[Cliff R]

+2

All of these engine have specific timing and fuel requirements and it is worth the effort to spend time in those areas if you want to get the most out of the combination.

Even with that said the parts sold to novice tuners are very poor quality and don't work as advertised. Those "hoaky" HEI kits and "adjustable" vacuum advance units are a perfect example. Complete waste of time/funds and WHY would you used a stepped cam on the BACK side of the VA to control movement when it needs to be on the other side of the arm to stop its total travel......DUH?

In any case and I'll add here that these super-quick timing curves don't cut it. I've removed countless aftermarket spring/weight kits from distributors and set them up with stock parts instead to correct tuning issues with these engines. Dumping ALL the timing on a well prepared street engine never has worked well dating back nearly 50 years when I got in this hobby and still doesn't work well today. Removing/eliminating VA doesn't work either. Even so countless numbers of these engiens are tuned in that manner and folks using those methods are quick to recommend them.

For what you are doing about all that is needed is a little "bump" in the base timing, tightening" up the curve just a tad and get it started right off idle and all-in by 3000rpm's or so. The overlap in that cam is going to favor adding some additional timing at light engine load, probably about 14-15 degrees would be a good place to start. If I were building your distributor here it would have 10 degrees in the mechanical advance (20 at the crank), and another 15 from the VA using a unit that's all-in about 11-12" vacuum. Then I could set the initial timing around 10-12 degrees and move forward from there.

When it comes to these topics I love real World stories so here goes.

Couple of weeks back I get a call from a guy who had his engine built and dyno'd by one of the big names in this industry. He claims it sucks WAY too much fuel for his liking and stinky. Says that on the dyno the folks doing the work had to go UP 3 jets sizes because it was "way too lean" during run-in. I was only getting involved because I sold him the carb kit and tuning parts, someone else installed them. So he's basically bellyaching and at the same time telling me I missed the mark on the tuning parts. So I asked about timing, specifically how much VA timing was being added.

He very quickly and firmly told me that those folks DO NOT use vacuum advance, they just put super light springs in the distributor instead. EURIKA, we have found the problem. You are MISSING about 15 degrees or so timing at light engine load so absolutely and for sure you are going to have to fatten it up some to compensate, problem discovered and solved. However that wasn't good enough and the customer still bellyached about it and told me that those folks have been doing this for decades and NEVER use vacuum advance.

OK, so they do it that way and have to deal with less efficiency and MORE fuel needs to run thru the engine to make it happy.......how is that my fault?

We never worked out a solution and the customer is just going to have to deal with heavier fuel consumption and running richer on the primary side of the carburetor.

As it relates here, vacuum advance is going to be your friend with the 428 engine and camshaft with over 80 degrees overlap. It's going to like, want and respond to a lot of timing at light engine load and be happy with around 44-48 degrees at cruise.......IMHO.

Total timing w/o VA with a higher compression engine on pump gas not so much. The big RAIV cam pushes peak VE up in the RPM range and flattens out the torque curve, which is all GOOD for what you are doing helping to minimize octane requirements at your compression ratio and quench distance. I still wouldn't throw a lot of timing at it and not early in the RPM range. You need to sneak up on thing s like that as it's better to fall a little short than to put rod bearings and pistons into the oil pan, even when they aren't all facing the RIGHT DIRECTION!..........FWIW......

[TRADERMIKE 2012]

Originally Posted by Cliff R

+2

All of these engines have specific timing and fuel requirements and it is worth the effort to spend time in those areas if you want to get the most out of the combination.

Even with that said the parts sold to novice tuners are very poor quality and don't work as advertised. Those "hoaky" HEI kits and "adjustable" vacuum advance units are a perfect example. Complete waste of time/funds and WHY would you use a stepped cam on the BACK side of the VA to control movement when it needs to be on the other side of the arm to stop its total travel......DUH?

In any case, I'll add here that these super-quick timing curves don't cut it. I've removed countless aftermarket spring/weight kits from distributors and set them up with stock parts instead to correct tuning issues with these engines. Dumping ALL the timing on a well-prepared street engine never has worked well dating back nearly 50 years when I got in this hobby and still doesn't work well today. Removing/eliminating VA doesn't work either. Even so countless numbers of these engines are tuned in that manner and folks using those methods are quick to recommend them.

