I am thinking about increasing HP. Thinking too much has gotten me into a pickle, but what the hell.

Here's what I have: 76 L-48. Car is in very nice shape and was well cared for. PO had added a mild cam, FiTech EFI, and true dual exhaust. It is #'s matching (which makes little difference to me since I intend to keep the car and pass it on to my son or grandkid. It has the TH 3 speed auto transmission and the 3.08 rear end. I added Bilstein shocks, new front/rear fiberglass bumpers, Borgeson steering box, and a real steering wheel.

Here's what I think I know: After some research, I learned that the TH300 is a very good tranny, so I would not replace it. I know I do not want to race, but I would like a bit more acceleration from the stop light. I think I know that switching the gears in the rear end to 3.36 will help in that regard, while not stressing the engine too much on the freeway. It seems like a good compromise between between hiway speeds and decent acceleration. I know I would like 300-400 HP. I know I would like to stay married, at least for a while anyway.

Here's what I am wondering: Do I go full meal deal and get a brand new crate engine or an Edelbrock E-Street top end kit? What is a stall converter, and is it added to the transmission in some way? Is it a big expense to change the gears in the rear end? Are there other considerations in making this upgrade?

Finally, I am not a mechanic, so I would have to have the work performed by a knowledgeable car guy. Thanks, any thoughts would be appreciated.

 

Since you are not going to do the work, wouldnt the first thing to do is find a qualified Corvette shop to give you quotes on the various options you have thought of?
Assume it was a typo you have a TH400 not TH300.
If you are considering a rear change, I feel 3.55 would be more appropriate.
If you are not racing I would skip the converter.

 

Yeah, probably got the number wrong. I just know it's a TH 3 speed automatic.
I have dealt with a Corvette shop which is very reputable but expensive as well as a few other good shops not Corvette specific.
Thought this would be a good starting place. Not to the stage where I want to start getting quotes just yet. Not sure what I want to do.

 

I think if you are farming out the work, I would buy a crate engine and have them install it. This sets you fresh with a new engine. If you have the shop do all of the top end kit and new cam etc......parts and labor will be as much as a crate engine and you still have a 40 year old bottom end......with a crate, the shop will charge R&R and tuning......

Jebby

 

I would suggest you be careful as the car was not meant for that kind of power in 1976.
We have a 1968 C3 Corvette with a four speed and 427 and it runs nicely but it was made to make power and get it to the ground. I rebuilt the 427 and bumped up the compression using L88 parts and now I have a Corvette that has a "Traction Issue". If it rains then I can't take the C3 out because it can not stay in one lane while accelerating on a wet road.

I have tried tires and that just found more weak points in my Corvette. I let the clutch out aggressively and my left half shaft inner U-joint exploded. It had been a drilled U-Joint and was weak but the first drive with D.O.T. Racing tires sure sidelined my Corvette. The C3 at a racetrack wants to run in the 11 second range all day and that is after spinning my tires to the 1/8th mile mark.

By making over 500 Hp with a 427 the car becomes pretty difficult to handle. There are days I think about removing the L88 pistons and swapping in some 11-1 pistons. It would make the Corvette more usable and more friendly to drive on the streets. Sometimes there is Too Much Horsepower. I love my Corvette the way it is but I am heading up in years and the Corvette is too much for novice or average drivers. My daughter wants it after I am done with my earthly duties and like you I will hand the keys to my daughter. After she has learned to drive High HP, mega torque monsters like this Corvette.

Yes, I love going fast and this Car is fine for scaring the hell out of people with it's acceleration and sound. I am in the final stages of installing and setting up a Holley EFI system to make the life easier for those down the road.

But there is a point where the Car even a Corvette is going to be overwhelmed by the power the engine is making. With too much power I would even say that this Corvette I have created is a monster and I don't want it to hurt an unsuspecting driver. For the sake of the future drivers it might be worth tearing it apart to replace the pistons. My C3 started life as a L71 Corvette and was made with the extra heavy duty parts for the go-fast Corvettes of the day. There are a lot of parts that are much different in the later cars because of the HP drop.

Good luck in what ever you do!

 

I am with Jebby on this. A new crate engine can get you a lot of upgraded parts and improvements. You can also get some type of warranty on a crate engine. Back in the early 2000's I went through this dilemma. I ended up buying a ZZ4 engine because it had a roller cam and forged crankshaft. For me to add those parts to rebuilding by stock engine would have cost the same. Now if you did the work yourself, you could save a bunch of labor money.

 

Thanks for the insights-all good ones. I would save a hell of a lot of dough just by leaving well enough alone. The car runs very well as is, and with what the PO had done, it is not nearly the dog that it was in 76. Unfortunately, there's a lingering itch for the giddy up experienced in my 68 Goat many moons ago. Damn it, I just need to grow up. If I do anything at all, it will probably be the crate route. Even though the engine seems to be in fine shape for 40+ years, there is an old saying about throwing good money after bad. Thanks again; I'm in awe at the depth of knowledge in this forum.

