Tuning For Detonation

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RustyRatRod said:
Ha! Well, I really cannot do anything else to limit total timing more. I have the plate installed in the 10 degree slots. If there were 8 and 6 degree slots, I'd experiment with those. I did email Don to see if he might make something custom. We'll see. I think though, the 5 degree drop in total might do it. It's gotta be really, really close now. I'll know tomorrow after I fix the fuel leak and drive it.

Nattering nabobs. LMAO
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I'd like to just say that nobody is arguing 10 to 1 compression on the street...
The issue is cyl pressure and there is a general guideline... kinda like everyone knows "pump gas street motor for idiots" and then there is the ragged edge different animal all in it's own that is closely dialed for max power in a very particular climate and octane to the titty nipple. That is for the advanced. Intake close @70abdc is in the realm of late, not terribly, but old school .509 is around the corner. You could close in the 40's with a roller and not ping...& with a better plug location and a less coffee can shaped chamber you would already be in clear. What am I saying? Idk.. some people need not make it into something it aint?
lol You got a handle on it, it sounds like. Neat stuff... But can we get a cranking number? Fer all we know.. it cranks 155 and it's all in a bad carb tune. jk
Been years..but I remember mine not liking 91 w/165 cranking & mp .460/268 solid.
Thanks for sharing.
 
MOPAROFFICIAL said:
I'd like to just say that nobody is arguing 10 to 1 compression on the street...
The issue is cyl pressure and there is a general guideline... kinda like everyone knows "pump gas street motor for idiots" and then there is the ragged edge different animal all in it's own that is closely dialed for max power in a very particular climate and octane to the titty nipple. That is for the advanced. Intake close @70abdc is in the realm of late, not terribly, but old school .509 is around the corner. You could close in the 40's with a roller and not ping...& with a better plug location and a less coffee can shaped chamber you would already be in clear. What am I saying? Idk.. some people need not make it into something it aint?
lol You got a handle on it, it sounds like. Neat stuff... But can we get a cranking number? Fer all we know.. it cranks 155 and it's all in a bad carb tune. jk
Been years..but I remember mine not liking 91 w/165 cranking & mp .460/268 solid.
Thanks for sharing.
Click to expand...

I would have a number by now, but I loaned out my compression gauge and never got it back. I have one, but it's the stupid little on with the pointy rubber end and a stem too short to insert through the hole in the head where the plug tubes go. If anything, the carb's a tick rich, which would be the wrong way to be a "bad" tune for detonation.....even still, I have not measured cranking compression. I'll come up with a gauge in a few days and post the number. It could have simply been 40 degrees beint too much total timing. That is a lot.
 
RustyRatRod said:
I would have a number by now, but I loaned out my compression gauge and never got it back. I have one, but it's the stupid little on with the pointy rubber end and a stem too short to insert through the hole in the head where the plug tubes go. If anything, the carb's a tick rich, which would be the wrong way to be a "bad" tune for detonation.....even still, I have not measured cranking compression. I'll come up with a gauge in a few days and post the number. It could have simply been 40 degrees beint too much total timing. That is a lot.
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I'm not saying it's a bad tune, that was just gas'n.
For me, I wanna know what the cyl pressure is, it's a compass.
 
MOPAROFFICIAL said:
I'm not saying it's a bad tune, that was just gas'n.
For me, I wanna know what the cyl pressure is, it's a compass.
Click to expand...

It's entirely possible.....that's why I'm tryin to zero in on it. Cylinder pressure is certainly a big part of the picture. Far as I'm concerned, it IS a bad tune, because I've not really messed with it until real recently to make sure everything was gonna be happy together. lol I'll see if I can run across a good gauge tomorrow or Saturday. I've been curious about it too.
 
RRR,
Your detonation problem is a great example of the useless dynamic compression #s people use to try & avoid detonation with high static CRs by using more cam. There are just way too many variables involved & at the end of the day it almost becomes a crap shoot...........
Two things that rarely get mentioned are engine load & A/F distribution[ rich & lean cylinders ], but big contributors to det.
The engine doesn't detonate when revved in neutral, does it? That is because there is no load on the engine. So how the engine is loaded with car weight & gearing is a factor.
A/F variations per cylinder. I used to run a 4 bbl intake on my engine; had different intakes & carbs, 9.98:1 CR, iron heads. I had to be careful with the timing curve, but even then on very hot days, I could get light throttle ping. I THEN changed to a IR intake, home made, running 4 downdraft 48 IDF Weber carbs. One throttle bore per cyl. With the 4bbl, I had to use 98 octane petrol. With the Webers, I have the dist locked at 35* & MVA adds 13* for 48* at idle. Engine runs happily on 91 octane & I have never been able to get it ping. Such is the difference A/F distribution makes.
The inline 6 engine with a single carb is a particular problem because the end cyls with the long runners are most likely running lean & causing the detonation. Cold air induction would probably help. A friend cured his detonation problem by fitting an engine cooler. Pistons ran cooler & those few degrees made the difference.
 
