where can i find a 4" downpipe for my rx?
 

i swear i've seen one somewhere, i can't remember where, any ideas? its gonna be a part of my big build soon...

nowhere...

1. the stock turbo outlet is only 2.5"...
2. 3" will handle 500hp without problems
3. if you want more then 300-400. you need a full turbo kit. which requires a custom downpipe anyways.

I'm assuming "big build" means big turbo. ;)

While several Japanese companies make 90mm (3.5") systems for later model cars, I've never seen anything that big off-the-shelf for FC's. You'll almost definitely be going custom for anything over 3", particularly for non-standard turbos.

Scott, while a 3" system will handle 500hp, bigger is always better behind a turbo. The less restrictions an engine has to overcome (both intake and exhaust), the less boost you need to make the same power, and that's always a good thing. :)

hey man i know dann... Burkett right?? so you bought his car?? he helped me get into rx7s.

I agree. When I talked with , actually translated for me, at FEED in Osaka, the tech says there is no such thing as too big for a turbo engine. The hard part is all has to be custom made if you're looking at larger than 3.5" .
Also, have some thought into how large the pipes will be under the car. I have 3" and it rubs when I go over speed bumps so I always need to take it in an angle.

I have the JIC Magic stainless Spec 90 3.5" turbo back exhaust.

You can buy the 3.5" front pipe seperately, but it is a bit longer than the stock cat forward as there is a bolt off adapter for the Spec 90 catback so it can be a full 3.5" turbo back w/ no neck downs OR a 3.5" catback that bolts to the small 2.5" stock catylitic flange.

Rishie (ARD T2 on this forum) can get you a great price on this system.

The Spec 90 turbo flange is stock sized to a reverse "velocity stack" to match 80mm pipe that makes up the 1st ~6" (the firewall bend) and them 90mm pipe all the way to the 1 muffler.

VERY LOUD

No turbo exhaust is too large for maximum performance, but you better have a large exhaust side on the turbo and a high flowing wastegate.

I have T4 "O" trim exhaust wheel clipped 15 degrees in a bored out '89 housing, ported/ relieved wastegates utylizing full 15mm of WG actuator travel (stock is 7mm travel) w/ wastegate flow divided and open air vented.

on a 60-1 Hi Fi compressor upgrade stock hybrid

Boost creeps to over 20 psi.

I will yank the turbo (again...) take out the WG flappers, hog the WG passages HUGE and put a 45mm or larger external WG on the turbo backplate.

Yes, it spools fast!

If you have an aftemarket turbo in the "standard" more forward position it is easier to go w/ 4" (or larger)downpipe as you can make the firewall bend earlier.

Also, have some thought into how large the pipes will be under the car. I have 3" and it rubs when I go over speed bumps so I always need to take it in an angle.

The JIC Magic 3.5" front pipe is tucked up so the "frame rails" are lower than it, BUT the catback has a section going past the rear axle that is lower than stock- but does not scrape (though a large square flange is lowest point- so there would be plenty of material to grind away anyways).

My car is lowered and only the exhaust cannister right before the tip drags going up very steep driveways.

Spec 90 is made so even a lowered race car can ride over the curbs of a racetrack w/ no scrapping. Race lowered, not show lowered, that is.

i already have a 3" downpipe... and 3" straight pipe exhaust... no cats, no mufflers, just pure 3" all the way back.... but i'd like to go bigger... as for stock exhaust manifold... yeah i can't use that with the turbo i'm going with.... way too big a turbo(either greddy t78 or t88)... we've got the whole build basically planned out, and i'm doing as much research as possible before we begin. yes i believe dan's last name was burkett... its the black TII that has Rotary Motorsport stickers all over instead of TII logos... i blew the motor 400 miles after i bought it from mike(the guy who bought it from dan and put a JDM S4 motor in it)... he didn't rebuild that motor, so it was a used motor, and he was thinking pushing 17+ pounds of boost wouldn't hurt it at all.... i paid 3500 for this car, worth 6000 if it were running still... now i'm going to drop somewhere between 10 and 12 grand into it.... and if you guys got a link to the 3.5" downpipe itd be greatly appreciated... i'll go ahead and message ART T2 about it

since you are going with an aftermarket turbo. as I posted above. you need a custom made downpipe. in which case you can make any size you can fit.

that is why nobody makes anything bigger. there is no point with the stock turbo.

speak to any heavy truck exhaust place. they make big exhaust.

A lot of places that do diesel trucks will work with upto 5in pipe.

thx for the info, i'll definately look into that! probly wind up getting 4" straight back...

Check scrap yards

Our local srapyard has thousands of pounds of stainless steel 4", 5" and larger stainless pipe w/ V band flanges and clamps already on it AND clamshell style contant volume/radius bends.

I presume it is from the old chlorice pulp mill that they had to retrofit.

Check around...

im probably gonna have to go with a custom downpipe because of my 3 inch exhaust (i plan on getting a 2.5-3 inch adapter). what degree bends so i need to match up to the turbo to the exhaust?

Exactly. Call up a shop that does exhaust work for diesel trucks and they should be able to give you a lead on a ~4" exhaust.

you guys can go too large with the exhuast you know


the idea is stil the same with a piston motor as with a rotary


velocity of the exhuast helps gives power
too large of an exhuast equals no velocity

Not after a turbo.

even with a turbo the exhuast should still have pulses as far as I know

wouldn't those pulses work better if the exhuast had a higher velocity causing a lower net pressure at the exit of the turbo?

Higher velocity = higher restriction. Basic law of fluid dynamics.

think about scavenging though
when the exhuast pulse leaves it creates a low pressure zone
the low pressure zone helps pull the next pulse


there is limits either way though

too large and you have no velocity and so no scavenging
go to small you might haev high velocity but it is overcome by the pumping losses


if we just follow your simple idea there NZConvertible
then N/A owners would even have 4" exhuast

sure you have less velocity but less velocity equals less restriction

I believe Carx7 has/had 4inch on his beast

Yeah, he had a 4" downpipe for his cat-eating turbo on his project AE. That thing's engine bay is soooo shiny. :D

carx7 has a 4" mandrel bent piece of artwork, and he put down 470rwhp on race/pump mix and 4" is bigger than he needs. so let that just be an idea.