I'm watching your thread on Net54, good stuff. Pushed algebra out of my head-no more headache.

Anyway, I've been waiting and wondering about the comment you made about using a vacume gauge to set (initial?) timing. What's the theory behind this? Would it be viable for tuning a "mystery" motor?

Thanks, Mike

 

I have read that the engine will make the most vacuum where it wants the initial timing set. Or, in other words, optimal initial timing will be where the engine makes the most vacuum at the desired idle speed.

In alot of instances, especially with stock, or mildly modified engines, it's probably not essential that it be perfect. After all, we are not concerned with peak performance at idle, as long as it will idle, and not kick back against the starter. We would normally only be concerned with total advance, and when we get it. But on a heavily modified engine, or an engine with a longer duration cam, idle quality can be difficult to attain. Therefore, it would be beneficial to have the initial at it's optimum setting to help nail the idle tuneup.

I will be trying it soon. I am waiting for some power steering hoses and fittings. When I have them installed I will be doing some detail tuning of the 511. Here is my plan: With the engine at operating temp, I will set the idle to 850, which is my desired goal, and then configure the idle mixture. I will then adjust the timing while watching the gauge. When I reach maximum vacuum, I will reset the idle speed and mixture. I will repeat this procedure until I have max vacuum at 850rpm (or 900 if necessary), and the correct idle mixture. Then it's just a matter of reading the timing light to see what it likes, and resetting the bumpstop in the dizzy to give me the total I want, then checking for kickback.

When I do it, I'll post the results.

-Scouder

 

When you finish you should submit a tech article....Its a very handy piece of info you got going on there.

 

Thanks Brian,

That should get me around my latest puzzle. One of my neighbors was swapping carbs on his 302 powered early Bronco, I couldn't resist.

He told me that he had the motor "rebuilt with an RV cam" a few years ago:
"Which cam?"
"I dunno"
"Did you get a build sheet?"
"What's that?"

OOOKAAAY! About 30 min. with a timing light and vacume gauge made it sound like a Ford again. If I get a few daylight hours to nail down his ignition and fuel parameters, it should do much better.

One more question: How much vacume fluctuation is normal with a typical, uh, "RV cam"?

 

RV is kinda like 3/4 race. It doesn't really tell you much.

Unfortunately, I can't be of any help with the vacuum fluctuation. When I put the vacuum gauge on my engine in a few days it will be the first time I've had an engine with a gauge on it.

Glad to hear that this topic helped though.

Interestingly, Egoman, I already have two tech papers started, but this one would be pretty easy to write. The other two are on 360/390,390/428 conversions, and torque v. horsepower. Both seem to be common topics.

-Scouder

 

Yea I love those tech articles....espescially the ones like the one wire alt, and the lorge distributer cap swap. Stuff like that is just fun and good to know.