Pistons down hole

General engine tech -- Drag Racing to Circle Track

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panic
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Re: Pistons down hole

Post by panic »

It was tough at first to convince "old schoolers"

Like David Vizard?
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Re: Pistons down hole

Post by piston guy »

More like people that read his books :lol:
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panic
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Re: Pistons down hole

Post by panic »

Perhaps you'd like to enlighten us.
What would be Vizard's worst mistake?
Whose books do you read?
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Re: Pistons down hole

Post by Nick payne »

Thank you everybody for the great advise.
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Re: Pistons down hole

Post by Mark O'Neal »

piston guy wrote:On BOOSTED applications ONLY , quench is not a factor like it is on naturally aspirated combinations. A round dish is more powerful but when the volume needed gets too great , a flat top "down in the hole" is the only alternative. The boosted charge has so much "mixture motion" is my opinion as to why it works. Been doing it for at least ten years. It was tough at first to convince "old schoolers" it would work , but it does.
I've been doing it since the late '70s.... :P

And, it's no longer the "round dish", it is now referred to as the "ULTIMATE RADIUS" dish... :D
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Re: Pistons down hole

Post by ProPower engines »

the only down side is if you get some oil consumption the carbon will adhere to the top of the bores easier and the chance of some falling down and being caught in the top ring area causing damage by jamming the ring.

While being that far down it would allow the bore top at the deck down the bore to be blended to the head way better to help the exhaust and intake sides of the chamber flow much better.
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Re: Pistons down hole

Post by 4vpc »

panic wrote:It was tough at first to convince "old schoolers"

Like David Vizard?
He wrote about an engine he tuned back in the 70s which went very well with no squish at all IIRC.
There is no S on the end of RPM.
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Re: Pistons down hole

Post by 4vpc »

As engine builders I guess we like to keep things tight, tight clearances, tight tolerances and er, tight squish just seems right.
So convince me otherwise, the OEMs still like it tight, is this for emissions, off boost performance and earlier turbo spool, economy?
It does seem to be dependent on fuel type and amount of boost/performance etc too. Does E85 need it tighter than regular gas? If I was building a low boost street car I'd want tight squish right?

Has anyone ever done a back to back test and published the results?
There is no S on the end of RPM.
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Re: Pistons down hole

Post by kimosabi »

How about using the Cometic .140 MLS gasket? I'm thinking about doing that going boosted as my flat top pistons are at zero and I'd rather shell out $400 on gaskets than $700+ on new pistons alone.

Only a suggestion, I have no experience using them. I know about shims but then you have two gaskets each side instead of one thick.
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Re: Pistons down hole

Post by roc »

Aren't 409's piston's down the hole by factory, kinda?
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Re: Pistons down hole

Post by bigfoot584 »

Part of it is, but look at it as a SBC chamber setup turned upside down
not the whole piston is below the deck, part is used as quench area.
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Re: Pistons down hole

Post by piston guy »

panic wrote:Perhaps you'd like to enlighten us.
What would be Vizard's worst mistake?
Whose books do you read?
NOTE!!! YOU brought up David's name , not me. I was not thinking of him when I said that. I have no problem with David, he is a smart man. David speaks from experience. He doesn't start a conversation with "I read in a book ...."

I don't read books. I have trouble getting past the pictures. I have done stuff people write about though , like pistons .200 down in the bore in a blown application. I'm a nobody to you but I'm OK with that. Others rely on my expertise daily and that is personally rewarding.
Last edited by piston guy on Fri Sep 15, 2017 1:47 pm, edited 1 time in total.
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Re: Pistons down hole

Post by piston guy »

roc wrote:Aren't 409's piston's down the hole by factory, kinda?
The nice thing about a 409 ( or 430-462 MEL) it when the combustion happens , most all of the force is directed at the piston. By that I mean the "burn" doesn't have a chamber full of air and fuel to "eat up" some of the energy. No different than diesel technology . Put all of the force immediately against the object you are trying to move with the least amount of wasted motion.
Large amounts of aluminum above the pin bore makes them load the cylinder walls a bit but they still make power well.
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Re: Pistons down hole

Post by pamotorman »

one problem with the chevy 409 and Z-11 was the combustion chamber was in the cylinder and it put extra heat into the cylinder wall making it harder to cool in oval track racing. worked great at drag racing which GM was into at that time period.
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Re: Pistons down hole

Post by gnicholson »

I don't have any experience running a piston down in the bore like that but I would still think you would be better off adjusting your displaced volume with piston dish or combustion chamber then running the Piston down like that. I realize in some cases it's the only way you can get the compression low enough
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