Shorty Header??
 

1. Does anyone make one?

2. Has anyone tried one?



I'm thinking a shorty header that takes up little more room than the stock manifold. Google didn't return anything for a 2-rotor, so I'm just asking here.

No one? Nothing?

nope. nothing.

Given the lengths that racers have gone to over the 30+ years in order to maximize the performance of this engine, I'm sure somebody tried a shorty header. It probably didn't work, so they threw it away. You probably haven't heard of it because nobody would you post a "check out my shorty header that loses power" thread. I certainly wouldn't.

the shortest i've seen numbers on is in an SAE paper, on a PP engine. they tried 500mm, which seems to work really well, 1m, 1.5m etc etc

the mid engine cars, and some of the PP cars end up around 18", but that might be more due to space that tuning...

actually i like the stock exhaust manifold, it matches the port well and is actually designed to have some anti reversion built in, when you switch to headers you actually loose this, because the port match gets fugly

Speaking from piston engines, shorty headers typically are only down a couple horses or so from a long tube. On most street engines you wouldn't notice the difference. Same thing goes for equal/unequal length headers.

I guess RB just kinda has the market cornered.

I'm just the kind of guy that thinks outside the box and out of the norm; I'm the one that puts a programmable ignition for a big twin on a small single, along with my own header and experimental cams and have land speed record holders asking how the f**k I made it work. There's peeps here on RX7club that have seen and heard that bike in person, 3 days ago.

Maybe we can get some of the real engineering/pioneering minds to come forward and discuss the theory and technicalities of why a shorty header may or may not be a good idea for those that don't want to drop the dime for a long-tube that won't pass Cali smog.

A shorty that could fit within the manifold heat shield would separate the exhaust pulses so they're not pumping into a common plenum, bouncing off the opposite wall and dampening the flow. It would also allow some scavaging effect seeing as they're not pumping into, again, a pressurized plenum. Keeping it all within the heat shield would make it almost impossible for anyone but a well trained eye to notice it's not stock at a smog check station. Some power benefit for the cost-conscious without the need to swap your exhaust back and forth every two years.

Believe it or not, not every person in the world is building the fastest car possible. Some would just like a little more umph. Throw on a shorty under the heat shield and go on their way with a few more horses and no labor to pass smog every other year.

been done before. go to the NA tuning section of the forum.

I must be blind, then. Link please?

why cant you find it on the front page?

I know where the forum is, but I can't find this subject covered in there anywhere. Since it's been "done before", I assume there's a thread or information somewhere...that's the link I'm asking for.

Search function has turned up nothing.

Google has turned up nothing.

i think the limitation to keeping it under the heat shield, is that its going to be hard to keep a good port match AND get the pipe bent fast enough to make it fit. the port outlet is like 48mm, but the pipe size should be around 43mm ID. the RB headers don't match up to the port, which is probably why they don't do much on an FC engine.

RB headers are 48mm or 43mm?

You say the pipe should be 43mm, maybe extend the header pipe into the port a little to help smooth out the 5mm transition and increase the flow. That 5mm lip can be quite detrimental.

...Or just make the flange at 48mm on the engine side and 43mm on the pipe side, so it's a quick-but-smooth transition down to proper size.

...Or flare the 43mm pipe to 48mm at/in the flange.

Did you play MMOWGLI? That's kinda what I'm trying to get going on here...bounce ideas, improves on ideas, counter thoughts and build the design right here in the thread, in a friendly/professional manner . Then move on to actually putting metal to metal and see how it pans out.

Yeah, you're absolutely ZERO help.

Everything is Corksport, Pacesetter or Racing Beat; all long-tube except for the dune buggy exhaust. You have yet to point me to any thread relating to a SHORTY header thread, especially one documenting any sort of loss over the stock cube-manifold.

*Probably* because nobody would take the time to document what ended up being a waste of time.

Think of how much of a market there is for this part:
-California people that want to legitimately pass smog with a non-CARB approved header
-Unwilling to swap exhaust components every 2 years, but will swap a header once.
-Something that is just as expensive as a long-tube header since all the labor and flanges are the same
-Header that is inferior to other long-tube systems that are legal outside california

It's no surprise nobody sells one.

How do you know it's a waste of time if no one has taken the time to document it having been done?

Yet people still buy shorty headers for their piston engine cars.

All your above points for NOT making one, apply as well to piston-engine vehicles, yet that market seems to fair pretty well.

Who says cost has to be the same? Less material required already lowers the cost of a shorty.

*Probably* because people are lemmings and rather than innovate, they just follow the crowd.

Why are you guys so adamant that it's a bad idea? You have nothing to show me that confirms your claims.

Furthermore, if one person failed, why can't their system be analyzed for its shortcomings to see if it can be modified or optimized to work better?

This is called R&D guys.

Well, it's pretty much just me so far. And I'm just discussing as well. If you think it's a good idea, go ahead and make one.

Rotaries are more sensitive to exhaust back pressure. So, the designs that cost a 'couple horses' on a piston engine could be double digits on a rotary. And there have been setups that improve on RB systems, but they have all been long-tube designs. Since the stock manifold is essentially a 0 length header, everything is longer than that.

