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Compression

General engine tech -- Drag Racing to Circle Track

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af2
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Compression

Post by af2 » Tue Jan 21, 2020 8:05 pm

Ok I am lost trying to figure out the static on this new build...... 3.75 stroke 4.135 bore. I have at .375" down 75 cc the head gasket at .040" and the heads 46 cc. I measured down .375 because of the domes. Thanks I have a head ache finding it out I am figuring 17:1 but making sure so I can get a good flow# for the injection set up.
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Re: Compression

Post by bentvalves » Tue Jan 21, 2020 8:33 pm


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Re: Compression

Post by CGT » Tue Jan 21, 2020 8:56 pm

Assuming ....0 deck with your .040 gasket. 75cc's at .375 down comes out to 7.4 dome volume. I get 18.3:1..unless I'm missing or not reading something correctly.
Last edited by CGT on Tue Jan 21, 2020 9:04 pm, edited 1 time in total.
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Re: Compression

Post by Mark O'Neal » Tue Jan 21, 2020 8:57 pm

We need the Bore, stroke, deck, gasket, head ccs, and net dome volume.

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Re: Compression

Post by af2 » Tue Jan 21, 2020 9:10 pm

Mark O'Neal wrote:
Tue Jan 21, 2020 8:57 pm
We need the Bore, stroke, deck, gasket, head ccs, and net dome volume.
First post.
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Re: Compression

Post by dannobee » Tue Jan 21, 2020 9:11 pm

http://www.wallaceracing.com/cr_test2.php

Somewhere north of 18.5:1, depending on the deck height and the diameter of the head gasket.

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Re: Compression

Post by af2 » Tue Jan 21, 2020 9:16 pm

CGT wrote:
Tue Jan 21, 2020 8:56 pm
Assuming ....0 deck with your .040 gasket. 75cc's at .375 down comes out to 7.4 dome volume. I get 18.3:1..unless I'm missing or not reading something correctly.
Thats why am asking? The dome volume was to be 3 cc???? Had to cut a bunch off to limit head contact now doing the measuring I see more.. True measuring with a burrett not some back yard stuff
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Re: Compression

Post by Elroy » Tue Jan 21, 2020 9:30 pm

af2 wrote:
Tue Jan 21, 2020 9:16 pm
CGT wrote:
Tue Jan 21, 2020 8:56 pm
Assuming ....0 deck with your .040 gasket. 75cc's at .375 down comes out to 7.4 dome volume. I get 18.3:1..unless I'm missing or not reading something correctly.
Thats why am asking? The dome volume was to be 3 cc???? Had to cut a bunch off to limit head contact now doing the measuring I see more.. True measuring with a burrett not some back yard stuff
Are you at 0 deck? If so...using 0 deck, 4.200 gasket bore. I get 18.3. Whoa! Lol

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Re: Compression

Post by CGT » Tue Jan 21, 2020 9:31 pm

Elroy wrote:
Tue Jan 21, 2020 9:30 pm
af2 wrote:
Tue Jan 21, 2020 9:16 pm
CGT wrote:
Tue Jan 21, 2020 8:56 pm
Assuming ....0 deck with your .040 gasket. 75cc's at .375 down comes out to 7.4 dome volume. I get 18.3:1..unless I'm missing or not reading something correctly.
Thats why am asking? The dome volume was to be 3 cc???? Had to cut a bunch off to limit head contact now doing the measuring I see more.. True measuring with a burrett not some back yard stuff
Are you at 0 deck? If so...using 0 deck, 4.200 gasket bore. I get 18.3. Whoa! Lol
Whoa X2 lol
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Re: Compression

Post by Fatman » Tue Jan 21, 2020 10:14 pm

What is piston to deck and gasket bore measurements?

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Re: Compression

Post by bentvalves » Tue Jan 21, 2020 10:29 pm

will a leaded 110 octane fuel be enough for those kind of ratios or is that methanol territory?

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Re: Compression

Post by travis » Wed Jan 22, 2020 1:20 am

More like diesel :lol:

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Re: Compression

Post by mag2555 » Wed Jan 22, 2020 6:16 am

Yes,so let me get this straight, your shooting for a 17 to 1 compression on your 403 cid motor?

I am hoping you have more then 4 head bolts per cylinder?

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Re: Compression

Post by LoganD » Wed Jan 22, 2020 9:19 am

mag2555 wrote:
Wed Jan 22, 2020 6:16 am
Yes,so let me get this straight, your shooting for a 17 to 1 compression on your 403 cid motor?

I am hoping you have more then 4 head bolts per cylinder?
Eh....why is this any different than running 25 psi of boost? As long as it doesn't go lean your peak firing pressure is just going to be similar to that of a boosted engine. Build it accordingly.

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Re: Compression

Post by CGT » Wed Jan 22, 2020 10:12 am

LoganD wrote:
Wed Jan 22, 2020 9:19 am
Eh....why is this any different than running 25 psi of boost?
You beat me to it. I was thinking the same thing. Mag, have you failed a sbc at or because of 17:1 compression lol?...There is literally stuff out there with 15:1 and a couple atmospheres on top of it...and that just the stuff I've heard of or seen. Im sure there is way more severe stuff out there than that.

AF2, got any pics of your pistons?
There are basically two types of people. People who accomplish things, and people who claim to have accomplished things. The first group is less crowded.
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Golf is a good walk spoiled.
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