XtremeClassics Headers advance look

[Mike Inglis]

If you want to make meaningful comparisons, then you must compare like with like. No two sound meters are the same, no two locations have the same accoustic properties. Ambient humidity, temperature and air pressure will affect the readings. The same motor will produce different decibel readings when static or under load. Noise from the engine, other than exhaust emission (such as intake roar) will have an effect on the total noise produced, so it is unrealistic to try to make such comparisons meaningful.
The only things that actually matter are the noise as measured by the offical marshal at the event, and the published maximum permitted for that event.
There are many different principles and designs of exhaust systems and mufflers around, some of which work very well, and some that do not. Some reduce noise very effectively, some do not. Some systems which at first glance look very inefficient reduce noise to acceptable levels at the cost of only a few BHP. Some absorb more power than others. Some are very heavy or ugly, some are relatively light or aesthetically pleasing.
The bottom line is that we are using big powerful motors that procuce a lot of noise.......and it's beautiful.

 

[Ron Earp]

Gary, you are very correct on what you say. The weighting can play a big role and this NEEDS to be defined more so than the distance.

But distance plays a role too. The distance you measure from can have a huge effect. That is, 1m or 0.8m, it needs to be accurate. Why? Because of the inverese square law.

You basically can treat the sound as a point source coming from one pipe(although you have two points and constructive and destructive interference play a BIG role here). If you treat it as a point source then the sound at twice the distance is 1/4 the intensity. I did a quick serach so folks could check it out:


The Good Old Inverse Square Law
So, if the meter has problems with linearity with loud sources you might want to be close or far, depending on how the meter reponds. That is, if it has problems with loud sounds with small differences (0.1 db etc) then you might come out better being close. On the other hand, if it has a high dynamic range and is very linear you might be SOL.

R

 

[Julian West]

I agree with Jasper. The bottom line is getting the car thru the noise test on the day.

FWIW I competed in a dozen of so sprints last year (in my Lotus) & at every event I was noise tested & just about every time got a different reading. Who gives a 5h1T as long as it passes! /ubbthreads/images/graemlins/cool.gif

Maybe someone could explain to me why it is apparentley so difficult to silence a GT(D)40. At every event I enter I see loads of cars with all manner of V8's, V10's, F1 style Judd engined single seaters, Westfield V8's etc etc & even a GTD on a couple of occasions!

There are a number of chevy & ford engined V8 Cobras & GT40's & the like running in SR & GT circuit racing & obviously these cars all pass the RACMSA noise test.

Correct me if I'm wrong here, but it is not impossible to get a big V8 thru a noise test, so why is there a problem with some GT40's??

 

[Ron Earp]

I take it these guys measure from your tailpipe at the specified distance? If so, then the other cars have an advantage in the fact tha the engine is far away, so its' noise isn't contributing and they have a real exhaust system. With the 40 you are stuck with a very short system which does much of nothing to spread exhaust pulses out and your muffler can only be so efficient because you have a small place to work in. You are limited in total chamber volume (pipes and muffler) and thus muffling ability and resonance tuning.

On the 40s that pass do they use a single muffler that mixes both sides, a single muffler that keeps them seperate, or two mufflers that keep the sides seperate?

R

 

[Mike Inglis]

Hi Julian, the big problem with GT40s in general is that we do not have very much room at the rear of the engine, particularly if we want the exhausts to exit in the normal manner.You need a big silencer box to muffle/dampen/cancel the noise produced by a powerful v8 motor, without losing too much power or having too many tight restrictive bends in the system. The standard GTD system that I originally had on my car produced about 104dB, and got me into Goodwood without fail. Howerever after increasing the power to something around 500bhp, it was 111dB on the same system.
I have now got a large bore system with several sets of mufflers which allow me to run at 103, 111, 117 or 122dB. You pays your money and takes your choice! /ubbthreads/images/graemlins/cool.gif

Incidentally, I think that Mark's system looks excellent, a real thing of beauty, and those Burns collectors are the business!

