Here is the best way to explain why it would not lean out if it was tuned correctly, when it is open you will just be in different cells and under normal exhaust then it well be in the normal cells.

This is why after tuning for the earlier boost there is no need in the computer knowing when the exhaust dump is open or closed

 

It could still lean out even if the tune was correct as the volumetric efficiency of the engine will change with the amount of exhaust restriction.

I really noticed this tuning with or without the tip silencer on my 3 1/2" exhaust. Had to tune it LOUD and then end up running rich all the time with the silencer in...

 

This thread has aids until we get videos!

 

i agree with iceman!

 

i think better exhaust systems should be an important issue.

as to the tune w or without a restrictor, i agree w post 27 that boost will build faster placing you in a different series of cells. i also agree w post 28 that the volumetric efficiency will change w differing backpressure.

my view is that you build the super exhaust, which will be too loud, and then design something to take the edge off it which could be easily adjusted. the key being it would not choke it down much, just enough to slide by the PO-leese.

maybe the butterfly/chokeplate in the system w a bunch of holes drilled in the plate. lots and lots of holes. the system would differ from a cutout as it would not redirect the exhaust to the open atmosphere, just contrict it a very small amount if set in the "closed" position.

hc

 

Yeah, years ago I saw a write up on a Mitsubishi with a "cut out" style butterfly valve just inline with a huge 4" or 5" exhaust.

He one decent hole near the middle of the plate for enough flow to cruise around with.

 

I'm sorry, but I've been busy working and lending Gotham a second hand in helping them with their 20b project. I'll post it up when steve tunes the car

 

any update on a sound clip really interested
z

 

I never replied to this thread because i forgot about it. I finished my 4in-2X2.5in exhaust with two Metallic Cats, then a X-Flow Muffler, It is REALLY quiet and flows better then my old 3in

 

 

where did you get the metallic cats? still waiting on that sound clip

 

i still think a cut out would be better and cheaper..

think about it. 4" dp to 4" cut out then leave the cat and rest of the exhaust stock.
A good smart owner should know not to go more than 1/4 to 1/2 throttle with the cutout closed.

But everyone knows open dp's make the best HP.

SO why wouldnt you want to make the best hp you possibly could have and also have the most quiet 400+ hp 7 on the road?

 

Rx7_Nut13B sorry but i was hoping to hear from the OP(onefast93RX7) on his exhaust but thats nice you got what you wanted out of your setup too.

z