Cams, Compression and Such. A Discussion.

[ducpainter]

Whichever one has the faster rider.

[koko64]

Pretty much everything.

This is as close to an apples-to-apples as I can get:





A FBF 88mm hi-comp, pretty sure it's a Wiseco on the left, vs. a Mahle 91mm on the right.
Mahle is 3mm larger, yet only 12g heavier with the pin.
FBF is naked aluminum, but Mahle piston is coated everywhere, and has some sort of other coating on the skirt.
FBF is pretty chunky, while the Mahle is pocketed above and outboard of the pin, and the pin bosses are contoured.
Mahle has a shorter pin, with a tapered bore.
Mahle crown and dome fit the combustion chamber better, so end up with a more efficient squish.

Neither piston fits the chamber all that well, which annoys me greatly.
The cost of doing it properly is minimal.
As an example, the squish area of the FBF is totally flat.
The mating chamber area is domed slightly.
So the squish is limited by the very edge of the piston, and gets wider as you go toward centerline.
So it's squandering compression.
Not a deal-breaker, but fixing it is troublesome.

It's not a totally fair comparison, as the Mahle are likely 2X the price of the FBF.
And in a street motor application, likely not much benefit.

It's just annoying that they both could have done the crown properly for maybe $10 more in machining and design per piston.
And it'll cost far more than 10X that to fix it even halfway.

That FBF piston a JE?
Off the shelf pistons that fit bang for buck rather than done for the specific bike ay? So a safety margin on the squish rather than max efficiency . I've been using JEs for cost and "drop in " fit. I note the domed Vs plateau crowns I've seen. I remember seeing Pistals with a "nipple" crown.

[koko64]

Whichever one has the faster rider.

[Speeddog]

Pretty sure the FBF's are Wiseco.

I've got some slightly tatty 900 JE's, and they've got the JE logo under the crown.

[koko64]

Yeah thats right. I forgot that. Its the Pistals with the nipple crown ay?

[Speeddog]

Haven't had my hands on a 2V Pistal, and don't remember from pics.

[ducpainter]

[Duck-Stew]

Yep thats right. I remember now.
You going to run a dual map switch, sea level and mountain maps?

No need.  I never get out of the mountains these days...

[Speeddog]

That looks like a good thing to do.

[Duck-Stew]

Update:  12:1 pistons installed w/the aforementioned R2525-9 plugs.  Wow.  These upgraded the non-existent mid-range to somewhat existent!  Bike has a noticeably more punchy exhaust sound.

I also filled it up with the Engine-Ice brand coolant.  Bike has yet to crest 180'F and that's high-compression and in New Mexico...

Feelin' good about all this! 

[koko64]

I might try that coolant in the Gixxer.

Does the 748 have a custom map for the elevation?

[ducpainter]

I run Kool_Aide from Maxima. I don't even have a fan and when running in the heat on the track I never see over 180. It will heat up if sitting in the hot pit idling.

[NAKID]

I run Kool_Aide from Maxima. I don't even have a fan and when running in the heat on the track I never see over 180. It will heat up if sitting in the hot pit idling.

Wow, commuting in warm (~90) temps and slowly splitting traffic, I've been seeing 200-215...

[ducpainter]

Wow, commuting in warm (~90) temps and slowly splitting traffic, I've been seeing 200-215...

I'm not sure if the additional airflow from speed is more effective at cooling than running 11 K is at heating. I suspect it is.

[Duck-Stew]

I might try that coolant in the Gixxer.

Does the 748 have a custom map for the elevation?

No, just running an FBF "Stage 1" chip for the 748.  Got a high flow air filter and some 50mm carbon cans (which I'd like to trade for some 45's eventually...)