Exhausts

[Mini1976]

I have an MG Metro engine running with and LBC and then 2" what looks like an 2 box RC40 (except the fist box just curves out to a wider diameter and then curves back into the 2" pipe). My problem is I find this Very loud especially as I have to occasionally do long ish trips on the motorway and this is my only car so it is a daily driver.

So what I'm after is something quite, but i dont really want to noticalbly loose performance if possible. What would people suggest?

[IainMac]

Dosent sound/look like a RC40 to me. The front box should like a usual silencer and the RC40 noise is nicely muted burble at idle.

[Cooperman]

I guess with a big-bore LCB and a 'straight through' type silencer it's always going to be a bit noisy. However, the RC40 seems to be the least noisy of the performance silencers, although not as robust as the Maniflow ones. What I use to keep the rally cars within the strict noise limits is a Maniflow 'Cherry bomb' as a centre box with an RC 40 centre-exit at the rear. My entire system, from the 'Y-piece' to the rear is then wewlded into one.
That's a reasonable compromise, although the noise inside my cars seems to be mainly the induction from the twin SU's.
It's all a trade off of 'noise v performance'.

[trackcar]

all silencers of the straight through absorption type work best towards the rear of the car with a smooth flow rather than individual bangs .. so some kind of expansion chamber type affair with minimal internal wadding woud be good, and a big absorption type silencer right at the back of the car also.

extra length in the pipewrok helps smooth flow, so getting a transverse silencer across the back with associated extra pipelength to reach it would also work .. guess you have to offset the extra weight against the noise reduction you require.

properly sized absorption type silencers though are the way to go, but as far back as possible.

[fwdracer]

RC40 exhuasts are easily identified - marked with Part No. "RC40" on the rear oval box. The twin box RC40 will knock noise levels down to sensible levels for road use (cylindrical centre box + oval rear box). They are 1.75inch pipe diameter.

I've tried both single and twin box RC40 systems on my road 1275cc Mini. Twin box is the way to go - far quieter and better mid range where you need it on the road.

I race with a twin box RC40 system on the track to keep inside RAC MSA specified noise limits too.

>> Edited by fwdracer on Tuesday 15th November 10:46

[mini1976]

If you look at my profile i have put a picture of the first of the 2 back box's. Has anyone seen anything like that before? (Also is there anyway to add pic's to my posting rather than putting it on my profile?)

[Cooperman]

Hi Tim,

That's a 'Cherry bomb', but it looks to have got really hot and probably the silencing has been degraded. The advice to use the two RC40 boxes, the small circular section one then the main RC40 fitted transversly, will really quieten it down A lot. The reason I use the cherry bomb on the rally cars is because the circular one has blunt ends and will hit the ground whereas the cherry bomb is tapered. For that reason I have to weld big skid plates onto the leading edge of the RC40. Incidentally, the reason the centre exit exhaust was developed was to reduce the chance of impacts on rough special stages knocking the entire exhaust system off. The cross sectional area thus exposed to rocks, etc, is significantly reduced. Mainflow systems are stronger and last longer, but are not so quiet.

[mini1976]

Thanks for that, is there any reason why it might have got very hot? May I have an engine problem that I also need to sort? Incidentaly the black end is towards the back of the car if thats what makes you think it have got very hot.

[Cooperman]

mini1976 said:

Thanks for that, is there any reason why it might have got very hot? May I have an engine problem that I also need to sort? Incidentaly the black end is towards the back of the car if thats what makes you think it have got very hot.

Maybe I'm wrong about the overheating. It just looked that way from the photo. Take a good look at it as it could just be the paint has come off locally.
Exhaust retention tip:
After you finally clamp up the 'Y-piece' to the ends of the LCB, drill a hole in each clamp right through both layers of pipe and tap the hole 1/4" unf. Use a couple of short 1/4" UNF cap head screws right through into the exhaust area, using a bit of Loctite, and that will keep the exhaust on and all together even if you ground it out on a rough road. This assumes, of course, that the remainder of the system is welded up as a 1 piece assembly.

[eccles]

we run a large bore maniflow centre exit exhaust on my mates hillclimb mini, that comes with a cherry bomb type first box, just like in the picture.

[Cooperman]

That's what I used to run on my '64 historic Cooper 'S' rally car. What I found was that after a couple of events it was right on the limit for noise and in danger of not being allowed to start. Since switching to the RC40 +Maniflow Cherry Bomb I've no more issues with this, although the RC40 in nowhere near the quality of the Maniflow in terms of material and strength. It's OK after I reinforce it, though.

[eccles]

this maniflow is a good few years old, but its still passing noise tests at scrutineering, and its survived the rear mount snapping at a particularly bumpy welsh hillclimb and being dragged up the top half of the course!

[love machine]

Mine is an earplugs job, there is no way around it. It's loud! Dont go losing your hearing for an old car.