10:1 Static Compression Ratio With Flat Top Pistons?

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Dan1950

Dan1950

1974 MK II Roadster
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In some applications, flat top pistons have proven to be most efficient as far as preventing detonation by promoting more efficient quench.

Is this possible in an 850?
 
Dan1950 said:
In some applications, flat top pistons have proven to be most efficient as far as preventing detonation by promoting more efficient quench.

Is this possible in an 850?
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With an 850, if you set the squish gap to around .035” +/- then with flat top pistons you should have around 10.5:1. Well, that’s if your combustions chamber shape etc is the same as mine.

Raised crown pistons or skimmed barrel or head will be required to achieve this.

You’ll most likely have to cut valves pockets in the pistons unless you buy them thus.

I used JS lightweight high compression pistons in my 850. Very light. Very nice.
 
Dan1950 said:
In some applications, flat top pistons have proven to be most efficient as far as preventing detonation by promoting more efficient quench.

Is this possible in an 850?
Click to expand...
Maney's high compression JE pistons, which he milled down for 9.5:1 to suit the 312a cam.

Muttster: A long, slow '74 resto-mod


Muttster: A long, slow '74 resto-mod
 
I think you can also boost CR using JS' .021 or .003 copper head gaskets, and.i think the former with no additional changes?

@jseng1 how much CR boost would you see with these, and would you need to do anything to the stock pistons with a 321a?

And as a selfish question, would the .021 bolt up with the Maney 9.5:1 pistons ok?
 
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IIRC, very roughly speaking, compared to a stock composite gasket, going the .021” route will get you nearly half a point increase and the .003” nearly a one point increase I believe (in an 850).

What would work with your Maney pistons is impossible to say without a) knowing what gasket is already in there b) removing the head to check piston to head squish clearance and c) checking valve to piston clearance.
 
Fast Eddie said:
With an 850, if you set the squish gap to around .035” +/- then with flat top pistons you should have around 10.5:1. Well, that’s if your combustions chamber shape etc is the same as mine.

Raised crown pistons or skimmed barrel or head will be required to achieve this.

You’ll most likely have to cut valves pockets in the pistons unless you buy them thus.

I used JS lightweight high compression pistons in my 850. Very light. Very nice.
Click to expand...
Don't forget to tell him he needs the long rods to use those pistons......and will need to consider crank balance to get the best from it all......

Oh, and that the JSM web site has a full write-up on the options and compression......
 
Fast Eddie said:
IIRC, very roughly speaking, compared to a stock composite gasket, going the .021” route will get you nearly half a point increase and the .003” nearly a one point increase I believe (in an 850).

What would work with your Maney pistons is impossible to say without a) knowing what gasket is already in there b) removing the head to check piston to head squish clearance and c) checking valve to piston clearance.
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AN composite gasket.

I think JS might also sell those JE pistons.

I thought that was roughly correct on the CR. Was just checking and furthering the confusion for Dan. ;-)
 
Some clarification. Longer rods for JS pistons, not required for Steve Maney's JE pistons.
 
gortnipper said:
No idea. I think he still has some he is selling off, so maybe send him an email and ask?


Or, I think @lcrken sells/sold JE?
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I received a PM from JS and indeed these are the Maney pistons. They are for stock rods. CR is approximately 10.1:1 with a quench height of .040"

I assume that is with the stock composite head gasket.

This is about what i am looking for.
 
Dan1950 said:
I received a PM from JS and indeed these are the Maney pistons. They are for stock rods. CR is approximately 10.1:1 with a quench height of .040"

I assume that is with the stock composite head gasket.

This is about what i am looking for.
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I reckon you’ll be alright with those.

I‘d opt for the nice coating that Jim offers too …

Plus, Jim does a great selection of accurate, different thickness head and base gaskets, so you can really dial in the squish gap nicely.

Big valves and beehive springs too sir…?
 
Fast Eddie said:
I reckon you’ll be alright with those.

I‘d opt for the nice coating that Jim offers too …

Plus, Jim does a great selection of accurate, different thickness head and base gaskets, so you can really dial in the squish gap nicely.

Big valves and beehive springs too sir…?
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1.56" intake valves and yes, upgraded valve springs, retainers, etc. The coating sounds like a good idea too.

Maybe retard the cam timing to reduce cylinder pressure at lower RPM. Looking to make the combo a little more user friendly and raise the power band a bit.
 
Dan1950 said:
1.56" intake valves and yes, upgraded valve springs, retainers, etc. The coating sounds like a good idea too.

Maybe retard the cam timing to reduce cylinder pressure at lower RPM. Looking to make the combo a little more user friendly and raise the power band a bit.
Click to expand...
The 312a as mine is set up idles beautifully.
 
Dan1950 said:
I received a PM from JS and indeed these are the Maney pistons. They are for stock rods. CR is approximately 10.1:1 with a quench height of .040"

I assume that is with the stock composite head gasket.

This is about what i am looking for.
Click to expand...
Then the .021 should work fine with 9.5:1 I would guess.

When my composite gasket goes, maybe I will put one on, because, why not? ;-)

Clay check notwithstanding...
 
gortnipper said:
No idea. I think he still has some he is selling off, so maybe send him an email and ask?


Or, I think @lcrken sells/sold JE?
Click to expand...
Lcrken AKA Ken Canaga is the one who developed the high compression JE pistons for Norton and he's the one who supplied them to Maney. Ken has done a lot for the Norton community and has been very helpful. He is retired now and is no longer selling pistons. Maney may have a few left in stock if you ask him.
 
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