RustyRatRod said:
It was 40 at 3000 RPM with 15 initial. Now it's 35 at 3000 RPM with 20 initial. Yes, I am running a vacuum advance.
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OK you are currently all in at a total of 35* mechanical advance, that should work.
Have you considered that the VA may be adding more timing than the engine likes?
Do you know how much advance the VA is adding? Is your VA adjustable?
 
512Stroker said:
OK you are currently all in at a total of 35* mechanical advance, that should work.
Have you considered that the VA may be adding more timing than the engine likes?
Do you know how much advance the VA is adding? Is your VA adjustable?
Click to expand...
To add to this line of reasoning, the shape of the advances can also make a difference.
 
I have about the same issues as RRR. 9.5 compression and too mild a cam,to run on 87 octane. It was ok with a recurved points distributor, but NG when converted to EI (not recurved). If I retarded the total timing to keep from pinging, my initial was so late it wouldn't idle. I haven't had time to rework the distributor, so I cheated. I set the total timing for no ping, and connected the vac pod to intake vacuum, which gives me enough initial advance for decent idle. Can you say "band aid"?
 
Picture time
If we look at the timing spec's for a stock 225 they look like this.
upload_2021-4-30_9-5-8.png


If your engine has high overlap and other factors that reduce efficiency at idle, that's fine. The point here is to look at the shape. We see from the graph that in the factory 225 combustion efficiency really picked up around 1900 rpm.
Then to any rpm on that timing curve add the matching vacuum advance.
upload_2021-4-30_9-20-38.png


If you (RRR) can identify whether the detonation is occuring when crowding deep (no vac advance) vs when not so deep(some vac advance) then you would know which one is more likely to resolve the problem.

With the mechanical advance, turning the spring perch for the long lopp spring will bring into to play at lower rpm.
With the vac advance add wahsers or turn the allen screw to move the vac advance timing to the right on the graph.
 
Charrlie_S said:
I have about the same issues as RRR. 9.5 compression and too mild a cam,to run on 87 octane. It was ok with a recurved points distributor, but NG when converted to EI (not recurved). If I retarded the total timing to keep from pinging, my initial was so late it wouldn't idle. I haven't had time to rework the distributor, so I cheated. I set the total timing for no ping, and connected the vac pod to intake vacuum, which gives me enough initial advance for decent idle. Can you say "band aid"?
Click to expand...
That works!
 
Charrlie_S said:
I have about the same issues as RRR. 9.5 compression and too mild a cam,to run on 87 octane. It was ok with a recurved points distributor, but NG when converted to EI (not recurved). If I retarded the total timing to keep from pinging, my initial was so late it wouldn't idle. I haven't had time to rework the distributor, so I cheated. I set the total timing for no ping, and connected the vac pod to intake vacuum, which gives me enough initial advance for decent idle. Can you say "band aid"?
Click to expand...
Nice - that works for me.
I give you credit for finding a temporary solution to the issue working with what you have.
I cheated and had Dan at FBO custom curve a distributor for my engine.
 
Rob, have you considered....(wait for it) EGR? A simple slant six bolt on if you have the correct manifolds for the EGR valve and then a sense line to manifold vacuum. It doesn't do **** at idle or WOT (both close it) but it does dilute the charge at cruise and lowers the chamber temperature. Can be adapted to older manifolds. Some have an adjustable pintle to change onset.
 
RustyRatRod said:
It's entirely possible.....that's why I'm tryin to zero in on it. Cylinder pressure is certainly a big part of the picture. Far as I'm concerned, it IS a bad tune, because I've not really messed with it until real recently to make sure everything was gonna be happy together. lol I'll see if I can run across a good gauge tomorrow or Saturday. I've been curious about it too.
Click to expand...

"it IS a bad tune"

(93) Supernatural Baloney - YouTube
 
Looks like you have tried just about everything under the sun to stop the ping.

Like the looks of the orientation of your carb facing forward and easy to do the throttle linkage.

But . . . Was wondering about you turning the carb 90° to face to passenger fender for more even fuel distribution to all 6 cylinders? Have seen other custom /6 4bbl setups with the carbs sitting on them sideways.

The way it is positioned now 3 cylinders are getting a lesser charge than the other three. Being the 4 bbl is spiit in half, sending the primary butterflys to the front 3 cylinders, and sending the secondary charge to the back 3 cylinders.

