Detonation and stock L28 NA

[Pharaohabq]

Seriously? You really believe that? I did what just about every other turbo car did in the 80's in Japan. You didn't even bother to show without at least 350PS... Less than that and it wasn't considered worthy. 300HP L28's in turbo trim were running as daily grocery getters.

I don't know how many miles JeffP has now on his L28, but I know he rues the money spent on the expensive forged bottom end he wasted two times whilst learning to tune... Now that he has it down that stock bottom end has run 475hp to the rear wheels (more than the stroked did at 21psi I might add) and he's dialled it back to around 450 for longevity.

Luck has nothing to do with it, it's not getting greedy and doing something stooped that keeps your engine in one piece.

The compressive strength of the rods and pistons aren't ANYWHERE NEAR their limits at these pressures and engine speeds.

In fact, for daily driver usage I was running 87 octane California Arco EC1 for as long as they had it, and my boost was turned down to 12 accordingly...

Detonation occurs in NA engines just as commonly as Turbos, and the head gaskets that routinely blow out are evidence of that. My Cherry Gasket isn't some gimmick-gasket to lower compression, it was an OEM Equivalent. You don't need MLS, In fact, if you put MLS in the engine, chances are good you WILL break something when you detonate. Jeff figured that out, after the third Fel-Pro blew out, he understood he was detonating. So he tuned accordingly...

I don't have a clue where you're getting your information, but explain to me why "15# is more dangerous on an L24 than an F54"--I mean really?

You have and are spreading some pretty egregious misconceptions here, one is the myth of boost and pressure. I can show you dyno pulls of an 8.5:1 engine at 8.5psi making 300+ HP, the bottom end BONE STOCK! With the sock head and cam that power was way down, and with a stock turbo, stock cam, and un ported head yeah, you would have to tune far more carefully because the heat that comes with a stock T3 pumping 16# is on the ragged edge. But a different turbo, pumping 8.5 psi...no inter cooler necessary baby! With the stock crap, and 16 psi, absolutely.

The bottom end can handle it. NA or Turbo. The difference they will make is negligible, the skill to tune may be different...

But the premise that the NA bottom end somehow can't handle it is ludicrous. And that the L24 is somehow inferior and like some ticking time bomb at the same boost levels is similarly ludicrous!

Frankly, if you go with the guys in the know, for maximum longevity and power production, rigidity in the bores is key, and for that the older blocks, and the N42 in particular excel,especially when bored oversized like so many want to do. F54 is nice in stock bore size, and that's about it. The 1100HP L28 was an N42...

NO engine is designed to handle detonation, save the knock engine the sae uses to test fuels... NA or Turbo, you detonate, you will go boom. Not if, when. As I said before, the key is not getting greedy, and doing something stupid. Know your limits as a tuner, and have realistic expectations from what you're building, and the engine will be as trouble free as a stocker, and blindingly fast.

***this has moved away from L28/VG30, if there is a debate about L-Engines ability to hold up and what it's design limits are, I'd suggest this move to a different thread***

 

 

Moved to new thread:

 

Perhaps Tony you can expand on the tuning required to prevent detonation in NA L-28's. I've only seen them blow up when boosted too much. I will admit my turbo experience is limited. I understand Detonation is VERY bad. I understand contributing factors to it. 1100HP on an L28 seems incredible.

[Tony D]

This is a thread asking what can be done with an NA L28 that has been converted to turbo duty, or NA detonation prevention in NA service?

Gollum made good follow up points to what is required, quench, tumble in the combustion chamber...and proper tuning in regards to AFR and Timing.

Gollum pointed out the misconceptions regarding enrichment when knocking.

The key as I have said is not doing something stupid...Gollum gives examples of this in his follow up post.

People who don't know what detonation is, and think only audible knocking damages engines...as I have posted before the detonation that kills your engine is the stuff you never hear. I've seen it in two dyno pulls. Engine went lean,never heard a single rattle at all, but sunk the ing lands on five of six pistons...forged pistons at that!

A piezoelectric microphone style knock sensor (like VW used) can be bolted to the rear cylinders, run through an amplifier circuit, and listened to through a good pair of headphones and you will be AMAZED how much most tunes detonate! And you think it's running just fine because you never hear that "marbles dropped on a tin sheet" sound.

Get good instruments to quantify detonation, tune away from it, and you will be amazed how much power you can make from an NA Turbo conversion.

As to NA failures on detonation, my bud backfired in a barrel of his Webers, it started a fire inside his air cleaner which got molten plastic sucked into his booster Venturi. Running to a normal 7,000 he blew his head gasket. Broke all the ring lands in that cylinder. Never heard a thing, the blob of plastic restricted fuel flow through the booster enough that the burn rate changed and cylinder temps soared, and boom! One blast in 3rd gear to 80mph and his engine was toast. It is that easy.

And you can put what ever head gasket on there you want, you just push the failure to the next weakest link in the chain!

[Snailed]

A piezoelectric microphone style knock sensor (like VW used) can be bolted to the rear cylinders, run through an amplifier circuit, and listened to through a good pair of headphones and you will be AMAZED how much most tunes detonate! And you think it's running just fine because you never hear that "marbles dropped on a tin sheet"

 

Yes! This is gospel. If you have a wideband oxygen sensor in your car, you should have set up knock ears the day you plugged the wideband in.

