Thoughts on tuning engines

[Sharps40]

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[Sharps40]

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[Sharps40]

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[luvbowties]

Originally Posted by Sharps40

So, what to do about it? Well we broke in the new motor at 8 degrees advance. But it wouldn't run well or strongly there. The carb was still jetted pretty lean over all....that quest to balance power and economy + delayed relearning of the basics could equal Bang went the pistons, 4 times in succession.

Don't want that again. So back to the board.....new motor would only run well at 18 degrees BTDC. And when I fixed the upside down and backwards PCV valve, Wow did it run better. Started pushing 16.5 mpg (up from 14 mpg) and somewhat better power and responsiveness.

But....its hard to read hot plugs with an HEI. The indicators of rich or lean is so subtle...sometimes only a kiss of tan on the tip of the insulator. I am finding the best indications of fuel ratio on the electrode and base of the threads. But I richened up the mains and secondaries on the carb, while still at 18 BTDC and the plugs started to tan out slightly and responsiveness improved and fuel mileage went to about 18 mpg combined city/highway.

Now the T5 is a wonderful tuning tool....if a bit expensive. A .76 overdrive gear gives you a wonderful feel for the engine output, at low speeds pulling back up and climbing hills on the highway. Little changes in the carb adjustment and timing can be felt in stroke of the pedal and the ease with which the motor pulls.

Figuring the new 18 mpg results and slight tanning of the plugs, responsiveness, etc were an indication I am finally tuning in the right direction (and had all those pesky vacuum leaks fixed....and it don't take much overpressure in the crankcase to push oil out past the rear main!) I decided to actually retard the initial timing.

18 degrees of advance is 4.5 times the factory recommended initial advance of 4 degrees. Its dooable...proven many times on many engines....but it probably needs high grade fuel (and think about it, 87 to 93 octane ain't much improvement!) and really needs exhaust monitoring to ensure the motor is not lean at critical times. Really, 18 degrees dosn't seem to provide much margin for error. And one of my first indications of trouble with this setting was kick back against the starter on hot restarts cause I certaintly was not hearing any ping or detonation....but I am a bit hard of hearing and the truck is a bit rattly noisy.

John Lee was running so good now that he's leak free and a bit richer overall I figured what the heck....lets see what 14 degrees BTDC will feel like.

Well! I am pretty darn pleased. Fired right off cold and settled into a smooth 750 rpm warm up idle. Previously, its been taking just a bit of cranking to get up an running, hot or cold.

And the ride? Suprisingly, the power, performance and overall feel is the same, or perhaps slightly better at 14 degrees BTDC. I am pleased enough with the feel that by the weekend, when its time for a new tank of midgrade (I alternate mid and hi test each tank) I intend to drop initial timing to 10 degrees BTDC and go driving.

I don't have an O2 gage yet...and I realize an HEI and Weber progressive both want more initial advance. But there are no reliable numbers out there for just how much total timing a Chevy I6 wants so, like carb adjustments....I'll proceed with timing conservatively untill there are performance issues and then retweak slightly in the other direction.

With luck, I'll increase my margin for error/poor fuel and maintain the performance I've gotten used to with this ol truck.

This is very interesting, as I have loved tuning since, as a kid too young to drive(could get driv-lic here in SC back then at 14 years old), I experimented on a '48 Chevy by hooking up 2 coils to see if my friend could make it go faster than 88 mph. It ran no faster, but no slower either; needless, but I was disappointed. So, how much total timing is the hei giving you? Have you modded the hei so as to shorten the total advance?

I recall my younger days when we bo't the Chevy F/I dual-point dist(IIRC, pn 1110891, complete, brand new from Chevy, w/points & cap, for $24 plus some cents!); we'd add brass to the mechanical wts. to increase centrifugal force & bring total advance in quicker; we'd stretch the weight-springs to help also. Then, we'd put brass on the tang that protruded thru a slot, so as to limit total advance. We'd then file, grind the brass until we got a total 'swing' of an aimed-for 20 degrees. With an initial timing set on 14-16 degrees--wherever the 283/327 liked it best, as determined by the starter kickback--that combo of 34-36 degrees gave us the best of both worlds: high initial timing to get out of the hole plus a held-back total advance on top end(to eliminate detonation)to allow whatever revs/rpms the engine was capable of.

