Solutions for too much compression

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Valiant360420 said:
My distributor is a Mopar Performance vacuume advance equipped unit with an orange ingnition box.
The advance curve is ...
9 deg at 1500 RPM
17 at 2000 RPM
22 at 3000 rpm
Give or take
The Vacuume advance adds about 16 degrees.

Engine vacuum at idle in neutral is about 18.

Compression test with only 1 plug removed is around 180 psi.

Carb is a 750 Holley vac secondary. Never touched the jets.
.
Click to expand...

There’s two parts to tuning a carbureted engine: timing, then the carb itself.
My thoughts-
Timing curve is too fast. If you have “two light”, or “one light and no 2nd” spring in the distributor you need to get a stock distributor “light” spring and either install in the empty spot, or replace one of the “MP light” springs. Or lighten the counterweights. The advance shouldn’t start until about 1500 or so and be all in above 3k.

I would use the vacuum on the ported vacuum port. You can adjust the level of vacuum required to move the plate by inserting an Allen wrench into the vacuum nipple on the vacuum can and engaging the screw inside there (11/32nds ?)

You MUST tune the carb. Check the idle vacuum in gear once you have 15-18* initial. Then buy a power valve that’s about 1-2 inches below that vacuum reading. I would also jet up 2-3 jet sizes (I think it has 72s), and buy the vacuum secondary spring package and install the purple spring.

That’s what I’d do.
 
roccodart440 said:
There is your problem(s)

That distributor brings in the timing FAST and LOW.

Disconnect and plug the vacuum advance. Use a NON-ADVANCE timing light preferably or use yours with no advance dialed into it. Use another light to confirm yours works properly as I've first hand seen one that doesn't. Mark your harmonic balancer at 34 degrees with a sharpie or paint pen. Shoot the light at it and rev to 3000 and make the line you made line up with zero on the pointer. Lock the dizzy down. Now check initial timing. Rev to 3500 to check total at 34 degrees again.

Let us know where the initial falls.

Then, with the vacuum advance still UNHOOKED AND PLUGGED, go drive it. Let us know how that goes. Your issues IMO are 100% timing related.
Click to expand...
Results are in...

Plugged the vacuum advance.

Total at 3000 is 34
At 2000 is 28
At 1500 is 20
Idle at 800 rpm is 10 degrees

Pinging it’s head off under power, even at 2000 rpm. Power feels pretty good until I have to let off because of the pinging.
I’m using a regular timing light, not a dial back.
I did recheck my timing mark today.

Question...

If I go buy a jug of high octane race gas, and then try to run more advance, and it doesn’t ping. What would that verify?
 
moper said:
There’s two parts to tuning a carbureted engine: timing, then the carb itself.
My thoughts-
Timing curve is too fast. If you have “two light”, or “one light and no 2nd” spring in the distributor you need to get a stock distributor “light” spring and either install in the empty spot, or replace one of the “MP light” springs. Or lighten the counterweights. The advance shouldn’t start until about 1500 or so and be all in above 3k.

I would use the vacuum on the ported vacuum port. You can adjust the level of vacuum required to move the plate by inserting an Allen wrench into the vacuum nipple on the vacuum can and engaging the screw inside there (11/32nds ?)

You MUST tune the carb. Check the idle vacuum in gear once you have 15-18* initial. Then buy a power valve that’s about 1-2 inches below that vacuum reading. I would also jet up 2-3 jet sizes (I think it has 72s), and buy the vacuum secondary spring package and install the purple spring.

That’s what I’d do.
Click to expand...
I like it. I guess you are saying that the mixture is too lean and that can contribute to pinging?What is the best way to see what the carb is doing?
Install an 02 sensor and gauge, or do I need dyno time ?
 
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Valiant360420 said:
I like it. I guess you are saying that the mixture is too lean and that can contribute to pinging?What is the best way to see what the carb is doing?
Install an 02 sensor and gauge, or do I need dyno time ?
Click to expand...


Can you pull a few plugs and post the pictures?

That thing should run on cat puss with full timing and not rattle.
 
Valiant360420 said:
Results are in...

Plugged the vacuum advance.

Total at 3000 is 34
At 2000 is 28
At 1500 is 20
Idle at 800 rpm is 10 degrees

Pinging it’s head off under power, even at 2000 rpm. Power feels pretty good until I have to let off because of the pinging.
I’m using a regular timing light, not a dial back.
I did recheck my timing mark today.

