[HWYSTR455]

Scope creep. You should really start a new thread for tuning, think the oil psi thing has been resolved.

As for manifold vs ported, you are going to get a lot of opinions there, but my personal experience has always to run full time/manifold. The exception is when you have a radical cam, and make little vacuum at idle. Just to say though, manifold/full time does help idle temps.

There is some true about the adjustable vacuum cans, since the adjustment isn't linear, like, a 1/2 turn may give you X, but the next half turn can give you XXX. You can still get reasonable results with them though, and they seem to work well for me.

Surge at 3k RPM would have nothing to do with where your vacuum can is hooked by the way.

This statement confuses me: 'So I have initial set to 12* and added 24* with the adjustable unit using MVA.' . A vacuum can isn't adjustable for the amount of advance it adds, that is a static value, and the adjustment is when it starts opening, like at a particular amount of vacuum. In order to limit the amount of timing it adds, you have to have a limiter. The crane units come with a cam that can be adjusted to control the amount of timing the can adds. Is that installed?

Remember, the can is just a diaphragm with a spring, and the adjustment controls the tension on that spring.

Just to say, the adjustable can has a range of 9.5 turns out (CCW) from the bottoming point (CW), and if you exceed the 9.5 turns, the adjustment screw pops out, and it's a biotch to get it started again. Most of the time it falls out, and you need to buy a new can. So turn it all the way in (CW), and if it doesn't bottom, it's fallen out, and it's junk and needs to be replaced.

Best way to test what the total amount of advance a can adds, hook up a vacuum pump with a timing light hooked up and suck the can down, watching the timing mark. That will tell you total advance a can adds.

Vacuum is the last adjustment you make when doing a timing curve. Initial, total, and rate are the 3 items you adjust before you even hook the can up, and generally in that order. Initial is obvious how you adjust that, total is by limiting travel or by the center cam and weights, rate is by the springs.

Plot your curve. Use a piece of graph paper, on the left do degrees, on the bottom, do RPM, and go in 500 RPM increments. With a dial back light, step the RPM in 500 increments, and write down the advance, all the way up to 4500 RPM or so. That's your baseline. That should be done with the vacuum can disconnected. All adjustments should be made to initial, mechanical, and springs with the can disconnected.

Oil weight depends greatly on engine clearances, wider clearances require heavier oil, and the general indication is seen by oil psi. If you're getting 15-20 at idle hot with 20-50, then run 20-50. You don't really want anything lower than that.

.

[AdamIsAdam]

Originally Posted by HWYSTR455

Scope creep.

I had to look that one up!

You should really start a new thread for tuning, think the oil psi thing has been resolved.

Will do. I know it will open up a can of worms, so I'll get my facts straight and work out a few things before I do this.

Surge at 3k RPM would have nothing to do with where your vacuum can is hooked by the way.

What causes surge at 3k cruising? I can get it to almost go away by just backing out the adjusting screw on the crane vacuum unit.

This statement confuses me: 'So I have initial set to 12* and added 24* with the adjustable unit using MVA.' . A vacuum can isn't adjustable for the amount of advance it adds, that is a static value, and the adjustment is when it starts opening, like at a particular amount of vacuum. In order to limit the amount of timing it adds, you have to have a limiter. The crane units come with a cam that can be adjusted to control the amount of timing the can adds. Is that installed?

Yes, I have the notch plate/adjustment cam. I used that to get the timing from 12* to 36* at idle since 36* is my car's sweet spot. then I was using the adjustment spring to fine tune that. I guess what I'm doing is fine tuning how much vacuum advance is coming in at idle and part throttle because as I turn it, I brought the initial timing (with vacuum advance connected) from 36* all the way down to 20* in order to get rid of the bad surge and also the slight part throttle ping. However, the engine really runs best and is most responsive at 36* at idle with MVA connected. Only down side is that surge.

Just to say, the adjustable can has a range of 9.5 turns out (CCW) from the bottoming point (CW), and if you exceed the 9.5 turns, the adjustment screw pops out, and it's a biotch to get it started again. Most of the time it falls out, and you need to buy a new can. So turn it all the way in (CW), and if it doesn't bottom, it's fallen out, and it's junk and needs to be replaced.

I think I've turned it more than 9.5 turns CCW already I'll close it (CW) and start again. I've read that about the screw coming out.

Best way to test what the total amount of advance a can adds, hook up a vacuum pump with a timing light hooked up and suck the can down, watching the timing mark. That will tell you total advance a can adds.

I don't have a vacuum pump. But I know that the notch plate/cam on the Crane gives 2* for every notch. It seems pretty straightforward and easy to get my initial timing connected to 36* at idle.

Vacuum is the last adjustment you make when doing a timing curve. Initial, total, and rate are the 3 items you adjust before you even hook the can up, and generally in that order. Initial is obvious how you adjust that, total is by limiting travel or by the center cam and weights, rate is by the springs.

My timing curve has been checked by Richie as being good. It's 12* initial, 32* total at 2,800 RPM and about 20* at 1,800.

[nytrainer]

Maybe I'm reading this wrong Adam but it seems you are calculating/adjusting total timing using vacuum advance? Initial and mechanical advance combined (with no vacuum advance factored in at all) will give you your total advance (for ex. 34* total with 12*initial & 22*mechanical). Springs will dictate how soon/fast in the rpm range the mechanical advance comes in (you should be OK as Richie said curve was good). The vacuum canister will further advance the timing at cruise with high vacuum signal or idle when connected to MVA as you have. This will help with engine cooling at idle and cruise (benefit to oil pressure too). The need for the adjustable vacuum canister is to compensate for your cam's profile that gives you a lower max. vacuum than stock type cams. Your lower max vacuum signal may not be high enough to actuate a stock vacuum canister.
Maybe you do have a handle on this concept and I read it wrong but just trying to help.