It was always a curiosity to me when I'd go into a dealership & get permission to use their distributor machine to read specs, known by us as "degrees", as I filed/ground brass & spun it up again to read new specs after brass-removal. What caused the curiosity was the svc mgr and some mechanics watched in amazement, as they had NEVER used this function of the machine--seems like maybe someone had once preset dwell before installing a dist! So often, there was a generous supply of dust on the machine from non-use altogether.

My 1st attempt at this, I was nervous as a long-tail cat in a room full of rocking chairs; as all I knew was what I had read, & was afraid I was gonna goof up somewhere for all to see & to laugh at that 'kid who thought he was a know-it-all'--and was just a theorist who probably couldn't even properly install a dist, setting on #1 on comp.-stroke! But, it worked out well & made my car feel really like a proper, new, hi-po cam had just been installed.

This modded dist. performed fantastic, was much cheaper than Mallory racing dist's., and only drawback was a little hit on the gas mileage. But, at 31.9 cents per gallon, who minded that?

If any info above is found to be inaccurate, please know that when I was doing it was just about 49 years ago!

And, Sharps40, pls. continue with this re-newed information. Already, it oughta save someone from busted pistons, "several times in succession"!

sam

[Sharps40]

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[PGSigns]

Well a couple of things I don't see in your tune up are total advance and the plug you are running. The HEI has little to do with the plug color as the way fuel is blended now does not leave the old school colors any more. From what you have listed in your list of tune up that you call aggressive I would call a fast road to a problem. One your HEI you need to look at the vacuum pot to see how much advance it will pull in and also ensure that the source of the vacuum is ported and not manifold. your advance curve is important. No more than 32 to 34 degrees of total should be run. Once you have your timing worked out then you need to look at the jetting. Who ever told you the story on the fuel killing even low compression engines is telling you a story. Very high timing and a lean mixture killed your engine with it detonating a good bit of the time. Just my thoughts based on 40 years of working on cars and 30 of those drag racing and tuning engines making a 1000 hp or more.
Jimmy

[Sharps40]

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[PGSigns]

Well the vacuum advance units are marked most of the time. It could be 12 degrees or so and since you checked it with it unhooked and got 35 you could be at well over 40 driving down the road. Got to remember that the initial just gets it running and puts it in a good place at idle to not build a bunch of heat. What you have under load running down the road is what counts.
Jimmy

[Sharps40]

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[Sharps40]

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[Sharps40]

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[Sharps40]

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[Rich 5150 69]

Just a thought I would touch on sense you had replaced pistons is your quench area, if its to wide this will limit timing and cause detonation, you can control some with head gasket thickness, and or piston design, newer gases work better with the d-cup pistons, with a quench of in the neighbor hood of 25 to 45, some of this work may require zero decking the block to achieve the desired piston to deck height.

[Sharps40]

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[PGSigns]

"They say part throttle up to 50 (initial + vacuum + mechanical) on a stock motor." Not sure who they is but they are full of something from a bulls back side. What Rich is trying to tell you is that the piston design along with the shape of the combustion chamber have a lot to do with how much timing you can run. Some shapes are more tolerant to timing and some are not. You just can't say for a stock engine. If higher octane fuel is getting rid of the ping you can hear then there is to much timing in the engine at that rpm and throttle position. The higher octane burns slower and that is covering up part of the problem. There is still detonation going on that you can't hear. Every engine has its limits and its sweet spot for timing and fuel that makes it happy. You can not compare any two unless they are the same combination. Here is something to ponder. In the late 70's I was a boat mechanic. They way we would set the final timing in the 6 cylinder Mercruisers was to run the boat wide open down the creek and adjust the timing till we got max rpm out the engine and then backed it off a couple of degrees to keep it safe. Same exact engine in lots of different boats and they all had a little different timing. And they were all Chevy 250's.
Jimmy

