3946074 ZL-1 & L-88 head - oddity

[Steve Antonucci]

Hi all!

While cruising ePay today, I ran across some '074 heads that I am considering
for an L-88 project. The odd thing about these heads is that they have "D"
shaped exhaust ports instead of the standard round port configuration. The
seller claims they are rare. Are they indeed rare, or were they welded-up to
mimic the '077 exhaust port configuration? Please see the auction link below.

I was of the opinion that all '074 heads used the round exhaust port design and
this is what made them ineffecient for street use.

Can someone clear up the confusion for me?

Thanks,
Steve

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=016&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=260097295391&rd=1&rd=1

[Clem Zahrobsky (45134)]

Re: 3946074 ZL-1 & L-88 head - oddity

i never saw a 074 head with a "D" shaped exhaust port that was standard on the 076 heads. i just sold a pair of 074 that were not ported,welded or damaged in any way.

[Dick Whittington (8804)]

Re: 3946074 ZL-1 & L-88 head - oddity

I agree with Clem, all 074 heads that I have ever seen were rectangular ports. I am wondering if these heads have actually been welded up. Something looks odd but it is not registering with me

[Warren Friedrich (12139)]

Re: 3946074 ZL-1 & L-88 head - oddity

Steve,

I've had a couple of mint sets of 3946074 aluminum heads, and actually have seen them with date codes as late as 1976. I have never seen any with that exhaust port configuration.......I'm baffled about this, but extremely intrigued at the same time.

[Steve Antonucci]

Re: 3946074 ZL-1 & L-88 head - oddity

I'm with you guys! They seem odd, don't they?

[Joe Lucia (12484)]

Re: 3946074 ZL-1 & L-88 head - oddity

Steve-----

These heads have been modified; no doubt about it. GM #3946074 is a CASTING number. The casting defines features like the port configuration. So, if there were to be a head otherwise similar to the 3946074 but with different exhaust ports, that head would have a different casting number. Indeed, the later GM #14011077 was such a head; the exhaust port difference is the primary reason that the casting number changed.

These heads must have been welded and re-machined. From what I can see, it looks like it was a pretty good job, though.

[Clem Zahrobsky (45134)]

the shop that did my machine work welded up

chevy aluminum heads exhaust ports like that.

[Steve Antonucci]

Re: the shop that did my machine work welded up

Thanks guys!

That's pretty much what I thought. Joe, ditto on the welding job. I don't
even see any porosity in the photos. Looks like a class-A job.

Steve

[Steve Antonucci]

Re: the shop that did my machine work welded up

Clem,

Did this welding-up the exhaust ports trick yield positive results over the stock round exhaust ports? I have long heard that the round port design was
a bust because you couldn't generate enough power to take advantage of them. Any truth to that?

Steve

[Warren Friedrich (12139)]

Re: the shop that did my machine work welded up

Steve,

I don't know if you have seen the current issue (June '07) of MUSCLECAR enthusiast yet, but there is an artile called Clash of the Titans, this is a comparison of the '70 LS6 vs '71 LS6 engines. The '71 made more horsepower than the '70, 490 versus 481, however the torque numbers were reversed with the '70 outperforming the '71 by about 26 ft lbs.

[Clem Zahrobsky (45134)]

Re: the shop that did my machine work welded up

BBC head exhaust ports but i never used them myself . it help prevent reversion back into the exhaust port and made for a smoother exit of the exhaust on the short side radius.there was a company that sold a bolt on item that duplicated the "D" shaped exhaust port that bolted between the head and the headers with a projection fitting into the exhaust port forming the "D" shaped exhaust port. i tied that on drag car engine and it slowed the car down.the "vane" is now used in most GM aluminum BBC head to prevent exhaust reversion back into the port.

[Mark #28455]

YUP!

The open chamber heads flowed better - so the higher RPM HP is better, but the lower compression - 9:1 vs. 11:1 dents the lower RPM torque.
Mark

[Mark #28455]

comparing the "D" port to the 074 heads

While the port shape at the exhaust flange is the most obvious difference, it is the shape of the port throat and the short side radius that was the biggest functional change. The bolt in plates that I saw missed this short side radius. The "D" port heads short side radius is vastly different.

Mark

[Joe Lucia (12484)]

Re: the shop that did my machine work welded up

Warren-----

I don't know how the horsepower tests in this article were conducted. In particular, the 1970 LS-6 and the 1971 LS-6 were essentially the same except for 3 things-----cylinder head material, compression ratio, and exhaust manifolds (1970 LS-6 was Chevelle only and used more restrictive "log" type manifolds; 1971 LS-6 was Corvette-only and used less restrictive "header" type manifolds).

However, regardless of whether the test included the exhaust manifolds, it seem to "put a big hole" in the notion that the drop in compression ratio (i.e. 1970's 11:1 versus 1971's 9:1) resulted in a big drop in horsepower.