^ cool thanks

what do other 3586's on 2.0 evo8's spool like?

 

from the dyno graphs I have seen all around 5k seems to be the average. What I really notice is the off boost response of the stroker motor it almost feels like an NA motor at times when I push that gas it just goes.

 

So from my experience it will improve spool of turbo X slightly but a lot of people upgrade to turbo Y at the same time and see about the same spool they had before (i.e. 2.0 to 2.3 and fp red to fp black). The biggest thing you will see for sure is making more torque down low and the same peak power will come at less boost....of course that just means you could then turn the boost up more, but if the turbo size remains the same you'll likely max it out sooner.

All in all the only drawback is cost and downtime IMHO

 

Yep, cost is the only downside I see assuming you go overbore.

If you go stroker you also lose some RPM but it makes a better street machine typically.

 

You're right that the example I used wasn't really relevant. I didn't think to take into account the relativities of a stroker vs factory displacement. But, you've seen the point I was trying to make.

What about the turbos ability to spool? ie. If you doubled the horspower and torque of a car you don't accelerate twice as fast. So by applying more force to spool the turbo, can the turbo spool relative to the extra force?

 

I could be wrong here ... but i did take my physics in university high enough to understand some principals in automotive combustion. I think the main problem is this:
when more air passes through the system (from more displacement) the air is carrying more heat energy which is acting against compression (as it naturally wants to expand like boiling water) so even though the turbo is receiving more air from the engine, it is also receiving more heat energy which is reducing its capability to compress air. Its kind of like trying to force a bunch of highly active kids in a small area, they just naturally spread out. Whereas if they were all sleeping(ie low energy air) you can just put them next to each other.

-edit I just reviewed a few notes on thermodynamics and the scientific term is 'density'. The colder the gas is, the more dense it becomes. The hotter the gas, the less dense it is. The reason more displacement increases the initial spool is because more gas is being expelled. Initially this is good because you need the flow energy of the gas to push the turbo. However the increase of gas also meant it brought along with it it's evil brother heat. Heat decreases the density. So on one hand bigger displacement brought more exhaust, the byproduct (heat) also came along. Thus we can see that because of the side effect of more exhaust, we are losing power from the heat (obviously why we use intercoolers in the first place).

Again i could be wrong here but that would appear to me what is happening.

 

A hotter exhaust stream actually increases spool, hotter gases are like you say more active, which means they take up more space - given they cant take up more space they instead increase pressure in the exhaust system (up until the turbine wheel that is)......

 

Turbo spool up is pretty damn simple; it depends on mass flow rate and momentum of the exhaust gas going thru the turbine.

Bigger turbines and bigger A/R turbine housings need more mass flow rate to spin up. Just look at the turbine maps in the Garrett catalog. We know that bigger turbos and bigger A/R turbine housings need more rpms before the turbo spools up.

Take a 2.0L engine. At 4000 rpm, it is pushing roughly twice the mass flow rate as at 2000 rpm correct? Assuming VE is equal, yada yada. A 4.0L engine has the same mass flow rate at 2000 rpm as a 2.0L engine at 4000 rpm.

That's basically all there is to it. Also, heat is energy. If you take the heat out of the exhaust flow before the turbine, the exhaust flow loses energy and losses momentum (i.e. loses velocity). Therefore, you want to keep as much heat/energy in the exhaust before the turbo as possible.

How do you think anti-lag works? It adds energy and mass flow, mostly energy, into the exhaust before the turbine greatly increasing the velocity of the exhaust gas spooling up the turbo.

 

Hmm, that part makes sense. I think what also could be happening is that EGT's are increasing and this is increasing the temperature of the turbo which is stressing the (water cooling?) which in turn breaks down the oil and causes the turbine to spin slower?

 

yeh I am not going to disagree with anything you said...

But I think thats the key here.

Doing a 2.5L probably means you actually loose a bit of VE... Even thou your adding 25% capacity your probably only actually adding 15-20% off airflow because of the lower VE of the 2.5...

 

Though, if you throw in some other changes such as intake, intake mani, exhaust, etc, maybe the 2.5L has better VE than the 2.0L.

Since it's all just ballpark guessing without real data comparing actualy setups, determining a ballpark change in spool up based on percentage change in displacement is a good first approximation.

 

Not quite. More heat means the oil gets hotter which reduces the viscosity of the oil, which should make the turbo spool up faster.

 

My experience with the 2.3 is that for what ever reason we could not spool a red much faster than a stock 2.0. It was possible to spool insanley fast but for what ever the reason you would surge the turbo. I think the problem is that below a certain rpm say 3500 rpm the is no way for the motor to deal with 30+ psi of boost. I just dont think the valves are open enough at low rpm to deal with the volume of air. I believe the issue would not be a problem with a turbo that spools at 4500 rpm on a 2.0. I just think there is a wall somewhere that will machanically keep you from spooling to fast. I am too new to this turbo sceene to have a real good idea if this is a lame concept but i know on my car i had to hold the spool back a bunch to keep from inducing surge. And yes this was with the newer style fp red housing.

 

The valve time that stays open can be controlled?