If you go with forged internals or specifically: pauter rods, Darton sleeves......Y would you still go with a low compression piston as opposed to a high compression piston....even if you go FI.....

Y lose off boost performance....Y not gain there as well....

Would it be nice to have the right now power of a 12:1 piston...combined with 10 psi tt boost......?Please tell me why my dream would not be realistic?

 

I know someones going to correct me but let me give it a shot:
In theory, the internals would be hold the boost better than stock, however, and do not quote me on this, but going up on compression while turning up boost even more? Not going to last as long as a low compression motor, thats for sure. Thinking 10:3:1 is stock and people are having trouble running a few pounds past 10 with stock,throwing a couple steps of compression into the mix makes it even more risky unless you plan on running some pretty high octane fuel
I think 12:1 would be able to hold probably 5 pounds of boost??? 7 if forged?
LS1 guys have 11:1 compression(i think) and they are careful going up to 10.

 

the theory behind it is just to fight off detonation. the more fuel stuffed into the cylinders acts as a solid and will raise your static compression ratio under boost. combine that with heated compressed air and you either need to be running the best race gas available, or drop the compression.

 

The biggest problem with high comp + high boost is the fuel. If you can run race fuel all the time, you could run high comp + high boost. But with 91 (or even 93) octane fuel, you'll detonate, no matter how good your internals are, they can't withstand sustained detonation, so you can't really go high comp + high boost on a street car.

 

I don't think this would be realistic unless you wanna run a diesel motor (high comp. + boost). Look at it in theory. With F/I you're taking an intake charge and compressing it before it enters the cylinders. This is what the piston normally does on a NA set-up, thus the more the piston can compress that charge the more power the motor will make. With high compression comes high temps, enough so to detonate the fuel/air mixture before the plug does. Race gas doesn't self detonate as easy as pump gas, hence the recommendation to run it with high comp. or high boost.
Basically, if you take an already highly compressed and heated intake charge and try to compress it even further with a high comp. motor set-up you will destroy it. Especially at 12:1 & 10psi boost.

 

ok I understand the theory......but I thought the Darton sleeves and pauter rods were supposed to be strong enough to support this kind of pressure....But I guess 93 octaine gas would detonate....regardless of tune???....

 

The strongest of racing motors can be destoryed very quickly by detonation. Detonation is like an explosion going off in your motor. The pressure spikes to 10 times the level of normal combustion, and it happens in an instant, instead of in a controlled, smooth fashion a with normal uniform combustion.

Forged pistons and rods can take more cylinder pressure, and can sustain more detonation than cast pieces, but eliminating/minimizing detonation is the critical factor.

As such, a lower compression piston design allows you to run more boost and power on lower octane fuels, and a proper tune. As mentioned, if you can 116 octane fuel, and higher compression, you could make massive power with very little boost, and very high ignition timing advance levels.

However, in the world of daily driven street cars, a slighly lower compression ratio strategy would be best suited for those using 93 octane fuels, and moderate amounts of boost.

Also keep in mind that the power difference between 10:1 and 9:1 CR is 5% or less. Lastly, I have driven 8.5:1 through 9.5:1 boosted VQ35's and I can never tell the difference, in terms of spool up, or boost response.

Hope that helps.

 

It is possible to run high compression and high boost on an engine. It takes a very good control system and engine design. The only reason to run a high compression/ high boost motor would be to take advantage of rules in a competitions series.

For the average Joe the added expense simply would not justify the cost.

But there are us silly bastards who like to do things different, just for the sake of being different.....