1SWEET7

iTrader: (1)

Is there any solid data on whether there are more gains with a header or stock manifold with a downpipe? Assuming the rest of the exhaust is straight though to the stock mufflers.

rotarygod

iTrader: (1)

All I'm going to say is that if someone claims a header doesn't give a larger gain, they've never driven a car with one! Peak power may not be a whole lot different between the two but a header will give you far more average power at every other load level. It's a great thing to have and definitely noticable. You don't need a dyno to feel it either. It's very obvious.

There are always going to be opinions on which header is better but remember they are just that, opinions. I've had a few different types and I can say that even the hated Pace Setter is lightyears better than the stock manifold! I'm not saying to buy one though as it is poor in quality. Damn near ANY header is better than the stock manifold. The outlet on the stock piece is only 2" anyways.

Don't worry about dyno proof to back up any claims uless you only care about full throttle power and nothing else. Dyno's don't prove a whole lot in real world driving situation. Dyno's are really only useful as a tuning aid anyways and that's all they are meant to be used for. The hardest part is convincing people that a dyno is a 2D representation of a 3D powerband. You can't see it all and only see a small percentage of where your engine actually makes power which is only full throttle. I know at least one person will argue this point (they always do and they are always wrong about it!) but the fact of the matter is that just because you may not make any (or much) more full throttle power doesn't mean you can't make considerably more average power across the load range. You'll feel this on the street since most people don't drive only at full throttle. Power where you can use it is what makes you faster.

diabolical1

iTrader: (3)

other than these two statements, nothing else really needs to be said.

diabolical1

iTrader: (3)

also, i don't think i'm capable of being quite as nice to the PaceSetter header as Rotarygod was, but the bottomline is ... he's right on that point, too. even that header is better than the stock manifold - but you're just better off keeping your exhaust stock until you can afford a better header.

Twins80s

iTrader: (3)

I recently installed a rb header and bonez cat. Ya I mostly got it since my car failed emissions and I thought a new cat could help, well why not get the header at the same time? Granted my cats were pretty clogged but when I first got the rx7 I wasnt really impressed as I come from alot of FWD turbo cars. With the cat and header on the stock cat back you can tell there is power to be had with just the header. Some people talk about how sharp some of the bends are on the header but honestly look at the stock manifold anything is better then a brick with holes in it.

1SWEET7

iTrader: (1)

Ok I see what your saying rotarygod i'm glad you chimed in, as I was touting your exhaust knowledge in another thread. I am pretty happy with my current setup right now, but I love to talk and debate topics. Maybe someone who has had both could express their impressions.

crispeed

Try convincing the dyno junkies!. They only drive/race their car in a one dimensional world.
I'm tired of saying a dyno is just a tool. Your lap and et time slips are what's important.
Sometimes I wonder if they drive and race their dyno sheets.
Average power always wins no questions about that.
Any rotary pre renessis should consider an exhaust sytem as #1 in the upgrade list. Start from the header and work your way back and the butt dyno is going to be very happy with the difference.

BlastinSideways12A

A downpipe on a stock exhaust manifold is a big jump up from stock.

A header-back exhaust setup is a big jump up from a stock manifold with downpipe.

I've had both setups on 12As.

anewconvert

iTrader: (1)

Since we are talking about headers:

The forum 'knowledge' (in quotes for a reason) seems to be that the RB collected header isnt perfect for NA power, but a compromise. Meaning the primaries are too short and the collector is not sized ideally.

Thoughts? If this is true what would make for the ideal header, or are we going to get into the fact that it all depends on your porting and power goals?


BC

diabolical1

iTrader: (3)

run a search with "SDJ" and you should see the reasns people gave for saying that RB is lacking. yes, porting type does make a difference in what is optimal.

however, you can circumvent all the "talk" by getting the engineering point of view of what would be ideal for your car and build a system out of an RB road race front section.

anewconvert

iTrader: (1)

I am sure we are talking less about power increase than we are talking about moving the power band around with primary length and collector size, but ti would still be interesting to find out.


Ill check out those threads.


BC

BlastinSideways12A

One of the ideas that I had for designing the exhaust for my personally engineered 12A peripheral port engine is to start with a separate runner header. (like RB but custom built to not weigh the car down)

Continue with separate runners... have sets of various pipe lengths which can be swapped with very little effort (2 before the collector and 1 afterwards so that the net length of the assembly remains unchanged)...

