Anyone understand advanced exhaust gas dynamics???

[skid]

Are there any techies here as got a few Q's on exhaust design and understanding the effects of changes...

plus....

Is any one aware of a PH'er who could give advice on aerodynamics re a roof design.

Cheers

Skid

[deltaf]

Get this book matey! Scientific Design of Exhaust and Intake systems. By Philp H Smith and John C Morrison.

isbn number 0-8376-0309-9

published by Robert Bently publishers.
www.rb.com

HTH.

[skid]

Cheers Deltaf.



Skid

[350matt]

This might help
Exhaust length tuning

To discover the best length and diameter of pipe for your engine, you will need to know the exhaust valve timing; that is the number of degrees before bottom dead centre that the valve starts to open. with this knowledge you can then set about making a tuned exhaust system by working out the following formula and applying it to your own engine:
850 (180 + N)
L =(------------- )- P
RPM
where L = length of pipe in inches
N = degree before BDC exhaust valve opens
P = distance from exhaust valve to manifold
and RPM = desired RPM For peak power

The diameter of the pipe needs to be calculated so that the volume of the exhaust pipe attached to each cylinder is twice the volume of each cylinder. The exact diameter of the pipe, incidentally, is not critical and should only be used as a guide in determining which standard sized pipe diameter should be used.
As a guide, these are Ray's calculations for the A65 engine. He began with the knowledge that the exhaust valve opens 50 degrees before BDC. The engine capacity was 700 cc per cylinder and the RPM ran at 2,200. His calculations were as follows:
850 (180 + 50)
L =(--------------) - 3 in = 223 cm = 88 inches.
2,200
To find the diameter of pipe, Ray used the following formula:
ð r^2 L = 2 * 700cc
ð r^2 * 223 cm = 1400cc
r = 1.4 cm
Diameter = 2.8 cm or 1.1 in

Bear in mind these calcs are for a rough starting point they will not be accurate to the last inch.

Matt

[skid]

Crikey!

Thanks for the deatiled response! Think I will have to get my thinking hat on.

FYI I'm trying to get the best out of an existing design by playing around with the perforated tube by varying the length perforated/non perforated and removing the insulation.

Cheers
M

[greenv8s]

Hang on, it sounds as if you may be talking about silencer design but I think Matt is talking about tuning the primaries. Perhaps you should outline the problem you are trying to solve?

[skid]

greenv8s said:

Hang on, it sounds as if you may be talking about silencer design but I think Matt is talking about tuning the primaries. Perhaps you should outline the problem you are trying to solve?

Yes you are right.

System is in place. SBC 350 with 1.75" primaries to side pipes. There is no balance pipe between each side.
The Primaries are of unequal length as on an AC Cobra rep and space restricted. Average Primary lenght circa 24". These collect each side into a 3" perforated tube in a 5" casing which is about 36" long.

Not worried about the noise but was wondering what the effect of replacing the perforated tube, or sleeving a portion of it.

The engine/carb has been set up in situ and wanted to know what potential gain/loss/effect could be achieved by doing this.

Would it effect back pressure and need rebalancing?

Cheers Guys.

M

[v8 racing]

Trust me if you want your sanity to stay intact forget about exhaust design!! i have spent the last 10 years trying to understand the bloody thing, what will work on one engine is an absolute waste of space on another, the main factor being cam timing, the one bit of advice i will give is to keep it as small as possible, the bhp you gain at the top by going big just does not even come close to the torque you loose low down and mid range.

[RichB]

v8 racing said:

the one bit of advice i will give is to keep it as small as possible, the bhp you gain at the top by going big just does not even come close to the torque you loose low down and mid range.

This rather goes against the "drain-pipe" sized pipes TVR fit then? Rich...

[v8 racing]

Absolutely Rich, about two years ago i was begging a man that does these wonderfull carbon jobbies on tivs to have a word with his mates at cheshire to make me some small manifolds for griffs, when they finaly turned up i did back to back dyno sessions on standard griff motors and modified ones with the original manifolds and then the small ones, in all cases the original ones matched the peak bhp as the after market ones BUT, the small headers gained upto 40 ftlb in the lower revs, lets face it even a tuned griff barely makes 320 bhp divide that by 8 = 40 bhp per cylinder x 4 = 160 thats about the bhp of a standard fiesta now days do you ever see those with big drain pipes?? Hope this helps anyone making a system.

[MGBV8]

Skid
This website is worth a read
www.burnsstainless.com/TechArticles/techarticles.html

At the end of day it can be a question of fit, mine is 2.5ins croud clearance and I can only just get over some speed bumps so increasing diam is not an option (road car) twins to rear require a new fuel tank.
Decision based on these facts.

Paul

[skid]

Cheers Guys.

The Black art still confuses me. Never mind.

I read before some David Vizzard articles about pipes and header diameters. Smaller pipes can help but I think they need to exit to a bigger chamber.

I got confused when he started to explain the swollen pipes seen on 2 stroke bikes but I got the jist.

Anyway, does any one know if sleeving the perforated tubes in the side pipes will be detrimental and in which way????

[greenv8s]

My guess is the only significant effect will be much more noise, no impact on the engine tune. But that's only a guess.