Jimmy

[Rich 5150 69]

Originally Posted by PGSigns

"They say part throttle up to 50 (initial + vacuum + mechanical) on a stock motor." Not sure who they is but they are full of something from a bulls back side. What Rich is trying to tell you is that the piston design along with the shape of the combustion chamber have a lot to do with how much timing you can run. Some shapes are more tolerant to timing and some are not. You just can't say for a stock engine. If higher octane fuel is getting rid of the ping you can hear then there is to much timing in the engine at that rpm and throttle position. The higher octane burns slower and that is covering up part of the problem. There is still detonation going on that you can't hear. Every engine has its limits and its sweet spot for timing and fuel that makes it happy. You can not compare any two unless they are the same combination. Here is something to ponder. In the late 70's I was a boat mechanic. They way we would set the final timing in the 6 cylinder Mercruisers was to run the boat wide open down the creek and adjust the timing till we got max rpm out the engine and then backed it off a couple of degrees to keep it safe. Same exact engine in lots of different boats and they all had a little different timing. And they were all Chevy 250's.
Jimmy

Jimmy

Boy Jim I remember those days, lay on the fender of my `65 chevelle, had friend keep in first and run down the street til we brought the rpms up and dial in the dizzy under load...fun days....LOL

[Sharps40]

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[Sharps40]

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[gimmy 64]

I can't say about the 6 but I know on a chevy v8 they like 32-36 degrees . But all in at 2500 rpms.maybe that's what you need to check.where the advance is coming in at and where it tops out at? I know --from experience that a lean situation will blow engines.a little fat on the carb won't get you great gas mileage but the motor will be in one piece !!!!!!!!!!

[Sharps40]

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[PGSigns]

Well all in at 3500 may work for an engine that turns 5500 a lot. Timing needs to be all in in a spot you can use it. If you shift the truck at 3000 most the time for daily driving then it needs to be in by then. You keep bringing up this is a 6 and not an 8 so think of it this way. The engine does not know how many cylinders it has so just because the 6 has 2 less does not mean things are different. Look at it this way you have 6 single cylinder engines that are working together. Problem is the single carb and a poor way of getting fuel to the engines on the end of the line. So 2 of your engines are real happy, 2 are doing ok but could use a little more fuel and the 2 poor suckers at the ends are really hating life with the lean mixture. Now you have to find the happy median where the cylinders on the ends are getting enough fuel and the timing is working for them. The ones right next to the carb are going to be a little fat but thats ok. All this was solved when they went to coil packs and direct port injection and now all the single cylinder engines bolted together can be tuned on there own.
Jimmy

[Sharps40]

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[66Submarine]

Just a note about all the "bad" gasoline. I call BS. Ethanol has much better anti-knock properties than gasoline; that's why pure ethanol and e85 are used by hotrod/racing guys. Refiners are also said to like it because they can use a lesser grade of gasoline and make up for it with the high-test ethanol. 87 octane is 87 octane. A lot of so-called "engine builders" can't build an engine to run down the driveway without putting a rod through the pan, and I would guess that's what you are dealing with if they are trying to cover with that excuse. Now, if someone has something built/setup for 93 and goes out hammering it with 87, sure, damage will probably occur. But that's because of octane/antiknock rating, not ethanol itself.

Now, I don't care for the ethanol stuff myself, but that's not the reason I don't like it.

For evidence, here's a clip I came across of a supposedly 1,200WHP 540BBC powered sand truck running on e85. Skip forward to about 1:00 in the video; looks like it works OK to me.

Team English Racing 1200 WHP Twin Turbo Sand...

[Sharps40]

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[PGSigns]

One thing you also have to think about is higher octane than needed hurts power. The higher octane usually goes along with higher compression and is used to slow the burn rate down. So running more than needed will hurt power. Not sure what Jeep the wife has but it should not ping on todays fuel unless something is out of wack. A weak injector will do it along with some other things.
Jimmy