Expected boost drop going to 2" LT
 

I had installed shorty header and high flow cats back before any plans of super charging. After installing my v-3 with a 3.33 pully I knew it was only a matter of time before the cats went just curious about how much boost I'd expect to drop? I was right at 10 at 6500

I would say maybe 1psi

Thanks

had exact set up...I'd bet if you are seeing 10psi with cats on a 3.33 you have an intake restriction. So, put the 2" headers on and drop 1-2, but put an ECS filter on the head unit and pick up just about that. Should keep you around 10psi. ECS or FSP can sell you the filter.

don't do 2" headers with 10psi! stick with the 1 7/8

^ explain why

because at this power level a 1 7/8 primary is not at all a restriction, you would want to increase the pipe diameter until the primaries are not a restriction, yet stay as small as possible to keep exhaust gas velocity as high as possible and as a result make the most average power.

The ballpark to when you should move to 2" is about 800rwhp

Yep cars going from dd to track only over the next year just figured I'd go for the 2" now

We have found No downside to the 2 inch headers on a ls3..The heads flow over 300cfm stock.If we can help you with your headers give us a call.

okay so you're saying there was no disadvantage to switching to 2" primaries, BUT was there any advantage? If you haven't lost low-end torque to gain some top-end HP, then the only way it would seem to make sense is if the 1 7/8's were actually a restriction.

I saw people gain hp switching from 1 7/8 to 1 3/4 on LS7's go figure.

http://ls1tech.com/forums/generation...xperience.html

This is a SMALL example, do a search and you will find the answers you're looking for :)

1 7/8ths is plenty. At 650whp FI kooks 1 7/8ths headers only gained me 5%. No cats in either comparison.
Doing a heads cam build on my ls6 now targeting 450-470 whp (if it was an ls3 this combo would yield about 50-60whp more), keeping the 1.75 longtubes I have now for this.

What happens more time's than not is the customer always wants more.At some point they start wishing they would have went with the 2 inch.Since it isn't but a few hp either way we suggest the 2 inch.Is it going to be the best every single time in every instance well no but on average it is the best call.

I had 1 7/8" but recommend 2" for any FI now. No reason to upgrade later and I haven't seen any power/torque loss on a good set of them.

I don't know what happened with mine but have a Procharger making 6-6.5 psi and 480 rwhp (no special tune, all stock other than cat back). After installing headers (no tune) I lost 3-3.5 psi and no one knows why I lost so much it wasn't common.