IgoSlow

kinda doesn't make since on what you are saying.. why make a split to create more surface area? why not just make a single 4" dp... the split in the knightsports and mazdaspeed look to be around 1.5-2" givne them a total SA of a normal 3" or 4" DP thus under your theory would give htem equal surface area thus defeating the whole purpose of creating a split. I"m no thermodynmics professor but it would just seem more ideal that smaller surface area would flow air quicker. then one large pipe.. Takes more pressure to flow air through one large single pipe then it would two smaller pipes.. ???? not sure but it just seems that way. I guess the spit would provide a lil more back pressure for low end response... kinda like when i stick my silencer on i get more of low end response but taking it off it lags a lil more throught he bottom end.. i think i need to go back to school so i can further argue this hahahah...

GoRacer

iTrader: (2)

If I remember correctly, the Mazdaspeed version has two 2" or 2.5" pipes into one 3" pipe and not two 1.5" pipes (could be wrong though).

There is no such thing as a 4" down pipe (that I know of). Even with HKS 4" mid pipe, it would still connect to a smaller 3" down pipe. Border Racing offers a DP with their exaust as a kit (HKS doesn't) and I beleive it's 80mm (3.149"), the same as their Converter and cat back piping.

Most DP's are 3". I do not know if HKS is 2.5" but that's what Corksport claims. Theirs is 80mm like Border but without a squished end and their prototype sucks donkey weenies.

The 2-into-1 is the same design/principal (whatever) as street Headers 4-into-2-into-1 on a pistons suck engine . Better low and mid range power. The racing headers are 4-into-1 and are for high end rpm power.

Whoops, and I remember also the JDM models have clearance problems and the 2-into-1 design gets around that limitation allowing more air volume in less space.

fdracer

regardless of if a 4" dp is made or not, igoslow's point is that dividing the dp is not to increase surface area. it's to increase low end power, just like your header example.

ZeroBanger

Look at my sig. I have the HKS downpipe. My first mods were HKS DP, Highflow cat, HKS Catback, power FC and intercooler and intake. I ran this at the track ALOT.

I did the following mods:

New Injectors (1200 cc) HF fuel pump, Mid pipe. Guess what? I did not lose ANY low end torque, my times at the track are identical and I have the same trap speed.

I called shiv today and I was told the problem is my HKS downpipe. He said the crimp is a major restriction. He also said the european versions had the same crimp and the rx7's only had 236 HP VS the 255 In amerca. I dont know what to believe, but i'm going to replace it.

BTW..My car is not any more loud with the Midpipe as it was with the High flow cat. Also M boost holds steady with NO creep or spike like every one says. The DP is the ONLY thing I can think of. I am sure I am running rich too.

David

GoRacer

iTrader: (2)

That doesn't make any sense if you realize that both versions would have had a crimped pre-cat.
------------------------------------------------

As for a 4" DP, I don't see the advantage unless running 4" exhaust. There is also the problem of the pipe hanging too low and clearance issues with the turbo and that is one of the reasons for the split pipe.

ZeroBanger

I dunno, I will know when I replace it.

Slipspeed

M2 no longer polishes their pipes...bff..bwahaa...whew..

I just ordered one from the Store and bitched at Jason because the pipe I got wasn't polished (which made me think it was the mild steel piece). He told me that M2 isn't doing that anymore because it takes too much time.

LAracer

Hmm. Thanks for the info. Is there any real advantages to polishing, other than cosmetic? (It's not like anyone sees the dp anyway, right?). I think I'm gonna go with what's easy to install, and that seems like the M2, polished or not.

fdracer

hey lemme know if you wanna trade in the future when you change out your hks dp. there is a reason why all the jap tuners have this crimp. they can definitely route their dp's around any obstructions if need be. that bubble is there to transition the turbulent flow outta the turbos to laminar flow to evacuate the exhaust faster. if the turbo outlet were just a round 3" hole then i think a perfect 3" dp would be best. but the outlet is a small square and the dp has to mate to this then open up to a 3" diameter circle. the jap dp's help to shape the exhaust flow at this point, kinda like a funnel. maybe we should post a pic of the us and j-spec styles in the single turbo forum and see what the gurus say.

RX7SpiritR

iTrader: (1)

I got an M2 DP myself...Very nice unit I might add!

jkekeisen

HKS stainless downpipe regularly goes on sale for $199 and the fitment is perfect without removing the studs. BUT BEWARE mine may have been a one-off mistake but the bung was welded inward enough to prevent the O2 sensor from going in (the top of the O2 hit the turbo housing). They wouldn't take it back so I had to have the bung cut out, patched and moved!

