Cuz your um.... Cough... Supercharged!! Lucky guy. The LS engines love long tubes and big 3" exhausts. I know for a fact even if you change our exhaust from 2.25 to 2.5" you will lose alot of bottom end power. Thus making our cars very weak to exhaust mods.

 

I am dying to find out if these cars lose torque when going from 2.25 to 2.5 and I am going to find out for once and for all. I dont think the TQ will decrease per say, but instead will move over in terms of where it starts in the RPM range and I do think there will be an increase in the TQ overall.
I am going to dyno my 01' 430 this weekend and am going to dyno it again after my mods have been installed.

Im keeping 2 primary cats, ditching the 3rd and putting on an X-PIPE and 2.5 piping all the way back into some highflow mufflers. Im also picking up an Injen short ram tonight. I will have full dyno numbers for everyone to check out.
Only time will tell...stay tuned

 

Back pressure is not really wanted in any case. If you increase the diameter of the exhaust piping, you're increasing the back pressure. You lose power down low with the larger piping because of the increased back pressure which ultimately leads to lower exhaust gas velocity. You want the gas to get away from the engine as fast as possible otherwise the ports will be pressurized by the pulsing back pressure which hurts air flow.

 

The longer the duration of the camshaft the more important long tube headers become as they help keep cross cylinder contamination down during the longer valve overlap. Our engines have next to no valve overlap so some of that is lost.

I would be very surprised if long tubes made much more usable power than the S&S shorties. My main concern in the design was minimal or no low to mid RPM loss and in fact they actually enhanced power in this range.

Backpressure is BAD for power at any RPM (except for some oddities not worth this discussion). If the pipe has the capacity to flow all of the peak RPM exhaust with minimal back pressure there is almost nothing to be gained at peak power by going larger in diameter. All that happens is velocity is reduced and this is not helpful at anything below peak flow.

The stock design does a nice job of creating a "one way valve" with the manifolds, catalysts and Y pipe. The high pressure flows out but the reversion wave is blocked. Bigger pipes allow more of the reversion to get back to the exhaust valve/port creating more backpressure at this critical point.

The stock manifolds are restrictive and that is why the S&S produced more power and torque. They work WITH the stock catalyst and Y pipe and keep that "one way valve" effect working while allowing more flow at all RPMs. By directing flow away from the ports some scavenging seems to be occuring even at low to mid RPMs. Scavenging works like siphoning where one ports high flow can pull some vacuum on another port.

I have yet to see conclusive evidence of an aftermarket X, H or Y pipe making a better power CURVE than stock. I believe the stock can be improved upon but is is NOT simply a function of larger pipe. The stock pipe works surprisingly well.

Long tube headers IMO are a poor choice for this application from a packaging, catalyst and gain vs. pain perspective.

 

Well I have made this claim, that, I lost low end tq when I put on my S&S headers. Me & jbrady have talked b4 about this. The only difference that we have come up with is that Im running 2.25 mandrel bent with a custom made X pipe & not the stock Y pipe. Look @ my dyno #'s in my sig & you can tell. Now granted I added the 430 block, but that should have made more TQ. The difference is 31hp & only 10lbs of TQ.

 

i am the guy who let Paul use my car to prototype the PPE headers for. Paul did a before and after dyno run, my car is a stock 01 ls430. and it had 223ish stock, and 246ish hp with the headers. i am very pleased with the results. the car is noticeably peppier. i am extremely happy with the headers

 

Wow 23whp!! Not bad. If im not mistaken S&S gained 19whp over stock? So thats a little improvement there. I wonder if theres more gains to be had on a modded car? This is great news.

 

azcamber, were you able to keep the OEM catalytic converters? Any modification to the O2 sensor wiring?

 

the factory catalytic converters are still in place and as far as i know there was not any modification to the O2 sensor wiring. i wish i could tell you more but PPE installed these. i have not had it in the air to look at it yet to see if the wiring is modified, but i dont think it is.

also on a side note the torque went from 203 to 223 with these headers

 

if ppe wants to get #'s on a boosted car...I'm game I've got the one and only JPI set...need to get rid of it just cause that shop leaves a bad memory in my head.....

 

i would imagine that if a stock ls430 will show 10% increase in power at the wheels than your boosted car would benefit greatly. even at 10% that should be about 40hp in your case, but it should be more since it has help shoving air into it.

 

This as sounds great. Hope to see a dyno sheet posted soon. Hope to see these go into production.

 

sorry i was off on one hp. i don't have a scanner so please forgive the sub-par picture but here is the dyno sheet

 

Wow look at that torque curve. These headers are the real deal. They gained torque through the whole rpm range.

 

The graph only shows from 4.25K rpm and up. It's roughly 2,000 rpm worth of data. Would be interesting to see how it performs down low, which is where I spend most of my time