initial/total advance

[Harlow]

Alright, tonight I got my digital timing light. I wasn't able to fully map it out because the damn thing started shorting out and showing 7,000 rpm at idle.  But before it crapped out I found that my initial is set a 27*. Is this too high? I set it there blind, it seemed to get the best power (by power I mean it spun the tires the longest). I was also able to see that by 1150 rpm it had advanced 6*, so by 1150 rpm I was reaching 33* total. That would explain why I seem to lose power shortly after nailing it off idle. My main question for now is, does that inital timing sound too high? I've got a comp cams 292 .510 lift cam in my 383. On wednesday I'll have my new light and all day to mess with it so i'll report back with the numbers I come up with.


- Scott

[firefighter3931]

Personally, i would change that cam....it's waaaay too much for a street driven 383. To really make it work you would need a 3500+ stall and 4.30 gears. As you're seeing it's making the engine difficult to tune and has no bottom end power. 


Ron

[Harlow]

what do you suggest would be a better cam? I still want a nice lope and I would rather have a good bottom end than a high top end since it will only be street driven with maybe going to the track for fun just to see some numbers. Thanks for all the help Ron. Trying to tune somone elses drag car project has been really annoying, but it also has forced me to learn alot.

- Scott

[firefighter3931]

Scott,

What is the rest of the combo ? Compression, headers, intake manifold, carb, rear end gears, stall speed ?

The Comp 292/501 has 244@.050 duration so it's a healthy cam....even for a 440. The 383 with less cubic inches makes it even more problematic to tune and it will have a high powerband....basicly 3800+ rpm before it hits it's "sweet spot" in a 383.


Depending on your converter and gearing ; i would be looking at something in the 225*@.050 range and around the same lift so you can keep your current valvesprings. There are lots of really descent options out there.....Engle or the Lunati VooDoo split pattern grinds work very well. With the shorter stroke 383 you need t keep the duration short to help it build torque at lower engine speeds. 

The newer cams will also be much easier to tune. 



Ron

[Harlow]

I'm not sure on the compression. How do I find it? I'm guessing with a regular compression test and some calculations. Its got headers,  a Edelbrock Performer 383 intake, and a edelbrock 750 mechanical secondary. 3.23 open rear end, not sure on the stall (I would have to open up the tranny to find out, right?) I've finally got the car running pretty good now. No more inconsistent idle speeds and I can lay a 20 foot patch of rubber with out any braking(I think with the timing curve set up right it will have a lot more). I'm pretty serious about wanting to change out the cam after so much trouble its given me, so once I figure out how to find the compression/stall I'll let you know (I think I'll get the timing set for now and drive it like it is until I pull the engine for paint in 1-2 months). I'm also thinking about getting a billet or msd distributor, something that allows me to limit the mechanical advance. Which distributor do you suggest Ron? Again, thanks for helping me out. 

- Scott 

[firefighter3931]

Scott, compression ratio needs to be calculated after measuring ; combustion chamber volume, piston to deck, valve relief volume and compressed thickness/bore diameter of the head gasket. That is the proper way....

Try running a cranking compression test on the engine to see what you've got with the current cam....that might give us an idea of your static compresson ratio.

Stall speed can be checked by footbraking the car.....hold the brakes and slowly throttle up....see when the brakes will no longer hold the car back....that will be pretty close. 

The new MP distributor with the mallory advance unit works fine....or you can spend the extra bucks for the MSD billet distributor....your choice. 


Let us know what you find.



Ron

[Harlow]

Ron, is this the mopar performance distributor you were talking about: http://store.summitracing.com/partdetail.asp?autofilter=1&part=DCC%2D3690427&N=700+4294925143+115&autoview=sku

[firefighter3931]

Ron, is this the mopar performance distributor you were talking about: http://store.summitracing.com/partdetail.asp?autofilter=1&part=DCC%2D3690427&N=700+4294925143+115&autoview=sku

Yes it is. The distributor is also available individually if you allready have a box and wiring installed in the car. 



Ron

[Harlow]

In the description it only says adjustable vacuum advance, does it allow me to limit the mechanical advance as well?


- Scott

[supserdave]

You can change the mechanical advance to, have to change the springs and weights to re-curve it.

I agree, I would change the cam....

[firefighter3931]

In the description it only says adjustable vacuum advance, does it allow me to limit the mechanical advance as well?


