Anyone thought about changing axle ratio?

With the discussions about improving performance through mufflers, pulleys, and chips, has anyone discussed with the shops the possibility of a rear axle ratio change (or if it can even be done)? That would be a significant modification that would not be an engine warranty issue (no, I'm not a lawyer so don't sue me).

In the street war days, that was the first thing we did. The 3:73 was real common as was 4:11, and lower were often seen. My last was 4:88 with the Chevy wide ratio (2:56 first). Even ran 5:38 for a while, but that was start in third gear, or pull stumps with first (in a car with Hilborne injected L-88 427 - did not have many people take a second ride). 6:17s or something like that were even around.

Anyway, the GT has a 2:61 first and a 3:36 rear. Seems like 3:70 or somewhere around there would be a blast. Would loose some top end, but ........ can't say I'm looking to drive 200 anyway, and I sure would enjoy the acceleration. You could also "run through the gears" more. Anytime I put my foot in it now, it is only 1 - 2. By the time I'm going to third, it is time to shut down. Takes a little of the fun away, though naturally I am a trooper and will suffer through.

The kick that the car has now with 3:36 is phenomenal, 4:11 would pull your eyes from the sockets. :ack

Just a thought.

centerpunch said:

We had a huge thread on this last fall, I thought lowering the final drive would be a big improvement, too, until I did the detailed analysis.

http://www.fordgtforum.com/forums/showthread.php?t=345&page=1&pp=10

Click to expand...

Thanks. I did a search before I posted, but did axle and ratio, not gearing so missed it.

I love your comment "Me, I'm a 50-year-old wuss, and 130 or so is as fast as I'll be going, even on a track". All I can say is DITTO. :cheers

I'll need to look at the graphs and digest. I know a lot of them were done with fairly low gears - wonder what 3:70 would look like.

Several of the posts by yourself and others seem very specific, detailed, and educated. However, something seems to be missing. If all of it is true, then why does almost every racer (not top end racer) use lower gears when they could get by with higher ones like a 3:36? I understand there are always diminishing returns, which was my 5:38 was too much.

Seems it may come down to an ET question versus a speed question. There is always the slower ET that has the higher speed. However, ET gets you there first.

Don't know - I think I need to fry some brain cells on those posts and get the full meaning.

I agree, the tires may be the weak link. No matter what we do with chips and pulleys, if it can't get to the ground it doesn't matter. Had the problem with with the hot rod - 31 inch tall 12 inch wide wrinkle walls (this was years ago), and it would fry them. Therefore, no speed (always did a rolling start).

Anyway, the whole idea made me do a little looking on the web (what a great place for info). The UTI post (below) indicates a final drive ratio multiplied by the first gear ratio of about 10.0 is ideal. For the GT, 2.61 x 3.36 = 8.77. The ideal final drive would seem to be about 3:83. 3.83 x 2.61 = 10.0.

Looked at information about the original GT-40. Figured they knew best. I see information that says the Mark IIIs had a five speed with a 2:42 first and 4:22 rear, though apparently there was an optional 3:33 (maybe for the street cars?). The 4:22 gives the total of 10.21. The Mark IV used a four speed with a 2:31 first and a 3:09 final. That is 7.13 - even farther away from what we have. Man, that confuses me.

The link to the police cruiser tests indicated the lower ratio car was quicker, though with a slower top end (of course, that was an automatic).

I think I am signing off on this one. Figured out I am not smart enough to know the answer.



UTI post

http://chevyhiperformance.com/tech/engines_drivetrain/induction_poweradders/0602ch_mods/

Effective change on final ratio by tires

http://www.summitracing.com/landing...{089CCB1C-D5A6-49B4-B914-4DEB0601C691}&Type=5

Police cruiser comparison

http://www.nlectc.org/pdffiles/msp2005bulletin.pdf