"Oh my bleeding ears" OR "Put a cork in it buddy"

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OK all you vast self-proclaimed Mazda gurus, here is the problem…

At Thunderhill the corner workers and officials alike all said my 1st gen 7 was making their ears bleed, their complaints were understood considering all I had behind my header was a 1 foot section of 2 ½” pipe into a dynomax strait thru bullet glass pack then another foot and a half of 2 ½” coming out in front of the right rear tire..

In 1983 I had the pleasure of standing downstream from the corkscrew at Laguna when the Mazda GTP car came thru so I know that sound, have you ever cut thru a 16 Penney nail with your skill saw?

So here’s the test.

One pro builder tells me a big single short pipe is sweet, another says two 2” to 2 mufflers is the best, yet another proclaims that without going all the way to the back im never going to achieve 93 DB which is required for Laguna seca in the AM.

Enter my vast pool of Mazda gurus and lead me to the promised land…


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Daryl Brightwell
ITA Mazda #77
SFR, NORPAC
CSCC, SOPAC
 
Why wouldn't you go all the way to the back? This allows for two things:

1. The inherent noise reduction in longer pipe and
2. The ability to put a "turn down" tip or in this case a "turn away" depending on what track you are at.

Send it out the back, put a bent tip on it and rotate it based on where the sound guys are.

AB
 
I've got a pretty popular setup on my 2nd gen. Two 2" pipes back to a collector near the rear axle into a single 3" through a Dynomax Ultra-Flo. Last time out at Mid-Ohio I had high score in my group at around 103db. "Turn-away" is on the way.
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Don't know how you'll make 93db without a good muffler.

Chris

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Chris Ludwig
08 ITS RX7 CenDiv

[This message has been edited by C. Ludwig (edited August 22, 2002).]
 
I stood behind a running CP RX7 on the grid back in 1979 or so (remember those days?), when the driver blipped the throttle. Fractured my, uh, femur. Yeah - that's the ticket...

K
 
93db? When I went for an open track event, it was only 90db at Laguna Seca. My car was too loud I had to lift at the microphone. Good thing it was just an open track event. It was my GSLSE, I have a R.B. header (2 to 1) into R.B. presilencer then a 2.5 inch pipe to a straight thru muffler (Apexi copy) w/ silencer. Without silencer at WOT it was 94 db. With silencer at WOT it was 91db. I started to lift after that. Now I am trying to build a 2nd gen for ITS but still have no idea what exhaust to run. I might go two pipes with two mufflers because it is quieter supposedly.
 
Isn't SCCA getting the 101/103 Db limits for group 5? Or are you going to try and run group 1 in the morning with ITE/X?

I'm running a 2 1/2" pipe back from my RB header, all the way back to a Magnaflow muffler. Mines freaking 10000% quieter than the PS2(aka ITA) RX7s I played with in Group 3 back in early August.

Anyway, that setup works for me, but dunno if I can meet 90 or 93dba for non SCCA events at Laguna. We'll see.

PaulC
 
Daryl,

I think your short system is "too-long". How far from the housing is the collector?.
The long primary style seems to work better, even though it is very difficult to get the collector far enough back (behind the axle) and still mount a reasonable muffler.

The Laguna limit my club had to achieve was 91db. I was not successful without an extremely suffocating supertrapp disc setup. The AROSC only runs 1 event a year up there, the last 2x I raced someone elses' car. Good luck. The old school "louder is better" isn't always the case. It's just hard to quiet the rotaries down enough without suffocating them...The high EGT's will quickly kill most cheap mufflers and any fiberglass packed muffler will be dead before your first session is over!
 
thanks guys. everyone agrees shorter means more power.

I have a racebeat header(30 inches from housing)

still too loud, but turnaway is good idea except SFR has 2 sound control stations.

AM practice for group 5 as far as i know still requires 93 DB.

and the burning glass pack explains why it got louder with time and the gray puffs coming out my exhaust before my motor blew last time out.

keep em comin guys.....
oh and by the way im tearin out the old motor as we speak readying the car for the new motor with will be completed by Mr Mobius monday and the exhaust will be welded up on tuesday so I need to order a muffler(s) friday..


