Hello, Guys

I'm thinking of replacing my 1978's original 350 ci engine L82 (220 hp) with a Chevy SB 350 Crate Engine. How big can I go and still use the original 3 speed Turbo Hydra-Matic transmission? Any pitfalls with swapping out the L82?
Any recommendations on a replacement crate motor? Just starting the process, but any advice will be appreciated. This Corvette needs more power. The 220 hp just doesn't cut it.....Cheers.

 

Why not just do an upper kit, heads, cam, intake, exhaust?
The L82 short block is a great start.

 

I agree, use the original short block as the basis for the refresh process. I understand that the crate is a good easy option. Install new heads, exhaust and the correct cam and you will have what you really want. There's benefits both ways as I have been going back and forth on this same issue but I only have an L48 or L83 to begin working with....neither are very appealing.

 

I thought about that, but the engine has been rebuilt somewhere along the way and I have no record of what was done. Also, I’d like to get up to about 400 hp and an upper kit won’t get me there.

 

.......Blueprint crate motor from Summit is the way to go.....

 

Are you using two different horsepower ratings to come up with that decision?
The 220 you start with is net, the 400 you and the crate engines are referring to are gross.
Remember the L82 is a low compression emission laden version of the 350/350 L46.

 

I think so too. Ecklers has a nice Blueprint Small Block Crate Engine with Roller Cam and Aluminum Heads. Dyno proven with 10.4:1 Compression. 383 ci. with 430 hp, 750 CFM Carb and HEI distributor. All for $4,600.

I'll check Summitt as well. Thanks.

 

Good point. I hadn't thought about the difference in net and gross hp. However, with the low compression ratio on the L82, it's hard to ramp up the hp. If I have to pull the old engine and completely redo the old engine, I'm better off replacing it with an new crate engine with more power. Then I have a warranty and much improved performance. Thanks.

 

I have gone Blueprint crate engine. Its a powerhouse. Go stroker. You going highway driving or tearing up the twisties? Might need to change your rear end ratio to suit (and a built transmission).
My stroker has 500/500+ hp/tq and has *****. People are asking me if I like my big block and I say no... its a 396......... Small block!

 

Wow! That’s a lot oh HP...I don’t want a cruiser. Just want more “pop” off the line. Right now, a VW will outrun this sled.
I was thinking a Blueprint SB around 400hp would work. That way, I could get by with my current trans and rear end.

Did you have any problems with matching up with the bell housing and torque converter???

Thanks.

 

I recommend you look at the available crate engines in the GM Performance Parts catalog. It's like turning a kid loose in a candy store. Most amazing, I think they have a modern SB, high horsepower engine, that is smog legal for any pre-1992 automobile. The catalog can be Googled and downloaded.

I bought a ZZ4 years ago for my 68. It's a SB, I think 415 flywheel HP. Aluminum recent technology heads, aluminum maniford,, roller cam, HEI distributor, Holley carb, mini-starter. Bolts right up to the stock bellhousing, stock manual or auto tranny.

 

Thanks. That’s sounds like just what I’m looking for. I would guess local pickup is available as well. I’ll check their website.

Cheers.

 

Maxacceleration, With your Stroker Blueprint, did you have to change the fuel lines to 3/8" from 5/16"? Did you use the stock manifold? The high rise manifolds at Summit Racing won't fit under my hood. What modifications did you make to the trans (mine is Automatic) and did you swap out the rear end? Also, did you upgrade the radiator with all that hp and did you replace the HEI distributor?

Thanks.

 

Dutch, 3/8" feed line & 5/16" return line. Mine is using the Holley Sniper fuel injection.
I have a higher rise hood than stock just to be safe for clearance. I used the crate motor, untouched or molested. (think about a low profile air cleaner) Blueprint thought their motor would fit under the stock Vette hood...hmmm...
My car is automatic also, but I upgraded to a different transmission, the 4L80E which is four speed OD (three speeds then overdrive) vs the 3 speed 350/400's.. A higher stall torque converter would probably be needed (mine is 2400 rpm).
My 10 bolt rear end is rebuilt stock with 3.55 gears, factory posi. We felt the auto might be gentler on the rear end. My car is pretty crazy, and needs to be matched, from motor to trans, to the rear end gearing. I have done a couple of drag race starts and the rear end is holding! lol
In keeping with your stock transmission, I would go 290-350 hp (aluminum heads for the best easier power gains). Find your rear end ratio - that will help for knowing how aggressive a cam you want to go. I would think a 3.55-3.73 ratio would be decent gearing with some highway ability still.
Headers, dual exhaust with a cross over pipe and you car will come to life I feel. Match it from front to rear!
Unfortunately, dollars kind of add up. Prepare so you can fund your car all the way through.

 

The rear end (differential, joints) will be the limiting factors in an engine upgrade before the THM-350 will have problems. You can probably get by with stock trans and rear parts up to about 350-400 hp. Beyond that, you need to get more strength into the rear, then the transmission.

 

Thanks, Maxacceleration

I have decided to dial down my hp to a BP 355/375 HP from TriStar Engines in WI. Their Crate Engine comes equipped with intake manifold, carburetor, aluminum heads,harmonic balancer, rear seal and flexplate. It also includes a MSD HEI distributor and timing cover. Since I already have headers, I can pretty much just drop the new motor in. I'm hoping that with this HP setup, I can still utilize my 3sp Auto transmission and just beef up the rear end. I thought maybe a 3.70 would work better with this setup.

How does this setup sound to you? I really appreciate your input.

I'm told deliveries are 10 weeks out, so it's time to make a decision.....

Cheers.

 

Ok. Thanks much. The setup I'm looking at will probably end up around 375 hp. I'm told I don't need to add a stall converter with this setup, a new flexplate. So you think my stock 3sp auto trans should hold up under normal driving? I do not plan to take this one on the track.

Cheers.

 

I would talk to your transmission shop and inquire about a shift kit. My '77 auto L-82 220 hp never was a good shifting transmission. Always had to let off for it to shift properly when on it. You want positive shifts. I am not experienced enough to know what can be done with an aging transmission (original?).
I would lean towards a rebuilt transmission I think. But that is just me.
Maybe someone can chime in on rpm's at 60 or 70 mph with 3.70 gears. 375 hp will accelerate good with 3.70's no doubt.

 

Great advice, Maxacceleration. I’ve read a little about “shift kits” and how beneficial they are. I will try to find a good transmission shop here locally that can advice on a rebuild and shift kit for a 375hp Chevy. With a new crate motor, I don’t want problems with the trans or rear end.

Thanks again for your help.

Cheers.

 

In the top picture in post #10 there are two leads going to the choke. On the Holley carburetor there is only one terminal. Can someone recommend the proper connection in this scenario? Recommendations for the fuel filter type and connections would be helpful as well.