Non ZR-1 Dyno graph help

[limey]

I took this car to the dyno yesterday and am having issues with it dropping power @ 6000 RPM, in both NA & on 5 lbs boost.

Any ideas what would cause the car to drop and then re-gain power at these levels? I have plenty of fuel & the car doesn't have knock sensors, as per factory.

Just looking for some other opinions on where to look, what is the key i think it it does it both NA & Boosted.

[jonszr1]

you might want to look at your fuel filter .what size injectors do you have in the car ?.do you have a boost activated fuel pump?

[jonszr1]

12.4 is a little lean for a boosted aplication . reburn the prom and shoot for 11.8

[Zr1 Destroyer]

I assume this is fuel injected? There's nothing mounted on the engine to detect any high-frequency vibration??

[limey]

Originally Posted by jonszr1

12.4 is a little lean for a boosted aplication . reburn the prom and shoot for 11.8

Under boost im @ A/F of 11.3 As per the bottom graph, the top is NA.

Ry, the car is Fuel Injected, the O2 sensors were unplugged though as i was using a FAST wide band meter to read A/F, would that cause the ECU to miss read fuel adjustments and such and cause this problem?

[Jagdpanzer]

Turbo or engine driven supercharger?

Originally Posted by limey

Under boost im @ A/F of 11.3 As per the bottom graph, the top is NA.

Ry, the car is Fuel Injected, the O2 sensors were unplugged though as i was using a FAST wide band meter to read A/F, would that cause the ECU to miss read fuel adjustments and such and cause this problem?

Which O2's unplugged, pre cat or post cat? In boosted application you need to look at fuel. Also look for evidence of belt slipping since you are using a SC.

[limey]

Originally Posted by Jeffvette

Which O2's unplugged, pre cat or post cat? In boosted application you need to look at fuel. Also look for evidence of belt slipping since you are using a SC.

Twin eaton M90's putting out 5 psi. Belt driven, i have no cats, used to have 4 O2 sensors, two removed and installed 02 sims and the remainder set was unplugged to allow installation of the FAST Wide band. The two old 02 sensor connectors that have 02 sims now were the pre cat ones, no belt slippage at all, you can see on the graph that there are no boost spikes, a very flat boost line.

[jonszr1]

just throwing this out could be a valve spring harmonic issue

[rkreigh]

Originally Posted by jonszr1

just throwing this out could be a valve spring harmonic issue

bingo many times the valve springs are weak and you are floating the valves the boost pressure requires a bit stiffer spring

check seat and open pressure probably need fresh ones!

also could be the "spark blowing out" might have too much plug gap

or detonation. could be lots of things, need some data limey!!