engineermike

Unfortunately, I put together these calc's into a graph several years ago and don't have access to them now, nor time to re-create them. Just keep in mind, though, that loss is a function of the square of velocity. So, doubling the velocity quadruples the losses.

Man, that's a complicated set of calc's and I haven't even been able to find sufficient information on common turbines to be able to calculate that. The published Garrett "turbine maps" don't even supply enough info. I can say, though, that I've logged hot-side pressure on my old T76 388 LT1. Surprisingly, the hot-side pressure (some call it "drive pressure") rises linearly with rpm. At low rpm, it's actually below boost (on mine, at least), and it rose to about 2x boost at red line. I've heard that on some corked up stockers it goes as high as 4x boost.

Unfortunately, this rule of thumb is buried in a major corporation's design practices. It typically is applied to gas flow in industrial piping ranging from 3" to several feet in diameter. Liquid flow has a different rule of thumb, ranging from 10-15 fps.

The engine does not create or destroy mass, so you are correct that mass in absolutely = mass out. If we were talking about liquids, you would also be 100% correct (at pressure below 20,000 psi, at least). However, volumetric flow of a gas is a different story altogether. Since the gas is compressible, the density varies drastically as the pressures and temperatures change. If the density changes, then the volumetric flow rate also changes while the mass flow rate stays the same.

That would be one way to do it, but I would go about it like this. . .

We know that 10 lb/min air flow is about 100 hp. So, if you're making 1000 hp, you're flowing about 100 lb/min (both into and out of the engine). You would need to divide this mass flow rate by density to get volumetric flow rate. Density is calculated using P=pRT, or p=P/RT (assuming pressure = 2-3x your boost level if you don't have a measurement and T = 1600-2000 F). Convert all the units and you should wind up with an exhaust volumetric flow rate that you can convert to velocity pretty easily. Don't forget that only half of the flow goes through the crossover pipe.

CameronVic

iTrader: (5)

So does too large of a crossover just slow down spool time? or are there other problems?

I ask because I had mine made with 2.5" (before I found this thread) and I can build pretty much as much boost as I want antilagging at the line, and all hell breaks loose immediately. If I couldn't antilag, I know I would have spool problems though.

Sarg

iTrader: (6)

I am not having spool problems on my little 5.3 with 2.5" divided flange set up. I have 2.5" going to each side of the turbo which has a 92mm turbine and a T6 1.10 ar turbine housing. Not ideal, but was what I had at the time and what I used. Currently pushing against the brakes by as low as 2800 rpms I am building boost and breaking the tires loose or if they are warm I am pushing through the front brakes. While I hope to build and compare one day using schedule 10 2" pipe (think it is around 2.15 ID vs my current 2.35) for now I am running the 2.5 piping. I don't think you have a lot to worry about Cameron.

Preston99WS6

iTrader: (7)

I just ordered all the stuff from columbia mandrel to build my hotside with truck manifolds and 2 1/4", pipes, using mild steel but will be sent off for coating, system will be twin scroll with twin Tial F38s, feeding a S480 with the 96mm 1.32 A/R housing, 5" downpipe exiting out the passenger front bumper. Motor is a forged 6.0 with a Tick Cam, ported 317s and a LS6 intake keeping it simple. Will post results/vids as I have them I expect to have it up and running in about 2 months.

Forcefed86

iTrader: (4)

Here is a good example of what 2.5" piping is capable of.... I know it's not a perfect example because it's a twin setup. Still, he is using 2.5" collectors on the headers. Also necked down the turbo outlet piping diameter and uses a smallish throttle body.

bldgengineer

iTrader: (1)

I love these kinds of discussions. I can't even tell you how many times I've read through Maximum Boost and Scientific Design of Exhaust and Intake Systems. Everything here is basically putting these into practice and why we build these things.

willizm

iTrader: (10)

I have a 3" crossover and haven't noticed any issues with spool I've had tuners say how impressed they were with spool on my car but then again I have a nicely sized turbo for the motor so that might be why. Anyway, yeah I'm just putting it out there that it seems to work for me and my setup. I also have the stainless works headers that have a 3" collector.

Forcefed86

iTrader: (4)

Is the WS6 in your sig the setup you are referring to? What do you have to compare it to? If your satisfied with spool now, you could probably run an even larger turbo housing/wheel and smaller piping resulting in more power at the same or faster spool. If a 2.5" collector isn't limiting a 480+ cubic inch motor at 7200 rpm on methanol and 40lbs of boost, common sense tells me most of us don't need 3" collectors and/or piping. I'm also not a professional racer and thats just my opinion.

Phil99vette

iTrader: (11)

So if the Pontiac turbo motor is considered ideal...
2" headers, 2.5" crossover, 2800hp, methanol

Break it down into a 1400hp 4 cyl

How would you size a 400" 1400hp, 7500rpm, 25-29# of boost x275 motor?

I have my answer....

Forcefed86

iTrader: (4)

I was just pointing out it makes all that power through 2.5" collectors. Not saying anything is ideal either, I don't have enough experience to say whats ideal.

But I get your point, it would pretty much be your setup...

71 chevy

iTrader: (18)

is that car the fastest twin 91mm car ever? if its not then it proves nothing. for all we know the 2.5 piping may be a big bottle neck.

Phil99vette

iTrader: (11)

LOL, Clearly Travis Quillen and Butler performance know nothing about turbocharging and Pontiacs. You should get out more. Nothing like turbo technology from 2010.

71 chevy

iTrader: (18)

No one said that.i guess because Travis quillen did it then it must be the right way and all the other turbo pro mods doing it differently are dumb

Phil99vette

iTrader: (11)

Who are you comparing it to? A 632"+ BB with twin 94s making 700-1000hp more? Please cite your reference.

71 chevy

iTrader: (18)

I can give you several names of turbo cars with the same size or smaller engines that have been faster than the car posted, eg
andy jensen
dal sangha

but all that would prove is that we are both in la la land arguing about stuff that has no bearing to what 99.9% of people here will ever do so ill give you examples that are more inline with this board.

3" merge, 355 sbc, 3600lbs,s480 1.32ar


no boost issues here
http://www.youtube.com/watch?v=6Miw9...ature=youtu.be


3" merge,331ci, pt91,1.0ar, doesnt seem lazy to me
the merge

the pass


and whats more interesting, both of them had trouble spooling with the wrong converter, but no issues spooling with the right CONVERTER.

back to you.

JAX04

iTrader: (17)

didnt we have a guy on here in a black trans am that built his car, bigger turbo, 91is? on a 370is motor that had alot of trouble spooling and then he rebuilt the kit to a 2.5" kit and all his spooling problems went away?

Just last year?

71 chevy

iTrader: (18)

Are you asking or telling ? Lol
Link?

JAX04

iTrader: (17)

Asking lol. Im usually pretty good at remembering old threads and things that have been discussed here before.

I'll track it down

71 chevy

iTrader: (18)

Please. I would love to read the thread.

Cam72aro

iTrader: (28)

Here ya go. . . 3" crossover

https://ls1tech.com/forums/forced-in...e-12-10-a.html

And here is the 2.25" crossover
https://ls1tech.com/forums/forced-in...e-06-29-a.html