[AdamIsAdam]

Originally Posted by nytrainer

Maybe I'm reading this wrong Adam but it seems you are calculating/adjusting total timing using vacuum advance? Initial and mechanical advance combined (with no vacuum advance factored in at all) will give you your total advance (for ex. 34* total with 12*initial & 22*mechanical). Springs will dictate how soon/fast in the rpm range the mechanical advance comes in (you should be OK as Richie said curve was good). The vacuum canister will further advance the timing at cruise with high vacuum signal or idle when connected to MVA as you have. This will help with engine cooling at idle and cruise (benefit to oil pressure too). The need for the adjustable vacuum canister is to compensate for your cam's profile that gives you a lower max. vacuum than stock type cams. Your lower max vacuum signal may not be high enough to actuate a stock vacuum canister.
Maybe you do have a handle on this concept and I read it wrong but just trying to help.

Maybe I wrote it wrong, but I do understand that the vacuum advance doesn't come into the total advance formula. These figures were all taken with the vacuum advance disconnected: 12* initial, 32* total at 2,800 RPM and about 20* at 1,800.

When I said that it idles at 12* initial, then I got it up to 36* by connecting the Crane advance, that was all at idle. The car likes to idle at 36*. That means that part throttle cruising maybe be as much as 58* or so. They say 54-56* is ideal for efficiency on the higway (that's mechanical + vacuum at part throttle like highway cruising at 3,000 PRM.) Maybe 58* is too much and giving me the surge. I'll go back and double check my Crane notch plate limiter and start that process again.

[STEELCITYFIREBIRD]

What is the casting #.

[STEELCITYFIREBIRD]

Check out 1976, same code, I have one that came in my 76. Really not a good candidate for a stroker.

[AdamIsAdam]

Originally Posted by STEELCITYFIREBIRD

What is the casting #.

Now you have me nervous. what year is it?

[STEELCITYFIREBIRD]

http://www.wallaceracing.com/enginesearch4.htm

Scroll down.

[jonmachota78]

Originally Posted by HWYSTR455

Scope creep. You should really start a new thread for tuning, think the oil psi thing has been resolved.

As for manifold vs ported, you are going to get a lot of opinions there, but my personal experience has always to run full time/manifold. The exception is when you have a radical cam, and make little vacuum at idle. Just to say though, manifold/full time does help idle temps.

There is some true about the adjustable vacuum cans, since the adjustment isn't linear, like, a 1/2 turn may give you X, but the next half turn can give you XXX. You can still get reasonable results with them though, and they seem to work well for me.

Surge at 3k RPM would have nothing to do with where your vacuum can is hooked by the way.

This statement confuses me: 'So I have initial set to 12* and added 24* with the adjustable unit using MVA.' . A vacuum can isn't adjustable for thehwysta of advance it adds, that is a static value, and the adjustment is when it starts opening, like at a particular amount of vacuum. In order to limit the amount of timing it adds, you have to have a limiter. The crane units come with a cam that can be adjusted to control the amount of timing the can adds. Is that installed?

Remember, the can is just a diaphragm with a spring, and the adjustment controls the tension on that spring.

Just to say, the adjustable can has a range of 9.5 turns out (CCW) from the bottoming point (CW), and if you exceed the 9.5 turns, the adjustment screw pops out, and it's a biotch to get it started again. Most of the time it falls out, and you need to buy a new can. So turn it all the way in (CW), and if it doesn't bottom, it's fallen out, and it's junk and needs to be replaced.

Best way to test what the total amount of advance a can adds, hook up a vacuum pump with a timing light hooked up and suck the can down, watching the timing mark. That will tell you total advance a can adds.

Vacuum is the last adjustment you make when doing a timing curve. Initial, total, and rate are the 3 items you adjust before you even hook the can up, and generally in that order. Initial is obvious how you adjust that, total is by limiting travel or by the center cam and weights, rate is by the springs.

Plot your curve. Use a piece of graph paper, on the left do degrees, on the bottom, do RPM, and go in 500 RPM increments. With a dial back light, step the RPM in 500 increments, and write down the advance, all the way up to 4500 RPM or so. That's your baseline. That should be done with the vacuum can disconnected. All adjustments should be made to initial, mechanical, and springs with the can disconnected.

Oil weight depends greatly on engine clearances, wider clearances require heavier oil, and the general indication is seen by oil psi. If you're getting 15-20 at idle hot with 20-50, then run 20-50. You don't really want anything lower than that.

.

Great write up hwystr. I've always had better luck with manifold vacuum too. The only issue i see is this quote
"Remember, the can is just a diaphragm with a spring, and the adjustment controls the tension on that spring."

I'm sure not all vac advance cans are created equal, I run one and the adjustment controls the amount of advance rather than the rate. For example mine is currently set to limit at 8deg. My initial is at 10 deg so at idle with manifold vac I'm at 18 degrees. I wish I could adjust the rate and make it pull the advance out sooner when the throttle is depressed. This is where suntuned likes the factory cans because he know which ones to use that have the spring rates desirable for performance apps.