L79 cylinder head help 3782461
Okay, I'm rebuilding my born with 1966 Corvette l79 engine. the car has 3782461 cylinder heads. one dated A266 and the other B196 with a F0224HT engine stamp. Now here is the strange thing both heads are casting 3782461 but have different design combustion chambers, my engine rebuilder says they are both 2.02 valve heads and look to be virgin untouched. one 461 looks like the print in Chevrolet by the numbers for the 462 (page 93) and the other 461 looks like the print for 461 head (page 89). Also on the under side of the heads one has "461" cast into it while the other has "462" cast into it, but both have 3782461 cast under the valve cover with the above mentioned dates. Does this different combustion chamber pose a problem? Should I look for an head to make a match? I'm 99% sure these heads are original, this car has been in the family since 1972 and has 40K original miles but has been parked for 34 years and need complete restore hence the engine rebuild.
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Re: L79 cylinder head help 3782461
Brian,
I assume your "3782461" cyl. head dated "B196" (Feb. 19, 1966) also has the "462" casting number. Apparently this was very near the end of the 3782461 cyl. head production. The earliest "3890462" cyl head that I have ever seen was dated "C16" (March 1, 1966). The combustion chamber is the 62.076 cc for both "461" and "462" heads made in 1966 according to "Chevrolet by the Numbers". The 1967 "462" cyl. heads have a 63.305 cc combustion chamber.
I would say that both of your cyl. heads are original. I would say there was a slight error at the foundry on Feb. 19, 1966.
Dave
There is a "3782461" cyl. head dated "A176" (Jan. 17, 1966) that also has a "462" casting number currently on Ebay (not mine).
Last edited by David L.; December 21, 2012, 12:22 AM. -
Re: L79 cylinder head help 3782461
Brian-----
The difference in combustion chamber configuration between the 3782461 and 3890462 is really minimal. Plus, both combustion chambers are of the exact same size. I expect that what happened here was that during the transition at the foundry from the 3782461 to the 3890462, one or more of the pattern elements for 462 head was used for a 461 casting. That's why you have a 3782461 casting number under the valve cover and '462' on the lower surface.
I have no doubt that these heads are original to the engine and car. I would not change them.In Appreciation of John HinckleyComment
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Re: L79 cylinder head help 3782461
Brian:
My April-built 66 L79 has one 461 cylinder head (dated February 7, 1966) and one 462 cylinder head (dated April 11, 1966). The engine assembly date is April 13, 1966. I have no doubt that these are original to this 25,000 mile car.Comment
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Re: L79 cylinder head help 3782461
Brian,
I agree with the other posters and to add if the engine only has 40000 miles be VERY cautious about boring because it may not be necessary. A little attention to a valve job may be all that engine needs. I would not mill the heads either, the sitting probably has not hurt anything in the bottom end of the engine.Comment
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Re: L79 cylinder head help 3782461
I question the need to rebuild the engine, unless it was seized, but if it's already apart...
If it has the first design connecting rods, they should be replaced. Internal modifications such as head massaging if you are looking for maximum power are optional along with cam selection. The L-79 cam is okay, but the L-46 can installed four degrees advanced is a better choice, and the LT-1 cam is an option.
Bank to bank CR can vary up to several tenths due to to different deck clearance and in your case the possible addition of head chamber volume side to side difference. The 461 heads have a small quench area on the plug side. On 462s this was replaced by a bevel that was part of the mold. Posting photos would help us determine what you have.
Dig our your last few years Corvette Restorer and read "Compression Ratio Explained" and "A Tale or Two Camshafts". Also search 327 LT-1 on the road under my name and follow the links to The Corvette Forum for all the system engineering an test data.
Many owners have been the victim of "engine builders" who install improper parts - like high volume oil pumps, roller tip rocker arms, and low compression pistons. Few understand how to actually restore a vintage Corvette engine, with or without undetectable performance enhancements. It's a very slippery slope.
DukeComment
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Re: L79 cylinder head help 3782461
Hi Duke, I previous got recommendations from you and always value you and your opinion. My engine rebuilder has completed the short block; it was NOT decked by my instructions. We went .030 on the bore could have gone .020 but couldn't find the correct pop up pistons in that size. I went with a NOS GM 151 L79 cam I had, I told him to use a Melling M-55 oil pump and gave him a GM oil pressure relief spring #3814903 to install. I did have the engine balanced and the harmonic balancer rebuilt by Winslow mfg (better safe than sorry). I went out and found a set of 67 used GM rods and had him recondition them and use ARP bolts because you mentioned the poor design 66 rods (it was funny he noticed the extra rods I gave him where 67's not 66's so he know about them), he wanted to stud the main bearing caps I let him (over kill maybe but I saw no harm). I had checked and recorded the head numbers and dates, but never looked at the chambers, he called me and I went and checked them out. I would post a pic but their at the machine shop, but like I said one is a 461 chamber design and the other is a chamber 462 design but has the 461 casting number under the valve cover by the date. Do you think this will hamper performance? I'm going to re-use the "O" rocker arms after reading how strong they are on this board, I purchased new GM valve springs #3911068 per your recommendation and I picked up new GM keeper and retainers, lifters. I had a set of GM push rods the welded ball type, I'm going to have screw in studs and guide plates installed over kill but I don't think it will hurt.Last edited by Brian K.; December 22, 2012, 09:20 AM.Comment
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Re: L79 cylinder head help 3782461
My Question is will having 2 different design combustion chambers effect performance? I'm not looking for all out horse power but don't want an dog engine rocking away in the engine compartment. Also I have a intake valley pan to keep oil from splashing do you think I should install this, not for the oil or perfomance but do you think it will help keep the heat away from the intake and help with fuel percolation?Comment
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Re: L79 cylinder head help 3782461
The issue with different chamber volumes is that one bank may be more prone to detonation than the other. You should take all the measurements like deck clearance and chamber volume and manage the CR per the previous article I referenced.
Since deck heights are sometimes different side to side, compute the CRs with the smallest chambers head on on side with the highest deck to see if you can equalized the CRs. If necessary different thickness gaskets can be used on each side to get the CRs as close to equal as possible.
For L-79 I recommend a NTE CR of about 10.3, which should be easily achieveable with proper head gasket selection. For precision engine restorations I like to see all within a range of no more than 0.1. This can usually be achieved with a little chamber grinding on the two or three that are highest.
I see no harm with the valley pan, but don't think it will do that much good either. Most of the heat that reaches the manifold is through the heat riser. This can be reduced by using shims with say half-inch holes, or shim one side only, which will allow some conective heat transfer, but no flow, so heat transfer will be significantly reduced.
My experience with completely blocking the heat riser was not good - bad start off stumble for at least the first 15 minutes of driving in mild weather.
In any case, wire open the heat riser of use the FI spacer.
DukeComment
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