Talon9871

Hey guys, I'm a bit stumped and need some input on this one...
I've recently built the H22/K20/F23 engine ("G23," anyone?) and currently have it sitting in a 6th gen accord (don't judge!). The setup is (otherwise) pretty much stock for the time being, being run by a P28 with S300. Here's what's going on:
I've noticed that my vacuum readings are much higher than they should be, for everything except idle. Meaning, at idle my MAP reads around 25 kPa (which is normal afaik), but by 40% throttle I'm already up to 90 kPa (the 8th column in SManager), and 50% throttle is 97 kPa (practically atmospheric pressure!). Pushing throttle any farther doesn't change MAP readings, and just makes the car run richer because of throttle tip-in. My TPS seems to be working fine, throttle plate isn't sticking and DOES open all the way when the pedal is floored. Wideband Lamda meter doesn't show anything unusual with A/F ratios. I'm also fairly sure I have no vacuum leaks. This can't really be the way things are supposed to work? The car runs great and nothing else seems off.

Any input is GREATLY appreciated! And additional info can be provided if needed, of course.

99V-unit

what map sensor do you have?

Talon9871

Stock Honda MAP sensor (for an Accord). I'm using an F23 throttle body (and MAP sensor) on the H22 intake manifold.

Sr420Det

Ii. Was going to say u got a vac leak or ur throttle body is to big but it seems uv already looked into those issues. Maybe check ur brake booster check valve. Did u do the tps setup before u started tuning?

Talon9871

I didn't actually do the TPS setup, no. From what I understood, it didn't seem that crucial unless the TPS was just WAY off (which is rarely the case?). Just eye-ing things, the TPS reading seems pretty well lined up with the throttle plate's actual position. But I can look into that, and the brake booster check valve didn't even cross my mind. Also, I'm just throwing this out here because I simply don't know, but could the IABs or EGR system be messing with things in any way? P28 doesn't support either, so they're both unplugged, and EGR is separated from the vacuum system.

Edit: I'm sure that IAB's couldn't be changing things, it's really more the EGR that I'm unsure of. Just thought I would mention both, as I'm not THAT familiar with either system.

david974

put a plug in your EGR system to see

Talon9871

I have the vacuum line going to the EGR plugged, with no effect. Or did you mean to actually take the EGR valve apart and put in a plate or something to completely stop any exhaust from getting through?

Talon9871

Ok, so I gave everything a lot of thought, and something finally hit me! Maybe there's really nothing wrong with the car? Maybe someone could tell me what they think about this...

Tuning theory! So, each cylinder draws in X amount of air on each intake stroke... So at 1000 rpm, each cylinder should pull in 500X amount of air... At 6000 rpm, each cylinder pulls 3000X air (this all assuming the cylinder has no restriction on airflow)... REGARDLESS of throttle position. So 15% throttle at 1000rpm will NOT have the same vacuum reading as 15% throttle at 6000rpm. There should always be a stronger vacuum the faster the engine is rotating. That's what's logical, but perhaps someone could back me up on this.

So I guess my real question in all this is, What vacuum readings are normal for a given rpm and throttle position? Or, rather, is there actually a way to calculate that out? (All kinds of things should impact that, no? Size of combustion chamber, IM, TB, type of air intake?) Or should I look at the fact that it's EASY to hit atmospheric pressure at low RPM's (25% throttle at 1500rpm?) and take that as a sign that my intake system is overall MORE than adequate for the engine? Conversely, if my MAP reading could NEVER hit atmospheric pressure, especially at high rpm, then that could be a sign that the intake is insufficient for the air needs of the engine?

I apologize for what are probably simple questions, but I'm VERY new to tuning theory (self-teaching!), and am using this poor car to experiment and learn. I've tuned up to ~5000rpm, still not using VTEC yet, so I haven't really seen how the MAP readings compare against throttle position in the upper RPM range or in VTEC.

ddd4114

This is completely normal for the reason you just mentioned. The throttle limits airflow, not manifold pressure.

The relationship between speed, manifold pressure, and throttle angle will change with the engine setup and, most importantly, the throttle bore. You can use math to get ballpark estimates of this by making some assumptions, but it still is not easy to do.

Bongnak

It is normal... I've tuned quite a bit of cars and this happenes a lot when itb are used. If you think about it the engine can take so much air and sometimes the intake system is so efficient that at 50% tps all the air that's ever going to go into the cyl is already in there to the point that even opening the trottle more isn't going to do anything.
If you google alpha-n megasquirt with itb , they explain it nice

Sorry I'm using my phone to type this