Porsche-O-Phile

Were the cup car 4" exhausts all the way back or did they "step down"? I have to make a correction also; I just looked again at the LR 4" system and it steps UP to 4", not up and down again as I thought - I must've seen that on another system. This setup is actually pretty good from a flow standpoint as the wider pipe at the back creates a lower pressure area closer to the exhaust tip (more volume = lower pressure) and will tend to "suck" the flow along the length of the pipe from the higher pressure areas upstream. I believe this is the principle behind the "cone" pipes that are sometimes seen on motorcycles, some 911s and VW bugs.

RolexNJ

Porsche-O-Phile:

You have a good question there about the Cup Cars and the 4 in exhaust. I honestly dont know if they were a "full" 4 inch. I believe the article didnt go into it if I recall. Maybe if we are lucky, one of the fellow Rennlisters who have a Cup Car can see this and respond? We'll see.

Regarding the LR 4 inch. This is what they say, " This exhaust is made from aluminized coated steel exhaust tubing and grows along it's length from 3", to 3.5", to a full 4" in diameter. Formed with mandrel bends making it free flowing throughout without pinch points and collapsed tubing like the factory system. All tubes are CNC mandril bent in one piece with no seams or sectioning. Welding is limited to flanges and hanger brackets and where we go from 3.5" to 4"."

So I dont know how people keep saying LR is stating it is a "full 4 inch". They don't claim it to be, it's right there in black and white?

And yes, you are right that it does step up and would "suck the flow along the length of the pipe from the higher pressure areas upstream."

NZ951

News Flash: The source is in my post, if you cared to look.

NZ951

Yes Rob keeps calling it a 4" system when its not. You can equally call it a 3". As much piping is 3" as it is 4". Still no dyno numbers about the exhaust or pressure drop info. I think Mark hit the nail on the head with Rob's followings. He based the decision on the Cup car having a 4" yet he does not even know what sections were 4". And comments that I think the car was faster with 4" from a company selling the exhaust. Not the most convincing position! I am all for these products if they are PROVEN to actually improve performance... NO EVIDENCE of that yet however when the base figures were not known.

sweanders

I believe that the only Cup cars with 4" exhaust were the Escort Cup ones..

NZ951

Anders, was it a full 4"?

jc22

I find it intersting that some say you need to be making 400+horsepower to justify a 4" exhaust but Porsche put them on the cup cars with only ~300hp. Comments?

evil 944t

cup cars are 4" from just before where a cat would go all the way back

TonyG

>>>indsey Racing is building up Rob's 3.0 liter monster to try and get as much HP as they can at 15psi of boost. They seemed to be hitting a wall at 350 rwhp.<<<

I'd say they're hitting a wall if they're only at 350RWHP with a 3.0 (a "monster" 3.0 at that... which we could presume to be a highly modified 3.0L).

My 2.5L (modified) made 375RWHP at 15psi (with a 3" exhaust) and an 8V head with stock valve sizes.

TonyG

hosrom_951

Guys, with everyone mentioning the exhaust being 4" (even on cup cars) and as also mentioned it's the turbocharger hot side and downpipe are the MAIN issues.

Obviously, the bigger the hotside, the faster gases flow out, thus less back pressure, also increases lag right?

Now, did the CUP cars come with a FULL 4" exhaust system as in from downpipe to muffler? i doubt it unless they used a different turbocharger (note i do NOT know the details of the CUP car).

So in theory, if you have a 4" or even a 5" exhaust (assuming the actual exhaust starts from the testpipe first and NOT the downpipe) the backpressure would decrease only slightly or maybe even no increase at all since the turbocharger's hotside and downpipe are still 2.5" right?

evil 944t

read my post.
thx

NZ951

So whats your position on the 4" cat back new LR exhuast evil?

hosrom_951

Evil: I did but i didn't understand, that is why i mentioned in my post (sorry)

evil 944t

crap.


just kidding. I would'nt endorse something unless I tested it or have seen dyno charts.
I would have loved to test my 4" exhaust put I did to many changes at once. I still have the original exhaust though. I guess I could do a test when I install the new 2.8 but thats alot of work...

NZ951

Thats exactly why I dont trust the product, no dyno exact before and after and guesses at psi drops. Thats why I like Powerwerks approach, they are testing and video taping their mods! No more secret turbo crap or magic dust, pure facts and data to back it up. TonyG makes a good point, he is one of the few guys that has experience a truly highly tuned 2.5 (not just bolt-ons). If LR are hitting the wall at 350 on a "monster" 3.0 then I have even less confidence in their products. Heck even Daniel951 hit 350 in a 2.5 with a SFR stage 3 turbo.