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Daryl Brightwell
ITA Mazda #77
SFR, NORPAC
CSCC, SOPAC
 
We're running a RB RR header into a Flowmaster Y pipe (2.5"(?) to 3" outlet) then into a single 3" pipe all the way back to a 3" small turbo style muffler, then straight out the back about 10" behind the bumper (dont wanna catch it on fire
biggrin.gif
). WAYYYYY to quiet compared to the other 7's. It's quieter on the track than many of the other cars. I want to say it was in the low 80's at Gateway.

Of course this is an unproven design and was put on under the gun (drivers school the next weekend).

Next season, when I get more track time under my belt and get a little more consistant, we'll start playing with mufflers for all that hidden hp
wink.gif




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Scott
It's not what you build...
it's how you build it

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E-mail me for deals on
Lightweight Replica Blocks!
 
I'm running a street-port with a Racing Beat header into two 2 1/8" pipes all the way to the back, over the axle and then a "Y" into a 3" Ultra-flo straight-through. Works good, and our rules say:
1. Must run to back bumper of car
2. Must not exceed 98 decibels

last time out, the track said I was 97 db...whew!

Our rules are changing soon, down to 92 db, so I'm not sure what I'll do, but we will all have to do it..
 
Originally posted by 7'sRracing:
thanks guys. everyone agrees shorter means more power.

I have a racebeat header(30 inches from housing)
Click to expand...

Daryl,

Call RacingBeat, ask them about their short system recommendations.

I did when building my first rx7 because I couldn't get the long system long enough (past rear bumper), nor the short system short enough!

Their short system requirement was shorter than THEIR OWN HEADER. I understood that their short system was utilized on custom built header systems on Sports Racers.

Ask Pablo or Paul Yaw what they think. If Pablo thinks the short system is better, why don't more people that use his motors use them? Not sarcastic, genuine question.

[This message has been edited by Quickshoe (edited August 23, 2002).]
 
I did ask paul and pablo and got two different answers, paul wants it short and pablo wants it long....
Im thinking the muffler would have less tendency to melt down the farther back I can get it so right next to my fuel cell is bout the only place big enough to put one of those two 2 inch in and two 2 inch out corvette muffs, but ill have to shield the cell from the heat.. that way i can run two 2 inch pipes from the housing all the way to the back bumper, what do ya think?
 
This is >>>>IMHO<<<<<<<

I am running an SDJ header (collects at the end expanding to a 3" round) and have 3" pipe running all the way to the rear. There are two 45s that put it in the proper position and I have a dynomax barrel style muffler. On the dyno...she is very hot!

NOW...last race, we were running 3" OVALIZED tubing which my engine builder and a few other collegues warned against...and...they were correct. The pipe blew out about 90"s back just past the first 45 degree section and when I say blew out...I mean BLEW OUT. I felt it happend AND I noticed a rather "noticable" drop in HP as well. (BTW...I am usually at 100db MAX)

Atilla Lucaks (39IT-7) on the other hand is running straight that turn 45 degrees and exit at the front of the right wheel. He is PLENTY good on power.

Now..what I have been told is the the "sound" wave traveling through the tail pipe is a Sin-wave. And the "trick" is to have the wave exit at the zenith of the sin. Only effective way to do this is on a dyno.

SO..IMHO...there are two answers...both relating to the sin wave upon exit.

A lot of people will experiment on the dyno with different "extentions" to see the variation in lenghts to HP. From what I have heard, Density Altitude (temp/PA) has no effect on this lenght so, once you find it, you find it.

Again, just my humble opinion....



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Balz
#67 IT-7
www.balz.myip.org
"I live my life one Apex (seal) at a time"
 
rpm changes wave lenght frequency(note), so that would only work at a constant rpm. right?
 
7's every think about a "slippy" pipe?

Would have liked to try it myself. A little short on re$ource$. Some ex-karter turned Wankle lover must have tried it.

A "slippy" pipe is common in Enduro karting to widen/flatten the power curve. In a nutshell the length of the pipe is not fixed and is adjustable while the kart is motion with a spring loaded, steering wheel mounted, hand control. Pull it as the rpms rise, release it when the rpms are low.

The stainless steel pipes with a 1 3/4" inlet are about $200 each. Contact RLV in Santa Maria and tell them you want one built with 3" inlet/outlet and enough flow and a workable range from 5000-8000rpm. When they stop laughing, tell us how it worked.
 
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