Timing on V8 - is 35* BTDC total the way to go?

[miketyler]

I ran across an article about timing up Mopars where they use the formula Initial timing (T_i)+ mechanical timing (T_m)+vacuum timing (T_v)= 35* total.

Using their illustrated method, my car has around 58* total! It starts good and runs ok but I cant help but think I'm running with too much timing. I did try and adjust my VA down and only got about 3/4 turn and it was min'd out. My initial was set at 13* 

Is the 35* a hard rule for total timing? Could this excessive timing be adding to my still slightly higher than normal operating temps?       

[67Vette427]

58 total is too much. I run my 528 Hemi at 35 total and it runs great. I have my base set at 9 and do not use the vacuum advance. When I ran it more it would over heat. Stock specs are usually TDC or a little more at base.

[miketyler]

my T_v=23*  Maybe I should drop the VA? Without it, I am right at 35* total. One other thing to consider, am taking my vacuum reading from the ported source on the carb and get 0 Hg at 800rpm and 23Hg at 3000rpm. Is my vacuum pressure in the correct ballpark?     

[dodge freak 2]

Total timing is without vacuum.

Running vacuum advance is a long story....some run it, some don't. I dislike it but then you see me crying about 10 mpg.

I believe if you have light springs in the dist. and the advance is all in at 2500 rpms, the motor is happier without running it. But some disagree, claim they get better mileage with vacuum advance.

[miketyler]

I want to say mine seems to run better in the lower RPM range with VA connected. Can you run a vacuum restrictor on VA to try and reduce timing?

[Mopar73340]

MT if you are running a mopar dist it should have an adjustable vacuum can on it. You need to use a small allen wrench to adjust the amount of vacuum advance. I run my 340's with 18* init and 33* total timing and about another 15* or so of vacuum advance at light throttle. I just adjusted the vacuum advance by ear to figure out how much it likes. It has much better throttle responce and runs better with the vacuum hooked up but like said before some will argue differently. Also, the more throttle you give it the less vacuum advance it will have,. Vacuum advance only works under slight and part throttle conditions. To much advance will cause it to run warm under light load. Also remember it needs to be hooked to the ported slot on the carb.

[miketyler]

Ok, thanks to you and DodgeFreak2 for explaining that to me. I was thinking that total timing included vacuum as well.

Man, if there was any chance I could get something wrong, I will.   

[67Vette427]

I like having more response off idle so I don't use the vacuum advance. If you have a timing light with an adjustable degree knob you can see what each one does is as the rpm's change. The bad part of having the base set high is starting problems and gas mileage.

[dodge freak 2]

I believe total timing is at W.O.T., vacuum advance does not work then. Thats when the cylinders are pack with A/F and under a heavy load...you can run more timing at P.T. because the cylinders are not pack with A/F and the motor has a light load...

But I have found my motor seem to like no vacuum but my advance is in all the way at like 2000 rpms...its been a long time since I tried it...maybe this spring I try again...even if it got 1 more mpg it be nice.

[miketyler]

All good info for a simpleton like me 

The book calls for 2* BTDC. Athough not optimum for performance, the lower timing makes for maximum fuel burn and increases fuel economy, right?   

[dodge freak 2]

I don't think so, might have been to make the EPA happy.

Why not set the total timing first to 36-38 degress, rev the motor up until the advance is all in-like 3000-4000 rpms and set the timing, might have to use timing tape to find 36-38 degress. Tape will not stay on so mark a line, I like white paint.

Then see how the motor runs after adjusting the idle speed.

I do not even know what my base timing is, all I care about is total timing and that it does back off as the rpm's go down. It does not ping and starts fine, what more do you want.

[miketyler]

I just like to know the affects of timing on fuel economy. My car is adult driven around town and I'd like to find a balance between performance and fuel economy.  I wasnt sure if less timing = more fuel economy but I think I am getting less than 10 mpg now.   Will give 36-38* and see how it goes

[Mopar73340]

I just like to know the affects of timing on fuel economy. My car is adult driven around town and I'd like to find a balance between performance and fuel economy.  I wasnt sure if less timing = more fuel economy but I think I am getting less than 10 mpg now.   Will give 36-38* and see how it goes

More timing to the point just before the engine knocks will result in MORE mpg. Less will = less mpg. Thats why the factory used the vac advance. Get the timing tape and find out where your total mechanical advance is.(without vac connected) If you have a MP dist you can adjust the total mechanical if not you will have to weld up the slots in the dist or get a newer MP or mallory dist. Based on my experience with a basically stock 340, it will not like anything over 33-35* total mechanical advance hopefully all in by about 2500-2800rpm.

[ntstlgl1970]

The base timing is kinda trial and error (depends on your engine configuration), but usually the total is about optimum at 35 unless you have a fully developed race engine.

[AMXguy]

My total is coming in to early at about 2000 with no vac advance being used. to bring it in later am I better off to lighten the weights or use heavier springs? I can't find mopar springs but Delco ones are everywhere, are they the same?

 I'm getting some stumbling between 2000 and 2500 at full throttle accereation, new carb changes nothing so I'm thinking too much advance too soon.