4722 replies to this topic

[Nev]

I still haven't been able to even test the car properly yet. Today the roads remained damp non stop and the stupid Xmas shoppers were dawdling everywhere.

 

Xmas morning is always empty roads though

 

I managed to get up to about 6000 RPM and I'd hazard a guess that I've lost a fair bit of power, though how much is very hard to know (last time I tried to guess my power I was 130 HP out).

 

Edited by Nev, 11 December 2016 - 08:46 PM.

[fezzasus]

Not surprising since you've effectively stuffed a pillow in your exhaust, at least you have a lot of space in the backbox to play around with.

[oakmere]

If this design is producing significant back pressure which it probably is I would be concerned about engine damage. Maybe 3 x 1.25" link tubes between the 2 main 3.5" tubes could be added?

[mbes2]

What make was your old system ? Could you just not rework that internally

[Nev]

The back pressure isn't huge at an educated guess, simply more than the last system (which was barely doing anything). Having studied the OEM back box design, I'd say my own design will almost certainly result in less back pressure up to mid/highish RPM. From about 6000 RPM my reflected wave pipe might cause more, though my turbulence strips in the perforated pipework seemed to help when I tested them. Hard to know really without some measurement.

 

If I feel intrigued, I might make a lambda sized bolt with a nipple outlet to feed to a pressure pipe + gauge into the cabin, so I actually see what pressure is in there.

 

Today I took the silencer off to install the lambda bung, which will give me a clue if it is running lean. I also reviewed all my welding and spot welded a few whisper holes which were showing small black "witness" streaks of soot. All of the welds on the hangers seemed fine which was my main worry and it's now re-installed in the car. I also wrapped the flexi pipe.

 

I have now installed my 275 Lb front springs and "nipped" out some of the tow out on the front (with a 1/4 turn of the rod end) which I'd been meaning to do for about 3 months. So far this car has had front springs of 225, 275, 350, 375 & 450 Lb !!

 

I am pretty certain I have the front set up how I want it now, TBH I would have preferred the 225 Lb springs for the sheer grip and positive turn in, but they simply weren't strong enough to stop the front of the car bottoming out on the road (which it did in a few places for the 1000 miles or so I tested them). Also at higher speeds there will be less squirming under heavy braking and the f/r brake bias will be as designed.

 

I also weighed my new silencer + flexi - it is 16 Kg. I don't know how that compares to an OEM silencer + cat + flexi + snaking pipework? Does anyone know by chance?

 

Edited by Nev, 12 December 2016 - 02:21 PM.

[tibby]

Got some weigth numbers from a NA system Backbox oem : 11.5kg Downpipe with cat : 6.2kg link from the above: https://www.google.b...mHhJGolF7hrSrLQ

[siztenboots]

2ubular 9.6Kg

 

incl. lambda, loom, decat, u bend , all fixings

 

 

 

the downpipe from turbo v-band , not included

[oakmere]

As an educated guess it must have more back pressure than your old box as there is no clear root for the gas to flow through. The glass fill is designed to absorb the sound not for the exhaust gas to flow through. Most off the shelf straight through boxes would work like your design if you put a blockage half way along the box forcing the gas out of the perforated tube through the fill around the blockage and back through the perforated pipe. Sorry Nev I don't want to sound negative but the design seems a little crazy to me unless I have missed somthing?

Edited by oakmere, 12 December 2016 - 03:34 PM.

[The Batman]

You are sooooooo gonna get told off

[oakmere]

Found this design which looks very similar to your spring loaded flap design. http://www.motoiq.co...-Mean-Slow.aspx

Edited by oakmere, 12 December 2016 - 03:41 PM.

[Nev]

As an educated guess it must have more back pressure than your old box as there is no clear root for the gas to flow through. The glass fill is designed to absorb the sound not for the exhaust gas to flow through. Most off the shelf straight through boxes would work like your design if you put a blockage half way along the box forcing the gas out of the perforated tube through the fill around the blockage and back through the perforated pipe. Sorry Nev I don't want to sound negative but the design seems a little crazy to me unless I have missed somthing?

 

The design (as always seems to be the case) was a compromise, so what seems crazy to you does have reasons, if you have a read of my pre design theory then you'd understand a bit more why I did what I did.

 

In short:

 

1. Flowing the gas through the wadding (whether it is (currently) wrapped around the pipe or simply near the pipe) should still work. In time it will detach anyway and then be trapped by the vertical wall hopefully, and still work.

 

2. The blocked off pipe was installed to try and stop the "drone" that most straight through designs suffer from. It seems to have been a success to my surprise, as I thought it would only partly work, and maybe only work at specific RPM.

