I have a 72 LT-1 that I'm looking to change over to take unleaded gasoline (I've been putting lead additive in since I've owned it - 8 years!). I am also going to go through the motor while I'm at it. 1972 LT-1's were only rated at 255 h.p., but 1970 LT-1's are rated at 370 h.p. I'm looking for suggestions of what I can do to boost the h.p. and mimic the 1970 engine. Anybody know what some of the key differences are between the 1970 and 1972 LT-1 engine that I can take advantage of while I'm going through it?
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Re: 72 LT-1
Beginning in 1971 ALL GM engines were set up to run REGULAR unleaded gasoline. This would include your engine. If it's original it doesn't need premium and it doesn't need "lead substitute" or any other snake oil additive. The change from the '70 version was dropping the CR to 9:1, which included different pistons, and I believe the heads also have larger chambers. There were also calibration changes to the distributor and carburetor.
If you rebuild the engine you could probably use the '70 pistons to regain some compression, but to achieve the full '70 value, you might also have to install an earlier set of small chamber heads.
In any event, owners of SHP 327s appear to have no more than minor detonation problems with the original type pistons and heads. By using a composition gasket the real compression ratio turns out to be about 10.5:1 and the dynamic CR works out to less than 8:1 due to the late closing inlet valve of the LT-1 cam, which I recommend to replace both the 30-30 and Duntov cams used on 327s.
When you disassemble the engine you want to measure piston crown/deck clearance very carefully, so you have the data you need to start computing actual compression ratio, Then pick a head gasket that results in a maximum of about 10.5:1.
Also, you do not need hardened valve seats. Valve seat longevity will be fine if you set the valves properly. E-mail me if you want the valve adjustment document.
Duke -
Re: 72 LT-1
I thought in 1971 all engines were using hardened vale seats?Comment
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Re: 72 LT-1
yes they had "induction hardened" valve seats. they had no inserts GM just using RF generators to heat the valve seat area to harden it.Comment
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Re: 72 LT-1
Don't forget that horsepower ratings in 1972 were expressed in terms of net horsepower (all accessories and exhaust attached). 1972 LT-1's might have slightly less gross horsepower than 1971's 330 horse LT-1, but most of the difference lies in the measuring, not the engine.Comment
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Re: 72 LT-1
clem and lyndon-----
The induction hardening of the valve seats did not begin until the 1973 model year. Although 1971 and 1972 models were designed to run on regular unleaded gas via the drop in compression, they did not have the hardened valve seats.In Appreciation of John HinckleyComment
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Re: 72 LT-1/71 LT1
71 and 72........... Same engine. NOTHING different. 70/71-72....different compression (11:1../..9:1), different heads..(64cc/72cc) and depending on production date, some 70's had 2.5" ex. man, some had 2"....
Hope that helpsComment
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Re: 72 LT-1/71 LT1
2.5 inch manifolds!!! It's always been my understanding that the last use of the 2.5" manifolds was 1965.
Anyone else have any comments on this?
DukeComment
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Re: 72 LT-1/71 LT1
Duke....My buddy has a 1 owner, radio delete car with 2.5" manifolds. He ordered the car and still has it, I can't remember for sure, but I think its a 70.
The editor, Terry McManmon, is the guy to look to for this answer............Comment
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Re: 72 LT-1/71 LT1
Bruce-----
I think that your friend has some misunderstanding regarding the outlet size of the exhaust manifolds. 2-1/2" outlet small block manifolds were not used after 1965.
Another "confirmation" that 2-1/2" outlet manifolds were used for all 70-72 LT-1s is this: ALL 1970-72 LT-1s were equipped with AIR (air injection reactor system). Therefore, the exhaust manifolds used with these engines had to be also equipped with AIR fittings. GM NEVER produced a 2-1/2" outlet size exhaust manifold which was equipped with AIR fitings.
If your friend's car is equipped with AIR (as it should be if it's as originally built), then it has to be also equipped with manifolds with AIR fittings. These manifolds have to be 2" outlet.
If your friend's car is not equipped with AIR, then it's been removed at some point. If so, the manifolds could have been changed at the same time to the 62-65 SHP style manifolds with 2-1/2" outlet. Without AIR, and assuming that certain, specific 62-65 style manifolds were used (there were originally 4 different castings), it would be a direct "bolt-on" and the engine could appear completely stock. However, it wouldn't be.
The only way that there could be a completely stock and original 1970 LT-1 with 2-1/2" outlet exhaust manifolds would be if there existed some hitherto unknown exhaust manifold castings. I really doubt that such exist at this stage of research.In Appreciation of John HinckleyComment
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Re: 72 LT-1/71 LT1
Joe...Let me check and I'll get back to you. Is it possible I'm confusing the size of the manifold to exhaust pipe? Is there one manifold that goes from 2" to 2.5 pipes, and one that is 2.5" to 2.5"?Comment
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Re: 72 LT-1/71 LT1
(1) Very likely. (2) Yes. All 70-72 LT1s. Exhaust pipe (2 1/2") swages to 2" at manifold. (3) Yes. 454s. 2 1/2" manifolds with 2 1/2" exhaust pipes.Comment
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Re: 72 LT-1/71 LT1
Bruce----
There were quite a few 66 and later small blocks, all of which used manifolds with 2" outlet, which also had a 2-1/2" exhaust system. The transition section was at the forward end of the forward exhaust pipe. Included in these are 66-68 L-79, 70 L-46, 70-72 LT-1, and 73-74 L-82.
The 62-65 SHP small blocks used 2-1/2 outlet exhaust manifolds and 2-1/2" exhaust, so no transition section is found on these cars. These include 1962-63 340 hp and 360 hp, 1964 365 and 375 hp, and 1965 350 hp, 365 hp, and 375 hp. Also, 1962 through 1965 with 300 hp and manual transmission also used the 2-1/2" outlet manifolds with 2-1/2" exhaust systems.
All big blocks use 2-1/2" outlet manifolds. All, EXCEPT 1969, use 2-1/2" exhaust systems. 1969 big blocks use a 2" exhaust system so there is a transition section in the forward end of the forward pipes.In Appreciation of John HinckleyComment
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