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Old 06-18-2012, 12:35 PM
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Can you guess this piston dish??

I am trying to calculate my CR and was hoping someone could take a stab at guessing the dish size of the piston. I suppose I will be buying some clay and a graduated beaker if not. IF I must go this route, do I measure it all the way across flat, or just the "eyebrows"??? In other words, do I include the big circle too? what about the outside circumference where it sort of slants downward?

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Pic 2 (Smaller and Better lol
Here is some info on the car/engine

74 Nova
350 Block
305 heads with 1.97/1.50 valves (58cc stock... also have to verify this)
Supposedly the pistons are Keith Black, but I haven't been in the bottom end yet.

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Old 06-18-2012, 01:18 PM
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Build it and stop making a fuss or this.
The 305 heads work find on any 350 with non domed pistons.

use a felrpo 1094 gasket for max cr. it will still be less than 10:1
which is just right.
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Old 06-18-2012, 01:27 PM
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Actually my compression ratio is a bit over 11:1 right now. Which is why I am tearing it down.

How can you make such a generalized statement about 305 heads on a 350?

Forgive me for trying to crunch the numbers and get it right. The damn engine hasn't ever run right.
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Old 06-18-2012, 01:50 PM
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Quote:
Originally Posted by txdude350
Actually my compression ratio is a bit over 11:1 right now. Which is why I am tearing it down.

How can you make such a generalized statement about 305 heads on a 350?

Forgive me for trying to crunch the numbers and get it right. The damn engine hasn't ever run right.
Cause I have built many of the 350-w/305 head motors.
-12 to -15cc dish volume is typical.
9.4:1 to 9.8:1 with a .015" gasket
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Old 06-18-2012, 01:57 PM
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Well... What do you think about this that I found. I have 416 heads btw

There's a fella over on HotRodders.Com that swears by 416 reworked heads, FireBird88 I believe is his handle. Do a search on that site/engine forum for 305 heads on a 350; there are a ton of posts. Butch/56sedandelivery.

Taken from This site
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Old 06-18-2012, 02:34 PM
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I don't know... I just swear that this problem is mechanical. I have ruled out electrical issues. Maybe I'll go get the heads checked out.

But with the stock 58cc and about a -5 cc piston (guy at machine shop guesstimate) I am getting over 11:1 CR. I figured this was the problem.

I think the only way to be sure is to actually check the volume of everything.
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Old 06-18-2012, 02:50 PM
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A stock replacement piston has about 8cc volume.
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Old 06-18-2012, 03:17 PM
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With that big of a dish you can't be at 11:1. I've also ran 305 heads on a dish piston 350 with no problems, on junk gas in a 4000 pound truck with 3.08 gears no less. I'm not sure what problem you were having before but I don't think you have too high of compression.
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Old 06-18-2012, 10:52 PM
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Quote:
Originally Posted by txdude350
Well... What do you think about this that I found. I have 416 heads btw

There's a fella over on HotRodders.Com that swears by 416 reworked heads, FireBird88 I believe is his handle. Do a search on that site/engine forum for 305 heads on a 350; there are a ton of posts. Butch/56sedandelivery.

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What's the point in posting this?
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Old 06-19-2012, 05:07 AM
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Looks like a typical 12cc dish to me.

plus the piston is most likely down 0.020" below deck. Maybe more.

727cc/cylinder (355 cid)
64c heads
8cc head gasket (0.040")
4cc deck height
12cc piston

(727+64+8+4+12) / (64+8+4+12)= 9.26

with 58 cc heads cr will be around 9.86:1.

Would need 48cc heads to get 11:1 with those pistons and a typical head gasket.
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Old 06-19-2012, 07:36 AM
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Quote:
Originally Posted by 454C10
Looks like a typical 12cc dish to me.

plus the piston is most likely down 0.020" below deck. Maybe more.
↑X2! A 5cc "dish" will be the valve reliefs of a flat top piston.

txdude350, what is the engine doing or not doing that has led you here?
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Old 06-19-2012, 07:58 AM
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Ok fellas, my bad... I didn't realize how much I was loosing with these pistons. That being said, the car runs terrible to be at 9anything:1. It's almost embarrassing.

It just doesn't have the power it should. My dad and I have had 3 different carburetors, 2 new distributors, the list goes on.

When I take of it's just slow as all get out. My old 97 Taurus 3.0 V6 was quicker off the line.

A buddy of mine says I should change the torque converter, but hell IDK. Any ideas/suggestions?
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Old 06-19-2012, 08:00 AM
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Quote:
Originally Posted by 68NovaSS
What's the point in posting this?
I posted that because I just so happened to come across someone talking about the same guy I was talking to, and also talking about the same heads that I am using. Small world, I guess.
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Old 06-19-2012, 08:04 AM
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Quote:
Originally Posted by txdude350
Ok fellas, my bad... I didn't realize how much I was loosing with these pistons. That being said, the car runs terrible to be at 9anything:1. It's almost embarrassing.

It just doesn't have the power it should. My dad and I have had 3 different carburetors, 2 new distributors, the list goes on.

When I take of it's just slow as all get out. My old 97 Taurus 3.0 V6 was quicker off the line.

A buddy of mine says I should change the torque converter, but hell IDK. Any ideas/suggestions?
To begin with, supply us w/ALL the specifics you know about this vehicle!

The cam specs are going to be very important, as is the rear gear ratio and torque converter stall speed (they need to be matched); a stock '74 Nova rear end may be geared very high (low numerically, like a 2.73). Next is the timing curve and how much initial timing is being used, as well as the total timing.

You can use this page as a guide for giving info- and more info is better than less.
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Old 06-19-2012, 08:15 AM
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Quote:
Originally Posted by txdude350
Ok fellas, my bad... I didn't realize how much I was loosing with these pistons. That being said, the car runs terrible to be at 9anything:1. It's almost embarrassing.

It just doesn't have the power it should. My dad and I have had 3 different carburetors, 2 new distributors, the list goes on.

When I take of it's just slow as all get out. My old 97 Taurus 3.0 V6 was quicker off the line.

A buddy of mine says I should change the torque converter, but hell IDK. Any ideas/suggestions?
I dont think there is any KB piston with that quench-killing bevel around the top.

Do a compression test. Anything less than 120psi is bad.

What camshaft do you have? If its a Comp, I would look there.
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