 

It sounds to me like all you may need to do is change the rear end ratio and leave the motor alone. After all, it already has fuel injection, and that is a nice upgrade by itself. You said you have a 3.08 ratio and are considering a 3.36 ratio. I would like to inquire about how much you drive it on the highway. Most people who own old Vettes like this mostly drive them around town and not so much on the highway. If that description fits you, I wouldn't be afraid of a 3.45 or 3.70 ratio. I once drove across the country in my 1960 Corvette which had a 3.70 ratio. Changing the rear end ratio will give you a noticeable improvement in acceleration, and won't cost an arm and a leg. And by the way, I hear you on the 68 Goat. I had a 68 442, which had a 3.45 ratio by the way. I miss that Hurst 4 speed.

 

Oh yeah, the Hurst 4 speed. In college, living at home for the summer to work and got two speeding tickets in one week. Ma was not happy with the Goat, but I sure loved it.

 

Thanks Cloth, that might be the ticket. I take her out on nice Saturday nights for a cruise, the car that is. I'm pretty sure I will not be doing a lot of freeway driving. I live on the west coast between Seattle and Portland, so I might be inclined to make the short hop over to the ocean once in a while. That's only 50 miles, and the speed limit does not get above 50 or 60 at any point. I'm guessing my driving habits in the Vette are similar to yours. I'm just an old cruiser, so the 3.45's might be the way to go. And The War Dept. won't sh*t her pants.

 

I think 3.36 or 3.55 rare gears possibly b&m shift kit in the trans and it will give you a lot of pep around town. If not satisfied then look at crate motors. I think you will see a big improvement with that. 3.08 are big block or slug gears.

 

Tom, I recommend you confirm just which transmission you do have before spending a lot of money making more power. There s a big difference between the TH350 and the TH400, both of which were available in '76. The TH350 was standard with the L48 and the the TH400 came only with the L82.

If the car is original, you should have the TH350 - of course it could have been changed. The TH350 was not a terribly strong transmission to begin with, so if you're wanting to add even more power, and use it, you need to be sure the transmission can handle it. Driven normally with an occasional burst of speed the TH350 should be fine with stock power. Driving it aggressively, especially with added power or sticky tires and you will be replacing it much sooner.

Changing the rear end gears is definitely one way to improve seat of the pants performance. It will get you to the top of the power band of the engine quicker and as long as you stay away from drag radials, not add a lot of stress to the drive train. Unless you have a cam and induction system that will pull to 6,000 however, I would recommend not going higher than 3:55's.

Good luck... GUSTO

 

Just a reminder, even though I'm sure your shop knows this, if you change rear end gears, you will also need to change your speedometer cable drive gear in the transmission accordingly to keep it accurate.

 

Another thing, do you know for sure that you have 3.08 now? Maybe someone changed the ratio in the past that you don't know about. If you haven't already done so, I would recommend jacking up the rear and doing a rotation test. It's a simple thing to do for some peace of mind.

 

All things considered, you should sell your C3 and buy a C5. If you actually do upgrade your engine, trans and rear and pay other people to do the work, the C5 option will be cheaper. The C5 will be fast, reliable and provide good gas mileage.

 

I you change your 3.08 to a 3.55 that will be a huge improvement. It will feel exactly like you added 45HP in first gear, and rev much quicker.
And a 3.55 is not terrible on the highway. with stock size tires it should be 3142 rpm at 70 mph. vs your 3.08 at 2726. Sixty is a little calmer like 2700 again.
Drove my old car with that rear gear in it for 27 years, and took 100 mile turnpike day trips in it.
If you only change it to 3.23 you'll say why did I spend so much for such a small difference?

 

Cloth, that is a great point. I assumed the car had the original 3.08 gearing. You know what happens when you assume stuff. Thanks, I will determine for sure what is back there. That could have been a costly oversight, not to mention embarrassing.

 

Thanks Leigh, that is probably what I will do. Do you know if the shop has to drop the rear end, or can the swap be done with the car on the rack? Can you tell this is uncharted territory for me?

 

I am pretty sure that they will have to remove the differential. If you open the differential be sure to buy a set of Posi Clutches while you are at it. To rebuild my differential they had to remove it from the Corvette.

 

https://www.gmheritagecenter.com/doc...t-Corvette.pdf

perhaps for MY1976 vette, L48's auto is THM350 w/ 3.08 rear
while L82's auto is THM400 w/ 3.36 rear

All MY1976 C3 have large comb chamber heads (~ 76cc) while OE L48 has dished piston; L48 needs compression.