the front stretch so some shifted while others didn't. Im not sure I saw a difference either way.

[davew]

We would prefer to shift about 6500rpm. But that puts you below the sweet spot on torque. So we normally shift beyond the horsepower peak in order to help out with the torque. But going above 7200 will put you over the cliff on horsepower and past the torque peak. A loose looose situation.

Everybody should test their stock tach. Every car is different. When leaving the pits, put it on the rev limiter for a second, note the tach reading. Then shift 400 rpm below that reading. This will put you very close to the correct shift point without having to do gear and dyno calculations.

dave

[pat slattery]

our 1.6 rev limiter is about 7150. I would like to have it at 7500 or so for those moments when you would rather stay in gear, vs shifting for just a split second.

Going down the straight, it would be no advantage to go that high in the rpm range