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!

maybe you didn't get the hint that not one exists and you are at this point a troll. we wont provide you with any insight because no one has cared to make a design so crappy. why make something when it wont work great?

get the hint already. there isnt one that exists.

shut up already about being an individualist.

no one cares, go make one yourself. spend the money on it yourself, and be happy yourself.

fuck

I'm the troll for trying to spark intelligent conversation that could lead to a product for our cars that has yet to exist? No. You, sir, are the troll


Wrong, you don't provide insight because you can't.


You've still yet to contribute any evidence (physical/link/argument) to support your opinion.


WHAT?! NO WAY!!! I never would have guessed that if you didn't point it out. Thank you so much for opening my eyes!


Wtf are you reading?

I don't recall asking anyone else to do it for me....again, what the fuck are you reading?

Please take your mightier-than-thou attitude and get the fuck out of my thread, the adults are talking here.

I intend on it.


If it works in multiples of 18", then 9" could theoretically work. It wouldn't have as great of a pressure differential after the exhaust pulse bounced that many times, but it would still have some.



I don't think the rear runner will be as difficult as you think. The front runner, just keep it tight to the engine and go straight back (and slightly down) with it. The rear, extend it straight out over the top of the front, turn it down then back. That should make up the difference in length. Pre-cats are easily solved by a pipe with two flanges, nothing spectacular there to design.



CARB certified? Wow, I wasn't thinking that far ahead. I think it'd be almost impossible to get it CARB certified. That would be cool, though. Seeing as a lot of actual catalytic converters can't even get that stamp, I won't hold my breath for a header to get the same.

Welded cast iron?! I'd love to see that!

My biggest concern is it won't be torquey, just inherent with the design of short headers.

A lot of people *cough*SirShitnus*cough* would interpret this as a crappy design.

http://i155.photobucket.com/albums/s...0012009664.jpg Short enough?:lol:

:eek:

*speechless*

That's the one. Thank you!


Actually 9" would cause a pressure wave to build against the exhaust gas trying to exit the port. Basically a worst case scenario.


Look at the picture. That "header" goes about twice as far out as the stock manifold. And the stock manifold flange would be about halfway down the collector.

True, but now you're disregarding your own requirement of being able to mate up to the stock exhaust for smog inspections.


You probably didn't think of it because it's a terrible idea. It would be next to impossible both economically and physically. You'll pay for a butt-load of testing and certification. Which is also why nobody makes one.

I am far from knowledgeable on header design, but the lack of information and examples should be a red flag that there is something inherently wrong with the design. I still think you're pissing in the wind here, but feel free to try something new. I just don't see any justification to undertake this project other than 'because piston engines do it' which is ironic, given your signature.

https://www.rx7club.com/showpost.php...56&postcount=7

somewhere there are more pics

that right there is exactly what he's looking for.

Still an uncontributing troll.

that's why i posted it, someday i will post something that isn't and you can compare the two :)

https://www.rx7club.com/1st-generation-specific-1979-1985-18/your-header-pictures-944176/

You fail to mention, though crude and ugly, he was pleased with the outcome. Would anyone else rock it? Probably not. Did he achieve what he set out to do? Looks like it.

true, i just remembered that someone had actually done a short header, and left my opinion out cause i haven't done it.

i remember him posting more pics

Depends on design rpm. Seeing as street engines operate over a very broad rpm range, tuning for the reversion wave is almost useless. Say you tune the length for 3500rpm, it'll be good at 1750/3500/5250/7000 rpm. What about the in-betweens? At 2625/4375/6125/7875 that 18" header will have the same effect your describing for the 9".

In a racing motor that spends 99% of its operating time at a specific rpm, then it's easy to tune for the reversion wave to scavenge the exhaust.


That "header" is shit.


How? I'm just saying that if a person wants to negate the effects of the pre-cats, replace them with a straight pipe, that's no secret. Maybe even do as I've seen on other cars; build a straight pipe and weld the pre-cat cases to it to look oem. I'm not building that straight pipe onto my header.


