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Old 03-17-2011, 09:45 PM   #11
streetjeep327
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Go with the Vortecs and standard pistons. I thought you only had one 487 head anyway?
I have one 487X and access to two 487's. In your opinion, would thicker head gaskets with the vortec heads bring the compression back to at least 9 or a bit under?
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Old 03-17-2011, 10:24 PM   #12
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Thick head gaskets with a bigger quench gap aren't really the right way to go, and you may not see much difference in the octane requirement. But the common wisdom is that along with that you'll have a drop in performance.

Unlike 461X vs. 461 heads, where there is a true difference, there is no real difference between 487X and 487 heads that I have been able to find. A few years back, I was going to build a 350 with 487 heads until I found that the heads were cracked. I ended up with Vortec heads and I looking back it was fortunate that I didn't use 487 heads.
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Old 03-17-2011, 10:41 PM   #13
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you might want to check world products Sr heads 64 or 76 cc with 202 intake 160 exhaust. the the valve cover rail is taller to prevent oil leaks. you can run roller rockers under short valve covers just a thought
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Old 03-17-2011, 11:03 PM   #14
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Quench distance is equal to the deck height plus the gasket thickness....On a street engine the very minimum is .035 and I believe the maximum that you would want is .045.....Usually, the deck clearance on a typical sbc is .025....However, you should measure it.

Also, there is a good compression ratio calculator here:http://www.kb-silvolite.com/calc.php?action=comp
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Old 03-18-2011, 09:25 AM   #15
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Quench distance is equal to the deck height plus the gasket thickness....On a street engine the very minimum is .035 and I believe the maximum that you would want is .045.....Usually, the deck clearance on a typical sbc is .025....However, you should measure it.

Also, there is a good compression ratio calculator here:http://www.kb-silvolite.com/calc.php?action=comp
My problem is my engine is torn apart, parts all in boxes, so I can't measure the volumes needed. But, the pdf I found on the chevrolet website for the 1968 Impala says the total combustion chamber volume of assembled engine with piston at top center is, for the L73 327 (which mine is supposed to be) is 5.38 cubic inches. According to a cubic inches to cubic centimeters conversion tool in the internet, this is 88.16 cc's. So, I would think my piston volume, with head on, should be 88.2 cc's minus 68.8cc's , or 19.3 cc's. Make sense?
But, the calculator link above doesn't convert that way so I am still unable to calculate.
It seems, if I wanted to use vortec heads and bring the compression ratio from 9.2 back down to 8.75 or close, I would need pistons with the wrist pins slightly higher on the piston than stock to increase the piston volume. I read on the internet (can't find it now) in a discussion about turning a 350 into a 327 you can use the 350 rods on the 327 large journal crank but would need to use 327 pistons and it had to do with wrist pin location, but can't remember if the location on the 350 piston was higher or lower than the 327's, as though that was the only difference. Gotta look some more!
This research is driving me nuts!!!!

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Old 03-18-2011, 04:45 PM   #16
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Quote:
Originally Posted by streetjeep327 View Post
My problem is my engine is torn apart, parts all in boxes, so I can't measure the volumes needed. But, the pdf I found on the chevrolet website for the 1968 Impala says the total combustion chamber volume of assembled engine with piston at top center is, for the L73 327 (which mine is supposed to be) is 5.38 cubic inches. According to a cubic inches to cubic centimeters conversion tool in the internet, this is 88.16 cc's. So, I would think my piston volume, with head on, should be 88.2 cc's minus 68.8cc's , or 19.3 cc's. Make sense?
But, the calculator link above doesn't convert that way so I am still unable to calculate.
It seems, if I wanted to use vortec heads and bring the compression ratio from 9.2 back down to 8.75 or close, I would need pistons with the wrist pins slightly higher on the piston than stock to increase the piston volume. I read on the internet (can't find it now) in a discussion about turning a 350 into a 327 you can use the 350 rods on the 327 large journal crank but would need to use 327 pistons and it had to do with wrist pin location, but can't remember if the location on the 350 piston was higher or lower than the 327's, as though that was the only difference. Gotta look some more!
This research is driving me nuts!!!!
327 calculated compression height is 1.7"
350 calculated compression height is 1.585"
the formula is deck height - rod length - (stroke/2) = comp height
so for a 327 its 9.025" - 5.7" - ( 3.25" /2)= 1.7

