YR,
The later heads have the 5/8 taper plugs. I will pick up some different plugs and try them out.
Cruise Seems Lean
- Thread starter 71GSSDemon
- Start date
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YR,
The later heads have the 5/8 taper plugs. I will pick up some different plugs and try them out.
This is why I was wondering everyone's thoughts on it being lean, running very hot, and slight surge but only at about 2400. 4000 seems fine, but lots more fuel being dumped in too
Update. I found a couple cooling system issues that weren't helping. When removing the radiator, I found there was a slight bit of trans fluid that leaked out of the lower radiator hose outlet when removing it. So, that tells me there was internal issues with the radiator I was using. Also, there wasn't enough wrap of the belt on the water pump pulley. With the radiator out, I couldn't get the belt tight enough to "grip" the pulley with the belt. It turned by hand with belt tight really easy. So, I will be waiting for the new Cold Case 26" radiator and redesigning the alternator bracket to get more engagement on the pulley. The crank pulley is ~ 7" in diameter while the water pump pulley is ~ 5.75" in diameter.
Its possible to be too lean as one circuit tapers off and the other tapers in. Higher load reveals things that are covered with high gear ratios and high stall converters.
Even more common (too common) is too much advance between 1600 and 2800 rpm, even though its fine for the upper rpms.
I'm not saying either of these is the what you experienced, but they fit the symptoms.
Get things fixed up and go from there.
Thanks I will and keep this posted as to what is going on.
512Stroker
We are all here because we are not all there.
Food for thought
What happens when your all in timing (say all in @ 3000 rpm, pretty common) is way above the cruz speed @ 2400 rpm and/or compound it and throw the convertor stall speed on top of it all ?
512Stroker
We are all here because we are not all there.
Well then, I think you already know what you have ahead of you.
Good luck
I am not sure. I have a 2400 stall. I was concerned that if it were slipping a bit yet at that cruise speed maybe it was causing a ton of heat too..
yellow rose
Overnight Sensation
Ok, didn’t know the later heads went to the tapered seat plugs. I’d still lose that plug with the huge ground wire on it. All it does is hold heat.
yellow rose
Overnight Sensation
I just looked it up. I didn’t see any big block that takes a tapered seat plug. Again, I just make a quick look but I don’t think that head takes a tapered seat plug unless it’s an industrial engine or something. Again, I could be wrong but I’ve never seen at tapered seat plug in any big block head.
Just trying to sort the plug situation out first. That’s where you need to start. With the right plug. Doesn’t have to be a Champion. I’ve been using them since 1972 so that’s what I have the most experience reading. Any plug with the correct architecture, a single ground wire and the proper heat range is fine.
The later 70's, mine is 1978, some of the RV heads have added cooling passages in them. They cast a bump in the head to ensure people use the correct spark plug. They are the smaller 5/8" socket taper seal peanut plugs. Just an example below for 440 engine. Looks like an Autolite 85 will work also.
When the mechanical advance continues above cruise rpm, that's OK. Mechanical advance is to compensate for the increasing speed of the crank and pistons until the improvement in flame development is so good that it matches the increase in engine speed.
A torque converter's relationship to engine load is something I don't have a great understanding of. If we take the stall speed as brake speed, we can say its similar to letting the clutch fully engage. But we also know that stall speed varies with torque. Under light load the 2400 stall converter will be driving the transmission with only small loss at 1400 rpm, and on the other side if we put that same converter behind a more powerful engine and do a brake stall test, it will go to 2600 or 2800 rpm.
So from the above, I would have thought that torque converter had little to do with cruising loads.
However after I had T/A tighten up the torque converter for my Barracuda, the car had issues with pinging at cruise along with some dead spots at heavy part throttle.
Now it also happened to be that the mechanical timing was all in early with that distributor. When used with the vac advance, the pinging at cruise was always in this range.
It happened even at low speed (50-55 mph) flat terrain after an hour or two on the road. Was this due to just the distributor, or also due to the change in the converter?
I still don't know for sure. And since the was down for a year, did changes in reformulated fuel at that time play into the equation?
Below is a graph of the timing where it pinged with red highlighting the problem rpms.
It shown in relation to the timing that it now has with a different distributor.
The factory always had the timing continue advancing well above typical cruising rpm.
Max and min here are refernces to the advance curves. Base timing could be set higher or lower as fuel and altitude permitted. That would shift the timing curve up or down.
