quick exhaust diameter question

[lansalot]

V8 3.5, with range rover exhaust 4-2-1. Am going to be replacing everything south of the 4-2 with jetex and am wondering what diameter I should go for? The 4-2 exits at about 2" diameter, so is there any problem with keeping the rest at that size (I don't know about expansion and such - is that a factor?) ?

It's going to be a single silencer box and side-exit.

Thanks

[Hybrid_From_Hell]

I may be able to help you a bit, just about to have the exhaust done on mine, and have done a load of research and spoken to many who know about zorsts.

For a 3.5 you don't need huge pipes, in fact you don't want huge pipes, too small = strnagled, too big will actually loose you BHP. There is also no point changing bore size bigger half way through, ie if you have a say a 4 - 2 - 1 and the end of the 1 is 2", jumoping the remauinder of the exhaust up to 3" doesn't do anythingother than mess up the internal flows, you'd be better sticking with the 2". Note that 4-2-1 = low down grunt and power,............ vs 4-1 = power up the high rev range

On a V8 the pipes are

Primaries

Secondaries

Y

rest

Its sounds as though you primaries (the bits from the heads and the 1st bit of the exhaust) are sorted, these are always smaller than the rest of the system as each pipe only has to carry 1 exhaust cylinder worth of gasses, the secondaries (which some V8s have and many don't ie don't = $ into 1 header) but if you have them then secondaries are a bit gigger as they now carry 2, then the 2 go ionto 1 and this pipe now carries 4 cylinders worth of gasses, with one of these from each side they then go into the Y opiece, again each side of the Y is carrying 4 cylinders worth, and then when the 2 bits of the Y join this is the final part of the system and it carries all gasses etc.

From what you are saying you have primaries and sendonaries sorted, what you should try to do is aim for the pipe and exit from the Y to all be 2.5", 2.25 is OK 2.75/3" will be too big.

HTH

Nige

[lansalot]

That's brilliant thanks. The Y-piece I have is NTC2726 (item 3, page 28 here) and that terminates around 2" diameter.

Jetex have 2.5" and 2" parts available, so I'll order the 2.5" variation (they do a nice little stepper-piece to go up a diameter, which is nice of them )

Thanks for the advice, much appreciated.

A

[Hybrid_From_Hell]

That's brilliant thanks. The Y-piece I have is NTC2726 (item 3, page 28 here) and that terminates around 2" diameter.

Jetex have 2.5" and 2" parts available, so I'll order the 2.5" variation (they do a nice little stepper-piece to go up a diameter, which is nice of them )

Thanks for the advice, much appreciated.

A

On that Y piece I think you'll find that the collector (where the 2 go into 1) will be around 2.25" at some point, so cut off the tail and make the tube out of it 2.25" so as then to match the rest of the system ?

Nige

[lansalot]

Ah OK, thanks. My slide ruler was a bit vague and I rounded down a little there. The sleeve thing should do the trick nicely. £186 up the swannee, so I better be happy after all this

Cheers