I think u can do all the math u like but ull never know for sure til its tried. I'd guess there wud be a gain, but not enuf $/hp to warrant the cost of making the change for real world dd. I have 1 7/8" now, but honestly, I think the cash I spent for custom true dual wuda been better spent elsewhere like porting my heads or finding more ways to cool the charge and bump boost into lo single digits. I always equate it to how much extra rwhp per $ spent. Once u get past the easy big gains and searching for tenths, its time to just bump up the cubes. I'm at the 'bump boost to lo single digits' stage now that I've coled my IATs - after this if I'm not @ 600rwhp with a port job, I'll either be happy with it or go Turbo or 408. R/

 

IMHO, you need to look at your primary use of your truck to determine which way to go. SC/Turbo's like Headers and the bigger they are and the better the tuning the more HP/TQ they make. However, peak hp is not always the answer.

In a Tow vehicle your primary rpm range is 1500-2500 rpm, with occasional hits to 4500 rpm. Your fueling, advance, PE, etc should be optimized for that rpm range as well as your trans settings. Headers in the 1 5/8" and 2.5" collectors and free flowing exhaust work very well.

For drag racing and active street driving, the upper rpm range becomes more important, WOT settings, shift points, etc should be optimized and the 1 7/8" and 3" merge collectors with cut-outs (for those who want it quieter on the street) or free flowing exhaust would be the choice.

 

How much of your motoring day is spent under full boost? If you're after max power under full boost, I don't think there's much debate. Bigger is better when you're trying to evacuate 500hp worth of spent gasses. I'd bet the only time the bigger would be better is at WOT and 4000 rpm up. Otherwise, you'd be fine, possibly better off, with the smaller tubes.

 

I don't want to confuse your decision anymore but your forgetting:

1 3/4" primary, 2.5" collector (Dynatech)
1 3/4" primary, 3" collector (Stainless Works)

Also where are you finding 1 5/8" primary long tube headers with 3" collectors. Same with the 1 7/8" primary header. I know American Racing has some in the works, but as far as I know they are currently unavailable.

 

both of my options are unavailable until the 1st qtr '09 and if I'm not mistaken, stainless works have 2.5" colectors and y-pipes, If they were 3" my search would be over.

 

I've ordered a few sets from Stainless Works with 3" collectors. They may not be on their website, you might have to call.

 

Aha, good to know, thanks

 

They have a couple different styles of 3" collectors...The ones they use on their truck headers aren't as nice as the ones they use for cars and the Trailblazer SS.

 

Pacesetter has a set of long tubes with 1.75 primaries and 3" collectors. PN 61C341. I have them on my truck and they've been trouble free for about 40K miles.

 

I'm stuck on stainless, thank