A few more tuning questions?

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Omie01

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Ok, I got to the point where my engine fires up good and seems to run well, but have a few questions. First off I notice the valve train is fairly noisy when cold, as it warmed up it did get quieter, I'm guessing this is normal for a full roller valve train? I did listen to it with my stethoscope and their are no "oh my god" noises jumping out at me, just the typical whirring/ticking sounds. Next, my idle still wants to be around 1000 rpm, 8-900 in gear. And my vacuum still wants to stay just under 15" of vacuum, around 13ish. Is this normal vacuum for a higher lift cam? I did spray some starting fluid around the intake ports and such and the motor did not suck it in so I don't think I have a vacuum leak. This is the first engine of this performance level I have ever built and I'm just not familiar enough with them to know what proper tune would be! I'm not saying anything is really wrong, I just want to know if some of these things are "normal"?

 

TommyK

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What is the duration @.050" of your cam?

What is your initial timing?

What is your static compression ratio?

What carb?

What intake?

 

red351

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A little Valve train noise that's gone after warm up nothing to worry over. A lot of people over look low vacuum as always the cam fault. Not all PCV valves are the same. Fram # 156 or 181 are the better working valves when running a mild cam. If you have a vac gauge try changing PCV. The 156 seems to work best for me . I always buy 2 or 3 of the same number even since they are same number one always seems to work better. Our 67 with the clever and AOD would stall most of the time when put into gear. Always had to mess with gas pedal to keep running. In park it needed to idle 1500 rpm to make it road friendly. Now it idles in gear at 6 to 700 and out gear under a 1000 rpm using .536/562 lift flat tappet cam. Vac. stays around 14 to 15 in. I could turn the idle down more but the wife happy with it now. No more chugging after turning key off and locking the doors...

 

Qcode351mach

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Your not going to get full vacuum on a new motor that hasn't broken in seated the rings-Check back after you put a few thousand miles on it

 

Omie01

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Adv. Dur. In 272 Ex. 280, @.050 In 221 Ex 229, Gross lift In. .594 Ex .611 LSA 112 In. CL 106, Compression around 10.5, Stock dizzy re-curved w/ Pertronix 2, spiral core wires, AP25 plugs, Pro Systems Carb 780XP body w/Venom 2 metering blocks. Air gap intake, Hooker headers. One more question: When I set my lifter preload, I did it with engine cold and turned the engine by hand, I noticed that some of the lifters did not offer much resistance during preload, but a couple did. I did allow 2 minutes for bleed down for each lifter. Is this normal or should I redo my lifter preloads?


I was also thinking to plug off all vacuum accessories and run motor again to see if that changes anything. I have been setting initial @6-8 degrees and it seems to like that.

 
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You could adjust your timing by putting a vacuum gauge on the engine, turn the distributor until you get maximum vacuum, readjust your idle, again adjust the distributor for maximum vacuum, then back it off about 1-2 degrees and see where you end up at. You could probably go as far as 14-16 degrees with your initial timing. I also like to verify timing at 3000 rpm as not exceeding 36 degrees with the vacuum advance disconnected with a 4V closed Chamber head or 38 with OC heads

If you did not soak your lifters in oil for 24 hours before installation, then it is not unusual for some to be "dry" inside initially. It should resolve itself on your first drive though.

Barnett will be along to disagree with me shortly :D

13-15" of vacuum is about right. If you have power brakes you'll probably need a vacuum canister, make sure it has a proper check valve.

 

TommyK

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^^Agree with the above^^

That came will want more than 6-8 degrees I believe and that should pick up the vacuum reading slightly.

Also agree with Scott that the engine needs to be broken in before the tuning can be finalized.

