Want to stop pinging/detonation on a L20b donk.

[Angelripper510]

Alright back at work and here is the height.

106.95 mm or 4.2105 inch.

But hasn't had its fresh shave either for this rebuild yet.

Also spoke to the engine tuner about pinging and he thinks I should just take away the sharp edges and even polish the combustion chamber. And he thinks he can tune out the detonation. Inc re curve dizzy.

He's a GREAT old Skool tuner with a nice dyno, had my 510 tuned by him and got good numbers with good street performance. The thing that bugs me is once the motor is together and it knocks still after its been tuned i will be spewing!!!!

[smoke]

You could always add a cheap water injection kit if it still does it.

[Angelripper510]

Nice thinking,

[Nuclear Water Boy]

I once was running an LZ2.2 with Tuned Ztherapy 240Z carbs, W53 SSS Head, 10:5 compression, Damb cam, header, aluminum flywheel, recurved electronic distributor on a MSD 6A. I had no ping issues running 91-92 fuel here in New Hampshire. I would run 89 octane running to Summit Point WV because it was cheaper, running steady and not romping on the throttle gave great results. On hot steamy summer days 91 octane no less at anytime. So I'd say a good recurve of your Dizzy will do the trick, but make sure it's set up so it will only give you so much mechanical advance at a predetermined rpm.

[Driftease]

Good tunning and a proper quench somewhere between .5mm to .8mm is the ticket good luck with your build..... by the way this is what donk is in america, eeeewwwww

[smoke]

Problem with getting a good quench with that head is this.

[datzenmike]

Piston dish also messes with it. The stock L20Bs have over 11cc of dish. Flattops are best for this.

[smoke]

I'm honestly not even sure if they would make that much difference (in quench) given the chamber design. Once you get past a certain distance from any pad in there (is the part above the plug even flat? it looks tilted) then quench is meaningless, I want to say past 60. At that point, you pretty much have none and are just adjusting the compression. Or is the picture of the chamber I am looking at giving an optical illusion?

[datzenmike]

On that head, none.

[smoke]

Oh, right, I get what you are saying.

[datzenmike]

Flattops and peanut chamber is what was used on the JDM L16/18 SSS motors. Roughly 30-40% of the piston top came within 1.2 (crushed gasket thickness) of the head surface. That's a lot of pinch.

[hosestop@msn.com]

Recurve dist. and check cam specs ,and change springs in distributor ,usually stiffer to make advance later or at higher rpms (Nissan comp catalog sold sss dist. springs for this )my dist. person even welds up overall advance slot if needed .Remember we got shitty gas in Ca. so other places still get 92. +.My 2ct. been awhile ,Have two old race motors here ,one has Venolia high dome pistons ,it will need help and race gas ,will try and post a pic of pistons.

[ggzilla]

92 octane USA = 98 octane AUS. Either way for 10.47 compression it should work if you don't advance it too far. Just spin the distributor back two degrees. It'll make more power too.

 

The 1985 nissan 910 bluebird came with Bosch electronic ignition.

[Angelripper510]

Yeah I've got a Bosch electronic dizzy for it.

And yes there will be No quench with this head.

And also as I said earlier the L18 head we have here, using them would pump the comp up past 11:1.

Thanks all

[smoke]

I personally would not be at all afraid to do that 11:1. I run more on much less efficient burning engines. Figure out what your dynamic compression ratio would be, or cylinder pressure, this will tell you more. 

[Driftease]

polishing the chamber will help too

[Z-train]

On a U-67 head,new is 4.26.

Minimum is 4.245

My head was at 4.24 and I couldn't get the rattle(2.3 stroker) out with 110 octane.Strokers change the equation completely.

[smoke]

Just a readers digest version here...

