Is 3.27:1 R/E Too High For A 3.27 340HP
 

I am removing my original 4.11 R/E and replacing it with a more highway friendly rear end. I found a 1963 station wagon Posi 3.27 rear end. Since I have the original 4sp T10 my final gear ratio is 1:1. With this final T10 gear ratio the 3.27 rear end ratio, the RPM at 70mph is about 2800rpm. Not bad, but I was thinking of using a 3.36 or a 3.55.
I am trying to beef up my 327 340hp to about 375hp with a roller cam and roller tip rockers. Great midrange Lunati Cam
I am wondering if anyone is using a 3.27 rear end with a similar engine and transmission? A 3.56?
Bob

I am wondering how a '63 wagon got a 3.27 rear gear?

A 3.36 gear with a wide ratio four speed will work fine for normal stop/go driving but you'll think you lost 50 horsepower over the 4.11.

A 3.36 gear with a close ratio transmission isn't too good at all for much stop/go driving.

I assume you are talking about a '62 with a solid axle.

Gearing depends on your mix of city/highway driving and the hilliness of your terrain. A CR trans with a tall gear will make starting out somewhat difficult, more sluggish performance off the line, and shorter clutch life.

Consider installing the tall gear along with a transmission swap. A lot of guys use various five speeds, but there are usually significant integration issues. Consider a Richmond Super T-10 with the 2.88. 1.91, 1.33, 1.00:1 ratio set. It should integrate relatively easy. The spline counts may be different, so a different clutch disk and driveshaft yoke might be required, but I believe the OE linkage will bolt right on.

The 2.88 first gear with a 3.27 axle would be equivalent to a 2.20 low CR trans and a 4.28 axle, so about the same as your OE combination. The intergear ratios are 1.51, 1.44, and 1.33. The one-two gap is pretty wide, but won't be than noticeable, and then the ratios become closer as you work your way up. This is the opposite of early T-10 and Muncie wide ratio transmissions that have close 1-2, 2-3 intergear ratios and then a huge gap to fourth.

If you have Excel search for threads stated by me and download the gear chart program and have at it.

Duke

I am assuming the '62 4 speed is a close ratio. Am I correct?
The ring gear had 36 teeth, the pinion had 11 teeth. It's a Posi.
Bob

Duke, I'm already swapping the rear end on a numbers correct car. I wanted to stop there so I want to use the OE 4sp. I assumed all '62's had solid axles.
I have a '56 BelAir 2dr HT with a 327 with about 300horse. I installed a 3.36 Posi unit in it. I am using the OE 3 on the tree with overdrive. What a sweetheart to drive. Just like driving a 5 speed. I can cruise at 70mph doing about 2300rpm.
With 3.56 gears I imagine I'll be spinning about 3 grand at the same speed?
Bob

the GM archive center shows the 62 with a 340 received the close ratio box with a 3.70 rear. it shows optional rears as low as 3.08. What does Lunati say is the appropriate ratio for their cam?
https://www.gmheritagecenter.com/doc...t-Corvette.pdf

Hmm, dunno about that. The 4.11 rear end seems to be correct to me. As for the Lunati recommendation, I wasn't aware they made such recommendations. Seems there's a myriad of possibilities as far as gear ratios go. Unless it has overdrive, final gear ratio is always 1.1 as far as I know.
Perhaps someone can enlighten me, The Lunati Voodoo roller cam number is #201207 with roller tip rockers.
Bob

If it were mine, I would install a 3.55 rear end with your 2.20 4 speed if you want easier highway miles. Maybe even a 3.70.

And I wouldn't install roller rocker arms. Or a roller cam. But it's your car.

What you propose makes zero sense. More performance with less axle ratio. You'll never get it to move from dead stop without slipping the shit out of the clutch. detune the engine to 300 hp spec or put in a 5speed overdrive or forget it.

If you don't mind the clutch slip needed to launch your much heavier 56' BelAir, with the 3.36 rear gear, the lighter Corvette should not be a bigger problem.
First gear in the CR T-10 with a 3.70 is very close to the 3-speed with a 3.36. GM did not fit a 3.36 with the CR T-10 in 1962, so it is unlikely that someone has the exact combination to offer advice.
Second gear in the CR T-10 with a 3.36 is very close to second gear with the 3-speed with a 3.36 (one you get out of first gear the performance through gears 2, 3, & 4 will be better than with your 56' BelAir).