- Scott

Scott, the mechanical advance is adjustable....there are stops on the advance plate to limit the mechanical advance. All the new MP distributors now have a Mallory advance mechanism installed and they work great. The rate of advance is adjusted with the springs.



Ron

[Harlow]

Thanks Ron, I'm going to order that distributor and also hopefully get some number on the mechanical advance tonight. I'll report back.

[Paul G]

I just put that distributer in my 440. I backed off the mech'l advance just a hair, maybe a 1/16" on the plate and found the timing to be right where I wanted it. 15* base and about 38* total.

[gojo64]

How do you check intial & total advance & how do you adjust it with an MP distributor? Sorry to sound stupid, but I'm a rookie at this. Thanks!

[Harlow]

Alright Ron. I installed my distributor and ecu today and took it for a 10 mile cruise. I set the timing to 27* again and it would only break the tires loose for about a second. Before I mess with limiting the mechanical and everything, where do you think I should have it set(total and initial)? I do know right now that I had 38* advance at 2000 rpm. I'm guessing that is too much.

2 questions:
1. How do I adjust the dwell on these distributors (there was nothing in the manual). Do I shorten the air gap? Right now the dwell is at 35, I'm thinking it should be at 32.
2. Is the total mechanical advance able to be limited using the 2 allan keys I see down on the weights? 

Thanks for all your help.


- Scott

[firefighter3931]

Scott, there is no dwell adjustment like a points system. The reluctor to pickup gap needs to be set at .008 and use a brass feeler guage so that you don't mess up the pickup 

If it's not detonating then don't worry about 38* at 2000rpm....that is fine. This engine is way overcammed so it's gonna want lots of spark lead anyway. You do however want to limit the total mechanical advance to 38* and that is done using the stops on the advance plate which are held in with Allen screws i believe.

Best thing to do is map out the advance curve and see how much total advance you have and where it stops....then tune from there.



Ron

[Harlow]

Thanks, Ron. I'll hopefully have some numbers for you tomorrow. I just want to get it running as good as possible with this cam for now and then in a month or two when I get it in for paint I'll pull the motor and change out the cam. 

- Scott

[Harlow]

Ron, I was able to get the timing curve mapped out.

With the initial set at 27*:
750 -   27
1000 - 27
1250 - 33.4
1500 - 38
2000 - 40.8 (all in)

Then when I had it out there at 2000 rpm I set the timing back to 38*
2000 - 38
1840 - 35
1500 - 35
1250 - 28.4
1000 - 24.6
750   - 24


Let me know what you think

- Scott 

[firefighter3931]

Scott, where does it feel better ? As long as it's not detonating then 40* is OK....some low compression combos actually respond to increased advance.  The big cam is bleeding off a lot of low end cylinder pressure....i'd be interested to see how much cranking pressure (dynamic compression) your engine is making. 


Have a look at the plugs for color.....tan to light brown means the jetting is good. Detonation will also show up on the plug reading as well....small black or silver specks on the electrode are signs of detonation. 



Ron

[Harlow]

Ron. I have the spring/rod/jet kit and I'm going to start messing around and see what I can get. As far as the new distributor, now I can't burn out from a dead stop like I used to. Is that due to the total timing coming in earlier?

[firefighter3931]

Ron. I have the spring/rod/jet kit and I'm going to start messing around and see what I can get. As far as the new distributor, now I can't burn out from a dead stop like I used to. Is that due to the total timing coming in earlier?

Usually, having the timing come in earlier will make it more responsive. You could try slowing down the curve with a heavier advance spring and see how it responds. Ignition tuning is trial and error....there are general guidelines but experimntation is the best way. 

On a combo like yours it will want lots of base timing as you've allready seen. Try advancing the timing (at idle) until the engine stops increasing in speed and take note of that reading. If the engine will turn over without kicking back then you will be close to what it wants for base timing....then you can tune for mechanical advance to limit it to 38-40* total.

How do the plugs look ? What type of color are you seeing ?


Ron


Ps. The biggest problem is the cam....of which you're aware. The 292 Comp won't make much power in a 383 until 3500-3800 rpm so it's not surprising that it feels "soft" off idle.

[Harlow]

Heres a picture of the plug on the #7 cylinder. I'll try giving it more advance at idle and see what happens. Sorry for all the questions, but I don't have anyone I can ask in person so here are a few more. The air gap is supposed to be set at .008. The only problem is that the gap is not even, meaning it narrows. Its because the pick up and the reluctor are not perfectly parallel. Is that a problem?

   

- Scott