LS5 1971 head

[Z28SSMAN]

Here's a pic of one of the original cylinder heads from my Chevelle. The other one was destroyed when my sister-in-law was driving it. It dropped a valve and busted a piston. Luckily she wasn't pounding on it and it didn't damage the block. This is one way they lowered the compression to 8.5 to 1. It also had flat top pistons with two valve reliefs.

http://imgur.com/PwbXLpg

http://imgur.com/LQYApRr

[MR.hp]

Those are the same heads as the '69 2bbl 396, 402 and others of that era. I have never used those, but they were supposed to have a good exhaust port that had a higher port floor which then pushed the spent gasses to the port roof. The head also had unshrouded exhaust valves also. I am not sure how they came to 8.5 comp with that chamber as it has less CC's than the 781 049 OC heads. I thought the head you have was 109 CC. I do know that my 461 with a 781 head and flat top piston was 8.5 comp.

[Z28SSMAN]

Date code if I recall is '70. If you do a google search for 3993820, it says 113 cc. 2.06 int, 1.72 exhaust.

3993820 1971 402 454 300 365 2.06/1.75 113.060 Cast iron, oval-port and similar to #3931063 with change to open-chamber design, redesigned intake and exhaust valve seats, and tapered spark plugs.

3993820 1971 402/454 Open 113cc 300, 330 LS-3 365 LS-5

http://www.chevelles.com/forums/18-e...820-heads.html

BBC oval port cylinder head casting numbers

Number Engine Size Year Combustion Chambers
336781 454 1973-1985 Open chamber
346236 454 1975-1978 Open chamber ("peanut" ports)
353049 454 1970-1973 Open chamber
3872702 396 and 427 1966 Closed chamber
3904390 427 1966 Closed chamber
3904390 427 1966 Closed chamber
3909802 396 and 427 1966-1967 Closed chamber
3917215 396 and 427 1966-1969 Closed chamber
3931063 396 and 427 1966-1969 Closed chamber
3964280 427 and 454 1966-1970 Closed chamber
3964290 427 and 454 1966-1970 Closed chamber
3993820 402 and 454 1970-1971 Open chamber
3999241 402 1970-1972 Open chamber
6272292 402 and 454 1971 Open chamber

Re: 3993820 heads
Those heads are from the Vette/Chevelle LS-5 units.

We've done a number of these over the years, and still do today, on our 100%stock-appearing builds.

Factory valve size, 2.060"/1.720", on our builds we use some SBC intakes,2.150" x .343" stems, and stay with the 1.720" exhausts.

They do flow decent and handle 525/550 HP on these resto's with a 4.250" crank. These are non ported, just very minor bowl work. All have the Q-jet carbs.

The average flow is 290/190 CFM @ .600". As stated, non-ported.

Thanks, Gary in N.Y.

P.S. CC's run in the neighborhood of 112 finished. This is a "nominal" number, we've had them with 110 and 113.

[MR.hp]

Date code if I recall is '70. If you do a google search for 3993820, it says 113 cc. 2.06 int, 1.72 exhaust.

3993820 1971 402 454 300 365 2.06/1.75 113.060 Cast iron, oval-port and similar to #3931063 with change to open-chamber design, redesigned intake and exhaust valve seats, and tapered spark plugs.

3993820 1971 402/454 Open 113cc 300, 330 LS-3 365 LS-5

You could be right on that Glenn, the same head that i had was an 820 casting and it CC'ed at 109 but I am sure there are variations of that. Funny because the 049 came in at 122CC and the other set of 781's were 114. I sold the 049 heads after that.