What piston size / CR for reliable 500 HP ???

[Master Chief]

Hi all.

As many of you know i got my Engine block ruined by what looks to be a bad Darton Sleeves install - that i didnt really need.

So i am getting another block from somewhere, and will use the OEM sleeves - No aftermarket sleeves !!!

Was wondering what would you guys recomand to bore it to, to be safe and reliable, and allso hold about 500HP + - ???

Allso, am going to use CP brand pistons, but i have to decide on the CR as well ?I am runing Tomei 260/12mm lift cams, so do i need to be concerned with the Valves hitting the pistons, with the 1:9 cr ???

What do you think ?

86/5 or 87 ?1:8.5 or 1:9 ?

Again, i aim for a reliable 500HP.

What sort of setup (piston wise) do you guys run, for these power levels ?

Thanks !!!

[Hijacker]

The bore size is really irrelevant to power production for our cars.

The bore size really should be up to you and how you feel.

I would have stayed with stock sized pistons on my motor build, but minor damage to the cylinder walls necessitated an overbore. Which I'm only doing a .020" overbore, and will be using 86.5 pistons

The CR is what you should be focused on. A higher CR will give you low end response, but limit top end on a boosted car. The lower CR will sacrifice a bit of low end, but give you top end freedom.

My personal belief is that the stock setup is good, and if you can try to emulate it as much as possible, you're doing yourself a favor.

I would like to see people running 9.1:1 pistons in their car and see what numbers/boost they're running. I want to know if the extra half a point of compression is a big sacrifice or a little sacrifice.

[Master Chief]

Yup ! Thats the type of thing iam allso trying to find out.

You have to agree thouhm that the bore size, has a lot to do with power, and defently a lot to do with reliability of the engine.Allso the bore size has a lot to do with the ability to rev high.

Anyway i know a lot of people here run cars with power around the 500 Mark - and was wondering what they recomand to use - piston wise.

Thanks.

[Hijacker]

bore size on a small displacement 4 cylinder only helps out turbo spool. the negligible displacement incease you'll see from a .020" overbore, or even a .040" overbore, is peanuts. a .040" may net you .1 or .2 liters displacement. However, the extra exhaust gas flow from the displacement increase will help turbo spool to a degree.

So long as you choose a good piston, and don't just crank the boost up without a fuel management plan, you won't have any reliability concerns. If anything, it's not the bore size, it's the piston and the fuel management you choose.

And I wouldn't say a larger bore size will help you rev higher. Everyone knows that the rev limitations of the SR is in the valvetrain.

If I were to take two pistons of different sizes, but made of the same materials, the smaller, lighter one will rotate faster. Now, you take a lighter CP piston made for a larger bore than a standard SR piston. The lighter piston may be of larger surface area, but because of how it's made and what it's made of, it will perform better than the standard, heavier OE one. But that has less to do with the size of the bore, and more with the lost weight. In the end, you can rev faster, not higher, because you have less weight to move in the rotating assembly. It's the same principle of getting a lightened flywheel.

I say as long as you stick with a known piston manufacturer, you will be good. Wiseco and CP are good companies with good reputations and you wouldn't be doing anything wrong using them for your internals.

[Master Chief]

In anyway i end up going, i'll be using CP's for sure.

About the bore size affecting reliability, i was reffering to the ability to bore the block without weakening the cylinder sleeves too much.

About the ability to REV high beeing affected by bore size, i was reffering to block beeing OVER-SQUARE or UNDER-SQUARE , and hence affecting the assembly balance at high revs.

Anyway, we are no talking too big a bore differences, so the above is not too relevant.

So, what to go for ? 86.5 or 87 ? 8.5:1 or 9:1 ?????

[DrifterProdigy85]

Im using CP Pistons 86.5mm 9.0 CR. Also using Darton Sleeves too. Mine were installed by Mazworx though. They have said themselves it takes some special skills to install sleeves in a aluminum block. CP Pistons have been known to handle over 1000hp. Id be more worried about the stock sleeves holding the power you want. Stock sleeves are relatively thin compared to Darton. And boring out the stock sleeves just makes them less reliable IMO. But if your dead set on using stock then you can go 86.5mm Pistons. 9.0 CR is pretty good i think. Still able to run 18psi pretty safely on 93 octane. With good tuning alot of people have gotten away with 20psi on 93 octane.

[DrifterProdigy85]

Oh yea, i rev to 8500rpm with my motor. Solid Lifters FTW.

[Master Chief]

Well, unfortunalty i dont have MazWorks in my country, and i am noot about to let my local machine shop to experimant with installing the dartons, on another block of mine.

From what i invewstigated, the OEM Sleeves are more than capable of handling the power.The only reason to SLEEVE and SR20 is only if you want to go above 87mm pistons, or have a damaged block you are trying to fix.

Check out the guys at MADTECH.DE - they run over 850HP on OEM sleeves.I am looking for only half the power, so i think the sleeves will be fine.

Its not worth the hassle - worying about sinking and leaking sleeves, like i have now.

BTW, i have a cut out block and i can assure you that the OEM sleeves are about 4.5 - 5 mm thik - wich is like the dartons after bore.

I made a tread about this, on here or on freshalloy - check it out (its before i had the block cut, but you can see the thikness in the pictures i've put up).

BTW: What solid lifter kit do you have ? I was looking into doing this as well.

How about some more opinions about piston Size and CR, from the guys here with big power ???

Thanks.

[Master Chief]

In anyway i end up going, i'll be using CP's for sure.

About the bore size affecting reliability, i was reffering to the ability to bore the block without weakening the cylinder sleeves too much.

About the ability to REV high beeing affected by bore size, i was reffering to block beeing OVER-SQUARE or UNDER-SQUARE , and hence affecting the assembly balance at high revs.

Anyway, we are no talking too big a bore differences, so the above is not too relevant.

So, what to go for ? 86.5 or 87 ? 8.5:1 or 9:1 ?????

[Hijacker]

I did some checking, and CP makes a standard 8.5:1 CR piston.