Finish it off with the rear section which will include a Magnaflow round universal straight-through muffler with a 2.5" core.

This way the collector location will be changed to find the optimum point. I will be able to obtain a good idea of the effect of the exhaust configurations based upon data analysis from the Megasquirt and find the best two or three to compare on a dyno.



For those interested, I intend to post some details as to the peripheral intake porting as well as the intake manifold and fuel system design once I get a chance to actually get the calculations formally documented and final CAD drawings created.

The goal for the engine is street driving. My plans to obtain this are:

1.75" internal diameter intake runners, tuned to increase VE at around 6,000RPM. I will design and test for the optimum setup based upon my plan for the exhaust (without the collector of course)

intake runners will undergo a VERY gradual reduction in diameter to 1.625" using 2" OD/1.5"ID aluminum tubing, machined to specs and press-fit into bored housings

An injector bung will be included in each tube as primaries. I plan on using Miata injectors here in order to keep pulse width as long as possible.

DCOE-style throttle body (48mm) will include a TII injector for each runner. I don't expect to need more fuel than that but if I do I will purchase larger injectors.

OEM 2 piece apex seals. (Redline will be kept under 9,000)

If I can hit around 220 at the wheels with reasonable idle and driveability I will be stoked.

rotarygod

iTrader: (1)

The RB headers aren't that bad. Too many people insult them but they are the most popular and best selling ones ever made for a rotary. Are they perfect? Nope. No header is. Not even SDJ's. There are different ways to go about header design and no one right way as each setup is different. RB's header is a good all around everyday header made for average power on the street. Sure there's room to improve on it but if there wasn't, it wouldn't be so cheap.

For a short primary system I actually feel that the RB header is too LONG. This is a primary reason why this header doesn't make as much total power as some other custom built ones. They built it for street use and it's power peaks lower than some would like but that means greater average power lower in the powerband. For max power from a short primary system intended for street use on stock ports, primaries should stay under 24" to the collector. The more aggressive the porting, the shorter this length should be. A peripheral port does well with a header that is only 10" to the collector. However fitting this into the allowed space isn't easy like it is on a tube framed car. Just like too long is hard to make fit, too short is too. A long primary is a different story when it comes to length but the same generalizations apply. Just with different numbers.

BlastinSideways12A

I've actually had Racing Beat headers and I think they are quite good. I used their long primary exhaust system on my stockport 12A powered FB and really liked it. Also used a Weber DCOE 48 carb with it. It was fun.

Given the luxury of a choice, however, I will be building a header/exhaust tailored to my engine to be as light as possible. Especially since the porting will be far from stock.

Latin270

How much lighter can one go w/o sacraficing durability? I agree for everyday use Racing Beat has built one of the best "universal" type headers available.

diabolical1

iTrader: (3)

yeah, i don't have any complaints about the RB stuff. the only way i'd take the chance of doing a fully custom exhaust is if i recreate the RB sound, too. i LOVE the sound of my streetport system and that alone is worth whatever extra horses i could otherwise scrape up with a custom system. above all else, my car will be a street car so i don't need to have every last HP in it.

GtoRx7

iTrader: (5)

Making a header using 321 stainless steel will shed over 50-70% of the weight off a mild steel version. Another benefit is no need to wrap the system to keep exhaust gases hot, as 321 will contain almost all of the thermal energy within itself MUCH better than mild steel. The downside? 321 is super expensive

ericgrau

iTrader: (1)

RB says right on their website that their headers do not provide a significant gain on a fuel injected vehicle. And I think they're great as far as headers go.

I did the calcs before, a sharp 90 degree bend will cost you 1 HP at high revs and WOT. Search if you want to see it again.

If you're not getting enough power at partial throttle, ever think about pushing harder on the gas pedal? And no, there is no downside to this (vs other ways to get more power) except perhaps a fabricated downside. Honestly, I can't believe someone would actually post such a thing.

Btw, did someone in this thread just (inadvertantly) say that he checked a dyno and it didn't show any gains? I've been waiting for a dyno.

Roen

iTrader: (2)

There's always custom shops like Speedsource and ISC Racing.