So I'm in the process of making an alum sheet metal intake and a new 304 ss turbo header. I'm gearing up to start ordering header pipe and was debating if stepping up the primary size would be a good idea or not. I'm currently 1 5/8 primary I was thinking stepping up to 1 3/4 to the merge collectors maybe even 2 inch if I can fit it between the intake runners.

I wanted some input or theory of pro and cons. I assume I would lose some velocity in the header but the turbo is going to be the bottle neck point anyway so I wonder if it would matter? I feel like it may free up some pumping pressure through the header then speed back up when it narrows down in the merge points into the turbine housing?

Thanks for any ideas or advice
I'm gonna start racing the car a bit again to dial in traction and what not while I'm gathering parts and fabricating!

Kev

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Sounds great, Kev. I am not sure I can help with primary size, except to say that 1 5/8" is already above the cross-sectional area of the exh port, so it may not matter? I would look at "Maximum Boost" by Corky Bell, or more recent references to see what they say. I doubt any velocity drop will matter in the turbo piping before the turbo, and the turbo provides a huge restriction/pump anyway. Worth a shot.

Have fun!

Lou

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Home of Slant6-powered fun machines since 1988

Are you going to keep the current stud attachment to the head? I've been looking at the flanges sold by Aaron Aames and thinking a lot about what could be done with that.

Any pics or drawings of your pieces?

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Brooks

'72 Dart Swinger
'71 Plymouth 'Cuda

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Kev,

The intake/exhaust gasket you just got from me can also be used as a porting template for your head. The exhaust ports in the gasket are the same cross section as an 1-1/2" header tube. I did this purposely so that there would not be any restriction when using my header flanges, and the tubes will be the same as the port size when you shape and install the header tube into it. No other header flanges are designed like this, so you usually end up with a header tube/shape smaller than the exhaust port which is not good for performance.

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There's no such thing as too much cam....only not enough engine!

I put the gasket on the current setup and my head is already the same as your gasket I ported the head a few years ago when I first built this engine so it all looks great.

Basically I'm just debating on the pipe size because it's one of those things if I'm building a fancy new header with some redesigns why not increase the pipe size unless it will affect me negatively lol

The current header seems to do just fine on 19psi and make good power but I always like improving if I'm making changes so with the additions of merge collectors I'll be making I figured I might step up the primary size. What do you guys think about leaving it stainless or should I get this one ceramic coated also hmmm.

I planned on keeping the studs for mounting I don't mind them. There are flanges for a bolt setup? I've done some reading Lou on those materials I'll have to re visit those and refresh my memory about the exhaust stuff.

Kev

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It doesn't really benefit you to have a header tube that is larger than the port size. You might experiment with a step header design starting out with an 1-5/8" and merging into an 1-1/2" tube 6 to 8 inches out from the head. But running an 1-5/8" all the way to the collector with the port opening no larger that it is will kill a lot of torque and HP. The port is the restriction, not the header tube, unless its smaller than the port opening.

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There's no such thing as too much cam....only not enough engine!

I run an 1 5/8 primary header tube and have no issues with loss of power or TQ. I found the 1 5/8 tubes work very nicely with the flanges that were available when I built my header.

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11.02 @ 120.56
http://www.youtube.com/watch?v=EAxRmoDgsdY
Chassis dyno
http://www.youtube.com/watch?v=wd6hFGzLJMc

I've been doing some reading seems like as long as the port isn't shrouded primary size doesn't matter to much. The general concesus seems to be too big will slow air speed and spool down but too small like less than port size will hurt top end so sounds like 1 5/8 is perfect with my ported head current header has always worked well power wise so I guess I don't need to reinvent the wheel I'll still with the same size as my current header but I am gonna smooth out the design and use merge collectors this time.

Kev

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