timing advance how much is to much

[aussie merc]

did a major tune up [valve set, carb rebuild ], etc engine is 239ci with i believe to be stock cam, compression, heads etc fitted with twin97s and fenton headers after setting carbs best vacum that i could obtain was around 16" at idle 700rpm so advanced ignition previously set at pointer i suspect is 4deg btc when rechecked found i had added added another 6 deg {now at a total of 10 deg} starts ok sounds ok its being fed on 91 octane but im worried it may be over advancing as revs rise your thoughts and experience appreciated

[Ol' Ron]

Timing is determined by load, and RPM. To start it should be around 2/4 degs. Idle is around 10. Cruise at 200 Plus is around 26 and under load 20. Thear are only ball park numbers and the stock 8BA, and Early crab come close to tese.

[aussie merc]

dizzy has been replaced with mallory unilite non vacuum [this is how i got it]

[Tinker]

Low vacuum reading could be due to the fact you now have 4 big holes on top of your intake vs 2.

Lot of questions I'd guess from carbs to chokes etc, at this point.

Maybe ignition, But probably A/F. Just a thought. wrong as it is.
.

[Talkwrench]

Carbs should be .043 mains and 69 pvs sea level up to 5000ft.
If the cam is stock you should be able to get it closer to 600 rpm.
Just vacuum time it to best and back off 1" Hg and try it .
listen for detonation and look at your plugs periodically make sure you dont have and silver or black spots on the porcelain.

[Tinker]

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Just to be clear. You don't time a engine with vacuum. Even on a 8ba you disconnect the vacuum advance to get initial timing. Spark to cam/crank. Maybe to fine tune the air movement a little. But I would not go hog wild.

[JWL]

Actually the "vacuum timing" method works pretty well as a solid starting point.

[Ronnieroadster]

You asked how much is to much. Set the initial at 10 degrees and go no higher than 24 for the total when the engine is turning over 2200 RPM. Works perfectly ever time.
Ronnieroadster

[Ol' Ron]

Most engines will run "Alright" when the timing is off and the AF readings alittle rich. Unfortunately, most people accept this if the car does what it's supposed to. I consider myself quite capable of tuning my engines better than that. No so ol great one. I had a problem with the 2GC carb on the 280, so i rebuilt it with a new kit with a set of jets an accelerator pump from Daytona carb. My surprise is, it never ran this good before. I think the problem was, i spent too much time on the ignition advance i neglected the AF. Both are very important. i might addd an engine running rick will wear out the rings quicker. I think tha's what was wrong with the280.

[frnkeore]

I have a question regarding higher output engines but, have no plans to build one.

With A/F ratio of about 13.8, what would be total advance, timing you'd be expecting to run, on a hard pull, with a 3/8 x 3/8 engine with three, 97's on top and a 400 Jr cam?

[Ol' Ron]

Sounds like one of the old stock car/ drag engines. 13.8 is alittle lean for a full power run, but 18/20 would be close. I had a fixed advance of 17 in the stock car, where it ran bett on the track. However, it made more hP around 20 on a chassis dyno. Gota go with what works

[Ronnieroadster]

Originally Posted by frnkeore

I have a question regarding higher output engines but, have no plans to build one.

With A/F ratio of about 13.8, what would be total advance, timing you'd be expecting to run, on a hard pull, with a 3/8 x 3/8 engine with three, 97's on top and a 400 Jr cam?

Read my post #8 it will give you the number your looking for. Set many records with the stated settings. A/F readings in the 13. range on most runs however not the best economy but the racing gas is only $18.00 a gallon so not a big deal.
Ronnieroadster

[frnkeore]

A separate issue but, do you need Av Gas for a flathead or are you talking a blown engine?

[Ronnieroadster]

Originally Posted by frnkeore

A separate issue but, do you need Av Gas for a flathead or are you talking a blown engine?

