Quench distance
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From: PacNW
Quench distance
According to everyone I've talked to the maximum quench distance should be right around .045. Once you get above .050 the quench effect is minimized to the point of being non-existent. I'd shoot for somewhere between .035 and .045.
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Postmaster
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From: Delaware
Quench distance
So with a deck to piston distance of 0.056 on a 400 quench is out of the question. If you deck the block 0.050, then you need quench heads with huge chambers to keep the compression ratio down.
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From: PacNW
Quench distance
If you're talking about stock 400 heads or even open chamber 351C heads then the 'open chamber' design makes quench virtually impossible even if you were to 'zero deck' the block. There's just no place in the chamber to generate the type of turbulence caused by 'close collision' between flat surfaces of the piston top and head surface necessary for the quench effect.
IMO the best combination for designing a serious, normally aspirated, streetable hi-performance 400 would be Aussie 302C heads with custom pistons set for 0 deck height but with a large enough dish to get the C.R. down to 10:1 or so. The head gasket would provide the .040 quench distance and the engine could still run 'pump gas'.
IMO the best combination for designing a serious, normally aspirated, streetable hi-performance 400 would be Aussie 302C heads with custom pistons set for 0 deck height but with a large enough dish to get the C.R. down to 10:1 or so. The head gasket would provide the .040 quench distance and the engine could still run 'pump gas'.
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From: Delaware
Quench distance
If I put 64cc closed chamber heads on my 400 (Aussie or otherwise), I would need a set of custom pistons with no more than 0.005 deck height and a dish area of 10cc that lines up to the combustion area of the heads. This would be a CR of 11:1 and would allow the quench effect.
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Quench distance
IMO 11:1 is pushing your compression to high for any pump gas. Best to limit it to 10:1 with quench, or 9:1 without quench, if you polish combustion chambers etc etc you can push that another half point to 9.5:1. But if you start building deposits in the chamber that act as hot spots for ignition you could be hurting. It is best to go conservative unless you want to be pulling your heads every few months to clean the chambers.
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From: Delaware
Quench distance
What is the difference in pin diameter between a 351C and a 400 piston?
Could a Zero deck piston for a 400 be fabricated by taking a blank 351C piston and boring the pin offset?
Could a Zero deck piston for a 400 be fabricated by taking a blank 351C piston and boring the pin offset?
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Posting Legend
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Quench distance
There are a number of posts here that can be found with the search function that cover piston pin sizes and piston fabrication for the 400.
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Quench distance
but off the top of my head, the 351M/400 pin is .975" and the 351C is .912". It's better to reduce the rod bore rather than enlarge the piston. Generally, I refer people to this site for quench explanation.
http://www.speedomotive.com/Building%20Tips.htm
http://www.speedomotive.com/Building%20Tips.htm
Posting Legend
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Quench distance
Good information and they list 0.5 compression points lower than I listed!
The 9.0 compression in a stock 400 in 1971 worked real well and ran on regular gas in the old days. The gas was a mite different back then but it should work on pump gas even now. They ran those engines in big HEAVY cars (LTD's) and they towed trailers etc well. With the skinny bias tires they had the wheels never did stop spinning -hehe!
The 9.0 compression in a stock 400 in 1971 worked real well and ran on regular gas in the old days. The gas was a mite different back then but it should work on pump gas even now. They ran those engines in big HEAVY cars (LTD's) and they towed trailers etc well. With the skinny bias tires they had the wheels never did stop spinning -hehe!
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From: Delaware
Quench distance
Custom pistons cost about $100.00 ea. If I use a 351C piston with a compression height of 1.657 and bore the pin from 0.912 to 0.975, but offset the bore center by radius2-radius1, I add 0.0315 to the compression height. The new compression height is 1.6885. Now if I deck the block 0.018, I get Zero deck height. Now the dish area needs to be milled to set the CR where ever it needs to be.
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Quench distance
If you're running open chamber heads there's no quench benefits so why do you need to shoot for a zero deck? Increasing compression .5 is worth less than 5HP. It's not worth spending $1000 extra to get it. If it's a daily driver, go for 9:1 and hope it runs on regular. If it's a weekend vehicle, bump it up to 9.5:1 with 351C flat top or dished 'eute pistons (BTW 1.67" CH for the KBs) and have the rods bushed for a 9.12" pin. That's only a couple hundred $$ over a cast 400 piston with no bushings.
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From: Delaware
Quench distance
It is not the compression, but >300 cfm at 0.550 lift that I am after. These are 64cc closed chamber aluminum heads. I'll take all the compression that I can get away with. I need zero deck height to get the quench effect.
Then the piston has to be dished to reduce the CR from 12.5:1.
If I use a flattop piston with 0.056 deck height, I get no quench and still have 10.9:1.
With my cam and 10.5:1 CR these heads will make near 500HP and be street driven(93 Octane).
This is a weekend vehicle (good weather only).
Then the piston has to be dished to reduce the CR from 12.5:1.
If I use a flattop piston with 0.056 deck height, I get no quench and still have 10.9:1.
With my cam and 10.5:1 CR these heads will make near 500HP and be street driven(93 Octane).
This is a weekend vehicle (good weather only).
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Postmaster
Joined: Aug 2001
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From: Delaware
Quench distance
Brian,
Are you sure about the KB's being 1.67 CH?
If that is true then my CH will be 0.005 after offsetting the pin. That means the quench distance is 0.045 with a 0.040 compressed gasket and I don't have to deck the block at all.
The only question now is: Can these pistons be bored like that and still hold up?
Are you sure about the KB's being 1.67 CH?
If that is true then my CH will be 0.005 after offsetting the pin. That means the quench distance is 0.045 with a 0.040 compressed gasket and I don't have to deck the block at all.
The only question now is: Can these pistons be bored like that and still hold up?