Jim

GoRacer

iTrader: (2)

HKS is mild steel. It wouldn't sell for $200 if it was stainless. http://66.216.67.51/product.asp?0=210&1=254&3=289

I would get the 2-into-1 DP if it wasn't so expensive. The header example was one reason and the other was to increase surface area while allowing for clearance. With two pipes, they can clear obscticals and also it does not hang too low to the ground that it scrapes the road and gets dented like a single biigger diameter pipe would.

Polished can be a benefit since the air will be smoother but that won't last, since the exhaust crap will eventualy stick to the inside walls of the pipe.

I beleive no one in the US made a 2-into-1 DP version is because of price. The strait pipe is allready over $300. They do not have to do the crimp thing. They could have had a rectangular peice come out three times as far as the JDM and then have the two pipes connect directly underneath like a 90 degree angle. Maybe have the ectangular peice end like a trianglar slope to minimize turbulance.

cover8

but if you are spiking to 16 psi and shooting flames....me with hks dp would that mean that your are fully utilizing available flow? if say turbo performance and exhaust were equal, other than dp wouldn't the boost peak indicate if it were breathing?

thanks

BoostedRex

Nobody bothered to mention the Racing Beat DP. I have it and love it. Though I didn't have to install it, it looks like it would've been easy. I've spent enough time under the hood to examine everything very well. Just my .02 though.

GoRacer

iTrader: (2)

Racing Beat? ...are you a 2nd gen owner? I don't beleive they make DP's for 3rd gen's.

WONG FRIED RICE

knights sports all the way! :P

BoostedRex

I'm a 3rd Gen owner. I will take a closer look at my DP in the morning, but if I'm not mistaken it's a Racing Beat pipe. I'll let you know when I find out for sure thought.

RX7SpiritR

iTrader: (1)

M2 Downpipe is really nice. Polished stainless steel is very nice and this unit is pretty light too. I'm going to put it on as soon as I get my car back from the shop and then I will tell you guys well it performs and how nice it looks while on my car, and of course how easy it was to put on.

rotary-tt

Given the same overall cross sectional area, 2 pipes will have more frictional losses since the flow will contact more pipe surface area. More losses mean more backpressure and less flow at the same pressure. I'm sure that this can be beneficial though, especially with separate exhaust pulses. I don't think this is the case with a turbo with 1 exhaust opening.

I have a RX7.com SS unit. Very nice but throw out the studs they give you. The stock studs work nice with it, though.

jkekeisen

GoRacer. I'll take a picture of it if you want 200 bones stainless steel on sale from the websitem brand new. It's at the shop right now having the bung rewelded in the right location. Maybe that was why it was 200!

Jim

GoRacer

iTrader: (2)

Maybe yours is a replica. I beleive it says mild steel on HKS's web site. Rotaryknight could answer that for sure though.

RMS sells a M2 "style" replica but according to the vendor section, I wouldn't buy from them right now. Corksport sells a SS DP but their original design is flawed and won't fit. There is someone on EBayMotors selling SS for about $100 but who knows about the fitment. I allready played ginny pig.

Kevin T. Wyum

Heh, it was funny reading some of these replies. The "Cobra Head" being there to improve performance was funny as well. It's there ONLY because they have a steering shaft etc. that gets in the way. It's not a benefit. It's a kludge they were forced to use because of how mazda crammed things in. I don't recall seeing the ultra high tech "Cobra Head" on any Formula 1 or Lemans cars. It must be beyond those budgets. Someone fed you a line of BS and you beleived them : (


As for two tubes vs. one... The person who brought up laminar flow was right. In laminar flow the area at the surface is static and not moving. In a two tube system there is more surface area that is not flowing which essentially detracts from flow area. They used the two tube design for the same reason they used a "cobra head". It's a narrow wide space and two tubes allowed them to use more of the width allowed. If two tubes was some big benefit they wouldn't use a collector back to a single pipe.

Kevin T. Wyum

GoRacer

iTrader: (2)

I think it would be a benefit if it wasn't squished/crimped whatever. It would work like a funnel but being crimped offsets the gain, most likely.

Headers end up to a single pipe and they are either 4-to-1 or 4-2-1. Not all the JDM front pipes are the header style, only the most expensive ones. The rest are similar to HKS but stainless steel and instead of mandrel bending, they like to weld. It has to end up in one tube or a collctor to a single pipe, the mid-pipe and exhaust are one tube. Would the formuala1 and Lemanse RX-7's be left hand drive?

If the 2-into-1 gave me more low end hp before the turbos kicked in fully, i'd consider it a benefit. Whether they actually use it in the race cars, maybe Inukai could answer that.

Kevin T. Wyum

P.S. I should have used Narrow and Tall or thick : ) Not Narrow and wide. hehe.

Alex

The whole purpose of 4-2-1 headers is to match exhaust pulses from the cylinders. Esentially the exhaust from one cylinder draws out the exhaust from the next one. The length of the pipes is critical in this case. Since the exhaust from both rotors flows into the same turbos, this benefit doesn't work on a 2-pipe DP.