Modifying shorty headers

[crazyman]

Hi all. I just recieved a new set of Pace Setter shorties for my 4x4 S-Blazer. Overall, for the price, I am impressed with the build quality. I have to do some cleanup work in the port area though. What I am not impressed with is the collectors. My question is this. If I cut off the stock collectors, clean up the merge, and weld on some pipe to effectively make these mid length headers, what size and length should I shoot for?

Stock 4.3 balance shaft block, CPI injection (early vortec), old school worked over 3.8 heads, worked over upper and lower intake manifolds with the runners shortened to approximately 7-8 inches from the valve, stock ECM, 3.42 ratio 8.5" f-body axle, and 1.5" primary tubes.

Right now I have the stock cam in it. When I do the spare block I have, I'll probably do 10-10.5:1 compression, the biggest cam I can run with the stock converter, and a JET stage 1 chip. Eventually I'd like to do the AWD swap.

I'm not building a drag racer, just a DD that will deliver potent acceleration with great mileage and torque.

[1989GTA]

According to Larry Meaux of PipeMax fame the length of the primary pipes is not the biggest hp gain regarding the exhaust system. From what you have said I think cleaning up the collector area will produce the biggest gains in your case.

Regarding where the 4 pipes meet do they form a +? If not you might want to weld a cone in that spot. They can be bought at Megs Exhaust Warehouse-Exhaust Systems, Exhaust Collectors, Components, Exhaust Conical, Mufflers, Exhaust Tips

As to the length that is hard to say without a lot of information. Here is what Larry says is the exhaust priorities for hp.

1. Collector length
2. Collector diameter
3. Primary pipe diameter(header)
4. Primary pipe length(header)

One last thing try to make sure that none of the header opening is covering up the exhuast port.

[crazyman]

It's a V6, so I have to make everything myself. From the looks of it, 2 1/2 would be easy to make work, 2 1/4 I would have to stretch some. All of the primaries are different lengths. Anywhere from 6" to 13" or so. Without software, intuition tells me that the 2 1/4 would deliver the goods I'm after. From what I've read of Mr. Vizard's articles, about 12 inches would suffice without test and tune. It's got to be better than that crappy merge that's on it.

[1989GTA]

Same company also makes a 3 pipe merge collector for your V-6.