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Old 04-13-2004, 05:51 PM
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Demon initial advance question

I posted an MSD distributor question earlier today which prompted this question and I thought a new thread might generate more feedback. I'm replacing my 800 Holley with a Mighty Demon 750 which their tech dept recommended and the initial timing on the Demon Selection Guide lists a pretty broad range of initial timing numbers.

www.barrygrant.com/demon/default.aspx?page=5

If you look at this chart you'll see that as the carbs grow more radical, the initial advance figure also increase to 20+ for the Race and King Demons while the Road Demons are at 10-12deg initial. I don't understand why a more radical engine needs more initial advance than a stocker? Will the total timing number be that much higher as well?

I know I read an article once where a 396 BBC produced maximum power with 42deg total timing. I realize this is on a dyno and you could never get away with that on the street but just sounds higher than anything I've seen anywhere else. The magazines usually achieve optimum power at 34-36deg total.

I did not list my engine specs as I'm looking for more of a general answer to how engine characteristics effect timing. Thanks.
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Old 04-13-2004, 06:02 PM
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A stocker engine as you say, uses vacuum advance at idle and off idle since leaner mixtures burn slower and richer burns faster, the stocker will be set on the lean side so it needs more advance to compensate. I run a Road Demon Jr. 625cfm, my timing is set at 12 degree`s initial, with vacuum advance 25 initial. I would think when you get into the stages of the mighty Demon in power, then it would need more timing as they figure you won`t be using a vacuum advance. when we built a 400 small block with 6 inch rods, edelbrock heads, comp cams solid lift around .555, we set the timing at 18 degree`s initial. Even so there`s more to it than what I posted, it gives the basic idea, but when I first got my demon, the techie I spoke to told me they like lots of timing, he wasn`t kidding.
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Old 04-13-2004, 06:58 PM
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My timing with the Holley is set around 14 deg initial with no vacuum advance and it is a little hard to start once warmed up. I wonder if adding a little initial advance will improve this situation. I was also running a little rich at idle which according to Demon's troubleshooting section might be improved if I bumped the initial timing up. Thanks.
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Old 05-03-2004, 10:09 PM
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68chevelle_ss

The reason for the different timing specs is that the more radical engines usually have a more radical cam and require more initial lead for complete combustion at idle.

My engine has a Road Demon and I am running 16 BTDC @ 700 RPM.

I had heard from someone (though I have never tried it) to set the timing with a vacuum gauge and advance the distributor until you stop gaining vacuum and then back the distributor off until you lose a half inch of vacuum and lock it down. You would surely have to recurve the distributor after doing this as you would probably end up detonating if you didn't cut the total back.
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Old 05-04-2004, 06:08 AM
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Timing

The more radical your engine, and cam profile the more timing.

The reasoning is as follows: A larger cam shaft will have more duration, and overlap (both intake, and exhaust valves open at the same time) this can lead to poor idle quality, and throttle response since raw fuel is being pushed out of the exhaust. Increasing your initial timing will start the burn sooner in the cylinder hopefully giving you more complete combustion, cleaner idle, and crisper throttle response.

When you increase your initial timing it is common to have to recurve your distributor so you can still maintain the proper total timing for your engine combination. Recurving the distributor will allow you to run more intial timing, without going over your total timing. On most aftermarket distributors it is done by simply changing a bushing. You can then change your curve (both mechanical, and vacuum) to adjust how quickly the engine goes from the initial timing to the total timing. Different engines will vary the timing required. Most street engines will vary from 32 to 38 degrees. On performance or race engines with power adders such as nitrous or a supercharger the total may need to be in the low 20's, or on a natrually aspriated engine it could be in the upper 40's or higher depending on the combination an altitude.

As far as cranking goes, there is no reason a street engine that is built and wired properly should ever have a cranking problem. It is very common on race engines with 15:1 or higher compression to have the timing locked out (at total advance) to crank over without any problems. On most street cars if you're having a problem with the engine cranking over when the engine is hot, you're most likely dealing with getting the starter (and solenoid) to hot. Installing a starter heat shield, and remote starter solenoid will generally eliminate this problem.
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Old 08-05-2004, 12:44 AM
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Mighty Demon

I am putting a mighty Demon 750 on my 350 on Friday....