Years ago I would use 100 NL Av Gas at the drag strip. But now for the longer runs I use racing gas. For my present combination 118 Octane VP brand.
Ronnieroadster

[aussie merc]

not a lover of avgas seen to many problems like bore washing but the i guess to some extent were spoilt here in aus as we can get 98 no ethanol out of the pump at just about any service center

[Tinker]

....

[JSeery]

Originally Posted by aussie merc

...guess to some extent were spoilt here in aus as we can get 98 no ethanol out of the pump at just about any service center

That would be nice!

[JWL]

Timing is NOT a one-size-fits-all number. The mechanic should strive to minimize negative work while maximizing the energy applied to the crank assembly at periods of the highest leverage.

Negative work is any pressure rise in the chamber which occurs before TDC. This is usually resulting from over advanced timing. Any pressure fights against the rise of the piston and reduces power. Therefor we always look for the minimum timing advance which will provide the highest torque value.

In all my test cases the maximum power was achieved when the timing was reduced from maximum torque numbers by 4 degrees for the upper RPM output tests.

During our Bonneville record runs we used 17 degrees total advance, with the racing gasoline, for the high RPM activities.

For better, more thorough explanations, read my book. I do not have a Stenographer for this typing.

[Ronnieroadster]

Originally Posted by JWL

Timing is NOT a one-size-fits-all number. The mechanic should strive to minimize negative work while maximizing the energy applied to the crank assembly at periods of the highest leverage.

Negative work is any pressure rise in the chamber which occurs before TDC. This is usually resulting from over advanced timing. Any pressure fights against the rise of the piston and reduces power. Therefor we always look for the minimum timing advance which will provide the highest torque value.

In all my test cases the maximum power was achieved when the timing was reduced from maximum torque numbers by 4 degrees for the upper RPM output tests.

During our Bonneville record runs we used 17 degrees total advance, with the racing gasoline, for the high RPM activities.

For better, more thorough explanations, read my book. I do not have a Stenographer for this typing.

Wow i must be doing something wrong setting all my very FAST records with the old valve in block Ford engines. Along with my real world thousands of miles running these engines just saying. My numbers quoted work perfectly but heck I should wright a book I guess. The title facts in the 21st century.

[aussie merc]

thanks to all i asked the question and got several answers and as for them 4 big holes thats how i got it a typical buy and bolt[ looks cool who cares how it runs ] also have checked the advance and it brings on way to much way to early [that explains why it was so retarded when i got it ] so next step recurve the dissy and try again while we are here any thoughts on maybe down sizeing carbs to say 81's instead of 97's

[Ol' Ron]

I run 28 in cruise.

[JSeery]

Originally Posted by Ol' Ron

I run 28 in cruise.

Yes, but that's with a vacuum advance/retard distributor isn't it Ron? The vacuum advance/retard capability allows for more total advance in a cruise condition (high vacuum) and pulling it off in an acceleration condition (low vacuum). So, with say 10 degrees of vacuum advance the total advance would be around 18 degree accelerating.

[Ol' Ron]

Yes, the engine in my truck is a "stock" 280ci engine, a former 276 with rusty cylinders. I put a stock cam in it and bored it .020 with new Egge pistons. Now with the milled EAB heads I have aprox 8.2 CR so I can burn a lean mixture in cruise, But WOT is only 20 degs. This winter I plan on modifying a set of 8BA heads to see how small of a combustion chamber I can make with out running the flow. Might have some Brazing in the future.

[BUBBAS IGNITION]

Originally Posted by Ol' Ron

Yes, the engine in my truck is a "stock" 280ci engine, a former 276 with rusty cylinders. I put a stock cam in it and bored it .020 with new Egge pistons. Now with the milled EAB heads I have aprox 8.2 CR so I can burn a lean mixture in cruise, But WOT is only 20 degs. This winter I plan on modifying a set of 8BA heads to see how small of a combustion chamber I can make with out running the flow. Might have some Brazing in the future.

