It-s Headers/ Exhaust
 

I'm about to start work on the exhaust system for my IT-s FC project and was looking for some input from you guys. I wanna keep my system as simple as possible with a single outlet.

Im currently looking at ISC's system, both the Racing Beat collected and uncollected headers (with a personally fabbed rear end), and the Mazda Trix collected and uncollected headers.

Im willing to pay extra for a legitimatelly better performing system, I just dont want to throw money away on imaginary Hp.

The collected headers would allow for a much easier job of fabricating the rest of the system, however somehow I understand that they produce a decent amount less of power.

Does anybody have any insight on this?

any help would be much appreciated,
Phil

run an uncollected header then have 2 pipes go straight back to their own muffler... True dual exhaust. If you want to get creative you could throw an x-pipe in for some back pressure.

The ISC does make more power from what I hear. But it is also SS and costs more than twice as much. You make the call on whether a few more ponies are worth it. You could also build a header, there was a topic I started a little while ago about that. As for true duals: no good. You want a collector and you want it at about 95" from the port.
Grant

My old man's SRX7 put out 126RWHP on a real dyno. I would suspect a dynojet would show in the neighborhood of high-130's to 140. I'll be sure to test it out as soon as I get a new rearend in the car... *DOH*

Anyway, it's running a RP header with home-fabb'd exhaust. Needless to say, all my racecars now have a strikingly similar exhaust setup. ;)

Please don't listen to this guy.


There are two main schools of thought. A long primary and a short primary system. In theory both will give the same peak HP number but the long primary will produce more power under the curve. A few years ago I attended the ARRC and took a long look under the two Speedsource cars driven by Tremblay and Haskell. One used a long primary system the other a short. The other Speedsource cars I've seen since have all used a short primary system.

The other varient is ISC's expansion chamber. I haven't talked to Mike himself about the theory behind his design but I've heard some bogus claims from others. The common un-truth is "two-strokes use an expansion chamber and a rotary is like a two-stroke". WRONG! The similarities between a two-stroke and a rotary end at both being piston port engines. The expansion chamber and stinger of a two-stroke pipe is designed to create a revision in the exhaust pulse. The pulse travels down the pipe away from the exhaust port, hits the stinger, turns 180*, and comes back up the pipe at precisely the right time to shove the fresh A/F charge that's spilling out the exhaust port during blow down back into the cylinder. This event doesn't occur in a rotary so why do we want revision? We don't. My only guess, and it's just that, is that Mike's design may be trying to emulate the use of a megaphone type collector that's proven to boost power through more effective scavenging.

And speaking of scavenging...this is precisely the reason you want to avoid the true dual systems. A properly collected system will ALWAYS make more power than an uncollected system. The key is in the proper placement of the collector. The collector can be an X-pipe. But once the two primaries are merged there is no reason to split them again other than aesthetics. For a race car keep it simple and merge the primarys and leave them merged. Further, the collector (or X-pipe in RMIGGIN's post) does not create back pressure. The proper collector creates a scavenging effect where by one exhaust pulse is literally pulling the charge down the other pipe. Again, collectors always make more power than a non-collected system regardless of Mazdatrix advertisements. Give Dave Lemon a call and ask him what he runs on his EP car.

In the end there are a few great choices. The best short primary headers are going to be from Speedsource or SDJ. If you want to go long primary the best place to start is ISC's or Mazdaspeed's header. Speedsource has, by far, done the most in the way of ITS RX-7 development. Their stuff isn't cheap but with one call you won't have to re-invent the wheel and you will know you've got good stuff.

I mean to say SDJ, not ISC. They are the really nice ones.
Grant

Thanks guys for all of the input....does anybody have any experience of what tested HP gains would be with any of these systems on an FC? Im still trying to get a hold on what kind of improvements Im realistically talking about. RB told me something in the neighborhood of 25hp-34 hp depending on the system.

Although it looks great on a street car, the full dual system was never really an option for my application. So what would be the benefits of a short primary, if the long primary would produce the same peak HP but yet more under? Are there other advantages to the short?

The SDJ header is the new collected $400 one that is being sold on mazdaspeed's site right? It seems that SDJ motorsports website is down so I can't really find out too much info about them.

I saw that ISC had a bunch of extra HP claimed with their system, but I too am having a hard time understanding the point of the expansion chamber.

Since im gonna be running in It-S the engine will stay pretty much stock. At first glance (although I need to do some more research on it) it seems like it would be a good idea to keep the 5-6 port system in working order, as opposed to just gutting them open. (please interject here if I'm wrong) so as my car is a '91 I believe I will have to tap a hole into the header...right ( or buy one prepped for it)??

