4080wrx

iTrader: (38)

3076r....dooo it

you will still want more out of the 20g in my opinion.

Krang

iTrader: (14)

L wagon does rule all. There is no denying!

BugeyeMilo

iTrader: (10)

the 3076 is an awesome turbo as well.

either turbo will keep you happy when she hits full boost.

ATP makes some very nice stock location 30R options.

now if only they had a billet wheel option

FXT FTW

what about the new blouch dom3 xt-r? stock location, ball bearing, billet wheel and 10cm2 hot side so the power doesn't drop off in the higher rpms. theres some threads on nasioc comparing the dom3 xtr vs hta green vs atp3076.

Jrocko

iTrader: (10)

I'll check that thread out. But honestly every one has there own opinion to the turbos.
I am getting a get deal on this ATP Turbo.

ReleaseDaKraken

iTrader: (12)

I know you said you want to stay stock location, but I would save up more money and go rotated. Listen to Reid, he knows what he's talking bout.

Jrocko

iTrader: (10)

Steve,

I would but I think Rotated to to much for my car.
I think =this is going to be the Last engine install on my ride. I think if I go more HP i am going to have to change more internals. I don't want to do that. My wife is going to give birth in Dec or Jan. So thats when the Car stuff Stops. Unless something breaks.

Thats why I am staying with Stock Location.

FXT FTW

what turbo did you decide on? whats the biggest turbo you would run on a stock sti motor?

reido

iTrader: (1)

Just FYI for anyone building their motor. generally compression ratio has very little effect on spool if at all. An increase in compression can net you more power per pound of boost, but your peak output may be limited. It depends on the rod ratio cam selection and quench.




So when you look at the torque curve, the power seems to come on earlier as for each pound the car is producing more torque, but the boost is not really coming online a lot faster as compared to a lower compression car.


Generally the longer rod ratio motors can withstand a bit more compression because they don't need as much timing because the piston speed is lower. The 25s have long stroke, kind of short rod ratio, and they already have pretty require pretty large timing numbers to produce, so when you up the compression ratio on this stroke, you really test the limits of the octane.

spinplay01

iTrader: (12)

You are right, to an extent. Power may not be coming along any earlier in the rpm's but it is earlier on a ticking clock, and in the seat of your pants.

A higher compression ratio is going to result in more mechanical energy from a given volume of air and fuel mixture. This happens because of higher thermal efficiency. Put identical oxygen and fuel molecules in a tighter space, and toss in the added adiabatic heat of compression, and this will result in better mixture and evaporation of the fuel. Ignition will then create a little more expansion. The amount of expansion is directly proportional with the amount of downward force on the piston. Addition expansion of the gas also means that there will be more gas turning the compressor.

The volume of air output/compressor rotation per engine revolution is also going to vary with low or high compression.

Even if there wasnt a little additional gas turning the compressor, while under load, the lower compression engine is not going to build rotational speed as quickly, so spool is still slower.

I don't study physics and I'm not a scientist. So if there are holes in my reasoning please let me know.

I welcome all rational thought and reasonable argument.

reido

iTrader: (1)

I didn't read the second paragraph because you lost me in the first sentence.
I guess the part about where it doesnt come on earlier in the rpms but comes in on the seat of the pants has me confused.
Your *** has a better feeling but the spool is still the same?
Whoa... that's some reversed viagra right there. If you mean that you're essentially spooling the same but making more power while doing so, then yes I agree.

Generally when you increase compression ratio, your hope is that you make more power pound of boost, as yes you're increasing thermal efficiency in the chamber.

