can anyone see any problems with making a manifold flange and welding on, say 3/4" of tube as a runner, and then using rubber (petrol resistant) hose as the main runner.

it would save too much trouble with
1, bending (or cutting and re welding) of tubes,
2, getting the angles all right, as the rubber will sort any misalignment
3, calculating runner lengths, as they could be changed really easily by shortening the rubber or putting longer pieces in

obviously the carbs would be supported on their own brackets, the alternator bracket has a handy provision for this on the ecotec engine

any thoughts?

this is for bike carbs on a vauxhall engine btw.

Bad idea,

rubber will deflect or even collapse completly when the throttle is shut the vacuum created in that event is enomous,

you could cut up the rubber tube into socks and fit as much alloy tube in between as you can, flow-wise... it's not all that good.

regarding lentgh,
are you going hemholtz? or have you got a RPM prefference for when the peak torque should be there? cams? exhaust?

grt Thomas

hmm, hadn't thought of the deflection... can't you get reinforced tube with spiral steel running through it?

at the moment, the idea is to get it running... i can think about the rest later

i tried that with silicon hose, even the 90 deg bend collasped under the vacuum.

What engine and carb are you using?

2.0 ecotec 16v etc, and zzr1100 carbs

Motorcyles use rubber intakes without collapsing...at least, my Kawasaki GTR1000 doesn't seem to have a problem with this. How about visiting a motorcycle breaker's, and getting the appropriate rubber ones for your carbs?

^ thats the reason i was thinking it, but bikes only seem to use short peices (lik an inch long) to clamp over the manifold and carb to make the join...

what about nylon (plumbing) tube with rubber bends at both ends?

edit: i'm thinking mylon isn't resistand to petrol is it...
ally tube then with rubber at both ends?

[Edited on 27/1/08 by blakep82]

I made a manifold out of 5mm thick steel with 45mm tubes. I used these because they were free from work

In order to match my carbs to the tubes (ZX9R) I simply made a couple of plates from the offcuts of the manifold plate and welded them onto the tubes. I then used the original bike inlet rubbers that bolt to the engine as a template for the holes.

The inlet holes were smaller than the 45mm tube behind so no matching required.


inlet


inlet2

The thing sits and ticks over smoothly at 700rpm but I've still to set them up and use it in anger over the whole rev range.
Steve

^ thats quite a nice idea

any idea on a starting point for the runner length?
i understand that the lengths have effects on how the engine performs, but how long is average?

Ha! no idea. I just made mine after looking through the photo archive and seeing some of the bespoke jobbies. Also the length of weber manifolds so fingers crossed they will be OK!!



Steve

what length are yours?