zwede

Just curious what your experiencies are. I have programmable EFI on my 454 so I can enter any timing advance I like. I did some experimenting this morning and found that the more advance I give it at cruise/low load, the smoother and stronger it runs. At 1500 rpm cruise I run 40 degrees. At 1200 rpm cruise I run 35. Idle is 23.

Lowering the advance only 5 degrees will start making it run rough @ cruise.

With enough timing I can now drive it in 5th gear at 900 rpm.

Fevre

I have the Accel DFI system in my Formula and one tuners manual I have says to run more adv at idle to smooth it out so I am also at about 18 to 26 at 900 idle. The computer adds/subtracts timing depending on how far the car is from the target rpm idle so it jumps around a bit.

WA 2 FST

Zwede,

As you know I don't have ANY experience with EFI on a BBC, but from all my time tuning EFI, I have found the same to be true as what you noticed. On my SBF I would run up to 44-45^ timing at cruise and it would run mean and clean. Like you, I would get incredible gas mileage in OD (also had a TKO trans in that car) on the highway, and the car wouldn't buck, surge, or stumble. Frankly, though, a lot of that IS in the tune. EFI itself doesn't make it all better. :) So kudos to you for experimenting with it and finding yet another sweet spot in the EFI tables.

shawn_cake

Same experience here Zwede. Doug Flynn sent me a timing and fuel delivery maps for my 532. When I looked at the advance, I thought there was an error. But Doug was right (as usual). When I am doing 70 MPH, I am turning 1800 rpm with my ROD 6 gear. I am using 48 degrees total advance in those particalr cells. Less advance makes the car hesitate...go figure!

:D :cool: :D

zwede

Wow. I'm running less than that. About 42 I believe. I will bump it up some more this afternoon and see how it likes it.

I remember looking at the baseline maps on holley's website, and the timing was very retarded. Only 28-30 degrees max below 2000 rpm. That fooled me into believing that's what I needed on mine too. Some time ago I mapped the timing on my 96 Z28 and found it advanced much more.

427Hotrod

Even works with ancient stuff like carbs. I've been preaching it for years. My 540 is running 31* initial and it's at 40* before 2000. Plus I have another 6* in vacuum advance for cruising. No surging and much more responsive!


JIM

MotorHead

You can run as much tinimg as the motor will handle without problems like detonation and hard starting :D

81vette

With fuel injection you get great fuel distribution and a slower burn. This allows you to run more advance than you could with a carb on the same engine. Increased mileage and power! Gotta love that FI. :thumbs:

Mark

lars

My curve kits for the non-EFI cars actually run up to 54 degrees max advance at cruise, and most engines respond really well to it - so I have the same experience with lots of timing at light cruise.

inqbus383

I have noticed the same thing, especially as I get a more highly modified motor. I have about 35 degrees at idle with vacuum advance, 20 degrees from vacuum advance, 15 mechanical. Its amazing but I think I need even more initial to give it enough advance at low cruise (1200-1600 rpm). Of course I have a sbc, but they're similar.

LAvetteman

My 71 runs much better with about 19 degrees initial and 40 total.

shawn_cake

The "big advance idea" wasn't mine - Lee (blue Chevelle on the Chevytalk forum) sent me a map for his ZZ502. He had the "big advance curve" programmed into the C950. At first I thought it was an error - but Lee and Doug Flynn said it was OK at low MAP / engine loads. It seems like the more advance, the leaner you can run the engine at low load cruise. Interesting...
http://temp.corvetteforum.net/c3/scake/index.shtml


:rolleyes: :rolleyes:

tshort

Same thing here. I've got 27 initial @ 850rpm and 48 total coming in at about 2000rpm. I've got no vacuum advance. It's starts up real easy too.

71coupe

How does it do at WOT with that setting and how far does it retard?

shawn_cake

I use a Holley Commander 850 EFI - so I can map advance any way I want.
I found the engine made max torque with 36 deg total avance under load.

At part throttle cruise, I am playing with total advance in the 45 - 48 degree area.

:lurk: :steering: :lurk:

Matt Gruber

Good topic!
i just added 6 degrees to my vacuum advance.
reminds me of the stone age. grinding the slot .060" instead of pushing buttons on a computer.
UPDATE: test drive OK :thumbs: no complaints with extra advance. good tip zwede :thumbs: thanks


[Modified by Matt Gruber, 8:20 AM 9/11/2003]

shawn_cake

Not with me! Gotta do the "computer thing"
:sad: Invariably something gets damaged when I touch a wrench!:sad:
:banghead: :banghead: :banghead: :banghead:

norvalwilhelm

All my timing is handled by electronics. I have no mechanical advance in the distributor, it is locked down. I found mechanical curves are not as consistent as electronic. I can adjust my timming in the car while driving along and by tweaking the **** I found it likes 43 degrees. I do run a boost retart so once the boost starts the timing quickly backs off.

WeasleVette454

I have a MSD Pro Billet w/ vacc adv. set at 16 with 36 total. Geez, by you numbers, I feel like I'm missing out. But aren't most distributors made with stops to not allow too much timing? IS this where the "Lars recurve kit" come in to play?

Thanks!
Weasle :D

tshort

From my understanding, no, the only thing the distributor really 'regulates' is the total advance from idle. For example, I have the 21 degree bushings on my weights right now. So whatever I set my initial timing to, the total timing will be 21 degrees higher when it is reached.

If I'm wrong, please correct me. ;)