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Old 08-24-2010, 08:40 PM
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compression ratio

I have a sbc with stock pistons. from what i understand 12 cc dish plus four valve reliefs. Im putting some 60 cc heads on them and a comp cams 268 and im wondering if anyone has an idea of what kind of compression im looking at with a .41 head gasket.

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Old 08-24-2010, 11:25 PM
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about 9.75:1. However, you`ll have to run 93 octane and keep taps on the timing advance to keep it out of ping being you have no quench.
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Old 08-25-2010, 05:02 AM
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Those Pistons are closer to 14cc.
With a .041" gasket = 9.1Cr but, .066" Quench.
As said above use the .015" Shim for .040" Quench & 9.7Cr
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Old 08-25-2010, 09:33 PM
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hmm really? i was not expecting it to be that low with the 60 cc heads. but ill trust you guys and go ahead with the thinner gasket to bump it up. What about the intake? ive been told it would need a thicker gasket but it seems to line up fine.
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Old 08-25-2010, 09:36 PM
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oh and while we're here im wondering about re using the stock pushrods. ive been told how to check em but off hand do you guys know if they will?
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Old 08-25-2010, 10:56 PM
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i can't figure out how to edit so sorry for all the posts but i wasn't very descriptive the first time. its a 350 of course. bored 30 over the heads are 461 castings and have 2.02 and 1.60 valves installed and they have been shaved to 60 cc so i dont know if that changes anything but just incase
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Old 08-26-2010, 05:06 AM
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Quench for the Camels

Quote:
Originally Posted by zoomo
i can't figure out how to edit so sorry for all the posts but i wasn't very descriptive the first time. its a 350 of course. bored 30 over the heads are 461 castings and have 2.02 and 1.60 valves installed and they have been shaved to 60 cc so i dont know if that changes anything but just incase
I always set the deck height to suit the build, but no matter how much you mill the deck or heads, those pistons won't really allow for a beneficial quench. If you want to stay in the 9 something cr range with those heads a D cup piston would be an efficient way to do it. Flat tops wouldn't be out of the question (with quench) if you're planning on running 93 octane anyway. Double humps can't do it by themselves.

I forget the flush velocity differential estimates between .038" and .058", but whatever it is, it was surprising the first time I heard it, like more than a 100%, maybe more than 200.. Someone here knows, I'm sure.

Remember it probably takes .020" off the earlier heads to equal the CR increase of of .010" off the deck, but no matter how much the heads are cut, moving the chamber closer to the piston, the quench area stays the same distance from the piston.

OK, for example, A customer comes to the shop with a 10/1 4vr flat top 350, he wants to freshen it and keep his forged slugs, and is now considering different heads to lower CR. Because last time it was built he did it himself with the intentional CR increase, using 461s for more power in his tow truck. Comments that he's been struggling with spark knock from the beginning.
We deck it down to about .004" in the hole, new rings/cam bearings ect and RV cam...Call him to come get it. He re-installs the same heads. Month later is towing without spark knock and claims he's got 50 more horses, and getting 13 mpg, up from 10. He's probably got 40 more usable foot lbs, and no more horses but he's happy.


I apologize if you already know all this stuff, but there may be a guest following your thread, who has never considered it. Duntov
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Old 08-26-2010, 03:03 PM
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no honestly i know nothing when it comes to engine building. I fix cars all day. But in my shop when it comes to engines i remove and replace. Im still extremely confused. If im understanding this correctly you are all saying im going to have pinging problems unless i use a thin head gasket or get my block decked to get rid of some quench? Please forgive me if im completely off track.
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Old 08-26-2010, 05:06 PM
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New recommendation >>>Stick 'um on and go...

Quote:
Originally Posted by zoomo
no honestly i know nothing when it comes to engine building. I fix cars all day. But in my shop when it comes to engines i remove and replace. Im still extremely confused. If im understanding this correctly you are all saying im going to have pinging problems unless i use a thin head gasket or get my block decked to get rid of some quench? Please forgive me if im completely off track.
No you're right on if you went to flat top pistons you would be on the edge of ping.

But I rethought it this morning, and I think if you just installed the heads you have on the bottom end you have and spend a few bucks extra on the thinner coated steel shim gaskets the other poster mentioned, you'd be running good that quick and easy. I might take the opportunity to go with a MTC1 which is a small RV cam which is fine for the pistons you have. Be torquey and good on gas. Most people like the combo for driveability....///slash tire spinning. You're fine, <<>>New recommendation >>>Stick 'um on and go... Duntov
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Old 08-26-2010, 05:22 PM
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alright then. anyone have recomendations of where to get the gaskets?
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Old 08-26-2010, 05:31 PM
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http://www.summitracing.com/parts/FPP-1094/ thats what i need right? theres a cheaper one at .016 for ten dollars each but i figured might as well get the better quality for twenty extra
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Old 08-27-2010, 02:37 AM
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I like the coated

Quote:
Originally Posted by zoomo
http://www.summitracing.com/parts/FPP-1094/ thats what i need right? theres a cheaper one at .016 for ten dollars each but i figured might as well get the better quality for twenty extra
F Bird is right but I used these coated Felpro several times this year and the coating just makes me feel better.

One of the things I do though when installing heads is to grind the hex off some long bolts and saw a screw slot in the top, to use for guide pins to make sure the heads rest down strait to the dial pins without bumping the gasket. That makes for lower stress for me too.
Also we use teflon pipe dope from the plumbing store on the threads because it doesn't cure out before you've had a chance to re torque even days apart.
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