Stock intake pressure at idle?

[x_atlas0]

Howdy, everyone!

I've been messing around with a Megasquirt in my coupe in preparation for an engine swap. I figure if I blow it up, it doesn't matter since I'm going to replace the engine anyway.

As a result, I've been slowly massaging the base tune that got the engine started. So far, I got it to idle reasonably well after significantly adjusting the idle air actuator setpoints, they were low by ~20% for me. That makes me wonder if I have bad vac lines causing excessively high intake pressure at idle. For reference, right now, I'm getting about 70 kPa at idle. That seems very high to me, I was expecting more around 30 kPa. It's also running pig rich (~11.5:1) but I think that's the base tune trying to be safe.

Alternatively, if someone would be willing to throw their naturally aspirated tune my way, I'd like to see where the differences are.

 

[Dick Steinkamp]

There is no intake pressure in a naturally aspirated engine. There is only the opposite...manifold vacuum. Generally, manifold vacuum is measured in inches of mercury. I've never heard of it measured in kilopascals but 70 kPa is just about equal to 20 in HG which is normal for most internal combustion engines. 30 kPa is about 9 in HG. I don't think the engine would run at no load with manifold vacuum this low.

 

[sfdon]

Adjust your idle mixture to 13.1 and idle rpm to 1000
timing at 15*

 

[deQuincey]

My case is manifold vacuum 0,6 bar at iddle

 

[x_atlas0]

While looking around, I found a very interesting site for anyone going MegaSquirt: https://msqur.com/view.php?msq=166

It looks like a great resource for comparing tune values for a variety of platforms and engines.

 

[Mike Goble]

There is no intake pressure in a naturally aspirated engine.

The precise answer is yes, there is pressure, unless it's a perfect vacuum. If you use a gauge calibrated in absolute pressure, as you hold it in your hand at sea level, it will indicate 14.7 psia. If you use it to measure intake vacuum and the standard gauge is reading 18 inhg, the psia gage will read 8.84 psia.

 

[Sven]

Running MS3. At idle I have ~47 kPa, 950 rpm and spark timing ranging from 8-12°, AFR 13/13.1.

Check vacuum hoses at the idle valve. Are all the connections hose clamped?

Which version of MS are you running, 2 or 3? What is the engine configuration displacement, injector size and compression ratio? I could send you a tune (for 3.5 l, ~23lb injectors (238cc/min), 9.5 CPR)