Hi, everybody, I recurved my HEI distributor today, and I thought I would share my experience with you all.
I have a 1980 'vette, L48, th350 tranny, and today I popped off the distributor cap and rotor, and replaced the mechanical advance springs on the stock advance weights with the silver (medium) springs out of the 929G Mr. Gasket advance kit. (Lars Grimsrud says to just throw the weights that come with the kit away, so thats what I did) This brought my advance all in at about 2800 rpm. I also replaced the vacuum advance canister with NAPA part number VC1838. I now have the engine timed at 16 degrees at idle with vacuum advance not hooked up, 32 degrees with vacuum advance hooked up. The mechanical advance moves 20 degrees, for a mechanical advance of 36 degrees, all in at 2800 rpm, and 52 degrees with the vacuum advance added in. All is well according to Lars Grimsrud's tech papers on timing, (which, by the way, I highly reccomend!) and the car runs like a champ. A noticeable increase in power, and a very noticeable increase in throttle response. I drove it into work tonight, and maybe it's my imagination, but I would swear that I didn't have to press down quite so hard on the gas pedal on the highway, and the fuel guage didn't move as much as it usually does. (of course, this will require some actual measurement of mileage to verify.) All-in-all, well worth the 40 bucks or so that I spent doing it.


Scott

 

It always feels good when you make a modification and it actually works well! Great writeup, thanks!

 

Definitely next on my to do list.... Thanks for the write up.

 

Do you have to do much surgery to change the can?

mk

 

its not your imagination! this is what was done years ago before computer chips and tuners. a great bang for the Buck. feels like a new car doesn't it

 

Nope, once you have the cap and rotor off, it's two philips head screws, bada-bing, bada-boom, easier than falling in love!


Scott

 

Be very careful only the mildest low hp smog motors can withstand 16 degrees additional advance. Crane makes an adjustable vacuum advance. 6 - 8 degrees is about all cars that require 91 or 93 octane to run.

 

Lars is awesome! I will try this soon as well.

 

I am so glad you did this with your write up. I have the kit from summit sitting waiting until after I take it to the track May 5. Didn't want to screw a working motor up this close to the schedule but I would like to end up near where you are....possibly less initial timing but I bet mine is set to 8 degrees or so now and I end up around 12 or 13 plus the new weights and medium springs too. Thanks for the write up. It will help me.

Lance

 

OK, what we have to get straightened out here is this: Are you taking about distributor degrees or crankshaft degrees? Vacuum advance canisters are typically rated in distributor degrees, which spins at half the speed of the crankshaft, so a vacuum canister rated at 8 degrees actually will provide 16 degrees at the crankshaft. It can get confusing, 'cuz when you are discussing timing, you're talking about crankshaft degrees, usually. E-mail Lars Grimsrud and ask for his 3 papers on timing, he does a really good job of making the whole subject clear.


Scott

 

GREAT to hear of your success. Wardog on this forum helped me tune my '79 L82 last summer using the Lars papers. Really woke it up as well. Only one spring was replaced to get the desired results on my stock L82. Running premium now, though.

Fun Stuff.

 

Yeah...but back in the day good shops had SUN distributor machines and you could set it up before installing in the car. It was just a matter of convenience. When I went looking for one awhile back, most shops didn't know what I was talking about. It seems only the old timers remember them.

 

No I'm not confused. I said that it is adjustable with a little allen. I am talking about timing lite verified additional advance. Motors with higher VME and fast burn chamber technology can't have wild big numbers of additional advance without detonation just cruising down the freeway

So you turn your motor up to 3500 rpm with the vac advance unplugged

verify your timing. I use 32 with Dart Pro 1 heads. When I had the adjustable I could plug on the hose an it would add 4-6-8 degrees what ever I felt like setting it to. Now I went digital and my choices are 5-10-15

 

Now, wait a minute, I just perused the thread, and you never said anything about anything being adjustable with an allen wrench. Get your story straight, will ya?


Scott

 

All right guys! Stop it! I understood it until you started with varying measures and technical details and all you've succeeded in doing is confuse those of us who aren't Lars Grimstad!

Never heard a car discussion about which ratio to use when setting timing...hook the darned light up and look at the timing marks and adjust to taste within broad parameters!

What some of us have read is that when the EPA came around the timing was set lower than it used to be for good power because that reduced "harmful" emissions so that today with newer cat converter technology we can readjust the timing using standard timing lights and advance the timing until it pings and back off a bit and recurve the advance as well to get more effective power out of the block.

Is that not correct amidst this confusing back and forth?

 

I very happy for you. Your on your way to more steps on the long road of hot rodding our old Vettes.

I did say adjustable............. I expounded on Crane adjust vac cans.

HEI's were wonderful compared to points. dizzy with Seperate coils were the next tech thing, digital dizzy or crank triggers are next, then distributerless ign. are even better with coil per cylinder

 

Hey, gkull, I'm sorry, I knew exactly what you meant, I just couldn't resist messing with you. My weird sense of humor gets me into trouble sometimes........

My car is a 1980, so it's got the old fashioned smog heads, and it runs like a top on the highway with 52 degrees of total advance, so I think I'm in pretty good shape with the 16 crank degreesof advance from the vacuum can. I have heard that the newer style heads like the fast burns and the vortecs, don't require as much ignition advance, something to do with the combustion chamber design being so efficient that the mixture burns fast, not needing to "light it up" quite so soon in the combustion proccess, Is that what you are refering to?


Scott

 

LOL! I want to do mine at some point soon...