 

[Jools]

Now if you really want to throw some accoustic theory into the mix.. It should be "possible" to attenuate the exhaust gases through a system of pipes that use different metals, and their inherent differing resonant frequency's , rather than " muffling" the actual gases.... Go play and let me know when you suceed!! /ubbthreads/images/graemlins/crazy.gif

 

[Mike Inglis]

Julian, you should be able to help with this....how about an "active" noise cancelling system? /ubbthreads/images/graemlins/wink.gif

 

[Jools]

Has allready been done Mike! A couple of prestige models use the cars speaker system for active noise cancellation of road rumble. A bit heavy all those speakers and amps for our use and unfortunately not very effective for scrutinering!... well compaired to the removal of a couple of spark plug leads anyway!! /ubbthreads/images/graemlins/grin.gif

 

[Brett James-McCall]

Jools,
Some other manufacturers do it as well... get a Fiesta up to speed and you hear the noise cancelling on through the speakers.....

Brett

 

[Jools]

Have heard plenty of noise comming out from Fiesta's , only they are normally parked outside Halfords!! /ubbthreads/images/graemlins/grin.gif Note: Can a Fiesta really " get up to speed" /ubbthreads/images/graemlins/tongue.gif

 

Jasper,

Yoodaman. I believe Lotus Cars worked with Bose and created an active noise cancelling system a few years back. The system produces sound waves inverted to those it senses. Presumably one could dial in total silence or tune it to sound to your particular liking. I have no idea of cost or weight of the system.

Nice way to thumb your nose at the sound police (scrutineers).

Mark

 

[Mike Inglis]

Hey, I could make my Lotus Elise sound like Concorde! /ubbthreads/images/graemlins/laugh.gif /ubbthreads/images/graemlins/laugh.gif /ubbthreads/images/graemlins/laugh.gif

 

[Jools]

You leave that poor little Lotus alone Mike!.. It's the only car in your toyshop that remains reasonably unmolested!! I know you've got a heap of F1 parts just sitting around looking for a project... but an Elise is not the vehicle for a V10 transplant!! /ubbthreads/images/graemlins/grin.gif

 

[Brett James-McCall]

Jools,
I believe a 911 Turbo got a shock on the M5 in August when I flashed him & overtook him in one of the Fiesta's I had borrowed for a weekend /ubbthreads/images/graemlins/tongue.gif /ubbthreads/images/graemlins/wink.gif

Brett

 

[Chris Duncan]

Mark,

Nice job on your headers. Did you make the collectors from scratch?

I assume when you sell them that each set will be "to fit" a customers set-up as your current example won't fit a drivetrain with a G50 transaxle due to inverted position of the transaxle.

Have you looked at Super-Trapps for people that need quieter mufflers? They have adjustable noise level, very light, compact and come in stainless at about 150.00 per.

 

[Chris Duncan]

Dave, I would think twice about coating stainless. I don't think you gain very much due to the fact that stainless does not transfer heat very much. All you end up doing is adding weight.

See www.burnsstainless.com for details.

 

[Chris Duncan]

Rob,

equal length headers need to have less that 1/4" difference between primaries in order to be effective. Very carefully measured on tube centerline which is difficult as the tubes twist and turn.

Nathan,

The horsepower loss between equal and unequal length header primaries is 5 percent or less. So on a 400 HP motor your looking at about 20 HP max loss.

I went with unequal for several reasons, equal length are not compact and thus don't look near as good, take up more room in an already crowded engine compartment and the original cars didn't have them. I think the crossover effect outweighs the unequal problem to a certain amount also.


Mark,

was your port match a piece of cake with that wide spread bolt pattern? Mine was jammed and difficult, it takes a special wobble socket and wrench to get at the bolts.

 

[Jim Rosenthal]

Not just the headers...the whole engine room is a work of art. I hope my engine and plumbing look that good. You ought to be proud of your work...I would be.

 

[Bill Bayard]

Jim,

Engine room? We're talking cars not boats!
Put the Hatteras to bed for the winter!
It's a pretty engine bay though! /ubbthreads/images/graemlins/wink.gif


Bill

 

To Kalin D , Like to see some more pics of your Chassis. Never have seen one Naked.

Vic
CAV 40