Chev 327 with a 2.75 gear. Comments?

If you're running a stock cam you might get by. If an HP cam it ain't gonna work.

 

I was wondering the same thing. Either he doesn't have 3.25 gears or his calculations are way off. As I mentioned, I am running about the same height tire and 4.30 gears, and I am only cranking 500 more rpms at 70 than he says he is. Something is off in the numbers.

Don

 

When I put my truck together for it's "shakedown" this fall, I was thinking that the 2.79 gears in back would be a problem, and that I would need to go with a set of 3.25 or 3.50 this winter.

I'm running a 327, 11:1 forged pop-ups, 461 heads, RPM AirGap, 670 Holley, LT1 solid lifter cam, TH350 with 2400 Stall, shift kit and 28" diameter tires.

I have to say the truck runs great.... It has no lack of power off the line, cruises at 60 at about 2400 rpm, and will run hard when you get on it....

The truck does have all fenders and running boards from gl***, so it is quite light however......

I may just leave the gearing as is, as I plan to drive this thing, and freeways are the norm around here to get anywhere..
Tom

 

That PG really changes things. The low gear on a PG is pretty tall at around 1.76-1.80 which combined with the tall rear gears might ake getting out of the hole pretty boggy. I'd keep what you have and do the taller tire change.

 

You are going to be pretty hard put to find any tires with an OD greater than 29" -

Need to determine the actual speed being traveled at 3000 RPM first and foremost.

Either way - I'd just drive 3000 RPM -

 

29" tires at 70 with a 3.25 and a Power Glide = 2636 RPM - the math don't lie

And that tall a tire with a PG and a 2.75 is gonna be a good race off the line with a Kia or a Hynudai

 

I have been messing with cars for over 60 years.. I gave up on drag racing, street and strip over fifty years ago opting for cars that performed well but could be driven for daily transportation, to and from work and on family vacations..
I found out about overdrives in the mid fifties, the cars that had them would run on the highway very well, in low range the cars were good on the street or on hills..
My '36 Ford has the Columbia option, 3.78 gearing which is unusual for a '36 Ford.. The car was very doggy with the stock 21 stud engine, when I put a hopped up 59 AB into the car, it woke right up.
As a general rule, OD equipped vehicle always have low ratio rear ends. i.e. a '59 Ford F-100 V8 with three speed will be .3.71, the same truck with an OD will have 3.89.
Fast forward to more modern thinking.. The modern AOD transmissions, 700R4 and 200R4 all use a gear ratio in the 3.25 range behind a SBC..
My '39 Plym has a 330HP SBC, 700R4 GM 10 bolt with 3.25 gearing.. the car cruises at about 2,100 at 70MPH.
Up until recently most people favored the 700R4 trans because of the low 1st gear. It has now been found that the 200R4 trans can be built up to take at least 700HP, the big advantage to the 200R4 is that it is the same size as a TH350..
I would strongly advise that you forget the 2.75/3.08 gearing, since you already have a powerglide with 3.25 gearing, replace the trans with a built-up 200R4 and drive on..
My brother has a very nice '54 Chevy 2dr post Bel Aire with a 350 engine and a 2.75 rear axle. He got talked into swapping the TH350 trans for a 200R4... I told him he would be unhappy.. He don't like to listen to the "big brother".. He can't drive the car in the OD range except on the interstate at speeds over 75, the smallest hill will prompt a down shift out of the OD range.. He messed up a nice car.. He is going back to the TH350 trans in lieu of re-gearing the rear end..

 

Keep the 'glide. Keep the 327. Put a QUICKCHANGE in it.

Have whatever gear ratio you want or need in about 15 minutes. If you build it right, it will be quiet and bulletproof with your combination.

And it's really nice to have all the ladies talking about what a nice rear end you have.

Game over, close the thread.

PS Use a GPS to determine your true road speed.

 

Comments? How about "wont pull a fat girl off a tricycle" ? And its traditional to boot!

Really, to be fair, performance is relative. I remember this woman I used to know refering to her Chevy Sprint as "Peppy". If you have ever used the word "peppy" to describe a vehicles performance, you'll be fine...

 

Why would he need to go taller than 29"??? His present tires are 26", so a 29" will make a huge difference to lower the rpm's.

 

Original Poster "old man's '37" said his exiting tires are 29 inches tall. I said he would have a hard finding a tire larger with a larger OD than 29". Where did you get his present tires are 26"?

 

as you can see opinions are many(including mine) pic you one out and run with it!!JUST DON'T MISS THAT SHOW,ITS A BLAST BROTHER. Good luck!

 

2.75's may be sluggish on the street, but they sure help if you ever decide to do the B'ville thing!

 

Every think you do to a car is a compromise. For me .here in northwest Iowa. most of my trips are going to be short trips no more then 50 miles at 55 mph. Over the last 50 years I have ran behind a small block anywhere between 3:10 gears to 4:11 . my personal compromise gear is 3:73. What I'm saying is yoy won't really know until you try it and get experience with it. Go ahead . It's only money and you gain knowledge so you can give the rest of us advice! Epp

 

That is an intelligent, informative post--thank you for posting it---used to run my 327 five hours at 3500 every weekend going home and back--3.70 gears 27 inch tires ----speedometer didn't work--early to mid 60's --cheap gas--my DAD and i made that trip just about every weekend for a year in my 62 vette--great times i loved that guy and those trips with him--he always wanted me to p*** and or race every car on the road------ me too

 

my wife has a '67 camaro. came from the factory 327 2bbl., powerglide, 2.70 rear. it is still a project for us. but someone drove it 60,000 miles that way. if you have a 350 or 400 trans you will have a lower first gear than the powerglide. you should be fine. gene.

 

This may help you find out what you need and want. 2661 RPM's is what you should be at right now at 70.

http://www.ringpinion.com/Calculators/Calc_RPM.aspx

 

I mentioned in an earlier post that my '41 pickup runs a 3.00 gear and 30 inch tire, and that I think it's a good compromise. After that, you posted that your car has a Powerglide. My truck was a complete pig with that rear gear combination and a 'glide. The TH350 made a huge difference in the drivability. Just one more data point for you to consider.

 

my apache had a small block with a th350 and a 2.73 10 bolt. i had no idea what the ratio was at the time but it ran great and wasnt a slug off the line at all. i cant wait to try out th emodified mill, muncie and 3.55 rear now.....

 

Jeez,what a firestorm.Simply put,you will be fine.Remember.KISS