Just bought a remaned Duraspark II distributor (A1-Cardone) and performed a recurve on it from some instructions off a web-site I ran accross (much simpler than it looks to do...). Although I've just run the rig a few miles, it does seem to have it bit more get up and go. The real test will come this towing season. I utilized the 13L slot with no alterations. A few questions from the hack mechanic please:

1) The site suggested replacing the springs with Mr. Gasket #925D spring set which I did. They seemed quite a bit "lighter" than the two I replaced and there was no difference between the two. Of the two I swapped out, one was quite a bit beefier than the other. My old distributor had the same set up...2 different sized springs. What's up with that and should I have swapped them out?

2) The site also suggested that since my application is mostly low rpm towing that the springs should be stiff so that full advance would be delayed to aprox 3,500 rpm (a very rare occurance for me). This is another reason why I'm not sure I made the right move with the lighter spring kit. Should I keep the Mr. Gasket springs in and just use the square access hole in the breaker plate to adjust the tabs out and increase the tension or give it a try as is?

3) I put the timing back to 12 degrees BTDC where I had it. Should that possibly change? I had problems with pinging during the real hot weather trying to tow with 87 octain & had to go to 89 (Darn, I was hopping to avoid that!). At only 9 to 1 compression on the pistons, could it be timing related?

Here's more information on the truck if it helps. 1978 4x2 F250 X-Cab with 4/10 gearing, 31x10.5R16.5 tires. Primarily used to tow an 8,000# TT @ hi-way speeds (60 mph=2300 rpm, auto/trans). I am aiming for gas mileage over quarter mile times. 460 w/ full re-build 5,000 miles ago. Heads (D3VE) mild porting smog "bumps" ground out. Hyper-U pistons up'd to aprox 9 to 1. Matched Eldebrock Performer 600 cfm carb & manifold. RV cam (Speed Pro 204/214 duration - .484/.510 lift - 112 lobe seperation). Headman headers, Flowmasters with 2 1/2" exhaust.

For the record, current mpg, 7.3 towing....ouch! Seems to be about average for the 460's checking out the mpg forum threads. There is an up side...no problem passing cars or pulling grades!

 

"Of the two I swapped out, one was quite a bit beefier than the other. My old distributor had the same set up...2 different sized springs. What's up with that and should I have swapped them out?"

The springs are two different sizes to fine tune the curve. If you notice, the mechanism makes the springs work together. So for the lightest setting you can have two light springs. The next heavier would be one light and one heavy, and the next would be two heavy springs.

I believe messing with the springs is going to make the biggest difference in acceleration of the truck. At 2300rpm, most any combo is going to be "all in" as far as timing.

Your one other hope is the vacuum advance. I would play with that to get the best gas mileage without pinging.

First decide what springs work best. And then play with the initial timing, advancing it as far as it will go without pinging going up a hill(like you said, hot weather will be worse).

After this, you should have the mechanical and the initial timing set. Do all these adjustments WITH THE VACUUM OFF.

Now, you set the vacuum advance. You will probably need to get an adjustable unit if the new unit doesn't have a allen wrench screw up inside the vacuum port. Plug the vacuum line into the distributor, and see what you have. If you use the stock vacuum can, it will probably ping terribly. If you get an adjustable one, adjust it for maximum advance without pinging on light throttle.

The vacuum advance advances the timing over and above normal settings at light throttle, when there is not much load on the engine. This is what will give you gas mileage. The only drawback is, if while towing down the highway you are "using" the engine a lot, then your engine vacuum might be a little low, and the vacuum advance may have less affect.

 

I just so happen to have a Sun distributor machine. I would be glad to test yours at no charge.

 

Franklin2, thanks for the reply on the distributor/timing set up procedure. Boy, it's a little more detailed than I imagined but not too difficult to handle. You mentioned an adjustable vacum advance can with an allen head screw. Is that something that can be obtained at the parts store and replaced? Never heard of one...

 

Mike W - Thanks for the offer to hook my distributor up on your Sun distibutor machine. What exactly will the machine do?

I suppose I could remove and send it to you postage paid to check out. I believe you are a California resident?

It might be easier to have a local mechanic check it out. Is a distbutor machine a some-what common piece of shop equipment and what do you supposed should be a fair charge if I brought it in for diagnosis?

 

Here is the vacuum advance.

http://store.summitracing.com/partde...RN%2D99607%2D1


"Thanks for the offer to hook my distributor up on your Sun distibutor machine. What exactly will the machine do?"

The machine will tell you exactly what advance you have at what rpm. I have heard that it's hard to get someone who knows what they are doing to use one. Plus it takes a lot of experimentation(time=money).

 

The Sun machine spins the distributor at variable speeds and a strobe lights up when it "fires". You can see exactly what advance you get at a certain rpm. You can to the same thing by extending the timing marks on the dampner. It is just harder to change springs on the truck.

 

I'm hopping to revive this thread since I'm still working to tune in this 460 rebuild.
Towing season started last week and I've still got major "pinging" problems.
Here's what I know or have tried so far...
* on 87 octaine with vacume advance plugged & removed from dist. there is no pinging (a good sign right?)
* timing currently set @ 11 degrees BTDC
* I've taken out the two "light springs" mentioned previously and replaced them with the stock units. One heavy and one medium with little noticable improvement.
* I've adjusted the allen screw on the vacume can all the way in (about a turn and a half) with little effect as well.
- Is clockwise the correct direction to go to retard advance?
* even with high-test (92 octaine) this setup still pings excessively!

1) Should I try two stiff springs instead of one?
2) Man, the thing runs like a champ with the vacume advance removed...I know that will affect my gas mileage adversly but could I tow like that and not hurt the motor?

As always - any suggestions greatly appriciated and always enlightening!


Paul