Turbo vs Paxton on DOHC V6

[Atilla the Fun]

So, I'm putting the 5-cam in, and I was thinking an ATI ProCharger, until I got a screaming deal on a Paxton for a Mustang 5.0. Only with the hassles of mounting and plumbing, the turbo starts looking better. My concern is the tires starting to spin about halfway through second gear, like if I stomped it coming out of a turn. Is this a real concern, or is it easily modulated with the right foot? The only turbo car I ever drove was at a dragstrip. I chose the 3.4 over a V8 partly for the gas mileage, not for the rpm. Thanks, everyone! -Atilla

[Shaun41178(2)]

remove the a/c and find a way to mount the paxton where the a/c compressor was.

[The Dark Side of Will]

Centrifugal superchargers are so top end biased that you don't have to worry about overwhelming midrange torque... at all.

[Kohburn]

yup - no boosting method is safer for a tranny than a centrifugal supercharger

[Atilla the Fun]

Thanks, guys!

[Aaron]

But the turbo will make much more power, make the car much quicker, and be much more fun.

You want the turbocharger!

[Atilla the Fun]

So, I'm always confused about turbo terminology, acronyms, and ratings. I get the idea that I need to explain to some of these guys the proper application of compressor maps, and how to properly interpret them.
This week I will find my printed set, then post a link to the maps that go with which turbo belongs with which engine at which output level.
Aaron, thank you for being so active on this site, with a running turbo DOHC, if I'm not mistaken. Have you broken any transmissions with it?
Have you tried drag radials? -Atilla

[Aaron]

I actually haven't had my engine boosted yet, it's still in the middle of getting there. This summer I plan on finishing it.

I don't anticipate any transmission issues, but I also won't be running very large tires (maybe 245s).

[Atilla the Fun]

Any chance of you finding the right map for your compressor and uploading it? IF I go turbo, I'm settled on a T66 if I go for a full build, see map at innovativeturbo.com, or the t4e60 if pure stock, or if 3800-2, also at innovative. Thanks Aaron

[Aaron]

Any chance of you finding the right map for your compressor and uploading it? IF I go turbo, I'm settled on a T66 if I go for a full build, see map at innovativeturbo.com, or the t4e60 if pure stock, or if 3800-2, also at innovative. Thanks Aaron

I do actually.

Here is the compressor map from ATP Turbo, for the Garrett GT35R.



Now I no longer have the flow calculations for a 3.4l DOHC, though it wouldn't be much to compute them. I'm going to send you an email, with an Excel Spreadhseet created by TimG. This visually shows a stock 3.4 DOHC, with a GT35R, GT4088R, and a T04Z. It's a really helpful sheet, showing the graphs at every boost level from 4-25psi, at 500rpm intervals.

On a stock 3.4l DOHC, with a GT35R, at 10psi, the turbo is above 70% efficiency from 2500rpm-7000rpm, with peak efficiency from 3500-5500rpm. It's basically perfect. The GT35R is going to be a bit small on my engine because of all of my modifications, but I kind of want that. I will have an extremely efficient air-water intercooler, so running the turbo a bit on the hot side (Past its peak efficiency island), won't hurt my power much. Also, I'll have all of the power my block can handle, and if I need more, I'll just push more boost. There's no downside with such a great turbo, and great intercooler. But by having it a bit on the small side, I will have great response. So lag will be minimalized, and it will spool very quickly. I honestly can't wait to drive it and really feel it, as the midrange torque curve should feel like a GenIII/IV LSX.

Check out my build thread if you have the chance, it's done the way every turbo car should be, but isn't. I engineered the entire system to make as much power as possible, keeping lag to an absolute minimum, and getting the best response possible.

phpBB/viewtopic.php?t=6364

[Atilla the Fun]

they say mimicry is the highest form of flattery, and I believe it. My e-mail has changed, I hope it's ok to put it here for all to see. idcsr1@aol.
I feel I have an excellent grasp of the cold side of turbos, but not so much the hot half. So, If you have it small enough to work at 2500, won't it be a restriction well before 7000? And if it breathes at 7000, can it "turn on" below 4000? Thanks!

[Aaron]

they say mimicry is the highest form of flattery, and I believe it. My e-mail has changed, I hope it's ok to put it here for all to see. idcsr1@aol.
I feel I have an excellent grasp of the cold side of turbos, but not so much the hot half. So, If you have it small enough to work at 2500, won't it be a restriction well before 7000? And if it breathes at 7000, can it "turn on" below 4000? Thanks!

