westside807

Good day!
I am always reading post on here, but I haven't posted anything in some time. I always appreciate the knowledge gathered on here, even when some threads get away from the original question(that always cracks me up).
I have a 4 door 71 cutlass with the 350 that was rebuilt(original). I have a 350 transmission. The engine was bored .30 to clean it up, and a stock cam was put in it. Not sure what heads I have. I have an edlebrock performer intake, headers and dual exhaust, edlebrock 600 carb ( I believe), HEI distributor, and 2.73(non-posi) gears in the rear (I think). Also I have 22" rims and I believe my tire diameter is 23-24 inches. I think of my car as a real cool family car for cruising!
I finally got the car running great and I'm almost at 1000 miles, but I noticed that it sounds good, but the "get up" is lacking. I was told with my tire size to put 3.73 gears and posi in the rear and go to a overdrive transmission. My question is, is that enough to get me more "getty up"? I've read on here that I'm making around 160 horsepower(71 350), would my the new tranny and rear end be enough, or is there something else I can do? Id like more power/torque (whichever one I mean) when I hit the gas, but not looking for 400 hp, not racing just some street and highway cruising.
thanks!

joe_padavano

The first thing to do is ensure the car is properly tuned and the aftermarket carb is adjusted for your application. FYI, the original heads would have been No. 7s.

Your tires are likely somewhat taller than 24", since that would only leave 1" of sidewall on a 22" rim. Even 255/35-22s are about 29" tall. Large diameter rear tires and low (numerical) gears make for sluggish acceleration. The added rotational mass of those wheels and tires also limits acceleration, as engine torque gets used up just getting the tires to rotate. Steeper gears are definitely needed here. Whether or not you also need an O.D. trans depends on your actual tire diameter and selected gearing.

westside807

thanks for responding. I'm working on the tuning I think I'm pretty close. the tire size was a guess because I couldn't find where I wrote it down. I did pick tires with some decent rubber not the low profile kind. the reason for the overdrive was for the highway. I plan on taking the car on family trips from time to time, that's one reason I'm not looking for a whole boat load of horsepower and just want some more of the line get up.

Octania

"The engine was bored .30 to clean it up"


4.357 is one hell of an overbore
:-)


Maybe they cleaned it up at thirty *thousandths* (0.030) inch oversize instead of 30/100 (0.300 a.k.a 0.30or 0.3) ?


All kidding aside, though, rear end ratio indeed matters greatly. You can trade economy for fun just like that. If you want more fun, and it does not get drive so much that economy is crucial, then get numerically higher gears. That gear ratio is the number by which your driveshaft torque can be multiplied when applied to the rear axles. Multiplying a given engine's torque by 3.73 is way different than doing so by a factor of only say 2.73...

westside807

lol, I meant .030. I do care about some type of economy. I was wondering if the big wheels along with the overdrive tranny and the 3.73 gears are ok or should I do 3.42's in the rear? I want more power but I don't want to completely wreck my MPG's as they stand, not sure how many I'm getting right now btw.
I was told that other than the rear end I should get my heads "ported and polished".

1BOSS83

Here is a gear ratio calc that will show your true ratio with changing the tire sizes.

https://tiresize.com/gear-ratio-calculator/

Starting at a basis of a 225/70/14 with a 2.73 rear and moving to the hypothetical 255/35/22 will yield an effective GR or 2.48, that, as noted with a 3,500lb+ car is going to create some issues with acceleration. I wouldn't mess with the heads, the juice isn't worth the squeeze in terms of $/hp. A 4.10 rear would yield a 3.73 final ratio and make a dramatic difference in the giddy up.

westside807

ok thanks to all. BUT one more question. understanding that ill need more horsepower to smoke the tires, what does the bigger numerical gear feel like while driving? I suppose what I'm asking is what does the bigger gear ratio do if in my application I don't have enough power to smoke the tires? What's the physical difference while driving? For example, my imagination tells me that it could possibly force me back in the seat some when I accelerate hard. Is this true or is there something else? I hope this question is making sense...

1BOSS83

I think I understand your question.

It's going to feel like the car is climbing the RPM band faster, because it will be. The increase of numeric gear means the motor will have to spin more times to achieve one rotation of the back wheels. When you are cruising at, say, 40mph and floor it the trans will kick down into 2nd and acceleration will begin at a higher RPM by virtue of new ratios and you'll accelerate faster. You aren't changing the power of the motor, however, you are changing the operating range and thus the effective distribution of power.

westside807

1BOSS83, thanks!! the picture painted of the transmission kick down helps out a lot!! I think I got it. I think I'm going to go with 3.73 gears coupled with an overdrive tranny. First gear in that tranny and the 3.73's should be enough acceleration and the overdrive gear and my wheel size should get me back down to 2.73 or less on the highway. BTW I measured my tire diameter and its almost 29 inches.