It's a give and take to reach MBT. It's possible to reach MBT under knock conditions. For example, you could let an engine knock through a run and still make more power, but we all know what effect detonation has on parts. Your goal is to reach MBT with the least amount of timing possible on an engine without detonation, but you can allow detonation to happen to reach MBT.
When you increase compression ratio, you're trying to gain more torque with less timing before detonation threshold, so you would try to make the most amount of torque possible. That may not be possible on some combustion chambers due to their design or their dwell times before detonation, so in those cases, the lower compression ratio works out better. In many engines with high piston speeds, such as the EJ25, which has a rather long stroke, it's a real gamble whether you'll reach the same torque figure at less boost versus one at higher boost before reaching detonation threshold. The chamber and piston design play a big role though.

reido

iTrader: (1)

If you're trying to argue that an increase in compression causes an increase in both exhaust pressure and EGTs, two large factors in getting the turbine to spin, then I can see where your logic is coming from.

It's been proven more times than not that this logic doesn't pan out, as EGTs shouldn't rise dramatically and while the exhaust pressure may be increased slightly, it's not going to be dramatic from a point in compression. Perhaps if you go from 8.5:1 to 14:1, the effect may see some reductions in spool.

I tested this on 2 motors: one was 10:1 compression ratio and the other 7.8:1--both at 2 liters. The 10:1 motor made the same amount of power at less boost, so it felt much stronger, but the logger showed boost came on at relatively the same time.
http://i281.photobucket.com/albums/k...M/image012.jpg
This was a high compression big turbo motor.

Compare that to this car, which was used to prototype the setup (same setup but with 7.8:1):
http://i281.photobucket.com/albums/k...M/DSC00745.jpg
I eventually moved the sheetmetal manifold and larger snail over to this motor, which killed it by the way.

The car spooled the same.

This was long ago though, when I had the same logic as you did, except that I sunk big bucks into that block (the first one you see pictured) and the pistons custom designed to match the headwork.
In the end, my final output on pump gas felt about the same (peak wise). The car felt a lot better and stronger though, but the data on spool was the same. What's sad is that after I built this motor and track closed, a lot of threads confirmed the testing on the compression ratios and spool through logs, and then I had no use for 10:1 motor that really only shined on race gas to reach MBT.

Also, I think you're mistakening piston speed with compression. Piston speed and stroke do play a role on spool. This is proven. Everyone thinks that the ej20 makes less torque because of the .5 liter lost in cubes, which is partially true, but the main reason for increase in torque is due to change in crank stroke. There are small bored stroked 2.0l that prove this. I believe the EJ22T can show this. Isn't it the 79 crank with ej20 bore? But this is from changing the engine geometry. The longer stroke motors have faster piston speeds and shorter rods, and that does have an effect on exhaust pressure.

spinplay01

iTrader: (12)

What I am talking about is the measuremenat of time between 1000rpm, and x amount of power at y rpm.

Keep in mind that the intention of this scenario isn't to get the max high rpm power or take the components to their breaking point.

Lets keep y at a low number like 5k

using the same stroke and bore.

8:1 boosting 14psi vs. 10:1 boosting 7 psi

Keeping target egt the same, and less timing advance for the higher compression up top.

Vague hp curve:



Are you saying that there is no time difference between 1000 rpm and the point where x and Y meet on the chart?

Trafic light to trafic light the lower compression guy is screwed.

Where the blue line dips (berween 1k and 5k), that is lost time between point a and b on the road.

Then, past a certian point, the ability to run higher boost and more advanced timing will come into play and win the race on the freeway.

reido

iTrader: (1)

You've just explained that the curve changes from more torque.
You're referring to area under curve.
That should be improved per pound of boost. Spool would not change.I don't see how that's different from what I stated earlier.

I'm not sure I understand your new point about timing

spinplay01

iTrader: (12)

I understand what you are talking about though. I see that higher compression results in more complete burn and higher egt. Thus creating the need to decrease ignition timing or add fuel to keep the burn cooler to maintain target egt. I'm not arguing the point of mechanical knock threashhold.

Higher compression equals more power per lb of boost (you said it yourself)

At high compression or low compression engine (at sea level) is already over 14 psi...without a turbo. This being said, a higher compression engine outputs more power per cc.

We just have to know the mechanical limit of out internals and keep that fu(king knock away.