Thanks :thumbleft:

I emailed it to that address, you should have it.

The turbocharger is a restriction, that is what causes the blades to turn. It takes power to make power. But you have the engine forcing the exhaust through the turbine, forcing the blade to spin. When you get the wheel spinning fast enough, the wheel on the other side will be flowing enough air, in the opposite direction, to overcome the engine's N/A breathing capacity, and it will build boost.

So although it is a restriction, it makes more power than it costs, much like a blower.

You're last sentence is why we use wastegates. We'll use my motor in a hypothetical. At 3500rpm, my motor is making enough exhaust to spin the turbine fast enough to make 10psi of boost. But at 4000, it is making more exhaust. But the wastegate has a valve that is pushed open at 10psi, and it bypasses some of the exhaust gasses around the turbine, thus only the amount I need to make 10psi flows through the turbo. And as RPM goes up, and more exhaust is made, more is bypassed through the wastegate.

[Atilla the Fun]

Then a wastegate not integral to the turbo, and sizeable to the volume of excess gasses, would be ideal?

[Aaron]

Then a wastegate not integral to the turbo, and sizeable to the volume of excess gasses, would be ideal?

Exactly. Internal wastegates work the same, they just interrupt flow, and pose more of a restriction.

I'm surprised you picked up on the "volume of excess gasses." Most people think that the more boost you run, the larger wastegate you need, when it's actually the other way around. A 38mm is the industry standard for performance aftermarket wastegates, and a single one of those will be just fine for most any turbo V6 you're gong to build.

TiAL Sport makes the most highly held wastegates, they are the one to have.

[Aaron]

What will you do for fuel mapping and timing? Any chance of me buying a copy to use as a baseline to get me to a chassis dyno-equipped tuner when my time comes? While I'd trust this shop to dial it in once it's close, I'd hafta go to Cali or the east coast maybe to find a shop I'd trust to create that baseline. I like your build, but I'm set on 1.625" primary, long-tubes, or 1.75 if a ceramic coating inside is very thick, so my tuning wouldn't end up the exact same. THANKS!!! -Dave a.k.a. Atilla

I am using a Split Second FTC1. It is a piggy-back, that works in conjunction with the factory PCM. When I don't have boost, the stock PCM runs the car like it is stock. But as boost comes on, the piggyback reads this, then modifies my airflow signal to the factory PCM. So it takes the MAF signal, modifies it for the amount of boost, then sends it to the PCM. I can tell the FTC1 how much to modify the signal, that's how I "tune" it. I have a base map that TimG had for his Monte Carlo, which will be good for me, then I will use my WBO2 to dial it in perfect. The FTC1 does the same thing for spark timing. Stock timing curves, it just pulls them back a bit as boost comes on. This also allows the stock knock sensor (ESC) to work properly.

They aren't perfect, but they are good enough. TimG has his MCZ34, with 160k on the original engine, running 325whp problem free for a few years.

His base tune will probably be pretty close for your motor, but I doubt it'd be anywhere near mine. I will be making more power, thus need more fuel, per psi boost because of my other mods.

[The Dark Side of Will]

The turbocharger is a restriction, that is what causes the blades to turn. It takes power to make power. But you have the engine forcing the exhaust through the turbine, forcing the blade to spin. When you get the wheel spinning fast enough, the wheel on the other side will be flowing enough air, in the opposite direction, to overcome the engine's N/A breathing capacity, and it will build boost.

You forget that the engine has to push the exhaust out against the high side pressure on the turbine. A larger turbine will generate the same horsepower (to drive the compressor) at a lower pressure ratio and higher flow rate than a smaller compressor and thus will allow the engine to make more power by reducing exhaust back pressure. The downside is that it has a higher MOI and does not take much power from low flow rates, so it spools later.

[Atilla the Fun]

I can't thank you guys enough for all the excellent comments! I'm not set yet, But I am saving up. $800/mo disposable should have me running this year.
I should be porting, polishing, cc'ing and flowing my heads in June, and from there, ordering pistons from JE.

[The Dark Side of Will]

But the turbo will make much more power, make the car much quicker, and be much more fun.

Comparably sized, the centrifugal SC will make just as much power as a turbo, but the turbo will make a buttload more mid range torque.

[The Dark Side of Will]

yup - no boosting method is safer for a tranny than a centrifugal supercharger

Not sure about that... the centrifugal SC is still geared to the crank, so the boost rise about to be pretty quick. Turbos may make a lot of torque, but they torque comes on very smoothly as the turbine RPM asymptotically approaches steady state.