The exception was for drag race only, running with no vacuum advance.
But even in drag racing, the tach drive distributors are set up with one heavy long looped spring to allow a slight increase with rpm when used with a quick ECU.
My coworker had experimented with removing that spring (because that trick had worked with the dual point distributors) and after many disappointing runs had put it back in and started hitting their times again. However a large portion of that relates to the time lost in the electronic switching.
I mention the drag racing because almost certainly that is where the remove one spring, all in early, clearly started.
512Stroker
We are all here because we are not all there.
We bad for stepping on the OP's topic, but it all goes hand to hand.
I may be way off here, but I find it a delicate balance between all in timing, convertor slippage, gearing/tire size vs cruising speed.
I have tried to get the all in timing just below the stall speed and the cruising speed determined by gearing/tire size that it happens at a point where the engine is happy while a around 70 mph.
I also run a vacuum advance just to complicate things.
I am at a point now where everything is working well together and the car performs well so I have decided to muck things up as I am having and overdrive tranny built for next winters project.
Sometime I am my own worst enemy. LOL
Being the OP, I am very interested in all parts of this discussion. Gearing, cruise speed/rpm and outside temp/engine temp is what changed from a very nicely working combination. In my attempt to make the trip easier on the car and me, I did the gear change. Then it also got very hot out. Literally was high of 50 degrees a week prior to 105 degrees this past weekend of the cruise. It is hard to tune for that change and never cruising a distance like before, there were unknowns. Timing could definitely be a factor as cruise used to be 3000. I am open to all discussion in regards to possible issues. I am learning. Lets go down the rabbit hole.......Thank you everyone.
yellow rose
Overnight Sensation
Ok...RV head. If that Autolite plug has a black shell find another plug. You can’t read he she’ll when it’s black like that. It’s needs to be cad plated like a Champion or that gold stuff that NGK uses. Autolite makes plugs without that black coating.
So, I will look into Champion RV12YC plugs unless someone thinks otherwise
512Stroker
We are all here because we are not all there.
That would be a good one to start with.
I use Autolite 63 plugs
If you wish you may want to try a 64 to help burn off some of the crust that formed on your current plugs.
yellow rose
Overnight Sensation
Or the NGK equivalent would be fine too. Any plug, as long as it doesn’t have that black coating is ok. I’ve used some AC Delco plugs that had a cad based coating and they were pretty easy to read.
Regarding timing, rpm, load, and torque converters, I'll offer some snips and links for discussion.
In response to my questions about timing, Tuner wrote:
"An engine used for circle track or road race is operated in a fully thermally soaked condition, as is a highway car, and cannot stand, does not require, the "all in at xx??" curve, they want the best timing for best torque at the torque peak RPM and then continuous advance to more timing which gives best power at the power peak. The rate and amount depend on C/R, chamber design and manifold pressure, restricted carb or not, etc."
With respect to too much vacuum advance when cruising:
Q. What happens if the maximum vacuum advance is not limited?
A. "It feels like a lean miss or surge. It may be an occasional hard miss like a bad plug wire, or a gentle surging that sort of nods your head. A common euphemism for the sensation is "trailer hitching" because it feels sort of like a 2" hitch on a 1&7/8" ball.
In all circumstances, the object of ignition timing is to peak the cylinder pressure at or near 15-20 degrees ATDC."
In sum:
"The advance schemes I suggested...will work OK for most engines with old school combustion chambers, Mopar, Ford or Chevy. The outliers are the fast-burn chambers whether new or old. Pump gas makes it particularly obvious because it is so easy to get knock. A fast burn chamber will need a less mechanical (RPM compensated) advance, but may need correspondingly more in vacuum (load compensated) advance, particularly if a large amount of cam timing overlap results in more EGR. The need for vacuum advance is related to the slower burn of lean A/F but the effect of exhaust dilution at high intake vacuum is a significant reason for requiring more advance."
In response to a question about setting up an FE, Tuner had pretty much the same thing to say:
"The FE and many other engines want more timing after the torque peak RPM than the amount which gives best torque at the torque peak. Your engine with the 224°@.050 cam will have peak torque at about 3000 RPM.
If you are using high octane fuel, like Avgas or race gas, it is not so important to slow the advance curve to avoid detonation although it will probably run better if you do.
