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Old 11-15-2017, 01:18 AM   #31
jocko
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Join Date: Oct 2009
Location: Godley, TX
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Re: What GM create engine to buy for 3/4 ton 72 C20

A little more info on the GM crates. Note that the L31 we've been talking about that lists for just a hair over $2000 is the base L31 - but it also has a slightly more expensive brother (I assume this is the L31R some have referenced - it's specified for 3/4 ton and up, whereas the base L31 is considered a 1/2 ton replacement). Anyway, L31R = L31 HD (same engine, just different terminology depending on where you're looking). From what I can see it has the exact same specs, but you get 4 bolt mains for your extra $200. If I were to go the GM crate with vortec heads budget route - either of the L31s is hard to beat bang-for-the-buck-wise. The HT383 has some impressive numbers (but an equally impressive price - more than double an L31).

Here they are:
L31 https://sdparts.com/i-19928727-gm-en...te-engine.html

L31 HD https://sdparts.com/i-19928425-gm-en...te-engine.html

HT 383 https://sdparts.com/i-19928346-chevr...SABEgKvj_D_BwE

Some interesting notes:
- The L31s have a hyd roller cam/383 has a hyd flat tappet
- 383 has a forged crank/L31s are cast
- L31s require electric fuel pump (as mentioned above)
- 383 includes manifold and ext balanced flexplate (not sure if L31s include a flexplate)
- 383 and L31 HD are 4 bolt mains, L31 is not.
- L31 CR=9.3:1 / 383 CR=9.1:1 (MUCH better than the 195/290 hp crates' 8.5/8.0:1 CRs)
- Both have decent lift cams, 383 is more aggressive, thus the hp delta..

Bottom line, I'm not building a race truck - but the extra 100 ft-lbs of torque of the 383 sure would be nice. However, very best bang for the buck imho is the L31 HD.
I think a set of center-to-perimeter bolt valve cover adapters may be in order... Anyway, just wanted to share. Hadn't heard of the L31 HD before - and I'd spring for the extra $200 to get 4-bolt mains personally, whether I needed them or not. I believe that $200 also gets you some upgraded exh valves and cyl head improvements (although I'm not sure what those improvements are). If, when the time rolls around and I happen to have won a small lottery, I might spring for the 383, but if it were gonna happen tomorrow, I'd go with the L31 HD. Significant improvement over the original 350 and for about the price of the Gen 1 195 or 290 hp GM crates. I guess maybe I can live with a vortec manifold bolt pattern and externally balanced flexplate after all!

EDIT: Note in the table below for the HT383 cam - it is a mis-print. HT 383 has a hyd roller, not a hyd flat tappet cam.
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Last edited by jocko; 11-19-2017 at 01:11 AM.
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