Sound requirement and straight-pipe

[Domino]

Does anyone know what the decible level is for a CRX with a straight-pipe ending right behind the driver and a tip pointing to the ground? I know it's fairly loud but does it meet the sound requirement? I don't want to have to engineer this thing only to find out its too loud and I'll have to go back to the drawing board.

[jc836]

I have no idea what the actual dB level will be for a fully open exhaust-except very loud. Some tracks generally will not let you run without some sort of muffler. There have been a few pictures of DIY "cherry Bomb" exhausts recently on the WEB. I would also doubt that they meet the CHP 95dB rule let alone the SCCA measurement rule. You might want to talk with someone from Flowmaster or DynoMax about your project. I do know that Thermal R&D tries to stay on the edge of 95dB with all of their products. I did a test here of the Thermal on my 99 Prelude and at 1 meter perpendicular to the center of the resonator I read 94dB max at 4000 rpm. What it is at the tailpipe-I have no idea-but definitely quieter.
Good luck

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Grandpa's toys-modded suspensions and a few other tweaks
'89 CRX Si-SCCA ITA
'96 Civic HB Just cruising daily
'99 Prelude=a sweet song

[Knestis]

The laws of physics make it such that lots of variables change sound level readings - air density (so temperature, too), physical surroundings, and others - so it is impossible to say what kind of actual readings your car will register.

Heck, it isn't even likely that the same readings will result at the same track on different days. Remember too, louder isn't necessarily faster.

Kirk

Edit - and noise contributes pretty dramatically to driver fatigue, FWIW.


[This message has been edited by Knestis (edited January 15, 2003).]

[davew]

I have run my crx w/ a 2.25" straight pipe as you describe, but with a dynomax bullet muffler on the end just before the trundown. It usually runs about 85-90db with a fresh muffler, and 95-105db once the muffler blows out. I just picked up a higher quality SS Borla bullet to try this season...hopefully it will be quieter and longer lasting.

I'd say that w/ a open pipe and no muffler at all you would be well over the 100db limit...but of course that depends on everything from your intake filter on through the whole motor and out the exh manifold, as well as enviromental variables, gas type, etc...

-dw

[Fleetcare]

I found an interesting thing that says the exact specs on how each pipe should be.

I suppose email me if you want the info

[Domino]

Originally posted by Fleetcare:
I found an interesting thing that says the exact specs on how each pipe should be.

I suppose email me if you want the info

Yes please. domino[][email protected] -delete the [] to email me.

[ITR#231]

<font face="Verdana, Arial" size="2"> Remember too, louder isn't necessarily faster.</font>

Wazzat? Speak up Kirk, you're mumbling...

davew,

What kind of life did you get out of the Dynomax bullets?

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'88 CRX Si - ITA/PS2 road racer: Handles like it's on jack stands
'98 ITR #0231 - DS autocrosser: Handles like I sold it
'02 Jeep Grand Cherokee - daily driver/tow vehicle: Handles like a jumping castle

[Richy Gonzalez]

I have the same setup, straight with Dynomax muffler and have been in the low 90 dbs.

Is Junktech out there? I know he redid his exhaust with a supertrap coming out the rear but I don't know what the dbs are.

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Richy Gonzalez
GB Racing - #24 ITA CRX
Racecar Sponsor: LAMIN-X Protective Films

[jasonb]

Originally posted by Richy Gonzalez:
I have the same setup, straight with Dynomax muffler and have been in the low 90 dbs.

Is Junktech out there? I know he redid his exhaust with a supertrap coming out the rear but I don't know what the dbs are.

Richy,

What diameter piping and muffler are you using and where does the exhaust end?

[B Breon]

I have done a straight 2.5" exhaust with no muffler and a turndown as you describe. I was bumping 104 with it. Was forced to move the turndown so it was pointed a way from the sound stand. VERY LOUD, better have ear plugs. I put on a Borla Bullet and am at low 90's consistently now. NO noticealbe change in power and I can hear now.



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Brent Breon
Cendiv ITA #26
www.360racing.com

[Richy Gonzalez]

JasonB,
I went with 2 inch pipe with the Dynomax round muffler at the very end with a turn down coming of the muffler itself. Also, it ends right behind the driver in from of the gas tank. The typical set up is 2.50 inch exhaust but I think that the smaller diameter will give a little more torque without losing any hp. ...but, I don't have any dyno numbers to prove my theory.

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Richy Gonzalez
GB Racing - #24 ITA CRX
Racecar Sponsor: LAMIN-X Protective Films

[Domino]

Originally posted by B Breon:
I have done a straight 2.5" exhaust with no muffler and a turndown as you describe. I was bumping 104 with it. Was forced to move the turndown so it was pointed a way from the sound stand. VERY LOUD, better have ear plugs. I put on a Borla Bullet and am at low 90's consistently now. NO noticealbe change in power and I can hear now.

I looked at the Borla Bullet on the website. Is this a muffler that doesn't allow you to put anything at the end, such as a turndown like on a typical muffler? I didn't want to go all the way to the back of the car (like stock) with the pipe. I want it to end right behind the driver. I don't think the Borla will fit underneath the middle of the car.

