I will be running 30% O'Donnells in both my boats this summer. My Supervee 27 will have a Go .18, and my Miss Vegas will have an OS 18TZ. Both engines are not modded at all. I'm trying to decide on plugs for both these motors. I am looking at the McCoy, O'donnell, and OS lines.

Based on my nitro content I am leaning towards the:

McCoy MC-59, OS A8, or Odonnell Purple for the Go .18

OS P-6 or Odonnell 77T for the OS 18TZ

Any thoughts/recomendations would be helpful.

I run 35% and use McCoy 9's with no problem.

Dan.

I'm no expert .... I use McCoy 59 & 9's on 65% nitro. Its cold up here (so no testing), but I've read that plug selection is one of the factors is getting an engine to run at good operating temps for a boat (@200 degrees). So run whatever you plugs have, and (if you can) then measure the head temp's after running. If it is running cold - go to a hotter plug - if its hot, go to a colder plug. Am I wrong in thinking this? (BTW Rod G restricted my head's water outlets on my .21 & .12 motors last summer but I havent measured the engine temps yet). Curious about this....

normally,

the lower the nitro%, the hotter the plug.
higher the nitro%, the colder the plug.

if your running too cold, too much cooling or too much oil (needle is too rich).
if your running too hot, not enough cooling or needle set too lean.

I do the same thing on my engines, it is better to restrict water a bit than to go too lean on the needle.

I don't have one boat engine running above 165, only my buggy engine runs at 220.

Dan.

Thanks Dan!

I decided to call Rod on this (havent had the chance to pick his brain on engines much). He tossed out 160-200 degrees as a rough rule, but said their are ALOT of factors that will determine optimum temps - % nitro, outside air temp, the plug your running etc. He did say I should start with McCoy 9's for my Novarossi's and if I want a hotter plug to try McCoy 59's or McCoy 8's. He said 1) it really comes down to reading your plugs; and 2) that "while most people can get their boat up on pipe and "x" temperature, but they aren't getting it hot enough to really take advantage of combustion and make power". The implication is that hotter is better (until you get to the point that the engine starts going through plugs).

He also mentioned that car/buggy engines have to much cooling for boats 'cause they're designed to run in an enclosed space (and in the hot sun) to ever get up to the temps that will make a boat really scream (and unless you do somthing to address this). Thought I'd share this info for everyone.

yup,

I run my Novarossi .21 LS on 35% with the Mc-9, water flow slightly restricted.
GPS speed has been consistent between 52 and 54.9 mph.

I tried the Mc-59 and Mc-8 and could barely last one race.

Dan.

Some interesting stuff that your rarely hear about plugs, and other stuff.

(1) compare a MC-59 and the MC-8 or MC-9. Look at the difference in the size of the "hole" where the plug element resides. The MC-59 hole is enormous,, the K&B1L is the same heat range as the 59 but will not change your button volume.

(2) compare a O.S.8 to any of the above and look at the length difference of the threaded portion, the O.S.8 is shorter.

The "flash point" of methanol is nearly twice as low as nitromethane, Methanol is 61*F and Nitromethane is 110*F.

Higher combustion chamber volume has a "cooling effect", where lower volume goes in the heating direction of the same engine.

Different plug heat ranges are like your ignition timing in these glowplug engines.

Combustion chamber volumes can affect timing also considering air temp and moisture content

The right glow plug can increase your RPM's by as much as 2000rpm.

[link=http://members.lycos.nl/helisonly/GlowplugHowTo.PDF]HERE[/link] is a comprehensive "how to" article on glow plugs.

Thanks for all the good info. I'm going to reed through that guide you posted Jetpack.

I think what I will do, instead of buying a bunch of one plug, is buy several different temps/brands to see what works best.

This is all good info. Gives me a real good starting point.