cshaw07

iTrader: (14)

My car came with a RB street port exhaust and a really crappy fart can type muffler that who ever put it on ran it under the axle, i dealt with it for maybe a month and then bought the RB power pulse muffler to get rid of the hideous and unbearable fart can. Fast forward about 15k miles and now I'm not really liking the power pulse that much, it's really quiet. I have a 3" stainless magnaflow muffler that i'd like to run with the street port header and mid section. I don't think it will be that loud, but will sound good (opinions?) I was reading on RB's site and I think they mentioned the stock exhaust piping being the same size, is this true? I dont have one to measure, but if that was the case I could get a good condition stock muffler rear section from a junk yard and then collect and weld my magnaflow to it rather than making it myself.

cshaw07

iTrader: (14)

the rear section from an 81-83

Cookboy

iTrader: (10)

Hmmmmm. This week I'm attaching a recently acquired street port center section and over axle pipe sans muffler. I'll be attaching this:



I have this muffler now behind an RB silencer and a 2" Magnapack, which I think sounds great. I expect my sound level will increase. I'm curious as to the quality of the sound. I'll let you know. If I don't like it I'll buy your muffler.

cshaw07

iTrader: (14)

you should just save your self the trouble and buy my muffler anyway!

Sh00bs

iTrader: (8)

always been a fan of the "true duals" all the way back, hard to find all the pieces to have one though

j9fd3s

iTrader: (3)

the RB street port is 2x 2" thick wall pipe, until it collects, and then its like 2 3/8" piping into the muffler.

the stock Mazda piping is ~2" also, except there is one pipe and RB is using two.

Cookboy

iTrader: (10)

I think the sans muffler axle pipe I got is Monza. It's 2 3/8 after the collector.

rotarygod

iTrader: (1)

When I had a first gen, I had an RB streetport exhaust. I didn't like the fact that the pipes on the muffler were smaller than the rest of the piping so I radiused the inlets to them at the flange to help flow. I was convinced that the exhaust was too heavy and didn't do that much so I sold it. Once it was gone I missed it. I went to a standard header and a 3" muffler. Power was down noticeably everywhere. I hated it. The RB exhaust was actually very nice power wise and I should have kept it.

Jeff20B

iTrader: (13)

I had a similar experience. I followed the advice given out on the forum from folks who did a short collected 3" trying to get up to 200HP NA. So I built a full 3" exhaust and used an RB road race header but collected it right after the flange. It was loud and had no power. It had a 5" Camden on it so I figured it would have at least some power.

Fast forward to last year when I swapped a full RB long primary on another 7 and this time just had a modded Nikki on a 4 port 13B (similar engine as was in the other car). This was much quieter and had way more power everywhere. The low end torque makes it far more pleasant to drive. The high end is better too as far as I can tell. It could spin up to 8k no problem. The 3" seemed to struggle.

Makes me wonder what that guy was smoking recommending an exhaust that was flawed. Think about it. You're collecting two 2" pipes into a single 3" collector. That makes for a nasty air slug at low to mid RPM. It only wakes up at high RPM. However the RB long primary is "awake" at all RPMs. Infact we know the high RPM flow is there because someone else with a Camden set a record of over 200HP on one of these RB long primaries.

There is another guy on the forum who recently got the same header as the other guy (I think it's SDJ or some other similar three letter name) which collects at 3" then goes into a newly designed RB PR extreme muffler. The muffler has a 2.75" inlet which is fine that far back from the engine, as you would know, due to exhaust gasses contracting a bit when they cool. He posted a video of the car driving and it's kinda hard to hear just how much noise it makes but I can assume it's a lot louder than the RB long primary. And knowing what I know about long primaries vs short collected, I can also assume it's got less low end torque with either the same high end or similar.

In my opinion, the extra noise and less low end driveability is not worth it.

There may be a reason to use an exhaust like his though, if you have a bridgeport or peripheral port, however if you are driving one of these on the street you'll need to cork it way down with mufflers thus ruining the flow capability of the ports and ultimately making less power than a simple streetport would have made. So I see no point.

rotarygod, this got me thinking. Has anyone tried an RB long primary on a p-port or bridgie? How does it work out? My thought is flow is flow and RPM vs sound frequency vs primary length holds true regardless of port style. Just pipe diameter plays a role. So if I were to design a streetable p or b port exhaust, I'd run 1.9" or 2.0" ID thickwall primary pipes like RB recommends (that'd be about 2 1/4" OD mandrel bends which I think you can get from columbia river mandrel bending and other places), then I'd fab up two presilencers copied from the RB long primary design in length and placement, just with 2.25" perforated cores. Then, because we now have access to RB's PR extreme muffler with its interesting 2.75" inlet, I'd look for a 2.75" mandrel bend to get it up over the rearend. Can be 16 gauge at this point but 14 would be better due to its size. I'd also connect the dual 2.25" outlets from the center section into a set of 2" pipes* to get them up over the rearend to join the 2.75" collector. So to put it another way, just a scaled up version of RB's long primary.

*where you mention how the RB muffler pipes are smaller than the center section, I did some thinking and measuring. Turns out the actual difference is pretty small and not worth worrying about. What you have is a center section ID of 1.75" flowing into a muffler section of 1.5". The OD of the muffler pipes is 1.6" as they are 14 gauge and not very thick compared with the center section's standard RB thickwall 11 gauge. The muffler's collector and inlet pipe is 2.375" 16 gauge. The ID is 2.25". Interestingly this 2.25" ID is the same as RB's thickwall 2.5" 11 gauge tubing.

But what does it all mean? The short answer is the RB muffler's smaller pipes aren't a problem as the exhaust gasses cool and contract back there, so you need the smaller pipes to keep velocity up at low RPM. High RPM doesn't seem to be affected but I could be wrong. If you want to radius or bevel the inlets at the flange, go for it, but with a tiny step like that, I wouldn't even bother. What will you gain? Like 1 or 2 HP?

As for the full 3" exhaust, this year I added an S5 turbo with a 3" downpipe and mated it to the full 3". It is so much quieter now and actually has the low end torque of an RB long primary. It has a bit much bass at idle, being a full 3" so if I had to do it over, or if it was available at the time, I'd have gone with the PR extreme muffler for the turbo. Quiet (I assume) and it would still flow plenty at high RPM due to being that far back in the system. You only really need a 3" DP with one of these turbos. The rest of the exhaust could be 2.5" if need be.

cshaw07

iTrader: (14)

Thanks for all the info guys, but i'm not replacing the whole exhaust, just the muffler. I have the complete RB streetport exhaust, but plan to put a 3in in/out muffler on it to see how I like it. Power is great as is, im just after a little more noise.

Jeff20B

iTrader: (13)

If you want more noise, get a 2.5" straight through like RB's universal 2.5" muffler or a Magnaflow 5x8" at 18" long with straight through, or actually a center/offset might allow easier pipe fabbing due to limited space back there (so it enters at the offset and exits at the center). Not technically straight through but will have plenty of noise. Heck I built a setup with a 5x8 straight through and it has plenty of noise for the owner. He really likes it but it's too loud for me.

Remember exhaust gasses cool and contract back there so no need for a 3" anything. You'll get an air slug. Low end will be less torquey. You've been warned.

rotarygod

iTrader: (1)

Long primary systems work equally as well on all porting styles but the overall length requirements are different. A stock ported engine would want a longer system than a streetported. A streetported would want a longer system than a bridge. A bridge would want a longer system than a peripheral port. You get the idea. A peripheral port would want a system about 2/3 as long as a stock port long primary. The same is true for short primary systems and porting styles.

Jeff20B

iTrader: (13)

Is this in regard to the RPM where max flow is achieved/desired? Or am I missing something?

It was my understanding the crotch of the collector wants to be a certain length from the engine to perform best at a certain RPM. Or to put it into terms of sound, the frequency. Then the tubing diameter plays a role as far as flow is concerned ie a 13B will want a slightly larger tube than a 12A for the same port size. Then I make up for the limits of what tubing material is available such as 2.75" being kinda hard to find compared with the much more popular and common 3" for example. Or in the case of primaries, thickwall 2 1/4" mild steel for the propsed P or B port exhaust idea.

I have a little bit of background in radio and understand how a 1/2 wave or 5/8 wave antenna works. I believe I could apply that to exhaust primary length and make a nice happy "1/2 wave" at basically half the length RB recommends. I recall they said 120 to 125 inches is ideal. But most of us don't have that kind of room so a 60" to 62.5" primary would still offer some benefits in the same way but just one octave up.

Am I making sense? For example let's say we have a peak at 2.5k RPM, 5k and one at 10k with the full long primary of 120 inches. If we went with 60, we'd still get a peak at 5k rpm and another at 10k, but we'd also keep our 2.5k peak, just not as effeciently as before. The point is they'd still all be there, just with a peak effeciency shift to the higher end of the RPM range.

I did an exhaust like this in the REPU. It turned out to be 61 inches. Perfectly half of RB's recommendation. It makes a wonderfull amount of low end torque the likes of which this truck had never seen prior. I've tried a couple different systems from an early attempt at a long primary fabbed in 1991 by someone else, to a more recent short collected fabbed in 2009 to the current 61" job fabbed in 2011 and it blows them all away. It's also very quiet due to plenty of room for big mufflers compelling me to swap out one in favor of a smaller one to get a little tone back. The midrange is fine too but haven't tried high RPM yet because it's got a fresh rebuild in it and the truck needs other work. But it's very free flowing so I assume high end will be fine too.

If I'm missing something here, please feel free to correct me because I'm eager to learn.

rotarygod

iTrader: (1)

Piping diameter doesn't affect piping length. It only affects flow. Tuning is determined by length. Obviously there are several variables but the main thing to remember in regards to why more extreme porting styles want shorter lengths is that port timing is a variable.

Siraniko

iTrader: (13)

So what lenght do you recommend for each category

rotarygod

iTrader: (1)

This is recommended lengths according to Racing Beat:

Short system
Non ported-Street ported: 22" to 25"
Bridgeport: 15" to 18"
Peripheral Port: 10" to 18"

Long system
Non ported - Street ported: 120" to 125"
Bridgeport: 113" to 118"
Peripheral Port: 89" to 94"

Both short and long systems require primary tube inside diameter of 1.7 to 1.8 inches except for peripheral ported which require an inside tube diameter of 1.9 to 2.0 inches.

My own personal recommendation is to use a 2-1/2" pipe after the collector for stock and street ported applications and a 3" for peripheral. Depending on the size of a Bridgeport, either may be desired.

If running a true dual system, limit it to only stock or streetported setups. Don't run a true dual with bridge or peripheral ports. You need the scavenging effect of a collected system. The total length of a true dual should keep each pipe equal length if at all possible. The total length of a true dual will affect the overall power band. A long primary is my personal favorite n/a rotary exhaust style.

Siraniko

iTrader: (13)

Got it. Thx

luiml73

iTrader: (1)

Love my RB exhaust. Worth every penny


upload gif


imagur

j9fd3s

iTrader: (3)

peejay has an RB streetport system on his BP car and he's as happy as a pig in poop.

the factory racing exhausts all use a thinwalled pipe, but they are ~43mm ID, just like the RB stuff, so 43mm is the right number.

i agree! the FC runs a 48mm ID pipe, stock, and this appears to be about the right size for a street car. 2.5" is slightly larger which is probably not a bad thing. 3" just isn't needed in a street car, imo, and i'm not sure its needed in a race car either. the 787 which makes ~700hp is only running a 4" exhaust.

do you think they would look at me weird if i took my micrometer to the 787's exhaust?

Bori rx

iTrader: (1)

Luim you gotta post some videos of that baby in action..
We have to hear it :-)

DriveFast7

iTrader: (1)

It will be horribly loud and droning. I had a 2.5" straight thru magnaflow and couldn't hold a conversation on the freeway. Had to lift when cops were around. If anything use some sort of chambered muffler. 3" is just big.

peejay

Full bridge:




It's a little restrictive but it's plenty quiet. I can't make any more power without more injector anyway so it works out fine. (I have since found that running the engine PAST the point where the injectors go static results in more power still... have tweaked times down to something like 13.7 at 103)