My setup is a +.060 350, 10-1 pistons, Comp XE268, Summit cast iron heads (reworked), Performer RPM Air Gap, Holly 670 SA and Mallory Unilite (mechanical advance).
This is a daily driven, camper pullin', grandson totin', highway driven 4-door 13 second race car.
I have the re-curve kit for the Mallory. I started out with purple and pink springs for this advance curve:
12 initial at 750rpm 22 at 1050rpm 32 at 2300rpm 36 at 3000
My engine guy wants me to flatten this out a bit so now with the stock V8 setup of purple and brown springs:
12 initial at 750rpm 22 at 1450rpm 32 at 2800rpm 36 at 3500
Now my engine guy wants me to add in 2 more degrees advance which is pretty easy to do as it is a plate adjustment in the dist.
My engine guy is more interested in my engine lasting longer which I am as well. I did lose 2 to 3 tenths at the race track which I would like to get back. I could do this by bumping the initial back up to 18 degrees and buy the race gas which I actually don't like doing because I must be getting lazy as I don't like to make changes between street and strip other than the slicks.
So knowing all this and the fact I like getting out of the hole quick what might be the best timing advance curve?
Thanks!
Scott Parkhurst said
Aug 23, 2010
I kinda like your first curve better. It's more aggressive.
Winston Wolf said
Sep 6, 2010
You don't need such a wide timing curve. Here is how I would set it up.
Figure out the timing that makes the best HP or MPH at the track. Be it 34, 36, 37, whatever. That will be max setting (all in) without vacuum advance.
I would limit the mechanical advance to around 15 degrees with it fully advanced by a couple hundred RPM's below what you cruise at, so probably all in by 2500. Most adjustable kits have a max advance stop or some kind of limit screw so you can adjust that. You will need to use whatever springs the curve needs to get it all in by 2500.
This needs to all be done with the vacuum advance unhooked.
You want the total advance under low load with the vacuum advance connected to manifold vacuum to be in the 50 degrees BTDC area, maybe a bit less. (this is under steady low load driving conditions) This will vary depending on where your engine likes the WOT timing. An adjustable vacuum canister is nice to dial it in better.
To give you an example, with the vacuum unhooked, my car is set at 37 deg total advance, all in at 2500 RPMs. My vacuum advance adds 10 degrees and is off at 4" of vacuum. I use a 15 degree mechanical curve, so at 1000 RPM's my timing idling is 32 degrees. 37-15+10. At 2500 RPM driving, I am at 47 deg advance under low load.
Once it's set up, then cruise around, checking for detonation at different throttle inputs and loads. If you aren't getting any and the car seems responsive, you are good to go.
The only thing that has an effect on your quarter mile is the total timing and whether or not the advance is all in soon enough. Vacuum advance has nothing to do with it as it doesn't work under load.
Winston Wolf said
Sep 6, 2010
I just re-read your post. You can see from your 1/4 times that your car likes the advance to come in sooner.
And the timing curve isn't going to make your engine last longer if you aren't getting to the detonation point. I think your mechanic is setting it up backwards, try it my way once and you'll be surprised how easy it is.
If your not running vacuum advance, you should be on any street driven car.
Also, the more timing you run at idle, the better your car will run and the cooler it will run.
-- Edited by Winston Wolf on Monday 6th of September 2010 09:47:49 AM
This is a daily driven, camper pullin', grandson totin', highway driven 4-door 13 second race car.
I have the re-curve kit for the Mallory. I started out with purple and pink springs for this advance curve:
12 initial at 750rpm
22 at 1050rpm
32 at 2300rpm
36 at 3000
My engine guy wants me to flatten this out a bit so now with the stock V8 setup of purple and brown springs:
12 initial at 750rpm
22 at 1450rpm
32 at 2800rpm
36 at 3500
Now my engine guy wants me to add in 2 more degrees advance which is pretty easy to do as it is a plate adjustment in the dist.
My engine guy is more interested in my engine lasting longer which I am as well. I did lose 2 to 3 tenths at the race track which I would like to get back. I could do this by bumping the initial back up to 18 degrees and buy the race gas which I actually don't like doing because I must be getting lazy as I don't like to make changes between street and strip other than the slicks.
So knowing all this and the fact I like getting out of the hole quick what might be the best timing advance curve?
Thanks!
You don't need such a wide timing curve. Here is how I would set it up.
Figure out the timing that makes the best HP or MPH at the track. Be it 34, 36, 37, whatever. That will be max setting (all in) without vacuum advance.
I would limit the mechanical advance to around 15 degrees with it fully advanced by a couple hundred RPM's below what you cruise at, so probably all in by 2500. Most adjustable kits have a max advance stop or some kind of limit screw so you can adjust that. You will need to use whatever springs the curve needs to get it all in by 2500.
This needs to all be done with the vacuum advance unhooked.
You want the total advance under low load with the vacuum advance connected to manifold vacuum to be in the 50 degrees BTDC area, maybe a bit less. (this is under steady low load driving conditions) This will vary depending on where your engine likes the WOT timing. An adjustable vacuum canister is nice to dial it in better.
To give you an example, with the vacuum unhooked, my car is set at 37 deg total advance, all in at 2500 RPMs. My vacuum advance adds 10 degrees and is off at 4" of vacuum. I use a 15 degree mechanical curve, so at 1000 RPM's my timing idling is 32 degrees. 37-15+10. At 2500 RPM driving, I am at 47 deg advance under low load.
Once it's set up, then cruise around, checking for detonation at different throttle inputs and loads. If you aren't getting any and the car seems responsive, you are good to go.
The only thing that has an effect on your quarter mile is the total timing and whether or not the advance is all in soon enough. Vacuum advance has nothing to do with it as it doesn't work under load.
And the timing curve isn't going to make your engine last longer if you aren't getting to the detonation point. I think your mechanic is setting it up backwards, try it my way once and you'll be surprised how easy it is.
If your not running vacuum advance, you should be on any street driven car.
Also, the more timing you run at idle, the better your car will run and the cooler it will run.
-- Edited by Winston Wolf on Monday 6th of September 2010 09:47:49 AM