[AdamIsAdam]

I thought it would be helpful to carry over a few detailed posts from the other thread:

Originally Posted by Cliff R

Here's part of an email to Adam, but it fits well here since we've pretty much turned this into a tuning thread:

"The order of tuning goes like this.

First find total timing, drag strip, dyno, seat of the pants, etc, without detonation.

Then find the initial timing the engine likes the best. If it likes 36 total and 16 initial, then a 20 degree mechanical curve is required. If it likes 36 total with 12 initial, then a 24 degree curve will be required, etc.

Tune the idle mixture screws with each test of initial timing to find out where they need to be, and make sure to do some fully heat soaked cranking tests to make sure it’s not “bucking” the starter.

Next add in vacuum timing (I use and prefer ported for most set-ups) and do some light throttle cruising and fine tuning the APT if/as needed for best results.

This part of the testing may take several tanks of fuel once you get close, but you can nail down the very best performance and fuel economy with this part of the testing.

At this point you have a choice as to add it initial timing via the VA with manifold vacuum for more timing at idle. This may help with some set-ups, typically those with not enough compression for the cam choice (low vacuum at idle), but is seldom if ever needed on an engine with a well chosen CID/compression/cam combo."

The reason we find total timing first, is that we do NOT want to damage the engine moving the distributor around trying to find initial timing. Detonation will destroy the best prepared shortblock, so we want to find the ideal total timing at full load before we start tuning the mechanical and VA.

The only part of tuning that leaves us with is how quickly the timing curve comes in and at what rpm it reaches full advance. Most engines don't want or need ALL the timing in right off idle, but to this day I continue to see folks installing "kits" that get total timing in really early. In almost all cases, the curves as so quick and springs so light that some of the timing is actually in at idle speed, which makes idle tuning difficult, if not near impossible, and for auto trans cars this causes a HUGE drop in engine rpms when the trans is placed in gear (sound familiar?).........Cliff

Originally Posted by PontGuy

Just one more thought from me (at least here).

One thing not discussed is what the actual mechanical advance curve looks like and how well it "fits" the engine setup. I worked with SunTuned to optimize the points distributor for my Lemans engine and the attached shows the difference in the original curve and where we ended up. The engine hated the original curve and there was no amount of base timing adjustment that could make it run really right. The curve that we ended up with is actually more aggressive than the target that we were aiming at but it turned out to be just about perfect for the engine- given the lazy cam lobes, 9.5:1 CR, etc. I set the initial at 10-12 deg and it manages 14 deg vacuum advance on top of this without any problems. The engine runs cool here in hot Georgia summers with just a 15+ year old 4-core stock replacement radiator, and never any pinging anywhere.

I don't think the curve has anything to do with your surging problem, but its always worth recording mechanical advance values at different RPMs to see what you are working with at least to make sure it is reasonable.

A sticky might be useful for the basic tuning process and guidelines for a "typical" stockish Pontiac engine, but agree with Cliff that it might result in a lot of opinions and opposing views once you get past that. I just don't think there is a magic formula that covers all of the various combos that we are working on, many of them far from optimum. Case in point- I tried a similar curve and base timing on my TA engine when I first started tuning, and with the XE cam it wasn't close to right.

Originally Posted by Cliff R

Tuning distributors then setting them up on an engine is pretty much like carburetor building/tuning. They must be set up exactly for the application. Sounds pretty much like an easy/blanket statement, then you have to consider that nearly every engine combination is different, and some folks have done a far better job of choosing their parts than others.

We used to get into heated debates with several folks on this board on this topic. Most have left and some still lurk around with PM's to nearly anyone who runs a thread on this topic. Probably for the better, because I spent more time on the crapper last week than most of these folks have in total experience with these things.

Not really, but you have to remember that I do this FOR A LIVING, and have tuned thousands of different combinations at this point in my learning curve.

You are NOT going to solve the issues with all of them by simply buying a Crane adjustable vacuum advance, running really light spring tension so the timing you add it at idle doesn't fall out, then advancing the timing till the engine smooths out to find the "ideal" timing point for that engine at idle.

This topic is far more complicated than that, and anyone who does that will NEVER get thru emission testing if their car is still subject to it. I'm not saying here it doesn't work, but more times than not it's just a "crutch" to make up for a carb that's lean at idle, or engine that is a poor air pump at low rpm's.

Tuning MUST be done to both items, carb and distributor to get the best overall end result. It's nothing but a "crutch" to advance the timing clear off the scale to make up for piss-poor dynamic compression, too much overlap, LSA too tight, and carb to lean.

What I have always done, and recommended for this topic if for folks to either seek professional assistance, or spend the time and funds fine tuning the carb and distributor until you have found the very best settings for your engine.

Some engines will like, want, and require a LOT of timing at idle speed. The lower the compression, bigger the cam, and greater the squish area, the more you are going to have to lead the timing and more fuel you are going to have to add to get a clean burn at idle speed.

