Jump to content

Problem with Compression or Timing on High Compression L20b causing pinging


510SSS

Recommended Posts

Hi all, I am having trouble with my newly build L20b. I think it has around 9.5 to 1 compression with a 284 lift cam, when I calculated it. However, it appears that it is pinging on high load, such as going up hills or flooring it. It is fine when I accelerate slowly, however it is fouling plugs occasionally as well.

 

-What do you guys think would be the best solution? I am thinking of mixing in race gas to see if Ignition timing is the problem.

 

-I have thought of getting the distributor re curved, based on my cam card settings. Anybody know a good company that offers this service? However, I am afraid this might not ultimately solve the problem.

 

-What would you guys suggest, should I maybe switch back to a dual points system or a Mallory race distributor? Currently running Electronic Module distributor, rebuilt, for a 1979 Datsun 620.

 

-The only other things I can think of to help the problem out, would be to install a choke, so I can retard the timing more, it would lose power but at lease not ping for now.

 

-Maybe I could put it on a Dyno, and build a map so I could run a crank fire ignition that would alter the amount of fuel delivered at different RPMs in order to help prevent pre-ignition.

 

-Otherwise, I would have to pull the head off and install a thicker headgasket, or polish my combustion chambers, which I really don't have the money for at this point, so I am hoping there is some other solution, besides running straight 100 octane,

 

-Any help is greatly appreciated-

Thanks

Link to comment
  • Replies 196
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Assume you're already running 92 octane. What is your timing set at? What plugs are you using? Which head do you have?

Lots of vital information left out. 

 

 

9.5 to 1 compression shouldn't ping. Hotter plugs and reduce timing? 95 octane? 

Link to comment

Hi all, I am having trouble with my newly build L20b. I think it has around 9.5 to 1 compression with a 284 lift cam, when I calculated it. However, it appears that it is pinging on high load, such as going up hills or flooring it. It is fine when I accelerate slowly, however it is fouling plugs occasionally as well.

 

-What do you guys think would be the best solution? I am thinking of mixing in race gas to see if Ignition timing is the problem.

 

High compression automatically needs less that stock timing. Yes within reason you can solve this by increasing the octane but at $7 a gallon for 144 aviation fuel this is not practical. Turn the timing back until it stops pinging and this is where you should run it.

 

-I have thought of getting the distributor re curved, based on my cam card settings. Anybody know a good company that offers this service? However, I am afraid this might not ultimately solve the problem.

 

It won't.

 

-What would you guys suggest, should I maybe switch back to a dual points system or a Mallory race distributor? Currently running Electronic Module distributor, rebuilt, for a 1979 Datsun 620.

 

Stick with what you have.

 

-The only other things I can think of to help the problem out, would be to install a choke, so I can retard the timing more, it would lose power but at lease not ping for now.

 

The choke has nothing to do with the timing. It's only used for about 8 minutes as the engine warms up

 

-Maybe I could put it on a Dyno, and build a map so I could run a crank fire ignition that would alter the amount of fuel delivered at different RPMs in order to help prevent pre-ignition.

 

Throwing money at it hoping to cure a problem isn't the way to go.

 

-Otherwise, I would have to pull the head off and install a thicker headgasket, or polish my combustion chambers, which I really don't have the money for at this point, so I am hoping there is some other solution, besides running straight 100 octane,

 

-Any help is greatly appreciated-

Thanks

 

 

Pinging causes.

 

 

Too high compression for the octane gas used. Or octane not high enough. Compression sets off the fuel just like a diesel.

 

Timing too advanced. This is not a stock compression engine so stock settings of timing are useless. Needs less timing.

 

Higher compression may need cooler plugs that the stock ones. Plug electrode gets hot and becomes an ignition source.

 

Fuel too rich, combustion chamber carbons up. Carbon glows from the heat and becomes an ignition source. Read the plugs. Black or dark brown it too rich. Light tan is better.

 

Engine running too hot. Should be around 180F. If over heating it will ping and diesel.

 

 

What head is on this L20B? Is it open or closed chamber??? What pistons? stock?

  • Like 1
Link to comment

Dosen't seem to be overheating have large radiator and dual electric fans, I was thinking maybe a heat shield under the carbs would help a bit, running Dual Mikuni 40mm's with jetting by Wolf Creek Racing for a modified long rod stroker L2.1. Head is a U67 open chamber with slightly dished pistons 88.5mm.

 

-Colder plugs, that sounds like a good idea, thx Mike. I will try to read the plugs tomorrow and get back to you on that point.

 

-Timing is around 5 degrees, seems to need to be retarded more than stock setting otherwise it won't start or run.

 

-I'm in Cali so max we have is 91 octane with Ethanol = shitty gas. IDK, if they have 95 octane available around here, I was gonna try to get some AV gas 100 Octane from the Airport and mix it in.

 

Anything else you guys can think of that could be the cause, could it be the cam timing?

 

Thanks again.

Link to comment

9.5:1 should be fine. That's not high. I'm 12.3:1 and I run 100 octane. I can allmost get away with 94. Maybe if I had water injection.

