Longlife Exh Quote

[T2Andy]

Phoned yesterday and was quoted 425+vat .that was for a 3in down pipe into a
cherry bomb instead of the cats then to one more box mated to my stainless
back box.The guy said the cherry bomb was to give some back pressure other wise
QUOTE it would go flat ,is it a 1.8 turbo},i thought the less the better on a turbo.

[s2dude]

The less backpressure IS the better on a turbo motor..
Sounds like the guy you spoke to didn't know his RS from his elbow!!

Looks like you may need to TELL them what system you want and just have them design and fit it!!

[T2Andy]

Thats what i thought .

[terrybullwon]

At least they called you back with a quote, a week on and i am still waiting

[Knight Rider S4]

Phoned yesterday and was quoted 425+vat .that was for a 3in down pipe into a
cherry bomb instead of the cats then to one more box mated to my stainless
back box.The guy said the cherry bomb was to give some back pressure other wise
QUOTE it would go flat ,is it a 1.8 turbo},i thought the less the better on a turbo.

I would find another place that knows what they are talking about ,would you trust them after them telling you that even if you gave them your own spec exhaust

[Rusty]

The Longlife near me seem to quote whatever they feel depending on whether there's an R in the month, the number of cups of coffee the manager's had and whether they've fleeced a Chav for an 18 pipe system in the last 2 days... Had quotes anything between £550 and £350.

The less back pressure you have the better on a turbo, the turbo itself creates all the back pressure you need, just a matter of how loud you want it.

Good luck! Always a Milltek with sports cat at £700

[s2driveruk]

Hmmm, sounds like a franchisee who doesnt know his ar*e from his elbow, I had this in conversation with the one in Basingstoke too about 3 months back.

Ask to speak to a guy called Mal, call the central number. Discuss with him what you want/need etc and get him to record it on their system, then when the local place pull up your details there is nothing to discuss apart from date!

He knows the S2 and as the owner of the company will usually do adecent quote too. I'm going to cardiff to get my work done on changing to a sports cat version...

[Jamo]

The less backpressure IS the better on a turbo motor..
Sounds like the guy you spoke to didn't know his RS from his elbow!!

Looks like you may need to TELL them what system you want and just have them design and fit it!!

Actually thats a common misconception

Some Backpressure helps turbo spool.

A turbo works of pressure differential if there is too big a pressure differential between the inlet and outlet of the turbo it's what causes the turbo seals too leak.

Hence why when people go and get 3" exhausts a month of so later the turbo gives up the ghost on chav cars as they haven't actually thought about the right size exhaust for the engine and turbo flow.

Search for the posts of pisobiker and the web.

[s2dude]

Actually thats a common misconception

Some Backpressure helps turbo spool.

A turbo works of pressure differential if there is too big a pressure differential between the inlet and outlet of the turbo it's what causes the turbo seals too leak.

Hence why when people go and get 3" exhausts a month of so later the turbo gives up the ghost on chav cars as they haven't actually thought about the right size exhaust for the engine and turbo flow.

Search for the posts of pisobiker and the web.

Please show some evidence of this
A lot of BMW guys in Sweden run side exit exhausts with no silencers on turbo cars. and vent DP to atmosphere. The cars run sub 10 second 1/4 miles

Not everything on the web is factual or correct....but this is a pretty good article on the subject of exhaust backpressure

here

Quote

In a turbo car it’s easy – you want the lowest backpressure possible straight after the turbine

[Jamo]

Larger diameter (read "freer flow") exhaust sistem, will reduce performances in the rpm range below boost treshold, but will increase turbocharger responsivness and power output in the mid to high rpm.

The reason is because turbine's efficiency is proportional to pressure drop between inducer and exducer.
Therefore, to increse turbocharger's efficiency you have either to increase inducer pressure, or decrese exducer pressure (better known as exhaust "backpressure") or both (which is even better ).
This way responsivness of the turbine is improved while power transmitted to the compressor side (therefore boost and flow capabilityes) is increased as well.

Some carefull matching of exhaust system with turbocharger and engine layout must be taken into account, though. Here, most important thing, as sayed, is FLOW. It is not always true that the largest the exhaust the better the flow:

to minimize backpressure, flow speed inside the exhaust must be kept high enaugh, while increasing section will reduce speed. Of course at high rpm flowing requirements increase, therefore needing bigger pipe sections, which are about proportional to power output.
Moreover, in a turbocharged application, flow comes out of the turbine in a very turbulent manner, which slows down flow therefore increasing backpressure. The optimum is obtained when increasing flowing section enaugh to produce flow gains in the high rpm while keeping flow as straight as possible, maximizing flow speed (for which some high flow metallic cat-converters seem to work pretty good).

