How important for exhaust to have x pipe or silencer

[kipsy]

My exhaust died on the weekend and my spare system doesn't have a x piece or a middle box it only has two pipes to the back box. Is this an issue and can it affect running

[steve_k]

Cant see why it would be an issue really as the system on my B25 has an X-pipe just after the down pipes & straight through to the back box & while it is slightly louder there doesn't seen to be any issue's.

[maggspower]

I think the issue here is not having a X-pipe. This helps scavange (suck through) exhaust gasses by creating a vacuum behind the exhaust valves. Many years ago I did a middle box delete with no X-pipe, so twin pipes from the manifold to the rear box, although not much of a difference I do think it lost a little torque lower in the rev range.

Sounded ok though

[kipsy]

Maybe ill give it a go then. Car is constantly above 4-5 k rpm and has very close ratios 4.4 cwp and direct final drive. Saves me buying a system. Did it round different to with the x pipe?

[maggspower]

Maybe ill give it a go then. Car is constantly above 4-5 k rpm and has very close ratios 4.4 cwp and direct final drive. Saves me buying a system. Did it round different to with the x pipe?

I just had the straight through, I never had it with a crossover and straight through. But with a standard box not bad at all, just a bit more burbley (new word), and raspy when pushed. With a scorpion box though, I dont know, definatly louder.

Do you have any noise regs with what you are doing?

[kipsy]

Yes noise regs. Think 105@4500 rpm. The car has standard knackered middle box and two cherry bomb silencers side by side and flys noise at the mo.

[maggspower]

Yes noise regs. Think 105@4500 rpm. The car has standard knackered middle box and two cherry bomb silencers side by side and flys noise at the mo.

Yes it did sound a little fruity when you where at mine

How did you get on with the prop? forgot to ask.

[HairyScreech]

If you are using a log manifold then you want the x pipe about where the centre box is. I guess the centre box is not there by coincidence.

[leeparkes]

Where do you guys buy the X pipe from?

[HairyScreech]

Jetex do them.

[kipsy]

Does anyone know what size bore they are? Will do some research in work ;)

[steve_k]

Bore size is from 1.75" (45mm) upto & somtimes over 2.5" (65mm).

you can also get them off eBay.

[kipsy]

Yes noise regs. Think 105@4500 rpm. The car has standard knackered middle box and two cherry bomb silencers side by side and flys noise at the mo.

Yes it did sound a little fruity when you where at mine

How did you get on with the prop? forgot to ask.

Prop seems ok. Well lasted a rally so happy with that at least! Just priced an x piece from jettex and it's £50 plus postage. I'll try it first I think. I'm going to end up with a nice manifold and system one day if I get around to fitting the m52 but it's going so well Id be silly to pull it out

[kipsy]

Bit of an update, after not liking the twin pipe set up as sounds weird (porsche like??) and not being as responsive as before I had an x pipe put in. Car not sounds sweet and seems to pull better. Fitted by Charlie at Prospeed in Cardiff for a very reasonable rate and also he helped weld some brackets on the rest of the system.

[MillRat]

When we first ran side pipes on the race car, we did not use an X-pipe. On the dyno we only managed around 120+ kW at the wheels, and the engine felt flat on the track.. we thought this was weird so we looked into it and fitted an X-pipe. The next dyno was around 140+kW...

The moral of the story.. fit a X-pipe. Also, make sure it is close the headers - next to the gear box is about right (approx 1.5m from the head if I recall correctly). If you have a common cat or resonator fitted in this location, you should not need a X-pipe.

The reason, as maggspower pointed out, is that the X-pipe scavenges the headers and leaves them under partial vacuum. This has obvious benefits when extracting the exhaust gases from the cylinder.