I have the oppertunity to purchase a set of 71 LT-1 heads from a local guy. They are 2.02, 1.60 75cc...Casting # 3973487... Build Date : 8-10-71. If I can get them cheap, and have a bit of machine work done on them to clean em up, what kind of horsepower gain can I expect on my 72 L-48 without changing my cam? I have a performer, rebuilt Q-jet and header sidepipes on it now. Thanks guys!
Eddie
P.S. Would it even be worth it without changing the cam???


[Modified by Silvr77, 7:05 AM 1/28/2004]

 

That same casting #, 3973487, was also used on the base engine in 71 and the base engine in 72. Check your engine, you could already have them :) The differences in the heads from the base engine to the LT1 was in the valve size. So you could pull your heads, have larger valves installed and be at the same place. Best bet would be to go with some modern aftermarket alumn heads. And by all means change that cam. The base engine is a chevy passanger car engine with a VERY mild cam.

tom...

 

Save your money on these heads. Get a set of more modern performance heads. You will see much more power with the modern heads. As was said these are the same heads used in the base motor just a little larger valve. I doubt you would see a big perormance gain. I have a set of these same heads from my LT1. They are sitting under the bench gathering dust.

 

Thanks for the reply guys. I thought if I could get them for $100 it would be worth it....guess not.
Eddie

 

Might be worth it for $100 if they have been ported some, all depends on your end goal.

 

DON"T BUY them! They were the main part responsible for the incredible 40HP loss of the 71/72 LT-1 Vettes. The best bet is to save your money for a set of aftermarket iron or aluminum heads. Most used heads will require around $250 parts/labor for minimum quality re-build.

 

The loss from 70-71 was due to a change in compression ratios (larger chambers in the heads). The loss from 71-72 was due to a change in rating systems (from Gross to Net).

The loss from 70 to 71 was a real HP loss. The loss from 71 to 72 was a paper loss.

tom...


[Modified by Tom73, 12:15 PM 1/28/2004]

 

Actually, the LT-1 was SAE 370HP rated in 1969 with the 30/30 Z/28-Fuel Injected Vete cam but, never made production because of the demands for the aluminum hi-rise by the Camaro group. I feel the 1970 LT-1 (I have owned an survivor 54K mile car) is probably a little better than 370HP, but the 71-2 LT-1's (I have owned 3 including a C60 A/C 72 model) are WAY "softer" in their bottom end/low mid range power band compared to a 1970 (it can be proven by re-reading the road tests of that era: 1970 car always OVER 100MPH 1/4 mile trap speeds 71-72 struggled to get 98-99 MPH trap speeds.) The reduced horsepower was due to SAE Net ratings in 1971 partially because of the compression loss and drag from the accesories being accounted for in the new test but, also because of the "open chamber" 487/993 (casting numbers) type "smog" heads (THEY SUCK!!) John Lingenfelter the famous Corvette racer (may he R.I.P.) made a plea to the NHRA in the mid 1970's to allow the substitution of earlier closed chamber cylinder heads for Super Stock Chevrolet racers because of the great disadvantage of these "smog" heads. I can prove my point by taking a late set of L98/LT1/Vortec chevy heads and proving that the chambers have gone back to the closed chamber "style" of the 1964-70 Small Block cylinder heads. I will repeat it again STAY AWAY FROM THESE HEADS, THEY SUCK!!! unless you are a NCRS type guy, then find a set of "low performance" 1.94/1.50 valve "smog" heads and have them cut for the proper 2.02/1.60 LT-1 valves and guide plates, because, the original heads probably have sunken valve seats and are REALLY JUNK!! Beter yet get some Dart/Pro Action 180cc intake runner volume heads and make your engine a good runner like we did back in the 1970's early 80's when we swapped out 492 LT-1 or 292 Turbo heads on these "smog" LT-1 Vettes and were delighted with the owners surprise when he drove his now HIGH PERFORMANCE Vette (DO NOT GET THE BIG 200cc volume intake runners! they will soften your 350 into a "Dog" motor.)

 

Your base engine '72 should have 487X heads. The x-head had an intake port that was 10cc larger than the 487 head. If I could get them for $100, I would get them. Not for use on your car, but they are recognized as the better smallblock head and they have value to the restorer. You could eBay them for far more than your investment.