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Discussion Starter #1
I'm designing headers for my 1985 Fiero 2.8 V6. Off the shelf headers tend to be shorties and not long runner. I want to do them right and at some point swap to the larger 3.4 block.

The engine is bored over .050, ported, with the stock GM HO cam with 1.6 roller rockers. The heads are ported and the intake is the Edelbrock with the Holley 4150.

The Fiero stock manifolds are poorly designed and although they are ported, and running into a mandrell bent 2.5" system with Magnaflow muffler, it could use improvement.

I've been reading up on headers, but there is a knowledge gap I can't seem to get by.

I need this car to do well on the street, so good response from 2000 rpm up to about 5000 is all I really need. The car currently pulls hard to 6000 and is putting out 132 hp at the wheels. I am trying to improve low end torque.

What I've read is that I need a primary length of 1.5" pipe somewhere between 28" and 36" to the collector. Does anybody know what works well on the 3.4? or better yet, the 2.8?

Thanks for the help

Arn
 

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Can't get it to work

Good thought. I've been trying to get on that website and no luck. It won't let me register or log in. Anybody who can help me on this?

Arn
 

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I would think a 1.5" primary tube size would be quite large for a cylinder that's only producing 25-30 hp. Pipemax looks for someting in the 1.25" range, about 47" long into a 2" x 26" collector. A 1-1/2" tube has 48% more area than a 1-1/4 " tube, which would result in a tremendous loss of velocity when you need it the most.
 

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Discussion Starter #5
pipe size

Thanks for the input,

Getting pipe sized under 1.5" is a real bear where I live. The engine's ports are 1.125" (1+1/8")wide and if I want to step the pipe at all, 1.25" pipe would not leave much of a step anyway. I can get 1.5" pipe no sweat, so it looks like 1.5 is what I'll have to use.

The cylinders are about 29 ci each, and using a 17% line loss on the dyno calculation, the engine should be producing about 155 hp, or 25-26 hp per cylinder at the flywheel.

The current hp is 130-132 from 4000 rpm to 5800 rpm, which is really flat. The torque on the v6 is peeking at 140 at the wheels from 3000 to 5000 rpm, which is also flat.

I'd like to lower my peak hp curve a bit, (cam timing) and raise my torque a bit.

The big question for me is the length of the primary runners using 1.5" pipe to get a the broadest torque and hp improvement for street application.

Any more suggestions?

Arn
 

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Discussion Starter #7
Thanks

Thanks for the links. They're bookmarked.

Here is another question regarding using 1&1/4. I don't think I have room for 47" primary length in the application. The engine bay is really tight. I think about all I can manage is 30-36" max. The collector at 2' is another challenge, but is ok for the right bank of cylinders, not sure about the left.

What does your program indicate for a 36" primary? That would make installation a whole lot easier.

Arn
 
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