Dak

Hey just curious how much hp these RB mufflers Road Race Muffler - Right for 86-92 RX-7 - Racing Beat will support in a turbo application? Reason I ask is eventually I want to put some sort of custom exhaust together for my n/a maybe using these mufflers but they are 2" ID vs the 2.375" of the Rev TII turbo mufflers. I think the n/a ones fit my current application better but in the case that I eventually go turbo would they flow enough for up to 300rwhp? Thanks.

jjandros

iTrader: (7)

After an ungodly amount of time losing myself in the pit of rotary exhaust online "experts," all I can say is maybe. Here's why I say that. In order to get a better idea of the power gains possible we need to know what peak power band you're looking at. Are you ever wanting to go over 300? Is this 300 to the wheels? Honestly your best bet would be to call or email Racing Beat with the setup you currently have, and the setup you plan to have and see what they're recommendation is. Back pressure, flow rates, racing beat's "megaphone" effect, all seem to play a part. I'd be curious to hear if anyone has personally run this setup or if not what Racing Beat recommends though. Let us know bud.

Dak

300 to the wheels max. I think that's as high as I can safely go with the n/a rotors. I don't think peak power band or megaphone effect matters like on a n/a as that will be determined by the turbo I run, probably a BNR stage 2. I know those have dyno'd over 300rwhp just need to know if these will flow enough. Current setup is a RB header and pre-silencer and an old HKS sport cat-back. All the welds on the cat-back are rusting apart hence the need to replace it.

jjandros

iTrader: (7)

I would grab some ID specs, decide what porting, rotors and turbo you're thinking of running and get a good compressor map for said turbine. I'm guessing you'll be running a 6 port 13b still and not swapping to a TII keg? If so be sure to include that along with if you're disabling the secondary ports or keeping them functioning. Take a few picture of your setup and shoot all the info over to Racing Beat.

Unfortunately there's only 3 ways someone can get you this answer. 1) someone here is currently doing it. 2) You take the things said above and begin doing some serious math. Or 3) you ask the guys who actually built the products and see what advice they can give to you.

OR

By basic math... (as in VERY basic and not scientific at ALL, I say this because flow rates are hard to just estimate like this especially since air can compress and fit through smaller holes with an increase in velocity, however... back pressure will increase. So if we just screw around with some basic numbers we can come up with a moderate guess) For this, we'll limit back pressure and air pressurization changes to flow rate by stating that we want the exhaust to be free flowing. Therefore the ID of the tubes will be the limiting factor here. I can't find much info on the HKS cat-back but if I remember right it's a single pipe, similar to the N1. So I'm guessing that you're planning to add a Y-pipe to this equation? If so, the math should look a little something like this. **Again, just to find free flow air rates at first...**

Restricting Diameter:
A 3" race pipe (still dual) will have an area of 18.84 sq. in.
A REV TII muffler with a 2.375" ID will have an area 14.915 sq. in.
A Road Race muffler with a 2" ID will have an area of 12.56 sq.in.

Exhaust length estimate:
2.5' of header + 2.5' of pre-silencer + 2.5' of Y-pipe + 2.5' of muffler and tubing = 10' of bent and curved tubing.

Free-flow rate estimate:
3" pipe = 18.84"sq. x 120" = 2260.8"cu.
REV TII = 14.915"sq x 120" = 1789.8"cu.
Road Race = 12.56"sq x 120" = 1507.2"cu.

Now we can take the 3" race pipe and divide it in half (one for each muffler since this is the limiting factor) and we get a 3" free flow race exhaust that will support 450 HP (conservatively, really over 500 according to Racing Beat's info.)

Safe power assumption: (Time for some more estimating)
3" pipe = (2260.8 / 2260.8) x 450 = 450 HP
REV TII = (1789.8 / 2268) x 450 = 355.12 HP
Road Race = (1507.2 / 2260.8) x 450 = 300 HP

So... IF these are the only limiting factors then you should hypothetically be safe running them for up to right around the 300 HP mark.
But just remember, exhaust pulses, pipe lengths, heat expansion, and back pressure will cause these numbers to change. Not to mention the fact that we don't know if the mufflers have a more restrictive packing that would decrease airflow. In my opinion I think you will be safe up to the 300 HP mark.

If you want anything more than that either someone can start doing the more precise math on it including differences in AFR and boost pressure with relation to heat expansion.... Or you can email Racing Beat.
Personally I think in the long run you'd be better off picking up a REV TII system and either modding the pre-silencer to hit the Y-Pipe or pull the downpipe of the REV TII and have an adapter built from your header to your new system (That's actually what I'm working on doing at the moment.)

**BTW, it is 4:30 AM and I'm still up. So if the math is weird oh well, just correct it for me.

Also take a look at the reference from Racing Beat down below DAK.