I am not doubting your ability. It's probably more than my own. It's the amount of time you've spent pondering the rotary compared to the decades that racers have dissected every single detail of these engines looking for an edge. The resultant trickle down of racing tricks have evolved into the street vehicle components we have now.

UCDavis says I'm an engineer :D
The stock header has a large volume, so the gas escaping the exhaust port has plenty of room to expand. This provides a small scavenging effect. The long-tube headers use exhaust gas pulse resonance to create a scavenging effect. A shorty header doesn't work on either of these principles.
It would have higher velocity at the exit of the manifold, but then it runs into 3 cats.

I understand the purpose of the shorty header is to mate up with the rest of a stock exhaust system. But the cat section of the NA exhaust sucks, plain and simple. Would you put a 1" pipe exhaust on the back of a GT35R turbo? No, it has to work as a system.

I'm pretty sure I know everyone and we all said the same thing. I just think it's a lot of time and effort for a very little amount of umph.

I'm not saying it's worse than the stock manifold. I'm theorizing that the gains would be minimal for the price when paired with the rest of the stock exhaust.

Are you familiar with the word "probably"? You're right. I don't know. I also don't know if using dog poop as an oven mitt will work, because google doesn't tell me it is bad idea.

Sheer volume keeps a lot of piston powered items and they probably don't have the same packaging and downstream exhaust issues to worry about.

As for manufacturing cost, you have to look at everything that goes into a product:
Long-tube : engine flange, 5' header piping, collector, exhaust flange, welding materials, welder labor, overhead, insurance, advertising, shipping
Short-tube: engine flange, 2' header piping, collector, exhaust flange, welding materials, welder labor, overhead, insurance, advertising, shipping
The piping is minimal.

I appreciate the educated discussion. Will post more after eating lunch.

Like I said, I appreciate the discussion. However links to a page of search results that doesn't answer any questions is completely unproductive. *cough*SirCygnus*cough*

I do intend to make one, but if others had already tried, I could see what things to avoid or what obstacles I might encounter; pull from their experience so as to not start at square one if I don't have to, ya know.

That's kinda where I'm coming from, it's zero-length already. Some length to separate and redirect the exhaust has got to be better than the horrible resonance of the stock manifold. I agree not the potential of a long-tube, but better than the manifold.


Ability is just knowledge + determination, imo. If you know how and have the drive to do something, you essentially have the ability.

Like I've said, and is common knowledge, long-tubes make more power than short tubes. It only makes sense that if race-tech trickles down to the street level, long-tube is the obvious buy-in. Again for those that are looking for a little, not the whole nine yards, I'm trying for an alternative. Not debating what is already out there, just trying to put other alternatives (or thoughts for others to expand on) into the mix.


I do the engineer work, I just don't have the paper. I do the drawing and the calcs, he looks it over and says "Yup" *signed*. Still dunno if I wanna do Mech Eng or Business Admin though.

I understand it has room to expand and cool (minutely), but it's exhausting into, essentially, a wall. How much gain is made from the 5th/6th port inserts? That's diverting the air from the wall into the port. Shorty's would essentially be doing the same thing, redirecting the exhaust from blowing against a wall, into the ready-to-go exhaust. It's not scavenging as much as a long-tube, but it's not blowing into a wall either.

My cats are gutted. First mod anyone should do to an N/A, imo. Either way, redirect the exhaust away from the wall of the manifold. Yeah, it's running into the honeycomb, but instead of a turbulent mass, it is more directional and has higher velocity.

Time and effort don't matter to me, I enjoy the journey and the result (as long as it's not a blown motor).

Can't argue with the sales volume to engines such as 350's, 302's and LSx.

Regarding cost, one of the largest factors is welding and shaping labor. If you reduce the length of the pipe, you're not having to work with as much metal. Time saved, penny earned.

Make sure you post a thread on it! haha.

The exhaust gases don't go straight out, bounce off the wall and head back toward the port. They expand outwards into the stock manifold which has a lot of volume whereas a tubular runner is much smaller. I *think* it is a bigger factor than you're giving it credit for. By switching to a tubular manifold, you are relying on the resonance for scavenging. Which usually occur in multiples of 18"~20". Nowhere near what can fit under the heatshield.


Smoothing out the transition is a sound theory. However, as mentioned beefore, the rear runner is going to be a real challenge. I still think you're overbuilding this one component in front of other parts in the system. Like the odd shapes and path of the pre-cats, even when gutted.

If this part actually got CARB certified and produced, I could see a market for it. But that's going to be prohibitively expensive. Otherwise, the selection of used exhaust components undercuts new ones by a wide margin.

I can't find it right now, but there's a picture of a header someone made with cast iron piping and fittings welded to a exhaust flange. With the exception of the materials used, it's pretty much the only design that will fit under the heat shield. It reeks of Lemons tech. Maybe someone has it bookmarked.

the race engines have a port exit that is 43mm, and use 43mm pipe, its documented in a few SAE papers and manuals

the FC engine has a 48mm port outlet, and 50mm inlet to the manifold, which gives an anti reversion property.

the RB header is 2" thickwall, which is a 43.9mm ID, so the RB pipe size is fine, it just doesn't match well with an FC port. the real fix would be a new rotor housing sleeve, but adding a bellmouth to the pipe seems to work well too, and its easier.

however to do the port match, AND squeeze the bend in under the stock heat shield isn't gonna be easy!