Rear Gear Question

njk53 · 09-16-2013, 02:40 PM

When it comes to rear gearing, I am not the brightest candle on the cake so, I need some help understanding the application of rear gear ratios and what the performance results of different ratios.

For example we are running a 4:56 gear and several people that I have talked to have said we are a bit over geared for our application. The people I have spoken to have said that we should be running a 4:30 gear.
My question is if we go to a 4:30 ratio gear as recommended, what performance gains should I expect? Quicker ET? Faster MPH? Both?
Also, if I changed to a 4:30 gear, does your shift RPM change? How about my 60 foot times?

SSDiv6 · 09-16-2013, 03:26 PM

What kind of car and class?

njk53 · 09-16-2013, 03:30 PM

K/SA 71 Chevelle Wagon 402 big block. 4260 lbs w/driver

Mark Yacavone · 09-16-2013, 03:38 PM

Quote:

Originally Posted by njk53

When it comes to rear gearing, I am not the brightest candle on the cake so, I need some help understanding the application of rear gear ratios and what the performance results of different ratios.

For example we are running a 4:56 gear and several people that I have talked to have said we are a bit over geared for our application. The people I have spoken to have said that we should be running a 4:30 gear.
My question is if we go to a 4:30 ratio gear as recommended, what performance gains should I expect? Quicker ET? Faster MPH? Both?
Also, if I changed to a 4:30 gear, does your shift RPM change? How about my 60 foot times?

I would say, if the converter is right..That is, it flashes right around peak torque, then you might see the same 60' but more mph, then maybe gain a little ET down track.
As many here know ..there's only one way to find out for sure.

tj310 · 09-16-2013, 05:04 PM

Powerglide or a 3 spd ? I run approx the same setup 65 Impala wagon 396-325, 400 trans 4.56 gear. If your running a powerglide I suspect you would be better off with more gear 5.57 perhaps ---Trevor

gsa612 · 09-16-2013, 05:26 PM

I run the same 402/315 but in a Camaro, it all depends on the cam, lobe sep.etc. I run a 4.56 with a tight cam,2.75 low, 4800 flash.I think you would lose 60' and ET with a heavy car like yours by changing the SLR.You can get away with a little more rpm on that motor because of more exhaust lift (.430). If you run the big hoosiers 94" as opposed to the 92.5" it will give you around 200 rpm. gsa612

ss3011 · 09-16-2013, 07:25 PM

I am surprised your only running a 4:56 and not a 4:88 . Even though it's a different combo, I have a 71 Lemans wagon I run in J/SA. To get it moving I have a 2.75 low gear and a 4:56 . Trap rpm is about 6500, I would think your 402 would turn at least that high. What rpm do you run through the lights ?

gsa612 · 09-16-2013, 07:54 PM

On mine at 3635 (G weight) in good air with the 94' tires I go through at 6700 with .56's.I can get away with .88's at altitude. You would have to check your dyno sheets and see where the motor falls off (cam type). At that weight you might be able to use 4.88's, if you have ceramic lifters make sure you have plenty of spring press, if not they might rattle at the top end with the extra rpm.

442OLDS · 09-16-2013, 08:48 PM

Quote:

Originally Posted by ss3011

I am surprised your only running a 4:56 and not a 4:88 .

I agree with a 4,260 pound car.

Mark Yacavone · 09-16-2013, 09:45 PM

I hadn't read your description yet when posting earlier.
I agree with most..4.30 is not gonna work.

09-16-2013, 02:40 PM	#1
njk53 Senior Member Join Date: Jul 2007 Location: East China, MI Posts: 504 Likes: 0 Liked 0 Times in 0 Posts	Rear Gear Question When it comes to rear gearing, I am not the brightest candle on the cake so, I need some help understanding the application of rear gear ratios and what the performance results of different ratios. For example we are running a 4:56 gear and several people that I have talked to have said we are a bit over geared for our application. The people I have spoken to have said that we should be running a 4:30 gear. My question is if we go to a 4:30 ratio gear as recommended, what performance gains should I expect? Quicker ET? Faster MPH? Both? Also, if I changed to a 4:30 gear, does your shift RPM change? How about my 60 foot times? __________________ Nelson Kowal Stock 345

09-16-2013, 03:26 PM	#2
SSDiv6 VIP Member Join Date: Feb 2003 Location: Glendale, Arizona Posts: 2,992 Likes: 693 Liked 1,458 Times in 544 Posts	Re: Rear Gear Question What kind of car and class?

09-16-2013, 03:30 PM	#3
njk53 Senior Member Join Date: Jul 2007 Location: East China, MI Posts: 504 Likes: 0 Liked 0 Times in 0 Posts	Re: Rear Gear Question K/SA 71 Chevelle Wagon 402 big block. 4260 lbs w/driver __________________ Nelson Kowal Stock 345

09-16-2013, 05:04 PM	#5
tj310 Member Join Date: Sep 2009 Location: Dresden On. Canada Posts: 460 Likes: 0 Liked 0 Times in 0 Posts	Re: Rear Gear Question Powerglide or a 3 spd ? I run approx the same setup 65 Impala wagon 396-325, 400 trans 4.56 gear. If your running a powerglide I suspect you would be better off with more gear 5.57 perhaps ---Trevor

09-16-2013, 05:26 PM	#6
gsa612 Senior Member Join Date: Jan 2008 Location: 100th Meridian Posts: 570 Likes: 116 Liked 280 Times in 139 Posts	Re: Rear Gear Question I run the same 402/315 but in a Camaro, it all depends on the cam, lobe sep.etc. I run a 4.56 with a tight cam,2.75 low, 4800 flash.I think you would lose 60' and ET with a heavy car like yours by changing the SLR.You can get away with a little more rpm on that motor because of more exhaust lift (.430). If you run the big hoosiers 94" as opposed to the 92.5" it will give you around 200 rpm. gsa612 Last edited by gsa612; 09-16-2013 at 05:32 PM.

09-16-2013, 07:25 PM	#7
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 891 Likes: 64 Liked 227 Times in 106 Posts	Re: Rear Gear Question I am surprised your only running a 4:56 and not a 4:88 . Even though it's a different combo, I have a 71 Lemans wagon I run in J/SA. To get it moving I have a 2.75 low gear and a 4:56 . Trap rpm is about 6500, I would think your 402 would turn at least that high. What rpm do you run through the lights ?

09-16-2013, 07:54 PM	#8
gsa612 Senior Member Join Date: Jan 2008 Location: 100th Meridian Posts: 570 Likes: 116 Liked 280 Times in 139 Posts	Re: Rear Gear Question On mine at 3635 (G weight) in good air with the 94' tires I go through at 6700 with .56's.I can get away with .88's at altitude. You would have to check your dyno sheets and see where the motor falls off (cam type). At that weight you might be able to use 4.88's, if you have ceramic lifters make sure you have plenty of spring press, if not they might rattle at the top end with the extra rpm. Last edited by gsa612; 09-16-2013 at 07:57 PM.

09-16-2013, 09:45 PM	#10
Mark Yacavone Veteran Member Join Date: Mar 2002 Location: Miles From Nowhere Posts: 7,475 Likes: 2,652 Liked 4,575 Times in 1,733 Posts	Re: Rear Gear Question I hadn't read your description yet when posting earlier. I agree with most..4.30 is not gonna work. __________________ We are lucky we don't get as much Government as we pay for..... Will Rogers