Surge in L67 under hi load/hi RPM

[VX L67 Getrag]

Can anyone see a reason for this VX L67 with all the regular mod's to surge from around 3500 onwards, I've looked at various logs of it & can't see any real reason for it, it's like the fuel pump is cutting in & out on pressure but I would have thought the AFR would be showing signs?

In this log it does it at the 16:02 to 16:04 time marks, any thoughts would be appreciated.

[Holden202T]

too much timing can cause surging.

[VX L67 Getrag]

it's only got 9 to 10 degree's at that load point, should really be able to handle 15, but it is a bit lean at that point too around 12.5 to 12.8

[ejukated]

what mods? just bolt ons? Whats the plug gap? could try closing it down a bit to say 1mm

[VX L67 Getrag]

it has 10Psi pulley, 1.9 ratio rockers, 69mm throttle body & internals stock.

yeah I'll check the plugs tomoz, I had 1 the other day with same mods less 1.9 rockers & had brand new 1.5mm gapped iridiums & didn't surge but had a miss under hi load/lo rpm.

[immortality]

I had issues with iridiums @ 8 psi with 1.5mm plug gaps. Closing up the plugs got rid of the hesitation/miss.

[VX L67 Getrag]

Yeah honestly if I'm doing the build anything around 10Psi I would go 1.0mm no matter what compound spark plug, anything over 12Psi 0.8mm & then 16Psi+ 0.7mm.

But generally I just tune how it comes in, then if there's issues then causes headaches, I really need to have a better layout as they come in.

but still doesn't really sort out what the surge could be.

[TdracerTd]

L67 gods specify bpr6efs at 0.8 gap for anything over stock boost.

[delcowizzid]

0.9mm gets us past 20psi no missfires turboed and rich

[VX L67 Getrag]

Yeah it's just sort of a rule I like to follow with the above faso I mentioned L67 or any forced induction, no matter what they say about iridium/platinum firing cleaner I don't believe makes that much difference.

Still doesn't really answer the surge, but I will check the gaps!