Pipe arrangement for Rover v8 manifolds

ratwing · Post by **ratwing** » Tue Nov 18, 2014 12:52 pm

I understood that the pipes from 1&5 and 3&7 on one side and 2&8 and 4&6 on the other should join, then join the pairs each side after long secondary pipes.
However, I noticed that the 4.6 manifolds I'm using for the flanges just join the front and rear pairs each side, ie 1&3, 5&7 and 2&4, 6&8 - so does it actually make much difference which pipes I pair up?
They're for a 4.6 with 1 ¾" SU carbs, a 3.9 cam and standard valves with some light work cleaning up the ports, I've plenty of room for the pipes (although not across the banks) and its for road use so am more interested in an arrangement that isn't biased towards the top end or track use.
Any thoughts guys?

DEVONMAN · Post by **DEVONMAN** » Tue Nov 18, 2014 3:35 pm

AFAIK the nearside (odd numbers side) is more critical due to 5 & 7 firing consecutively in the firing order of the RV8.

On cast manifolds previous to the tubular 4.6 types, 1 & 5 are merged and 3 & 7 are merged and on the offside 2 & 4 are merged and 6 & 8 are merged.

If it's a 4 into 1 set up I'd say it may be of benefit to discharge into the collector in rotational firing order to induce a smoother swirl/flow in the down pipe but many other factors come into play.

Regards Denis

sidecar · Post by **sidecar** » Tue Nov 18, 2014 4:52 pm

From what I've read messing about with tuned length headers and also the order in which they are connected is directly connected to the camshaft duration and overlap, if you are running a mild cam then an exhaust that is in or out of tune will make very little difference.

ratwing · Post by **ratwing** » Wed Nov 19, 2014 4:18 pm

Thanks for the replies, I'll have a think about it. Tempted to go 1/5, 3/7 & 2/4, 6/8, will see how tricky it'll be to get the pipes crossing and looking good too.
I wasn't expecting big power gains but no point in using a design that'll rob power if theres a better one that doesn't!

ChrisJC · Post by **ChrisJC** » Wed Nov 19, 2014 6:54 pm

I think (although I have no evidence) is that you are just tweaking the shape of the torque curve. Because the Rover V8 has a dual plane crankshaft, you cannot make a decent exhaust manifold in the way you can on a four cylinder engine. Therefore you end up with a compromise, and adjusting the plumbing just moves the rev-range where the compromise is.

Chris.

kiwicar · Post by **kiwicar** » Fri Nov 21, 2014 7:06 am

Hi
with an engine like this in a very mild state of tune as Chris says you are just really tweaking the shape of the torque curve maybe 2 bhp added at 2500 revs 3 taken away elsewhere, and we really are talking +/- 2 or 3 BHP. If you want to do all the welding and cutting then I would try 1&5 and 3&7 and 2&8 and 4&6 the other but it is a lot of work for little change. Simple 4 into 1 with reasonably long pipes will be simpler to make and at the end of the day will look better unless you are a very impressive tube bender/welder. What will make a worthwhile difference would be a balance pipe between the two manifolds.
best regards
Mike