 

Detonation and pre-ignition are two different animals. However, both of which are normally caused by a less than optimal combustion chamber or more to the point, lack of quench or being able to cool the mixture. With detonation, high pressure (high compression) and heat will make an explosion AFTER the normal combustion process. In other words, your piston is coming up, the spark plug ignites the mixture normally but the pressure and heat set off an explosion of the gases left over, or "end gas". The End gas does not have the octane rating to control itself form lighting under the heat and pressure, so you get a goofy pressure spike where there should be a nice controlled burn. Detonation can and will cause damage, but light to moderate detonation will not, engines run many hours with it, with no real harm. The ping you hear from detonation is just the structure of the engine reacting to a pressure spike. It occurs around 6400 hertz, which is why knock sensors are set to that frequency. If you are driving down the road with an engine that has a lot of advance, you will hear pinging and while that is FAR from an optimal situation, it will do that for thousand and thousands of miles without damage. BUT, when you get to an engine with higher output (more hp per cubic inch) the more sensitive it will be to detonation, the more powerful the detonation will be and this can start to do some damage. This is due to you making the nature of the detonation spike more powerful. This can break ring lands, spark plugs, make the piston look like it was sand blasted with course sand and so on.

 

When an engine like this detonates, it causes heat. This is due to the spike breaking through a layer of "protective gas" (thing force field) in the combustion chamber. This heats the chamber, which heats the head, which heats the water which makes the engine run hotter....which causes more detonation. Soon it just snowballs out of all control. This is where fuel mixture and proper combustion chamber design come into play. A fuel mixture that is rich (more fuel mixed with the air) makes the combustion cooler. This become a balancing act and really has a lot to do with how well your combustion chamber was designed. The less efficient your chamber design is, the richer you will have to run your fuel mixture to keep detonation down. In other words, you would be using excess fuel to cool the mixture rather than the chamber design.

 

Octane rating is based on when it will start to detonate. Or more accurately, how resistant it is to detonation. Your engine will like X amount of ignition advance with a fuel that has enough octane not to detonate. This is where your engine will build it's very best power. But...what happens if you run a lower octane fuel that does not like your timing up that high and starts to detonate? Right, you lose power and also have the heat/detonation thing going on, so what if we lower the timing to stop the detonation? Well, you can do that and it WILL stop detonating, but your engine is no longer running at the timing it likes to be at, so not optimum anymore.

 

Alright, so now what? Run high dollar fuel, retard timing, dump too much fuel in to cool it? Oooor, a better combustion chamber. There could be a book written the size of war and peace on combustion chamber design and I won't even scratch the surface with this. So here is a rough outline. There is something gear heads refer to as "LPP"  (location of peak pressure) a cylinder SHOULD be at its peak at 14 degrees after top dead center if everything is working like it should, this is where you will run the best, The LPP at 14 degrees after top dead center without any detonation is the end goal you want to shoot for. The ability to hit this falls at the feet of your combustion chamber. This is why you hear the term "fast burn heads" often. It's simple really, The faster you complete your burn, the less time your end gas has to explode and cause detonation. The end gas won't just sit there soaking up heat and pressure until it ignites. The burn happened too fast for that.

 

On the flip side, if you have a slow burning chamber (like the one we are talking about here) you will need to advance the timing if you want to hit that 14 degree LPP mark. In other words, since it burns so slow, you need to light it earlier to try and hit that 14 in ATDC. What does that do? It give the end gas lots of time to detonate. This is why the better combustion chamber you have, the less lead timing you will need to hit the optimum 14 degrees. The LPP will still happen in the same spot, but you just made it happen without so much build time. Also, this makes the engine have more power, due to the fact that your piston did not have to fight a bunch of degrees of pressure before it hit TDC. Without getting into a bunch of fluid dynamic, swirl and tumble stuff. the fact is (proven fact) you can run regular fuel in a car with 10:1 compression with the right combustion chamber. Cadillac did it (does it) and that is not a light car.

