lt1/l48 engine heads

[Eddie R.]

Hi. Will the heads from a 1970 LT-1 engine fit a 1975 L-48 engine. I'm trying to get more power for the 75. Thanks Eddie Robin

[Edward J.]

Re: lt1/l48 engine heads

Eddie, Throw in a Lt1 camshaft and the heads, and loose all the emission stuff. the 75 Corvette engines was really at the bottom of the food chain for GM, some of the lowest horsepower engines for corvette. If you could find the rest of the 70 LT1 engine then you'll have something. Don't expect much of a HP gain. The flat top pistons are a killer for compression ratios and the cat. convertors and y-pipe choke the engine, it like putting your hand over your mouth and trying to breath.

[Ron G.]

Re: lt1/l48 engine heads

Like Ed sys, you need more than just the heads to improve its performance. Heads work in conjunction with the proper camshaft. Just something to think about.

[Joe L.]

Re: lt1/l48 engine heads

Hi. Will the heads from a 1970 LT-1 engine fit a 1975 L-48 engine. I'm trying to get more power for the 75. Thanks Eddie Robin

Eddie------


Yes, the 1970 LT-1 heads will work just fine on a 1975 L-48. The larger valve size will not do too much for you but the LT-1 heads have 64 cc combustion chambers versus the 75 cc on your original heads. This will increase your compression ratio significantly. The 1975 L-48 uses DISHED pistons. With these original pistons and the LT-1 heads I would estimate you'll end up with a compression ratio of about 9.5:1, a full point higher than the original compression ratio of 8.5:1. If you change the pistons to flat tops with 4 valve reliefs you'll have a compression ratio of about 10.25:1. That's the highest I would recommend for a street engine.

The original camshaft installed in your engine is the GM #3896929. This is an excellent street camshaft. However, you could increase your engine's performance significantly by installing a GM #3896962, the L-48/L-82 camshaft. This camshaft is still available from GM, the ONLY 53-81 Corvette original camshaft still available from GM.

[Joe L.]

Re: lt1/l48 engine heads

Eddie, Throw in a Lt1 camshaft and the heads, and loose all the emission stuff. the 75 Corvette engines was really at the bottom of the food chain for GM, some of the lowest horsepower engines for corvette. If you could find the rest of the 70 LT1 engine then you'll have something. Don't expect much of a HP gain. The flat top pistons are a killer for compression ratios and the cat. convertors and y-pipe choke the engine, it like putting your hand over your mouth and trying to breath.

Edward------


Actually, flat top pistons are the best for performance. Chevrolet used domed/"pop-up" pistons on certain small block high performance engines in order to use mainstream cylinder head castings (and their combustion chamber volumes) on those low-volume applications. The best way to have achieved the desired compression ratios would have been to design and manufacture cylinder heads with appropriate chamber volumes for the compression ratio desired and use flat top pistons. However, that would have been more expensive and unjustifiable given the low production volume of these engines.

[Edward J.]

Re: lt1/l48 engine heads

Edward------


Actually, flat top pistons are the best for performance. Chevrolet used domed/"pop-up" pistons on certain small block high performance engines in order to use mainstream cylinder head castings (and their combustion chamber volumes) on those low-volume applications. The best way to have achieved the desired compression ratios would have been to design and manufacture cylinder heads with appropriate chamber volumes for the compression ratio desired and use flat top pistons. However, that would have been more expensive and unjustifiable given the low production volume of these engines.

Yes Joe I had flat top pistons on my mind, but know they had a low compression piston( dished pistons).

[Duke W.]

Re: lt1/l48 engine heads

The 1975 single catalyst exhaust system is HUGELY restrictive. Internal engine modifications will do little more but lighten your wallet unless you FIRST do something about the exhaust system.

There is also much to be gained by optimizing the spark advance map.

A more aggressive camshaft can increase power and rev range once you fix the exhaust system, but it will lose low end torque, which could reduce around town performance, especially with an automatic and tall gear. How much time do you spend under 4000 versus over 4000?

Much has been written about how to extact more across the range power using an engine system engineering approach without screwing up the idle quality, low end torque or visual appearance in the engine compartment or turning the engine into a kluge with a lot of hot rod parts.

Duke

[Peter S.]

Re: lt1/l48 engine heads

Hi Joe,

Were the valves different sizes between the L48 and L82 in the 882 cylinder head? I had thought they were all 2.02/1.60.

I'm sure you meant L46/L82 camshaft in that 2nd to last line.

[Joe L.]

Re: lt1/l48 engine heads

The 1975 single catalyst exhaust system is HUGELY restrictive. Internal engine modifications will do little more but lighten your wallet unless you FIRST do something about the exhaust system.

There is also much to be gained by optimizing the spark advance map.

A more aggressive camshaft can increase power and rev range once you fix the exhaust system, but it will lose low end torque, which could reduce around town performance, especially with an automatic and tall gear. How much time do you spend under 4000 versus over 4000?

Much has been written about how to extact more across the range power using an engine system engineering approach without screwing up the idle quality, low end torque or visual appearance in the engine compartment or turning the engine into a kluge with a lot of hot rod parts.

Duke

Duke-----


Installed with flat top, hypereutectic cast pistons, the engine mods I suggested would, basically, convert the L-48 to an L-82 which was a pretty well-engineered package. It would, of course, lack the forged crankshaft and special connecting rods, but I think it would live just fine with the cast crank and existing rods.

You're correct about the exhaust system. However, removing or modifying it is a violation of federal law and, likely, state law in most states. I hesitate to recommend here that anyone violate federal law.