Powerflow exhaust help please

[sparkielew]

My most recent Stag has a powerflow exhaust system connected to a tubular manifold. It finally exits via a pipe either side under the rear bumper from twin tail pipes each side.
The sound is good but there is an incredibly loud low frequency "drone" between 1800 and 2400 rpm -which is a regular range when driving.
Just wondered if anyone had some ideas - I would quite like to retain the exits on either side but not worried about changing the end pipes. I'm trying to do this without resorting to a whole new system
and am keen to keep the cost down.
I remember reading an article previously about the science of exhaust sounds on a Stag but couldn't find it.
Any help would be greatly appreciated as I end up with a headache after 20 minutes of driving.
Thanks

[Phil S]

do you have a link pipe between the 2 sides? I had my system made by vortex in grays and they said not to link the 2 sides.
I don't have any drone with this setup, so perhaps try blocking your off if fitted and possible. 2 inch system with straight through boxes, no difference now that my tubular manifold are on.

[bullstarz]

To increase performance and the scavenging you need the link between both banks, the best is to have an "X-pipe". If you want the quite life but still want to go loud when you want it, like driving through a tunnel or by some youths, fit a pair of exhaust cut outs. I fitted a set (what a surprise ) certainly turn a few heads and stops people in their tracks.

[jakesmig]

I made my own system when I replaced the headers with Monarch items and had a cross branch and a 22" 100mm straight through silencer on each bank in the tunnel area under the floor pan and a 2" pipe out each side. It was loud, tested at 97Dcbls at tickover and 107.5 Dcbls at 3500 RPM, checked at the SRC Rally sound check a couple of years ago.
It was awesome at full chat and even drowned out the wind noise at naughty speeds but was tough to live with on longer trips.

I recently fitted 22" x150mm diameter straight through silencers to each pipe under the boot and the car is now decidedly silenced to the extent ti is virtually Ninja unless being enthusiastically worked. Mine is a 3.9 RV8 so doesn't have the cute Chitty Chitty burble (thankfully) so I'm not missing out on the burble, theRV8 is more a growl. If I was doing so again, which I may, I would opt for smaller items, probably 20" x 100mm because the 150mm's are certainly visible.

I bought the items from Midland Exhaust via Ebay and made my own hangers, silencers + a chrome tail pipe were about £125 the pair.

[flying farmer]

A lot depends on the type of tubular manifolds and also whether there is a balance pipe fitted between the two halves of the system.

If the manifolds are the Monarch variety that both point straight forward you have equal length exhausts, but if they are the Pheonix type with one manifold exiting towards the front and one to the rear (just like the original cast manifolds) the two halves of the system have very different lengths if the original exhaust is not used. This is because the rearward pointing offside manifolds exhaust has extra length added after the silencers as the offside pipe loops around the rear axle. I think it is the difference in length of the two downpipes to the link pipe that gives the stag engine its distinctive burble, but as soon as you lose the extra length of pipe around the rear axle you can end up with boom periods from the exhaust at various rpm.

Three of my Stag engines have equal length exhaust pipes, although all these manifolds exit rearwards on both sides and non of these have any boom periods.

My Stag engine estate has the Pheonix manifolds and no loop around the rear axle and suffers from several boom periods, the worst being at about 2500rpm, but strangely this is less bad now I have fitted efi.

I think the rpm the boom periods come in at will depend a lot on the pipe diameters being used. All 4 of my cars use exactly the same rear mounted silencers as I have found in the past that centrally mounted silencers are generally louder than rear mounted ones, and it is always a deep bass note that travels a long way!

The first time I installed a Stag engine (in my TR) I kept the two halves of the system separate. I subsequently fitted a link pipe, and rolling road tests did show a power loss. However, the loss was only from 169bhp to 165bhp, and the loss was only over 5300rpm. At lower rpm there were huge torque gains, and in addition there was a 10% reduction in fuel consumption which was significant as I was doing 12,000 miles per year in it at the time.
I also noticed the exhaust system was quieter, I think this was probably because linking the two sides of the system reduces the strength of the pulses down the pipe after the link.

If you have not got a link pipe fitted I would suggest fitting one, but keep it well back behind the gearbox as I have just realised the most likely reason for my P reg Stag's poor torque output is that I have the link pipe about 12 inches closer to the engine than the other system I made for my TR. Another job on the list of things to do!

Apart from that the only thing I can think of is changing the silencer boxes for something a bit more effective, I don't think messing with the tail pipes will make a great deal of difference, particularly if they are large bore ones.

Neil

[sparkielew]

Thanks for all the advice so far-I need to digest but having read various other items on other cars with twin pipes I think the link pipe seems a likely way forward.
Will update with results.
Andy