Contour Enthusiasts Group Archives Forums Modifications Forced Induction Turbo

I've been getting alot of questions as to why I'm selling the 280hp 3L, so I've decided to sell it to make room for a turbo engine. I've been wanting to do it for some time, but it was just too expensive, so up until now I wasn't able to do it. The most expensive part was the turbo (about $1500 bux) and the header, which doesn't cost much in acutal parts but required lots of labor for quality work.

I'm going to be using a relatively stock 3L engine and a medium sized T04E turbo. I'm not going to be using any forged rotating assys. or custom parts. Just the heads have been polished but better flow. I'm not going to give out the entire detials of the heads because I'm not done with them just yet, but once again its going to be mostly stock. I would have used the engine I have now, but it has too much compression and cams for the turbo. I haven't had time to adj and measure the cam timing for a smooth idle and optimal lobe separation. Thats why I'm selling the cams with the engine since it was working good without any adjustment to the timing.

I'm trying to get the most out of the midrange power band so I won't have to rev the heck out of it to make power and I don't want a quick spooling turbo that will smoke the tires immediately, so my goal was for linear boost. So I chose a 60 series, which would make boost at about 3000 rpm and come on strong at around 5000 and hold the power band cloee to the redline. It would also be good for 450+hp, but my goal is for a streetable 400hp.

If you have any question feel free to drop me a line...

for 400hp I'm guessing somwhere along the lines of 15psi, and fwiw, I believe you will definately need forged rods for that power level.
If you truly are gonna run in the neighborhood of 15-20 psi I think that turbo is ok, but anyhting less would demand a smaller turbo, or you will end up with a power curve like the last turbo 'tour that was posted.

Good luck, and let me know if I can lend a hand in any way.

I've calculated that I'm going to need about 1 bar to get 400hp in race trim using VPC16 or something similar along with a test pipe. 400hp will be pushing the limits of the stock parts, but I'm not going to be running around with that much boost just to get from point a to point b.

In street trim I will be using a cat and pump gas and probably 7-10 psi which should net about 325-350hp. This should do nicely with a good amount of torque when compared to the N/A 3L.

I don't think there was anything wrong with that Siboney SVT power curve, I just think that he started the dyno at a late rpm. I've seen that dozens of times for cars that just don't make power in the lower rpms, they do that so it wont take up alot of dyno time. Not even the soggiest T4 would do that unless he is having tuning issues and even if he had tuning issues it would have probably shown up in the dyno.

its a matter of not having enough exhaust energy to drive the turbol. He was only running at somehting like 6 psi, the dyno plot was there, he was sitting at 100hp until like 4k, and then the turbo had enough energy to get moving. Its a simple case of an oversized turbo for a given application. oh, and the dyno plot also had the a/f curve on it too, and that was all over the place, so tuning is definately a problem there too.

1 bar is supposed to be 14.7psi, so I guess we agree on the needing 15psi to get 400hp, and for that setup, I think a T04 is right on, but for anything less, it is too large, and a T3 of some sort is in order. or a T3/T4 hybrid in there somewhere.

This is not a matter of not having enough exhaust energy to run the turbo. You, I, we don't know that, unless you ask the person that was doing the dyno.

But, there is a threshold that turbo needs to get up to spool and before that threshold a turbo will generate a of boost exponentially to its input. Once that threshold is passed it will "spool up", but before that a turbo will not simply sit there not create any boost and make the engine not have any power. Maybe if you run something like 6-7:1 CR, the low compression is going to make the car powerless until the turbo spools.

But its a stock 2.5L V6 engine, a 6-7:1 CR would have much less horsepower so it can't be that and if it was at WOT you would have seen a power curve similar to one looks like without a turbo.

Here, take a look at this wild Supra...

http://www.walserrz.com/dynos.html

Look at the last dyno sheet, see that little flat line right before the the chart flys up and make tons of HP. Same thing, leave a car on the dyno and don't give it any gas you will get nothing but a flatline...



Here's a theory and a little explanation of whats going on. In the red you see nothing but a flat line because the throttle has been closed, at that point the ECU has gone into a close loop mode and is starting to lean out as part of its standard programming (trying running your car at 55mph and let go of the gas, you will see injectors and a/f ratio goto 0).

The Yellow, its a common trick to run it really rich in the lower RPMs to get a turbo spooling. You can see this as it reaches 13:1 Its a bandaide but it works...

In the green the turbo is spooling and you adjust the A/F mixture to get the desired EGTs. If there was a tuning problems they usually show up as spikes or power dips, somtimes the dyno plot is a squiggly line which I don't really see.