I didn't think about it because it's just not practical to think California would stamp an aftermarket header as CARB legal when they're already stingy with it in regard to catalytic converters. California wants cars to be stock, so why would they EVER make a header CARB legal? They wouldn't. Regardless of money and testing and benefits, it's a performance part that is not OEM.

It's not "because piston engines do it", it's because it's not done. Everyone is sticking to the long-tube mentality because it's been tried and true. I've now been shown two examples of a short header, one that looks like a joke and the other where the guy had better results than he got from a long-tube. So besides SirTroll up there, there's still no good evidence to not put forth the effort.

Yes, it will be my money, my time and my labor.

Bigger ports with more overlap like shorter headers than smaller ports. A peripheral port would be happy with a 10" primary whereas a stock ported engine would be happier with 22" or so. FWIW the stock exhaust manifold still has runner length albeit very short. The result is that the runners tune to around 7500. The intake is centered at 6500 (all on stock ports of course) so the powerband is broadened a bit with the different tuning spots. Mazda's main goal of course was to keep the exhaust quiet hence the configuration.

I've been awaiting yours and/or Aaron's input on this thread, whether for or against my idea (in this case neither, but informative none-the-less).

I have a large street port from the pineapple template. Stock exhaust ports, sans diffusers.

The headers on the market are all longer than optimal for a stock or street port. Racing Beat's headers have around 30" primaries which is about 6"-8" longer than optimal. For a street port 20"-22" would be better. RB does everything they do for a reason and not necessarily the same reason that many here would use. They probably found that the slightly longer length may have ultimately cost only a couple of peak horsepower but gave favorable gains a little lower in the usable powerband as a nice tradeoff.

I think it's obvious you are going to go through with this regardless of how little support you get. Since I am only giving you an opinion, I'm going to stop debating and wait for your thread. Looking forward to installed pics (without the heat shield because it's going to be hidden) and a back to back dyno test with stock manifold vs shorty. Good luck.

Yes I am doing it regardless. The point of this thread was for insight.

As for a dyno, I don't know where one is locally, other than a motorcycle dyno. It will be seat of the pants for now.

There will be pics, don't worry.

Don't be discouraged from trying things that people say not to try. That's a great way to learn. Sometimes the naysayers are correct. Sometimes they aren't! I've tried many things that others considered a waste of time. In the end I learned something regardless of the outcome.

Exactly. An experiment isn't a failure just because you didn't achieve the results you expected (or wanted). Since you're a bit more open to learning from the process, you'll have success, regardless of others' non-input. Although I have no invested interest in the CA smog rules, I'm still interested in seeing what you discover.

MindTrain used to offer a shorty header for the FC and I had a friend with one.

Gave the car that awesome/annoying rotary raspy chainsaw sound of a header even with a high flow cat on it.

After he sold that header and put the stock exhaust manifold to a race pipe on the car it lost the raspy sound but didn't seem to lose any power.

In fact, it seemed to gain power; however, we did lighten the chassis and lighter wheels and tires so I am sure that was the perceived gain.

The stock exhaust manifold may have some anti reversion properties as stated but it is also documented that working with the tuned intake manifold it has exhaust reversion properties that gain it power in the dynamic effect intake supercharging.

Never heard of MindTrain. Link or pics?

https://www.rx7club.com/forum/attach...1&d=1188023265

Is that what you're talking about? (12A system pictured)

i just bring that up because its a feature that RB headers lack. there is enough meat in an RB header to fix it too.

and well B if you're going to make something, you might as well incorporate that feature. the hard part of course is doing this AND making the bend under the heat shield, HKS does this with the T04Z manifold, and they use some weird technique to do it.

if you're not worried about the heat shield you can swage the pipe and then bend later...

In design, I can get 18" out of the rear runner, but that doesn't leave much room to get the front runner much past 15", so still working on it to get equal length headers.

Waiting on flange and pipe to get it all cut and start tac'ing it together to get a more solid idea.