Pinging after 40-45 mins of driving?
 

Hey guys, I'm havin some issues with pinging, but only after I drive around for a while. I let the truck warm up before moving it, and it runs great for a half hour to 45 minutes, and then it starts pinging and idling a little higher. I set the timing when it is completely warmed up and sitting at operating temp, and it runs and idles and drives great for a while, then after 40 mins or so it changes. Any thoughts on that?

It's a 1970 C10, 10-1 compression 355 with a comp 280H cam, RHS 170 heads, edelbrock performer rpm manifold and 650avs carb, long tubes with flows dumped. Also has a GM performance HEI ignition

Matt

Re: Pinging after 40-45 mins of driving?
 

Have you checked your timing when it starts pinging? Not sure why it would change but it'd rules one thing out. How old is the gas?

Re: Pinging after 40-45 mins of driving?
 

Fuel geting hot ? Vapor locking ? Do you have electric fuel pump mounted as close to tank as possible?

Re: Pinging after 40-45 mins of driving?
 

Where's your vacuum advance connected? Manifold or timed? In what load condition does it ping? Down low with your foot in it or kick-down?

Re: Pinging after 40-45 mins of driving?
 

No I just figured it was something else, the timing can change?

Re: Pinging after 40-45 mins of driving?
 

I'm not sure if the fuel is getting hot or vapor locking, what causes that? It's brand new fuel

Re: Pinging after 40-45 mins of driving?
 

It's connected to the drivers side port on the carb. It pings when I hold the brake and give it gas to check for ping, foot braking I think it's called?

Re: Pinging after 40-45 mins of driving?
 

What octane fuel do you run? My 72 custom deluxe has 11:1 compression and I have to mix 4 gallons of 112 octane race fuel to 93 octane to make sure it doesn't ping. Also what's your temperature like? Does it rise after that 45 minutes?

Re: Pinging after 40-45 mins of driving?
 

I usually put a couple gallons of Sunoco 110 in at fill-up, but maybe I should try 4-5 gallons. I ran to the gas station on empty and it was fine from the last full-up and race fuel combo, and this started right after that so you might be on to something. Can just a couple gallons of 110 make that much of a difference? This is the first semi-high compression engine I've had.

The temp stays around 180-185* until I started having this problem with pinging

Re: Pinging after 40-45 mins of driving?
 

The race fuel definitely helps. According to a chart I saw, the minimum octane for 10:1 comp. is 92 octane, but not sure how accurate that is. But if your putting 2 gallons of 110 in 93 then you may have higher compression than you know, unless you built it and know for sure.

There is a way to figure out them mean octane of fuel you put in by math.

This is what I do:

4 gallons of race fuel(112) and 15 gallons of 93 octane equals 19 gallons total.

Divide 4 by 19 and get .21, then multiply that by 112 equals 23.6

Divide 15 by 19 and get .79, then multiply that by 93 equals 73.5

Add the totals and that's your total octane, 23.6 plus 73.5 equals 97.1 octane

Try that and see what you get. On the safe side you should probably shoot for 94 or 95 octane.

Re: Pinging after 40-45 mins of driving?
 

Also depending on your driving, I would change your vacuum advance over to manifold vacuum and not ported vacuum if that's how it's setup.

The difference is that when your truck is in neutral or park and at idle, if you pull a rubber line or cap off a vacuum port and get instant, fairly strong vacuum, then that's manifold vacuum. Ported vacuum only increases if the throttle plates are opened up (acceleration).

Now putting the rubber line on a manifold vacuum port will instantly shoot your timing up how ever many degrees it is rated for, stock gm's were 20. So you need to set your base timing somewhere in the neighborhood of 3 to 6 degrees before the rubber line is attached.

Now the reason for manifold vacuum advance in a high compression engine is that if you step on it (fast to moderate acceleration) the timing does not jump higher, as if ported vacuum were used, than your base and centrifugal timing, which increases the chance for ping if the octane fuel is not correct or the quality of fuel is just not there(today's pump gas). When you step on it, the manifold vacuum advance setup will allow the timing to back off some and reduce the chance of pinging.