References:
http://www.racingbeat.com/manuals/perf-guide.pdf

Dak

[QUOTE=jjandros;12239952] I can't find much info on the HKS cat-back but if I remember right it's a single pipe, similar to the N1. So I'm guessing that you're planning to add a Y-pipe to this equation?/QUOTE]

The HKS sport was similar to the RB cat-back at the time but the mufflers were of a slightly different design so it has a y-pipe and two mufflers. It was discontinued somewhere around 2002 or 3.
Could you post the formulas you used? Thanks.

I'd like the REV TII but for some reason RB charges almost $100 more per muffler and I don't want to pay it. I could use the turbo mufflers from their cat-back. I think they have the same I.D as the Rev TII. I just wanted the extra length of pipe before the flange.

jjandros

iTrader: (7)

I re-read my math this morning and just to let you know, the exhaust length wasn't need since we have so many constants. The thought behind the basic math is finding a correlation between proven horsepower abilities on the REV TII. Taking the smallest part of the exhaust, grabbing the ID surface area of the smallest part of the system and then giving a correlation to a straight 3" pipe. In all honesty, The combined surface area of dual 2 ID pipes vs is this:
(2in. surface area) vs (3in surface area)
((2*Pi*R)*2) vs (2*Pi*R)
25.2"sq. vs 18.84"sq

So in theory, the flow rates of the true dual exhaust will support the same flow rates; in fact the combined inside volume of the true dual exhaust would be more than that of a just fully straight piped 3"exhaust. And I know there are race motors utilizing 3" single exhausts supporting over 500 HP. Again though, Just straight volume is only the beginning of the equation. This was literally just to find a small correlation between potential power and the volume of the exhaust. With that being said, your biggest issue will be finding out the baffle design and packing material in the mufflers to see if one muffler is more restrictive than the other. If both exhaust use the same methods then I'm pretty sure 300 HP is completely feasible.

If you want a really easy method to see if the exhaust can support flow rates for 300 HP simply look to see if anyone is using the True Dual setup on a Peripheral Port NA motor and is beating the 300 HP mark. Pretty sure you're good bud. I would just verify it with Racing Beat. I can do basic math, but these guys still designed the things lol.

Dak

That makes more sense. Didn't look like you were accounting for the two pipes before.

As far as I know both are straight through with no baffles and stainless steel wool packing. At least that's how a buddy's cat-back muffles were an from what I understand that's how they're still made. So no difference except for pipe dia.

I think most if not all the Peripheral port setups I've seen on here are running singles. PP need to be collected sooner than a streetport IIRC and they then use a single since it's all custom anyway. IIRC true dual would hurt power on a PP. From what I've read even a Streeport needs collecting and the true dual works best on a stock port so I'm out of luck there. That being said I did find a dyno of a BNR stage 1 making 247 rwhp with a 3" DP + 3" mid pipe with the stock cat-back and mufflers. I think I should be good as the RB mufflers are much less restrictive and flow much better compared to stock.

Jager

iTrader: (10)

Check into what J-Rat did on an NA catback. I think he ran into the 10's?

The mufflers won't be the biggest problem you'll have have IMHO homebread (if it's okay to call it that).

I got a homie who runs close to 800hp through a 3" chambered off the shelf flowmaster, not ideal? Maybe, but there's a point where power is power.

https://www.youtube.com/watch?v=Q5NE...ature=youtu.be

FührerTüner

iTrader: (5)

More than you'll ever make on an NA.

Dak

Right. I doubt I'll even break 200 as I've decided to not go to ITB's as the money spent on that setup could be put towards turbo parts. If it ever happens the plan is to go standalone ecu and learn to tune on it. Try to get as close to 200whp as I can on the stock intake manifolds then go turbo.

Jager

iTrader: (10)

https://www.rx7club.com/time-slips-d...10-7-a-802107/

Ran this down for you. Rest post 18.

Go for it brosef stalin.

Dak

Cool thanks. Looks like I should be fine. I would probably try to eventually go 3" (sometime after the swap to turbo) till the split at the Y then 2" per side to the mufflers.
6.9 in the 1/8 mi . is impressive. I drove my brother in law's V8 civic( mustang front. tube back half with a civic body) some one race season years ago. I think I ran 7.20's in the 1/8mi. I realized just how slow my n/a is after that. It ran low 10's on the stock ports. I need to go back and see what the streetport does. If I could hit low 8's I think I'd be happy.

Jager

iTrader: (10)

Word. I have never gotten into 1/8th mile drags. I should see what my LS1 FC did back in the day.

12.7's and 119MPH with a 2.260ft iirc in the 1/4 mile. I wonder what a Cartech will do?

Dak

1/8 mi. is all they have close to me. I'd like to get 1/4 mi. times but I think the closest track is like 3 or 4 hrs. away vs. 30min. for 1/8 mi.

insightful

i think i'd have to start riding a bicycle if i got trolled by a turbo V8 s10...

lol


but anyways, yeah, turbos don't care much about mufflers. but they will respond better with less restriction. in n/a applications though, the backpressure from the exhaust and mufflers actually can improve or hurt the powerband, so there is a lot of math involved with the n/a exhaust and where you need your power.