1999 SS

iTrader: (3)

two summers ago i upgraded my entire exhaust system and that included going from 3" header back to a 4" setup. after talking to some members here i think i might be loosing power by having such a big single exhaust setup with a stock cube motor (full bolt ons, H/C). supposedly im loosing velocity with the bigger tubing and thats costing me hp.

my question is; if the big 4" straight pipe was reduced to 3" or 3.5" from the headers than connected back to the 4" tubing before the muffler would that be enough to increase velocity and pick up the horse power i might be supposedly leaving on the table?

the reason i say supposedly is because i havent gotten a 100% for sure answer that my 4" set up is costing me hp (my car dynoes low for all the mods it has) other than one persons claim that he regained alot of hp and tq by swapping in his old exhaust set up after have his 4" set up removed.

what do you guys think

02NBMWS6

iTrader: (22)

I don't think the 4" exhaust is costing you anything. On the contrary, i bet it flows damn good, just make sure you have a nice flowing muffler in it. I don't think with our EFI motors we need to worry too much about losing "backpressure" beyond the header's primary's size

SuperSport01LS6

iTrader: (3)

Well im in the same boat but i actually just got in my True dual setup. So thats going in soon. I have the X4 cam full bolt on, 02 ls1 and only put down 387whp. People with simular setup are dynoing at over 400 whp. but they have 3" exhaust.. for example on my buddies lt1 383 car. he had the mufflex 4" just like mine. dynoed his car put down 416 hp. That same day we built a true dual setup and redynoed and he put down 435 whp. the 4"is a killer as far as hp. sounds damn good though!

02NBMWS6

iTrader: (22)

I think that that gain probably had more to do with the muffler in his previous 4" system or the benefits from scavenging added by the new duals. It makes no sense to think that the exhaust is costing power because it's too big. Otherwise, the duals would make even less power then by your theory since they have more overall volume

02NBMWS6

iTrader: (22)

what is your setup 99 SS? Maybe you have another power killer that's casuing your car to dyno low

SuperSport01LS6

iTrader: (3)

Well its true about velocity and how there isnt any in the 4". Im sure that there is a lot of turbulence in a 4" pipe and still is unnecessary. Granted the Spintec muffler is one of the worst designed mufflers out there for flow. I truely believe that a 4" does not do its job until after 7000rpm. Im sure it would rock on a turbo car but as far as N/A 346's I believe that a true dual 2.5 Is the perfect setup as far as making power goes. But everyone has there own POV

02NBMWS6

iTrader: (22)

I agree about the 2.5 TD statement, but a 4" exhaust shouldnt COST you anything. It hsould be virtually the same as having no exhaust, it has so much volume that there is no velocity right? You wouldnt expect to lose power going open header would you?

SuperSport01LS6

iTrader: (3)

Well that is depending on the setup! Cam specs, header size, etc etc. I've personally seen running open header. The car made crap worth of power until it cam up to 4800 rpm. From then on it was insane. yet a turd down low. Its like putting 1.75 primary headers on a completely stock car. very unnecessary. Its all in the setup really what works on ones car might not work on another. For my setup 4" is not the way to go. Thats why I'm putting on true duals.

1999 SS

iTrader: (3)

it sounds like you and i have a similar situation. with all the work i have done to my car and i only dynoed at 385rwhp. i have a stock cube 99 ls1, with a futral f14 cam, ewp, fast 90mm, nw90mm tb, 85mm maf, k&n fipk with ram air mod, pulley, 36lb injectors, qtp race headers, custom y pipe, 4" exhaust, and 241 casting heads that have been ported and with bigger valves and springs.

when i switched from a comp cams 230 232 to the f14 and added the ewp, replaced the headers with the current qtp race headers with merge collector, and went from the 3" to 4" exhaust i only gained a totall of 10 hp. i was totally pissed and the installer and tuner were baffled as to why its dynoed so low. the cylinders hold good pressure, the motor doesnt burn oil, and the af ratio is dead on, so now i dont know what else to do so im chasing around the small thing like i plan on putting new aftermarket heads and rocker arms, installing better lifters small stuff like that.

Kalgorn

iTrader: (6)

Way overkill. I don't have any technical data to back it but I will use my buddy's '02 Z28 as an example.

With an SLP lid, free mods, and Pacesetter headers to an offroad y-pipe; no exhaust past y-pipe. Dyno tuned, he made 369hp/376tq.

Over a month ago, we installed a TR233/239 112 LSA cam, patriot dual springs, ported LS6 oil pump, and LS2 timing chain. Right before his most recent dyno tune, he had a true dual 3" exhaust fabbed up. One side over axle, one side under. No muffler, just straight mandrel bent pipes. Fully tuned, he dynoed 412hp but only 361tq.

That should tell you something. Unless someone wants to explain to me how that's possible.

Hilton

iTrader: (36)

"...true dual 3" exhaust fabbed up. One side over axle, one side under..."

I'd like to see a picture of this frankenstein exhaust.

Kalgorn

iTrader: (6)

It's disgusting, that's all I can tell you until he gets some pictures. I absolutely hate it. I'm not sure who fabbed it up... someone in NJ, but it doesn't look like a very good job. I would think the guy could have tucked things up a little better but he didn't. It sounds absolutely mean even at all RPMs but it just doesn't look right. The under-axle side drags when you hit bumps if you put 2 or more people in the car. Put 4 people in and there's probably sparks the whole time.

He's looking into slapping 2 mufflers on to give him a little backpressure to gain some of that torque back. He might lose some of the upper HP but at least he can get that low end torque back.

I'll see if he can snap some pictures of it.

Kalgorn

iTrader: (6)

Here's a picture of the rear of this car:



Here's the video of the dyno tune after the cam swap: http://www.youtube.com/watch?v=SdacDLcjrtM

mOtOrHeAd MiKe

iTrader: (8)

Here is your simple answer (nominal dimensions):

a) 4" Single: Area = 12.57sq/in
b) Dual 3": Area = 14.14sq/in

Keep in mind that as exhaust gas travels down the pipe away from the exhaust valve the density of the gases increases as it cools, reducing the need for pipe diameter. However, this is unrealistic from an aesthetics point of view. That and building a fully tuned exhaust system is time consuming and expensive.

You are not seeing a loss in performance due to excessive flow. I run dual 3" on my MCSS and a single 4" on my Turbo Buick with no ill effects.

Enough said.