Usually pistons vary a few thousands from above to get a desired level below the block decks. but as you can see a 350 piston pin will be closer to the top of the piston than a 327.
Using 350 pistons on a 5.7" rod with 327 crank will result in the pistons being "down in the hole" .117" this would drop you almost 2 whole compression ratio points using 350 pistons with the same dish/dome or valve relief size as a 327 piston it would also have a side effect of making the quench area ineffective . If you wanted to use 350 pistons in a 327 you need a custom rod length made.
I dont know which would be cheaper having custom dished pistons made with a 327 compression height to set the c/r where you want or to use a dished 350 piston and a custom rod.


keith black makes dished ( 13 cc ) pistons for a 327 p/n KB158 that they list as 9.0 c/r with 64 cc heads. I think with proper cam selection to achieve a reasonable dynamic c/r around 7- 7.5 you should be able to run it on 87 octane pump gas. but like anything its a try it and see as there are other factors that can cause you to get into detonation.
a Aluminum head of the same cc's will also help keep you out of detonation over a iron head in most cases.

note also that vortec headed motors usually require less total timing than other head designs to make their best power

scoggin-dicky has a vortec head kit with bolts,gaskets, rocker arms, performer vortec dual plane manifold for $ 945

http://sdparts.com/details/scoggin-d...nter/sd8060kit

Regards, Robert

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Old 03-18-2011, 05:42 PM   #17
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If you are still worried about using 87octane there are still 2 options available. use a thicker gasket or pull about 4 degrees out of your total timing.
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Old 03-18-2011, 07:20 PM   #18
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Using 350 pistons on a 5.7" rod with 327 crank will result in the pistons being "down in the hole" .117" this would drop you almost 2 whole compression ratio points using 350 pistons with the same dish/dome or valve relief size as a 327 piston it would also have a side effect of making the quench area ineffective. Regards, Robert
Good info! But, can't afford Aluminum heads. I am on a serious budget build due to income restraints.
But, based on what you say above, would it be possible that by using year 1968 350 pistons (10.25comp) with 327 double hump heads (11.00 comp) and by placing the pistons a bit lower in the 327 cylinder I would bring the compression ratio down to around 9.00?
Or, is it that the quench area problem means using 350 pistons in a 327 is not workable?
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Old 03-18-2011, 07:22 PM   #19
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If you are still worried about using 87octane there are still 2 options available. use a thicker gasket or pull about 4 degrees out of your total timing.
Thought about thicker gaskets, and figured I would have to tweak the timing. Read that elsewhere also.

Thanks!
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Old 03-18-2011, 07:56 PM   #20
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Using the 350 pistons produces too much clearance between the flat part of the head surface and piston killing quench and a side effect could also be that the bottom part of the piston skirt may interfere with the crankshaft counterweights.
If you use a 64 cc head and that Keith Black or a similar 327 piston with the 13 cc dish I mentioned you will be right at 9.0 to 1. Since if I read your previous posts correctly you plan on boring the block for new pistons anyway this would be a good way to go.

I did a cr calculation using a .030 overbore , 64 cc head chambers, the KB 13 cc dish piston and 0 decked block with a 4.1" bore x .039 thick gasket and it came out to 8.95 to 1.
based on the cam lift in your earlier post I think your looking at using a comp cams 246pe correct ?

If so with 8.95 static c/r you will be better served by stepping up to the
265deh .442 intake / .465 exhaust

It would require you to carefully check the bottom of the retainer to seal clearance at the max lift of the cam on the exhaust side for sure if using unmodified vortec heads.

If you go with 75-76 cc heads like gm 441 castings or world products s/r torquer's and the common flat top 327 piston you will be at
about 8.55-8.6 static and that combo would work better for the 246pe cam that may end up being the least expensive way to go and get you close to 300hp with headers and good dual plane manifold

Regards, Robert

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