Interesting Larry Rengar info

nitroairplane wrote:If running lean it was running hotter and then the hotter head would come into its own or he's turning tee dee rpm.

Ok, but, it wasn't a hop up guide it was an engine care guide that happened to touch on some performance "Dont's"

Unless you were referring to Rusty's engine......

Yes I was referring to Rusty's engine, sorry for the confusion.

So you are saying on a lower RPM engine like say, a babe bee, popping a 1702 head on it will hurt performance like Larry mentioned?

Good info to know, especially for us less seasoned folks.

I think he's referring to the single port cylinder.

Mark Boesen wrote:I think he's referring to the single port cylinder.

Well, he did say all but QZ,throttled and TD. So I would assume that would mean all engines besides those ones. Which would include dual port etc. Not being argumentitive mind you

Plus if you know otherwise please share. I started this thread to learn something and pass on knowledge. Has anyone popped a TD head on a run of the mill reedie .049 and saw an RPM increase/decrease? Tach?

For high rpm's you need a higher compression ratio, ask anyone who runs diesel engines. Glow engines work the same, there is an ideal compression ratio for a given rpm but the head shape is also important. A squish band will enable a higher compression, and the high compression cox heads has something that looks a little like a squish band. The level of nitro in the fuel also affect the ideal compression setting, you'll need a lower compression with more nitro.

Long story short, on the TD 05RC with 10% nitro fuel and a 6x3 prop, the ideal compression is somewhere between the low and high compression heads. I.e. you can use the low compression head with a thin or no washer, or the high compression head with extra head shims.

I believe Rusty had lots of other problems with his engine, he meantions running at 4-5 turns out on the needle?
It is quite easy though to test all this if you have a good tach. Pick your favourite fuel and prop, then increase compression till you see a drop, then and go back one step (on the compression that is) for safety...

Another note on compression and pre-ignition. A leaner needle setting works in the same direction as a higher compression setting, i.e. moving the ignition to happen earlier. So when/if you overcompress an engine you'll not be able to lean it out properly, as it will then sag due to the too early ignition, and you'll end up chasing a stable needle setting.

Not sure if that was Rusty's problem or not though, it just leaves plenty of room for that tinkering we all love and will ever get from electric stuff...

cribbs74 wrote:

Mark Boesen wrote:I think he's referring to the single port cylinder.

Well, he did say all but QZ,throttled and TD. So I would assume that would mean all engines besides those ones. Which would include dual port etc. Not being argumentitive mind you

Yep, thats a better clarification. I think it’s safe to say any performance increase (if any, and possibly less) by the addition of a 1702 head to a single port engine would not be as significant as it would be a dual port cylinder.

I had a bad backplate after the first rebuild causing it to not needle. I documented in my thread that after I changed it to a new backplate it ran fine after that fix. I have to crank it cold at 4 turns, but warm, it cranks every time at 3 and peaks at about 2.75 turns. Still does, I've run it every day since I last posted in the rebuild thread and it's consistent. But, I am not using a 1702, never did. I used Bernie's 5 fin head clamp with 3 and 4 washers. It runs fine with 3 so I left it that way. It's more compression than stock, but I don't have a comparison to a 1702.

Hi Rusty
I was wondering if you saw Hal Howards paper on Cox hop ups in Marks website?
There is a lot to chew on there. Ive got it in PDF format but cant post it here.
Enjoyed watching you work your BW thanks for the posts.

I have been using a 1702 head on my black widows for years, they always seem to preform well although no black widow ever came with a 1702 head (there must be a reason behind that...). For my Babe Bees, I have always used a 325 head but I have tried a high compression head that really didn't seem to affect it.

crankbndr wrote:Hi Rusty
I was wondering if you saw Hal Howards paper on Cox hop ups in Marks website?
There is a lot to chew on there. Ive got it in PDF format but cant post it here.
Enjoyed watching you work your BW thanks for the posts.

No I don't think I've read that one. I'll look for it over there. I still have not gotten the hang of picking through the topic listings on that site.

I have a tach now. I'm rigging up a strong flashlight to shine through the prop so I can use it indoors. I never expected incandescent lights to be able to cool and reheat fast enough to affect the tach like florescents do. But they do. I have to run it with most of the lights off and point the tach at the flashlight. I'll get a speed reading on it tomorrow afternoon. It runs pretty freakin fast, everywhere except in that lame video I did last Sunday. That was my fault for over tinkering before I went out to fly.

RknRusty wrote:

crankbndr wrote:Hi Rusty
I was wondering if you saw Hal Howards paper on Cox hop ups in Marks website?
There is a lot to chew on there. Ive got it in PDF format but cant post it here.
Enjoyed watching you work your BW thanks for the posts.

No I don't think I've read that one. I'll look for it over there. I still have not gotten the hang of picking through the topic listings on that site.

Hi Rusty,

It will take a couple beers to get thru the 'PHOTOS', they're in alphabetic order, starting with plastic RTF's, then the 'ENGINE' section, then MEMBERS and Misc. The 'FILE' section has the articles and info and 'LINKS' just a bunch of cool sites. As far as researching posts, about all you can do is use the search feature for words.

Found it. I'll start reading it now.