Here is my cam specs.... Comp Roller Cam

350 bored .30 over
block decked 60 thousands
Comp Roller Cam 244 duration, 600 lift (640 lift with 1.6 rockers)
I have 11.7 compression
2.02/1.60 camel hump heads
Torker II Single Plain Intake
1 " carb spacer 4 hole
MSD 6A Ignition
Mallory Comp 9000 Uni Lite Distributor
Timing is currently set at a 12 intial, 36 total
3200 stall.....
3.73 gears

And have been running a Edlebrock 600 Performer since my motor was built ( 1200 miles)

So is 18 degrees intial timing where I need to start? And also could someone explain what role intial timing plays? Do you get detonation from intial timing, total advance, or both? And will I notice a huge difference in the Mighty Demon 750 compared to the Edelbrock 600 I was running......??

And will my current throttle linkage and trans kickdown cable bolt right up to the Mighty Demon....??

Thanks....
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Old 08-05-2004, 06:09 AM
Technical Support Barry Grant
 
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The Mighty Demon should give you much better performance on your combination vs. what you were using.

18 degrees initial would be a good place to start on your combination. You'll need to re-curve your distributor to keep your total timing in the same range as you are currently.

Too much initial timing can cuase detonation if you're running a lower octane fuel than is optimal for your engine.

The throttle linkage, and kickdown should convert pretty easily from your Edelbrock carb.
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Old 08-05-2004, 10:27 PM
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Carb

I almost always run 110 VP race gas. So BG Tech if I keep my foot out of the throttle will the Mighty Demon still suck down the fuel compared to my Edelbrock 600? I am not looking for mpg out of this carb. But just was curious. And can you explain the four corner idle system. And how hard is it to get tuned? Thanks for the help.....

Dave
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Old 08-06-2004, 07:59 AM
Technical Support Barry Grant
 
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It's hard to say MPG wise. There are two ways to think about: First since you're going to be producing more HP it's going to use more fuel at WOT. Second, since it's producing more power, you're not going to need as much throttle to cruise at the same RPM, so it could be a wash as far as cruising goes. That is if you don't get on the throttle to as much.

The four corner idle just allows you to get a closer, or finer adjustment then two corner systems do. They aren't any harder, but they do take a little longer to adjust since there are more adjustments.

The twobiggest problems most people make while adjusting the idle is not having the timing set properly before starting ot adjust the idle, and rushing. Take your time, and make small adjustments. Generally no more than a 1/4 turn at a time on the mixture screws (at a maximum). I generally go 1/16th to an 1/8th turn at a time. Make your adjustment, and let the engine react. If you're not sure if it made the problem better or worse, press on the accelerator pump arm without moving the throttle linkage. This will add fuel without changing the volume of air the engine is seeing. If the engine is too lean the RPM should climb, if the engine is too rich it should want to almost stall.
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Old 08-14-2004, 10:07 PM
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Carb on!!!!

I put the Mighty Demon on. I intially ran the carb with 14 degrees initial with 36 total timing. Car ran great but was running rich. I switch to 18 degrees intial and 36 total and now the car seems a little sluggish and still running rich. I have read the manual and watched the video. Is it possible that 18 initial is to much? Here are my option for my advance.....




At the intial 14 I was running the dual stage advance. I switched to the single stage to see the difference. My car now seems a little slow out of the hole and on the freeway......

I get mixed oppinions on whether I should run single or dual stage advance.

Here is another look at my setup:

350 bored .30 over
block decked 60 thousands
Comp Roller Cam 244 duration, 600 lift (640 lift with 1.6 rockers)
I have 11.7 compression
2.02/1.60 camel hump heads
Torker II Single Plain Intake
1 " carb spacer 4 hole
MSD 6A Ignition
Mallory Comp 9000 Uni Lite Distributor
Timing is currently set at a 18 intial, 36 total
3200 stall.....
3.73 gears



Also I have a slight hesitation when I take of from a normal start. And at around 2800 rmps on the freeway I have a slight surging...

My car idles great. So any help with my setup would be greatly appreciated.... Thanks......

Here is a short video of how the car is sounding now.....

Car Sound

Dave
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