Hi compression piston??

It seems everyone has upgraded pistons to a HI comp piston. How hi can you go before you have to change valves?

What's the (HP) benefits and or issues with HI comp pistons?[/b]

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Go as Big as you can find .... you wont hurt your valves here so long as you use the proper fuel .... If you start doing crazy stuff like decking the head to increase your squeeze then you will have to start to measure your clearences along with going with a BIG Cam Shaft, but your valves will be fine and your piston will have to be cut out around your vavles for it to clear ....

Only thing that will hurt your valves is TIME and ABUSE (which too much time is ABUSE) ....


OH YEAH .... Benifits .... GREAT Throttle response, with great bottom end power yet still have the over rev that most Big Bores dont give you ... Compression just gives you more power EVERYWHERE when it comes down to it ....

^^^^^yeah like the throttle response the FCR gives you, oh I forgot, your old school. lol

I buy the highest compression piston's i can find in the bore i need them then clay check them and then deck my head depending on the clearence i like 45 thou squish

I have seen people on here say they are running 15.5 to 1 comp ratio.. I am sticking with 13 to 1

I have seen people on here say they are running 15.5 to 1 comp ratio.. I am sticking with 13 to 1[/b]

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Stupid question?????

So I can't just buy an OEM bore J and E at 13:1 and install it. I have to get the head space checked?

Why don't they make them head space set already?

with a 13:1 je depending on the cam you shouldn't need to clay check it just put it in and go

that should be a bolt on and go...

It has more to do with the cam you run, not the piston. Some huge cams dont fit any pistons. Most cams fit all pistons.

Unless you have a mamoth sized camshaft, you can pretty much buy any piston you want and as long as its installed properly, there will be no clearance issues.

Think of compression like this...two piles of gun powder.... one is just a lose pile with a fuse placed in the middle and the other is tightly wrapped with a fuse in the middle. The lose power will just fizzle like a sparkler and the tightly packed power will explode.

The tighter a combustionable mixture is packed, the more violent and quicker the mixture will burn (explode) That pushes the piston down in the cylinder harder.

Thats about as layman as I can think of right now. A good compression range is 12.5-14:1. All depends if you want to run race gas or pump gas.

^^^^^yeah like the throttle response the FCR gives you, oh I forgot, your old school. lol[/b]

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You would have a STROKE, Vet Boy, if you had the Snap that my motor had with he FCR on it ....

Plus this guy has a 05 R so he wont have a problem with the SNAP that is Capable from the FCR ... But if he wants that Arm ripping power then i know where he can find it ...

From my experience with designing pistons for the TRX, here's what I know is true:

The larger overlap the camshaft used, the deeper the piston valve cutouts have to be to provide adequate piston-to-valve (P-V) clearance,...

the deeper the pistons cutout, the lower the static compression ratio of the piston (except for the case with a tulip valve cutout relief design)...


I've measured plenty of pistons on the market that do not provide adequate clearances and can't even properly clear a 208 all due to their physical piston design limitations...

In fact, all the pistons I've measured typically have about 0.085" valve relief depth, where as with a tulip design it can easily achieve over .110" up to ultra compression.... 0.085" is typically good for 'drop-in' camshaft profiles.....

the 13.5 cp seems to be a good one if youre not decking the head.
but then why not just go to 14.1

it all depends on what available fuel you have.

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^^^^^yeah like the throttle response the FCR gives you, oh I forgot, your old school. lol[/b]

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You would have a STROKE, Vet Boy, if you had the Snap that my motor had with he FCR on it ....

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you think???

what makes you think mine doesn't have the SNAP

and I might add that yours is better than everybody else's.....

Vet Boy? I'm gonna give ya that one

Is it woth the money$$$$$ for the HP gain?

How hi can you go before you need to up your octane. I usually run about 100 octane anyhow.