Tighter heads for a PM 300 SVS

[ToffenG]

Hi!
I trust you are well.
I have now been boating one season with no problems using RapairÂ’s custom curve on my PM 300 SVS (Brucato Intake & High Flow Reed Plate). I gained another 100 rpms doing this (in total 250 rpms with the whole package + far better acceleration).
Do you have any experience with aftermarket / CNC cut stock heads (blueprinted) for Promax 300?
Is it necessary for me to recurve my ECU again to be able to add tighter / blueprinted heads? Or can I use the curve Rapair made for me this spring? Have anyone of you this package on your PM 300?
What kind of gain should be expected?
I look forward to hearing back from you.
Cheeers, Toffen G - Norway

[Boatmaster]

I have not seen enough of a gain from cut heads on 300s to make it worth the money and headache of running race fuel.

[stoker2001]

drew has a good point and being a merc dealor i would take his suggestions to heart.if your not drag racing i wouldnt do it.it will improve bottom and mid and maybe a little on top.it will want more fuel and if you dont give it more then kaboom :cry: if you cheat on octane requirements then kaboom again.my fly weight responds real well when i change lake heads (175 psi cranking) to race (220 cranking) :rollside: :rollside:

[carreracat257]

These guys are telling the truth.I had wayne from madefi cut my heads and its been a diaster.Three motors and 30,000 $$$$$$ later i but my stock heads back on :frown:

[ToffenG]

Hi!
Thanks for straight answer guys.
Cheeers, Toffen G

[Propster]

CarraraCat,
How much compression were you getting after you shaved the heads? What went wrong with the motors?
The reason I am asking is because I am thinking of cutting my heads to go from 120 lbs compression to 140 lbs cranking compression. I have heard that anything under 150 lbs cranking compression is fine for pump premium.

[stoker2001]

CarraraCat,
How much compression were you getting after you shaved the heads? What went wrong with the motors?
The reason I am asking is because I am thinking of cutting my heads to go from 120 lbs compression to 140 lbs cranking compression. I have heard that anything under 150 lbs cranking compression is fine for pump premium.here in caly we get 91 octane only (research+motor/2).150 cranking will detonate.in my opinion even 140 is on fine line and all it takes is one bad batch :confused:

[carreracat257]

Propster
I was running 135-140psi at 4,500 elevation.I was using half 91 octane and 101 octane.Motors ran verry hot about 165 compare to about 130 stock,with 12lbs of water pressure.Both motors at different times blew holes about the size of my fist on the number 6 piston.The third time was in havasu using 104 octane same deal hole in number 6 piston. Lakeland relpaced all 3 motors with new short blocks from merc about 10k a pop.

[stoker2001]

Propster
I was running 135-140psi at 4,500 elevation.I was using half 91 octane and 101 octane.Motors ran verry hot about 165 compare to about 130 stock,with 12lbs of water pressure.Both motors at different times blew holes about the size of my fist on the number 6 piston.The third time was in havasu using 104 octane same deal hole in number 6 piston. Lakeland relpaced all 3 motors with new short blocks from merc about 10k a pop.165 is a little to hot in my opinion,my drag never gets over 120,even on llooonnngg runs.the 3 liters might be desighned to run hotter tho.its always#6 with those,are you detonating,cold siezing or leaning out?did you hear merc has a bulliten out about powerhead torque sequence?something to do with causing distortion to #6 hole?

[carreracat257]

165 is a little to hot in my opinion,my drag never gets over 120,even on llooonnngg runs.the 3 liters might be desighned to run hotter tho.its always#6 with those,are you detonating,cold siezing or leaning out?did you hear merc has a bulliten out about powerhead torque sequence?
something to do with causing distortion to #6 hole?l
lou at lakeland said he was aware of the torqe sequence.With stock heads new tuners reeds and reed blocks i have about 100hrs no problems

[Propster]

Man, that sucks. I wanted a little better midrange and was hoping that new high flow reed blocks and tighter heads would get me there. 135-140 compression does not sound too extreme for pump gas. I ran 140-145 compression with shaved heads on my 2.5 for 4 years with no problems on pump premium. I ran it hard too. From what you explained with the raise in engine temperature, sneezing at idle and holes in the pistons, it may have been running very lean. I wonder if bumping up the fuel pressure would have helped? Not sure if I want to experiment with it. If I blow my powerhead, I am on my own.

[ToffenG]

Hi!
I have also been told that everything below 145 psi should be ok running 91 octane / 98 RON. My compression at the moment is 125-130 psi, so the big question is if the increased compression 15- 20 psi will make any effect at all.
Cheeers, Toffen