Author Topic: Flexible exhaust (Read 283 times)

Jimr1999 · « **on:** 23 Apr 22, 07:06 am »

Has anyone had experience of this type of flexible exhaust with the Honda engine?
The flexible pipe bit, not necessarily the can...

Chris Brown · « **Reply #1 on:** 23 Apr 22, 09:29 am »

My only thought is that the convolutions will tend to disrupt the airflow, probably be OK for short connecting pieces.

Tinworm · « **Reply #2 on:** 23 Apr 22, 12:11 pm »

Would you need some kind of reducer, as the exhaust manifold on our engines seems very small?

Jimr1999 · « **Reply #3 on:** 23 Apr 22, 01:19 pm »

It seems to have an I.D. of 25mm, which the standard exhaust has a flange from the manifold bit to the silencer that is about that. I am tempted to try it for the price, just wondered if anyone had had a go with it.

Tinworm · « **Reply #4 on:** 24 Apr 22, 12:59 am »

Quote from: Jimr1999 on 23 Apr 22, 01:19 pm

It seems to have an I.D. of 25mm, which the standard exhaust has a flange from the manifold bit to the silencer that is about that. I am tempted to try it for the price, just wondered if anyone had had a go with it.

Well, if that is so, I might join you

Applejack · « **Reply #5 on:** 24 Apr 22, 09:50 am »

I tried it and found it reduced performance

Jimr1999 · « **Reply #6 on:** 24 Apr 22, 10:17 am »

Thanks for that @Applejack

Chris L · « **Reply #7 on:** 24 Apr 22, 10:24 am »

Would also think it would need extra support either side of flexible area ?

As our Wee little single cylinders are rather prone to vibration

. Last year before deciding on current design (see two braces/support brackets) , i broke a couple pipes at the flange .....thank goodness for welding kit

Chris L

Jimr1999 · « **Reply #8 on:** 24 Apr 22, 12:15 pm »

Good advice @Chris L, thanks for the pic

Tinworm · « **Reply #9 on:** 24 Apr 22, 12:25 pm »

Quote from: Jimr1999 on 24 Apr 22, 10:17 am

Thanks for that @Applejack

Thanks Applejack. I suppose you could have a sort of expansion box....a sort of big area in the spare space of the boot, with an outlet to the outside of the car, so that there isn't that sudden back pressure, which I suppose is the problem?

Chris Brown · « **Reply #10 on:** 24 Apr 22, 04:40 pm »

Perhaps I should have given a better explanation when I commented about turbulence. In an exhaust system the aim is that the flow is as smooth as possible, turbulence will kill the power of an engine.

David F-R · « **Reply #11 on:** 24 Apr 22, 05:57 pm »

Quote from: Chris Brown on 24 Apr 22, 04:40 pm

Perhaps I should have given a better explanation when I commented about turbulence. In an exhaust system the aim is that the flow is as smooth as possible, turbulence will kill the power of an engine.

I have absolutely no knowledge about exhausts.
So, Chris, would a smooth bore positively tapered pipe be the most efficient?
And what about any silencer? Should we plan one into the design? Are they needed?

I've a feeling that some system will be needed that's better than the one the engines come with, if only to carry the exhaust outside the engine space.

Chris Brown · « **Reply #12 on:** 24 Apr 22, 07:57 pm »

Smooth bore parallel is fine, no need of a taper, but each change in pipe cross section should be an increase. I've got an aluminium pit bike silencer on mine, but others use plain pipes and are within the noise limits for the tracks we use.

RhysN · « **Reply #13 on:** 24 Apr 22, 08:18 pm »

As I was the person who used the decibel meter at Stretton I can say positively that a number of our cyclekarts exceeded their noise limits as publicised when using the straight pipes. This would be true at a few other venues.
I know this sounds negative, and I don't want that to be, but a little effort would be helpful.

Chris L · « **Reply #14 on:** 24 Apr 22, 09:02 pm »

Yes this was true of Castle Combe Kart Track last year. Some of our Ck's were over limit.

Good idea to fit one (Free Flowing) or have the facility to bolt one on when needed.

Chris L