Shorty Header??
05-23-12, 05:49 AM
#26
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.
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.
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.
****
05-23-12, 08:43 AM
#27
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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?
Please take your mightier-than-thou attitude and get the **** out of my thread, the adults are talking here.
Last edited by Jet-Lee; 05-23-12 at 09:07 AM.
05-23-12, 08:50 AM
#28
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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!
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.
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.
Last edited by Jet-Lee; 05-23-12 at 09:00 AM.
05-23-12, 09:16 AM
#29
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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.
A lot of people *cough*SirShitnus*cough* would interpret this as a crappy design.
Short enough?
05-23-12, 11:08 AM
#32
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.
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.
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.
05-23-12, 11:32 AM
#33
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05-23-12, 01:48 PM
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05-23-12, 02:29 PM
#37
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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.
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.
05-23-12, 03:18 PM
#38
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https://www.rx7club.com/showthread.php?t=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.
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.
i remember him posting more pics
05-23-12, 04:07 PM
#39
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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.
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.
Yes, it will be my money, my time and my labor.
05-23-12, 04:13 PM
#40
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.
05-23-12, 04:26 PM
#41
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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 have a large street port from the pineapple template. Stock exhaust ports, sans diffusers.
05-23-12, 04:40 PM
#42
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.
05-24-12, 10:33 AM
#43
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.
05-24-12, 11:17 AM
#44
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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.
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.
05-24-12, 11:35 AM
#45
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.
05-25-12, 05:19 AM
#46
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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.
05-25-12, 12:21 PM
#47
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.
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.
05-25-12, 02:45 PM
#49
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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...
05-25-12, 05:04 PM
#50
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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.
Waiting on flange and pipe to get it all cut and start tac'ing it together to get a more solid idea.