Gear change/ 60' loss

Posted By: 340B5

Gear change/ 60' loss - 10/27/12 07:11 PM

I need a gear change in my Duster and just 3 days ago had a new best of 1.49 60' and a 10.95 ET. Problem is that it hits the rev limit (7k) in 3rd around 1000'

I wonder how much 60' I will give up going from 4.86 to 4.56 gears? This is a 3.58 stroke 374 inch engine. Any guesses or personal experiences?

Posted By: 70dusterjohn

Re: Gear change/ 60' loss - 10/27/12 07:14 PM

We lost none, at all... I really dont think that the 56 is going to be a big enough drop to make a difference, I think I gained maybe 200 or so rpm. So I still feel that you would hit the rev before the line. I ended up going to a 4.30 and the car picked up a little more on top end, and again lost nothing in the 60ft. Thats with a 30" tall tire..

Posted By: slippery440

Re: Gear change/ 60' loss - 10/27/12 07:21 PM

What size tire? Try a 2 inch taller tire and that would be close to the 4.56s.

Posted By: J_BODY

Re: Gear change/ 60' loss - 10/27/12 07:24 PM

is the combo done at 7K?

Posted By: 340B5

Re: Gear change/ 60' loss - 10/27/12 07:35 PM

Quote:

We lost none, at all... I really dont think that the 56 is going to be a big enough drop to make a difference, I think I gained maybe 200 or so rpm. So I still feel that you would hit the rev before the line. I ended up going to a 4.30 and the car picked up a little more on top end, and again lost nothing in the 60ft. Thats with a 30" tall tire..

I would be happy if I didn't loose any, and yes I thought about still hitting the limiter, but it should be for less time anyway.

Slippery: I already have the gears, so that fits the budget better.

J body: The combo should be done before that. I have factory iron J heads(worked over some)I'm gonna guess 6700 or so, but I haven't felt it nose over before the limiter. I've only made 5 complete passes w/ the combo and I'm still getting re-acquainted with the car after a 2 yr hiatus.

Posted By: Dodgem

Re: Gear change/ 60' loss - 10/27/12 08:43 PM

That gear change should drop you 500 rpm may cost you .01 in the 60 foot.

I would just race the limiter to 7600 RPM is your friend! :-)

Posted By: Triple Threat

Re: Gear change/ 60' loss - 10/27/12 08:54 PM

If the converter is big enough, it shouldn't hurt too much, maybe .02 to 60 foot, but the car will run better down track...

Posted By: skrews

Re: Gear change/ 60' loss - 10/27/12 08:59 PM

Few years back I tried 4.30, 4.56, 5.13. No notable difference, except that the 5.13 would turn the tire a little off the line sometimes making the car inconsistent. This was running in a 7.5 ET 1/8 mile car for what its worth. I've watched alot of guys try really deep gear hoping to shave of some ET and lower the 60 footers, only to find no gains at all.

Posted By: 70dusterjohn

Re: Gear change/ 60' loss - 10/27/12 09:01 PM

Like I said we did it with zero change. Didn't make a difference at all. If you have them and can do it, heck try it. What are you out? Then if need be you could go up 2 in the tire size(if you can) or go to a 30 for next year. Are you running an 8 3/4 ? Where you located. I have complete pigs in 489, 456, and 430.. Heck I got a 410 also....

Posted By: 340B5

Re: Gear change/ 60' loss - 10/27/12 09:16 PM

Thanks for the replies. It looks like I'll be good to go w/ the 4.56's. The trans has the 2.74 low anyway.

Posted By: gregsdart

Re: Gear change/ 60' loss - 10/28/12 12:22 AM

going from 4.86 to 4.56 is only a 6.2 percent drop in gear ratio, so it should see 400 rpm drop. I am betting it will run as good or better. With the 2.74 low you still have a 12.49 starting line ratio, and that is pretty high.

Posted By: tboomer

Re: Gear change/ 60' loss - 10/28/12 12:40 AM

Quote:

going from 4.86 to 4.56 is only a 6.2 percent drop in gear ratio, so it should see 400 rpm drop. I am betting it will run as good or better. With the 2.74 low you still have a 12.49 starting line ratio, and that is pretty high.

Greg...I find that interesting. If I crossed the line at 6400 instead of 6800,I would still be in my powerband. Might run a hair faster with 4.56 instead of 4.88s..

Posted By: cudabin

Re: Gear change/ 60' loss - 10/28/12 01:23 AM

One school of thought is that you should peak at the 1,000 foot mark which by then most of the acceleration has reduced your ET and you are already at a higher MPH for the last 320 feet...

This assumes the engine can handle the rpm and is not nosing over...

My motor made peak HP at 7,200 rpm and I cross the stripe at 8,000 - 8,100 rpm. I think it ET's decent...

Best way to find out is to test it, so let us know how the 4.56's affected the ET and MPH once you cahnge.

Cheers,

Arnie

Posted By: perfmachst

Re: Gear change/ 60' loss - 10/28/12 05:27 AM

hi, changing gears does affect E.T. and 60' times. went from 5.13 & 29.5 tire to 5.57 & 30" tire, E.T. dropped .30 & gained 1 MPH. 60', dropped .13. car was faster period!!! also, rpm was 6400 after is 7000 rpm +. it doesn't lay down last 300 ft either.

Posted By: 340B5

Re: Gear change/ 60' loss - 10/28/12 03:24 PM

I've tried to factor in everything. The tires will turn 7.6 times in 60', stall is increased ever so slightly w/ the 4.56's, etc. I think I'll check the logbook today and see what going from 4.56 to 4.86 did for the 345 in engine a few years back.