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'81 K5 Blazer pinging PLS help me with the PING-PING.

J

Jason Thompson

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I need some help with pinging. I have a 400 sbc in has a COMP Cams Xtreme Energy 4x4 Cam
Duration 270/278, Lift .480/.498. It is Edelbrock 1806 Carburetor, Thunder AVS, 650 cfm. The heads are also Edelbrock 60899 aluminum 64cc chamber and the intake is Edelbrock RPM air-gap no egr valve. The compression ratio is 10.5 to 1. I run a MSD street fire HEI distributor with MSD 6al box. The only gas I put in it is 91 octane premium and thats the highest octane the have around in Peoria, AZ (N.W. Phoenix). I have run 100 octane racing fuel 10 gallons and that eliminated the ping but I can't afford to do that all the time or octane booster every fill up! My mechanic thinks increasing the jetting will help the pinging. Oh also I have advanced the timing quite a bit to stop pinging but I do still hear it at times. Im thinking the air/fuel is running lean. My question is can re-jetting the carb to increase fuel help the pinging? What would you guys recommend? Also, my valve lifters are 1.5 ratio and I was thinking of changing them to 1.6 to increase air/fuel. Please, let me know what you all think. I will start off with the jetting then maybe move to valve lifters and if that doesn't work maybe change the cam or heads! I'm frustrated and hope someone might help me out that had same situation! I think COMP CAMS recommended a cam that might not be producing enough air/fuel, however, I'm fairly new to a lot of this and don't know crap! I told Comp Cams all the information on the 400 sbc(the specs) and the recommended this cam! Like I said I'm a noob who doesn't know SH!T. Or if someone knows a good shop that could dial in air/fuel ratio and eliminate the ping would be awesome! So frustrated with the mechanics I've been dealing with lately. Thanks for any input!
 
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I just cleared up the opposite of what you have with this picture. May help you too?7582126_orig.jpg
 
If you are pinging now, advancing the timing is not helping.
I would dial in ignition timing; base, curve, and total first.
10.5 to 1 compression with those tiny 64cc chambers is probably always going to need high octane fuel.
I believe 400's came with 76cc heads and low compression.

But have you tried setting base timing at 10 btdc?
 
Thanks for all the help! I will look into a couple of these things after I get my Blazer back from my mechanic.
 
Jason Thompson said:
Thanks for all the help! I will look into a couple of these things after I get my Blazer back from my mechanic.
Click to expand...

*Generally* 10.5:1 is considered doable on 87 octane if things are setup right, with AL heads.

I don't know the 400 well, but if you can't get it to stop pinging even with 91, I would suspect your issue is fueling and timing. I wouldn't be changing hard parts until I was sure the AFR and timing was optimum, that is for sure. Dished pistons and a thick (~.043") head gasket on an undecked block don't help FWIW, you didn't mention either of those. Are you running plugs Edelbrock recommends? More concerned with the reach of the plug than whether they are fancy.

Lots of engine theory here, but aren't 195 runners and a larger than stock cam probably a mismatch for a 400?
 
The gasket is .039" in thickness and the pistons are flat with 4 valve reliefs +12.5cc. It was not zero decked, I believe it is .010 or .015(My memory fails me :confused:). Yes I'm using recommended plugs. The Blazer has returned and after installation of bigger jets in Edelbrock 650 carb. the pinging has went bye bye. I plan on installing a AFR gauge soon and then I can really dial it in to 14 to 1 ratio. The weather has cooled off quite a bit recently, so I hope the pinging doesn't come back in summer(when it gets hot out here in AZ).
 
Dyeager535, the 400 sbc is very similar to 350 sbc, it just has siamese cylinder walls because of the 4.155" bore (.030" over) and as far as I know the 350 and 400 small block chevy's Gen. 1 are very similar. Please, correct me if I wrong guys! Heavy Iron, I will definitely install one of these gauges soon and thanks Tenderfoot for the picture and info of the Edelbrock throttle linkage, that will definitely help dial things in better! Like I said before I'm a noob, however, I know with some of the ck5.com members guidance that I'll be able to fix some of the problems that I have encountered. Thanks again guys!
 
