Chasing down detonation w/UPDATE!

[JerseyJoe]

Hey guys, it's freezing in Jersey, can't get in the garage so I have some time to think about this.
I'm pretty sure my problem is heat related (intake air temp) but I uncovered some things that probably aren't helping, with pics...
Specs:
493" RB/4spd/Dana 3.54
Holley HP series 1000cfm 84 jets/6.5 power valve/blue pump
Street Dominator intake
84cc Stealth heads, non ported
1-7/8" uncoated headers
Flat top pistons .012 below deck atdc
10.9CR w/.039 head gasket thickness
Comp XS290S cam .540/.558 lift installed straight up
6AL/pro billet dist/ngk BKR6E-11 .038 gap
16 initial/38 total at 3000rpm
175-178 psi cranking pressure on all cylinders
Engine runs at 180 degrees
uses sunoco 93 pump gas

Here's the deal...
Car sat for years before it was street legal. It mostly ran at idle and took short trips around the neighborhood after it reached operating temp, but it was definitely a "short tripper".
I've recently fixed a valley pan leak, oil was getting into the intake ports, and discovered the fuel pressure was set too high, I think some fuel was getting dumped in to the carb. So I think I have carbon buildup as an issue.
It's been on the road for about 8 months now, after it reaches temp and is driven for more than about 15 minutes, I get the marble in a coffee can knock.
This is heard when accelerating under load (about 3/4 throttle) up to about 3500 rpm. It seems to get better at higher rpm.

It does not knock like this when first starting out. At least I don't hear it. So I'm leaning toward under hood temps and I'm looking at coated headers and a carb insulator.
But I also stuck a camera in the plug holes and checked out my timing and advance curve and found this:

Is this too much carbon in the chamber?
The blue advance spring rusted and the pickup is rusted including where the reluctor passes it. Could this affect the signal enough to mess with the spark?
Since it last ran about 2 weeks ago, I replaced the blue spring and put the black 18 deg. bushing in, it had the purple 21 degree.
Thanks in advance, I get/see the best advice from the guys in this section.

[firefighter3931]

Hey Joe,

Try backing the timing down to 34-35* total timing. Both of my closed chamber aluminum headed builds made best power at 34-35* total timing. Your cranking compression numbers should be fine with pump gas.

I would start by adjusting the timing and you could go up to a 7 series NGK plug.....the "6" is too warm for that compression ratio, inmo.

If it still detonates after that i'd look at hooking up a wideband O2 guage and see if it's going lean as you step into the throttle. Too lean will also cause detonation.

Does that carb have 84 jets on both the primary and secondary side ?


Ron

[BSB67]

Try backing the timing down to 34-35* total timing. Yup

Your cranking compression numbers should be fine with pump gas. Yup

I would start by adjusting the timing and you could go up to a 7 series NGK plug.....the "6" is too warm for that compression ratio, inmo. Yup.  I run -8

If it still detonates after that i'd look at hooking up a wideband O2 guage and see if it's going lean as you step into the throttle. Too lean will also cause detonation.  Yup.
   Low fuel pressure can make it go lean too.  You'll need about 3.5 psi at the carb at WOT with .110 N/S to support 550 hp

Also:

Total advance no sooner than 3000 rpm.  Maybe even try 3500.

160° Thermostat

Intake crossover blocked

Good mufflers (they can fail internally causing issues)

[JerseyJoe]

Thanks Ron and Russ.
I'll start with backing down the timing. Plugs are cheap so that's easy to try.
Yes, the carb came with 84 jets on both. I thought it was rich but it looks like the pressure was around 9 psi.
I have a Russell liquid filled gauge on the dual feed at the carb now so I think it was rich because the pressure was dumping gas.

There's no heat crossover with these heads, and a 160 thermostat is easy enough to try out. Mufflers are dynomax  ultra flows in good shape, you can see right through them!

Should I worry about the buildup in the pistons or will that clear up as I get it tuned right?
Thanks guys, I was hoping you'd chime in. 
I'll post up any results.

