NA is best - 3.1L M20 w/ ITB's

[Raxe]

Whew! Long day but a good one.

First started by disabling the vacuum to the FPR like ForcedFirebird recommended. It made a pretty huge difference in idle mixture stability, immediately richer but way less jumpy.

Synced the throttles properly using the synchrometer and set the idle at 1000RPM - I found 900 a little too 'slow' and unresponsive.



Final assembly pre-box:





Onto the airbox. Fitment is obviously really tight, I know RHD is coming out with a revised backing plate to help with clearance but mine is fitting alright I think. Needed to modify the cylinder 6 trumpet to fit the box overtop but it works.

I had a new Dinan E36 M3 air filter sitting around that I had been saving for years without a use, amazingly it's a perfect fit... very lucky. I wouldn't mind extending the intake down further behind the headlight in the future and possibly making a heat shield, but for now I'll leave well enough alone.







Loaded up some new numbers and took it for a drive! Everything is working pretty well, still need to fine tune the idle as it's still trending very rich but cruising is stable and acceleration seems good. I'm taking it easy at this point until I'm more confident all is well, but it's very driveable. Now to figure out VEAL and see what it can do.

Still a few things left to do besides tuning:
- Get the tachometer working, far as I can tell I need to wire it via the MS accessory port but maybe I'm just missing a simple setting? :\
- Install the catch can and hoses
- Find a permanent home for the IAT
- Clean up engine bay

Video of it running:

https://streamable.com/ah95h

[digger]

Very good. So a plenum chamber on a typical intake manifold eliminates most of that pulsing?

I should go out and look at my old Alfa - it has dual webers. But I think it has weights and springs for advance in the dizzy, so maybe no vac fittings anywhere.

yes, if you mean the actual intake runners and plenum rather than the little vacuum hose and vacuum rail they work similar

[LateFan]

Very good. So a plenum chamber on a typical intake manifold eliminates most of that pulsing?

I should go out and look at my old Alfa - it has dual webers. But I think it has weights and springs for advance in the dizzy, so maybe no vac fittings anywhere.

[Northern]

How does that or the buffer / canister idea work? Do you get a constant vacuum number by doing that, even with the various port pulses?

I love these threads. You guys are amazing.

Here's an ultra shitty pic of how more cyls will dampen the pulses, if you're more of a visual person...

Disregard the scale on the y axis and the timing of the sine wave

[nando]

Just FYI (and many in this thread already know) the S54 come with something like this stock.

[digger]

it still cycles, just less than would it taking a reading off a single runner.

most people steer away from MAP based tuning with ITB because even if you have a rail the pulsing still exists. the pulsing will depend on the cam, small duration and less overlap the nicer the signal

[LateFan]

Is it consistent, or is it cycling up and down within limits?

[digger]

the plenum (volume) that connects each vacuum hose helps dampen the sharp pulses, kind of averages them out so to speak to try and create a more uniform vacuum reading.

[LateFan]

How does that or the buffer / canister idea work? Do you get a constant vacuum number by doing that, even with the various port pulses?

I love these threads. You guys are amazing.

[ForcedFirebird]

I've always thought about either the shop air manifolds - some come with enough ports.

Or something for an aquarium like this:

http://www.ebay.co.uk/itm/6-x-4mm-x-8mm-Barbed-Air-line-Manifold-Air-Stone-Pump-Pond-Aquarium-Airline-/282237183461

Ideally, CAD something up and 3d print it as one piece...

I found plain old fuel rail stock works well. Drill/tap the flat for threaded fittings, then the two ends can be used for the IAC and brake booster. The latest RHD stuff comes with a small manifold now.

[digger]

rama sells one of those with the kit, does FPR, booster, ICV etc. if you still dont like the FPR with ref in the vacuum rail because it still pulses too much for your liking just open it to atmosphere and route the open ended hose somewhere that wouldn't shoot fuel onto the exhaust if the FPR ruptured. the other option is a restrictor in the vacuum line that is a great way to dampen pulses on steady state but may react slower

[Northern]

I've always thought about either the shop air manifolds - some come with enough ports.

Or something for an aquarium like this:

http://www.ebay.co.uk/itm/6-x-4mm-x-8mm-Barbed-Air-line-Manifold-Air-Stone-Pump-Pond-Aquarium-Airline-/282237183461

Ideally, CAD something up and 3d print it as one piece...

[nando]

you can use a large lawn mower fuel filter as a buffer/canister, cheap and effective.

[ForcedFirebird]

Correct. Leave it to atmosphere and tune it out, or use a vacuum manifold to average the cylinder pressures. Even a manifold won't be very accurate without a buffer/canister, the pulses will still be strong.

[Raxe]

Might not be a good idea, though. With it hooked up to one cyl, it will pulse vacuum every time that cylinder pumps. It's interesting to watch a mechanical vacuum gauge hooked to just one. I have been leaving the FPR open on open trumpet cars and using a manifold when they have them.

Oh that's an interesting point, I hadn't considered the pulsing effect. Probably was messing up the MAP reading too as nando suggested since that line was set up the same way.

So until I set up a vacuum manifold it would be better to temporarily leave the line off the FPR for a more stable pressure? And if so, expect to compensate for a richer idle mixture for now because the regulator is seeing no vacuum and running at full load?