Effects of Primary Size on Turbo Motors

Pretty much what it says. What effect does it have on spool-up, Exhaust flow, etc. I was thinking of making my own Kit since PTK would want me to bring the car to them. I have the ability, and some knowledge, I just need to finish what I need. The motor is going to be a 383 with a PT-96 Turbo. The question is 1. can 1 3/4 support 1600 crank HP? 2. will going to 1 7/8 hurt spool-up that much that I won't be able to use it all in the power band?? 3. And what other bad side effects would come from upping the primary size, aside from the delayed spool??

I guess this is for you hard core Turbo guys... :D

Chris

Pretty much what it says. What effect does it have on spool-up, Exhaust flow, etc. I was thinking of making my own Kit since PTK would want me to bring the car to them. I have the ability, and some knowledge, I just need to finish what I need. The motor is going to be a 383 with a PT-96 Turbo. The question is 1. can 1 3/4 support 1600 crank HP? 2. will going to 1 7/8 hurt spool-up that much that I won't be able to use it all in the power band?? 3. And what other bad side effects would come from upping the primary size, aside from the delayed spool??

I guess this is for you hard core Turbo guys... :D

Chris

If you are really getting 1600 fwhp, you need to size the primaries to handle the exhaust flow that represents. 1-7/8 will be too small.

1600 hp turbo 383's are being successfully built by very few guys. You might go to them (and take a trunkfull of cash). Look at what size headers they use.

I'm not sure where you are going to use 1600 hp other than a VERY fast drag car, so why does a wide power band enter the picture? Lag comes more from total pipe volume (lenght X crossectional area), not just diameter. IOW, using 16 gage tubing, 20 inches of 1-3/4 has about the same internal volume as 12 inches of 2-1/4 tubing.

"Short and thick does the trick."

Did you mean 800 hp? :)

My $.02

If you are really getting 1600 fwhp, you need to size the primaries to handle the exhaust flow that represents. 1-7/8 will be too small.

My $.02


Well, 1 7/8 would be too small if it was naturally aspirated.

You don't need huge primaries with a turbo engine, as they are operating under pressure.

I would personally use 1 3/4 primaries, though there are combinations out there with 1 5/8 headers and 1500+fwhp.

Also, Wheel to Wheel did a single turbo LS1 car with over 1500 horsepower using -stock truck manifolds-.

yep, 1-3/4" will be plenty. You need to keep velocity up. backpressure will be caused by the turbine wheel. PTK has (they said) a couple mustangs making 1800 with 1-5/8 headers.. Mine are 1-3/4 fwiw.

yep, 1-3/4" will be plenty. You need to keep velocity up. backpressure will be caused by the turbine wheel. PTK has (they said) a couple mustangs making 1800 with 1-5/8 headers.. Mine are 1-3/4 fwiw.

Cool! I stand corrected. There must be some big back pressure there @ 1800 hp!

For that kind of power are we talking 2 turbos? or more?

I figured I'd be using 1 3/4 Pipe for the primaries, as I feared getting into the 1 7/8 would be to big. I talked with PTK about the turbo kit for the car and they need me to bring them the car for two months...I guess I'll just be buying parts from them. And INTMD8, We're still going for Pat's car so I hope he's ready :cool: But Everything I'm hearing has been right on with what INTMD8 said, with the 1 3/4 primaries. Now comes the fun part of cut and weld, cut and weld....yeah

Cool! I stand corrected. There must be some big back pressure there @ 1800 hp!

For that kind of power are we talking 2 turbos? or more?

Probably around 70# of backpressure, quite a bit ;)
Figure around 2x boost pressure for backpressure on a properly sized turbo system.
They are single 106mm turbo cars..

I figured I'd be using 1 3/4 Pipe for the primaries, as I feared getting into the 1 7/8 would be to big. I talked with PTK about the turbo kit for the car and they need me to bring them the car for two months...I guess I'll just be buying parts from them. And INTMD8, We're still going for Pat's car so I hope he's ready :cool: But Everything I'm hearing has been right on with what INTMD8 said, with the 1 3/4 primaries. Now comes the fun part of cut and weld, cut and weld....yeah
I dont see how 1 7/8 would be too big :confused:

sure it can be done with smaller but IMHO 1 7/8 is better.

I mean too big in the fact that it'll take so long to spool. I'd rather not have to launch and wait for the turbo to spool. If I go with the smaller pipe, it'll keep the velosity up, therefore keeping the spool time shorter...If I'm not mistaken... I could always go with a 1 7/8 and step down to a 1 3/4 if I really had to. But I think the 1 3/4 will support the turbo nicely...I was just wondering...

Chris

I mean too big in the fact that it'll take so long to spool. I'd rather not have to launch and wait for the turbo to spool. If I go with the smaller pipe, it'll keep the velosity up, therefore keeping the spool time shorter...If I'm not mistaken... I could always go with a 1 7/8 and step down to a 1 3/4 if I really had to. But I think the 1 3/4 will support the turbo nicely...I was just wondering...

Chris


but for the power numbers you are looking at, the smaller exhuast will pose more of a threat once the turbo IS spooled.

you shouldn't be lagging much past 2500 on a 6.3 liter. make sure your intake is well built as is your exhuast. and by well built, i mean tuned.

with any DECENT setup, you will be fine.

Actually the intake we're using is a production LT4 that's going to be ported and matched to the heads, as well as about as smooth as you can possibly get aluminium....If I could find someone to CNC it to match the heads I would do that, but I have a feeling that'll be kinda hard...

Chris

1600hp
no sheetmetal intake?

you sure are making this difficult on yourself :D

I REALLY doubt you will see a large spool time difference between say 1 3/4 and 1 7/8. Yes, there is more volume but think about the volumetric flow rate we are talking about here- its huge.

I think either will support the power levels you are talking, I would error on the larger side if you are really going for 1600hp.

1600hp
no sheetmetal intake?

you sure are making this difficult on yourself :D


We're even using a Fiberglass version of the WS6 Ram Air hood, to make the car still look stock.....of mostly anyway. We may end up with a Sheetmetal version of it depending on how everything goes... But I think we're going to do the LT4 first, and if we're not happy with power output, we'll make a sheetmetal variant....

We're doing this mostly for fun and the trill of going fast...

Yes We're Crazy....

Chris

what kind of boost levels are we looking at? RPM?

a sheetmetal intake to LT4 specs wont help much. the MAIN reason for a sheetmetal intake is that it is custom. This means shape, volume, lengths, etc

Well if we do a sheetmetal it'll be done bigger and better, but still keep the hood line is what I meant. RPM and Boost levels are still to be determined...Probably gonna try and push it, but we're not sure yet,as the motor is still coming together...And There is a chance of going to sheetmetal to begin with, but we're still debating, as the car is going to the frame shop on Saturday, and then going for the cage. So we're getting the chassis set first, then we're going to worry about the top end of the motor...

I highly suggest the SM intake if you have the means to do it correctly. it will increase power, driveablility, decrease lag etc

what is your header length/specs?

1 3/4" is plenty big. My exhaust ports are actually a tad bigger then the headers themselves. On a turbo motor it does not pose a big threat like a N/A or nitrous motor would. The back pressure is about 2x's the boost and the header size is not going to make a difference, like Brady said it's from the actual turbo. Another thing that will affect spool up is the crossover tubes, I run 2 1/2". Try to keep them short, running the turbo up front like mine takes a little longer to spool. JFYI next year I'll be looking to make around 1700-1800 FWHP with the silly LT1 block. Crazy eh? :eek: