Presilencer recommendations
 

Anyone know of a good quality presilencer we can use on our rotary engines? I'm trying to quite down the exhaust on my '75 REPU just a tad without changing the flow any. Right now it has headers into a single 2 1/8" pipe into a muffler. It's quite tinny and loud even at idle under no load so I would like to have a presilencer of some kind welded in where the straight pipe section is. I talked to a local muffler shop and they recommended just going down to my local auto parts place and picking up one of those cherry bomb things. I've heard those are crap and don't last very long with our higher exhaust temps, hence the question. I'd rather avoid buying some junk from a general auto parts place that won't last, but that's all anyone seems to know about.

Thanks,
Mike

I use Magnaflow mufflers successfully with Mazda Rotary. It can take the heat.

http://magnaflow.com/

FWIW I replaced the cheap 2" turbo muffler on the rear of my REPU with a Magnaflow 2.5" 33" long 6" round muffler and it is both quieter and makes more power!!! It just barely fit in after the diff and before the rear of bed.

I bet the same muffler would work well under the cab of REPU!
IN/OUT LENGTH OVERALL PART
2.5".......... 27"....... 33".... 12640

Yeah I did a little research today and discovered that Magnaflow seems to be pretty high quality while not being overly expensive. I visited a few muffler shops and they showed me a Magnaflow muffler, I think part #10415 & #14415. They are the same thing, just the 14 number is the stainless version. Inside they are identical I was told.

Hmm, 33" definitely won't fit on my REPU - at least with the muffler I have on there. One muffler shop I went to said mine was "blown out" anyway, so I might just have that replaced. The Magnaflows I was looking at were the 14" model but I guess they have several lengths available. I wonder if I should just ditch my unknown brand blown out muffler and put a longer Magnaflow on like you did. I'm not sure the 6" round would fit under the cab though, I'd most likely have to go with one of the 4" round versions.

So how does it sound? Got any photos of it? Do you have just headers into the Magnaflow? I'm wondering how sound would change if I replaced the muffler with a Magnaflow. I'm thinking it would probably get louder if I went that route.

If I hadn't used it for myself, I wouldn't have believed it. I'm using the complete RB setup for streetported engines, consisting of header, dual presilencers and primaflow muffler. I got it from a friend for $100. After rebuilding my streetported 13b and getting it running with just header and dual presilencers, it was very loud. Since this system came off his GSL, it was quite short for my 3. After adding some pipe to make it reach the muffler(RB Primaflow muffler), this thing is soooo quiet, the Holley is actually louder than the exhaust at WOT. U might even try the muffler first.

Racing Bleat presilencers sound good, last a LONG time, and are mildly restrictive at most.

Anyone know if the Magnaflow "Powerpack" is just as sturdy (ie. same internal construction) as the round body mufflers we were talking about?

Here's what I'm talking about:

http://www.magnaflow.com/02product/xl/xlpower.htm

Thanks,
Mike

Hi Mike,

You can see pics of my exhaust on my signature. And I'll post another here.

RB road race header.
Dual side by side glasspacks under the cab that are 40" long each and 2" inlet/outlet diameter.

Flowmaster collecter dual 2" into single 2.5"

about 6" of stainless steel 2.5" flex pipe over axel

Aforementioned 6" round 2.5" inlet/outlet Magnaflow muffler. 27" long can, 33" overall length. Just barely fit under there but the flanges for the muffler are 3" long each and I could have cut 1" off either end and make it shorter.

Overall the sound is very, very nice. NOT loud. Still has some rotary raspiness so you know the motor's got rotors. The Magnaflow is definately quiter than the cheesy cheapo 2" inlet/outlet turbo muffler that was on there. And the magnaflow plus collector and 2.5" diameter makes more power too!!!

For reference, the exhaust is now quieter than my dellorto carb with 41mm chokes revving up to 8000rpms!

I bet those Magnaflow Powerpacks will work well as presilencers and at a better price than RB.

I don't know if my dual 2" dia 40" long glasspacks have 'blown out' like so many people say they do because of exhaust heat. They just look black and sooty inside. But like I said now my exhaust is quieter than dellort carb so I like what I got.

I say go for the Powerpack!

Oh and the Magnaflow collector is a REAL nice pice of work. I'd buy one of those over flowmaster collector next time.

Here's a closeup of my exhaust after glasspacks and before magnaflow. I'm holding the POS pipe that used to reside in there when I bought the REPU. I think my exhast is over 15 years old.

You can also see the glasspacks sticking out of the cab. They look like big sausages.

https://www.rx7club.com/forum/attach...postid=2255784

Ah, yes. Very nice, thanks for the info & photos. I was talking to my pal who builds race cars and he recommended DynoMax stuff. I'm still doing a little research on the whole subject but I think I'm going to go with something similar to yours only my header collects before the flange so I'll only have one "bullet" or presilencer before the muffler, and probably about 2 feet of pipe.

Either that, or I could try to find a road race header and build a true dual system. Not sure which is really best in a NA application.

For some reason my current muffler exits out the passenger side near the back bumper/bed. Was this the normal exhaust exit point on REPUs?

Mike

dual exhaust merging together before the axel will make more peak power and wider powerband in my experience. For my 1st gen I ditched the RB short primary system for RB dual presilencer 'street port' system and that's what i experienced.

I bet RB would be able to make you one of their road race headers for REPU.

Otherwize I really would not have 2' of pipe under the cab. Makes it louder and California is getting much stricter these days on loud cars. At least put two bullet or presilencers in there in series!

My exhaust exited at the same place.

Hmm, we'll the 2' was just a guess. I'll have to actually get the parts in hand to see how much piping will be required.

I think we're going to go with 2.5" diameter piping and components instead of the existing 2.25" or whatever it is. I assume any 86-92 NA 13B header would fit, that's what is on there right now only it's the collected street version.

Mike

Hey, I know this is a REALLY old thread but I thought it was worth an update. Today I had the exhaust totally redone on my '75 REPU.

Ever heard of Gibson Superflow mufflers?

http://www.gibsonperformance.com/mufflers2.asp

Well, I went to the muffler place with a 3" inlet/outlet Dynomax muffler and RB presilencer which I already had but the guy said the Dynomax was a little large for my application which I agreed with. He said he would trade the Gibson muffler straight across for my Dynomax since mine was brand new also and they sold for about the same price. We also opted to leave out the RB silencer since it was only the 2" inlet/outlet version and I wanted 2.5" piping. I was thinking that would be a little loud, but I'm pleasantly surprised with the results. You wouldn't believe all the leaks my old system had, no wonder it was so freakin' loud. Heh.

Anyway, now I have 2.5" piping from the header all the way back to the muffler. The muffler itself is the round style, I believe it's 36" long, 6" tall but I don't see that size listed on their website. Perhaps it's an older style or some specialized size. Either way I'm very happy with the results so far, it has a much meaner tone than before and it's 10x more quiet in the cab now. Apparently most of the leaks were right underneath the cab which made it nearly impossible to even hold a conversation most of the time.

Mike

Sweet!


?Pictures?

Nah, didn't think to bring my digital camera. I'll try and get some when I get the tranny mount fixed, that's on the agenda this coming week.

Mike