It is well known that the JDM downpipes are "crimped" vs the American made ones that are flow through.

It has been argued that the crimp offers a restriction greater than the more open American models.

It has also been argued the crimp converts non-laminar exhuast flow to laminar creating a better exit flow.

Yet, there is a member on this forum that just recently posted his dyno at 315hp with HKS dp, MP, HKS catback, blitz smic, koyo and pfc.

I also understand that the increase, given all else equal, of DP install is approx. 20hp.

The above member's numbers would argue for the crimp having a flow improvement intentions vs just meandering around the steering column. Any feedback?

Oh yeah, search ***** stay the fxck off my thread! I have searched this matter only to see more search ***** saying the same thing. Several hundred post with "search" and irrelevant ramblings that should be in a chat room.

Most of the posts remained unresolved on this issue. I wonder because I am at a point where I can reinstall a new dp.

Thanks

 

I have the m2 without a crimp and it flows really well. With it, hi flow cat, apexi cb, and pettit ecu I ran 289rwhp. Which is better than his 266rwhp with similar mods. Both of us ran at 12psi so what can you pull from that? You could guess that the open m2 dp is better but there are a ton of factors that I could never realize that would affect these #s.

 

It makes sense in theory, but that is the problem.. it is a theory that needs to proven or disproven. The only real way to test this is on the same car, you would have to change only the DP and run the car multiple times with each setup and see the differences. The differences between two cars miles apart from each other means little to me really, who knows that else differed between the two?

 

I agree with mjw...more rigorous test data is necessary and I have not seen qualitative information on this matter isolating just the dp as the variable.

I do know from my studies through chemical engineering (fluid dynamics/Re=Reynold's Number)
that a funneling effect would increase flow velocity profile and convert the flow "eddies" (non-laminar) to a slipstream (laminar) with an increase in delta P (pressure drop or restriction). This also depends on the orifice reduction, friction factor of the material and an endless amount of fluid variables.

But isn't some restriction good? Analogous to the HFC vs MP argument where the HFC dynos reveal low/midrange torque improvements at the compromise of high end HP gains?

Thanks for your feedback btw. We tell newbies to search and 1000 threads come up with little to nothing but more "search" and worthless info.

 

Definitely, some restriction is good. Not only for low end grunt, but for also helping out the wastegate.

Honestly, I doubt there is a signifigant difference in the crimped or non-crimped downpipes. However, I've been wrong before, and I'll be wrong again.

 

how does backpressure affect the wastegate operation?
is this something only related to internal wastegates?the reason i ask is because some people with external wategates vent them to atmosphere.

 

i still feel that the crimp increases hp by turning turbulent exhaust flow into more laminar flow. it is not a restricition as the exhaust manifold outlet is the limiting factor. the dp has to merge a square hole w/ 3" diametere tubing, and the crimp acts as a funnel to where these two different shapes converge. the bottom line is it's just personal opinion, but i believe the japanese companies put it there for a reason. i'm sure it's not for space constraints, because they can bend the piping any way they want around the engine bay. the one thing i know is that japanese companies put more money into r&d'ing their products than american companies do. even a lot of their body kits go through wind tunnels for aerodynamic testing, american companies like wings west don't do this. imo, through the course of their research they found that the crimp increases hp.

 

Well, just a thought... If the design purpose of the crimp was for flow improvements, than it would have to be designed for a inlet fixed flowrate (cfm) else the pressure differential, friction factors and gas compressibilty limitations would become counterproductive. I say this because some of the single guys running "plaid" CFMs suspect they have breached the design flow limitations of their respective JDM DPs. There was a thread on this but with no final results.

 

With backpressure you are less likely to overboost. Without any restriction then the wastegate has to be the only factor between getting enough gas around the turbo and you not blowing your motor

 

Most of the time (and it is most of the time, not all), it's subjects that have been discussed over and over again that get a 'search, dammit' response. ie. tranny conversion, 20b, etc. If you have a worthwhile subject that has not been discussed/discussed little (like this), then more then likely you will not have to worry about having the 'search' flag pulled.

Searching for 'crimp', 'downpipe', and 'laminar' turned up only one other thread besides this one:

https://www.rx7club.com/forum/showth...wnpipe+laminar

What might help for those searching (and I'm suggesting this to all of us, myself included) is to keep posts together in a single thread - as much as possible. Ex. posting your original question to the thread I found above.

Having various viewpoints/questions in the same thread makes it easier to navigate, and lead to meaningful discussion - as opposed to little threads here and there that just touch on the subject.

Not trying to pick on you, but it's obvious you have concerns on what goes on here - and I'm pretty sure we all (those that truly care) want this Forum to be an excellent resource.

 

oh, ok. I thought that he meant it in a performance, not safety respect.