 

NOW...pre-ignition. This is caused by a hot part, such as a glowing spark plug, a heated carbon deposit, burnt exhaust valve and so on. It acts like it's own spark plug (or more accurately, glow plug). It will light your air and fuel mixture before your spark plug does. Here is the thing, when your mixture is under really high pressure, it's not easy to light off, it takes the spark plug. However, when your piston is at the bottom of the bore or just before it, almost anything would light that mixture (no pressure) and if you have something glowing in there like an edge on a combustion chamber (thus the mention of polishing them being good) or carbon it will light your mixture when you piston is all the way down at the bottom of the cylinder. So now your piston has to come up to the top, fighting against that explosion that happened at the bottom. This puts all sorts of strain on engine components. Here is the REALLY sneaky part....contrary to popular belief, you do NOT hear pre-ignition happening. There is no rapid pressure spike like detonation to resonate through the block. The only part of it you hear is when your engine turns into yard sale parts. Pre-ignition will turn an engine to junk really fast, unlike detonation that takes some time.

 

While detonation and pre-ignition are indeed two different things, detonation can be the cause of pre-ignition due to it creating so much heat it can make things glow. I have went on for way too long here and could go on for a lot longer, but it's time to stop. Really, the whole point would be, get the correct chamber design to start with and a bunch of band-aid fixes wont be necessary to avoid detonation. Older heads will not be perfect of course, but you can sure do a lot better.

[paradime]

Yet another option is running e85. Here's an article I wrote over at NWD

 

If you want to really geek out on e85 are lot's of peer reviewed research studies out there that show very detailed data on the performance characteristics of e85 Heres an abstract below of one covering the topic detination. 

Number: 2007-01-0473

Published: 2007-04-16 

Publisher: SAE International

 

 

An Experimental and Modeling Investigation into the Comparative Knock and Performance Characteristics of E85, Gasohol [E10] and Regular Unleaded Gasoline [87 (R+

 

"This study looks at the performance and knock characteristics of E10 and E85 in comparison to regular gasoline. Detailed experimental engine data and analysis as a function of compression ratio, ignition timing and fueling are presented with associated physical explanations. Comparative results are presented. Increasing ethanol content provides for greater engine torque, efficiency and knock tolerance, yet fuel consumption worsens. Knock limited trends and sensitivities are presented, for example, 5 degrees of spark retard are required with E10 and gasoline for each compression ratio increase, while the much less sensitive E85 requires only 2 degrees of retard for each compression ratio increase. Trends with efficiency and torque are described amongst the fuels tested. Companion modelling was performed to isolate the chemical kinetic differences between E85 and isooctane fuels. An adiabatic-core model revealed significant differences in reaction rates with an E85 fuel versus a pure isooctane fuel. These differences can be traced back to reactions that produce HO₂ radicals which ultimately lead to H₂O₂ buildup as a precursor to autoignition."

 

 

What's the up side?

1. Increased power: 

This is a claim that has seen it's share of skepticism and controversy, so I found a reliable scientific source of information. An SAE laboratory tests actually proves that on a N/A motor ethanol provides greater engine torque, efficiency and knock tolerance than than 92 oct e10 pump gas. For example, 5 degrees of spark retard are required with E10 gasoline for each compression ratio increase, while the much less sensitiveE85 requires only 2 degrees of retard for each compression ratio increase. This sounds good, but with forced induction e85 becomes a whole other beast,

Ethanol is not in and of itself a high performance fuel, but it does let you push compression far beyond the normal detonation limitations of pump gas and even straight race fuel. Detonation occurs when excessive heat and pressure in the combustion chamber cause the air/fuel mixture to auto-ignite. e85 is not as volatile in that respect, but that has nothing to do with the stored potential energy of each fuel. In all reality gas has more PE than e85, but there are limitations to how much, or how efficiently you can get that energy out of gasoline. It is that lower sensitivity, and natural cooling effect of ethanol during atomization that keeps auto-ignition from happening. This allows for higher compression which releases greater potential energy, thus producing more power. Greater access to it's PE is also one of the reasons why e85burns cleaner, because more of it's energy is converted during combustion. 


2. Cooler combustion:

Test studies report an average difference of 218 deg F lower peak exhaust gas temp than 87 oct E10 pump gas. I must admit, I have no idea how they defined base optimal tune for each fuel, or I should say I couldn't understand how they did it. Still, with a peak EGT of 1650 F on an average turbo charged motor, 200 deg is significant. As any turbo guy will tell you, heat is the number one barrier in getting the densestair/fuel mixture into the combustion chamber. To that end we use bigger inter coolers, water spray, ducted fans, heat shields, on and on. Take 200 degrees right of the top and you can see the benefit.

