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Discussion Starter #1
Just swapped out my 600 cfm Holley for a Summit 500 cfm carb and the engine seems much peppier. I bought a vacuum gauge and an adjustable timing light. I want to fine tune things and also learn a little bit about the process. I've done some reading and watched a ton of videos on how to do it and I get the jist of it, but just to be sure:

After I bring the engine up to temp, unhook the vacuum dizzy and plug the hose. Hook vacuum gauge up to full manifold vacuum. With a timing light, advance the timing until I get the highest vacuum. When the vacuum starts to drop, I've read go back to max PSI and drop by 1 PSI. Also read go back to max PSI and drop timing by 1 degree. Which is correct? Does it matter?

Once I do that, adjust the A/F screws to max vacuum. I've read slight equal turns to both screws at the same time. Ive also read to just adjust one side at a time than do the other.

When I advance the timing, I should expect my rpm's to increase as long as the vacuum is increasing, correct?

Currently my timing is set to 12' BTDC with 15 mm of vacuum. I put my timing light onto it yesterday and it seemed that if I advnaced it more my RPMS and vacuum went up but I didn't want to advance it too much and I got worried so I put it back to 12'.
 

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All above process is good but its a starting point. Go drive it with fresh gas and make changes, dont know your motor but 15 deg is not crazy, Your motor will ping if advanced to far so take a wrench to back it off. After you get initial timing good you can work on vacuum advance and mechanical.
 

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It's good to know, what how much mechanical advance you have in that distributor. Also, is your Vac canister adjustable. sorry, if I missed this in a previous post. It appears you have the right process there. It's always advisable when tuning to make slight adjustments, wait for the engine to respond, then proceed.
Is your cam preventing no better than "15 mm of Vacuum". Otherwise, could be a couple points higher for better response? Always, always, document your adjustments, before you begin and after. You need a baseline to establish a track record of the outcome of each series of adjustments. experiment with a couple more degrees, if the Rs go up, that's not a bad thing, as you can dial it back via the throttle idle screw. Typically, depending on the cam events, if your CR is 10.0 (example), your actual under operation will be lower, so, any worry of "pinging" may not occur. If you worry about this. It's all "test and tune", but document it.
 

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Discussion Starter #5
We did the initial install with the Holley carb and the engine seemed to like 12'. I'll get all the baseline numbers, initial, mechanical and vacuum advance and get back. Wasn't very impressed with my new engine, T5, and 3.55 gears. With the smaller CFM carb, it's much better but I know there is more there.

But to start, I can add more timing until vacuum drops, correct?

@awhtx , I had a brain fart.

@kenash , I had my dizzy refurbished from Dan.
 

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I have never heard of setting the timing with a vacuum gauge. You set the initial timing so that the engine doesn't ping under hard acceleration at maximum advance which is initial + centrifugal. There is no vacuum advance when the engine is at WOT. Most SBFs like somewhere around 36* total timing. You can advance the timing until the engine pings and then back it off a couple of degrees.
The vacuum gauge is used to set the idle mixture. Turn the screws in or out until you reach maximum vacuum and then turn them out (rich) about 1/4 of a turn.
The spark plug color or AFR gauge is used to adjust jet size to set the mixture at full power.
 

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Discussion Starter #7
So here are some numbers, tell me if I did this correctly:

Engine warm-vacuum line to dizzy unplugged and capped. Initial timing 12'. Revved the engine up till the timing stabilized and dialed back using my timing light and got mechanical 13'. Then at idle put a vacuum pump on the dizzy and pulled vacuum until the unit advanced completely and got an additional 14' from initial.

From here I should get engine up to temp, unplug dizzy, rev the engine up to 2500 RPM's, and advnace the timing until I hear pinging, then back off a few degrees?
 

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25* total advance is not enough. You should be getting 25* just from the centrifugal advance. 12* initial + 25* centrifugal = 37* total.
And the engine must be under a load for pinging to occur. Revving it up with no load won't work.
 

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Discussion Starter #9
25* total advance is not enough. You should be getting 25* just from the centrifugal advance. 12* initial + 25* centrifugal = 37* total.
And the engine must be under a load for pinging to occur. Revving it up with no load won't work.
Got it. I’ll check it again. What rpm should the mech advance be full advanced? 2500?
 

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We did the initial install with the Holley carb and the engine seemed to like 12'. I'll get all the baseline numbers, initial, mechanical and vacuum advance and get back. Wasn't very impressed with my new engine, T5, and 3.55 gears. With the smaller CFM carb, it's much better but I know there is more there.

But to start, I can add more timing until vacuum drops, correct?

@awhtx , I had a brain fart.

@kenash , I had my dizzy refurbished from Dan.
You say you had "Dan" refurbish your distributor? What specs did he recommend? He would have provided all of the specs for your distributor. That is, suggested initial, built in mechanical, and the VAC canister.
 

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Discussion Starter #12 (Edited)
Just spoke with Dan. He set it for his Boss 302 specs, a total of 38-40', 10-12 initial, 5-6 vacuum, and the rest mechanical.

Really nice guy, gave me a little tutorial on testing timing and why you do things certain way. Glad I took everyone's advise and sent out my distributor to him.

Also, what does spark knock sound like?
 

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Just spoke with Dan. He set it for his Boss 302 specs, a total of 38-40', 10-12 initial, 5-6 vacuum, and the rest mechanical.

Really nice guy, gave me a little tutorial on testing timing and why you do things certain way. Glad I took everyone's advise and sent out my distributor to him.

Also, what does spark knock sound like?
FYI, pretty much the same for mine. I've the car out twice, just before this "fertilizer hit the ventilator" and the engine responded well. This was in January. Haven't done any further testing since. Yeah, he's a "good guy"!
 

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Discussion Starter #14
Just got a wrench throw into the plans. Called my engine builder and told him about the 10 psi pressure at idle when warm and he said something is wrong. He said it should be in the 40's and wants the engine back so he can take it apart. So.....out it comes and off it goes.
 

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Just got a wrench throw into the plans. Called my engine builder and told him about the 10 psi pressure at idle when warm and he said something is wrong. He said it should be in the 40's and wants the engine back so he can take it apart. So.....out it comes and off it goes.
Hope his labor and parts are "on him"? Really, should give you a refund, of sorts too.
 

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Discussion Starter #16
Hope his labor and parts are "on him"? Really, should give you a refund, of sorts too.
He said its all under warrenty. All on his dime. He's gonna rip it apart, look at everything, and rebuild it.
 

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Just got a wrench throw into the plans. Called my engine builder and told him about the 10 psi pressure at idle when warm and he said something is wrong. He said it should be in the 40's and wants the engine back so he can take it apart. So.....out it comes and off it goes.
10 psi oil pressure?
Assume oil level is correct, known good oil pump? Accurate gauge etc?

Sent from my SM-G950F using Tapatalk
 

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Discussion Starter #18
10 psi oil pressure?
Assume oil level is correct, known good oil pump? Accurate gauge etc?

Sent from my SM-G950F using Tapatalk
Oil level is correct. Brand new mechanical gauge. New Melling HV oil pump. Builder wants it back.?
 
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