Technical Power Flowed

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Technical Power Flowed

PNL

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Yesterday I took the stilo in to have a S/Steel cat back system fitted in Newport but the night before i thought i would do a bit of research on the workings of Exhaust systems :eek: and I tell you what it aint just a case of big pipes and noisy boxes in fact its quite a science :confused: for example did you stilo owners know that from the centre box back the dia of the pipe decreases from 2" to 1 3/4" and its all to do with pressure and flowing i had a good and very informative talk to Peter [OLDSKOOL]and he is a mind full of information so if you ppl are thinking of getting this done its worth looking into beforhand (y) thanks again Peter I will contact you again if thats OK when I am ready to sort out the induction side of things and I will need to sort out a source for a pair of camshafts (y)
 
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PNL

PNL

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Ok from the cat pipe work is 2" this goes then to a s/steel flexy before the centre box at this stage he started the car for me and asked me to comment on the volume of the exhaust :eek: he said did i want it quieter or kept at this volume iI went for quieter but still notice a differance in engine responce (y) remember these cans are pre manufactured and not made on site so there is a differance :D then from the centre box pipe work is 1 3/4" to back box and this I had made up removable as in original spec and there is no big chrome snorting pipe at the back just the same old limp dick pipe because the recent body mods do not allow the pipe to exit at the back so thats about it :D
 

1.8Stilo

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i fort the quieter you have it meant that it was de-tuned, not getting as much power gain? And saying that gain from anything cat back alone is alot on its own! so u just had the centre section and didnt bother with a tailpipe and kept the old stilo back box :confused:
 
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PNL

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No 1.8 read my post again I had a cat back system COMPLETLY made in s/steel people are under the impression that it has to be noisy it HASNT :) saying that the system has a RASPY note but not excessivley loud these boxes are tuned not made bespoke on site ie- large pipe end caps and the thing stuffed with glass fibre think about it :idea: why are all the pre manufactured systems like supersprint etc so expensive ? its because their tuned and tested to give you that little extra bhp unlike IMO a one off big piped snorting think ime going faster system :)
 

custard

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more of an issue on N/A engines.on a turbo application technically no back pressure is required.
though its been mentioned that having no back pressure on the turbo puts big pressure on the turbo due to the pressure differences before and after.
a proper exhaust for a given application requires testing
 
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PNL

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Yes agree how many ppl go out and get a s/steel system fitted and dont consider the implications until you find out that for some reason youve lost power at the top end :cry: i know cos it happened to me and i swore never to go down that road again :) To 1.8 i notice in your posts that Quote -things to come include a SUPERSPRINT zorst system (y) yes thats the way to go FORWARD (y) not backwards (n) but the choice is yours :)
 

custard

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course thats for those of you who can get an off the shelf unit for your engine ;)
 

chaos

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1.8Stilo said:
i fort the quieter you have it meant that it was de-tuned, not getting as much power gain? And saying that gain from anything cat back alone is alot on its own! so u just had the centre section and didnt bother with a tailpipe and kept the old stilo back box :confused:

Noise is no indication of an exhaust's capability, just like the biggest bore isn't always the best :)
 

1.8Stilo

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alrite, alrite.. calm down :rolleyes: i read the post quickly!

and i probaly didnt write my reply rite, reference the sound of zorst!!!!!

Well, ive actually decided not to go for the supersprint system and have booked in for a full s/steel cat back system @exhaust uk in sheffield on friday! So u say if i go for this im gona loose speed off my top end :confused:

I didnt realise this?
 
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PNL

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Hi 1.8 its all according if the guys that are building these systems know what their doing theres more to it than stuffing a lode of fibre glass into a tube sticking on some end caps and pipe work and calling it an exhaust system :eek: yes man that a crazy note brum brum but is it doing the job correctly coz if its wrong then its your car that suffering with loss of MPG torque and top end as i said earlier i lost 10 mph of one off my cars (n) and also suffered loss in mpg aswell so think before you go ahead cos once you have spent you hard earnt money it is an expensive mistake to make good luck to you ime sure Peter would be only to glad to offer some advise but whether you listen is up to you .If we had to pay him for this advise the guy would be a millionare :D
 

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For designing an exhaust system you first need to know, whether it is a turbo or non turbo application. There is distinctive differences between the two types when designing an exhaust system.

Looking at the non turbo engines (including kompressor) the designes in principle differ between the number of cylinders as well as the configuration of the cylinders.

To start this this means that the design of a V12 exhaust is not only different from any 8 cylinder, but also from any straight six. To make things even worse the Volkswagen group threw the W-configuration in.

Also between the straight six and V6 exhaust designs are differences that are quitye substantial, which are not related to the extra length of the engine than rather because of the different firing angles. Although physically a bit more tricky to build right the straight six exhaust system is technically easier to optimise than a V6 configuration.