Drag strip only use a fast curve is tolerated because an engine is never loaded at mid RPM for sustained periods like it can be on the street or oval and road racing. The longer duration of load at any RPM increases the temperature of chamber and piston surfaces and the heat speeds combustion and so does not require or tolerate as much advance as the same engine used in only few second bursts at a drag strip."
I know most people reading this don't know Tuner (except YR) so as far as you know he could be a keyboard guy making stuff up. That's why earlier I mentioned a few of the road race cars he helped the owners with. He prefers to go just by Tuner on the internet, and I will respect that.
Bruce "Shrinker" Robertson" Regarding initial timing:
"If you enrich the mixture at idle it will require less timing and the volume of gas expelled from the chamber will be greater (because there is more fuel in the cylinder ). The greater volume exhausting resists reversion backwards up the exhaust port therefor it actually runs with a cleaner chamber. Funny stuff isn't it"
"BUT what you have to do is enrich it correctly with the right processes in the carburetor, sometimes it's not just a matter of winding out the idle screw or changing the IFR. Every engine has a design to it and Chrysler's are a bit different to the other US products, they are not chevs or fords, they are better. They have better combustion and its not necessary to follow the rules of the hotrod industry, as the industry is very Chev orientated. Now what i just said should get plenty of people jumping up and down( hopefully in fun)."
from here: Motorsports Village • View topic - Initial timing
Shrinker may make your brain hurt, but I appreciate his way of approaching thing even though I'm not even in the same league of understanding, experience or knowledge.
"Tuning is the process of visualizing the progression of combustion and its conversion to mechanical energy."
He provides a stage by stage explanation of the combustion in this thread about dynoing a 440. Reading this you can see why even a single groundstrap shadow can play a role in flame development.
Motorsports Village • View topic - Dyno time
Finally, here's a case (non-mopar) where he warns that cruise timing and AFR could cause problems when going to full throttle. But I don't think 71GSSDemon's engine is in this situation but maybe worth keeping in mind.
"Your engine has a big cam for that low a compression so I'm not going to get into helping you tune it. My advise is to be careful about the tuning because if you go the wrong way you will end up making NOx at light loads and damage the engine when you stomp on it. If you run it rich it will be safe and the reading on a WB cannot always be trusted. If you used a gas bench and a dyno you will find that engine has plenty of unused Oxygen in the exhaust and thats a bad thing, it means there is unused hot Oxygen's left in the cylinder and thats dangerous,thats why you need to be rich and no where close to stoich. Pick the wrong ign timing at cruise and you will have hot carbons glowing waiting for you to open the throttle and give you some preignition woes. So id put up with a rich cruise, maybe not as rich as you describe but more in the 12.5 12.9 range. I wouldnt advise to go leaner than that unless gas bench and dyno confirmation showed otherwise."
http://motorsportsvillage.com/forum/viewtopic.php?f=6&t=915
In response to my questions about timing, Tuner wrote:
"An engine used for circle track or road race is operated in a fully thermally soaked condition, as is a highway car, and cannot stand, does not require, the "all in at xx??" curve, they want the best timing for best torque at the torque peak RPM and then continuous advance to more timing which gives best power at the power peak. The rate and amount depend on C/R, chamber design and manifold pressure, restricted carb or not, etc."
With respect to too much vacuum advance when cruising:
Q. What happens if the maximum vacuum advance is not limited?
A. "It feels like a lean miss or surge. It may be an occasional hard miss like a bad plug wire, or a gentle surging that sort of nods your head. A common euphemism for the sensation is "trailer hitching" because it feels sort of like a 2" hitch on a 1&7/8" ball.
In all circumstances, the object of ignition timing is to peak the cylinder pressure at or near 15-20 degrees ATDC."
In sum:
"The advance schemes I suggested...will work OK for most engines with old school combustion chambers, Mopar, Ford or Chevy. The outliers are the fast-burn chambers whether new or old. Pump gas makes it particularly obvious because it is so easy to get knock. A fast burn chamber will need a less mechanical (RPM compensated) advance, but may need correspondingly more in vacuum (load compensated) advance, particularly if a large amount of cam timing overlap results in more EGR. The need for vacuum advance is related to the slower burn of lean A/F but the effect of exhaust dilution at high intake vacuum is a significant reason for requiring more advance."
In response to a question about setting up an FE, Tuner had pretty much the same thing to say:
"The FE and many other engines want more timing after the torque peak RPM than the amount which gives best torque at the torque peak. Your engine with the 224°@.050 cam will have peak torque at about 3000 RPM.