Know you mentioned it does not make a difference, but think worth a try being everything is right on the edge of getting it right. Nice even fuel mixture to all cylinders. 10:1 compression without ping should be easily achieved.

It either gets better or it gets worse, process of elimination.

I would even try another carb you have laying around, either gets better or worse. Then go from there.

☆☆☆
 
RustyRatRod said:
It's entirely possible.....that's why I'm tryin to zero in on it. Cylinder pressure is certainly a big part of the picture. Far as I'm concerned, it IS a bad tune, because I've not really messed with it until real recently to make sure everything was gonna be happy together. lol I'll see if I can run across a good gauge tomorrow or Saturday. I've been curious about it too.
Click to expand...
Despite what bullshit others are saying about dynamic/cranking... it IS important.
Could be chasing your tail. Definitely wasting your time IF you were determined to a particular total timing and fight tooth n nail to tune out the ping.
I fall into the middle of the crowd, I definitely am a proponent of running high cyl pressures and maximizing the usage of the octane in search for thee most power tq/efficiency out of my combos. I also start out at 30 total when its blueprinted 'already known to be boarderline or on the high side for the fuel' and work from there 2 degrees at a time up or move to 25 and go from there. Depends on the parts. Some stuff will NOT tolerate more than a few clacks @ wot before you hurt the ring lands.

The others can cheerlead for each other and their method of proving some nonsensical 'over the shoulder not even looking' way of tuning... good for them.
That's not my way to dial in a new motor, that's for sure.
So if it doesn't surge at cruise ..the primary isn't far off...if it doesn't blubber, it's not too fat. You don't have any jerking on acceleration ...so your pump shots not necessarily an issue ...what's left- the timing is. Does it do it at 30 total?
Have you put a bottle of booster in it to see if it stops/give it octane?
What do the plugs look like, pictures?
 
Last edited:
RustyRatRod said:
Now it's 35 at 3000 RPM with 20 initial.
Click to expand...

Mattax said:
With the mechanical advance, turning the spring perch for the long lopp spring will bring into to play at lower rpm.
Click to expand...

maybe this will help complete the picture.
Lets say the advance looks like the dotted line; And lets say you want to keep the 20* initial and 35* max.
upload_2021-4-30_12-43-19.png


Turning the long loop spring's perch or using a shorter loop will change the advance like this.
upload_2021-4-30_12-54-1.png

It only takes a few degrees out of the mid rpms and leaves the top and low rpm timing as is.
 
My experience with the slant, is they don't like the same amount of timing as small blocks (12/34)
If you are experiencing pinging, I believe you are using to much timming. Lowering the expectations of the thing will produce a better running motor.
 
Bewy said:
RRR,
Your detonation problem is a great example of the useless dynamic compression #s people use to try & avoid detonation with high static CRs by using more cam. There are just way too many variables involved & at the end of the day it almost becomes a crap shoot...........
Two things that rarely get mentioned are engine load & A/F distribution[ rich & lean cylinders ], but big contributors to det.
The engine doesn't detonate when revved in neutral, does it? That is because there is no load on the engine. So how the engine is loaded with car weight & gearing is a factor.
A/F variations per cylinder. I used to run a 4 bbl intake on my engine; had different intakes & carbs, 9.98:1 CR, iron heads. I had to be careful with the timing curve, but even then on very hot days, I could get light throttle ping. I THEN changed to a IR intake, home made, running 4 downdraft 48 IDF Weber carbs. One throttle bore per cyl. With the 4bbl, I had to use 98 octane petrol. With the Webers, I have the dist locked at 35* & MVA adds 13* for 48* at idle. Engine runs happily on 91 octane & I have never been able to get it ping. Such is the difference A/F distribution makes.
The inline 6 engine with a single carb is a particular problem because the end cyls with the long runners are most likely running lean & causing the detonation. Cold air induction would probably help. A friend cured his detonation problem by fitting an engine cooler. Pistons ran cooler & those few degrees made the difference.
Click to expand...


Ok...this made me LOLOLOLOLOLOLOLOLOLOLOLOL a because it’s damned funny. Good one.
 
MOPAROFFICIAL said:
Despite what bullshit others are saying about dynamic/cranking... it IS important.
Could be chasing your tail. Definitely wasting your time IF you were determined to a particular total timing and fight tooth n nail to tune out the ping.
I fall into the middle of the crowd, I definitely am a proponent of running high cyl pressures and maximizing the usage of the octane in search for thee most power tq/efficiency out of my combos. I also start out at 30 total when its blueprinted 'already known to be boarderline or on the high side for the fuel' and work from there 2 degrees at a time up or move to 25 and go from there. Depends on the parts. Some stuff will NOT tolerate more than a few clacks @ wot before you hurt the ring lands.