On a V8 engine at a 90 degree configuration a balancer pipe between the two secondary pipes is required, which is in most other angles not necessarily required and in some angles at relevant applications not even wanted.

5 cylinder engines are very hard to do and again Volkswagen was able to top it up with the VR5 engine, which is an absolute pig of an exhaust to design.

Coming to the 4 cylinder engines, the worst design to do is the one with siamese ports, which we fortunately do not have to deal in Fiats with. A rather easy one to deal with is the good old Alfa boxer engines. Unfortunately they are history.

V4 engines haven't been in production for a long time, but proove a bit more complex problem on exhaust design then a straight four.

Now being confronted with any of the normally aspirated Fiat engines, exhaust design gets comparatively easy. This should not lead to the conclusion it is just a walk in the park.

Before the design of the actual system can be started it needs to be determined, whether the car is being used for peak power or a more torque oriented use. This affects the the manifold. If you wish to go for peak power but are willing to sacrifice some torque the 4-1 design will be your choice. The more road oriented version would be the 4-2-1 design giving you a much wider torque band.

Having decided to go for the slightly more complex solution (technically, but not necessarily physically), which is the 4-2-1 manifold two more things then on what engine it is going are needed. This is what cam design is the one that is finally in the engine and where the peak power point is supposed to be. From the engine we have we know the individual cylinder volume is known and the show can begin.

I am not going to bore you with a string of formulae for the principle design now.

More important is to know that there is an effect on the hole system when altering lengths and diameters of the individual pipes. By making the primaries of a different length you can widen the torque delivery but will loose a bit more peak power. Also you can achieve it by altering the pipe diameter of the primaries. Once the primaries are calculated you gon on to do the same with the secondaries and finally with the collector pipe. The collector pipe will have to be stepped down if it is not fairly short to help scavenging.

By altering any of the dimensions of the system when not done in a professional manner the result will be a loss of power due to getting the hole system out of balance. By increasing the pipe sizes you always will increase the peak power (when based on proper calculation). The only problem that will hit most of the applications is that because the hole torque curve shifts downwards that the usable torque is inferior to the standard setup or a fast road setup and the peak power delivery is coming in so high that it will be well above the rev limiter.

Additionaly there is quite a few more points to look at. The exhaust ports shape, the optimal step between the port and manifold, the junctions, the leading edge of the junctions, the bends (quality, shap and angle), the back box design, the cat design and the exit.

Welds and joints are important too, which is often neglected by a lot of the so called exhaust specialists.

If you ever have the opportunity to see an F1 exhaust in real life, take a very close look at the detailed work done on it. Then you will find out why Supersprint as an off the shelve provider and a lot of the real specialist places are not as cheap as you wish them to be.
 
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PNL

PNL

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Thanks for that Peter hopefully this very good explanation of how an exhaust system should work will make members now see its NOT a thing for the none professional to mess with (n) I am glad i consulted you before I did so (y)
 

1.8Stilo

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all ive gota say about that post is wow pete! you know your stuff and im glad im having my other work done with yourself!

I am confident with the company i am going with as they are very highly recommend but i will go armed with some of these facts to make sure the system is upto the grade! I suppose i am not to bothered about top end - i get just over 130mph atm, so i'll have to test it on the ride back and see what i get then? Because i barely ever get change to hit it? I would like more lower range power and torque!

ThanQ for the help guys.
 

Oldschool

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1.8Stilo said:
all ive gota say about that post is wow pete! you know your stuff and im glad im having my other work done with yourself!

I am confident with the company i am going with as they are very highly recommend but i will go armed with some of these facts to make sure the system is upto the grade! I suppose i am not to bothered about top end - i get just over 130mph atm, so i'll have to test it on the ride back and see what i get then? Because i barely ever get change to hit it? I would like more lower range power and torque!

ThanQ for the help guys.

If you get a full system you can ask them to give you maximum torque at about 5500rpm. If you get a catback then you are lumbered with the manifold design. Still you can tell them to do their best for torque rather than power, whivh means that the pipes are a bit smaller than peak power oriented.

Anyway, hope it goes well. And don't forget about the progress report.
 

1.8Stilo

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Oldschool said:
If you get a full system you can ask them to give you maximum torque at about 5500rpm. If you get a catback then you are lumbered with the manifold design. Still you can tell them to do their best for torque rather than power, whivh means that the pipes are a bit smaller than peak power oriented.

Anyway, hope it goes well. And don't forget about the progress report.

I am going for what they say is a full system and i think most custom places do, which is a cat back system!

i will keep you updated with a progress report :D also if i go for more torque on the exhaust instead on power? will choosing either way between torque or the power aid any of the other modifcations to come i.e. the induction and remap!

also what would you recommend to go for with the remap and induction to be added?

and will i loose top end if i choose the torque?

and finally could i add a supersprint manifold later? i dont think i will add a manifold though, as the insurance will high enough as it is? and lookinbg through my policy - a manifold and exhaust system are two different modifications!!!
 
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