jps
|
| posted on 2/9/13 at 02:44 PM |
|
|
'Tuning' an exhaust correctly
I'm no expert - but it's my understanding that the airflow OUT of the engine can be as important as the airflow IN to an engine. I.e.
there will be an ideal length/diameter to an exhaust system, an ideal way in which the exhaust manifold combines into the silencer(s), an ideal amount
of 'resistance' in a silencer, etc.
But from reading a few threads it seems a common attitude is sort of "get the pipes together, get them out of the side of the car where it looks
nice, pick a silencer that looks good, job done"...
Where can I find some good info on how to do it 'right'? Or, with a 1.6 Pinto going into my build - and not being too bothered about
masses of power - do i just go with the 'looks good, job done' approach?
|
|
|
|
|
carlknight1982
|
| posted on 2/9/13 at 02:55 PM |
|
|
id be more worried about the noise level for IVA to start with,
Logic will get you from a A to B
Imagination will take you everywhere.
|
|
|
Bluemoon
|
| posted on 2/9/13 at 02:58 PM |
|
|
quote:
Originally posted by jps
But from reading a few threads it seems a common attitude is sort of "get the pipes together, get them out of the side of the car where it looks
nice, pick a silencer that looks good, job done"...
Most people seem to take that approach including some kitcar manufactures (and myself!!). It is possible to tune the exhaust there are
forumla's out there to work out the lengths of pipe in the header to increase "scavenging", difficulty for an amateur is finding out
if you have made a difference you really need use a rolling road before and after to see what effect you have have..
http://en.wikipedia.org/wiki/Exhaust_manifold
[Edited on 2/9/13 by Bluemoon]
|
|
|
loggyboy
|
| posted on 2/9/13 at 03:02 PM |
|
|
As youy say its not just air getting in, its getting out - but its also getting it through, so unless you are doing inlet AND head/cam work AND
exhaust, the total gains you can make with an exhaust are nominmal to minimal, you might get a few hp,
Gains are almost defautly made over a standard pea shooter system with a tight cast manifold. Stick a four branch on (standard for these cars 90% of
the time), followed by a 4-2-1 or 4-1 which ever your preference (generally 4-1 = boost of high end power, 4-2-1 = more mid range power - but of
course theres always exceptions), add a decent silencer to get yout though trackdays/iva/past policeman - what ever you need. Equal length headers
shows good design, but its not always (easily) possible and again, gains are minimal.
As with most mods, its about adding lots of little gains to get a large gain.
However spending lots of money and time getting a well designed manifold for boat anchor engine may seem a lil silly to some.
Mistral Motorsport
|
|
|
jps
|
| posted on 2/9/13 at 03:21 PM |
|
|
Cheers chaps - as always some good info!
The reason i'm thinking about it is:
a) i've got to fabricate something as it is - my pinto will be low power output anyway - i don't want to strangle it even more if there is
a 'wrong way' which I can easily avoid with some research
b) the long term plan is to replace with another engine years down the road - I don't want to exit in completely the wrong place now - and find
that when I swap engine in the future I have to remove the side panel if i've gone out there when i would have been better going out over the
chassis rails / side of the bonnet first time round anyway, or vice versa...
|
|
|
MakeEverything
|
| posted on 2/9/13 at 03:58 PM |
|
|
quote:
Originally posted by jps
Where can I find some good info on how to do it 'right'?
Bell, A. G., 2005. Chapter 16 - The Exhaust System. In: Forced Induction Performance Tuning. Yeovil: Haynes Publishing, p. 464.
and
Bell, A. G., 2011. Chapter 9 - The Exhaust System. In: Four Stroke Performance Tuninig. Yeovil: Haynes Publishing, p. 478.
Both offer calculations on runner sizing and lengths etc. amongst other things.
[Edited on 2-9-13, by MakeEverything]
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
|
|
|
designer
|
| posted on 2/9/13 at 04:30 PM |
|
|
Exhaust tuning is a science and you can't tune an exhaust to be efficient at all rev. ranges. Tuning depends upon use.
|
|
|
snapper
|
| posted on 2/9/13 at 04:33 PM |
|
|
If you are running a standard cam any 4 branch will help
Proper tuning includes intake length as well as exhaust and will be based on your cam
I found that the Robin Hood manifold from 1997 was pretty close to perfect for my RL31 cam and just needed the collector enlarging and extending
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
|
|
|
mark chandler
|
| posted on 2/9/13 at 05:24 PM |
|
|
I cannot recommend this book enough
Bell, A. G., 2011. Chapter 9 - The Exhaust System. In: Four Stroke Performance Tuninig. Yeovil: Haynes Publishing, p. 478.
I purchased it years ago, it teaches you that a little of everything gives the best results.
I had a 2.0 litre Capri, standard cam and carb, 1/4" off the head, ports shaped using bells principles and cut the valve seats out, 4-2-1
exhaust, just took time building it up carefully and dialling in the cam. On the rollers it was 4bhp less than my mates 3.0litre Capri, same day same
rollers ~ 130 BHP.
Regards Mark
[Edited on 2/9/13 by mark chandler]
|
|
|
snapper
|
| posted on 2/9/13 at 05:34 PM |
|
|
1/4" off the head?!?!
That's 6.35mm
2.5mm would give 12 to 1
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
|
|
|
Canada EH!
|
| posted on 2/9/13 at 05:43 PM |
|
|
There is a well known bike header manufacturer here in Canada who holds a PHD in music, speaking of tuning exhaust systems
|
|
|
mark chandler
|
| posted on 2/9/13 at 07:06 PM |
|
|
quote:
Originally posted by snapper
1/4" off the head?!?!
That's 6.35mm
2.5mm would give 12 to 1
Humm thinking about it 60 thou, I had 1/4" taken off my landrover head as it was 8:1, something low like that.
|
|
|
macc man
|
| posted on 2/9/13 at 08:06 PM |
|
|
With most 7 type cars the exhaust is a compromise between what will fit the limited space available and looks. I made my 4 into 1 system to fit rather
than to be super efficient. I was happy with the result and plenty of power too.
|
|
|
Slimy38
|
| posted on 2/9/13 at 09:11 PM |
|
|
quote:
Originally posted by macc man
With most 7 type cars the exhaust is a compromise between what will fit the limited space available and looks. I made my 4 into 1 system to fit rather
than to be super efficient. I was happy with the result and plenty of power too.
I have to admit that's what I'm expecting on my build, I will be more interested in getting the pipe to the back of the car than anything
too fancy. Even the choice of a 4-1 or 4-2-1 will be determined by the space in the engine bay.
|
|
|
ettore bugatti
|
| posted on 2/9/13 at 11:35 PM |
|
|
Apparently, PipeMax is a great tool to figure out the dimensions.
This should give some ballpark figures:
http://www.mez.co.uk/mezporting/exhaust_length.html
In general, dimensions are defined/constrained by:
- engine spec (intake, head, cam)
- available room
- focus on peak power or peak torque
and found some more info:
http://www.turbosport.co.uk/showthread.php?t=151004
|
|
|