Running a 650 dbl on my 350 no problems .or a 990 cfm from carb shop no longer in exsiexist on my 461 olds motor and take that Edelbrock carb and sell it they suck for making power .efi good for rock crawl .I'm sick off all the new car problems that's why I'm back to carb 46 years old had a lot of time with carburator
 
So I had bigger jets installed and the pinging has ceased however, my Blazer seems to have less power or should I say sluggish. I don't know but it seems to be less responsive and slower. I would have thought the opposite hence more gas more power. Also, if I punch the throttle it has a hesitation. Any suggestions? I guess my best bet may be to wait and get the air/fuel gauge. What do you guys think of fuel injection? Anyone have the fuel injection kits that look like a carburetor and what was your experience?
 
heavy iron said:
Running a 650 dbl on my 350 no problems .or a 990 cfm from carb shop no longer in exsiexist on my 461 olds motor and take that Edelbrock carb and sell it they suck for making power .efi good for rock crawl .I'm sick off all the new car problems that's why I'm back to carb 46 years old had a lot of time with carburator
Click to expand...

Did you try using a fuel injection instead of the carburetor and if you did which one? What did you not like about it?
 
I haven't gone to fuel injection yet myself. Plenty here have though. The reason I want to go is much better off road capability. I have my carb dialed in much better now so my motivation isn't as present. It was flooding real bad so could forget any off road fun.
You should really figure out what's going on with yours before you make the switch. I wouldn't rely on FI to fix your problem. I would think it's better to have a good running engine before the switch. Other wise maybe compounding the problem. Should give the FI unit a normal slate to work from.
These guys here know their stuff. Be patient, ask questions. But be thorough with explaining what it's doing and what you've done. And what you have. Like when is it bogging down now? In neutral when you raise the idle? Under load at a certain speed? Details
 
Jason Thompson said:
Assuming you switched to fuel injection. Could you tell me the pros and cons of fuel injection and which one did you use.
Click to expand...
I think we should call a time out. Lets put FI talk on the back burner. Because you need to be able to understand the carb and timing tuning in order to make either the carb or FI work properly

So back to where @K5wrench was asking what the base timing is: vac advance disconnected, timing light, and a vacuum gage on the carb
 
Yeah, the thought train is running wild. It's almost always faster and easier to fix what you got than to change everything. But you have to tackle this 1 thing at a time. Pay attention to numbers and record the results (yes, write everything down!)

Start at the beginning and try the easier stuff first. What causes pinging:
1) timing is too far advanced
2) mixture is lean
3) hot spots in the combustion chamber
4) engine/intake too hot
5) compression too high or too much boost.

So first you must answer - under what conditions is it pinging? What range of RPM? Only at WOT or under lighter throttle conditions? Are you sure it's ping and not something else? If 100 Octane fixed the problem - under the same conditions (including temperature) - this question is answered. As you adjust fuel or timing, you want to adjust only this operating condition.

Which jets were changed - the primary or the secondary? Assuming the pinging is happening at heavy throttle, the secondary jets are all you should touch. It's possible your sluggish performance comes from making it too rich everywhere.

When you started, what was base timing? What kind of curve parts (springs/weights) are in the distributor? How many degrees have you adjusted in each direction and what were the results? If reducing the base timing several degrees cures the ping, the a little re-curve is all you need (you know, $10 in parts).

Other questions: what exact spark plug are you using? What thermostat do you have and what temperature is it running at?




RANT:
More fuel does not mean more power. Don't oversimply how a carb works by thinking of AFR being the same all the time. Even your weed eater has an idle jet and main jet. A 4-barrel is even more complex, delivering one AFR at idle, transitioning to another for cruising and even richer when the butterflies are way open. Some even have "off-idle" circuits. Then there is an accelerator pump, choke, air valve, etc, all affecting AFR under different temp, load and transients. So know what operating range you're in or you have no idea which section to adjust. Peak torque does improve as you go richer, maybe as much as 13.2:1, but that's a terrible ratio for cruising. Forced Induction engines will sometimes go even richer just to drown out spark knock, but it doesn't improve power. The biggest torque mixtures are more dangerous in those conditions.
 
SBC 400's can be very sensitive to the quench. Ideal is .035-.045. Any more and it'll ping at different rpms/ loads.
 
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