I would do it in stages if you are not confident it will result in good gains/driveability. Go with some 100 cell metal primary cats.......then do the secondary.......then do..... You get the point.

 

Hey blackbenzz:

I have been running blown cars for almost 20 years now, and I can tell you with MANY backup references " There is NO such thing as too little back pressure for a supercharged engine" period. The easiest way to look at this is everytime your exhaust valve is off its seat, the engine/supercharger is trying to force the spent gases out. Unlike NA cars where scavenging takes place from the exhaust pulse wave. There is NO pulse for a FI car due to the pressurize intake track, hence there is NO reason to have ANY back pressure for your engine. By the way, Turbo cars fall under this same approach, but for them being exhaust driven instead of belt driven, it can lead to the dreaded turbo lag.

See yeah

PS: Just check out Kennebell, vortech, ATI, etc websites and they will confirm this.

 

What mods excl. nos exists to even get to 591 rwhp...doesn't seem attainable. He also trapped just 124.7 or so. I would think he would have trapped higher since cars with 480 whp trap 121-123mph.

 

Great info! Thanks! I knew about turbo cars but wasn't sure about blown ones.

 

not to argue this point because for the most part i agree...but open the exhaust on your e55 without making any other changes and you WILL feel a loss of low end tq.

 

So I will gain top end power AND stop breaking axles? Sweet! lol

 

and maybe not cut another 1.5x 60ft...

 

The times where I broke the axles it felt like it would cut 1.4x 60's 1.5x is not a problem The 11.0 run was only on a 1.62 60'!

 

Hey mikey:

Not to argue here myself, but I would really like to see a dyno that shows this loss I am only asking this because everything I have learned/been informed/and taught says otherwise my friend. On NA motors I couldn't agree more with you due to the scavenging effect mentioned above, but for FI motors

See yeah

PS: maybe one of the tuners here can chime in, as I am sure they have tried/experimented with this issue. VRP, LET, Anyone, Bueler Anyone

 

If you have too much flow, you compromise exhaust velocity. Too little flow will create back pressure or an exhaust that is too restrictive. There is a balance with an exhaust system even in a FI car.

Chiromikey is correct in the fact that too much flow can hurt the exhaust velocity thus causing a loss of power on the low end. You want to keep exhaust velocity and flow in mind when creating or doing exhaust modifications to any car.

 

Just get rid of the resonator...there will be no back pressure loss problem at all...just nice sound.

 

Again, please show me data to back this statement up for a FI car
I really am not looking for a pissing contest here, it just goes against everything that I have been taught, informed and have done in general practice with ALL my FI cars. Their sites, Kennebell, Vortech, ATI, etc states EXCACTLY what I am stating here.
As we have POSITIVE pressure in the combustion chamber at all times, how does the exhaust pulse ever reach back into the combustion chamber?
As I said above as soon as the exhaust valve lifts off its seat the spent gases from the combustion process push out, and once the intake valve starts to move during the cams overlap cycle, the positive pressure from the blower further facilitates this movement. Hence there NEVER is this scavenging wave that NA cars see from the exhaust system.


Oh well, FYI.

See yeah

PS: If there was a need for ANY backpressure on a FI car, why don't ANY of the racing bodies do it? AKA Cart, Drag racers, SCCA, IMSA, etc

 

Did we ever figure out what Nate's car has done to it to get 591rwhp. Thats not normal w/o NOS.

 

like i said, i agree with you for the most part (turbos). backpressure does affect low rpm tq on our s/c cars in street applications. none of the racing bodies have a concern because none of their motors operate in low rpms...unlike our cars that are almost always in the lower rpm band and make full tq around 2k rpms. i'm only speaking from my own experience and i promise you will lose low end tq with the wrong exhaust on our cars. if anyone wants to pony up the costs of dyno time, i'll gladly provide the graphs afterwards.

...and i fully agree that the affect is not as significant as it is on n/a motors.

 

HP on a dyno means nothing without proving it on the track...a dyno technician can alter any results...I want to see if he does well at the track before I believe in his power output.

 

.

 

Nate ran an 11.05 at 124.7 if not mistaken.

 

He has the quickest 55 no nitrous pass to date. It is deifnitely making power Maybe that 591whp was with the nitrous, I dunno This is exactly why I dont have much faith in dyno's

 

why not isn't Jim's (JackPro) close to that?

 

Isn't his 11.05 enough proof?