The 3" turbo back system is known to be the best choice in the 350-430 hp configurations. For a std. K24 turbocharger I personally wouldn't go larger than a 65mm ID exhaust system.


Marco

http://www.s2forum.com/forum/showthread.php?t=4696

Key note: Larger diameter (read "freer flow") exhaust sistem, will reduce performances in the rpm range below boost treshold, but will increase turbocharger responsivness and power output in the mid to high rpm.

To get round it increase backpressure with a cat ala as suggest by the longlife guy to improve responsiveness off boost.

[Rusty]

The cars running side-exit exhausts are full race cars and so max power is the only aim.

From the conversation above it would seem that, for a road car, a slight restriction in the exhaust would be better as it would give off boost performance and therefore driveability. It's fun to have loads of power but not always practical!

I would hope that a 3" turbo back with both centre and back box would be fine for a balance between the two especially on the small k24, remove the centre box for a bit more guts up top or add a CAT or silencer for best off boost performance and therefore driveability.

Just my 2p.

[Jay]

I'm with S2dude here...

Yes you do want as big a pressure differential!

On drag cars and old race cars this is done with a conical stub exhaust just to direct gases away from drive and body work and it was as short as pos (read inchs!!)

The only difference on a road car/track car is noise limits and a need to have the exhaust exit the back (fumes/heat)

The performance gains had by having a slight back pressure is on NA cars (whos driven one with a exhaust blow and felt it had gone flat eg lost power!?) this is down to the scavenging effects of the manifold/exhaust, wack a turbo (read restriction) in the system and you get big back pressure and loose the scavening effect.

The only point where you get slight gains is tick over (smoother) and just of tick over response (eg easy to stall) from having a slight back pressure specially if cam timing and or lift have been alterd.

The gains with going for a restiction free exhaust are great (on a turbo car) the down sides are small (rough tick over, noise)

If you want back pressure leave the exhaust standard

No brainer really

There are lots of books on the subject and anyone with a engineering, fluid flow and or tuning back ground will agree

dont believe all the hype you read on the net (its mostly sales pitch!)

Jay

[Rusty]

If you want back pressure leave the exhaust standard

No brainer really

There are lots of books on the subject and anyone with a engineering, fluid flow and or tuning back ground will agree

My background is engineering and I have chosen to think about it a bit more. I understand both sides of the arguement but am also interested in Marco's comments about fluid flow through the system relating to effective back pressure, I assume this relates to the Reynold's Number of the exhaust gas throught the system and therefore to the linear / turbulent characteristics of the gas, slow gas higher losses due to wall friction.

I also see that there is a requirement for an exhaust system that is freer flowing but that is an intermediate option between 3" all the way back and the standard system a not everyone wants maximum power and no useability out of their cars. Mine's a daily driver and I quite frequently find that I require good performance off boost, my cat back system has freed up around 15bhp and the off-boost performance has not noticably changed from stock, in fact the car's running so much better now that there's no comparison now anyway .

Finally, I'm amazed by the quietness of the original system every time I go in a car which has one, it might not fit the balls-out-racer S2s but it sure makes for a comfortable drive, especially long distance!

[Rusty]

Don't bother with a complete exhaust system, just get one of these bad-boys

[Rusty]

Just for my own understanding:-

Having researched this it would seem that there is little use for a restriction in the exhaust pipe on a turbo car as the manifold and exhaust constitute the bulk of the restriction and the contribution of the exhaust is minimal. There apears to be few off-boost advantages when compared to the power advantages and IMHO noise supression is the only reason for silencers and therefore restriction in a turbo car. NA blow-by effects off boost are reduced due to the aforementioned turbo & manifold backpressure and also due to the shorter duration of turbo car camshafts. Back pressure can be further reduced with longer primary runners on the EM as these approach the ideal primar length and so begin to aid ehaust gas expulsion by setting up a pulse in the EM which aids the gas flow, this is obviously frequency related and therefore RPM related.

I am currently discussing the question of exhaust pipe diameter with a friend who develops engines (as I did with teh above thread) and will post my understanding of it for anyone whe either cares or is bored and fancies reading something for the fun of it!