 

3. Even though the bocked off pipe seems "crazy", you probably haven't appreciated that the x-sectional area of the holes are something like 7 times the x-sectional area of the 3.5" pipe. Thus there is ample scope for the gas to squeeze out of the perforations (even taking the laminar flow issues of gas going though hundreds of tiny holes).

 

Edited by Nev, 12 December 2016 - 04:10 PM.

[Nev]

You are sooooooo gonna get told off

 

It's fine when people don't understand stuff, particularly if it's off the wall and seemingly counter intuitive like the blocked pipe.  

Edited by Nev, 12 December 2016 - 04:06 PM.

[Nev]

2ubular 9.6Kg

 

incl. lambda, loom, decat, u bend , all fixings

 

 

 

the downpipe from turbo v-band , not included

 

Gosh, that is impressively light.

 

I wonder how much it would have reduced my noise down by. Would it have managed 116 db to 99 db?

Edited by Nev, 12 December 2016 - 04:12 PM.

[siztenboots]

 

2ubular 9.6Kg

 

incl. lambda, loom, decat, u bend , all fixings

 

 

 

the downpipe from turbo v-band , not included

 

Gosh, that is impressively light.

 

 

a lot of the weight is in the exit section and tailpipes.

 

if you went for a tailpipes integrated into the silencer and a Z flow inside , then you could drop a lot more.

[Ormes]

 

2ubular 9.6Kg

 

incl. lambda, loom, decat, u bend , all fixings

 

 

 

the downpipe from turbo v-band , not included

 

Gosh, that is impressively light.

 

I wonder how much it would have reduced my noise down by. Would it have managed 116 db to 99 db?

 

 

I know it isn't apples with apples but my 2bular on stage 2 records between 89 and 92 db  

[Exmantaa]

Your design is far of what aree accepted car muffler designs, but the proof will be in how much power is left and what backpressure this creates. (I assume your turbo wastegate will compensate for the raise in MAP pressure, unlike an SC.)

Just wondering why all the trouble with 3.5" diameter and then effectively designing a corc inside the muffler.

 

 

[Nev]

 

Just wondering why all the trouble with 3.5" diameter and then effectively designing a corc inside the muffler.

 

 

You guys need to read here and here if it seems confusing, it is explained.

 

[oakmere]

I appreciate the surface area is large but the glass matting wrapped around the perforated pipe dosn't seem to be accounted for in the design. Lots of talk of exhaust gas speed through a straight pipe but then no thought of the effect of trying to shove this through a dense material. Would you be happy filling your intake airbox with the same GF matting?

[Mopeytitan]

The idea of the perforated tube is not to allow the exhaust has to exit through it into the GF it's too allow the sound waves to pass and be absorbed by the GF. The exhaust gas speed shouldn't be affected by using them. I made my own 2.5" straight through exhaust with GF wrapped perforated tube and made a lovely noise when flooring it but went almost silent when holding any speed. And now I currently in the middle of building my own 3" system for my new engine

Edited by Mopeytitan, 12 December 2016 - 07:24 PM.

[Nev]

I appreciate the surface area is large but the glass matting wrapped around the perforated pipe dosn't seem to be accounted for in the design. Lots of talk of exhaust gas speed through a straight pipe but then no thought of the effect of trying to shove this through a dense material.

 

It was always my intention to use g/f in the silencer (as it's such an easy/cheap win), though my designs only show the metalwork side of things.

 

It might look/feel dense, but it really isn't in practice, I bet on a molecular level there is 20 units of space for every 1 unit of g/f. As a demonstration if you got a 1 CM thick layer of it and put it to your mouth and then then blew through it, you'd barely notice any resistance. Having said that, it does create a mild resistance for sure, and this is the drawback of using it (with the benefit of a 2 dB © noise reduction according to my measurements). Even if the g/f alone lost me 15 HP and the whole assembly cost me 40 HP it's still worth it IMO, as that is only a 8% drop which I could recover with a map tweak if I wanted.

 

I have double wrapped certain sections of the pipe to promote the gas to flow in/out of certain areas of the pipe. However within a few weeks/months it will probably all be in tatters no doubt, with the shredded remains hopefully being trapped by the "wall" and the exit (where it can still partly work).

 

 

 

 

Would you be happy filling your intake airbox with the same GF matting?

 

In an airbox it would create a mild resistance and serve no purpose. In an exhaust it creates a mild resistance and serves a 2 dB purpose. QED.

 

The material really isn't as dense as you might think, I got sent a box that was about 2 cubic foot and the whole thing weighed less than a KG at a guess.

 

 

This evening I have ordered up a M18 x1.5 threaded bung to shove in the lambda sensor hole. Once this is in I can connect it via a pipe to a gauge in the cabin and really see how much back pressure is there. Maybe I am wrong and it's vast (like over 10 PSI !), we shall see.

 

Edited by Nev, 12 December 2016 - 09:23 PM.