[BSB67]

Build up will increase cylinder pressure, but your cylinder pressure is only 175 so it is still manageable, and not the problem, IMO

[c00nhunterjoe]

If it still pings at less total, i would be leaning towards a lean condition at the lower rpm with the cam profile and a 1000 cfm carb on a 493.

[firefighter3931]

Build up will increase cylinder pressure, but your cylinder pressure is only 175 so it is still manageable, and not the problem, IMO

Agreed....cylinder pressure, even with some carbon buildup is in line with pump gas.  

I like the 160 Milodon high flow stat and run it in mine.

Coated headers will make a huge difference. I saw a 250* drop in surface temps between ceramic coated vs painted headers as measured with a laser temp gun. This upgrade will significantly reduce underhood temps.

The carb spacer works fantastic as well. Several years back I helped a buddy with his car and recorded some interesting data measuring carburator surface temperatures with a phenolic space installed. See link below :

http://www.dodgecharger.com/forum/index.php/topic,52284.0.html

I would also look closely at your fuel lines and make sure that they are not touching the block, heater hoses etc...

I've used DEI conduit insulation to heat insulate fuel lines with good results.

Keep us up to speed on your progress  



Ron

[JerseyJoe]

If it still pings at less total, i would be leaning towards a lean condition at the lower rpm with the cam profile and a 1000 cfm carb on a 493.

Interesting. Do you think its a mismatch for my combo? If it is lean at lower rpm would you suggest tuning or swapping parts?

[c00nhunterjoe]

Im saying check all the basics 1st. Then address from there if the problem is unchanged. People think throwing a 1000 cfm carb on means it will throw more fuel automaticly. Its alot easier to run an engine lean with too much carb. Not saying this is your problem. Not enough info yet.

[JerseyJoe]

Im saying check all the basics 1st.

Got ya. Definitely going to go one thing at a time. Throw all the fixes at once and you don't find out what did it.

[JerseyJoe]

Alright now we're really getting somewhere!
Salt was washed off the roads and its 39 degrees today, so the air temp helped I'm sure.

I put NGK BKR7E-11 plugs in, gapped @ .038 (one step colder)
verified 7 psi of fuel @ idle
total advance @ 34 deg

Took it out for an hour around town and a little highway speed (50mph around here). Coolant temp never got above 180.
There's a noticeable difference in power. I had to try and make it knock at mid-throttle. If I have it in 3rd gear and stab the gas down around 25 mph it'll knock, but not even like before. Not that I'd be doing that normally.
A couple of good rolls on the throttle and going through the gears it still pings slightly around 4000 rpm and above, at almost WOT (and at WOT), but man, it's a real handful now.

How do you feel about jetting up the secondaries? They're 84's now.
If I need to get an O2 gauge, are we talking dash mounted gauge or a diagnostic tool?

[XH29N0G]

The others who replied know way more than I do.  If they correct this - follow their advice.

I don't think it matters on the A/F gauge.  I bought one of the innovate units and found it worked really well for what I wanted.  I also have a 1970.  I wanted to gauge out of the way, so I pulled to casing off and put it in the ash tray.  Open it when I want to read it. 

What you will want, and what I have done, is to log from the gauge to my computer.  It will give so much information that it can be difficult to know what to do (or at least that is what I found - and some things basically boil down to how the car behaves, not what the gauge reads).  but I learned a lot.

Concerning size and tuning, they will have to tell answer that question.  I have run various carburetors on my setup which is a few steps down on cam (more like the Comp 284 hydraulic) and it is a 450 ci not 493.  What I found was that a mechanical secondary carb that was too big required a huge accelerator pump and also a lot of playing with air bleeds to make the transition to full throttle work with the A/F, but there still appeared to be an optimal size for the transition to work.  I think that is why people say smaller carburetors are more responsive.  I ultimately went for a smaller carburetor.  But as I mentioned, I don't know what is best for your set up.