Other engines, with very well chosen parts, tight squish, higher compression, optimum cam timing, etc, will not want, like, require or even respond well to a lot of timing at idle speed, or anywhere else.

My own engines and most of what we build here fall into category number 2, so we do not have to get stupid with initial timing, or super-quick advance curves that get all the advance in by 1500rpm's, then have to add a bunch more via the vacuum unit to make them happy.

I've put this clip up here many times, but notice while you watch it how smooth the engine idles, smooth right off idle, and clean it is across the entire load/speed range. I run 10 degrees initial timing, 20 degree curve all in by 2800rpm's, and 10 more degrees to the VA via ported vacuum. My engine doesn't like, want, need or respond well to more timing at idle. Moving the VA over to manifold vacuum actually puts a very slight "skip" in the exhaust note, where on ported it idles smooth and steady, and the rpms barely move at all when the trans is placed in gear. Some may ask "why" at this point, as my engine has a hefty size HR cam in it with nearly .630" lift. It's about compression, very tight squish and carburetor that is tuned exactly for the engines requirements at idle speed. I'll also add here that I cool this engine with a stock 3 row Modine replacement radiator that's at least 30 years old, stock water pump, stock pulleys and stock "worn out" clutch fan. The engine doesn't even think about running hot, it actually does just the opposite, it takes nearly FOREVER to heat up, especially in cool/cold weather.

https://www.youtube.com/watch?v=6zVdoLR-VzM

Another thing I notice while we're on the subject is that more often than not, engines that fall into category #1 above tend to run hot, overheat, detonate, and REQUIRE a ton of timing to make them happy and minimize these negative attributes.

So combustion efficiency is a big player in this deal. If you find yourself having to run a lot of timing on your engine, and temps creep up in warm/hot weather, or it tends to want to run 200-230 degrees on long runs on hot days, or temps "creep" up that high at stoplights, there is a root problem.

Without exception ALL of the Pontiac engines we've had in our shop that ran hot, overheated, pinged, etc had a LOT of quench in them. We've also had a few in here that had those cheap 3 keyway timing sets installed in the +4 keyway and/or "modern" cam profiles with advanced intake closing points and tight LSA than ran extremely hot.

Quite a few years ago we worked a 400 than just ran hot no matter what we did to it. Kind of a neat story, if you don't mind a lengthy read, but it was early in my learning curve so I spent the time to figure it out.

It was a fresh 400 engine build, stock cast pistons way below the deck, 6X heads, and Ultradyne cam from Butler. This engine ran quite well, but just too hot, and the longer you ran it the hotter it would climb (sound familiar?). After doing ALL the basic carb and distributor tuning, trying MVA and all amount of timing everyplace we moved on to deeper issues. First, we installed a 4 row Desert Cooler, didn't help much. Upgraded to a 7 blade fan and HD clutch. Then we upgraded the 67 timing cover/waterpump to the later design with different pulleys to speed up the water pump.

After all those changes we were able to pull the temps from 230 plus down to about 190-210 on long runs. I still wasn't satisfied with the results, feeling that we more or less "crutched" the situation and didn't address the "root" cause.

Anyhow, just for the heck of it I removed the timing cover and retarded the camshaft 4 degrees. Not sure to this day why I did that, but we were nicely rewarded with an engine that ran too cool, took nearly forever to heat up, and didn't even think about going past 180 degrees for any reason!!!!

Wow, all that money and time spent and the entire time it was a combination of too much quench and cam timing. I didn't know at that time that the quench was a big player in the deal, but did figure that out a few years later on another 400 with similar issues.

Anyhow, I'm not sure if a tuning section would really be all that helpful here, the basics of this deal aren't all that overly complicated, but the combinations of parts folks come up with continue to amaze me, and with all the good information out there on engine building, and tuning, etc. If I can offer advice here, it's best to take steps early in the game to come up with a more favorable outcome. Building an engine and doing things during the rebuild to improve efficiency pays big benefits later on, rather than to throw a bunch of parts together then find out it idles poorly, runs hot, overheats and you have to go thru all sorts of hoops to correct all the issues......FWIW......Cliff

Originally Posted by Squidward

Adam, I set up my timing similar to yours. I don't have as much vac advance, tho, like 17 max. Geoff from across the pond had PM'd me to help me accomplish pretty much the same thing.

I like the MVA setup that he PM'd me. It was one of the more comprehensive attempts to give me some setup instructions. Let's face it... I had little to go on, so he stepped in and gave me way more than any other advice I had received before. My car ran way better than at any other time, and it helped me understand some things. I thought he was helpful.

I'm running a 220/227 cam in a 350. It idles nice at 700 rpm. Compression is 9-something. It runs a little hot, so I am am willing to revisit my timing and tune once I get my cooling system bulletproof.

IIRC, while monitoring my truck's 5.3 LS with a bluetooth plug-in and android app, advance at cruise was something like 47*. I actually plan on plugging in again and I want to plot out some timing on that engine over various operating conditions.

