117 build

[Sunny Jim]

Seeking advice of you boys who have been putting kits together.
So finally I have the RG in bits. I am installing CP 117 piston kit on my 107 this week.
I am  Currently running the CR460 , stock exhaust, canons and PV target tune.
So going through the gaskets supplied,
I see I have a 0.010 base gasket set and a 0.036 head gasket set.
Given that these piston kits are rated @10.75:1 , and the gaskets are as above, is this Cam suitable for this build.
Thank for the Kit Murph! 🇦🇺

[rigidthumper]

CR460 has a 20 degree close, which puts your CCP around 225, and with static @ 10.75, corrected CR will be ~10.5:1. The dual plugs & a great tune help. Do you happen to have 104-106 octane fuel available?

[Sunny Jim]

I believe our premium unleaded is 98 ron. Aussie fuel is generally not as good as US fuel, as I understand. GMR once spoke to me this issue, many moons ago.

[Sunny Jim]

What are the factory standard sizes for head and base gaskets?

[Prostock]

Base is .014".  Not sure what the head is cause I never put stock back on.  Always cometic MLS.

[rigidthumper]

Last M8 set of heads I saw was 88.8cc F & 89.0cc R.

[Durwood]

The 460 will work great in your 117 Jim.

[Jamie Long]

Agreed, the CR-460 works well in a 117. No worries about 225 CCP, that's less than stock. Here's a chart from a build a user did with the FM 117 piston/cylinder kit, CR-460 cam and stock TB

[Sunny Jim]

225 psi with those gaskets? I have assembled
Cylinders yet to check deck height. I was concerned that the running comp may be too high.

[Sunny Jim]

So I am scratching my head here, thinking about CCP an running compression. I consider what was safe and reasonable in a Twin Cam eg. My previous 120r 660sm set up, and I wonder why the same rules wouldn't apply to an M8.
My calculations with the pistons down the hole at 0.008 would put me at around 10.6:1 running comp.

[Hillside Motorcycle]

So I am scratching my head here, thinking about CCP an running compression. I consider what was safe and reasonable in a Twin Cam eg. My previous 120r 660sm set up, and I wonder why the same rules wouldn't apply to an M8.
My calculations with the pistons down the hole at 0.008 would put me at around 10.6:1 running comp.

Combustion chamber design, and multiple spark plugs aid in controlling the known issues associated with big ccp.

[Sunny Jim]

Thanks for responding Hillside!
I struggle to see how high CCP and corrected compression is acceptable and indeed, rideable on tourers with an M8, yet not on a twin cam.
My new hold completed is a dragging hot
Rod! 240/245ccp.
My perception was different.
I don't like it.

[Herko]

Durwood recently completed a 124 with a CR480 cam in a Touring  bike.
Post tune checks showed CCP 246/250.
No knock in sight.
His incremental testing has shown M8s can be squeezed tighter than Twin Cams for a given usage application.
But, part of his process is to land the net squish at .030 during the build.

The result yielded a great arrives early and stays late power curve btw.

Cheers.

[Scotty]

I believe our premium unleaded is 98 ron. Aussie fuel is generally not as good as US fuel, as I understand. GMR once spoke to me this issue, many moons ago.

That is actually incorrect and just a theory made up by some idiot many many years ago.
Australia only use the RON (research octane number) were as the USA & Canada use a combination of RON & MON (motor octane number) which then gives you the AKI or PON (posted octane number)
So 98 octane fuel in Australia is 92 octane in the USA but the advantage in OZ we don't mix ethanol (E10) in with most of our fuel and you can avoid it like the plague.
The fuel we use here in OZ is just as good as the fuel they use in the USA anyone who tells you different has their head up their ASS

[Sunny Jim]

Thanks for clearing that up Scotty!
I am still trying to get my head around M8 vs TC maths.
For the exercise - Presumably if you were to set up an M8 to comparable numbers in a nice Twin Cam, shall we say around 200 CCP and a corrected comp of around 9.5:1 , the M8 would be a slug!

[Scotty]

Thanks for clearing that up Scotty!
I am still trying to get my head around M8 vs TC maths.
For the exercise - Presumably if you were to set up an M8 to comparable numbers in a nice Twin Cam, shall we say around 200 CCP and a corrected comp of around 9.5:1 , the M8 would be a slug!

Without going into it to deep the advantage of a 4 valve head, combustion shape, twin spark plugs all come from the chase for HP & torque.
As well as the adage there is no "replacement for displacement" throw on some 4 valve heads etc and you can also up the cranking compression and no ping.
M8 220psi would be the lowest I set a street bike and I know some of the guys on here are around 240-250.
Seems wild compared to a twin cam but throw what you learned about Evo's and Twin Cams out and enjoy it.
I should also add the EFI and the ECM also contribute to this and it does need a good tune once you deviate from stock and a carby would not cut it on a M8 with the compression that high.

[Sunny Jim]

So after some soul searching, rectifying some mistakes, and getting back on the saddle , Auto tunes and all, I am getting into this new build.
My curiosity has now extended to the consistent high engine temp readings on my PV verses the temps I am logging via HD mega log viewer.
The data collected indicates the PV display is reading 310 - 320 degrees F, whilst the HDMLV has gathered temps at and around 280 - 290 degrees F.
So where is the accuracy here?
I find the HDMLV is consistently recording lower numbers both in temp and AFR/ lambda.