LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Side by side image of 643 vs. 561 castings inside..

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Old 07-13-2006, 11:44 PM
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Re: Side by side image of 643 vs. 561 castings inside..

643's they look to be by the casting number, too.
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Old 07-13-2006, 11:46 PM
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Re: Side by side image of 643 vs. 561 castings inside..

Strange...did any '97's come with 643's, or were they strictly 561's?
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Old 07-13-2006, 11:51 PM
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Re: Side by side image of 643 vs. 561 castings inside..

I purchased 643 cores from Lloyd to have done. To me it was alot easier than pulling mine off and sending them out. Plus I got to drive my car while I waited. Ill sell my stock heads when they come off to make up the money
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Old 07-14-2006, 12:07 AM
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Re: Side by side image of 643 vs. 561 castings inside..

[QUOTE=SStrokerAce]No they are all 54cc.

The big deal is to make sure you can tell the castings apart so you can get the right set to send to the porters. The internal parts of the port are hard to see the differences unless you have a well trained eye.

Bret[/QUOTE
i can prove otherwise. i had a set of lt1 heads that came right off of my 94 lt1. they flowed 56.6 cc after beeing milled. chambers were'nt touched a bit. so that equals out to be a set of 58cc heads.

back to the topic, can u tell what heads you have with the heads on the car?
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Old 07-14-2006, 01:23 AM
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Re: Side by side image of 643 vs. 561 castings inside..

[QUOTE=blackztpi]
Originally Posted by SStrokerAce
No they are all 54cc.

The big deal is to make sure you can tell the castings apart so you can get the right set to send to the porters. The internal parts of the port are hard to see the differences unless you have a well trained eye.

Bret[/QUOTE
i can prove otherwise. i had a set of lt1 heads that came right off of my 94 lt1. they flowed 56.6 cc after beeing milled. chambers were'nt touched a bit. so that equals out to be a set of 58cc heads.

back to the topic, can u tell what heads you have with the heads on the car?

The few sets I have CC'd were 53.7/8 to 54.6/7 and that is MORE than one set.
Don't know what the difference is unless it was the plug ya used.If ya don't use the same plug for comparison it don't work.

Only by part number.
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Old 12-20-2006, 06:16 PM
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This might be a direct question to LLoyd or Brett.
So, what is the best aluminium casting for LE2 porting? 643 or 374???
I'd like to know before I shop around for castings to send to LLoyd.
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Old 12-20-2006, 08:36 PM
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Which year model LT1's came with the 643's? Just for general knowledge in the future.
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Old 12-20-2006, 09:15 PM
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I did 3 sets of heads so far, all 3 sets were around 54, I had to work to open them up to 58 so I could get my compression down.
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Old 12-20-2006, 09:25 PM
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I have the 643's ported/polished, so are yall getting them done by LE? How much does he charge? Also are aftermarket heads better or getting them Ported and Polished with like 2.02/1.60 valves? Thanks
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Old 12-20-2006, 09:34 PM
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How do the LT4 heads compare in-line with this conversation?
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Old 12-21-2006, 01:03 PM
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So, what is the best aluminium casting for LE2 porting? 643 or 374???
I would also like to know ttt
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Old 12-21-2006, 07:08 PM
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they already said 643 because you can tell from the picture there is more metal, more room to port and take out of, the walls on the 374's are thinner, bigger isnt always bigger though, you wanna keep the right flow.
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Old 12-21-2006, 08:02 PM
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i always thought 374's and 643's were very similar if not preferred,
and the 561's were the ones to avoid if possible.
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Old 12-22-2006, 02:12 PM
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???
I thought the 374s are the thickest.
I'd like to know what's the ultimate head for porting? 374 or 643?
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Old 12-22-2006, 07:49 PM
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do a search, you will notice this has been an agument for a long time.
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