 

Your timing must be out or something weird is going on. What do you have in there for plugs? If this is a new motor, did the edge of the chamber get the sharp edge rounded off?

Link to comment

Also with a bigger cam it will like more advance at idle, but it will want less on the top end. I have mine set at 15 degrees at idle, if I go down to 5, my egt goes crazy and my exhaust glows at idle. I have a spare matchbox dizzy that I'm just gonna lock up and try running it solid at 30 or so. Right now I have about 36 degrees with full mechanical advance

Link to comment

Also with a bigger cam it will like more advance at idle, but it will want less on the top end. I have mine set at 15 degrees at idle, if I go down to 5, my egt goes crazy and my exhaust glows at idle. I have a spare matchbox dizzy that I'm just gonna lock up and try running it solid at 30 or so. Right now I have about 36 degrees with full mechanical advance

 

This! Especially if your pinging up top. These distributors put out a shit load of advance at RPM. Figure out what your initial timing is, how much you gain at Vacume and how much your total mechanical is at full RPM. The total shouldn't be more than 34-36 degrees.

 

If your timing light has the adjustable advance on the gun, run the RPM's up to around 2500 and see where your total is by turning the advance dial till your marks line up. 

You will be surprised. 

  • Like 1
Link to comment

You should get or make a heat shield, Thays a MUST, you can make one for under $25 or buy theirs for $125, are your fuel lines wrapped in heat shield tape? I doubt this will cause the pinging but it will prevent vapor locks.....here's my setup, it's a single 48 mikuni all stock running the BP7ES NGK and I have a whole set of jets, the hotter the weather the higher jetting she wants, you need to check what you have now....

 

IMAG0249.jpg

 

IMAG0315.jpg

 

Jetting and timing are important, get those two sorted out before trying any special blends of fuels...

  • Like 1
Link to comment

For plugs right now im running NGK BP6ES-11's, it seems like every 2 hours of drive time or so so, it will foul and drop one cylinder. Hmm good idea about heat wrapping the fuel lines, I did notice one day when it was 95 out one of the carbs did sound like it was bubbling when I popped the hood to check my ignition timing.

 

-I will try to throw a timing light on it and see what my exact Ignition timing is, do you guys think that maybe converting to a MSD 6 box could help with the issue, I have heard of people running 11:1 compression with the MSD boxes and 91 octane, just a thought.

 

-I will buy a couple different sets of different plugs and see if this has any effect on the pinging/plug fouling issue.

 

-Do you guys think installing a crank fire ignition would help the problem, this Datsun guru I talked to said he used to do it on his 510 race motors, and it helped him to provide different fuel amounts when it came on cam.

 

-Could it have to do with my cam perhaps, maybe it has too much lift for my application? Not positive just throwing some ideas out there.

 

Anything else I might have overlooked?

 

-Ratsun rules btw.

Link to comment

I had 9.38:1 on my bored out L18, U67 head, stock L20 cam. Chevron Premium gas was the only thing I could run, Everything else made it ping on load. 195 thermostat. 7 heat level plugs. Slightly rich tune on carbs (fixed dieseling and pinging). Ignition timing was set by trial and error, if it pinged I dialed it back a bit.

  • Like 1
Link to comment

Get a box around the air filters and run cold air in from in front of the rad. Pinging is basically the heat of compression firing the fuel mix.. just like a diesel. Do everything to reduce the heat in the combustion chamber, including NOT using hot air from the rad.

 

Make sure your fuel return line is working or make one by using what all L20B engines came with. The return line constantly circulates fresh cool gas from the tank past the carb. Fuel does not absorb heat while waiting to get into carb.

 

Heat shield or header wrap to reduce radiant heat to the intake. What head you running? If U67 it doesn't have the water cooling ports for the intake. If you have after market intake it may not either. If running stock intake get one from a '78-'80 L20B and drill holes in the U67 head. Coolant flow through the intake runners absorbs heat.

 

Oil cooler.... Oil gets hotter than the coolant so reducing oil heat takes some of the cooling load off the cooling system and avoids temp spikes. Oil also goes places coolant doesn't, like the underside of pistons.

 

Valve lash. Valves are cooled only by heat transfer to the seats when they are closed. Make sure the lash is correct so they have the time needed. A tight valve will run hotter.

Link to comment

Again, I would check your timing to make sure it's timed right.  Set it to TDC first and should line up with marker. If not your distributor can be off.  Similar thing happened to my 65  Mustang and it was pinging so I tried octane booster and retard my timing - nothing and still pinging, was even gonna try sea foam thinking it was carbon build up.  Glad I did not do this cuz I heard mixed reviews. Upon close examination I noticed that my harmonic balancer was all messed up, the hard rubber between the metal parts was all cracked up because of the HB being out of whack my timing was off by 20 degrees or so.

 

Our datsuns don't have a HB but I'm guessing your issue is an easy fix and don't drive around too much with the pinging, it can mess up your engine.

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.