Hi folks,

Great day here allowed me time to play with tuning on my newly redone engine (no longer a fuelie!). i have been digesting all the recurve thinking here and broke down an bought a good inductive lead timing light that has one of the knobs on the back that let you match light to total advance.

This engine has never been on the road and has only run for maybe 45 minutes total to set valve lash and look for leaks, break in camshaft and so on. After reading the thread the other day about wrenches for the bolt under the distributor, I decided to play with various under- and hold down bolt combos. Without going on a road test (still no brakes) I have to ask if slant sixes are this forgiving..

Idle set to spec at 750 rpm, 19.5 inches of vac, advance hose attached to carb; and total advance of 54 degrees at 2000 rpm 19 inches vac. At 450 rpm vac is 20 inches.

Yet I was able to have this engine run what seemed equally well at 32 degrees total advance at 2000 rpm and idle at 450 with this distributor setting also.

I realize that 54 is pretty early, but are slants so forgiving that they will run on the road equally well between 32 and 54 degrees total advance?

Nice smooth idle, no hesitation on accelerationi, return to idle with no problems....(edelbrock 500 cfm performer on offy 4bb intake)

Thanks and happy 4th!
rock
'64d100

I ran 32* total on my slant. I had a Holley 390 w/ an Offy. Seemed to be a good setting.

That's just a little much, but not impossible.

The factor that you are missing here is engine load. You can run lots of advance if the engine is just spinning freely.

For 'on road' driving, you will be safe somewhere around 30* of total mechanical advance, but maybe not quite so early. You'll have to drive up a few hills with the vacuum advance not connected to be sure you don't knock under load. That would mean the light mechanical advance spring is too light and allows the advance too soon in most cases

Next,
Additional vacuum advance at light throttle will help with fuel economy but it will need to be adjusted so that the vacuum advance 'falls out' during heavy throttle for hill climbing or other hard driving.

Good luck, it takes time and practice to get a good balance.

You forgot to mention what your initial timing setting was.

_________________
1980 Aspen 225 super six

I set my stock slant at 32 degrees. Sounds like you have the dreaded 15R governer! You'll need to play around with your distributer (changing or welding the slots in the governer and play with the wight springs) to get the curve you want for your engine. Vacuum cans have different values also, so its something you want to look for.

Thanks slant6, eric and andy!

I "fell" into ivory tower thinking....the kind of engineering thinking that nver got the machine on the road or in the hands of a mechanic...I was thinking in the abstract and FORGOT all about LOAD...can you hear me kicking myself?!!

THe three answers did better than answer me, together they helped me learn some more, just like those great recent threads about recurving where I believe it was emstivil shared his graphs. I had been afraid I had a 15R. I bought a used Pertronix equipped distributor that I just popped in and didn't want to remove the apparatus to look at the plate til I got running good...now I will have to look "into" it. That dist. also has an adjustable vacuum can, so the threads here have been REALLY useful, as is your advice.

Again, many thanks, guys. Oh, I started with initial timing of 12* BTDC to get to 32 and 54.
rock
'64d100

Just set it back to 10BTDC, for safety (that's the MP distributor's curve 10 BTDC...30total, 50 with vacc. adv.), get it run on the road and set the vacc. can and springs according to load and ping. Riding with a tach and vacc. gauge attached will help you see where things need polishing at, also using a dial back timing light and vacc. gauge to "plot" the curve of your distributor for a "baseline" also helps to see what it's going to do.

-D.Idiot