Replacing exhaust balance box with H or X pipes

[MartBlak]

I have a bad rattle in my GD Mk3 underslung exhaust balance box and am considering replacing it with stainless X or H pipes. I have a Ford 289 smallblock and am concerned that the noise increase might also be an issue if I am replacing a baffled balance box (I do not want to be barred by the noise police on any trackdays I might go on).
Can anyone share their thoughts/experiences as I believe the H pipe configuration gives a deeper sound with higher torque but lower power and Y pipes give a raspier sound with less torque but better power.
I posted this on the UK Cobra Club forum but expect most to have sidepipes......so hope there is more underslung exhaust experience here!
Thanks for any suggestions / advice.
Martin

[peterc]

I am about to replace my entire exhaust system so have been investigating accordingly. My book of words on tuning albeit for a Rover certainly says a cross pipe of some form is a good idea.

Yes, an X pipe will have a high pitched rasp whereas the H pipe a deeper classic growl but both will improve power and also make the system generally quieter by around 1-3db.
Yes, generally an H is better for low down torque and X better for high end power.

I would suggest that you talk to GD as one of our members has recently and get them to provide the parts. Maybe they have an answer to replacing just a portion rather than than the whole lot.

Also important is to have the correct dia to suit the power available.
220-270 BHP needs a 2.25” twin system whereas 270 - 360 BHP needs 2.5” for a twin system.
Peter C

[MartBlak]

Thanks Peter.
I am only replacing the current balance box which is pretty heavily baffled; GD do an H pipe but cannot advise whether I will keep within 100db with it. I am not sure what I would have to do to add a noise supressor of some form if it exceeds that.

[peterc]

I had recently seen that GD did a combined silencer/ cross pipe and thought that was a good idea. Presumably that is where your rattle is.
Why not just replace like for like. I assume it’s not practical to cut the balance box open and weld up whatever had come loose.
Peter C

[MartBlak]

GD's H pipes have a cross tube but are not "silenced".
My current set-up was supplied by GD some 20 years ago but they no longer supply the silenced balance box. I have spoken to an exhaust manufacturing company and they said that, from their experience, when cutting a box open they usually find the baffles are in a poor state and the cost of refurbishing then welding the stainless box back up again would be a lot more than buying a replacement.
I have 2 more, smaller, silencers on the exit end of the pipes and have no idea if they would suppress the increased noise enough or whether they can have something done to increase their silencing capability.
The trouble is that it looks like I will have to go down the H pipe route before knowing how loud it will make it. No-one can tell me what it is likely to be so I will then potentially have to find a further solution to a different problem!.......the joys of owning these cars!!

[peterc]

If your current cross over is combined inside a box then surely it will get louder with just a simple H. You can’t rely on just the two rear silencers. Which is the bigger box. Front or rear. I would have thought a decent exhaust system design/ supplier would advise what you need for reasonable noise level.
Peter C

[clive]

I would be interested to hear what increase in power there is from having a balance box. I have never had one on my car as I am using the system supplied from Gerry and feel that my engine provides more than sufficient power as it is.

[MartBlak]

This is a new area for me but my present balance box is pretty big and is baffled so I expect it will certainly be louder with an H section. The balance box is a lot bigger than the individual end boxes......I will try and add some photos. According to Andy at GD you get a proper V8 burble by having a non-balanced exhaust system. The H section, I believe, has the central part that can be either opened i.e. balanced, or closed i.e. unbalanced......does that make sense?
The exhaust chap I have been speaking to says it is really a case of choosing something then working out how to get exactly what you want afterwards depending on the sound and noise level.

[clive]

One comment I would make is that having a balance box makes it harder to remove the exhaust. When removing Bill Telford's gearbox it was extremely difficult to remove/replace the exhaust due to the fact the pipes are not parallel and converge leading up to the manifold so it was almost impossible to do without completely disassembling the downpipes from the balance pipes.

[peterc]

It sounds like the major silencing is being performed by the box you are having issues with. Removing it will certainly put the noise up considerably. The fact that both pipes go in and out of it is as you suggest a balance box. Therefore combining silencing with a cross over.
By way of clarification adding a cross pipe will only improve noise and performance over totally separate twin systems. You can’t think of that as an alternative to the correct amount of silencing.
A friend suggests that I am wrong about the X pipe and that it improves performance throughout the range.
I confess I do not understand why you would want an H pipe with the facility to close it off.
Peter C