 

barnett468

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exactly what lifters do you have?

exactly what spark plugs do you have?

do you have vacuum advance?

if so is it connected to manifold or ported/timed vacuum?

how much advance does it add?

what oil are you using?

the preload should always be set by starting at zero whether the lifter offers a little or a lot of resistance . i sometimes have people use a feeler gauge then set it to .002" then remove the gauge and turn the nut in around 1/2 to 3/4 turn depending on the pitch of their threads . this helps prevent them from over tightening the nut.

with the engine idling, plug the pcv . if the rpm drops by around 100 rpm or more, i would buy an adjustable one.

after that test, plug the pcv until it is properly tuned just to eliminate a variable and possible source of a prob.

plugging the other vacuum sources sure won't hurt and if the rpm drops after you plug one, it has a leak.

unfortunately, just because a distributor has been ecurved, it doesn't mean it has the ideal setting for your engine, and more performance can sometimes be done by testing the timing curve yourself.

remove the front spark plug from each bank and post a photo of it.

 

barnett468

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do you have vacuum at the ported/timed vacuum port at idle?

do you have a heat insulator under the carb?

unless you are drag racing it, the first thing i would do is set the gas level in the carb so it is just below the inspection holes or near the bottom of the clear site windows immediately after you turn the engine off . having it much higher than this can sometimes cause hard starts when it is hot.

for a quick test for idle timing only, you can plug the vacuum advance then warm the engine up and let it idle as low as possible, then advance the timing 4 degrees and listen to the rpm or watch it on a tach . if it goes, up noticeably and still runs smoothly, it prefers that timing setting.

if it went up, reset the idle speed then advance it 2 more degrees, if you get the same results, it prefers that timing setting although the increase in rpm should be less.

if the engine turns over more slowly at any time, you can reduce the timing slightly until it turns over normally or get a timing delay unit . some people choose to connect the dist vacuum to manifold vacuum instead which can work if the vacuum can is properly set but i prefer the other methods.


i just saw jeffs post . using a vacuum gauge for idle timing also works . the more tools the better.

 
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Don C

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The important thing that needs to be realized when making any modifications to an engine is that the standard idle and timing specs most likely will no longer work. Even a different intake or adding headers will change things. Changing cams and compression will make even bigger changes.

What now works for a similar engine will likely not work for yours. For those of us that have been around this stuff for a while it has become second nature to adjust, readjust, and adjust again until we find that sweet spot for that particular engine combination of parts, not to mention transmission type and rear end gearing. Don't count on finding the ideal settings the first time, or maybe even the tenth time. After you drive it you'll want to improve the way it runs off the line, or at a certain cruising speed, or driving down the street. There will be compromises, the more modified the engine is, the more you will have to compromise.

Bottom line, get used to making changes :)

 
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Omie01

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Thanks Guys!! Sounds like I have a lot of stuff to try!!! Will keep you posted!!

 

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The method I use for adjusting hydraulic lifters is simple. The lifter has to be on the base circle of that particular lobe. 1 full rotation of the crank after max lift on that particular lobe is a sure way to be on the base circle. With the rocker slightly loose, spin the push rod between two fingers. Slowly tighten the adjusting nut until you feel a slight change in the feel of the pushrod spinning. That's the zero lash position. Try it a few times to get a good feeling for it. After you've established zero lash, turn the nut the appropriate amount to achieve the specified preload and tighten the lock screw. As barnett said, the # of turns on the adjuster will be based on the thread pitch of your rocker studs. You should have 7/16-20 threads, so each turn will give .050" of preload. Typical is .020-.030, which would be 1/2 turn, but your lifter paperwork should specify.

 

Qcode351mach

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The important thing that needs to be realized when making any modifications to an engine is that the standard idle and timing specs most likely will no longer work. Even a different intake or adding headers will change things. Changing cams and compression will make even bigger changes.

What now works for a similar engine will likely not work for yours. For those of us that have been around this stuff for a while it has become second nature to adjust, readjust, and adjust again until we find that sweet spot for that particular engine combination of parts, not to mention transmission type and rear end gearing. Don't count on finding the ideal settings the first time, or maybe even the tenth time. After you drive it you'll want to improve the way it runs off the line, or at a certain cruising speed, or driving down the street. There will be compromises, the more modified the engine is, the more you will have to compromise.

Bottom line, get used to making changes :)
So, so, true ! :goodpost:

 
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