Ron , i think your 28 is a overlap of vacuum with mechanical..Vac is high and you have x amount and then vac drops and mech advance is high= x.
The typical vac advance is 14 degrees and the mech is 14 ( using a example) the 14 and 14 overlap as you cant have both at the same time . ( the reason for vac advance to start with) Engine then has 17 total all the time , thats the logic for using the vacuum....is that right ???

[flatjack9]

Why can't you have full vacuum and full mechanical at the same time? If you have the mechanical all in in at say 2000 rpm, at light load you'll still be pulling 16 - 18 in hg.

[40cpe]

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I agree with flatjack9. I agree with Bubba that the two advances do overlap, at times. I think you can have both at the same time. My 276" with a L100 cruises at 2500 rpm with vacuum of 17". The spec on the vacuum canister is all in at 13". Why wouldn't the mechanical and the vacuum be cumulative?

[flatjack9]

Exactly.

[frnkeore]

If you have centrifugal advance weights and your vacuum advance chamber is attached to the breaker plate. They work independently. The weights work on RPM, only. Then the breaker plate advances with vacuum, increasing the advance, given by the weights.

So, you have initial advance, plus centrifugal advance, plus vacuum advance. Each one changes the the total advance as it is designed to.

[frnkeore]

In reality, how it works, is that you set your initial, then with the vacuum advance, unpluged, rev the engine to 2000 or, what ever the book gives as max advance RPM and check the total advance. Then adjust the initial advance, to what you want or, what the factory says the total advance should be.

The vacuum advance is a economizer and is not available under load.

I set my total advance, before the engine goes in the car, with a degree wheel. You find TDC, on the wheel, then move it to what you want the total advance to be. You then twist the weights, to full advance. With a ohm meter hook to the points, you rotate the distributor until you see the points break, with the ohm meter.

Lock it down and you have it set for max advance. The only setting that counts, for max power.

While you have the degree wheel on the engine, you would mark the pulley for TDC and total advance, using a convenient pointer, to align with the marks.

Add more marks, if you like, for initial timing but those two are what you really need.

[frnkeore]

When I was a mechanic, on our Sun diagnostic machine, the timing light had a knob and once you reached total advance, you could turn the knob to align the light to the TDC timing mark and then be able to read the total advance. Not the norm for old hot rodders but, it works, too.

[Ol' Ron]

I have 20* at 2000 mechanical. 8* in the vacuum can. In cruise I usually turm between 2/2300 rpm. I set the AF at around 15+ Hard to get with the 2GC. Using 51 jets now. PV drops it to 12.8/13.1

I have a megasquirt universal engine management computer that was given to me. I've picked up a GM throttle body from a 90/96 truck/ I have a 4bl intake I can mount the TB and just run the computer for AF and Ignition timing. Got too many projects going for my age, and i feel like a roll of toilet paper. I;d jut like to know the limits of this tuning sh*t. Get fom facts, everybody has a different slant on it

[FlatheadTed]

Frnkore , I think you explained that real good ,

[tubman]

"ol' Ron" - You constantly amaze me. I have to say that what you are talking about (Megasquirt) is about the last thing I am thinking about these days".

[frnkeore]

Thank you, Ted.

[BUBBAS IGNITION]

You can get good vacuum and good mech with rpm. The discussion is forgetting the word load .
With load its very hard to have proper rpm and vac at the same time ,

expecially on a flathead.. I agree with all thats been said , a good set up with a vac can will get ya 2-3 mpg ....

[BUBBAS IGNITION]

Originally Posted by FlatheadTed

Frnkore , I think you explained that real good ,

I agree good explanation...

[flatjack9]

Originally Posted by BUBBAS IGNITION

You can get good vacuum and good mech with rpm. The discussion is forgetting the word load .
With load its very hard to have proper rpm and vac at the same time ,

expecially on a flathead.. I agree with all thats been said , a good set up with a vac can will get ya 2-3 mpg ....

Why would the flathead be any harder than any other engine? Most systems are a compromise. Engines are so much better today because they are controlled electronically.

[BUBBAS IGNITION]

Originally Posted by flatjack9

Why would the flathead be any harder than any other engine? Most systems are a compromise. Engines are so much better today because they are controlled electronically.