For what you are doing about all that is needed is a little "bump" in the base timing, tightening" up the curve just a tad and get it started right off idle and all-in by 3000rpm's or so. The overlap in that cam is going to favor adding some additional timing at light engine load, probably about 14-15 degrees would be a good place to start. If I were building your distributor here it would have 10 degrees in the mechanical advance (20 at the crank), and another 15 from the VA using a unit that's all-in about 11-12" vacuum. Then I could set the initial timing around 10-12 degrees and move forward from there.

When it comes to these topics, I love real World stories so here goes.

A couple of weeks back, I got a call from a guy who had his engine built and Dino'd by one of the big names in this industry. He claims it sucks WAY too much fuel for his liking and stinky. It says that on the dyno the folks doing the work had to go UP 3 jets sizes because it was "way too lean" during the run-in. I was only getting involved because I sold him the carb. kit and tuning parts, someone else installed them. So, he's basically bellyaching and at the same time telling me I missed the mark on the tuning parts. So, I asked about timing, specifically how much VA timing was being added.

He very quickly and firmly told me that those folks DO NOT use vacuum advance, they just put super light springs in the distributor instead. EURIKA, we have found the problem. You are MISSING about 15 degrees or so timing at light engine load so absolutely and for sure you are going to have to fatten it up some to compensate, problem discovered and solved. However, that wasn't good enough and the customer still bellyached about it and told me that those folks have been doing this for decades and NEVER use vacuum advance.

OK, so they do it that way and have to deal with less efficiency and MORE fuel needs to run through the engine to make it happy.......how is that my fault?

We never worked out a solution and the customer is just going to have to deal with heavier fuel consumption and running richer on the primary side of the carburetor.

As it relates here, vacuum advance is going to be your friend with the 428 engine and camshaft with over 80 degrees overlap. It's going to like, want and respond to a lot of timing at light engine load and be happy with around 44-48 degrees at cruise.......IMHO.

Total timing w/o VA with a higher compression engine on pump gas not so much. The big RAIV cam pushes peak VE up in the RPM range and flattens out the torque curve, which is all GOOD for what you are doing helping to minimize octane requirements at your compression ratio and quench distance. I still wouldn't throw a lot of timing at it and not early in the RPM range. You need to sneak up on thing s like that as it's better to fall a little short than to put rod bearings and pistons into the oil pan, even when they aren't all facing the RIGHT DIRECTION!..........FWIW......

You stated this: " The overlap in that cam is going to favor adding some additional timing at light engine load, probably about 14-15 degrees would be a good place to start. If I were building your distributor here it would have 10 degrees in the mechanical advance (20 at the crank), and another 15 from the VA using a unit that's all-in about 11-12" vacuum. Then I could set the initial timing around 10-12 degrees and move forward from there".

Mikes reply:
I am going by memory so don't Quote me please: I assume you mean after I install the new parts into my dist. or Mill my factory Cam and Weights to a tighter tolerance and using only the factory springs, since you don't favor aftermarket kits.

( MEC. + CENT.) + INITIAL = TOTAL TIMING

10 + 15 + 20 = 45

Note: then set the initial timing to around 10-12 degrees Initial and move forward from there.


You stated:
"As it relates here, vacuum advance is going to be your friend with the 428 engine and camshaft with over 80 degrees overlap. It's going to like, want and respond to a lot of timing at light engine load and be happy with around 44-48 degrees at cruise".......IMHO.

Mikes reply: I have also read this about the 428 ci Pontiac Engine, OfCourse, we don't ever see these numbers while tuning, because we are not at cruising loads to WOT.

I have just found a site on the Internet:

https://www.motortrend.com/

That shows many of the old magazine ads and their books that you can view (for free) along with many more informational resources to add to your collection.

This is what I found interesting: Does this relate to our Pontiacs?

The Chevy 427 ci Engines (ZL-1 and L-88) factory suggestion is that you maintain a finished, everything installed air gap of about 0.035" between the closest points of the Head and Piston top.