[BSB67]

You need fuel pressure at wot.  At idle it means nothing.
When is your timing all in?
If it rattles at 39°, it will get worse with more temp.
Are you using the highest octane available locally.  What is it?
For a trial, I would jet up 2 on all four corners to see if that helps.

[JerseyJoe]

You need fuel pressure at wot.
Understood. I just mentioned it because it must have been dumping into the carb before. Holley says no more than 7.5psi

When is your timing all in?
It's all in at 3000. I have springs and I can go a little heavier to see how it is around 3500.

If it rattles at 39°, it will get worse with more temp.
160 stat, carb spacer, and coated headers are in the plan anyway for the underhood temp. I had vapor lock issues at Carlisle last year and I don't want to go through that again...

Are you using the highest octane available locally.  What is it?
Sunoco Ultra 93. Haven't tried a different brand yet FWIW, but 93 is it around here. I'm 20 minutes from Atco Raceway if I have to try higher. I'm 5 minutes across the bridge from PA if there's better over there.

For a trial, I would jet up 2 on all four corners to see if that helps
Check. I'll try before the temps drop again.

I do appreciate the help.  It's already running better.

[cdr]

Also if your fuel pressure gauge is liquid filled, a lot of them read the wrong pressure as the gauge gets hot or cold, mine has a little rubber plug on the side that I have to burp to get the correct reading.

[c00nhunterjoe]

34° timing, pinging in this ambient temp and those cylinder pressures on sunoco 93 is starting to push me towards a lean problem now. Definatly verify fuel pressure at wide open as suggested, from there i agree upping the jets and trying again. Also have you verified that your fuel lines are not touching the engine or too close to the exhaust and such?

[JerseyJoe]

34° timing, pinging in this ambient temp and those cylinder pressures on sunoco 93 is starting to push me towards a lean problem now. Definatly verify fuel pressure at wide open as suggested, from there i agree upping the jets and trying again. Also have you verified that your fuel lines are not touching the engine or too close to the exhaust and such?

Will do. I have a 1/2" aluminum line up the firewall in the corner of the engine bay, closest it gets is about 3" from the tube from the #8 and the collector. It'll be worth it to insulate the line.
I must have the same fuel pressure gauge as cdr. I don't really trust it now. I'll pick up a different one and try that.
Thanks Joe 

[c00nhunterjoe]

34° timing, pinging in this ambient temp and those cylinder pressures on sunoco 93 is starting to push me towards a lean problem now. Definatly verify fuel pressure at wide open as suggested, from there i agree upping the jets and trying again. Also have you verified that your fuel lines are not touching the engine or too close to the exhaust and such?

Will do. I have a 1/2" aluminum line up the firewall in the corner of the engine bay, closest it gets is about 3" from the tube from the #8 and the collector. It'll be worth it to insulate the line.
I must have the same fuel pressure gauge as cdr. I don't really trust it now. I'll pick up a different one and try that.
Thanks Joe 

I just reiterated what others suggested and added a few things to check if all else checked out. Keep us posted with the results as you check things.

[firefighter3931]

Joe,

Do you have a chassis dyno local ? A trip there with a set of jets would answer a lot of questions. 

You could also tape a fuel pressure guage to the windshield to see what the psi looks like at WOT. 

Good progress 




Ron

[JerseyJoe]

Joe,
Do you have a chassis dyno local ? A trip there with a set of jets would answer a lot of questions.  
You could also tape a fuel pressure guage to the windshield to see what the psi looks like at WOT.  
Good progress  

Ron

There's actually a few near me, Ron, since there's several dragstrips and motorsports parks in my region. I checked a few of their websites and it looks like about $100 or so for 3-5 pulls and the printout.  
We're getting another cold blast this week, looking at 50's early next week so I'll jet up again and run my fuel pressure gauge where I can see it.
I'm currently at 86 jets, it already has .110 n/s that BSB67 mentioned.
I added a 1/2" phenolic open spacer I had when I jetted up.  
Is WOT in 2nd gear okay? It's running out of road fast by the 3/4 shift  

Thank you for the advice, Ron.

