OMC Cross Charge Mod questions

**spybot** · 02-25-2018, 02:12 PM

Is there a point where too much compression is bad for the engine ??
What is the ideal range to try and hit say 130 psi +/- 5psi ?
If you wanted a strong mid range motor what would you go for ?

**Mark75H** · 02-25-2018, 04:43 PM

Originally Posted by spybot

Is there a point where too much compression is bad for the engine ??
What is the ideal range to try and hit say 130 psi +/- 5psi ?
If you wanted a strong mid range motor what would you go for ?

Where's my popcorn?
This should be interesting ...

**FMP** · 02-25-2018, 04:50 PM

[QUOTE=spybot;3023809]Is there a point where too much compression is bad for the engine ??

Nahh

**powerabout** · 02-25-2018, 07:27 PM

Like racer I have seen many 135's over 150psi especially after a rebore
There is a SAE paper on the Japanese testing comp, at about 18,000rpm it needs to be reduced.

**FMP** · 02-25-2018, 08:39 PM

Different application but still xflow, above 195psi cranking too far was shown to hurt high rpm ability, meaning didn't hit the same rpm or rate of climb . That info came from a factory R&D man back when.

**Mark75H** · 02-25-2018, 10:51 PM

Originally Posted by FMP

Different application but still xflow, above 195psi cranking too far was shown to hurt high rpm ability, meaning didn't hit the same rpm or rate of climb . That info came from a factory R&D man back when.

I have a "different application" smaller bore Merc crossflow with significantly higher cranking compression; I get pretty good rpm and fantastic acceleration/rate of climb, acceleration much greater than stock and at least the same top rpm as stock compression motors, so I am not blaming compression for limiting my rpm. Looking at stuff that may be limiting the stock motors and working around that.

**FMP** · 02-25-2018, 11:06 PM

It wasn't the low and mid which suffered, but just the top end in that example. The max was about 205-210 range , which was about 10-15 over stock, low and mid wasn't hurting. Likely increasing dynamic pressure values at high rpm vs over rev hp curve I believe was mentioned.

**spybot** · 02-26-2018, 11:57 AM

I think this will be a good thread so will start up a new thread on the subject.
Sorry Mod
Not ment as a double post.

**FMP** · 05-26-2020, 09:51 PM

Someone was mentioning coil mounts. Xflows v4, some nice ones in this thread.

**GPRACING** · 09-11-2022, 04:14 PM

Yeah I’d love a set of those coil mounts for my build

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