Question...

If I go buy a jug of high octane race gas, and then try to run more advance, and it doesn’t ping. What would that verify?
Click to expand...
That it's not lean like some ex'spurts claim.
If it was lean... it would surge at cruise, not necessarily ping at all. I swear ...some people read a bunch of **** and think they mastered the universe. Lean tune... if it's that lean, you're already breaking ****.
34 or whatever is too much total timing/power timing for the octane and your dynamic.
Bring it down to 25... then drive it and increase it 2 degrees at a time till it pings again....then take 2 out. That's what your motor likes on the gas you use.

Remember what I said to you in my first response, 25 is all I can run and I have a hair more than you ...so if you're pinging at 28, lower it to 25... if you're still pinging go to 23.

It's not that your carb may not need tuning, it's just well known you cant run that much with that amount of cyl psi.
 
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MOPAROFFICIAL said:
That it's not lean like some ex'spurts claim.
If it was lean... it would surge at cruise, not necessarily ping at all. I swear ...some people read a bunch of **** and think they mastered the universe. Lean tune... if it's that lean, you're already breaking ****.
34 or whatever is too much total timing/power timing for the octane and your dynamic.
Bring it down to 25... then drive it and increase it 2 degrees at a time till it pings again....then take 2 out. That's what your motor likes on the gas you use.

Remember what I said to you in my first response, 25 is all I can run and I have a hair more than you ...so if you're pinging at 28, lower it to 25... if you're still pinging go to 23.

It's not that your carb may not need tuning, it's just well known you cant run that much with that amount of cyl psi.
Click to expand...
Cool. I just received my FBO advance limiter plate and I’ll be messing with that tomorrow.
 
MOPAROFFICIAL said:
If it was lean... it would surge at cruise, not necessarily ping at all. I swear ...some people read a bunch of **** and think they mastered the universe. Lean tune... if it's that lean, you're already breaking ****.
Click to expand...

You do realise that the transfer slot is cruise and max power (WOT) is mains and secondary's? At maximum power the engine requires a richer mixture.
 
Hysteric said:
You do realise that the transfer slot is cruise and max power (WOT) is mains and secondary's? At maximum power the engine requires a richer mixture.
Click to expand...
You cruise at 15 mph? Maybe on the strand..lol
Better re think that.
I have read enough and had enough run ins with the same couple people..but I'll entertain this one more time before I wad this adventure up and toss it in the trash. I have way more fun working on **** ,by myself, than marching in this death march. This what under moderating leads to.

If you drive down the road @45 -50mph and it surges, its lean on the primary side jetting.



This window is closed.
 
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MOPAROFFICIAL said:
You cruise at 15 mph? Maybe on the strand..lol
Better re think that.
I have read enough and had enough run ins with the same couple people..but I'll entertain this one more time before I wad this adventure up and toss it in the trash. I have way more fun working on **** ,by myself, than marching in this death march. This what under moderating leads to.

If you drive down the road @45 -50mph and it surges, its lean on the primary side jetting.



This window is closed.
Click to expand...


You’d have to know his gearing, tire size, MAB and emulsion stack to know whether or not he’s on the MJ at 45-50 MPH.

So you don’t know. He could have a really small MAB and it doesn’t get on the booster quicker enough. He could have a low PV number delaying the PV circuit.

A look at the plugs would be helpful.
 
post #46 nailed it.
If it's the Mallory Mopar Performance distributor put it in the round file #13.
Normal driving will be ok but as soon as you get on it the tiny weights will centrically advance the timing
too to far too fast!
...and it'll detonate a lot of the time
 
yellow rose said:
You’d have to know his gearing, tire size, MAB and emulsion stack to know whether or not he’s on the MJ at 45-50 MPH.

So you don’t know. He could have a really small MAB and it doesn’t get on the booster quicker enough. He could have a low PV number delaying the PV circuit.

A look at the plugs would be helpful.
Click to expand...


yellow rose said:
You’d have to know his gearing, tire size, MAB and emulsion stack to know whether or not he’s on the MJ at 45-50 MPH.

So you don’t know. He could have a really small MAB and it doesn’t get on the booster quicker enough. He could have a low PV number delaying the PV circuit.