[c00nhunterjoe]

A 2nd gear pull should show enough given the worst of your pinging was at low rpm under full load. If the jetting has little to no effect you may want to hold the initial back to get past the pinging as 34 total should be the sweet spot for that build. Pinging at 4k and above i dont beleive is the timing causing it at this point.
   I ran a gauge to the windshield and propped it under the wiper arm for my testing.... doesnt have to be pretty, its only temporary.

[INTMD8]

I may have missed it but have you verified your timing mark is correct?

[firefighter3931]

Joe,
Do you have a chassis dyno local ? A trip there with a set of jets would answer a lot of questions.  
You could also tape a fuel pressure guage to the windshield to see what the psi looks like at WOT.  
Good progress  

Ron

There's actually a few near me, Ron, since there's several dragstrips and motorsports parks in my region. I checked a few of their websites and it looks like about $100 or so for 3-5 pulls and the printout.  
We're getting another cold blast this week, looking at 50's early next week so I'll jet up again and run my fuel pressure gauge where I can see it.
I'm currently at 86 jets, it already has .110 n/s that BSB67 mentioned.
I added a 1/2" phenolic open spacer I had when I jetted up.  
Is WOT in 2nd gear okay? It's running out of road fast by the 3/4 shift  

Thank you for the advice, Ron.

Hey Joe,

The 1/2in phenolic spacer is fine....same one I run on the 572  That will help, a lot....with the conductive heat transfer. Keeping the fuel as cool as possible in the bowls will prevent vapor lock and fuel boiling. Hot fuel will detonate....especially the pump swill they sell nowadays that is designed for high pressure fuel injection. The other thing to consider is the currently available fuel will be "winter grade" which has anti freezing additives and less detonation resistance than summer blend stuff. If you can tune out the ping on winter fuel....summertime operation should be no problemo     


I'm thinking it will want more jet on the secondary side once you get it onto the chassis dyno. A second gear roll on should be fine for street testing purposes as Joe indicated in the post above  I like to shoot for 13-13.5 AFR at idle, 13 at steady cruise and high 12's-low 13's at WOT. It'll be interesting to see what your baseline numbers look like. You might end up jetting down a bit on the primaries and adding some additional jet on the secondary circuit....but the O2 readings on the chassis dyno will point you in the right direction and be the final word. 

You're not that far off....just a matter of a few tweaks and she'll be dialed in.



Ron

[Kern Dog]

I had a combination almost the same as yours except for the cam. Same compression, same cranking compression numbers too. Mine knocked at anything over 3/4 throttle just like yours. I ran RC9YC plugs. I ran the best pump gas we have here, 91 octane. I had the timing set to 16 initial, 31 total and it still knocked. I had an air/fuel gauge and it showed me running a little rich...not enough to be a problem. My advance came in all before 2500. I added a stiffer spring to delay the full advance to around 3000 but it still knocked. I changed to a bigger cam and it still knocked. I tried 100 octane and it still knocked. I ran 110 leaded and there was no knocking at all. Since I did NOT want to spend $60 for 5 gallons of gas for a car that got 10 mpg at best, I pulled the heads and put in thicker head gaskets to lower the compression. Now I am at 10.07 to one, cranking compression is at 165 and it does not knock at all on 91 octane and 34 degrees total timing.

[BSB67]

Flat top pistons .012 below deck atdc
10.9CR w/.039 head gasket thickness
Comp XS290S cam .540/.558 lift installed straight up

175-178 psi cranking pressure on all cylinders

I'm not sure what you call straight up on the cam.   But if you installed it per manufacture's spec, it will be 4° advanced.  For comparison purposes, I have less compression, and a later intake closing, and I have 195 psi cylinder pressure.

Maybe your gauge is wrong?

What is your elevation?