Turbo BS Thread

So like...it just loses pressure, or what? Idk what that means...
VE drops? More exhaust stuck in the next combustion stroke?

 

Back pressure rises, VE drops. More pressure doesn't directly mean more power. The scale isn't 1:1 at least. An appropriately sized turbo may make 8psi and 285hp (example nums), a too small turbo may also hit that number but at 11psi but also dramatically increase the potential for knock because of the exhaust restriction and at a certain point you just can't flow more exhaust and it planes off at that higher RPM where the exhaust flow is key. I think the issue with turbo sizing is everybody focuses on the compressor side. But in a lot of cases you won't find restrictions there You're going to find them on the exhaust side first.

 

Nice. Makes sense, hard to quantify from provided manufacturer intel. Seems to be more of a trial and error thing here - so will definitely heed yours and Jon's advice. Thx

 

So with that in mind, potentially the G2 G30-725 could do with a 0.83 housing instead of Jon's recommendation of 1.06 (1.01) on his Gt3076r since they flow better? Or still go towards the larger?

 

At minimum a G30 with .83. If you are chasing high hp/drag race only stuff then do a G35 with 1.21 housing.

 

You already know which one, I still go g30-770 with the .9 housing

 

Fwiw I'll probably move to a gtx3576. Only because it will drop into the Tial housings i have. Probably the .82. Btw the Garrett housings are heavy! The Tial are thinner stainless.

 

@treyus30, how much power do you want to make now and and how likely is it that you're going to build the engine later? If you do, what will the power target be then? The turbo will have to be a compromise on one of them if the two goals are far apart.

Yes, both, largely from high exhaust pressure causing mixture dilution on the next intake stroke. One of the big advances in turbocharging and related controls is being able to get the turbine drive pressure down to a 1:1 ratio with boost so it acts more like an NA engine. In years and decades past it was common to see drive pressure 2.0-2.5x the boost pressure even on pretty high performance engines. The ones that got it a lot lower had horrendous boost thresholds.

 

@treyus30 a 5vz truck I tuned with a 3076 with a .82 housing got on the dyno a little while ago. The people operating the dyno weren't the brightest and did a weird run, weird axis on the graph, and started the run at 3500rpm for some reason so the numbers are scuffed. However the shape of the graph said a lot. His turbo held 13psi to redline perfectly, but the torque literally started falling off at 3600rpm, and by 5800rpm with boost it was making almost stock torque. The back pressure goes up in the exhaust manifold which then keeps exhaust gas from leaving the cylinders efficiently, which then takes the place of air that could be making power. It also increases heat in the combustion chamber as well. A 3076 is realistically too small for a 5vz, but the new g30's look very promising, especially the G2 series. A .82 on the newest g30-725 would probably give a reasonable amount of top end while still giving the response you'd be looking for, but artec makes a .90 housing that I think would be SWEET for a responsive 5vz setup. To give a back to back comparison though for the two turbos I tune the most, 3076 .82 and 3576 .82, the 3076 will make 12psi at 2700rpm on a 3rd gear pull starting from about 2500, and the 3576 will make 12psi at about 2950rpm from the same, but the 3076 ve starts falling hard at 3700-3800 where the 3576 holds pretty strong on the ve until 5200 where it starts falling, which is likely more due to the head flow

 

This makes sense to me, simply from an intake and cam profile perspective. I would expect the torque profile to be similar to as stock with a constant scalar if you have constant pressure. Idk that you can attribute that to backpressure. Correlation and causation and all that

This is a fair question, and one I can't answer definitively. Ideally I will not open up my engine ever again, but I have a sneaking suspicion it'll happen at some point - if for no reason other that I can't leave well enough alone. I would probably go as far as the stock crank could take me, whatever that is.
Given that my current priority to to spool fast and ride it out through redline (the low 5500RPM that it is), I'm leaning towards something smaller that has the capability to push a bit past that 450-500HP stock engine mark. A G30-770 like Speedy is suggesting would be the answer if I was 100% sure I'd be building it.

 

I think you should order the really small turbo you wanted. You know, prove everyone wrong. Or at least reread what Jayson wrote because I think what you responded without reading it all.

 

That's too small if you're going to build to go all out. I was suggesting that is a good all-around average turbo choice with a tiny amount to grow into.

 

It sounds to me like a $3,000 turbocharger isn't a good investment until you have a better idea of what you want to do. How is your current setup not meeting expectations?

Or go down the rabbit hole of compound turbos. There are ways to gate and control them so the boost rise is additive instead of just throwing the exponential switch that turns 15psi into 45psi. Compounds also have low boost:turbine pressure ratios.

 

Twin charge it.

 

If someone could fit a larger bypass valve to the supercharger that would be a fun project with the 1320 at least

 

Honestly just want to clean things up.

 

Wouldn't be the first time... Or the tenth time

 

The horsepower ratings of the turbos are the max compressor flow potential if everything was in a perfect world. You can't put a g30 on a bigger displacement engine and expect to get 725 horsepower out of it. Horsepower is directly related to torque and rpm. If you can't make torque at higher rpm, you can't make that horsepower. And that will be the same with a smaller turbo for your 500hp range. If it can't flow at higher rpm to maintain tq, you aren't going to make that power. The turbo being rated for 900hp max does not mean it's the wrong turbo for your setup if you are going to make 450-500 because you have more exhaust volume to flow through the turbine side. Otherwise you should be able to put a g30-900 on an LS and make 900hp. You can't. It won't happen.

 

Did the 3rd Gen airbox with with the hole in fender? I have a dorkel and would like to keep it functional.