Well I have been catching up on the forums and see a lot of gear ratio questions and answers etc and I have to say I am more confused now than ever .

My train of thought is that the gear ratio selected should assist the engine in obtaining a certain speed it’s a force multiplier.

as an example you have a motor with x amount of torque let’s say a small block Chevy so it goes through a transmission then drive shaft to a differential, the engine say puts out 250 ft lbs so it needs fairly steep gears to move it from a dead stop say 3:55 gear ratio

now we have a big block olds engine

It goes through the same transmission but it has 500 ft pounds of torque, because it has more torque I am able to use say a 3.08 ratio because the motor doesn’t need to rev as fast to create the torque?

I see folks with big blocks upgrading to 3.90 or higher at the very least 3.42

in my mind the big motor which is limited in rpms as opposed to a small block Chevy etc doesn’t need the steep gears to accelerate? And will reach the redline faster requiring a shift or easing off the throttle from a stop all that torque will just spin the tires unless they are sized and sticky enough to keep traction

my car has 3.08s and an m20 it has a 455 with the 500ftlbs so I decided to leave the ratio and let the motor do its thing did I screw up?

I am not going to drag race it but don’t want to crawl away from a light either lol


any thoughts?

 

You did not screw up. I've talked to a guy with your set up and he has a 68(?) Cutlass that can do wheelies.

I on the other hand have a 455, th350, and 3.55. The only thing I can do is burn gas and do burnouts.

 

Hi Ed
You should be fine with that setup
Alain red W-31

 

I think you made a good decision. I wouldn't second guess it unless your desire or goals change in the future.

 

Eddie, don't over think this thing. Drive it for a while and then decide if you want more "Get up and Go" (lower gears). Those little engines need lower gears to try to keep up with the "big inchers". The M20 is a better tranny for around town and with taller gears.

 

Over thinking is my arch nemesis I fight myself with every decision, lol that’s why it’s taking me forever to finish this thing lol , but back to the gears the car ran well with the 3.08s and m20 and that’s when it was a 350 , I was thinking back though that my 69 gto had 3:55 and a 4 speed ( m21) I believe and a stockish 400 in her she ran very well , only remember getting beat in the stoplight wars by some hooligans in a 442 lol so was pondering the decision again

 

Not tryin to be a dick but I think you may have omitted a few relevant details on that ‘68.

To the thread-
My 530 ft/lb engine loves the 3.90 in the car. For that matter, my built LS6 loved the 4.56/M22 and short tires in my 70 SS, then there was my 65 442 with 4.11 and M20, who needs low range and a transfer case?!?

In my observation, gearing for the track is optimization, for the street I see it as finding a good compromise to balance manners and performance.

Ed, that 3.08 is fine with the torque you have available. 3.23 - 3:42 likely better accelerating but not everyone can tolerate 3:42 on the open road. Get to high 3’s and it’s a narrow group that can tolerate the engine speed, noise and potential cooling issues. As noted with some of my old cars, I have settled kind of in the upper middle on gearing and tamed the cruise with overdrive. Kind of like having your cake and eating it too. I am happy with mixing eras of components, just need money and/or ability if you want to limit concessions.

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If you're not racing, don't worry about it.
Another factor in your engine comparison is torque curve. A 455 (usually) has a big fat torque curve, meaning it is available over a wider rpm range. That's where you can "get away" with a wide ratio trans like the M20. A small block is usually more "peaky" with a more narrow window. In that case, you would want the gears closer together to stay at the power peak. Hopefully, that makes sense. The problem with Muncies is that the close ratio kills 1st from a 2.52 to a 2.20, which affects the launch, depending on rear gearing.
The general rule of thumb is a 10:1 overall launch ratio- 1st x rear, in your case 2.52 x 3.08= 7.76. Changing to an M21 or 22 - 2.20 × 3.08 = 6.78, a full point and much further away from the "magic" 10.

 

Thanks fellas your all pretty damn awesome

 

Just curious what diameter tire are you running?

 

I previously ran bf radials and 295/60 15s I plan on running 275 60 15s if they fit I took the air shocks out and replaced the springs worse scenario I’ll run 255/60 15s

 

That’s 28inches on diameter

 

​True because excessive torque makes up for lack of gear. Up to a certain point.

Motor Trend September 1968 tested 2 Hurst Oldsmobiles. One with a 3.08 rear gear and another with a 3.91 gear. Both ran identical 0-60 times of 6.65 seconds. And were still even up to 75 MPH. That tells you all you need to know ... While the 3.91 version had a more agressive cam and was non AC. Both were making 500 lb ft of torque... ( By the 1/4 mile marker however the 3.91 version was 3 MPH faster)
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I believe you have an ideal set-up for your wants. As much power as you have can never crawl off of a line ...

If drag racing and searching for that ultimate et was your thing. And extreme gear, 3.42 and up would be needed.

That is killing your rear gear ratio. You are effectively turning the 3.08s into 2.86s with those tall tires. But again if it suits your current needs I would not alter anything. I personally would love 3.42 gears on my 69 because I believe it will result in a much quicker et at the track. But my daily driving will be even more challenging. As it is with my current 2.78 she wheelspins for quite a while from a dead stop stomp before achieving traction. If I want to take off hard and fast, pedal play is a must.

 

I'd say there are big relevant details missing or.......it wasn't the truth.

 

Well it's not my car, so I don't know all the details of the build, and I'm recalling a conversation from like a year ago.

It's definitely built up, it's a gasser. I could be wrong about the gears, could be 3.23s. I just remember him saying that my switch switch to 3.55s was a bit overkill. I also remember that his 455 is built up, but nothing insane for 455 standards.

 

I think I remember that j from Chicago ran a big ok delta with a 455 auto and 3.08 gears and was somewhere in the 13s in the quarter ? It’s been a long time so I could be wrong I believe he pulled the front wheel but I digress that isn’t what I’m after, I just don’t want the old girl embarrassed by a fart can Toyota at a stop light lol

 

Your thinking correctly. It was great to read your thoughts. Especially since your not drag racing it, as long as your comfortable easing off the stop light with M20 and 3.08 gear It is smooth and can still drive on the highway leave it as is. On a different note, drag racing with high torque 455s and mild gear combos with low rpm shifts is totally doable.. I have ran 12's in various 2.93 and 3.08 geared combos and had friends do 12 with 2.73s and a 455. Seen really good ones run even 10's with a 3.08 NA. Even lately on Youtube Vice Grip garage showed they could drive that beater Chevelle thats packing a boosted 496 and 2.73 gear mini spool rear and went a 9.7@140 .... Those much less highway friendly changes to 3.42 or 3.91 from a 2.73 or 3.08 often on a 455 if it was even tracked tested may only give a whole .1 tenth of a second improvement at the expense of driving pleasure ! Not worth it .

 

Just accept that it'll probably be beat by the Toyota, but all the attention will be on you since nobody cares about a Toyota.

 

My 70 Cutlass wagon pulled the the steel SSII front wheels a bit with 3.08's on 26" slicks running 12's