Question: Piston protrusion

[maine04max]

with .012 -.013 piston protrusion on all cylinders and stock pistons just delipped . block was milled but pistons tops were cut to keep protrusion down to the .012 . the bores were also punched out .020 . I know the spec section says to use c gaskets . but im concerned with too much compression . iirc Ive heard that just delipping doesnt lower compression much . do you guys recommend D gaskets that are .008 thinker to keep compression down ????? or should the bowls be open more to lower it so i can run higher boost ???
thanks in advance Craig

 

[duramaximizer]

I would keep all of the compression you can if you have enough clearance.

 

[TrentNell]

I would keep all of the compression you can if you have enough clearance.

why ? depends on boost , and whether you have the money to repair it if your gamble on the subject is wrong, I don't myself so i went low , I went with 14.9-15.0 and i dont think it has hurt HP much on my truck and do think it will help the stock pistons live for a bit .

Craig my protrusion was .012 and i went with grade c gaskets , but I didnt have anything taken off the heads or block but it sounds like with the pistons cut down to compensate you would be identical ,I was wanting low compression anyway so i went with C's just to not have to hassle with it .

 

[bullfrogjohnson]

how much boost are you wanting to run?

 

[sweetdiesel]

Correct me if I am wrong but if you are bored over you don't have the option of C gaskets?

I was under the impression that those gaskets are used for over bore,perhaps I'm wrong

 

[sweetdiesel]

Also consider how high you want to rev
too.


I've read about members that are high reving. Feel a lot better with the extra clearance

just a thought

 

[bullfrogjohnson]

Also consider how high you want to rev
too.


I've read about members that are high reving. Feel a lot better with the extra clearance

just a thought

x2 nothing like some piston to valve contact to ruin your day

 

[duramaximizer]

I would keep all of the compression you can if you have enough clearance.

why ? depends on boost , and whether you have the money to repair it if your gamble on the subject is wrong, I don't myself so i went low , I went with 14.9-15.0 and i dont think it has hurt HP much on my truck and do think it will help the stock pistons live for a bit .

Craig my protrusion was .012 and i went with grade c gaskets , but I didnt have anything taken off the heads or block but it sounds like with the pistons cut down to compensate you would be identical ,I was wanting low compression anyway so i went with C's just to not have to hassle with it .

I have a friend that changed pistons 5 times last year, and I know which set of pistons let him spool the biggest charger and which one made the most power. Hint it wasn't the 13.5 to 1 that required starter fluid. This was on a 6 cylinder. Apples to snowplows. :spit:

x2 nothing like some piston to valve contact to ruin your day

Hense my previous comment. You deffinately want plunty of clearance from what I have seen.

I figure it's 50 hp per point and a huge difference when spooling large chargers unless you have insane RPM/fuel to make up the difference. For truck pulling you're ability to lug a large charger depends a lot on static cylinder pressure otherwise you're limited to tighter A/R ratios which aren't good.

 

[x MadMAX DIESEL]

Never mind

 

[bullfrogjohnson]

Okay I might sound like a complete idiot. But wont the compression be the same no matter the gasket?

The different grade gaskets are different thicknesses. A's are the thinnest B's. C's, and so on. You get the picture. If you use thicker gaskets you are increasing the area the fuel and air can be compressed between the piston top and head. With the thinner gaskets you a doing the opposite.

 

[x MadMAX DIESEL]

Yea thanks for explaing.. I guess I was thinking of changn the rod length and calling it a stroker... I blame the beer tonight lol

 

[TrentNell]

I have a friend that changed pistons 5 times last year, and I know which set of pistons let him spool the biggest charger and which one made the most power. Hint it wasn't the 13.5 to 1 that required starter fluid. This was on a 6 cylinder. Apples to snowplows. :spit:



Hense my previous comment. You deffinately want plunty of clearance from what I have seen.

I figure it's 50 hp per point and a huge difference when spooling large chargers unless you have insane RPM/fuel to make up the difference. For truck pulling you're ability to lug a large charger depends a lot on static cylinder pressure otherwise you're limited to tighter A/R ratios which aren't good.

I agree with what you said 100 % , but the HP increase comes from cylinder pressure being higher on the higher compression motor , which if you hard parts can handle it isnt a bad thing , but in the case of stock cut pistons I dont care to gamble , that is all i was saying ,and yes on a cummins they need all the spooling help they can get ,us duramaxes have some room to play IMOP

 

[maine04max]

my thoughts on boost were to be in the 60-70 range with twins eventually . initially Im going to run a 366 , then after I recover from the motor build twin it with a s480 . im sure with just a 366 ill be safe on boost limits , but my concern is later with twin boost

 

[duramaximizer]

Can cam overlap design limit the injuring cylinder pressure that's made by a high compression ratio while still being able to use it's benefit on the low end for spooling large turbos?

 

[S Phinney]

Can cam overlap design limit the injuring cylinder pressure that's made by a high compression ratio while still being able to use it's benefit on the low end for spooling large turbos?

Yes cam design will have an effect on cylinder pressure and how larger turbos spool. Stock cams are ground on 108 centerlines. You can get after market cams with greater centerlines as in 112-113 degrees that help spool turbos better. They help create more cylinder pressure down lower in the rpm range.

 

[wdino73]

I used .20 c's with the .20 over bore an had o.12 out of the hole, c's compress to .40 thats a safe go in my opinion, I've had my motor down twice, and that looked good. and that' all I'll say on that. LOL

 

[JoshH]

Correct me if I am wrong but if you are bored over you don't have the option of C gaskets?

I was under the impression that those gaskets are used for over bore,perhaps I'm wrong

Actually you can use standard bore gaskets in an overbore application. I didn't think you could until Guy told me otherwise. I used grade C gaskets in my engine, and it is bored .020 over.

 

[sweetdiesel]

Actually you can use standard bore gaskets in an overbore application. I didn't think you could until Guy told me otherwise. I used grade C gaskets in my engine, and it is bored .020 over.

Thanks for clarifying Josh

 

[Bluemax]

Yes cam design will have an effect on cylinder pressure and how larger turbos spool. Stock cams are ground on 108 centerlines. You can get after market cams with greater centerlines as in 112-113 degrees that help spool turbos better. They help create more cylinder pressure down lower in the rpm range.

What effect does that have on the upper rpms?

 

[Stingpuller]

Go big or go home!

Really, I would never give any up again! Been there and done that. Jeff