DJmaya

So what should I expect to happen if i was to switch the rear gear from a 3.7 to a 3.08 on an 1972 LT1 with a close ratio transmission.

The purpose is to have a nicer highway speed drive (looking to drive it up to 3 hours at 70mph+), I am not interested drag racing and a full transmission change it's just too expensive.

Really, I am concerned about the "close ratio" part mixing with the low 3.08 rear gear.

Gordonm

It will be a dog off the line. The low 2.20 X 3.08 gives you a 6.77 1st gear ratio. That combined with the long duration cam the LT1s had with not a lot of bottom end will make the car a dog off the line. The close ratio trans was designed for road racing and is a terrible street trans. Some will disagree but unless you have a ton of low end torque which LT1s are not known for this combo will not be a good one.

Les

My thoughts exactly.

63mako

A honda civic will literally blow your doors off if you do that.

roadblock69

Besides being quite difficult to drive away from a stop, expect exagerated clutch wear too.

Buddy1980

Go ahead and do the job right, install a Richmond 6 speed with the 2.77 1st gear and a .62 6th gear. That will give you awesome acceleration with a 10.24 overall 1st gear, and then give you a final drive in 6th of 2.29 which = better fuel mileage. The trans will bolt in with no changes to the car except for the trans mount bracket needing minor alteration.

Les

That would be a nice option except for the fact that he said a trans swap would be too expensive. That's a shame because I'll bet he'd love it.

Danish Shark

No experience with the LT1 here, but the whole point with the LT1 is that it's relatively high revving, so putting a low gear ratio in it is sort of counterintuitive?

I have a 3.08 gear and even with the M20 it's kind of a pain.
I have a big block, so low end torque isn't a problem, but just the fact that it's actually going quite fast in first gear, even at idle, gets annoying in traffic and cruising arround town.

63mako

If you can afford a 1972 LT1, plan on driving it distance, are concerned about highway rpm and are willing to spend the money on a gear change spend a little more and improve your car, driving experience and fuel mileage rather than ruin what makes an LT1 an LT1.

Matt Gruber

if u want to have your cake, and eat it too, with 9:1 CR,
get the 3.08 and swap the cam to an XE262 Only adds $160-180 expense. Or if you like the solid lifter sound like the LT-1, get the Magnum 270S. about $80 more than the XE262. EDIT OK would need $40-50 valve springs too and might need the center divider on the intake sealed off to give it a low end torque boost.

And if u want to KNOW how it will drive off WITHOUT a cam swap, just try starting out in 2nd gear. Can u get the hang of it?

63mako

Or just sell your LT1 and buy an L48 car with a 3.08 already in it. If your tearing the top end down and pulling the rear differential and spending $1500 or so on redoing it to turn it from an LT1 to a base corvette it is a sad day in the corvette tech and performance section. Not what I would do or recommend and just wrong on so many levels. Drive it as is and appreciate the solid lifter RPM buzz running down the interstate or drop the extra $ on a trans upgrade.

Les

Matt Gruber

Still get the solid lifter buzz with the comp magnum SOLID 270S. it just pulls hard from 1500 instead of 4000. (according to an old dyno test i have.) LT-1 cam has No advantage over a L82 cam in a low CR engine until 4000. Seriously mis-matched parts in 1972 due to EPA. LT-1 cam likes 10.5-11:1
Correct to factory mis-match and enjoy the car!

Dan H.

Agreed, from a fellow LT-1 owner. These cars are hot rods, leave them that way!

I don't understand the obsession on this forum for "better gas mileage" and "highway driving comfort". Its not a prius or a lexus. I tear up the back roads and ride the slow lane on the highway @ 3000 rpm.........

joewill

no one is answering your question.. going to a 3.08 from a 3.7 will drop your rpm across the board by 17%. cruising at 3000 rpm with a 3.70 will now cruise at 2500 rpm.. at the same speed.

most corvettes of that era had 3.08 as standard gears with a standard m20 4-speed. a very popular spec. the M20 had a 2.52 1st gear, the close ratio was 2.20 1st gear, which is 13% lower. hardly a giant difference. you will see that is is harder to get moving by just a little, but the cruising RPM with your rear end ratio change will be a bigger difference since 4th gear in both trans are 1:1 straight thru

63mako

Right. Most Corvettes of that era had 3.08, wide ratio 4 speed and L48 engine. This is not one of those and should never be converted to one of those anemic vehicles. It is a LT1, close ratio 3.70 gear chrome bumper vette. It is a dying breed and should stay as is. If it is "upgraded" It should be with keeping it's heritage in mind. A 5 or 6 speed is a valid upgrade provided you keep the original trans for posterity. JMHO. The point not addressed above is the cam in the LT1 is designed for high RPM operation and will fall on its face with the 3.08 as pointed out earlier.

63mako

Solid LT1

If you don't care about originality, go with the 3.08 and a Super T-10 4 speed with a 2.88 first gear we used to do this all the time back in the 70's in our Camaros. The Vette guys always had the $$ for a Doug Nash but, we did it economically. 74 and later Vettes had Super T-10 so shifter is readily available.

Matt Gruber

Super T-10 is a nice trans!
.
There is another trans not as nice shifting they say, but some C2 guys like it. I never drove it. It is used in 80's vans. a 4 speed with ~ a 3:1 1st and has about a .85 OVERDRIVE! Talk about a WIDE bunch of ratios!
Leap off the line in 1st with a 3.08 and in 4th it is like a 2.62 rear.
Any problem has multiple solutions.

cv67

Sounds like, for the money a cam change is his best money spent. He can always put a solid back in it later if he wants.
If it were me Id cruise it at 3k or whatever and enjoy the sounds. It wont hurt anything