Re: Pinging after 40-45 mins of driving?
 

I used a fel-pro 1094 head gasket on the stock short block, and the compressed thickness is .015, so I figure 10-1. It could be higher but I'm not sure. I'll try the math you suggested

Re: Pinging after 40-45 mins of driving?
 

If you haven't done this already, summit racing has a compression calculator you could try. As long as you know how many cc's, or close estimation, your Pistons add to the compression chamber and how many cc's your heads are, you can get a close estimation of compression.


http://www.summitracing.com/expertad...ion-calculator

Re: Pinging after 40-45 mins of driving?
 

After all you've been thru with this engine I'll bet a donut that a crate 383 is looking really good right about now ?

Re: Pinging after 40-45 mins of driving?
 

It is haha I'm actually going to build an all forged 383 from the bottom up, then throw a bunch of boost at it.

Re: Pinging after 40-45 mins of driving?
 

Well I was off a little on the compression, so that might be part of it lol

Re: Pinging after 40-45 mins of driving?
 

Sounds incorrect. On a Q-Jet, at least, the proper (ported) vacuum port is above the throttle blades on the front of the carb, and you usually have the metal line run around the side where it crosses the exhaust heat.

Put simply, vacuum advance must be connected to ported, not manifold, vacuum.

Except: I saw my first ever "vacuum advanced on manifold vacuum" setup on a 66 Corvette yesterday, but the base timing settings are ATDC (as in so retarded they are after TDC). Then vacuum advance brings it up to something reasonable at idle. But our distributors are NOT set up that way, and need to be on ported vacuum.

Otherwise when you tip into the throttle off idle you will ping from all the static plus vacuum timing, because there's lots of vacuum just off idle. There's almost no ported vacuum at all until air starts flowing. I think that's why you're pinging.

You've said you're running a domed (not relief) piston in the calculator, just FYI. Could be right, not sure.

Re: Pinging after 40-45 mins of driving?
 

Yea you definately need to run 4 to 5 gallons of race fuel per tank. According to the chart I looked at 11:1 compression needs atleast 96 octane and 12:1 needs
atleast 100 octane, so you should try to get between them.

How much does it cost there? Costs me $10 a gallon at the pump. Trying to get it wholesale though.

Re: Pinging after 40-45 mins of driving?
 

I changed the piston cc and that made a huge difference

Re: Pinging after 40-45 mins of driving?
 

I am betting the carb is sucking up a lot of heat and giving you a headache. Try putting a phenolic (sp) spacer under the carb and see if that helps. Another thing you can try is disconnecting the vac advance and see if it pings. You may have a can that is pulling in a little more advance than you need. Most people don't realize that the cans have different amounts of advance and vacuum levels needed to pull it in. For instance if the can pulls in 10* at 12"s of vacuum and your throttle is at 12"s then the extra timing won't fall out. Another thing to check is that the fuel line is not touching the radiator hose. Putting 200 degree water in direct contact with the fuel line will heat the fuel up fast.

Re: Pinging after 40-45 mins of driving?
 

That's not pinging, it's full on detonation!
Pull your timing back.
If the timing is spot on you shouldn't hear anything when you hot brake it.

Re: Pinging after 40-45 mins of driving?
 

It doesn't run good with the timing pulled back though. This cam wants ALOT of base timing. I'm gonna swap the vacuum advance over to the passenger side and see if that helps

Re: Pinging after 40-45 mins of driving?
 

What are your plugs gapped at?

An HEI needs at least .045"

I have an MSD Pro Billet HEI and a digital 6AL box and I run my plugs gapped at .055"

Gary

Re: Pinging after 40-45 mins of driving?
 

Take the vac advance totally out of the equation. Plug it off. Tune without it.
What's your timing curve like?
Initial? At what rpm?
Timing at 900 rpm, 1200 rpm, and every 300 rpm after that.
All in by what rpm and how much?

With your big initial you likely need much less timing until higher in the rpm.

Re: Pinging after 40-45 mins of driving?
 

I finally had a chance to start tinkering and noticed that the fuel line lays right on the heater hose, could that be causing the fuel to heat up?