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 · 09-17-2013, 02:47 PM

Something's not right, your trap rpm seems low with 4.56's, I don't know what cam you got. What's the spring pressure? I'm going through at 6700 with.56's with the 94'tire. Mine goes 11 teens on a average day with 1.45 60' in G.(with no ice or lw oil).I found on these motors because of the cyl. heads (105cc) and the lower piston dome require a different set up than a 325-396 in terms of total timing, jetting, cam position, usable rpm. I would try .88's on your car if the springs check out ok. On a side note NHRA's Danny Gracia ran a wagon like yours a while back(80's). I was going through teardown 20+ years ago and he gave me some good advice/tips on the 402 combo lol..

njk53 · 09-17-2013, 04:07 PM

GSA612 you have a PM

ss3011 · 09-17-2013, 04:42 PM

Would you happen to have run the engine on a dyno, and know what the basic HP and Torque curves are ? When you say you have a 4800 stall converter, is that what it flashes to off the starting line ?

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 ?

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: 3,044 Likes: 712 Liked 1,582 Times in 582 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

09-17-2013, 02:47 PM	#6
gsa612 Senior Member Join Date: Jan 2008 Location: 100th Meridian Posts: 569 Likes: 116 Liked 280 Times in 139 Posts	Re: Rear Gear Question Something's not right, your trap rpm seems low with 4.56's, I don't know what cam you got. What's the spring pressure? I'm going through at 6700 with.56's with the 94'tire. Mine goes 11 teens on a average day with 1.45 60' in G.(with no ice or lw oil).I found on these motors because of the cyl. heads (105cc) and the lower piston dome require a different set up than a 325-396 in terms of total timing, jetting, cam position, usable rpm. I would try .88's on your car if the springs check out ok. On a side note NHRA's Danny Gracia ran a wagon like yours a while back(80's). I was going through teardown 20+ years ago and he gave me some good advice/tips on the 402 combo lol..

09-17-2013, 04:07 PM	#7
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 GSA612 you have a PM __________________ Nelson Kowal Stock 345

09-17-2013, 04:42 PM	#8
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 909 Likes: 70 Liked 239 Times in 114 Posts	Re: Rear Gear Question Would you happen to have run the engine on a dyno, and know what the basic HP and Torque curves are ? When you say you have a 4800 stall converter, is that what it flashes to off the starting line ?

09-16-2013, 05:26 PM	#9
gsa612 Senior Member Join Date: Jan 2008 Location: 100th Meridian Posts: 569 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	#10
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 909 Likes: 70 Liked 239 Times in 114 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 ?