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If your issue is in the heads to piston crown shape (we have not established that yet), you could remove the quench pads however that would drop your compression further. (like your typical drag head builds)

If it is from the chamber, my guess is the piston crown shape, to have a recess leaves a large area for combustion, those sharp valve reliefs arnt helping.

However before you go that far into things, have you checked your knock sensors and how they are mounted?

Did the tuner try some external ones?

On a side note, my domes stick up about half of Shootas for around a 8.5:1 with a 26 head in a 30 block.

Yeah that's right, don't know for sure if that's it yet. Just getting some ideas.

Perhaps I could try smooth out the valve reliefs a bit on the Pistons, take off that sharp edge.

I've got two sensors on the block (bf falcon sensors) I have bungs that screw in to block and the sensor bolts onto that. And tuner tried his as well

Tensioner above water pump as guide says and idler down in stock location.

Using BF sensors as my tuner recommended them and uses them for tuning (Bosch sensor).

Sent pics of Pistons and head to Lewis engines and he's done a few of these combos recently and thinks it should be fine with those Pistons.

Edited by Huzqld

did you google the part number on the pistons? i get 11.3cc dish

WISECO 6577M87 PRO TRU PISTONS
$132.22

Pro Tru Pistons; Sport Compact Series; Replacement/Individual Piston; Recommended RingSet: 8700XX; Rings & Pins Included
Part Number: 6577M87


SPECS:
Comp Ratio: 7.0:1
Rod: 152.5
Bore: 87mm
Comp Height: 32
Dome Volume: -11.3
Stroke: 85
Gram Weight: 384

Last year Blah_Blah had an issue with his car not making power as it wouldn't take any timing. Unopened Rb25.

Turns out the cas was dodgy. Replaced it and boom, power made as expected.

  • Like 1

I didn't bother googling them tbh. They cc'd up to 9... So maybe that was a stuff up, not sure.

Either way it brings the comp to 8.7:1 if they are -11.3cc so that's fine, not make or break.

Cheers Ben, that' something to try

What were the symptoms of that apart from not taking timing and making power?

*found the thread. Will have a read

Edited by Huzqld

I'm sure you'll read for yourself, but basically his car wouldn't take timing as it should have, was knocking and not making power for an unknown reason, with a known engine turbo combo.

Cas replaced , issue gone.

  • 1 month later...

Changed a couple things.

Cam-tech 270 9.2mm cams

Got rid of the CAS completely

And used a different tuner, He still uses the exact same model dyno.

420HP @22psi

AFR in the 11s

Boost falling off up top, we couldn't get it to make anymore. So wastegate is on the cards later on (We could of put some more preload on the actuator but left it there). Also injectors are starting to get up there. 660cc @ 80-something % duty cycle.

Happy with the way it runs and also the power at that boost level. Through an Auto

Edited by Huzqld
  • Like 1

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