MadMaxSC400

Most of the problems I've had with the Lexus exhaust is the dumb design from the cat to the end of the mufflers. No real thought went into it at all. But, I'd like to quiet my car down without losing power (if the exhaust is wide open it's not as fast anyway)- so does anyone know what those things are like inside, or do you know any specifics or comparisons about restrictiveness?

007lexus

hey madmax,

what have you done to your exhaust? what makes you say if the exhaust is wide open its not as fast??

007

MadMaxSC400

If the exhaust is wide open torque seems to suffer. Also, it doesn't make any difference on the top end.

awj

Off the line - due to a loss of backpressure causing a reduction in torque.

SupraCoup3

I may be posting what you already know... but here's Pete's tech stuff about the backpressure on every single part of the SC400 exaust. The rear is a real killer.

http://www.users.bigpond.com/pgscott...asurements.htm

MadMaxSC400

That's what I thought.. the middle section is what builds pressure, and I've put in a better flowing cat too. I'm going to polish up my old mufflers and have them re-installed.

SupraCoup3

what about replacing the rear mufflers?
http://www.users.bigpond.com/pgscott...ar_Muffler.htm

They're a big blockage, and putting some new ones on proably would help out some...

dumdumgreg

iTrader: (5)

hey im kinda new to this... i just got myself a sc400...
i was interested in your guys convo...
i was wondering... so your sayin if you upgrade the catback you'll lose power or gain power?
i kinda thought you guys were saying you would lose power due to the pressure?
also what is a good mod to the exhuast to gain a lot of power?

thanks
greg
aim - dumdumgreg
aol email - ax568@aol.com

SupraCoup3

from the info on that guy's site I posted, you'll gain HP. Changing the rear mufflers alone results in a great deacrease in backpressure shown from the graph.

The risk of no back pressure is like having no exaust moving in the pipes, and then having the new exaust have to push the exaust sitting in the pipes out... this results in loss of HP...

I'm sure somone will correct me somewhere, but that's the rough idea. A little back pressure -- good. Ooodles -- BAD.


John

MadMaxSC400

Supra, doesn't the first thing you posted there indicate that removal of the muffler results in minimal pressure reduction?

lex400sc

I've removed my rear mufflers to observe it's effect. It's extremely loud and resonant and sluggish off the line.

Giro

The JDM versions have a more restrictive exhaust than the US versions. The US version has no problem flowing the exhaust gases.

SupraCoup3

if you look in the graph, it shows that the 3 in pipe has the shortest graph -- it flows the easiest. The Rear Muffler Section flows with the highest amount of resistance out of any part of the exaust. Peter (UZZ31 ?) tested every single part of his Soarer's exaust peice by piece and found that the rear section & the middle section were the most restrictive parts.

Giro, I may be wrong, but I've had my car up on ramps and the exaust looks virtually identical to Peter's Active Suspension Soarer in stock form. (He's got an X-Pipe on there now w/ his BFI & Loves it!)

"97% improvement in back pressure for $179 AUD. That's the Lukey Ultra Flo stainless steel double off-set straight through muffler. I tested one last night and it looks the business"
(Lukey is the same as Dyno Max.)

Here's a pic from Pete's site... stock exaust for his car (same as mine)

SupraCoup3

here's his exaust now...

SupraCoup3

in simplier terms... the higher the graph, the more restrictive the exaust part. (Lower numbers are better)

John