Pre Silencer
05-27-15, 07:53 AM
#1
Pre Silencer
I have read many threads about various muffler recommendations but I can't find anything on pre-silencers. RB is backordered 6-8 weeks and I need one now!
Does anyone have any suggestions? I am using a RB muffler. Is it even that loud without one?
Does anyone have any suggestions? I am using a RB muffler. Is it even that loud without one?
05-27-15, 09:16 AM
#2
Moderator
iTrader: (3)
Join Date: Mar 2001
Location: https://www2.mazda.com/en/100th/
Posts: 30,835
Received 2,603 Likes
on
1,847 Posts
i'd be tempted to try without one, if its too loud than you can put something in the middle, but it won't last very long
05-27-15, 02:36 PM
#4
Customizer
iTrader: (4)
Join Date: Mar 2009
Location: Chagrin Falls, OH
Posts: 333
Likes: 0
Received 0 Likes
on
0 Posts
I used a Borla XR1 race muffler as a pre-silencer and it worked great. You can also use a bullet muffler. Just make sure you buy one made of stainless steel and that has SS baffling material to prevent burnout. IMO the pre-silencer is a must-have to prevent droning in the cockpit at highway speeds.
05-27-15, 03:10 PM
#5
84SE-EGI helpy-helperton
Whatever you install, be sure to use copper anti-seize on EVERYTHING when you put it in. Something about the hot exhaust on our cars tends to sinter the bolts and nuts to the threads over time from expansion/contraction and I cracked off one of the pre-silencer mounts to the tailpipe the last time I pulled mine out. I had to order a new one from RB, since the studs aren't really studs but bolts inserted from the inside. Once broken off, there's no way to repair it easily without either cutting it open or welding a new stud in place which may not last long.
I once ran my -7 with a header and nothing else and it was so ear-splitting loud that I probably made every dog deaf for blocks around. I still have a ringing in my ears!
You need that presilencer in there to help damp out some of the high impulse exhaust blast when the ports open and close so rapidly as the apex seal passes - this event happens much faster than a somewhat slow poppet valve on a boinger engine. Without it, you'll get a lot of tinny and raspy exhaust at the muffler, even with a RB Powerpulse muffler (same as what I have).
I once ran my -7 with a header and nothing else and it was so ear-splitting loud that I probably made every dog deaf for blocks around. I still have a ringing in my ears!
You need that presilencer in there to help damp out some of the high impulse exhaust blast when the ports open and close so rapidly as the apex seal passes - this event happens much faster than a somewhat slow poppet valve on a boinger engine. Without it, you'll get a lot of tinny and raspy exhaust at the muffler, even with a RB Powerpulse muffler (same as what I have).
05-27-15, 06:29 PM
#6
Moderator
iTrader: (3)
Join Date: Mar 2001
Location: https://www2.mazda.com/en/100th/
Posts: 30,835
Received 2,603 Likes
on
1,847 Posts
i fired the P port up open header, and it was like cannon fire. its kind of a good thing it didn't want to stay running, it would probably break stuff.
05-28-15, 11:04 AM
#7
I don't always use anti-seize, but when I do, I use the aluminun powder type, not the copper type because I experienced seizing with the copper version. The tube pictured above is the aluminum type.
I nearly jumped out of my skin once when my friend reved his long primary without a muffler installed. He drove it around the block and I could hear it all the way around. Then when he got back, he did a quick rev and I was shocked at how loud these can be.
The reason to run an RB presilencer is because they have an expansion chamber in front of the perforated core. The chamber allows the supersonic pulse to expand rapidly, then get sort of traped inside as the rest of the pulse is flowing through, then towrard the end the blast, having lost most of its power, can then follow into the core.
RB also uses a slip fit on one end of the core to allow the rapidly heating perforated tube to grow with heat while the external shell is still cold. Without the slip fit, the core would buckle.
That's not to mention the big industrial strength pot scrubbers used as noise absorbing material. Thy don 't really muffle but they absorb high frequencies.
No aftermarket mufflers like Magnaflow or Borla have these two rotary-specific features. They will either blow out in time or the core will buckle and crack/break and can block flow.
I experimented with building my own presilencers and employed these features. I also added a layer of coarse SS wool on top of the pot scrubbers to act more like a muffler and it worked. Not sure how long it will last compared to genuine RB stuff, but I posted a how to thread a year or two ago showing the parts used. Decide for yourself. https://www.rx7club.com/1st-gen-non-.../#post11844263
I nearly jumped out of my skin once when my friend reved his long primary without a muffler installed. He drove it around the block and I could hear it all the way around. Then when he got back, he did a quick rev and I was shocked at how loud these can be.
The reason to run an RB presilencer is because they have an expansion chamber in front of the perforated core. The chamber allows the supersonic pulse to expand rapidly, then get sort of traped inside as the rest of the pulse is flowing through, then towrard the end the blast, having lost most of its power, can then follow into the core.
RB also uses a slip fit on one end of the core to allow the rapidly heating perforated tube to grow with heat while the external shell is still cold. Without the slip fit, the core would buckle.
That's not to mention the big industrial strength pot scrubbers used as noise absorbing material. Thy don 't really muffle but they absorb high frequencies.
No aftermarket mufflers like Magnaflow or Borla have these two rotary-specific features. They will either blow out in time or the core will buckle and crack/break and can block flow.
I experimented with building my own presilencers and employed these features. I also added a layer of coarse SS wool on top of the pot scrubbers to act more like a muffler and it worked. Not sure how long it will last compared to genuine RB stuff, but I posted a how to thread a year or two ago showing the parts used. Decide for yourself. https://www.rx7club.com/1st-gen-non-.../#post11844263
Last edited by Jeff20B; 05-28-15 at 11:14 AM.
Trending Topics
05-31-15, 12:12 AM
#8
I ran the turbo engine with only an open downpipe for a while, right underneath the passenger's side floorboard.
I am convinced I lost hearing from that endeavor.
Can't you guys build your own presilencers with steel wool though? Jeff or Mike posted about that a while back.
I am convinced I lost hearing from that endeavor.
Can't you guys build your own presilencers with steel wool though? Jeff or Mike posted about that a while back.
06-01-15, 08:41 AM
#9
I have very little welding abilities and no access to a welding unit even if I could weld, so making my own is out. I'm just going to try no pre-silencer. Bringing it to the shop this week to have them fab the exhaust from the manifold to the RB muffler. Just selling this car anyway. If the next owner wants a pre-silencer I guess that will be up to them.
06-01-15, 05:33 PM
#10
84SE-EGI helpy-helperton
When you sell it, be sure to tell him about RX7Club.com!
We need to keep as many of these cars on the road as possible, and he'll probably want to know where to find information. Good luck,
We need to keep as many of these cars on the road as possible, and he'll probably want to know where to find information. Good luck,
06-01-15, 11:49 PM
#12
Moderator
iTrader: (3)
Join Date: Mar 2001
Location: https://www2.mazda.com/en/100th/
Posts: 30,835
Received 2,603 Likes
on
1,847 Posts
the lake cities intake rocks! we put one on FM's car, and surprisingly its really torquey
Thread
Thread Starter
Forum
Replies
Last Post