X Pipe diameter

[bembo449]

Any of you with an X pipe in your exhaust system know what diameter it is , i specifically want the size from a V8 , any other info about your set up is welcome
Thanks

 

[LostKiwi]

The rule of thumb is inlet and outlet same size as the rest of the pipework. The joined section should be smaller than 80% of the combined and bigger than 50%.
The pipes should join and exit at as shallow an angle as possible and the X-pipe must be after all lambda sensors.
Length of joined section should be 4"-10".
In general the longer the joined section the better.
This is a decent pipe that's easy to make.

The best X-pipe I've seen was made from a 5" section of pipe. 2 x 2.25 pipes were put into it and 2 1" rods used to press the 5" pipe into a 8 shape around the 2.25" pipes. The 2.25" pipes are removed and 2.5" pipes welded to the open ends. This gives a very smooth internal merge area.
Very time consuming and difficult to make but makes a superb pipe.

Similar to this (the manufacturing was refined from this design).

 

[McDonald]

The best X-pipe I've seen was made from a 5" section of pipe. 2 x 2.25 pipes were put into it and 2 1" rods used to press the 5" pipe into a 8 shape around the 2.25" pipes. The 2.25" pipes are removed and 2.5" pipes welded to the open ends. This gives a very smooth internal merge area.
Very time consuming and difficult to make but makes a superb pipe.

Just curious. How much would this cost made and fitted on R230?

 

[flowrider]

Just curious. How much would this cost made and fitted on R230?

I would expect the X-pipe in the video to cost about £250 fitted. I had a cheaper version installed on my SL for £180 about 3 years ago which whilst not being perfect does the job.

 

[LostKiwi]

I would expect the X-pipe in the video to cost about £250 fitted. I had a cheaper version installed on my SL for £180 about 3 years ago which whilst not being perfect does the job.

Probably a bit more - I had one done about 15 years ago for my A8 and it was £250 then. Took him hours to do.

 

[AMGeed]

I believe the V8 Mercedes uses a 2.75" diameter pipe in the system.
When I had my x-pipe fitted to my E55 it cost £400 but that included removing the secondary cats and resonator.
£250-£300 sounds reasonable, possibly a little more.

 

[McDonald]

I would expect the X-pipe in the video to cost about £250 fitted.

Thanks. I had no idea of the cost I imagined much more.

Probably a bit more - I had one done about 15 years ago for my A8 and it was £250 then. Took him hours to do.

Specialist establishments only, I'm sure?

I believe the V8 Mercedes uses a 2.75" diameter pipe in the system.
When I had my x-pipe fitted to my E55 it cost £400 but that included removing the secondary cats and resonator.
£250-£300 sounds reasonable, possibly a little more.

Good information, Thanks all.

 

[bembo449]

All good stuff guys , my 02 215 has 51mm pipe through to 55mm where it meets the silencers , i had a quick look at my mates CLS 5.5 and the X pipe and system are the same diameter right through , im looking to re-do my set up as i currently have 51mm to 54mm into 63mm X pipe and then to 57mm tobthe back boxes , just think there isnt enough back pressure and hence it not running smoothly

 

[LostKiwi]

Back pressure is a myth.
The whole point of a decent performance exhaust is to remove back pressure and get exhaust gases away from the exhaust port to the tailpipe as quickly as possible.

A common mistake people make is to fit too large an exhaust (young lads with 1.1 Fiestas with exhausts the diameter of a small county are a prime example).
To get the gases out efficiently you need to keep them moving. Gas has momentum and it is this we rely on for the scavenging effect of an exhaust. As the gas passes an opening the momentum of the gas carries it past the opening and the Bernoulli effect creates a slight vacuum in the pipe the gas passes. A bigger pipe reduces the speed of the gas reducing the effect.
Too small a pipe can't flow enough gas at wide open throttle but will give great gains at low rpm. Going from a small pipe to too large a pipe therefore often results in a loss of torque because the low rpm scavenging becomes compromised.

There are other factors too - for example turbulence caused by sharp edges, changes of direction, imperfect joints, step changes in diameter etc. Then there are boundary layer effects, laminar flows, resonant frequencies, standing waves and the effect of the number of cylinders and so on. It gets very complex very quickly but in general size the pipe for power output but bear in mind that the more cylinders there are the smaller it can be for a given power output.

In your setup you're slowing the gases at exactly the place you want them moving faster. This is probably allowing gas to flow from one bank back into the other, particularly at low engine speeds.
Remember I said the merge section needs to be 50-80% of the combined area of the two inlet pipes? This is to speed the gases up as they flow through the pipe into the merge, the divider between the pipes effectively forcing the gases into a narrower cross section just at the point the merge happens.

This technique is also useful for anti reversion chambers (something we messed with when racing). But that's a whole different subject...

 

[bembo449]

Thanks LK , all brilliant info