Thanks again for all the help guys!!

The SDJ Header is $450. It consistantly makes more power on the dyno than the RB, Mindtrain and ISC's.

Speedsource claims 175whp for their setup with stock electronics. They also claim an additional 10hp across the board when using their Motec system. We're currently in the 170+whp area with our long primary setup on stock electronics. That ought to give you an idea of the numbers you're shooting for. Most racers I've talked to that have a well developed powertrain see 160+whp on stock electronics. Someone saying their header makes 10hp more than the competition doesn't tell you much if they consider the competition to be the stock iron manifold. Ask them for real world wheel HP numbers. The SDJ header is sold through Mazdaspeed. Part #0000-06-7406


Ditch the 6-ports all together. The RPM range that they are effective in is never seen uder race conditions. We rarely see anything below 6000 rpm. A well developed ITS powertrain is kept in the 6-8500 rpm range with over rev capability to at least 9000 rpm.

Two other things. Sounds like you may have already but if not get signed up with Mazdaspeed. There is no better parts deal. Also run over to www.improvedtouring.com There is a very active Mazda section and great general racing info.

Some good info...keep them coming....

Designfreak,
ISC's does make more power than the twin 90 inch primaries. I have seen back to back dyno tests and IIRC, it was about 4 hp and 8-10 lb-ft. Honest HP...

Jim

the hp gain was only at the top end Jim?

Duals or collected
 

I sold my old 12A car to a fellow racer about two years ago. The best HP number I put down was 112 rwhp with an old engine and a true dual exhaust. (2" pipes all the way back, under the rear axle, Y'd into a 3" and then into a 3" racing muffler). The fellow who bought my car ran the same motor for another season and a half and then changed the exhaust to a collected expansion system and he put down 120 rwhp. Same motor, another year and a half of abuse. So I'd say the exhaust was good for at least 8-15 hp (trying to factor the lost hp from an old engine getting even older)

-Trent

Can you mate an ISC back half to a racing beat or pace setter (yuck) header?


$$ issue...


Marcus

sry dunno

:confused:

I asked this same question to Mike at ISC and he says they will mount up just fine.

Yes, I have the ISC stainless header and it bolts up to the RB dual presilencers. In other words the ISC and RB flange occupy the same space.

What are you running for a muffler and how loud is it? I have the RB SP header and center section and just bought a Dynomax Ultra flow 6" round with 3" IN and Out. I started it without the muffler and scared everyone in the neighborhood! Damn that thing is loud!! :-) I’m hoping the Dynomax quiets it down quite a bit.

I've got the RB street header hooked to a 2.5" Flowmaster "40" series chamber muffler... then a home built 2.5" tail pipe that dumps in front of the right rear tire. The engine is a pure stock 13b with the stock FI ('85 GSL-SE). The car is road raced at Pacific Raceways in Seattle. The track takes db readings on every car on the track and this setup hovers just under 102db at (I think 100 ft). 102 is the limit for that track. If the air is heavy and cool sometimes they get it at 103 and throw the meatball at us. When this happens, I have a Flomaster "10" series that I slip on the tail pipe till the weather clears. The tech support guy at Flowmaster suggests the 2.5" "30" series for my application. He states "no reduction in hp" and "it's a conservative choice for quietness". Plus, he said that his mufflers don't melt.

I started with a used ebay unbranded chamber muffler which worked ok until it literally melted and the internal vanes came loose. They plugged the outlet and the muffler blew up like a balloon... very comical... although I didn't think so at the time... I was relieved to find it was my $2 muffler and not the engine.

Cheers,
Jim

I got the ISC header, RB dual presilnecer center section, and a 3" inlet supertrapp. Loud as shit.

Your dynomax will quiet it some but 3.0" is pretty big. I used the same setup but 2.5" dia. magnaflow 6" round and it was streetable but hard to talk above 80MPG from the drone.

It's a CSP car not street legal; trailer queen all the way. It'll never get above 80 on an autocross course. ;-) But, I’m hoping the Dynomax works out well anyway.

F me.. I they just shipped my last order.. oh well. its only money, right? :)

Got the Dynomax installed this weekend. Sounds good but it’s still a bit loud. I’ve ordered one of these from Summit just incase the DB police come a calling. http://store.summitracing.com/

I know this is pretty old, but the post was brought up so I figured it was ok.


anyways, I am like 95% sure that expansion chambers are not allowed in ITS class.