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07-08-2017
I have been reading through past posts on gear changes but have not found an answer.
I am racing a 2004 Grand Prix on a 1/3 mile dirt track. The rpm through a race seems low never exceeding 4800. The easy option is to try small diameter tires with a reduced contact patch. The other option being a gear and differential change.
The race is run in second gear there is no shifting. Can a gear/differential change run well without a tune in this application?
Cheers Jim
07-08-2017
i'm not sure how well it would do, but if you have HP Tuners, you can tell the transmission to only drive in the specified gear, and that might be handy in this situation.
07-09-2017
you cant run in just second unless you have a way to command the tranny to stay in second gear. aka 2 nd gear start off the line.
your not changing gears with out a pcm tune for them.
and a 1/3 if a mile is 500 foot longer then a 1/4 mile. my last track runs i shifted into 3 rd at the finish line at 97 mph, that was a 6000 rpm shift, way higher then stock. stock is like 80 mph it will shift into 3 rd.
so how your rpm's seem low is kinda odd sounding.
if you do start off in 2 manually, it will start in first, shift to second, and stay in second gear. but you'll blow it up like that trying to go a 1/3 mile wot.
07-09-2017
Hes not going to hit 97 on a dirt track. He'll be able to stay wide open for the short straights, then have to get out of it in the curves, then back in it. Tops, I bet he hits is 45 mph.
07-09-2017
wow i missed the whole dirt track part lol
07-09-2017
Thanks for the replys, HP Tuner would be the way to go, I can't swing that until much later this season.
Yes it's dirt tracks, so some braking before returning to wot. The transmission is manually set to second gear with a rolling start.
The videos I have show the rpm on the dash never reaching 5000, maybe 47-4800 regardless of the track conditions. My quick math would put the 3.69 final drive at 6000 if it could hit 5000 in stock trim.
This could be a better rpm range with some over rev but I didn't know if this is possible without the tune. Should the revs end up too high a change to taller tires would help.
So this change shouldn't create a safe mode or induce a rev limiter but shifting will be horrible.
07-09-2017
smaller tires will get the rpms higher and make it feel snappier, not sure if they would net more speed tho.
stock engine has no power past the 5500 rpm's either. it just flat lines really.
are you supercharged or na?
07-09-2017
if you can get a set of 15" wheels, then you can get the good dirt track slick's, but i'm not sure how wide you could go. my inlaws do dirt track racing with modified's, there is a lot of science behind it. it actually might be beneficial to run a 15" wheel and tire on the passenger side and a 16" wheel and tire on the driver because of the angle of the track. another thing you might try is to put lowering springs on the passenger side. I'm sure you understand all the theory behind having different geometry for the dirt track.
07-09-2017
What gears do you have now? If 3.29's, you can probably switch to 3.69's without a tune. I did this once. It threw an incorrect gear ratio code and shifted goofy. But if you aren't shifting, it shouldn't matter.
07-09-2017
The engine is NA, and a 5500 limit would be fine anything higher would allow for over rev into the corner.
The current diff is a 3.05, I have a 3.29 in the garage this would get me on par with all the 2nd gen motors.
Current rims are 17" with low profile rubber, not ideal for dirt but not as tall as 225/60/16. I haven't tried 15" rims over the calipers. Rubber has been by chance no by choice, picking it up from are wreckers. There is a claiming rule so there s a real tight budget.
I am going to start looking at what is needed to swap a differential.
07-09-2017
The diff should swap with no issues. You'll just need s few quarts of trans fluid as some will come out when you pull the axle.
07-30-2017
Looks like I will going to a 3.69 final drive, waiting to receive the chain and gears.
I haven't been into a trans before looking for recommends on manuals and video/YouTube as well as links.
Cheers Jim
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