Manifold Pressure Hoses

[Geoff]

Can someone give me a feel for what's acceptable and what's not with respect to manifold pressure hoses? I've seen some different installation methods, but not much explanation about what's really necessary and what isn't.

I have a VM-1000C manifold pressure transducer mounted in the standard 3-slot Vans transducer manifold, and I have two P-mags. The P-mags came with some small black tubing, but I have no idea what kind it is. I bought the Vans manifold pressure hose, but it's not long enough to reach my transducer manifold from the #3 cylinder so I have to send it back.

Questions:

1. Do I need to order some fancy Aeroquip hose for this application? That seems like overkill when compared to the tiny tubing supplied with the P-mags. What types of hoses are acceptable, and what types are not? I've seen some installations that used what looks like radiator hoses with standard hose clamps.

2. Is a restrictor fitting required in the engine port? Some say yes, some say no.

3. What's the most common and acceptable way to plumb this whole thing up? I'm thinking some sort of hose from the engine to the transducer manifold, and then a T-fitting (1/8" NPT with two hose barbs) in the spare hole on the transducer manifold.

4. The T-fittings I've seen with 1/8" NPT threads and hose barbs are for 1/4" hose, but the hose that came with the P-mags seems smaller than that. Am I missing something here?

5. Does anyone have any pictures of a similar setup?

Thanks.
-Geoff

RV-8

 

[Davepar]

Bumping this up as I have the same questions. I'm also planning on mounting the MAP sensor in the manifold. One less hole through the firewall. I was thinking about getting a custom hose, maybe from a racing shop, from the cylinder to the manifold. However, it does seem like overkill when the P-mag has that tiny hose and a barb fitting (1/8" I think?). You could cobble together a bunch of reducer and T fittings and hose from Spruce.

I saw a picture either on this forum or on someone's web site of how they hooked up their E/P-mag hoses, but I don't remember where at the moment.

 

[captainron]

Manifold pressure

Maybe not related, but maybe helpful, I added a manifold pressure/Turbo boost gauge to my car, and it just used the plastic 1/8" line from a plug on the manifold to the gauge. At idle especially, the gauge needle would fluctuate rapidly, almost a vibration. I dampened it in stages to the point where it was smooth, but still has instantaneous response by inserting varying lengths of the tubing you find on aerosol cans of WD-40 or carb cleaner into the 1/8" tubing.
It turned out that in this case, about an inch and a half did the trick.

 

[Radomir]

I skipped a "fancy" (and expensive) Aeroquip. We used a kevlar hose from a race shop.. looks nice (sorry no photos yet)... it was very affordable. Bulkhead fitting and plastic hose on the cockpit side.

 

[KayS]

geoff had the same questions i have in mind right now... could somebody add more light to his subject?

thank you. Kay

 

[aerhed]

First, I think you need a good fitting in the cylinder head. 1/8 (-2) to 1/4 (-4), AN steel. If you use -2 and it breaks somewhere other than the cyl head, it will still run sorta OK. If you use -4 and it breaks, you're hosed. So a restrictor on -4 would be a safer setup. Any quality fuel resistant hose should be sufficient, no real need for a medium pressure hose.

 

[RV8RIVETER]

I used bare teflon hose, high temp and flexible. Used stainlesss swagelok fittings on each side. For a restrictor I followed someone else's idea (don't remember who) of a -4 rivet JB welded inside the 1/4 to 1/8 NPT fitting on the cylinder. Then drilled a small hole in the rivet. Worked very well and there is no way for the restrictor to fall out.