timing advance how much is to much
 

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

Re: timing advance how much is to much
 

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.

Re: timing advance how much is to much
 

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

Re: timing advance how much is to much
 

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.
.

Re: timing advance how much is to much
 

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.

Re: timing advance how much is to much
 

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.

Re: timing advance how much is to much
 

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

Re: timing advance how much is to much
 

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

Re: timing advance how much is to much
 

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.

Re: timing advance how much is to much
 

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?

Re: timing advance how much is to much
 

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

Re: timing advance how much is to much
 

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

Re: timing advance how much is to much
 

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

Re: timing advance how much is to much
 

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

Re: timing advance how much is to much
 

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

Re: timing advance how much is to much
 

....

Re: timing advance how much is to much
 

That would be nice!

Re: timing advance how much is to much
 

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.

Re: timing advance how much is to much
 

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.

Re: timing advance how much is to much
 

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