Problem with Compression or Timing on High Compression L20b causing pinging

[Stoffregen Motorsports]

Having the distributor recurved is an excellent idea for a street performance engine. Making sure the advance comes in at the right moment is crucial to eliminate pinging.

 

You can buy some parts from Nissan Motorsports like a solid breaker plate and a distributor cam that is already advance limited, but even if you bought those parts yourself, I would still have someone assemble it to make sure all the inner workings are functioning properly. I usually delete one of the springs during the modification process.

 

With a proper distributor curve, I would set the initial timing around 12 deg and total timing at around 30-32 deg. You should also delete the vacuum advance (the solid breaker plate will take care of this.)

[banzai510(hainz)]

If a L20 with flattops and open head its a PINGER!!!!!!!!!!!!!

[KoHeartsGPA]

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.

Side drafts don't use a return line to the tank unless you mod it, they suck so much fuel all it needs is shield tape to reduce heat exposure from hot engine and vapor lock prevention, and intake manifold doesn't have coolant passages, (let's not confuse him).

[racerx]

510SSS, was it pinging after newly built or ran okay then started pinging?

[john510]

My L20 has 10 to 1 compression and does not ping with 91 octane and 12 degrees timing.A87 peanut head and .488 lift cam.Somethings not tuned right,like everybody has already stated.

[datzenmike]

Side drafts don't use a return line to the tank unless you mod it, they suck so much fuel all it needs is shield tape to reduce heat exposure from hot engine and vapor lock prevention, and intake manifold doesn't have coolant passages, (let's not confuse him).

 

Rubbish. A two liter engine uses 211 cu feet of air per minute at 6K. Doesn't matter if you have the stock Hitachi, SUs, R-1 or side drafts the amount of fuel used to mix with this is going to be close to the same unless you plan to run 6 to 1 mixture.

 

What about around town, stop and go, waiting at the lights. Hot re-start? ALL carbs will benefit from a return line. 

[KoHeartsGPA]

Nobody using side drafts without return line including myself have any issue whatsoever by not having one, that is not his problem.

[G-Duax]

NGK-6s are OK for a dead stock engine, which you don't have.

Like someone above said, run a colder plug.

 

You may also be too lean at the rpm that it's pinging at.

I really would never consider figuring this problem out these days without an A/F meter.

[datzenmike]

Nobody using side drafts without return line including myself have any issue whatsoever by not having one, that is not his problem.

 

No way you know everyone with side drafts or weather they run a return line or not. Didn't say it wouldn't work said ALL carbs benefit from having it. Gas tank stays cleaner too. It's an L20B and they all came with a return line for a good reason. They run hot and even hotter under the hood. Heat soak is a problem in hot weather. Removing it is counter productive.

 

Probably not his problem but anything that will reduce adding heat to intake air will reduce pinging. Sometimes it isn't one obvious thing but many smaller ones that add up.

[KoHeartsGPA]

Quit spinning shit, Mike, I said..that's not his problem, jeez!

[510SSS]

-Ah ok, nice one Mike ya I guess I couple try to funnel some cooler air in through the front of the engine bay and direct it toward the carb intakes. Right now I am running it with Air filters over the velocity stacks, maybe with open stacks and just a screen it would run cooler?

 

-I am not positive about the jetting on the Mikuni carbs, however I am pretty sure Wolf Creek sent me an entire set of different ones with my Carbs for tuning, so perhaps I could change the jetting size.

 

-To answer you're question about dieseling, no it does not regularly diesel on shut off, but it did do it once when I got back from a long trip on a hot day, but it was only for a second, barely shook the car.

-As for the fuel return line, yes I do have it deleted, Idk if it can be hooked up again, I will ask my  mechanic.

 

-I hope the carbs don't have a small vacumm leak or something? Isin't that a common problem with Mikuni's

in that the covers shake loose causing a small leak on the carb?

 

-Today I ordered in some NGK BP7es-11 plugs, I am going with you're advice and seeing if going a step colder will help out.

 

-I'm considering ordering a Heat Shield for the Carbs from Futofab, seeing as with the oversized valves and cam, it seems to be producing hotter exhaust, therefore it is causing the fuel to overheat.

 

-I am thinking about just filling the tank with 100 octane to see if it eliminates the pinging, then I will know it is a compression issue and not Ignition related.

 

-To answer racerx, yes it is a newly built engine and it has been pining a little and fouling plugs since the beginning, not a new problem, still trying to get the kinks worked out with a custom build.

 

-No Hainz, it does not have flattops, as I already stated, It has 88.5mm dished pistons.

 

-Do you guys have a Datsun Comp part number for the breaker plate? I don't exactly what you mean, set what up properly? Could you elaborate Stoffregen?

 

-Thanks everyone, I think I am beginning to zero in on the problem, got any other ideas, throw em my way.

[KoHeartsGPA]

Always check bolts and nutts, the L20b likes to rattle them loose, I do so every week and especially around the carb area.

[datzenmike]

Heat is the cause. The most obvious source is under hood air. Even Datsun ran a hose from the snorkel on the air filter to in front of the rad on stock L20Bs. You're sucking HOT under hood air from the rad and the exhaust that's 8" away.

