MAP for multiple carbs

[david jenkins]

I'm planning to set my system up like this:



Should I use the standard diameter vacuum pipe (1/8" inside dia), or should it be larger or smaller? Is there any benefit in restricting the flow?

Would the length of connecting pipe make a difference? I'm thinking of fixing the reservoir just above the manifold, so each of the pipes would only be a few inches in length.

I had thought of mounting a suitable tube directly onto the runners, with restrictors between the runners and the tube, but I'm not sure how practical that would be - it would certainly be difficult to fix if it didn't work first time.

cheers,
David

P.S. I'll finish this carb upgrade one day...

[brentp]

Hi David,

This writeup: http://www.autosportlabs.org/viewtopic.php?t=1171 seems indicate that the reservoir size has the largest impact on the map reading stability. I don't think the hose diameter is really critical, but you might want to try two different sizes to see if that affects your readings.

What is also common is to install a restrictor between the map sensor and the reservoir.

[david jenkins]

On re-reading my post I realised that I didn't explain myelf very well!

What I plan to do is to put a long tubular reservoir over the inlet manifold, with short (2 or 3 inch) flexible tubes down to each runner. The MJ MAP sensor outlet will come off this somewhere. This should be (a) convenient, as the reservoir will be accessible and in a tidy place, and (b) cleaner, as any muck from the runners will simply run back out of the reservoir.

My concern is whether I'll get a reasonably accurate MAP reading (experience will tell, but that other thread gives some good clues), and also whether I'll cause some 'interference' between the runners if the passageways are too big or the tubes too short.

[brentp]

Although I'm not a fluid dynamics expert I'm sure you will be fine with what you're proposing. As an example, many OEM designs (like the TR6) incorporate a balance bar between the runners for purposes such as feeding power brake boosters.

But please keep us posted on your testing results!