Its a little phoenemon called starting to record the dyno before you give it gas.

Ok,
so clarify a few things for me... Since I have seen quite a few dyno's and this is a new one to me....
So you are saying if I run the dyno up and don't give it any gas, the HP should be a flatline ALL THE WAY UP through the RPM's????

That doesn't seem to hold water with me... the HP curve cannot be the same throughout the RPM's at Closed throttle?(also how would you get the car to go through the RPMS without giving it gas and opening the throttle???)

Not trying to be snide here, but that just doesn't make any sense If you could just clarify this for me, I'm more than willing to listen, hey you learn something new each day....

So you are saying if I run the dyno up and don't give it any gas, the HP should be a flatline ALL THE WAY UP through the RPM's????

Yes, is you don't give your car WOT on a dyno you are not going to produce a power curve. It will be bland flat line line an electric motor. It makes a constant amount of TQ at all rpms.

wow, that is just sooo wrong, I don't even know where to start.

Ok, here goes.

uh, huh, sure.

Boost threshold is the point at which (in a given application) there is enough exhaust energy to spin the turbine at a speed to begin generating a useful amount of positive pressure in the intake tract, ie the turbo "spools up".

Yeah, because there isn't enough exhaust energy to spin it fast enough! c'mon this isn't rocket science.

Well, this completely depends on how much power the engine makes without the positive intake air pressure. Some make a decent amount before additional pressure is applied to the intake tract.

Yeah, but if you size the turbo properly, you don't have to wait very long, especially not to over 4k rpm!

Dyno plots of forced induction (and even between turbo and s/c) and naturally aspirated engines are usually very different and distinctive, often enough so that a skilled eye can determine the type of induction merely by the shape of the graph. Oh, and in reference to a low CR and the power curve of a turbocharged car, ask terry haines' what a properly sized turbo setup will do on a low CR zetec.

Okay . . .

I see a little flat line that extends for, oh, 50 rpm MAYBE, easily explainable by any number of things, from a slow foot on the gas pedal to turbo lag, etc.

In the Siboney turbo contour dyno plot, I see roughly 500rpm worth of flat line.

Whew, I was getting scared there for a minute that you were a little confused . . . oh wait, is it your theory? or is it an actual explanation?

So, uh, does your car typically increase rpms when the throttle is closed? Cuz mine doesn't, nor does any car I've ever been in. (though there have been a couple lawsuits in the past, somehting about "unintended acceleration" or something, but I doubt it applies here) I also dont know of a single intelligent calibrator that will let an a/f ratio go to 18:1 under acceleration

Well, duh, this is because the injectors SHUT OFF under no throttle deceleration.

I'm not going to argue your "common trick" in and of itself, simply because I've never calibrated an engine for transient events in turbocharging (though I will say I really believe your logic to be incorrect here, excepting one small possibility, that I don't believe comes into play here anyway).

1. The turbo is way too big if it isn't spooling till over 4400rpm and only being used to make 6 psi of manifold pressure.

2. I see significant tuning problems in that a/f curve. I see a very inadequately controlled a/f ratio; harmful to overall power production, and often to the engine itself, especially in the lean areas (the two large, breast shaped areas of the curve). If you want to see a better a/f curve, go look at the one on the last dyno on the Supra you so kindly linked us to earlier. It isn't perfect, but much better, and he is probably a little extra rich on his tune to compensate for a lower octane fuel than he should be running at that dynamic compression ratio.

If they aren't giving it gas, why in the world are the revs increasing? Its not a graph over time, its a graph over rpm. And don't say, "oh they were only giving it part throttle" because that is ridiculous (then again, so was the quality of constrution of that setup, and the choice of turbo, and the venting of the blowoff/compressor bypass valve to the atmosphere on MAF controlled car) why would you not want to record the entire rev range of operation? and why would you only give it part throttle? it'll take even longer to accelerate up to the start point at part throttle over WOT (unless serious tuning issues prevent WOT from being a good idea under 4400rpm which makes things even worse)

Um, sure, perhaps you needed to pay a bit more attention in physics class, or this wouldn't make sense to you either.

I don't have a good understanding of dynos but according to the graph the flat line occurs at 4k right, or is this a base for the graph? It seems as if the operator would have to have a steady foot, or has not given gas yet. Yes I am confused. Oh and Rara about the injectors shutting off with no throttle under accel I think it would stall, right? (maybe you meant slow down?if not explain please.) O ya were in Novi do you live or use to live.