[jasonb]

Originally posted by Richy Gonzalez:
JasonB,
I went with 2 inch pipe with the Dynomax round muffler at the very end with a turn down coming of the muffler itself. Also, it ends right behind the driver in from of the gas tank. The typical set up is 2.50 inch exhaust but I think that the smaller diameter will give a little more torque without losing any hp. ...but, I don't have any dyno numbers to prove my theory.

Did you use the Dynomax Bullet muffler? If so, what diameter Dynomax muffler did you use?

[Richy Gonzalez]

JasonB,
The Dynomax muffler is 2.5 inches and I was able to stretch out the 2 inch pipe to fit snug inside the muffler, then welded it together. Then the turn down goes right over the 2.5 inch muffler end.

The Dynomax bullet (I think that's what they call the straight round mufflers) doesn't come any smaller then 2.5 inch diameter.

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Richy Gonzalez
GB Racing - #24 ITA CRX
Racecar Sponsor: LAMIN-X Protective Films

[ITR#231]

Does anyone have pictures of these set-ups? I'd like to see where you weld hangers and what kind of down-turns are being used.

My current exhaust setup is a custom "OEM + hacksaw" design, but it's too loud.

------------------
'88 CRX Si - ITA/PS2 road racer: Handles like it's on jack stands
'98 ITR #0231 - DS autocrosser: Handles like I sold it
'02 Jeep Grand Cherokee - daily driver/tow vehicle: Handles like a jumping castle

[CRX Lee G]

We tried a lot of systems (Supertrapp, various cans, straight, long, short, etc) and shorter was better. We ran the straightest possible 2.5 tube with only a turn down at the gas tank but it blew 102-104db and would vibrate your body in the car at wide open. Put a Dynomax bullet on it and it blew 90-92db with good power. On another car, we had a 2.0 inch (available) open and it blew 106db and was really raspy. Threw on a Cherry Bomb for the weekend and it was like stuffing a cork in it, very slow. Larger tube is deeper, quieter and better.

FWIW, I am a be believer in spring mounted breakaway exhaust that won't wreck your header and drag if hit on a berm, etc. I turned my best laps at M-O after being run off the road while leading and stripping the exhaust away behind the header. The uncorked header was LOUD and fast, maybe a second per lap. I didn't get busted by the sound cops and finished. Just picked up the pipe at the corner station and only had to replace two 50 cent springs to the header.

[SMSP]

Magnaflow has 4" round resonators in 2", 2-1/4" and 2-1/2" sizes with varying core diameters and lengths. These are just a little more costly than the bullets but won't blow out.

[Tom Blaney]

Originally posted by SMSP:
Magnaflow has 4" round resonators in 2", 2-1/4" and 2-1/2" sizes with varying core diameters and lengths. These are just a little more costly than the bullets but won't blow out.

Did you use the 2 1/2" dia? and how long, my last car had a 4 " bullet that must have been 25 feet long. Did you dump it before the gas tank with a down pipe? Appreciate the install information, this was always a problem install on the last car.

Turned out that the kid that built it had the exhaust aimed at the rear lower control arm front bushing, the bushing finally melted on me at Watkins Glen, and I crashed out a guy and angered that really fast Saturn driver. So this time I want to get it right

[SMSP]

I use a 10444 2" in/out with a 2" core for ITC cars. A 10415 2-1/4" in/out with a 2-1/2" core for ITA cars but open the outlet to 2-1/2" OD. On ITS cars I'll use a 10416 2-1/2" in/out. All these are 14" long x 4" round. 18" and 22" versions are also available if you need a little more sound control but all the cores are 2-1/2".

For a tunnel turn down I use either a mandrel bent 45 or a section of a U bend. Make sure the rear part of the tailpipe is not cut in a way to expose the opening when looking at it from the front. You don't want any air traveling under the car to be able to "see" the opening you'd rather the air rushing around the opening then hitting the opening. The same is true for side exit applications. Rear exits are a little more tricky since you want the tail pipe to be located in a low pressure area but the trick is finding that spot.

[This message has been edited by SMSP (edited January 25, 2003).]

[HiRcc#21]

I have done alot of dyno testing different exhausts over the last 2 years and here is what we found:
on my ita crx, we found a reading of over 120hp (year old .020 over bottom end) at the wheels with this set up:
Using a new Landspeed Racing Powercore header, and a Magnaflow muffler (part# 10425). 2-1/4 in and out, 18" can.
If you measure from the flange of the header back 3" and install the muffler (edge of the can)into a 2-1/4" pipe,(with a rotateable flange and stock springs for hardware-like Lee suggested) the DB's ran at Nelson in Oct.'02 was 87. Lots of top end and it didn't hurt the bottom end either.
The straight pipe ends 7 inches after the linkage. (measured from the attachment point of the shifter to shift linkage arm.)We welded on a piece of round stock and bent it to the similar specs of a factory pipe, and used the rubber hangers to the factory "hooks" on the tub, and it works fine. No vibrations in the seat at full song.
We built approx. 15 different styles to arrive at this one.
The header, just released, gave us 2 hp over the old DC 4-2-1 with no header wrap.
Hope this helps you out... It does work!