If you are using high octane fuel, like Avgas or race gas, it is not so important to slow the advance curve to avoid detonation although it will probably run better if you do.
Drag strip only use a fast curve is tolerated because an engine is never loaded at mid RPM for sustained periods like it can be on the street or oval and road racing. The longer duration of load at any RPM increases the temperature of chamber and piston surfaces and the heat speeds combustion and so does not require or tolerate as much advance as the same engine used in only few second bursts at a drag strip."
I know most people reading this don't know Tuner (except YR) so as far as you know he could be a keyboard guy making stuff up. That's why earlier I mentioned a few of the road race cars he helped the owners with. He prefers to go just by Tuner on the internet, and I will respect that.
Bruce "Shrinker" Robertson" Regarding initial timing:
"If you enrich the mixture at idle it will require less timing and the volume of gas expelled from the chamber will be greater (because there is more fuel in the cylinder ). The greater volume exhausting resists reversion backwards up the exhaust port therefor it actually runs with a cleaner chamber. Funny stuff isn't it"
"BUT what you have to do is enrich it correctly with the right processes in the carburetor, sometimes it's not just a matter of winding out the idle screw or changing the IFR. Every engine has a design to it and Chrysler's are a bit different to the other US products, they are not chevs or fords, they are better. They have better combustion and its not necessary to follow the rules of the hotrod industry, as the industry is very Chev orientated. Now what i just said should get plenty of people jumping up and down( hopefully in fun)."
from here: Motorsports Village • View topic - Initial timing
Shrinker may make your brain hurt, but I appreciate his way of approaching thing even though I'm not even in the same league of understanding, experience or knowledge.
"Tuning is the process of visualizing the progression of combustion and its conversion to mechanical energy."
He provides a stage by stage explanation of the combustion in this thread about dynoing a 440. Reading this you can see why even a single groundstrap shadow can play a role in flame development.
Motorsports Village • View topic - Dyno time
Finally, here's a case (non-mopar) where he warns that cruise timing and AFR could cause problems when going to full throttle. But I don't think 71GSSDemon's engine is in this situation but maybe worth keeping in mind.
"Your engine has a big cam for that low a compression so I'm not going to get into helping you tune it. My advise is to be careful about the tuning because if you go the wrong way you will end up making NOx at light loads and damage the engine when you stomp on it. If you run it rich it will be safe and the reading on a WB cannot always be trusted. If you used a gas bench and a dyno you will find that engine has plenty of unused Oxygen in the exhaust and thats a bad thing, it means there is unused hot Oxygen's left in the cylinder and thats dangerous,thats why you need to be rich and no where close to stoich. Pick the wrong ign timing at cruise and you will have hot carbons glowing waiting for you to open the throttle and give you some preignition woes. So id put up with a rich cruise, maybe not as rich as you describe but more in the 12.5 12.9 range. I wouldnt advise to go leaner than that unless gas bench and dyno confirmation showed otherwise."
http://motorsportsvillage.com/forum/viewtopic.php?f=6&t=915
Last edited:
512Stroker
We are all here because we are not all there.
The 63's I run are cad plated
512Stroker
We are all here because we are not all there.
Wow that pretty much follows some of my thoughts on "cruz tuning".
My ways I am sure are nowhere near as complex but I think I may be on the same path.
Great stuff, keep posting
Random thought. With 660 center squirters not having a power valve, does this play into the lean transition spot? I know they are designed for tunnel rams but more geared around drag racing than street cruise
How deep into the throttle was your foot???
Enrichment is for heavy load relative to the engine's maximum capability at that rpm.
If the throttles were signifcantly over halfway open, then maybe yes.
Otherwise no.
Enrichment is for heavy load relative to the engine's maximum capability at that rpm.
If the throttles were signifcantly over halfway open, then maybe yes.
Otherwise no.
Sorry Matt, maybe some confusion in this. I was just thinking about the carb design at this point and fuel flow/availability at part throttle being these are designed for WOT.
This is all relative to that long drive. With 2400 stall converter in 1971 Demon with 2.91 rear gears and 275 60 R15 tires. This was light throttle to maintain 2400-2500rpm cruise (~70mph). This was my concern originally, that maybe I wasn't in the main jet, and just out of idle mixture and/or transfer slots. It is a stack up issue? I didn't have an issue with the other gears and higher cruise rpm. Then the ambient outside temp/engine coolant temp as well.
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