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Old 09-10-2004, 12:37 AM   #1
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Join Date: Sep 2004
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Car: 87 Firebird
Engine: 355
Transmission: 5 spd

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Vortec Heads w/ High Compression????

so i got your basic 355 except for new .125 domed speed pro pistons. the compression ratio with my stock 76cc heads is 9.34. now i really want a pair of vortec heads for this engine, but i get mised results when i bring them up. Mainly because the high compression with 64cc heads and my pistons, which should be 10.68. Basically some say great power adders and others say high compression not really "streetable". Well what i really wanna know is what you guys think about this idea. What problems might arise, gas guzzler?, what can be done to safely put these on with no problems.

Thanks
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Old 09-10-2004, 03:08 AM   #2
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The chamber on a Vortec head is designed to function best with a dished piston.

FYI
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Old 09-10-2004, 09:00 AM   #3
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Im running a bigtime dish on my 383 , a whopping 8.64 to 1 compressiona nd a turbo setup within the next yr or so

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Old 09-10-2004, 11:34 AM   #4
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Moving to tech...
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Old 09-10-2004, 12:19 PM   #5
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You might want to check with the manufacturer on this one chief. Vortecs have a chamber design that will interfer, read hit with dome pistons.

Normally it is a really bad idea to run dome pistons in any application. It is a crutch for having a mismatch of parts.
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Old 09-10-2004, 12:52 PM   #6
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Are you talking about the sealed power 10.7:1 CR .125 domed pistons? I run them with 64cc protopline vortecs.

My advice is to use the sealed power flattops (rated at 9.7:1 CR w/ 64cc head) and get the block decked. The extra compression isn't worth the timing and tuning hassles it's given me, my buddy runs the 9.7:1 pistons with the same cam as me and it ran 14.1@ 98 (and that was with ported 462 heads, hes putting dart iron eagles on now, and he should have mid 13s). His motor is much more tolerant of timing and such.

Last edited by StealthElephant; 09-10-2004 at 12:54 PM.
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Old 09-10-2004, 03:38 PM   #7
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You could try to run a thicker head gasket to take up some of the volume. As for the compression vs streetability problem, I am running flattop pistons with a decked block and a stock Vortec truck head gasket. i suspect my comression is at LEAST 10 to 1 if not more. My motor runs the best on 88 octane gas. May be it is just because I live up at 6000 feet. I have been told you can run more compression the higher you are. I had a friend running 11:1 on a 383 on pump gas with iron heads but he was pushing the limits of 91 octane.
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Old 09-10-2004, 03:55 PM   #8
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I don't think compromising the gasket thickness to lower CR is a good idea, but what do I know.

My machine shop suggested I use Fel Pro 1003 which is for higher compression and also require the drilling of the block to promote better cooling. The stocker summit kit head gaskets I used the first time had major seepage issues, just were not up to the job.
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Old 09-10-2004, 04:35 PM   #9
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You could carefully rework the combustion chamber to enlarge it. You can do this without ruining the hi swirl design by taking *some metal* from every where in each chamber. leaving the general shape of the chamber to same as stock.

Depending on exactly what fuel you will be running
you should be ok with a finished cr of 10.3 or less.
a 68 to 70cc finished chamber should do it.
(93-94 octane)

Then run the motor with just the amount of total timing as it requires to make the best power and no more.
less is better. if the car goes just as fast with 30deg timing as 34 or 36 ( usually optimium) then run 30deg and live with it.

Or you could run a simple water/alcohol injection system that will eliminate the detonation of running too hi of a cr for the fuel octane. This will allow you to run the optimum ignition timing for best power without knock and damage.
Because your actual cr with 64cc heads is not that much higher than it should be, a expensive computerized electronic controled water injection system should not be nessessary.
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Old 09-10-2004, 07:21 PM   #10
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your best bet is to run flattop pistons, with the heads, deck them to flat and zero deck the block. should get you in the range of 10.25 or better.. i'm about 10.7:1 with that setup.
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Old 09-10-2004, 07:21 PM
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