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Old 12-10-2012, 09:26 AM
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Help Me Out Before I Purchase

What's going on fellas,

I have a 350 bored 30 over, in a 74 Nova. The block is 69-79 model (3970010). It has head some crappy 305 heads on it, so I am changing those, the cam and the intake. I am using a 650 CFM Holley carb. Here's what I plan on buying today or maybe tomorrow. Let me know if you see problems or anything.

The guy at Summit said this should produce about 9:1, or if I went with 64cc heads, maybe 10:1. I plan on driving on the street with this thing, but I want it to be quick and sound good obviously. Is 9:1 enough? And surely I'll be okay with 93 pump gas?

COMP Cams CL12-242-2 - COMP Cams Xtreme Energy Cam and Lifter Kits - 477-480 224-230
Edelbrock 2101 - Edelbrock Performer Intake Manifold
Edelbrock 60739 - Edelbrock Performer RPM Cylinder Heads - 70cc chamber - 2.02/1.60 - 185cc intake runner and 65cc exhaust runner volumes
Edelbrock 9629 - Edelbrock Hardened Steel Pushrods
+ gaskets of course.

My grand total through summit is $1636. Thanks

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Old 12-10-2012, 09:32 AM
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should run high 14s and sound good
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Old 12-10-2012, 10:57 AM
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Thank you vinnie. Any other opinions? I'm about to click purchase and don't want to regret it!
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Old 12-10-2012, 01:24 PM
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Originally Posted by txdude350 View Post
Thank you vinnie. Any other opinions? I'm about to click purchase and don't want to regret it!
any idea what pistons you have in there or what the deck height/clearance is?
those two things are huge contributing factors to what your compression ratio will be, i wouldn't order any parts until you know those things.
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Old 12-10-2012, 01:50 PM
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They are low compression pistons. I don't know anything about them but heres a picture.Click image for larger version

Name:	Piston1.jpg
Views:	63
Size:	1.77 MB
ID:	69728
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Old 12-10-2012, 02:03 PM
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Here is a screenshot of what I came up with, assuming a few things of course.Click image for larger version

Name:	cr.png
Views:	98
Size:	260.4 KB
ID:	69729
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Old 12-10-2012, 02:14 PM
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Originally Posted by txdude350 View Post
Here is a screenshot of what I came up with, assuming a few things of course.Attachment 69729
your piston to deck height is probably out a bit. can you still see numbers on the front tab on the block? if thuse are still there it hasn't been decked, and your clearance would probably be around .025, if they are standard height pistons. looking at them they are likely a rebuilder style and the pin height is 1.540 vs. 1.56, making the clearance closer to .045. the heads are probably closer to 65-66cc, so your compression is going to be down from what you are thinking.
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Old 12-10-2012, 03:07 PM
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Help Me Out Before I Purchase

Like plaintoast said you need to know the effective head volume or the part# of the pistons that are in the block. If you don't know you can't buy the heads with the correct combustion chamber. The cam and the heads you are going to purchase are great but you need to know which to buy 64cc heads or 76cc heads. If you have flat top pistons which have a 7cc effective head volume the compression will be too high 10.88 with 64cc heads. With the pistons you have in the picture and if the deck of the block has not been milled your compression is about 8.99 now.

Last edited by cdminter59; 12-10-2012 at 03:26 PM.
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Old 12-10-2012, 07:47 PM
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Well based on what I can gather I think the pistons are about -13cc. This is sort of an estimate, but I am about to research ways to measure this. I remember someone saying I could use clay and a graduated cylinder to measure. My old man and I have about decided to not pull the motor and just do the top end. The block was rebuilt, god knows why someone put these pistons in it... or maybe back in it.

So the 8.99 compression is with the 64 cc head with these pistons? Well damn... they don't even make this head in with a smaller comb chamber. And the 305 heads that were on this block were supposedly 58cc.

I also tried to measure deck height today but wasn't sure how to deal with the "bevel" around the piston. I guess the deck height would be less than the measurement to the bottom of that bevel.

I guess I'll try to find a way to measure these pistons and report back. Thanks for the help.
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Old 12-10-2012, 07:53 PM
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you'll want to measure from the deck surface to the highest spot on the piston, not real sure what you mean by bevel.
but by my calculation, i actually come up with 8.49:1 with the "64" cc heads.
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Old 12-10-2012, 08:06 PM
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Okay so I guess the question now becomes... How do I get my CR over 9:1 without changing these pistons? Or am I SOL?
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Old 12-10-2012, 08:13 PM
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Quote:
Originally Posted by txdude350 View Post
Okay so I guess the question now becomes... How do I get my CR over 9:1 without changing these pistons? Or am I SOL?
You can have the block decked which does not look that bad what is the deck hieght i got a feeling the pistons may not yield that ow a compression.

You can buy a gasket that is .015 compressed thickness over the stock .041 thickness.

Mill the heads or buy heads with smaller combustion chambers.

Change the pistons.

Usally decking the block is the hot ticket if its already been done you need to figure your compresion ratio. It looks to me like the pistons come right up to the top of the block.
United Engine & Machine Co. Incorporated

Use that link and actual measurements to figure out the details.

Hope this helps.
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Old 12-10-2012, 09:30 PM
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Okay so I guess the question now becomes... How do I get my CR over 9:1 without changing these pistons? Or am I SOL?
the easiest way, if you aren't pulling the lower end apart, would be to use a thinner gasket and angle mill those heads.
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Old 12-11-2012, 09:59 AM
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Those look like the Cast 13cc 4VR w/Dish Pistons to me.
Silvolite Pistons-CHEVROLET

4.030" Bore X 3.480" Stroke.
.025" Deck Ht., .015" Shim Gasket.
64cc Head, 13cc Piston = 9.52:1Cr
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Old 12-11-2012, 12:18 PM
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Thanks everyone. Do yall think I should go with a higher lift cam? Someone mentioned to me that it is dumb to go with these heads and not a bigger cam. If so, how big can I go without going to rollers?
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