IDK maybe we could shy away from changing the rods because they are forged, were the rods in the 4g94 forged? The 4g64 had a CR of 9:1 and forged rods and that engine took to boost extremely well(upwards of 20psi on stock engine, but stopped making power after 16psi because of the head)

 

the evo x is stock at 22psi the engine block is designed for hi psi.

 

If it's the CR that's worrying people, then it should be easy enough to swap to an EvoX head. I'm almost willing to bet that all you need to do is swap the head to get a lower CR.

OR if you don't want to swap the head, you can have your cylinder head reworked to reduce the CR... a deeper/bigger combustion chamber will reduce the overall CR... That is assuming that there is enough "excess" material available in the stock head to allow for chamber reshaping. And while it's in for chamber reshaping they can port, polish, and flow the intake and exhaust ports to allow the head to gulp the air even better and install heavier duty valve springs to allow for higher redlines... and ... and ... and .... the list goes on...

Any machine shop worth a damn would be able to handle that type of work, but it would cost ya...

 

We have a similar block, but it's not exactly the same. You run 22psi on a stock 4B11, I bet it'll go boom...

 

It's probably the pistons that are responsible for the compression ratio difference, not the heads. The thing is found in the STI vs WRX difference. The block is the same but the pistons are slightly difference. The heads are more or less the same save for the cams. Comparing the lancer to the evo is silly, I'm sure there are some subtle differences that make the evo a streetable race car and the lancer an econobox.

 

true, but the main point to my post is that there are ways around the issues. I mean, if you're gonna toss a turbo or SC on the car, then you're probably not worried about getting warranty work done to the engine. Which also means that you probably won't mind doing what it takes to make it deliver the power you want reliably...

Though, not everyone thinks of reliability when it comes to "bolt on power"...

 

Why make things more complicated than it has to be? If you want to lower the compression, just buy diffferent pistons.

 

well, if you can't find hi-perf pistons there's always the option of having the head reworked...

I dunno, maybe my line of thinking is still attached to my old car where the bottom end of the engine was "bullet proof", and the biggest gains and most cost efficient part to mod was the cylinder head. The stock cylinder head in my old car was a POS. You could increase the HP & torque out put by 30% or more just by having the head reworked. Changing anything else attached to the engine would yield minimal gains until the head got massaged.

 

But since you have a completely different car now, you have to throw all that out the window. We have no idea how strong the bottom end is, nor how restrictive the head is.

It's all new to all of us...

 

Yeah, it's an all new engine to all of us, but basic engine theory still applies... the only true unknown, IMO, is how much the 4B11 block can handle...

But based on information that we DO know (we're seeing low gains from axle backs, CAIs, and piggies), we can *almost* assume 1 of 2 things: 1) The stock systems were already pretty darn close to optimal, or 2) the bottle neck is not in the bolt-on parts and in the engine itself.

I suppose there's a little more to it than that as well, because this also happens to be the first car I've owned with variable valve timing. However, seeing as how all the dyno sheets I've seen so far follow the same basic curve as stock (just offset a bit or slightly increased in amplitude), I would venture that the top end breathing needs to be increased (whether it be via hi-perf cams or reworked head), and the valve train components need upgrading to push the red line up higher, assuming the bottom end can handle going past 6500 RPM.

I mean if you have a SRI/CAI, headers, and a better flowing exhaust, but the engine is still running out of breath around 6K RPM then it seems to me that there are breathing restrictions within the head or valve train. I suppose the ECU could be artificially reducing HP in that range, but the piggies are supposed make up for that, no?

 

But what you're talking about isn't engine theory, it's very much an application dependent situation. Some heads flow very well, some don't. If you port the lancer head, you might gain 20 hp or you might gain 2 depending on what the limiting factor is. It's entirely possible that the car simply can't flow that much without forced induction, much like the old 4G94.

 

As amby said, you're making a very expensive assumption, nunyas. You could end up paying $2k for head work and seeing no gains. Or it could turn the car into a fire-breathing monster. I just know that I'm not going to be throwing down my paycheck to find out...

 

well, I agree with ya on that last one... it won't be me spending that cash... I wish I had the facilities and cash to be able to bench the head and figure out if it needs to be worked.

 

watched a show of guys boosting lancers/ford focus' and they put new pistons in for the lower CR and also ring gap is a big player in this as too small a gap not enough bypasses and like you say, boom.

Bottom line you gotta pay money to get it tuned for forced air. A small psi turbo or SC should be fine without having to take the engine out and do everything. But more ponies always comes with more money, parts.

 

The pistons do determine the compression ratio. It has to do with the bowl at the top of the piston, relative to the height of the block when the piston reaches to apex of its rotation.

You can also reduce the ratio by swapping out the head gasket This is controversial though because its not a true measurement and can cause damages, but it has worked on some cars.

I am trying to get Tim from Raptor superchargers in Australia to join our discussion.