A look at the plugs would be helpful.
Click to expand...
speak for yourself
 
I just set timing for
14 initial
23 total,
No vacuum advance at a
And put in some stiffer springs ...
I think I’m finally going in the right direction. It feels like it has more power when it starts to approach 4000.
I tried advancing more but I got pinging again.
It now feels more healthy with The higher initial.
 
MOPAROFFICIAL said:
You cruise at 15 mph? Maybe on the strand..lol
Better re think that.
Click to expand...

So the T-slot miraculously stops working at 15 mph?. I've recorded primary booster flows well into the 2000's rpm range on some carbs so what does the carb run on until then?
 
yellow rose said:
You’d have to know his gearing, tire size, MAB and emulsion stack to know whether or not he’s on the MJ at 45-50 MPH.

So you don’t know. He could have a really small MAB and it doesn’t get on the booster quicker enough. He could have a low PV number delaying the PV circuit.

A look at the plugs would be helpful.
Click to expand...

Exactly. Not to mention float height.
 
Valiant360420 said:
I just set timing for
14 initial
23 total,
No vacuum advance at a
And put in some stiffer springs ...
I think I’m finally going in the right direction. It feels like it has more power when it starts to approach 4000.
I tried advancing more but I got pinging again.
It now feels more healthy with The higher initial.
Click to expand...


You have something else wrong. Can you pull a couple of plugs and post some pictures?


That should run on WD-40 and not detonate.
 
My thoughts
Elevation of SanRamon is ~500ft
A modest cam will have an Ica of ~58*. That's like a [email protected]
The Wallace says this should make about 164psi.
Depending on the chamber, this should go like the proverbial cat on fire.

But OP claims to have measured 180psi.
To get that, with a 58* Ica would take about a 10.4 Scr

Ima thinking there is no easy solution to this with tuning.
At least one head will need to come off, and the cam will need to be measured and degreed.
Then you can start assessing your options.

9.7 Scr is a total chamber volume of 84.74cc
10.4 is 78.43
That is a huge difference, and 78ccTOTAL, requires a very small chamber, which an OEM-360 head does not have.

The math does not add up.
 
AJ/FormS said:
My thoughts
Elevation of SanRamon is ~500ft
A modest cam will have an Ica of ~58*. That's like a [email protected]
The Wallace says this should make about 164psi.
Depending on the chamber, this should go like the proverbial cat on fire.

But OP claims to have measured 180psi.
To get that, with a 58* Ica would take about a 10.4 Scr

Ima thinking there is no easy solution to this with tuning.
At least one head will need to come off, and the cam will need to be measured and degreed.
Then you can start assessing your options.

9.7 Scr is a total chamber volume of 84.74cc
10.4 is 78.43
That is a huge difference, and 78ccTOTAL, requires a very small chamber, which an OEM-360 head does not have.

The math does not add up.
Click to expand...

Yeah, I’d like to see his math and some plugs.
 
Valiant360420 said:
I just set timing for
14 initial
23 total,
No vacuum advance at a
And put in some stiffer springs ...
I think I’m finally going in the right direction. It feels like it has more power when it starts to approach 4000.
I tried advancing more but I got pinging again.
It now feels more healthy with The higher initial.
Click to expand...
Now that it's not pinging, show us the plugs and let's tune the carburetor.
Sorry for may lay, some people are just up their own ***. I live near you, have the same gas, have 185 cranking w open j heads, 540 ft elevation here.
You got a healthy motor, you just need to carefully tune it for the piss we have here in ca. All these over complicated reasons are unnecessary imo when it's very obvious to me. I'm just trying to help, it's a touchy tune but it makes tire frying power off idle in a blink.
 
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Valiant360420 said:
So I took off the drivers side valve cover and turned to motor over by hand. Had a friend watch the rockers and as I passed 360 degrees past tdc ( where the exhaust is just closing and the intake is just opening )I had him tell me where exactly the exhaust fully closed and the intake just started opening. I looked at the timing mark and the piston was exactly at the top. I repeated this several times to make sure he was seeing it right. I got this idea from another post on FABO and it made sense to me.
Click to expand...
That is the lamest method for checking cam timing that I have ever heard of.
Folks buy 12 and 18 and 24 inch diameter cam timing wheels to do what you say you are doing by putting an eyeball on a rocker arm,,,,
 
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