A little comparison from the past.
My old V8 a 351ci Ford Clevland V8 at a modest 375hp had 1.75" down tubes into 2.75" collectors.
That's 5,735cc's / 8 = 717cc per cylinder
vs 3,500cc's / 6 = 583cc's per cylinder

Old technology low on HP at 9.0:1 c/r but I'd say those seem large for the same RPM range. If they were kinked up with bends, bends drop velocity and heat. A good system has less bends, proper volume, and a slight reduction past the axle which helps retain heat and increase velocity. And they sound good.

 

@PPEHeaders

Can you confirm the IS350 vs IS250 primary tube size? Is this an option? And if so, what are the actual sizes of each?

And more important, can anyone post the the full dyno pull on the 350 headers on a 350, we need to see what happens to the mid-range! If you loose the mid-range punch into the 5k zone I might opt for other choices.

Please show a comparison of the two as WOT is not everything on a DD.

Thanks!

 

^^^^IIRC the PPE Headers primary tubes are 1.75" for the IS350 and 1.63" fir the IS250.

Lou

 

See my sig! Though the graph lines are thicker than I would have hoped, the key on the graphs are that they're consistent and linear.

 

2013 ISF with PPE headers installed in 2014, It is a tight install, but they sound great and definitely increased the power.

 

None of this seems convincing...does the manufacturer have before and after dyno charts?

 

Sorry your nor convinced. But maybe if you would take the initiative and visit PPE's site, you might see for yourself. Or, maybe your just not a candidate for a set

Lou

 

 

See my sig for a post-PPE header install dyno chart. IS350 with over 110k miles. Only other "performance" mod is a Fujita intake. The proof is out there!!!

 

PPE finally wrote back - DickH and Flowrider have the correct OD/ID for the 250 vs 350.
250 = 1-5/8" OD 1.5" ID
350 = 1-3/4" OD 1.625" ID
16 gauge walls subtract 0.125"

If I ever go down this path, it'll get the 250 headers.

Anyone ever measure the OEM flange at the head?

 

Would there be any issues pairing the ppe header with the invidia midpipe on a 250?

 

Nope.

10 char

 

Well I have put my money where my mouth is and have paid for a second set of headers to be made with 1 5/8" primaries and a flange to mate up to a 2.5" mid pipe. I currently have a dual 2.25" exhaust setup on my car and have stuff on the way to switch over to 2.5". I will do some before/after testing when switching over to 2.5" exhaust before the new headers and then use that to compare against the new headers. I am hoping to determine if there are any restrictions past the headers that will show as top end gains with the 2.5" exhaust before trying the headers. With the smaller headers, I expect to see improvements in the mid range with high hopes that I don't lose anything up top.

 

Build as in 250 primary size but w/ larger collectors?
i.e. 1.50" ID primary?

And what shall you do w/ your old headers! Haha! Hint hint... but we both know they are too big!

 

Yes, I suppose they are IS250 headers with a larger collector. After I receive them I am going to send them out to get ceramic coated, hopefully the quality of these will be better than the last set. I might sell my old headers, might keep them... I guess it depends on what, if any differences I see in going with the smaller headers.