 

My car is the same as it has been stated before, VR 675+ I have a ICE box aux heat exchanger setup, custom 3" exhaust and a few other custom pieces. No nitrous has ever been run on my car at the dyno or on the track....I dont think anyone would believe what it should do with it!!!!! I have since got a better tune, only pulled to 6,400 rpm on the 591rwhp and done a few other tweaks. I bet if i am on the chassis dyno again it would be well over 600+ now. All of my dyno's including this one posted are done on a newer model Mustang dyno too. You know what everyone says about there #'s too but I am not gonna speculate nor dispute the mustang #'s because my car backs up the numbers @ the track!!! BTW, last week I trapped 126+mph 3 passes in 1 day. All 11.0-11.1 None have beaten the 11.05 yet though so not worth osting about Best mph was 126.5, so I guess you got me beat for now.....this was in positive altitude too

 

nice job brother!!!

 

This is basic thermodynamics.

http://www.x-pipe.com/Scavenge.html

Each time that the cross sectional area of the exhaust system increases, exhaust gases are forced to expand to fill that new, large area. When gases expand they cool down, contract and become denser. Expanding/cooling gases slow down as their energy is lost. Each transition in size creates sonic shock waves that travel throughout the system, absorbing even more kinetic energy, slowing the exhaust gas flow further, in jerks.
FACTS:
1. As airflow expands into a greater cross sectional area pipe, it tends to cool down.
2. Exhaust airflow is driven by combustion chamber pressure, released into the exhaust when the exhaust valve opens. The potential energy in the combustion chamber (high pressure) is converted into kinetic energy (velocity, up to the speed of sound), when the exhaust valve is opened.
3. When the cross sectional area is increased in the header, velocity drops, see above.
4. When the exiting, high velocity, gases pull a vacuum, energy is converted from kinetic energy (velocity) into potential energy (scavenge: negative pressure), thereby slowing the exiting exhaust gases by absorbing some of their energy (velocity is reduced).
5. When a gas stream expands into a larger cross section pipe, it cools, due to that expansion.
6. The speed of sound in the exhaust gases is reduced each time that those gases expand and cool. (The velocity of the exhaust gases is limited to the speed of sound. When gases cool, they can not exceed that cooler, slower, speed of sound. They are forced to slow down, preventing exhaust gases from exiting at a higher velocity, creating back pressure.)
REASON:
There is no free lunch, even in a step header. The valve seat I.D. limits the rate of exhaust gas escape, because gas flow rates can not exceed the speed of sound. As exhaust gases enter the head pipe, they are forced to expand, cool, and slow down. With each increase of inside diameter of the exhaust system, the process is repeated. Even though the pipe is larger, the gases can not flowing faster. In fact, the gases slow down with each step. A larger diameter pipe has a greater circumference, and therefore greater surface area to allow exhaust gas heat to escape. The cooler the gas becomes, the more energy it loses from its velocity (thermal energy is lost, allowing the exhaust gases to contract, becoming denser and heavier) and the slower its speed of sound (maximum velocity) in those gases.

 

Okay, sir being an engineer, I am fully aware of the laws of thermodynamics, boyles gas law, etc, etc, and my favorite PV=NRT.

And YES everything above is true, although it is has a MUCH greater effect on NA engines. Please contact ANY Supercharger/Turbo Manufacturer and they will inform you that you will want to use the most free flowing exhaust system that you can run for best performance, PERIOD. Not one that is only 2.27" or 2.65" but the BEST LARGEST header, cross pipe, muffler and tailpipe my friend.

Okay, I am done on this one. Good luck to all

See yeah

PS: I guess NATE above is loosing all his power because of his 3" custom exhaust as he ONLY did 126 mph

 

If that were true, turbo Honda engine builders would have 3" primaries running into dual 5" exhaust plumbing. If you go too big, it hurts exhaust velocity. Once you slow exhaust velocity you create disturbances in the system and actually restrict flow. Bigger is not always better. You have to match the exhaust sytem with the power your engine is producing. Too small and you will lose power from backpressure and too large will cause losses from decreased velocity.

Bigger is not always better:
http://www.magnaflow.com/07techtips/faq/question10.asp
http://www.sandersonheaders.com/tech...ce_exhaust.php
http://www.dynomax.com/tech_support/exhaust_tech.html

Exhaust Design, Turbo and Naturally Aspirated:
http://www.cobbtuning.com/info/?ID=3222