MAP fluctuations from long intake plumbing (4A-GZE)

[mullett]

Heh...silly me. i think Nick and I sussed it the other night. It's caused by not having a bypass valve, so the MAP is flying all over the place as it sucks air through the SC at low throttle openings: IE the speed of the SC as it flows and stops, etc etc. Which would explain a lot. So I bought a Bosch bypass yesterday and I'll try and fit it up tomorrow if I get a chance, along with the adjustable cam gears. Fingers crossed, it surges like a BITCH at the moment at low throttle.

RM.

[cswan]

!

I had my car tuned the other day for the first time with the EMS (DualSport), and it drives like a pig. The guy who tuned it said it was very hard to get a smooth tune, because the MAP was jumping all over the place, from -kpa to positive boost pressure, on anything other than WOT. I watched it, he's right, it jumps a lot, and of course because the fuel map is MAP based, that dumps in far more fuel than it needs. The best (and only) was I can think of to overcome this is to move the TB to just ahead of the intake. If anyone's got any suggestions about this (Ben Wilson ) I'd be well keen to hear them, or if someone else has found a way to solve this problem in the past. Oh...and kinda OT, but what spring pressure suits a BOV being used on a supercharger?

Cheers, RM.

Ooh, geez. I remember this problem from a whiled back.
I found the same erratic map readings with tuning my Moteced 4AGE with HKS supercharger. The map sensor was located after the supercharger on the intake manifold.

In the end I went with throttle position sensing for load and an MAP sensor compensation only. But just let me have a think and ask my brother... and I'll come back to you...

[nick.parker]

Pretty much any solution you come up will be a way to get around not having angle based MAP capability.

Edit : Sorry I jumped the gun there. In the case of SC right next to manifold, yup, I'd think a smooth MAP signal would be nigh on impossible to get due to the small volume between SC and head and also the influence of the supercharger's pulsing and even the intereference between this and your inlet valves opening and closing. TPS may just be the best solution there without some clever software or heavy filtering!