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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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Discussion Starter · #4 ·
Ok - I had mine rebuilt at art carr in Huntington beach 200 miles back- so far ive been happy but not sure if a better one will make that much of a difference? Im going to try a 750 and see if the performance increases..

higher stall or lower? currently 3200

Look at optimising what you have first. I'd be looking at a better convertor.
 

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Weight reduction, suspension and traction tuning, and then you can look at adding power(which will require more tuning) then if that is still not enough you can look at a gear ratio change.


I ran 4.56 in a few rides. Gives a nice 0-60mph and makes even a pile feel powerful. As long as you dont plan on going over 60mph much they work out good. Your going to push a bit more rpm and have a bit more wear. But the acceleration is worth the trade.
 

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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.
What size tires?
 

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Back in the day, I had 4.56 gears in a 57 Chevy sedan with a 292 (283 + .060) and a M20 trans. Revs were almost unbearable on the highway (so be careful what you wish for). But it would put Chevelles and Impalas with larger engines to shame in an impromptu street race. But then there was this 350hp/327 Nova that ruled the roost!😯
 

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Discussion Starter · #9 ·
Well suspension been worked, all rear redone, added rer sway bar poly bushes, mono leafs.. not sure how to and if I shd remove the front door crash bars.. 77 camaro.. super heavy doors.
 

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Here's the formula to calculate engine RPM:

RPM=(MPH x Rear Ratio x 336 x Trans High Gear ratio) / (Tire Dia inches x Torque Conv Efficiency)

Your case:

Assume 70 MPH Speed
Rear Ratio 4.56:1
Trans OD ratio .70:1
Tire dia 28"
Torque converter efficiency 1 because lock up torque converter. Non lock up is about .9 or .95 efficiency.

Plugging in the numbers, your engine will be spinning 2681 RPM at 70 MPH

Obviously if you're not running a lock up torque converter and you're OD ratio is something other than .70:1 the engine RPM number will change.

Plugging in 55_327 numbers and assuming 28" dia tires, his engine was spinning 3830 RPM at 70 MPH. Big difference. He also probably had tires smaller than 28" which would make it scream even more. Let's assume a 25" tire. That would make his engine spin 4290 RPM at 70 MPH. Not a good highway gear at all.
 

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Discussion Starter · #14 · (Edited)
I'll probably grab a set of 4.10s as well and compare down the road-

With 4.56:
65mph rpm is 2400rpm.
125mph est trap speed 1/4 mile its 4585rpm

4.10
65mph = 2150rpm
125 mph= 4250rpm

373:
65mph = 1950rpm
125 mph= 3750rpm
 

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1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
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18-20 initial, vac adv disconnected .. Hei stock.
Have you checked the total timing on this set up? Figuring out where it is at various RPM may provide some benefit.

When you have some free time do a google search on "recurving HEI distributor" and "limiting vacuum advance." It would take pages to explain the whole thing. What I can say is the way it is now can certainly be improved. I think getting the mechanical advance in a little earlier than the typically slow advance of the stock HEI and operating with an adjustable vacuum advance should be an improvement at part throttle and overall.
 

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I'll probably grab a set of 4.10s as well and compare down the road-

With 4.56:
65mph rpm is 2400rpm.
125mph est trap speed 1/4 mile its 4585rpm

4.10
65mph = 2150rpm
125 mph= 4250rpm

373:
65mph = 1950rpm
125 mph= 3750rpm
The numbers look correct,....
But you should never be in overdrive in a drag race, the Od gearset is not capable of living with that for long. It is strictly a low power, cruising speeds gear, not a performance gear.
Trans valvebody shouldn't even make/allow the WOT upshift to OD.
You also shouldn't be in lock-up on the converter at WOT, most converter clutches aren't capable of withstanding WOT for long either.
Takes an expensive converter to get one built to handle full power in the converter clutch.

Figuring 1:1 in Third gear, 4.56, 28" tire, 7% converter slip for a nice tight 3200 stall converter would put you at 7300 rpm @ 125 mph for a WOT drag pass.
 

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Discussion Starter · #19 ·
Thanks Eric .. yes aware of lockup for cruise only.. and will avoid 4that the strip.. I did use comp beehives and full roller rockers .. 7300 is high but only for a few s anyway ..

Cool, in process of moving shop so won't be getting round to it this month..
 

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Ok - I had mine rebuilt at art carr in Huntington beach 200 miles back- so far ive been happy but not sure if a better one will make that much of a difference? Im going to try a 750 and see if the performance increases..

higher stall or lower? currently 3200
Stall is going to be determined by the camshaft specs, as for the carburetor nowadays fuel injection delivers better performance and drive ability.
 
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