something im curious about, and cant find anything "definitive".

Id like to know HOW you decide on a tube/pipe diameter for your fabbed headers, and for the same engine/turbo install what effects too large a header would have over a too small variant.

ive read a bunch about quick cars using logs, a bunch of 1 5/8" fabbed headers making bullshit high HP, and standard cast manifolds doing the job too, but whats the "right" way to design your hotside?

thanks

 

what size is your exhaust port in the head ?

 

some cut and paste from another thread..






Re: Will stock 1 7/8" outlet manifolds work to feed a S475?
« Reply #7 on: Yesterday at 04:02:45 PM »

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just make the exhaust pipe, same size as your exhaust port in the head...it will be fine

ive seen 2000hp from 1 1/2 tube
ive personally got twin 72's and twin 76's on 1 5/8 tube

one of my sponsors have 1 3/4 on twin 91's


at the end of the day, the turbine wheel is the restriction, and its good to keep the exhaust flow speed UP , and constant all the way to the turbine.
having a LARGE exhaust tube off the head, slows the gas down, due to increased volume of the runner, then... the gas has to speed up again , as it goes thru the turbine...

basicly make the tube same size as your port in the head.

 

Re: Will stock 1 7/8" outlet manifolds work to feed a S475?
« Reply #9 on: Yesterday at 04:44:52 PM »

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Quote from: 10secgoal on Yesterday at 04:20:44 PM
Have you seen back pressure testing to verify a hp loss or increase with a larger tube ? I have talk to more than one guy who basically says to make it as big as you can. Thoery is for the gas exiting to have "somewhere" to go. I'm usually stuck buy space limitation and radius dictating exactly what I can put in there. I am curious, and would like to back to back someday. but space make it hard sometimes, let alone making another set of headers.


no back pressure test, more spool time etc

while the gas is still relitivly hot, it flows quiet well, so its sensible , not to slow the speed of it down, until after the turbine
the main physical properites that drive a turbine is : speed of gas , temp drop across the turbine, denisty of gas, speed differential across the turbine.
alot of the data i get, gets run past a thermodynamic engineer, and professional turbo / procharger tuner..

 

good info there, thanks mate!

ok, port exit CSA dictates pipe size?

pretty much rules out everything except 1 5/8" 16 gauge tube for my 355/6000rpm deal.

Id like to use thick wall pipe, but one size is too small, the other too big, neither are even close.

FWIW ive got 1.88"^2 of exhaust port exit, the thick wall stuff i can get my hands on measure out at 1.49"^2 (too small perhaps) or 2.14"^2 (far too big i reckon)

If i can ease the transition from exhaust port into the smaller CSA tube (no dodgy restrictions to flow) will it work, or choke it in the upper rpm?

i better do some more reading, lol.

 

sq area probaly not required this build..
just go exhaust port diameter, and match up from there

 

1.5" schedule 40 pipe has a cross sectional area of 2.04"... That sounds like a pretty good match.

 

I thought so too, until i measured the actual I.D. of the pipe and found it larger than the listed spec.

 

Interesting... I used the 1.5" sch 40 pipe to build my headers for my 358" 6000rpm street motor, works great for me.. If you can fit it, I'd go with that. What kind of power are you going for?

 

well, im parts limited on this build so if it makes 600 at the fly thatll be it, i wont abuse it and it should live long enough for my needs.

stepping out of a 460 moroso NA deal, to hopefully a 550 moroso turbo deal with less cam/rpm/stress etc. (same engine, with a piston change)

im hoping to get it well into the 10's, the NA 355 engine went 11.3 @ 121 at a touch under 3500lbs.

I do have another (proper) short on the build which should cope with a few more ponies, but its a while off and i cant wait that long for my car to be running again lol.

edit: I dont want to use logs, or factory casties.

 

can you link me to your build thread?

 

https://www.theturboforums.com/smf/index.php?topic=55258.0

Some of the pictures have gone down, but I think most of the header stuff is there. They're somewhere between headers and logs, but I was very space-limited.

 

cheers mate,


I ordered some 1.5"nb today.