LS7 exhaust

[wtfx100]

What are people doing 3 inch into a single 4? Or dual 3.5? Having problems clearancing the samberg diff mount.
Does such a flow chart diameter for hp exist for oval exhaust?
https://m.roadkillcustoms.com/determine-proper-exhaust-tubing-size/

[MPbdy]

You won't fit dual 3.5".  They sell oval exhaust with a nominal rating equivalent to a round tube for flow area.

I made ~530 whp with dual 2.5" and a 402" engine.

I'm going to run my ls7 first with the dual 2.5" and see how bad it is.  I'd guess it leaves 10-20hp on the table which might be ok.

What are the specs on the LS7?

[Exidous]

Dual 2.5" is heavy. I honestly didn't like how it sounded. I also had issues with drone at 2000rpm.
Now I run dual 3" into a vibrant merge to 3.5" single with a Varex muffler and couldn't be happier.
Dual 2.5" is about the same internal area as single 3.5".

I'm running a 440 LS7.

[wtfx100]

Mine is a 12:1 comp built heads/cam motor from Mark Corbetts. He told me it was good for 700 whp but might have been fwp

I'm running a 4 inch varex muffler so it will be quiet as stock when i want it to be. No worries about drone.

[Exidous]

You can try to fit single 4" but you may need to oval some spots. 3.5" after the merge fits nicely.

[MPbdy]

You'll find more rotary guys trying to fit 4" single exhaust if you start searching around rx7 club.  I can't imagine how it could possibly fit with any kind of reasonable ground clearance.  I'm not sure the juice from 4" exhaust is worth the squeeze even with a 427 unless it is a track car and you won't have to deal with normal roads.  Dual 3" would be easier to fit, but you'll still be scraping it imo.  My dual 2.5" is tucked extra tight compared to other FD exhaust I've seen and still scrapes.  Exidous is right too dual exhaust is heavy as shit (sounds good though). 

I'd love to see someone do an oval exhaust it is just so damn expensive.

[shainiac]

I have an FC instead of an FD, but FWIW I made over 700whp through a single 3.5" muffler and dual resonators. There's a pretty big gain to be had from 3" to 3.5", but smaller gains from 3.5" to 4". I also did a short oval section where the exhaust goes under the subframe, which saves about an inch of ground clearance. I have a couple scrapes on the rear v-band flange, but I don't think the actual exhaust has ever touched pavement.

[Cobranut]

I have dual 3" with an X-pipe, 2 Dynomax Race Bullet mufflers and 2 Dynomax Ultraflows out back.  It is pretty heavy, but sounds and flows good.
The only part that scrapes is one of the bullets near where it goes under the rear subframe.

[gnx7]

I ran dual 3" on my first FD and it was heavy as hell... plus loud like.... crazy loud.

Next build I ran dual 3" into a single 3.5" and it is IMO a better setup.  We have run something similar to this on a 440ci LS with TFS 235 heads making 595rwhp all motor with what seemed to be very little restriction.  I run high flow cats as I hate the smell otherwise.

[wtfx100]

I'd like to go oval but the part that sucks will be having to go back to round for any connectors/flanges.

[cholmes]

gnx7, what brand of cats did you use? I want to run cats on mine as well.

About exhaust size: an Engine Masters episode comparing crush bent vs mandrel bent 2.5" dual exhaust on a 530 hp (crank) LS (think it was an LS3?) was surprising. The exhaust was long, like station wagon long, with an h-pipe, and bent to go over a stick rear axle, so 90* up to 180* back down to 90* out the back.

Even the crush bent 2.5" exhaust cost virtually no power from open headers, and the mandrel bent was no better! We are talking ugly crush bends, too. The hosts, Dave Frieburger, Steve Dulcich, and Steve Brule were really surprised.

Also, the difference between no mufflers and straight-through 2.5" Magaflow muffers was nil.

[Cobranut]

gnx7, what brand of cats did you use? I want to run cats on mine as well.

About exhaust size: an Engine Masters episode comparing crush bent vs mandrel bent 2.5" dual exhaust on a 530 hp (crank) LS (think it was an LS3?) was surprising. The exhaust was long, like station wagon long, with an h-pipe, and bent to go over a stick rear axle, so 90* up to 180* back down to 90* out the back.

Even the crush bent 2.5" exhaust cost virtually no power from open headers, and the mandrel bent was no better! We are talking ugly crush bends, too. The hosts, Dave Frieburger, Steve Dulcich, and Steve Brule were really surprised.

Also, the difference between no mufflers and straight-through 2.5" Magaflow muffers was nil.

That's really surprising.
The 3" duals on my FD are swept upward at the rear, and the sheer volume of exhaust standing behind the car at idle is pretty large.  I can only imagine what it would be like under full power. 

[gnx7]

gnx7, what brand of cats did you use? I want to run cats on mine as well.

These are Random Technology high flow cats.  Just about any 100 cell or 200 cell cat will be fine.  Magnaflow makes a whole bunch of options

[cholmes]

Good to know, thanks.

[Exidous]

The 100 cell will still flow well enough, kill the stink and pass almost any sniffer.