If anybody has anything to offer up other than "drive it until it pings, and then back off 2 degrees", then I'm listening. What's unfortunate for those of us NOT in the know is that those that ARE in the know might risk undermining their professional livelihood. I get that.

Maybe a timing/tuning sticky thread is in order. It would be nice to have some of the experts hash out some details, like how to set optimal initial, mechanical, and vacuum advance. It would be nice to know the goods and bads of too much or too little timing, like "runs hotter", or "less power", etc.

Even things like mechanical advance: how much to add and why, because that will influence where the initial has to be for WOT. Should mechanical timing come in early or later, and why? What is the upside/downside of either? Everybody has heard of the magical 36 total init+mech, but the mystery comes in what proportions and at what rpm.

If someone wants to lay out how THEY would set up each facet of timing (init, mech, and vac) and what parameters they use for optimum determination (idle, manifold vacuum, etc.), then I'd say start a thread with your technique. And then others can offer up their technique along with their "whys".

THAT would be a gift to the community.

Originally Posted by PontGuy

Now you are heading in the right direction.

I've adjusted the APT on my Lemans carb as much as 1-1/2 turns richer from where Cliff had it set and per my wideband this resulted in less than 1.0 richer cruise A/F ratio. So don't be afraid to turn it. But record the changes you make so you can always go back. FWIW After a few thousand miles and tuning to get everything optimized I ended up with APT set exactly where it started.

A bit embarrassed that I assumed the head cc numbers were correct in calculating CR. At least I wasn't alone.

So at the end of the day your setup is not all that much different than the engine in my TA with the XE 268 (except you have the nicely ported heads). My seat timing is even shorter than yours and tuning has been pretty tricky but it is running pretty good now. As mentioned I have a 10 degree vacuum can on that engine. More than that would be asking for trouble. Yes it still tends to run a bit hotter than I like, and yes the oil pressure is lower than I like when it gets over 200 deg during a long hard run in hot weather. Sound familiar?

If the engine won't crank with more than 13 deg initial and the engine wants more timing then suggest you invest in a mini-starter, or get the distributor reworked to bring in more mechanical timing. Trying to add timing with too much vacuum advance isn't the way to go.

Originally Posted by Cliff R

Couple of comments in the FWIW department.

Right to start with the cam is too small and LSA too tight for a 469cid engine with 10.4 to 1 compression. It's going to be sensitive to total timing, especially at light throttle cruising.

This will cause several things to happen. First, the engine will not like or want a lot of timing at cruise, so ignore the PM's from the "part timers" and forget the nonsense about trying to find a "sweet spot" by adding in 22 degrees of vacuum advance at idle speed then ending up with nearly 55 degrees of timing at light throttle cruising.

Second, there isn't one ounce of difference once you move the throttle an 1/8th of an inch running ported vs manifold vacuum to the advance provided you are using the ported source in the main casting. Both sources are FULLY uncovered and providing the same exact vacuum to the distributor off idle, light throttle cruising, and any heavy or full throttle.

The ONLY difference is at idle speed. If your engine wants, likes or requires a LOT of timing at idle speed then use manifold vacuum to the advance.

Most of the "quirky" symptoms you are getting from the engine combination is the cam choice. It's simply too small and LSA too tight for that much engine with that much compression. I've tuned a number of them and the symptoms you are getting are pretty much on par with what I've seen here, the XE274 camshaft is a piss-poor choice for a 455 build right to start with. It leaves too much power on the table and builds too much cylinder pressure too early in the rpm range. It might work OK at 8.5 to 9 to 1 compression, but will not work well, or at least not nearly as well as a bigger cam on a wider LSA over 10 to 1 compression.

These days I usually just sit back and watch these threads run, because telling the truth quickly gets me labeled as the Comp XE cam "basher".

Anyhow, in lieu of changing the camshaft, do the following things instead.

Unhook the vacuum advance and time the engine to where it makes absolutely the most power everyplace when you are running it hard, heavy and WOT throttle. Play with the advance curve and initial and total timing. A dyno or drag strip would be the best place to do this, but you can get close on the street. Use the fuel/octane that you plan on running all the time, nail down the mechanical curve, initial and total timing and be done with it.

Next, reduce the travel of the vacuum advance unit to about 10-15 degrees and start tuning with it. MVA or ported really doesn't matter, if it idles cleaner on MVA then that's fine, but try both places and fine tune the idle mixture screws accordingly.

Next, remove the set screw over the APT and raise it up slightly, about 1/8th turn CCW at a time and dial in the part throttle A/F for smoothest operation at light part throttle/normal driving. To really nail down the part throttle A/F and tune I would also make changes to the VA unit and vary timing added between about 10 and 15 degrees till you find the "sweet spot" for light part throttle operation. Keep in mind here that ported or MVA is exactly the same when doing this, the only difference is that MVA adds timing at idle and when coasting, otherwise no difference.

Give this stuff a try and let us know what happens. I really wished you were closer, I could nail all this down in less time than it took me to type this!.......Cliff