The others can cheerlead for each other and their method of proving some nonsensical 'over the shoulder not even looking' way of tuning... good for them.
That's not my way to dial in a new motor, that's for sure.
So if it doesn't surge at cruise ..the primary isn't far off...if it doesn't blubber, it's not too fat. You don't have any jerking on acceleration ...so your pump shots not necessarily an issue ...what's left- the timing is. Does it do it at 30 total?
Have you put a bottle of booster in it to see if it stops/give it octane?
What do the plugs look like, pictures?
Click to expand...


He still needs to get the engine temp down. He’s doing this on 87 octane. Once he gets the temp down and a better timing curve he will be fine.
 
Thanks yall. To clarify a few things.....I don't necessarily want a specific amount of initial or total. I want enough initial where it will crank quickly and not so much total where it has detonation.

Now to answer a couple of questions/points. Yes, I am 100% dead sure that now it only spark knocks when crowded and the vacuum advance is not in play. 100%, no question. It happens when there is either zero vacuum or not enough to pull in anything. In fact, I don't think it ever does it on the primary barrels, so that tells you how far into the gas it happens.

@Bewy in post #30. I would agree with that first part, but in this situation, it's not so. It's my fault we are where we are. I knew going in this would be a "ragged edge" kinda build. I COULD have put the limiter plate in the distributor THEN, but I didn't that wouldn't have done anything though, because I would have put the plate in at the same 14 degree slots I put it in now and would have had the same 40 degrees total, so the spark knock would still be there.

Doing it how I did, I have a better view about what it actually needs and what is actually going on. At the 14 slots, which should have been 34 total with 20 initial, I still got 40 total with 15 initial, just like before. I've read where these plates don't always have their marked outcomes with the slots, so I was ready for that.

Now, with the plate in the 10 degree slots, I have 20 initial and 35 total. Again, I don't really have a specified goal in mind with timing, other than getting it to crank good hot, as it's been having classic long crank times holding the throttle partially open.....a classic sign of retarded initial timing and the detonation, a classic sign of too much total timing.

I just got done fixing the fuel leak. It was a leaking NEW fuel pump, so I swapped on the new one off the 170 and that's done. It pops right off now at 20 initial, so that issue seems better. I don't know how it starts hot like that yet, since we've not driven it since I limited total to 35. We're leaving now to run to the post office, so I'll report back in a bit. THanks for all the good ideas. It's much appreciated.
 
RustyRatRod said:
Also, keep in mind, this is ALL without the high flow 160 thermostat. It'll be here Monday. I also still plan on scheming up some kinda cold air intake. I appreciate your help and guidance more than you know.
Click to expand...

I was just getting ready to ask if you had some type of cold air intake set up. If you can get it tuned without it, then add it, it might give you some cushion for those 95 degree plus days we have coming here in GA soon. Hope you are feeling better.
 
yellow rose said:
He still needs to get the engine temp down. He’s doing this on 87 octane. Once he gets the temp down and a better timing curve he will be fine.
Click to expand...

We drove it to town and back. It runs better, liking the more initial. That said, Kitty says the rattle is about the same and I think I know why. It's the heat. I cannot MAKE it rattle ONE IOTA until it gets some temp on the gauge. When cold, now with more initial, it pops off almost without hittin the key. I mean it's READY. But when we went into the post office and it sat there heat soaking, it still had long crank time with the throttle open a hair....and the temp gauge was almost at 3/4. As soon as it busts off it starts cooling right down. I think the high flow thermostat is going to help a good bit. It did on my truck. It was running in the half way range and when I put in a high flow thermostat now it barely comes off the cold line.....and it's right. I've checked it with the heat gun. I'll get on top of it. I may file out the zero holes on the limiter plate and get them to 6 degrees and see what's goin on then. Obviously, for "whatever" reason, the slots are different for this distributor. Whether it's because it's a slant six distributor and maybe a little different, I don't know. I still have several tuning options left, so we'll get it. I'm pretty confident. If nothing else, now I have some room to retard the initial and that will get it out for sure. But I believe the cooler, high flow thermostat will pretty much solve it. I am going to try that first and report back.
 
mgoblue9798 said:
I was just getting ready to ask if you had some type of cold air intake set up. If you can get it tuned without it, then add it, it might give you some cushion for those 95 degree plus days we have coming here in GA soon. Hope you are feeling better.
Click to expand...

Thanks! I felt bad yesterday because I forgot to take my med regime from the day before. You caint just "stop" blood pressure and diabetes meds. LOL Feel better today. Hopefully my thermostat shows up and I can put that in. We'll see.
 
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