what the heck? look like 18:1 compression pistons.? lol

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340plot

340plot

the bushy bush
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can anyone help me figure out what brand pistons these are? they have number 90825 on the dome. and right below it, it says .030 so i know it is 30 over, but cannot find anything on what brand they may be.

the second pic, i took to show how far out of the bore they are
 

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Looks identical to the old speed pro piston for 340's it was advertised 13.5.
 
i guess i would not be able to run them on pump gas then?
 
LOL, pump gas, I doubt it, for a street motor I would go back flat top. Probally even get by with the factory 10.5 to 1 pistons, as they wont be true 10.5 to 1 unless everthing is blueprinted.
 
Cometic can provide a thick gasket as per your specs. Perhaps, they might be able/willing to work with you since you have pistures on the ready.
 
rumblefish360 said:
Cometic can provide a thick gasket as per your specs. Perhaps, they might be able/willing to work with you since you have pistures on the ready.
Click to expand...

Not thick enough!! He'll need to change pistons for pump gas for sure.
Those big domes don't make any more power than small domes because they cutoff the flame front severly.
 
Maybe. Alot depends on the build of the engine, like, as you know, a monster cam and alot of head chamber.

Though, I tend to beileve your more on track then myself, it's just what is possible and not hasn't been tried. I'm opting for a possible cheaper way out. Does MoPar still offer the steel shim @ /060 thick? I've used that before. Not a preety site, but a gasket (040 ) on both sides did the trick for me once. The intake needed a few extra gaskets as well.

Cheaper than new slugs and a balance job. Though neither is a happy route.
 
yea, ^^^^^^^^ is what bothers me, as i know it was all balanced
 
rumblefish360 said:
Maybe. Alot depends on the build of the engine, like, as you know, a monster cam and alot of head chamber.

Though, I tend to beileve your more on track then myself, it's just what is possible and not hasn't been tried. I'm opting for a possible cheaper way out. Does MoPar still offer the steel shim @ /060 thick? I've used that before. Not a preety site, but a gasket (040 ) on both sides did the trick for me once. The intake needed a few extra gaskets as well.

Cheaper than new slugs and a balance job. Though neither is a happy route.
Click to expand...
I assume you are speaking of compressed thickness.Gaskets do compress when torqued on.
 
Well, what I was saying may not work and it aint preety.

Brian suggest what I woulod say is the right way to do it.

New slugs and a balance job. Also requires a bit more time and parts, gaskey=ts and new oil and ....you know the drill.....but it is a better way by a wide margine of "Best way."

My way may be a few bucks ill spent at worst. You gotta know a bit about the engine and where it all sits before you jump.
 
You cant just put a big duration cam in it either, sure it will bleed cylinder pressure at low speed, but if it is timed properly, it will still detonate at WOT under load with that much compression on pump gas, period. The proper fix is to replace the pistons.
 
That engine looks likt it was built back in the day,If so it,s a manly .030 over 12.5 to 1 .Mark
 
the part number on the piston is 90825.... any one able to tell me the brand?
 
trw/speed pro/manley....they are the same piston...big and heavy...

I got a set of the trw 340 .060 sitting in a milk crate now for about 10 yrs...
 
maybe weigh one and find something close but heavier and mill the new ones to match the old.
 
If they are the old speed pro or trw pistons, you can cut the domes off (lathe) and make them into flat tops! There is alot of aluminum there!
 
if you have the pan off you should be able to shine a flashlight down into the cylinder and either on the bottom of the piston or on the skirt there should be a manufacturers name/logo or an additional part number.
 
YEA, but i do drive the car at leat 500 miles a week.lol. the gas offset will catch up real quick
 
Hmmmmmm.................................

Timing curves, biggest set of chambers you can find, nice thick gasket, and like 140* of overlap......... It just may work with 100LL......... But owuld get like 6MPG, LOL.

Rregardless of how "heavy" those pistons are, they are some tough SOB's!
 
With alloy heads and a fat duration cam ground on tight lobe centers those could run on pump premium.
 
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