3. Zero carbon build up. 
Shit, that ones self expiatory.

4. Average price per gallon of $3.50
OK it is 30% less milage, but 105 oct race fuel is $12 per where I live. you do the math.

And 5. last but not least it is better for the environment.


What is required to convert to e85?

Honestly it's not for the faint of wallet, or the average weekend warrior. A list of fuel system upgrades are:

Teflon fuel lines
Bigger fuel pump, maybe two ethanol approved
Silica tank vent
Bigger high quality injectors (see calc below)
Adjustable fuel pressure regulator 
Tunable ECU,
REALLY GOOD DYNO TUNER WHO KNOW E85
O2 sensor.

Tuning for e85 is not as easy as simply upping the fuel delivery by 30%. It requires different timing and fuel curves, and the O2 levels need to be monitored by the ECU. plotting these curves is not something you can DIY by data-logging hard accelerations. It requires a dyno and a tuner that knows his shit.

When selecting injectors it's a good idea to select a slightly smaller injector than needed. You can make up the difference with higher pressure, but you will also get better dead time results with smaller sprayers. A good rule of thumb to select an injector than will run peak hp at no more than 85% duty cycle.

For instance, say I determined that I would need 1250cc injectors to produce 450hp on e85. I could get 1000cc injectors and push fuel pressure to 57psi to get 1250. That way I will get a much better dead time response than I'd get with a 1650, or 2000cc injector. 

Here's a quick calculation to determine the correct injector size for the amount of hp you'd like to produce. 

HP (1) X BFSC (2) Number of cylinders X duty Cycle (3) 

* Brake Specific Fuel Consumption: This is the amount of fuel consumed (in lbs. per hour) for each horsepower made. This should be .45 to .50 for naturally aspirated engines and for Turbocharged engines .60 to .65 

To calculate the injector size for E85 use a multiplying factor of 1.47 . The 1.47 number represents the difference between the stoiciometric fuel ratio of gasoline and E85. Gasoline is 14.7 and E85 is 10.0

Keep in mind, all these numbers are averages and can depend on tuning, boost, and so on, but this will get you in the ball park. 

A new development in the market are electro-voltaic sensors that can monitor ethanol levels and average it to an O2 sensor so your ECU can adjust it's map accordingly; basically turning any motor into a flex-fuel system. Again not a job for the average tuner/programer,

Measuring Ethanol Content Vai O2 Sensor 
http://www-personal.umich.edu/~annastef ... nkovic.pdf

Cheers, and I hope this come in handy for anyone interested.

Ron M..

[Z-train]

Fuel should not be used as a Band-Aid.

[paradime]

Agreed, but if you have a high compression engine that pings on regular are you saying you should lower the compression to make it run right? Or would you use 92 octane as a bandaid?

[Z-train]

Apples & Oranges.High comp motors are designed that way with particular parameters in mind(usage/driving habits/fuel). What is going on with strokers,mine included is that the wearing(milling) of the head exacerbates the CR issues and I'll be willing to bet it's not a linear curve.These engines are called "Frankenstein Motors" for no reason.

[smoke]

Why is it you milled the head?

[paradime]

What's your point Z-Train?

 

If you have a high compression engine that pings on regular, are you saying you would lower the compression, or retard the ignition 10 degrees to make it stop pinging? Or would you use 92 octane as a "bandaid"? 

 

My point is that e85 has a relative octane of 107 at high compression, it is more resistant to preignition than 110 race fuel, runs with 300f degrees lower EGT, and it's 1/4 the price. That may fix the stroker issues yes?

[Angelripper510]

I'm now thinking of welding up the opposite side to the spark plug hole to get some quench then send it off for CCing and give some relief around the valves to drop the comp abut to keep it around 10.5.1

While I'm at it here's some pics of the twin carb manifold I've made for this motor!

It not finished yet, need to join the 2 manifolds and make a couple of threads for the linkages and vacuum line for the brakes.

Killa I'm happy with it!