Theory Question on a 2.5 FF

[DieselDood]

A buddy of mine has as 200 FF block. Carb motor.
He sent the heads out and had them shaved for more power.
He's running 93 Octane
He's been running Penzoil at a 40:1.
It's still pretty cold here in MN but he's been out on the lakes.

Roughly 40 ambient.

He fouled a couple plugs, only running a couple hours.
He pulled the plugs and they had a milky substance that wiped off. To me it feels slippery. I'm thinking maybe because he's at 40:1, and the higher octane burns cooler. Maybe that he's getting a little moisture separation due to the colder combustion and colder temps? The additional oil is probably also assisting in lower combustion chamber temps as well.

I thought maybe dropping to 45:1 or 50:1 may help with that in the colder temps. Carry a spare set of plugs just in case, and once we start seeing warm temps he can go back to 40:1 if he really wants.

What do you guys think?

Keep in mind that higher octane doesn't burn hotter. Octane is how hard the fuel to ignite. Generally the higher octane means lower the combustion temp for the same quantity of fuel, which is why you shouldn't run higher octane fuel in a vehicle rated for low octane.

[EuropeanAM]

I wouldn't alter the fuel/oil mix based on what's been stated. I would, however, be checking to see if the fouled plugs with milky substance happened to be on adjacent cylinders (which would make me suspect a cooling system break, head gasket, or even a cylinder wall/sleeve that's cracked).

[DieselDood]

I wouldn't alter the fuel/oil mix based on what's been stated. I would, however, be checking to see if the fouled plugs with milky substance happened to be on adjacent cylinders (which would make me suspect a cooling system break, head gasket, or even a cylinder wall/sleeve that's cracked).

We were wondering about possible water intrusion, but it was all 6 plugs, pretty evenly across all cylinders.
Compression test was even across all 6. He doesn't have a leak down tester, so we were unable to try that.

[lpugh]

be sure there are no under cowl water leaks, look for white stains, even a small drip can become quite serious at speed with more water pressure.

[DieselDood]

Well... The world may never know.

He was out over the weekend with it. Running about 5200rpm cruising and #6 went down. Looking at all holes, he should have gone up at least one jet size maybe 2. He did a rebuild with .030 over last season, over the winter he shaved the heads. Apparently between those and the cold water and air (it's still pretty chilly here in MN) it went lean.

So.. he already found a new block but was told it needs a crank. So, thankfully he's pretty sure his crank is still good. We are going to make one good motor out of the 2.

It's a fishing rig, so I'm going to try and talk some sense into him that fast is fun, but reliable is better. Maybe we can do this build as just a stone cold reliable one and he can pick up another boat/motor to play with down the road. LOL

[JOE54]

what do the other 5 cyls look like (rich/lean ), got any pics of head chambers / piston tops

[DieselDood]

what do the other 5 cyls look like (rich/lean ), got any pics of head chambers / piston tops

Got a look at it last night. All 6 were starting to melt, 6 being the hottest was the first to go.
Next time I stop by I'll try to grab some pics. Last night it was a flash light in the dark.

Downside, the "new" to him motor had the plastic cage bearing fail and what we thought would be a quick easy rebuild appears to need a sleeve in that cylinder because they must have kept running it. It looks like chunks of the rollers made it to the cylinder and we think there is a hairline crack in that sleeve. Add in some pretty good damage to the piston and sleeve and it looks like that one won't clean up with a .030 and will need a sleeve anyway.

So... looks like he's gonna sleeve one cylinder on that block. Then taking time, he's going to put all new sleeves in the other block and build up a mean 2.5. That way he can still "play" but if it goes down he has a stock, solid powerhead to throw back on it.