I think what you mean is will a high compression engine make power sooner than a lower compression engine. Answer, yes of course, it's already making more power before the turbo is even added into the equation.


Lucky, enjoy it man!

 

Thank you sir, I will whenever/if I get my damn car out here. still in a battle over it...

But thats exactly what I was asking, just over-complicated the question I suppose lmao. I know 10:5:1 compression isn't crazy high, but it's higher then 420 factory pistons and will help my out of boost driving

 

Ill accept my apologies anytime now.....RYU

 

I didn't take the time read every post in this thread. But I do have some real world experience about the compression topic and engine theory.

I have personally built and tuned multiple high compression, high boost engines. The engine I run in my own car is 12.5:1 @ 40+psi. In my personal experience I have had the opportunity to test identical setups back to back while only changing the compression. I did this twice, once on my own car and once on another. Not only can I tell you, but I have logs and logs of data to show for it. Z and I have spent many hours on the books and in discussion about turbo theory. Then we spent hours and hours on the streets learning to apply our knowledge. As a result we learned an astonishing amount about engine theory and thermal dynamics involving our field.

Z and I have always been proud of the fact that when we stroke a key on the laptop, we not only know what result the key stroke makes, but how the result is achieved. We do not consider tuning to be just with the laptop. Tuning, IMO, is more than stroking keys. It is an understanding of valve timing, ignition timing, fuel properties, engine clearances, volumetric efficiency, (and so on) and being able to apply your understanding into an application that makes your customer happy with the build path they have chosen.

Here is what you should know about high compression. It produces more torque. It slows your spool time. It has considerably faster throttle response. It produces more energy with less fuel.

Here are some things to consider. Your engine revolves around fuel consumption not air consumption. The more fuel you can burn, the more power you will make. The turbo provides more air for the fuel to burn. This come clearly into play when you start talking about static engine compression. When you raise the compression you allow a more efficient combustion to take place and thus make the same amount of power using less fuel. I noticed this even with the car at idle. It takes less fuel to maintain a 1000 RPM idle with 12.5:1 as opposed to 8.5:1. The higher the cylinder pressure that is achieved before the spark plug is fired, the greater the combustion will be. This is where your torque comes from.

It slows your spool time because you raised the efficiency of your engine. You are using less fuel to accelerate with higher compression because the burn is more complete and the cylinder pressure is higher. Because you are burning less fuel, you are consuming less air. This means you have a lower volume of exhaust gas to spool with. You have to understand that your engine can make more power, and at the same time be using less fuel/air. Your turbo needs exhaust gas pressure to produce boost. Raising your engine efficiency simply produces less exhaust gas.

When I first got my car together with the 12.5:1 parts, it was like a new car. I have a 2.0l and it felt like a 2.3/2.4. The car would climb steep inclines idling in first gear without any hesitation. My 8.5:1 engine could not do that. The first time I got on it, I was amazed. "OMG I cannot believe how much faster it spools". When in fact later, comparing the logs of both engines side by side, I discovered it was actually slower. But how could this be? The car transitions into boost so well and is so much more streetable?! It turns out that the torque curve increases at a much faster rate even with the turbo moving less air. This causes your acceleration before significant boost to be more liner like you would expect from a NA V8. Stab the throttle and the car just jumps.

Now that you are using less fuel and air to power the car, that gives you more room to work with before you max out your setup. Now instead of making 640@40 psi, you make 640@36psi. You know what that means, turn the boost up till the turbo runs out of steam. As it turns out it was about 52psi. You can add the figures up yourself.

I choose to build the high compression 2.0l because I wanted the torque of a stroker without compromising a 9500-10,000rpm rev limit. I have a power band from 4500-9500 (That just doesn't fall off till you lift the throttle!!) and that is a blast to drive in traffic around town. I get 24 MPG in the city if I keep my foot out of it and around 30 MPG on the highway. How wonderful it is to have a car that can make a 1,000 mile trip on less than 35 gallons of fuel and still be an AWD roller skate from an 80 roll!!

I also built a 2.3l high compression engine. The result was continuous transmission failure. The torque was so high, nearly matching the HP, even at a sustained 48 PSI. The car was shredding built transmissions like they made of glass even on a reduced curb weight of 2400 lbs.

Here are pictures of the pistons I ran in my personal car, both 8.5 and 12.5. You might notice a difference between them.

 

In reference to the stroker engine and bore size concerns. The rod angle does in fact negativity affect the wear of your cylinder wall; however, increasing the bore size does NOT offset cylinder wall wear due to piston rock. The most important factors in cylinder wall wear include piston skirt design (such as a diamond skirt, half skirt, full skirt), piston taper, piston ring pretension (pressure the piston ring exerts on the cylinder wall), Floating/Non-floating wrist pin. wrist pin clearance, piston to wall clearance, piston material, spark plug placement, wrist pin offset and oil temperature.

Limiting factors in RPM in the 4g63 are not the rod angle, but the piston speed. The piston speed is a direct correlation to stroke. Rod length and wrist pin placement have nothing to do with piston speed. As you engine speed increases the reciprocating weight of your rotating assembly is multiplied exponentially. Because the piston (and rod) are moving faster at the same RPM than the 2.0 counterpart, you reach your maximum reciprocating mass sooner. If you want to rev your 2.3 higher, lighten and strengthen your rotating assembly. Switching to a long rod 2.4 will only reduce torque and add reciprocating weight.

 

And to answer the original question of the thread topic.....

Be honest with yourself and decide what your end goals with the car are. Choose the smallest turbo than can reliably produce what you ultimately want from your car. The smaller your turbo is the more fun it will be to drive. If you want 400hp using pump and a meth kit, buy a 20g. If you want 450hp get a 50 trim, 500hp a 30r, 600hp a 35r, 700 a 3586r or any other variant that suites you.

The bottom line is that the smallest turbo that will make your desired number will always have the largest power band. Other factors like displacement and fuel types are negligible because it takes a certain amount of fuel to produce a certain amount of power regardless of the number of cylinders or displacement. Larger displacement will make more power per PSI until the turbo cannot provide enough air to burn more fuel, both engines will eventually make the same number once that point is reached (the turbo becomes the bottleneck).

 

/Thread

 

Well as of now, my spare motor has the following.
full crower valve train, AEM adjustable cam gears, Crane 12's (246/246), Eagle rods, and soon to have .020 JE 10:5:1 pistons (and just a few other odd's and ends will be on order....)

In all honesty tho, the future for this build will be if i can get ownership of the car and the title transferred over.
I was honestly thinking about taking RYU's idea of running an evo 8 manifold and turbo. I'm hoping to land between 350/400hp. I've had a few people tell me that the evo8/9 16g will be more then perfect for my goal. and honestly, I think it'd be something a little differant so i'm completely game for the build. Also, i'll be hoping to redo my fuel system and swap over to E-85 since it's pretty accessible out here and alot of mitsu guys are running it. I have a shop out here willing to help with all the custom fabrication since they don't have to many people trying to build a 420 come through the door. sound like a plan to anyone? open to suggestions..

 

your putting a 16g on a built motor??? in all honesty thats pointless you dont need such aggressive build to make 400hp. You be better off with 30r or somthing like that.

 

E-85+16g will put you right where you want to be. There are plenty of bolt-on turbos you can change to later if you ever get bored.

The stock 420 engine is made from balsa wood. If you don't forge it, it will blow the fuck up!