I'm just going to drop off my rear end to do the torsion Carrier upgrade to my 9 bolt. The question is do I leave the 327 gears or put in a set of 370 I have. I'm about to install Is ported intake runners planum. And refresh motor incl heads and n cam. I have read some posts that say 3 seventies will put you out of the power range and can actually slow the car down. With these upgrades is it worth putting 3 seventies or stick with 327? Does anybody have some real world input rather than theory??? Thank you in advance!

 

I don't think there's a definitive answer regarding gearing. Depends on powerband, transmission, intended use and personal preference. I have a hsr (short runner, higher rpm) intake, 212 218 cam, 5 speed and still prefer 3.08 gears. 3.42 would probably be the best compromise for me but I don't feel its lackluster with the taller gear. I don't race, I like low rev street cruising. And the engine has plenty of low speed power to support it and be comfortable.
Your intake is likely forcing a peak hp rpm of 5k or so, but that's purely an assumption. If you don't like your engine revved up street driving, then 3.27. You want to mash and go but don't care about top speed, 3.70. That's my general take anyway. If you're racing mostly then the question becomes more numerical for peaks where you want them.

 

Ive had a Borg Warner rear end with 3.27s and it was perfect in my opinion with a mild 350. I run 3.73s now and while it does have a great launch it blows through first gear so fast it makes it easy to over-rev the engine. If you had a huge cam that pulled 7000 RPM the 3.70 would benefit you. If you run 5500 rpms I say the 3.27 or the 3.45 gearset will be perfect

 

I'm leaning on sticking towards the 327 I'm just so unsure considering I already owe the own the 370 sitting in the Box.
I'm pretty sure I've read in the past that installing the 3 seventies in some cars slow them down. I'm really only looking for the car to be quick in the quarter mile. Thanks for the reply

 

If that's truly the case, powerband, transmission gear ratios, torque converter(if auto of course) all factor into axle ratio. You don't want to upshift right before the traps or an axle ratio low and kill your 60ft. Which is more important, the quarter mile time or the drive to and from the track?

 

True! I think everybody's answer is the QM time. Lol

 

So many factors will determine which gear set is best suited for your car. It's almost a trial and error to see what works best.

My race car uses 4.86 gears. I run a powerglide with a roughly 6000 stall converter. All the drag software programs said I was running too much gear. I swapped in a set of 4.56 gears for one weekend and didn't change anything else. Car slowed down terribly. With more tuning, maybe the converter stall needed to be different etc, it could have been faster. Put the 4.86 gears back in and the car picked up back up again. Always wanted to try some 5.14 gears but never got the chance.

Current gearing, converter stall, shift points etc are just about perfect. The engine internals are designed to make power to 8000 rpm however I shift around 7400. RPMs drop to around 6200 after the shift and peak to around 7200 as I cross the finish line. If I had more gear, I could shift a little higher but that increases the risk of breaking more things.

Converter stall depends on cam grind because you want the stall speed to get you into the powerband as quick as possible and stay there while at WOT. Gearing and tire height need to be matched so that you can get off the line quickly and max out the engine as you cross the finish line in high gear.

If you are currently crossing the finish line with the 3.27 gears and are nowhere close to the shift point when you cross, then you need more gear and the 3.70's will probably help.

In the early days racing my car, it also had 3.27 gears and a 2800 stall converter. Only had a 383 under the hood back them. Was shifting around 6800 but crossing the finish line around 5000 rpm. Car was very slow off the line but near the top end of the track, the engine was starting to get into it's powerband. I ran out of track before running out of rpm. Swapped out the 9 bolt diff for a 10 bolt with 4.10 gears and the car ran much better after that.

 

thanks I agree I think I will stick with 327 and have to see the results appreciate the feedback