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Turbo manifold for straight line racing

Schwitzer_Turbo

New member
Joined
Dec 31, 2006
excuse the topic, building a new manifold but haveing trouble decide what type of manifold and pipe diamater to use.

first there are a few trail of thoughts i would like to get some input on,,

some people have the opinion that spool is everything so stock log would would be best. then some say that a properly designed tubular manifold can spool just as fast and give make more power than a POS Stock log manifold.

Now choseing pipe diamater:

corky bell saying when building a turbo manifold always use the same size pipeing as the ports NEVER bigger.(is he saying this caused its forced inductiion and regardless of the pipe size the turbo is gunna push the air to what ever velocity /flow i want regardsless if it damages thge motor) but then ther are some folk that say whenbuilding a high HP or boost car the piping must always be bigger than that of the ports.

now building these two manifolds will yeild a much differen ride, which one will be suited best for straight line race, i just wanna get the car over the quatermile as fast as possible.
 
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You've opened a can of worms. There are as many opinions on this as there are people who build manifolds. I've yet to see a definitive "best design" and the theories vary wildly on why a manifold should look a certain way. I think a good basic design to start from is something with the largest possible radius bends, 10-20 inch long equal length primaries and a really nice merge collector. It's imspossible to say what will work best for you so I'd say build a few different ones and see what your car and setup seem to like.
 
1.65 ID pipe is a good choice for size

manifold wise stock is junk, almost any custom built manifold will spool faster and make tons more power.
 
What about tubing volume, I thought it was advisable to get enough primary length to completely empty a cylinder before you reached the turbo to minimize reversion? Am I misunderstanding that? Please let me know.

Thanks
Renny
 
What about tubing volume, I thought it was advisable to get enough primary length to completely empty a cylinder before you reached the turbo to minimize reversion? Am I misunderstanding that? Please let me know.

Thanks
Renny
 
What about tubing volume, I thought it was advisable to get enough primary length to completely empty a cylinder before you reached the turbo to minimize reversion? Am I misunderstanding that? Please let me know.

Thanks
Renny

I've never heard of that before. I always thought reversion was more related to high back pressure than it was to runner length. Since transient response is a lesser concern in drag racing it becomes easier to justify a large enough hotside to where back pressure is at an absolute minimum (that is to say, less than boost pressure).

The two prevailing schools of thought that I've seen concerning equal length header design are to either minimize runner length to get the exhaust to the turbo while it's as hot as possible, or to build with pulse tuned runners, which can get very long (30+ inches).
 
some people have the opinion that spool is everything so stock log would would be best. then some say that a properly designed tubular manifold can spool just as fast and give make more power than a POS Stock log manifold.

Tubular will usually make more power and usually take longer to spool generally speaking. The honda guys have tested this fairly extensively. The most well known test shows a full-race header spooling 500rpm slower than a log but making 10% more power (50hp on a 500hp motor with just a header is nothing to sneeze at).


corky bell saying when building a turbo manifold always use the same size pipeing as the ports NEVER bigger.(is he saying this caused its forced inductiion and regardless of the pipe size the turbo is gunna push the air to what ever velocity /flow i want regardsless if it damages thge motor) but then ther are some folk that say whenbuilding a high HP or boost car the piping must always be bigger than that of the ports.


Choose a diameter that creates a reasonable transition from the port. You are going to merge them all into 1 (or 2 if it's twin scroll) - so killing yourself over 1/8" of runner diameter is a waste of time and pointless. If you are debating between 2 sizes that seem like they will work, evaluate how much space you have,. Use the smaller if space is a concern.

now building these two manifolds will yeild a much differen ride, which one will be suited best for straight line race, i just wanna get the car over the quatermile as fast as possible.

Tubular. Look at what competitive modern race motors, built by people with huge budgets are using.

Anyone who says a log manifold is preferable in some cases for a race engine needs a better grip on reality because it simply isn't true unless you are having durability issues, which is another thing entirely.

People can tip toe around however they want, but a manifold with smooth, efficient runners with a symmetrical, low angle merge, is always going to work better when it coming to making power than something that aims the runners into each other like a log manifold generally does.

If you run into a situation where it doesn't something else is wrong with the system.

