Will these heads fit my SBC with domed pistons? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 06-27-2008, 07:13 AM
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Will these heads fit my SBC with domed pistons?

Found a used set of Holley SysteMax heads for sale at a great price. Only thing I'm wondering is if I'd have any problems with clearance and/or chamber shape given that I have domed pistons (SpeedPro H168P, +3.5cc)?

Here's a link to the heads with good pics of the chamber...

http://www.holley.com/types/Chevrole...ll%20Block.asp

Deck clearance is ~0.025" and gaskets will be stock 0.040" compressed.

Are the chambers on these heads what is termed 'D-shaped' or heart (or something else)?

Thanks,
Ian.

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Old 06-27-2008, 08:17 AM
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Judging by the picture they do have heart shaped combustion chambers. Big quench and domes equals detonation. What are these going on? 350, 383, 400? And what cam? As it stands now with a 4.03 bore, 3.48 stroke I get 10.25:1. If I use zero deck clearance I get 10.9:1.
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Old 06-27-2008, 09:00 AM
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Quote:
Originally Posted by RippinRon
Judging by the picture they do have heart shaped combustion chambers. Big quench and domes equals detonation. What are these going on? 350, 383, 400? And what cam? As it stands now with a 4.03 bore, 3.48 stroke I get 10.25:1. If I use zero deck clearance I get 10.9:1.
Sorry, should've provided more detailed info...

355
Comp XE274 (230/236 @ 0.050")
Static CR will work-out ~10.3:1

I was also concerned about the chamber shape and whether my domes might hit it?

Thanks,
Ian.
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Old 06-27-2008, 09:49 AM
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I wouldn't think with that small 3.5cc dome that you'd have any interference problems with standard 23 degree heads. However, the heads you're looking at have the valves laid in at 20 degrees, so all bets are off as far as dome or valve relief interference.

I would reconsider the squish if I were building this motor. The cam looks well matched to the static c.r. of 10.3, but the squish is a little loose. If you don't want to cut the decks, at least use a thinner gasket like the GM 10105117 composition gasket that compresses to 0.028". With a piston deck height of 0.025", you'd be at 0.053" squish. Detonation tendencies from the additional static c.r. gained from a thinner gasket will be more than offset by the reduced squish.
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Old 06-27-2008, 10:07 AM
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Quote:
Originally Posted by techinspector1
I wouldn't think with that small 3.5cc dome that you'd have any interference problems with standard 23 degree heads. However, the heads you're looking at have the valves laid in at 20 degrees, so all bets are off as far as dome or valve relief interference.

I would reconsider the squish if I were building this motor. The cam looks well matched to the static c.r. of 10.3, but the squish is a little loose. If you don't want to cut the decks, at least use a thinner gasket like the GM 10105117 composition gasket that compresses to 0.028". With a piston deck height of 0.025", you'd be at 0.053" squish. Detonation tendencies from the additional static c.r. gained from a thinner gasket will be more than offset by the reduced squish.
Thanks for the info. Agree about the quench area, but if I shoot for a thinner gasket, that means even less clearance between pistons and valves.

Do you think Holley tech support would be able to tell me decisively I these heads will clear my pistons? The deck clearance, piston volume, compressed gasket thickness and heads are all known factors, so somebody must surely be able to say, for sure, if I'd be safe, or not.

Thanks,
Ian.
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Old 06-27-2008, 10:30 AM
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Yeah, give 'em a shot....
http://www.holley.com/TechService/TechRequest.asp
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Old 06-27-2008, 11:51 AM
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Quote:
Originally Posted by techinspector1
Holley tech support can't give me a definitive answer either; all they can suggest it to clay it up and see, which means purchasing the heads and hoping they're OK in my application. Bummer.
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Old 06-27-2008, 02:14 PM
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Another thinner gasket that would work is clevite 5746 with a .026" compressed thickness and 4.100" bore.
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