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Author Topic: Compression Opinion  (Read 2722 times)
mopar346
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« on: November 29, 2010, 09:47:59 PM »

As I discussed in other threads, I am building a motor for my son's truck. I have been told a few diffent answer to the final compression and was wondering what the collective views are here. It is a 93(ish) 350 4 bolt roller block with forged flat top speed pro pistons and a 64 cc head. Neither the block or the head has had any significant decking in the past.

Thanks in advance, Kevin
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BlackoutSteve
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« Reply #1 on: November 30, 2010, 12:54:01 AM »

Have a look at the cam you're selecting and it should have a minimum recomendation.
I'd go at least 10:1
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Restoring my RHD 69 Jane in Melbourne, Australia.
http://www.usmuscle.com.au/Forum/showthread.php?t=2840
mopar346
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« Reply #2 on: November 30, 2010, 07:21:10 AM »

I believe it is in the 10s and that is what the cam is calling for, I was just curious if anyone knew what it would be with the above combo.
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Mark
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« Reply #3 on: November 30, 2010, 11:51:26 AM »

Got any valve relief cuts in the pistons?  If so  and theirs 4 of them then it should be about 9.3 to 1 if not about 9.7 to one assuming a zero deck height.  I've got 1/8" knuckles on my pistons and I'm only pulling about 10.7 to 1.
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Mark C.
1969 Indy Pace Car
350/300HP RPO Z11
mopar346
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« Reply #4 on: November 30, 2010, 12:44:39 PM »

Thank you, I believe they have 4 reliefs, I will have them in hand this week end.
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Boston14
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« Reply #5 on: November 30, 2010, 09:22:04 PM »

Here's the calculator I use, works great.  http://www.csgnetwork.com/compcalc.html  hope this helps.

boston14
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boston14

1969 RS/SS 350 Convertible
Dover White with Black Top and D90 stripe, Red Standard Interior
mopar346
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« Reply #6 on: November 30, 2010, 10:49:24 PM »

Thanks, found one at Summit as well, 64 cc heads, with 4 vavle reliefs (+6.1 cc according to summit info sheet), .010 in the hole, .053 compressed gasket, it shows 9.7:1. At 0 deck height it is 10:1. They remaining uncertain is deck height, which I cant measure till the week end.

Thanks folks!
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mopar346
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« Reply #7 on: December 04, 2010, 06:33:18 PM »

Checked piston heigth today, .015 in the hole, giving it 9.6:1 compression as long as the head gasket compressed thickness is .053 as I think. The thickness number came from an internet search, does anyone know for sure? It is a regular good quality Fel Pro blue gasket.
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Boston14
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« Reply #8 on: December 04, 2010, 10:49:12 PM »

What number Felpro head gasket?   They range from 0.015" to 0.071" thick and have bore diameters from 4.080" to 4.250", giving you a compressed volume anywhere from 3.2cc to 16.1cc. Quite a range and effect on compression!

boston14
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boston14

1969 RS/SS 350 Convertible
Dover White with Black Top and D90 stripe, Red Standard Interior
mopar346
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« Reply #9 on: December 04, 2010, 10:53:48 PM »

Any way to tell which is which, not that it matters at this point I'm not gonna change anything. Just curious thats all.
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Boston14
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« Reply #10 on: December 05, 2010, 08:26:13 AM »

The numbers are stamped into the gaskets.
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boston14

1969 RS/SS 350 Convertible
Dover White with Black Top and D90 stripe, Red Standard Interior
mopar346
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« Reply #11 on: December 05, 2010, 08:36:47 AM »

Thank you, part number or compressed number?
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BlackoutSteve
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« Reply #12 on: December 05, 2010, 06:43:35 PM »

Possibly both, but definitely the part number.
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Restoring my RHD 69 Jane in Melbourne, Australia.
http://www.usmuscle.com.au/Forum/showthread.php?t=2840
mopar346
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« Reply #13 on: December 06, 2010, 09:28:53 PM »

Steve,

Thanks, I was reading a little of you post down under. You're pretty creative and talented. Great job on creating a unique piece.
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BlackoutSteve
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« Reply #14 on: December 10, 2010, 11:08:54 PM »

Thanks for the compliment.. It helps to be single and a little compulsive!
The stuff I have done is pretty easy. I found that out the hard way Tongue -by just having a go before deciding to pay someone. Cheesy
Thanks Kevin.  Wink
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Restoring my RHD 69 Jane in Melbourne, Australia.
http://www.usmuscle.com.au/Forum/showthread.php?t=2840
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