Edit: and the suggetsion of somehow evacuating a cylinder worth of exhaust gas into a single runner makes little sense. The exhaust gases are expanding rapidly as they leave the chamber, we are pumping sewage here. How do you calculate the needed volume for gases that are expanding at continuously variable rates through the rev range?
 
Simply having the tube a little larger than the port will stop a great deal of the reversion pulses.

Like anything else it's more important to determine your goal and how to get there. The "best" design may not apply to your application. You have to take into consideration, camshaft, CR, rod length etc.
 
Simply having the tube a little larger than the port will stop a great deal of the reversion pulses.

Like anything else it's more important to determine your goal and how to get there. The "best" design may not apply to your application. You have to take into consideration, camshaft, CR, rod length etc.


So any tips on how to calculate runner length and primary diameter based on those parameters? I hear lots of guys hand wave about it, but I've never seen a formula.

What do you mean by the "best" design may not apply?
 
So any tips on how to calculate runner length and primary diameter based on those parameters? I hear lots of guys hand wave about it, but I've never seen a formula.

What do you mean by the "best" design may not apply?

Kenny, Ive always seen it as a function of cylinder volume, port speed, and port diameter.
Jonathan
 
Kenny, Ive always seen it as a function of cylinder volume, port speed, and port diameter.
Jonathan

What I was getting at is I've never seen anyone present some equations and say "I use "X" formula, I used it for these headers because of x and y and here are the dyno sheets that demonstrate the influence of the parameters I changed and this is why they changed and this is what happened and these are the important things to consider because they change things in a and b ways".


I've never met anyone where I could say, "I have x cam duration and overlap at y timing, valve size is z, turbo is a p, redline is q, port size is s, etc" and have them pump out an ideal runner diameter/volume/length.

But lots of people talk like they can do that who would probably be lost if you stood them in front of a bench and said "ok, build a header". Which i find annoying. :rofl:
 
What I was getting at is I've never seen anyone present some equations and say "I use "X" formula, I used it for these headers because of x and y and here are the dyno sheets that demonstrate the influence of the parameters I changed and this is why they changed and this is what happened and these are the important things to consider because they change things in a and b ways".


I've never met anyone where I could say, "I have x cam duration and overlap at y timing, valve size is z, turbo is a p, redline is q, port size is s, etc" and have them pump out an ideal runner diameter/volume/length.

But lots of people talk like they can do that who would probably be lost if you stood them in front of a bench and said "ok, build a header". Which i find annoying. :rofl:

This is my new manifold almost complete...

Boksie said:
I'll post some pictures later on, but have since finished the manifold. Well I thought it was finished, and then remembered I still have to do the waste gate take off... :oops:

Anyway, I flowed the collector perfectly, no sharp edges or anything to hinder gas flow. The turbo flange was welded up in the corners, and flowed to match the mouth of the turbo itself, and ports were also flowed to remove any sharp edges and high spots.

Now it just needs to be skimmed and cleaned up, and it'll look good as well...

EDIT: Ok here's some pictures, started cleaning it up, but you can see the final product, except the waste gate take off. Ports all flowed, and collector flowed as well. Of course the runners are slightly larger inside than the ports in the head and flange, but the step that's created is actually a bonus, as it stops reversion. It's the same thing 88RSI would have been trying to stop by using those cones...

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I figure if you're building a manifold yourself, you could just as well make the runners equal length... it's not that much more work.
They may still be the wrong length, but at least all cylinders would be balanced...
 
So any tips on how to calculate runner length and primary diameter based on those parameters? I hear lots of guys hand wave about it, but I've never seen a formula.

What do you mean by the "best" design may not apply?

I'd try these books;

http://www.amazon.com/Design-Tuning-Competition-Engines/dp/083760138X


http://www.amazon.com/Scientific-Ex...ring-Performance/dp/0837603099/ref=pd_sim_b_1

On the second book:

This is one of the best-selling technical books in its field. For years, engineers, engine designers, high-performance tuners and racers have depended on this book to help maximize their engines' potential. Dr. John C. Morrison is one of the foremost authorities on the analysis of the induction and exhaust processes of high-speed engines. Together with Philip Smith, he gives a thorough explanation of the physics that govern the behavior of gases as they pass through an engine, and the theories and practical research methods used in designing more efficient induction manifolds and exhaust systems, for both competition and street use. An outstanding, authoritative book.
 
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