Help me solve kpa discrepancy

[robz]

Working on an auto heads/cam vette.

New Vararam
New cam
ported heads
fast 90/90
78mm granatelli MAF

Key on/engine off MAF reading was 102kpa on the track but at WOT we were getting 98kpa on our logs

Same thing on the dyno we were getting 4kpa less at WOT then with key on/engine off.

Any ideas what is causing this?
Does this suggest a restriction?
Do we need a larger MAF?
How much loss of power is 4kpa?
Thanks

[dfe1]

Granatelli MAFs are always suspect-- stick a stock MAF back on and see if anything changes. Also- a bit of confusion here- MAFs do not read in kPa-- I assume you mean MAP sensor when referencing manifold pressure. A wide open throttle MAP reading of 98, when key on/engine off reading is 102 does indicate a possible restriction-- which makes sense considering a 90mm throttle body and a 78mm MAF. However, it could also indicate that the throttle isn't opening all the way. Have you checked to make sure the throttle plate is wide open when the TPS says it is?

[joecar]

There's a thread somewhere here where a bigger MAF was found to reduce the difference between WOT MAP and BARO...

but, as dfe1 said, do check for restrictions (dirty filter...?) and check the throttle plate opening.

[cmitchell17]

How much would you say map would have to drop below baro to indicate a restriction in the intake?

[BlackGMC]

was it 4 kpa less the entire pull or just at the end or at the higher RPMs? Posting a log or tune might help

[joecar]

Read thru this thread, see post #15: showthread.php?t=6919 (http://forum.efilive.com/showthread.php?t=6919)