I think the flatheads are very different as they are pretty low cubic inch engines with the valves are in the engine block.

Just went to a car show this weekend and they had a new 840 horse power Dodge Demon drive in.

I agree the engines today are very much better today.

[Ol' Ron]

I've never had the opportunity to play with a "Stock" 239 engine, and if I had one in the 3400 lb truck, it would certainly have an affect on the tuning. I got the truck (47 Int.) back in 84, ran it stock f or a few years. Engine, steering and brakes were junk. So I replaced them with a 52 front axle, a 51 Merc engine and Merc o matic. 3.3 rqr xle. I needed a truck for my business. All this was stock and lasted for about 10 years with little or no problems. I replaced the Merc with a 350/350 Chevy and that lasted until I decided to install a blown flathead in it. Unfortunately, my Partner at the time passed away, and I got evicted from the shop. THe property was put up for sale in 06. and here I am. Putzin!!!

[Tinker]

Is it fair to say timing and tuning is separate or the same. You can't time an engine with vacuum only if the top end is funky or leaking. Both are needed ultimately under load.



.

[Tinker]

Originally Posted by flatjack9

Why would the flathead be any harder than any other engine? Most systems are a compromise. Engines are so much better today because they are controlled electronically.

Flatheads might be around longer. All that electronic and plastic has time limit less then metal. But I could enjoy 800hp and not complain!

[Frank Miller]

While electronic engine management systems are superior they're more complicated with many parts prone to intermittent failure making them a pain to diagnose. With a flathead you can pretty much see what is or is not working. Even when it is not you can still make it home many times.
Back to the chevy distributor. As Charlies NY explained to me once, it is all about the ping. You can run a few more degrees total advance and when you open the throttle the vacuum drops out giving you enough retard to avoid pinging.

[Ol' Ron]

To a Hotrodder, nothing is ever perfect?

[JSeery]

Originally Posted by Ol' Ron

To a Hotrodder, nothing is ever perfect?

So true!!!

[aussie merc]

parts arrived on Friday so Saturday spent reworking dissy reinstalled at 4 deg with 18 deg at 3500 just back from a 450 klm day run today ran like a swiss clock never mjssed a beat THANKS TO ALL for their help comments and thoughts

[Ol' Ron]

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Not sure why you would ignore the timing advance numbers from Charley. Your sustem will work, but it ain't the best available. yet! 18 at 3500 is not enough.

[Ronnieroadster]

Originally Posted by Ol' Ron

Not sure why you would ignore the timing advance numbers from Charley. Your sustem will work, but it ain't the best available. yet! 18 at 3500 is not enough.

Only Charlie has the correct info? Wow the guys original question for this post is Timing Advance and how much is to much.

[JSeery]

Not only is the total advance a little low in degrees, it is coming in late isn't it? You would want total in around 2000-2400 rpms.

[aussie merc]

yes and done by educated guess work and checked with only a tacho and a advance check timing light not a bad effort considering the parts sent where for a different dissy not a yh series but its better than what some YOYO in the usa bolted together as i said before looks cool pity it runs like shit yes ron not the perfect curve achived but better and all advice was taken into consideration AGAIN thanks to all who took the time to reply

[Phil Gillespie]

Originally Posted by aussie merc

thanks to all i asked the question and got several answers and as for them 4 big holes thats how i got it a typical buy and bolt[ looks cool who cares how it runs ] also have checked the advance and it brings on way to much way to early [that explains why it was so retarded when i got it ] so next step recurve the dissy and try again while we are here any thoughts on maybe down sizeing carbs to say 81's instead of 97's

Interested to know how the vacuum is looking now at this set up. Improved?
Phil NZ

[aussie merc]

yes Phil much improved now have 18" at idle 550rpm again no off idle stumble and it just drives much happier will try again when i can locate a set of YH keys and springs as mallory/msd say they are nil stock and only appear to carry the latest spares watch their freight $18 dollars us turned into $65 aus by the time it got here