4AGZE - Manifold vacuum crushing silcone piping at idle

[ach_66]

Hi guys, this may be a noob of a question, but couldn't find anything relating to it, so thought I'd brave the forums.

Today I rerouted the pipework on my FMIC setup. I did this for two reasons:

1. To shorten the overall pipework length (reduced length by about 400mm) and;
2. To fit a smaller FMIC (old cooler was 500x300x70, new cooler is 500x140x70)

Both of these in an effort to improve throttle response.

Anyway, I did this by using a combination of the alumimium pipework used in the old setup, and some new silicone fittings (1x135 deg elbow, 1x45 deg elbow, and 2x90 deg elbows).

The result was looking good until I kicked it over, the new silicone fittings all collapsed at idle due to manifold vacuum. Give the throttle a blip, and they return to their normal shape.

This wasn't an issue with the old setup, as pipework was 99% aluminium pipework, with some silicone joiners.

Any ideas why or what could be causing this to happen? And can it be fixed?

Any help appreciated.


Cheers,
Az

[Nikkojoe]

Its normal for that to happen on a gze because the intercooler is POST throttle body, not PRE (like most turbo cars). Therefore treat it like a giant intake manifold, it will be under vac (lower pressure than atmo which is what forces the silicone down) until you give it gas.

To fix it, use straight couplers with only a small amount of exposed silicone. If you made your cooler pipes out of silicone bends, get stainless/alloy bends welded in place

[ach_66]

Cheers mate,

Kind of thought that, but wasn't sure.

Az.

[ae8zn6]

if you can find a spring that can cover the bends that should also stop them from collapsing, doesnt matter if they fit inside or outside the silicon bend

[burcoty]

um yeh it does, the spring needs to be on the inside stopping the hoses from collapsing inwards
When its on the outside it may not because if there is enough vacuum they will still fold in on themselves.

what size are the hoses? there is springs for this exact purpose on the inside of the bottom radiator hoses on ford ba's and many other cars.

[Gunner]

In my experience using a lot of silicon for pipes, will always result in a lack of response. Now I can't say for sure in this application, as it is different to a turbo set up, being under vacuum. But imo, any gain in response you have gained by shorteing the plumbing, may very well be lost through expansion of the silicon sections you have used. It will not effect overall power, but but boost ramp will be slower, and in turn it will take longer to make power.

From the testing I have done with Subaru's on dyno's over the last 5 years or so, this is the case. There are hundreds of silicon plumbed kits on the market for subaru's, like those from APS, tht cost near on $2000, but I have seen more power made earlier with cheap ebay plumbing set ups. In some cases up full boost is on a whole 1000rpm earlier.

[ach_66]

Thanks for the feedback guys.

I too thought of the internal spring idea. But as an interim solution (until I get Alu. piping all the way), I used some offcuts from my old setup and jammed them into the silicone bends to stop them collapsing. Works a treat. But I still have one problem, the majority of the pipework is 2", except where it connects to the cooler. Here I have used 2"-2.5" 90 deg elbows, and cannot use the solution above.

Any ideas for this? Can you get 2"-2.5" Alu. bends?

Will try and get some photo's on to show my setup later tonight.

Cheers,
Az.

[ach_66]

Ok, here are some pics:

This is the old setup (best photo I could find sorry),

Basically out of the SC to the cooler, through the cooler then the long way around the engine bay and over the top of the exhaust and cam covers.

Here's the new setup,



The start of the setup is virtually the same as the old, but now the return comes back over the cooler inlet pipework and straight to the ITM.

Feel free to comment.

Cheers Az