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Gear ratio decision, 4.1 4.3 or 4.56?

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Currently a blast to drive but I want to try dial in the whole system even more, wondering of the 373 are just too mellow for what this combo needs? sometimes at part throttle acceleration it seems a little sluggish.. id like more instant snap if that makes sense..

Currently have 373, and its nice, but i wan to push the street factor the the limit - the 383 doesnt always have the brute low end of the big bocks, so some mods are necessary.

Cam is around 2000-6000 236° / 242°, 288° / 294°, 11:1 (installed straight up), 200/64cc alu heads, 5.7 rods. 850 dbl pumper brawler, Vic JR, 1-3/4 LT headers into 3 inch collector and 2.5 true duals. 373 posi, 2004R, 3k stall..

18-20 initial, vac adv disconnected .. Hei stock.
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I would make sure the centrifugal isn't coming in until maybe 4500 or so as it might be what is making it doggy. Get another set of weights and drill an 1/8" hole in the end of them but install one at a time. That will tell you where you need it to come in. May need heavier ones or even leave a spring off. I would use 4.30s. Then a looser converter if you wanted more.
 

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I guess the only comment I have is the engine is built for top end power, that leaves the gearing choice of pursuing where the power is. This doesn’t really have any street drivability as the OEMs would define it.

I run a 2800 stall in a light vehicle with high gearing and a 350 with a lot less cam, so one of my impressions is you need more stall as well as stiffer gears and eliminate the lock up which probably isn’t available with higher stall anyway.

Basically sounds like a good design for a super T10 or equivalent 4 speed stick more than a TH200.

Bogie
 

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You can be stupid like me and run a manual sm465. I plan on running a BBC clutch dropping 5500rpm into the 3rd(1.7) gearing then pulling straight back into 4th(1.0) turning a wide selection of ratios in a 9" depending on the situation. Basically running as much as I can that will keep the thing going straight and stay off a 6500 limiter.

The sm465 is heavy at 250lbs w steel bell. But you can find one for around $300 and the 2wd ones can handle 600ft/lbs. BBC (500ft/lb) clutches can be had for around $250.

So for under $600 you can have a transmission that will handle 500ftlbs all night long. Thats less then most "stage" kits for other 5/6 speeds and is a fraction of what any "built" automatic will cost.

This is just what I am doing. Most people consider running a sm465 as a 2 speed dumb when there are others that will save 100+lbs of weight.

A 200r4 still has a few tricks to make it live behind a high reving sbc. Your not using that overdrive so a th400 would be the next analog choice. After that a built 4l60e or 4l80e could give you programable shift points and a bit of data logging.

A solenoid shifting 3 speed automatic can do some great things. But great things often cost great amounts of cash. You start getting over 400ftlbs on a 200r4 and the prices will go up.

If this thing is a weekend warrior and you plan on staying under 400lbs and under 6000 with that sbc then a 200r4 may live a long time.
 

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Discussion Starter · #24 ·
Hi, yes have limited the hei vac adv long time ago with bushing and stop screw. Good info. I did buy upgraded parts from art carr.. I'll look into the sm465, and maybe 4L80e.. down the road. Good answers thanks folks
 

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My brother used to street race a '64 GMC with a SM465 and would launch it in 1st gear. Not for the faint of heart. It sounded like a prehistoric monster howling. But it held together on some scary hole shots.
 
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