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-   -   rear gear selection (http://www.hotrodders.com/forum/rear-gear-selection-228520.html)

dave350v8 01-18-2013 08:51 AM

rear gear selection
 
Hi Everyone
My car is running a 350 sbc with procomp 210 heads, 480/480 magnum cam,600 holley,rpm intake,and about 9.8 comp ratio.
At the moment it really doesnt pick up very quickly, no big difference over the camel humps I replaced.(intake runner on the large size)
A few on here suggested a rear gear change.

My car weighs 2470lbs
5 speed T5 manual (2.95 1.94 1.34 1.1 0.80 ratios)
23" tyres
3.08 rear gears

Just been offered a 3.73 and a 3.31 set of rear gears.

Mainly want to use it on the strip, standard bottom end so I dont want it reving past 5500

What rear ratio would you choose??
Thanks in advance

ap72 01-18-2013 09:14 AM

what gears do you currently have? I'd go with AT LEAST the 3.73's with your OD if you plan on track use. hopefully you have a locker or posi or something like that to help prevent a one wheel burn out as well.

dave350v8 01-18-2013 09:35 AM

Hi, rear gears are 3.08 as stated in my post, dont want it screaming around the streets as my tyres are only 23" in diameter.

prostreet6t9 01-18-2013 09:40 AM

Quote:

Originally Posted by dave350v8 (Post 1636223)
Hi, rear gears are 3.08 as stated in my post, dont want it screaming around the streets as my tyres are only 23" in diameter.

23" tire is pretty short. I'd do the 336's

ap72 01-18-2013 09:59 AM

Quote:

Originally Posted by dave350v8 (Post 1636223)
Hi, rear gears are 3.08 as stated in my post, dont want it screaming around the streets as my tyres are only 23" in diameter.

going from 3.08 to 3.73- adds about 20% more rpm at the same speed, so if you're at 2500 rpm now then you'll be at about 3000 rpm with taller gears. just an easier way to look at it to help you make your decision.

68NovaSS 01-18-2013 12:54 PM

Moving to the suspension/drive-train forum, you'll get more responses there.:thumbup:

big gear head 01-18-2013 01:19 PM

Calculators

vinniekq2 01-18-2013 11:29 PM

That car should be all but impossible to hook up?light weight and low tires? What do you call"doesnt pick up that quickly"?

vinniekq2 01-18-2013 11:37 PM

5500 rpm nets you a top speed of;1st=41 ////// 2nd=63 //// 3rd=91 /// 4th=111 /// 5th= 153
you should be shifting into 3rd after 4 seconds?

what carb are you using? what is the model number?

if you changed to 3.73 gears,then your speeds would be;

1st=34,,2nd=52,,3rd=75,,4th=92,,5th=126? That would be silly.

vinniekq2 01-18-2013 11:43 PM

If your car finished the 1/4 m at 120 mph,then your engine is making 370 horses?

if your car only goes 110 mph,then the engine is making 285 hp.

125 =420 HP

dave350v8 01-19-2013 03:06 AM

Hi
Thanks for the infomation, Im using a holley 1850 600 vac sec at moment
I just feel it has more to come in the higher gears! 1st gear waste of time!
2nd ok, 3rd feels feel a little slow to pick up,I suppose I need to get down the strip in the spring and get it timed.

vinniekq2 01-19-2013 07:39 AM

If you steepen the gears then first gear wont improve.If you use a taller tire,then gears may need to be changed.Is there room for taller tires?

dave350v8 01-19-2013 07:55 AM

I could possibly go another inch with tyre size, I would like more acceleration
in 3rd gear, my rear gear is 3.08 at moment, I think by going to a 3.36 rear I
would make 1st a waste of time,but would it improve my 1/4 time?

vinniekq2 01-19-2013 08:11 AM

short tires and drags do not go together usually.Slicks are tall and quite often grow under acceleration. If first gear becomes useless then essentially 3rd gear becomes your second gear,,,,
with out MPH its not possible to determine what to do for your combination.What you feel in the seat of your pants is not usually a very good indicator of what is happening .If it was my car,I know I would have a single plane intake and a 750 or 850 double pumper carb.That hydraulic cam does no justice to the heads you bought.Also,the gear spacing you posted is a big jump from 2-3,the rpm drop is bigger than 1-2.Raise your shift point for 2-3,maybe shift 1-2 about 200 rpm sooner?

dave350v8 01-19-2013 09:24 AM

Thanks for that! People did mention before about going up to a 750 carb.
Because Im changing the plates in the diff I thought I might give the 3.36 a
go.
I think I will look at upgrading the cam as you suggest,I think it was you who
thought I needed more cam before!

Thanks again


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