ISB 275 hp pistons vs ISB 325 hp pistons

GOT-Torque

GOT-Torque

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Jul 2, 2007
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Looking for info on which would be better for a performance build on a p-pumped 24 valve.

A picture of a ISB275 (RV 275 hp) piston would be great... still haven't seen one.

Also like to know the dish size of either piston (cc's) and what you guys would recommend for piston to wall clearance.

Truck will still see some limited street use in the off season, but during the summer will see 4500 rpm on the track...
 
i believe the 275 and 300 are the same piston i think the 325 is the same also
but not positive
 
ISB 275 and 300's are the same (or I am told they are). Here's a pic of the 325 hp ones (04.5+ CR pistons)

lateCRlmills.jpg


Here's a stock 24V piston

1998-24V102039-1.jpg


I will get the cc's of my stock pistons tomorrow when I call my machinist...

I don't know what the 275 piston bowl looks like, but it seems like the 04.5+ piston bowl would allow for ALOT of timing to be run and still have the injector spray in the bowl...
 
piston to wall clearance i think is .010 with factory rings and .020 with total seals, Correct me if im wrong

i would bet the piston in the ISB 275 is the same as the 98 to 02 24v piston! but who knows i have one sittin in front of me but haven't torn it down yet!!
 
275 on the left
 

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It depends on what CPL engine your going with. The older 1997 and 1998 CPL's used a 3800333 p/n piston. When the 2000 CPL's came out with the ISB 300 engine 3948465 P/N pistons are used. Engines over 230 Hp have cylinder heads with valve seat inserts.
 
going by the performance parts matrix 2000 cpls some 260 hp the 275, and 300 Hp all used the 3948465 pistons. This is grade A. 3948466 is grade B, 3948467 is grade C
 
thanks for the picture. So why is there a color difference on the top of the piston? Different materials or a coating? The bowl seems to be the same...
 
roachie said:
275 on the left
Click to expand...


LOL, at least someone is keeping track of my pics for me!!!

Bowl on the 275/300 is wider, but I did not measure the depth. The black coating is some sort of ceramic, may loast a while on a stock engine, but could come off on something that gets some BIG heat. Since I only have at best a 550 HP engine, I am prolly safe there.

If you are going +.02 on the bores, I believe you can only get grade A pistons from Cummins (that is what my parts dude told me).
 
My stock pistons are HO pistons.

So that is where the difference in CR came from between an HO and SO truck? The piston bowls were different?

Weston, did you mean 2mm larger (as in diameter of the bowl) or 2cc's larger bowl?

So, if I go with the 275 pistons and have a certain amount milled off the top, I would lose the coating then...
 
Well I should have the cc of my HO piston this afternoon. Going off your numbers (59mm and 61mm) I came up with a difference of 3.59 cc's between the two pistons assuming the bowl is about 3/4" deep (going off memory). Using an online calc, this would be a 0.8 point drop in CR. Makes sense, my manual says an HO truck is 17:1 and an SO is 16.3:1. I always wondered where the difference was made.

I'm hoping to just use a standard size piston and then use a grade "C" for the least amout of protrusion. The difference between A, B, and C grade pistons is only 0.008". My stock pistons were "A" and if I use "C" that will reduce CR by another 0.4 point. Then a 0.020" over gasket is about another point drop in CR.

Don't know what the block will get decked yet (this will affect it some).

It would be nice to just be able to drop the 275 pistons in without the need to mill them (extra expense and lose the coating).
 
My stock HO pistons had a 45 cc piston bowl.

Also, my 145,000 block and pistons had 0.0065" piston/wall clearance. Piston skirt was 4.010", bore was 4.0165". Simply amazing an engine that has been used for that many miles (most of the first 125,000 were towing) can still be that tight...
 
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