Hi..

Whats the best downpipe for the bnr stage 3 turbo? to the fd3s?
I also whant a good midpipe but a catback that dosent make that much noise.

 

SMB down pipe.

It has a cast upper (expands at the same rate as the manifold/ turbos)

$pendy, but worth it (from what i've read)

but if you looking for something on the cheap, go with the HKS down pipe.

 

For maximum flow, nothing is going to touch a dual downpipe.
MazdaSpeed

Knight Sports

Autoexe / Maxim Works


piping size
MS = 50mm x 2 = 100mm
KS = 60mm x 2 = 120mm
autoexe - 54 mm x 2 = 108mm

Most aftermarket downpipes range from 70mm to 80mm. Can't personally say if it is worth the extra money, but you will definitely see an increase in flow and thus an increase in HP.

 

RHD or LHD?




Quiet cat backs include SMB and Racing Beat

As far as midpipe - does that mean you plan on running w/o cats? If so make sure it is a "resonated" or mufflered mid pipe if you want to keep sound levels reasonable. SMB has a good product for this as well but there might be other options from vendors in the EU or UK that are closer to you.

 

Bryan, can you get your hands on one of those KS 120mm downpipes?

 

Pure it should be noted that flow isn't linearly correlated hence why two 2.5 in pipes flow the same as a 4in.

 

I think for RHD car those 2 piped DP is the way to go.. But for LHD FDs I think pettit or other DP should be fine.. LHD DPs don't have that square head.

 

I have the rhd rx7...
But is there any use of the best dual pipe downpite if you have an resonated midpipe?
I was thinking about to have a catback that dident noise to much like the RB ... I tought that the catback was the best place to reduse sound and not conflict with the flow and power,am I right?

And what does w/o cats means ? Im sorry for not understanding this

 

Do they sell the mazdaspeed or KS dual downpipe new anywere? can someone put out an link?

 

I am interested in this link as well.

w/o = without

 

i picked up an smb downpipe! i'll know in about 30 days how well it works with the bnr's. i'll let ya know.

 

The HKS and other Japanese market downpipes have an indentation to clear the steering rack. That is a good, cost effective solution unless you want to get the dual downpipes but I have my doubts about how much power they actually add.

By cats I meant catalytic converters.

Mufflers in the cat back and midpipe together help keep sound levels reasonable.

 

The mazda speed downpipe is discontinued and very rare to find, the ks downpipe is still inproduction and retails for $840 + international shipping. We offer it for $625 (http://rx7boutique.com/Exhaust.html), but that is used of course, and they are pretty hard to come by - not as rare as the MS downpipe though.

Sure can, takes about 4 to 5 weeks to source,as with all Rx7 Boutique items, you don't pay a dime until we actually have sourced the item. If you want to be put on the list, shoot me a PM.

 

Quite frankly, any good downpipe will work perfectly fine on a set of BNRs. The restriction lies within the factory shared turbine housing. I ran an old school N-tech downpipe for many years when I was making 420+ rwhp with the BNRs.

 

+1, I agree completely.... I have flowed all portions of the turbo, manifold & downpipe assy's and have quantitative data to support the foregoing contention. Furthermore, I recommend that the DP should be the aftermarket 3" version (not a modified stock one or the smooshed one used for RHD apps.

 

Those dual downpipes sure are cool looking though.

 

Al, I agree, the dual arrangement looks cool as hell....

However, any gains are probably going to come from improvements in the transition from the turbo flange exit to the pipes' inlet. Here's why more is less:

50mm pipe x 2 does not equal a 100mm pipe, rather it equals a 70.7mm pipe in cross sectional area. (Because this is geometric, it is calculated as the root of the sum of the squares.) Similarly, 2 x 60mm = 84.9mm and 2 x 54 = 76.4mm equivalent diameters--almost. Two pipes, when joined in parallel for the same effective area as a larger single pipe, will have much greater surface area relative to their combined cross section, and as a result, have more frictional loss and resistance to flow; i.e., they're less efficient than one single larger pipe.

 

SMB 4" downpipe, I run one

 

ahhh feel like I am in physics class all over again, this is why I am in the banking industry.

 

if the collector at the end of the dual downpipes ends in a 3" flange it will still flow like a 3" downpipe regardless if the dual pipes have more area, right?

with this in mind, my 4" smb dp tapers to a 3.5" flange connected to a 3.5" resonated midpipe connected to a 3.5" bent single tip catback...

 

What is the SMB4 " downpipe... were do I get it?
I was thinking about to have a larger downpipe together with an open midpipe w/o resonation or cat. and have an good high flow cat back that dosent make that much sound.
I would have gone for the single tip catback without soundreduction but if the local police see that and notice the sound I would be getting a quit large ticket
;( and thats alot in Norway

 

Your contention is essentially correct, the 3" flange is going to define it. I think the pipe is desiged to solve fitment problems and I wouldn't expect it to perform better than a good 3" DP.

As to the 4" / 3.5" question, there is likely some flow benefit if you carry the 3.5" pipe all the way back.

 

look on the bright side: your math is good for investors, lol.