 

 

 

In the graph below, (BLACK LINE) room temperature air (about 60F) is compressed to 100 PSI. the air temp is approaching 500F!!! Now imagine 200 F under hood air compressed to over 200PSI

 

 

 

 

 Makes a lot of sense to run 80F air from in front of the rad

[510SSS]

Hmm ya Id rather not have to build some ugly air ducting, maybe I can just play with the timing some more and the carb jetting and get it to run cooler with the new plugs and get the heat shield, I will let you guys know what effect that has on the overall problem. Would maybe running a colder thermostat cause the engine to not get as hot? Does it matter 3 hole vs. 2 hole thermostat housing? I heard a rumor that the 3 hole cooled better? Maybe I could have my intake and header ceramic coated inside and out...but that's talking some major coin at that point would rather find some other way to mitigate the pinging. 

[Stoffregen Motorsports]

 

-Do you guys have a Datsun Comp part number for the breaker plate? I don't exactly what you mean, set what up properly? Could you elaborate Stoffregen?

Sure.

 

The breaker plate replaces the plate to which the points are mounted. I guess I should clarify that this is for the L series single point or dual point distributor found in early 510's, trucks, etc. It does not have any rotational movement. The vacuum advance is hooked up to a plate that does have rotational movement and when vacuum is applied, it rotates the plate and changes the timing. You don't need this plate, you could simply unplug the vacuum advance and the spring in the vacuum mechanism will hold the plate static.

 

The distributor cam also has rotational movement, but is limited by the length of the slots. There are two weights inside the distributor that pivot and move when the engine changes revs. They are affected by centrifugal force and controlled by two springs that hold them back. The pins on the weights ride inside the slots on the cam, and allow the cam to advance mechanically (vs by vacuum) when the revs increase. The length of the slots delegates how much "mechanical" advance (vs vacuum advance) your distributor has. A stock distributor cam usually has too much allowable advance for a higher performance engine. You can also adjust the length of the slots by welding them up and filing them to suit.

 

So to recap, the plate allows for vacuum advance, which you don't want in a high performance motor.

 

The weights move by centrifugal force when the motor is revved, allowing mechanical advance, denoting when the mechanical advance comes in.

 

The slots in the cam denote how much mechanical advance you get.

 

Rebello Racing has been modifying distributors for decades, and it's a pretty simple operation. You could send it to them and have them go through it for about $200.

[flatcat19]

Hmm ya Id rather not have to build some ugly air ducting, maybe I can just play with the timing some more and the carb jetting and get it to run cooler with the new plugs and get the heat shield, I will let you guys know what effect that has on the overall problem. Would maybe running a colder thermostat cause the engine to not get as hot? Does it matter 3 hole vs. 2 hole thermostat housing? I heard a rumor that the 3 hole cooled better? Maybe I could have my intake and header ceramic coated inside and out...but that's talking some major coin at that point would rather find some other way to mitigate the pinging. 

 

 

Stop spending money. Set base timing, go from there. 

 

I didn't read you had a header prior...toss that junk. Get an L16 manifold. Headers do nothing but radiate heat. 

[510SSS]

Ya I would but headers so shiny...L-16 manifold so restricting...have 2 1/2 inch exhaust.

[racerx]

How much hp do you think u gain with header?

[Stoffregen Motorsports]

5 to 10 hp on a L20B with a cam and a side draft.

[datzenmike]

Hmm ya Id rather not have to build some ugly air ducting, maybe I can just play with the timing some more and the carb jetting and get it to run cooler with the new plugs and get the heat shield, I will let you guys know what effect that has on the overall problem. Would maybe running a colder thermostat cause the engine to not get as hot? Does it matter 3 hole vs. 2 hole thermostat housing? I heard a rumor that the 3 hole cooled better? Maybe I could have my intake and header ceramic coated inside and out...but that's talking some major coin at that point would rather find some other way to mitigate the pinging. 

 

 

There is no short cut to lowering under hood temperatures. Playing with adjustments won't do it. Engines make heat .... about 30% of gasoline energy is turned into motion, the rest is waste heat and noise. Just like you header, no one can see your cold air ducting so who cares as long as it runs well?  

 

The three hole thermostat covers are found on '79 and '80 L20Bs and that's all they are... 3 instead of 2 bolts.

 

You can try and force the engine temps down with a colder thermostat but this isn't how they were designed to operate and you are not really fixing anything.

[racerx]

let me try this again....is your distributor rotor facing your number one spark plug wire at compression stroke/TDC?  take off the valve cover, are your 2 front valves at 10 and 2 o'clock?  is your oil pump shaft tange at 11.25?

[510SSS]

Ya the oil pump tang is at 11.25 I triple checked that, not sure about the number one spark plug though, I know I checked it but that was months ago, I will double czech that. Ya I guess you're right Mike running properly is more important, maybe I could utilize some high temp header wrap? Or how about cutting some shark gills into the hood, JDM Bluebird-U style? That might let some more air through? Thanks for any other advice you guys can give, maybe I will just have the distributor sent out to Rebello, they seem pretty damn reputable. 

[racerx]

when you say you are not sure about number one spark plug, what does that mean? Be specific and true with base line first before you start spending money.  As they say measure 3X and cut once, not cut 3X and measure once. Trust me on this one. I, and others, have been through this and we are trying to help you.

[datzenmike]

Cutting the car is mutilation. Header wrap may reduce the heat but won't cure the hot air the carbs are using. Build a plenum around the air horns and duct cold air to it. You can still see the carbs, don't worry. This is for twin DCOE

 

[510SSS]

Wow, that does look like a good solution, I think I will have to order one of those Mike, kinda pricey, but sounds worth it to make this thing run right after two years of headaches. Do I have to eliminate my highbeams in order to install it? Hey Mike i'm looking at his Plenum from http://www.boiperformance.com.au/cold-air-box-intake-, would that work with 40mm Mikunis or is it only compatible with 45mm DCOE, any info is appreciated.