The model of your cam selection in earlier threads indicate engine performance similar to the GM 350hp hydraulic cam, with an expected improvement in low rpm torque over the GM cam due to the roller lifter cam profile (making low rpm launches less trouble). Maybe someone with a CR Muncie and a 3.36 in a later 350hp/327 can offer what they experience (the closest real world comparison)?

Nobody but you can make the comfort call you are asking opinions about (use your 56' experience as your guide).

Yah, engine is being dropped from 11.5:1 to about 9.6:1 with flat top pistons. Heads will not be ported but the sharp edges will be smoothed out or chamfered (?). I want the performance at midrange with lower rpm at 1.1 GR. I am also adding hardened seats.
In essence, what I'm doing is dropping my compression ratio, adding an excellent mid range cam, improving air flow from my camel back heads with 2.5" exhaust, keeping my original T10 4sp, and replacing my original 4.11 Posi with a 3.55 Posi. I have no idea where my HP will wind up at, but the machinist sez it will be better than the original 340...
Still make zero sense, please tell me where I'm wrong so I can stop payment on the last check I gave my machinist.
Bob

I would go with a 3:55 and 5 speed with .6 overdrive - great on the highway and great around town.

I have a vette with 3:36 + stock auto and it's not bad as an all around setup.
I also have a 3:55 and 5 speed vette - much more fun....

Thanks for your voted of confidence. Please keep in mind I have an overdrive 3sp in the '56 with the 327. That means that with the Borgward overdrive I have two different speeds for every gear shift...including 1st, which is near impossible. So in reality I have 5 speeds out of a 3 speed with my final OD ratio at 1 to .070.
Bob

Lemme guess...... your engine builder also recommended that the block be align bored too?

Keep in mind, your '56 Bel Air transmission has a 2.94 1st gear ratio which makes a whole lot difference vs the 2.20 first gear in your Borg Warner in the overall gear ratio.

One of the posters here has often said he bought a new 340 hp Sting.Ray/StingRay with the close ration transmission and the 3.08 axle. Ask him how he liked it for everyday stop/go driving.

Do a search on threads started by me to get accurate answers to your gears.:D

Do I read sarcasm in your "guess"? The block is being bored .030 over and honed. Does your machinist charge you extra for align boring your block?
Bob

Maybe I'm wrong but I get the feeling your engine guy is going to sell you as much non necessary machine operations as possible. As an example, read some of the dozens of discussions here about hardened valve seats. Absolutely not necessary for our engines. And often dangerous/fatal on these heads.

I would get at least one or two more opinions from different shops on this build.

I also wouldn't drop the compression ratio to 9-1. That will kill any possible horsepower that the new fancy cam may add.

And hopefully, he won't recommend going to larger (1.6"-2.02") valves. That's another instant death.

Take your time and do some research on this.

There are a lot of very knowledgeable people here. (not me....... I'm just a dope that stops in here sometimes)

Thanks Mike. I'll be ordering the new Posi rear on Monday. My initial preference has been the 3.55. I opened this thread to find out if I was on track. I've driven a 265ci with 3.08 gears and my 3 on tree. I couldn't beat a Prius off the line.:-)
Bob

Keep in mind an overdrive has no effect when starting from a stop in first gear. I have owned a number of vehicles with an overdrive box behind the transmission, and none effected the lowest gear available for selection for starting from a dead stop.

If you want the same 2.94 first gear grunt of your 56' BelAir 3-speed, and the .070 high gear cruise rpm of the 3-speed with the OD, then you should be looking at wide ratio 5-speed or 6-speed transmissions.

Keep in mind, any transmission without a wide range like the BelAir combination will be a compromise, either on a start from dead stopped, or with the cruise rpm (pick you favored benefit, and decide).


Keep in mind, that every bit of free advice is worth what you are paying others to ignore it (your choice of words and phrases, and final decisions, come off reading a bit unappreciative).