What is the differences in the heads?
I just bought a 1968 L89 Coupe. What exactly are the differences, if any between the aluminum and cast iron head besides the weight? Are the combustion chambers, valves and ports different?
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Re: What is the differences in the heads?
Same everything, dimension wise, as a L-71 cast iron head engineDick Whittington -
Re: What is the differences in the heads?
Didn't the Al heads have slightly larger exhaust valves - 1.88 vs. 1.84"?
DukeComment
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Re: What is the differences in the heads?
Joe
As there is a difference, is there any performance difference that has been quantified betweeen the aliminum and cast iron head?Comment
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Re: What is the differences in the heads?
Robert-------
Well, both the 1968 L-71 and L-71/L-89 were rated at 435 HP. So, as far as GM was concerned, there apparently was no difference. If there actually was a difference, I would expect it to be quite small and pretty much insignificant.In Appreciation of John HinckleyComment
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Re: What is the differences in the heads?
This is a June built car and a may engine assembly date. It is a 321 block casting which according to Colvin was a very early 68 block and was used until only approx Jan. 1968. Is this possibly correct? I have been told it is the original motor. ThanksComment
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Re: What is the differences in the heads?
Robert-----
I suppose something like you have described is possible. I'd look to the block casting date first. If it's cast after January, 1968, then we know that Colvin is wrong about this block not being manufactured after January, 1968 and it could very likely be original to the car. If it's cast in January, 1968 or earlier but with a May, 1968 assembly date, that's possible, especially for big blocks. Sometimes, there were significant time lags between cast dates and engine assembly dates for big blocks. In any event, I'd be looking to see how all the other numbers on this engine "line up" and I'd be looking really close at the stamp pad.In Appreciation of John HinckleyComment
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Re: What is the differences in the heads?
Can you read the pad? How does it look?
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Re: What is the differences in the heads?
How is this one?
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Re: What is the differences in the heads?
Robert-----
It looks a little suspicious to me, especially because there are "non-aligned" characters in both the engine code and VIN derivative. Also, the characters appear to be of randomly different impression depths which is uncharacteristic of a gang stamp. However, I'm certainly not expert at stamp pad issues. Let's let some others weigh in on this.
How about the block casting date?In Appreciation of John HinckleyComment
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Re: What is the differences in the heads?
Everything is good. The casting date of my 321 block is A118(Jan, 11, 1968. The stamp assembly date is My 5, 1968 and the build date of the car is June 27, 1968. I have no doubt it is the original motor.Comment
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Re: What is the differences in the heads?
Robert------
That's a very long time between the block's casting and engine assembly. It is possible but it's unusual.
For example, looking through Noland Adams' rather extensive survey of C2-era big blocks, I couldn't find even a single instance of a 4 month lapse between engine block casting and final assembly.In Appreciation of John HinckleyComment
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Re: What is the differences in the heads?
I have a 66 Impala 427 2 bolt block that was cast in Dec 65 and assembled in May 66, so I believe wide time gaps are possible. However, Robert's pictures of the pad do not appear on my computer, so I cannot guess about originality of this particular engine.Comment
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