Has anyone ever thought of or installed HC pistons in there engines?
Everyone goes the route of increasing the boost pressure and strengthening the block but with the same amount of boost and a higher compression engine shouldn't that allow you to make significant gains while inproving drivabilty. I would think that this would be the ideal set-up if you were doing anything besides drag racing.

Any comments would be appreciated as I'm considering going this route.

Thanks

 

Ask Slowboy Racing (SBR INC is the user name here), they have a high compression engine in ACP's rally car they built.

Edit: Here's a link: https://www.evolutionm.net/forums/sh...d.php?t=262260

 

thanks for the super mcdonalds speed reply

 

the only thing is that i was thinking about installing hc pistons without increasing the displacement of the engine.

 

My guess is the displacement increase is in stroke from a different crank, but the pistons would be the same.

 

I have always had high compression 4g engines, they are slightly trickier to tune but any good tuner can get r done. <~(Brad Brooks)

My current engine is 10.1:1 compression, the drivability is amazing and the powerband is super linear. It feels like there is no lag bacause the engine has enough power on the little boost that the turbo does provide at low rpms to kick you back and about 4600 rpm on a 2.4 hc engine with a T4 .68 PT67 was when full boost hit. (hold on!!!!) at 30psi it was nuts.

Think of a Honda with a good tuner at stock compression, those things scream well till they crack a sleeve or something...lol

Something to think about, Mitsu started at 7.8:1 and ended at 8.8:1 it seems that factory turbo car compression keeps going up. The cars respond even better now and make more power with less mods of course other things help but thats the majority of it. Thats why back in the day people where puting 2g pistons on 1g rods for there 6-bolts

Spool up, is increased and a better powerband is created but it just has to be tuned really good. I took the engine out and refreshed it then put it in my civic. I ordered the HTA 35r to go on it, man its going to be an earth ripping torque monster.

For anymore info, pm me!

 

Pics of AWD EK!

 

generally,
lower compression has less chance of pre-ignition
Higher compression has very increased probability of pre-ingition...(think deisel motor)

either will produce great results, just so long as you tune it well...
speaking generally:
higher CR= higher cyl temps

 

BRAD BROOKS FTW!!!!! (he tuned my EVO).......

 

Higher compression engines are more thermally efficient. This means less combustion energy gets converted to heat (but more heat spools the turbo faster). This goes contrary to the common belief that higher compression spools the turbo faster. Likewise, spool is a function of several, more influential factors. Because higher compression is more thermally efficient it is also more fuel efficient and is cleaner from an emissions standpoint. This is why modern automakers use higher compression engines in general, turbo or not.

Each full point of compression (e.g. 9:1 to 10:1) tends to increase average torque by about 5%.

The problem with raising the compression is octane. If octane is limited, higher compression is going to create a problem. Where octane is limited, a 9:1 engine will outpower a 10:1 engine, simply because it can use more boost.

 

Wouldn't the engine with the hc make more power with less boost than the lc engine. You are right that does go contrary to common beliefs, I have personally seen the difference in my own engines. Not going to argue, just my standpoint.

 

pm'd

 

About 5% more torque per full point (e.g. 10 vs. 9), all else being equal.

A higher compression engine feels a bit better at very low rpm when large cams are involved, simply because less cylinder pressure is lost due to overlap.

In on-boost situations when cylinder pressure rises, the question is if octane is a limiting factor. If not, higher compression makes more power. If so, the lower comp motor out powers the high compression motor, simply because increasing the dynamic compression with greater air mass makes more power than squeezing a smaller air mass a little harder. Dynamic compression is the endpoint in the equation, static compression is just a factor.


I wondered the same until I performed my own research. Think about what anti-lag strategy does, and why it works. Also, think about why retarding the ignition timing and leaning the mixture (at certain points) both tend to spool the turbo faster as well.

 

There is some merit to the "high compression = better boost response" argument. Yes, high compression reduces the exhaust gas energy available for the turbine...

BUT a high compression engine has less clearance volume in the chamber, which promotes higher VE due to less dilution of the incoming charge during the intake stroke. Higher VE = more mass flow through the engine at low rpm = better boost response.

Provided that the reduced exhaust energy doesn't more-than-offset the VE gains, it will have better boost response (and better off-boost torque).

Clearly, the resulting boost response is highly dependent on the specific engine in question. There is no universal "this will provide better boost response than that" answer.

 

Just throwing this out there for the guru's - but think of this...

10:1 in a 2.0l car is a flat top piston - 10.5:1 in my 2.5l motor has almost an 18cc dish --- I like a dish, not so crazy about a flat top - why?

Discuss.

Mike Huml
Slowboy