[madkaw]

This is a thread asking what can be done with an NA L28 that has been converted to turbo duty, or NA detonation prevention in NA service?

Gollum made good follow up points to what is required, quench, tumble in the combustion chamber...and proper tuning in regards to AFR and Timing.

Gollum pointed out the misconceptions regarding enrichment when knocking.

The key as I have said is not doing something stupid...Gollum gives examples of this in his follow up post.

People who don't know what detonation is, and think only audible knocking damages engines...as I have posted before the detonation that kills your engine is the stuff you never hear. I've seen it in two dyno pulls. Engine went lean,never heard a single rattle at all, but sunk the ing lands on five of six pistons...forged pistons at that!

A piezoelectric microphone style knock sensor (like VW used) can be bolted to the rear cylinders, run through an amplifier circuit, and listened to through a good pair of headphones and you will be AMAZED how much most tunes detonate! And you think it's running just fine because you never hear that "marbles dropped on a tin sheet" sound.

Get good instruments to quantify detonation, tune away from it, and you will be amazed how much power you can make from an NA Turbo conversion.

As to NA failures on detonation, my bud backfired in a barrel of his Webers, it started a fire inside his air cleaner which got molten plastic sucked into his booster Venturi. Running to a normal 7,000 he blew his head gasket. Broke all the ring lands in that cylinder. Never heard a thing, the blob of plastic restricted fuel flow through the booster enough that the burn rate changed and cylinder temps soared, and boom! One blast in 3rd gear to 80mph and his engine was toast. It is that easy.

And you can put what ever head gasket on there you want, you just push the failure to the next weakest link in the chain!

Tony,

Isn't one of the issues when coverting NA to turbo engine is that builders throw a mega thick HG on there to lower CR and only ruin the anti- detonation characteristics of the OEM squish?

I know your not a big Corky Bell fan, but I remember reading that he said the wrong thing to do with a high CR. Build is to alter the stock squish.

When I do my turbo conversion on my L24, it will be staying at 9.5

But I will be running MS

[OldAndyAndTheSea]

Tony,

Isn't one of the issues when coverting NA to turbo engine is that builders throw a mega thick HG on there to lower CR and only ruin the anti- detonation characteristics of the OEM squish?

I know your not a big Corky Bell fan, but I remember reading that he said the wrong thing to do with a high CR. Build is to alter the stock squish.

When I do my turbo conversion on my L24, it will be staying at 9.5

But I will be running MS

 

 

Yeah, I am converting my N42 combo right now. Sticking with the 8.3:1, with SDS

 

Didn't understand why someone would build a N42 block to only throw a huge gasket in there to lower the compression.

 

Why not just build an l28et from the start....

 

I want the higher CR, so this motor is my first choice.

[johnc]

Its not just the AFR or engine tune...

 

Inaudible detonation in number 5 (due to a localized hot spot around the exhaust valve seat) on my NA 13.6 to 1 compression ratio engine created enough vibration to drop the seat out of the head on a 3 to 4 upshift. Found most of the seat in the intake manifold. Six new pistons and a lot of welding and machining on the chamber in number five got the engine running again. Cooling system changes as mentioned in other threads solved that problem.

[Tony D]

John C speaks the truth.

I called JeffP to check his progress, stock bottom end and is now at 17psi on pump gas loosing traction at 4000 in 3rd gear, and sometimes in third if he isn't running wrinkle walls. He has now surpassed his 3.0L build when it was featured in the magazine. He's at close to 500RWHP, and out of load scalar and injector pulse width on the Ford Lightning MAF and 729CC Injectors. He's running to 7200 and now wishes he dad his VO7 short block so he could do what I suggested and run it to 8,500!!!

The key is cooling the head properly, and proper fuel and spark control.

He says he's just now sensing some ping in the mix (and I as soothsayer reminded him "don't do anything stoopid!") so now wonders if he should get some race fuel, or start with he Methanol injection...

The mantra repeated to Jeff and I by the E-motive guys was "cooling, cooling, cooling" we would ask about fuelling, they would talk about cooling. We would ask about timing, they would say "we never had a DNF from the cooling system!"

The stopgap methods of addressing detonation (lower CR) are just that, a poor bandaid.

MLS gaskets and O-Rings aren't meant to contain NORMAL cylinder pressures... Do the math at 1,100 HP to find peak cylinder pressures for the piston crown and you can see your material strength requirement.

Oh, did I mention Jeff is running a FelPro. He thought they were crap because they kept blowing...until on the third one he saw detonation damage on the piston crown. Damn, they blew because pressure was ABNORMAL!

There are so many myths out there from tried and proven "works good enough" band-aid remedies, that finding the real SCIENCE behind the ROOT CAUSE of the failures...

And Jeff now wholeheartedly recommends my approach o turbo engine building: spend your money on fuel and spark, bolt ons, and head/cam work and learn to tune on the STOCK BOTTOM END, when it goes, it's not material failure...it's your inability to properly tune that detonated and broke something. Once you have your stocker tuned (7,000 rpm map) by then you should know how to tune, you will have AT LEAST one core for he forged buildup, go build it and tune the last 1,500-2,000 rpms of turbocharged screamer power.

But if JeffS build is my indication, he's at or near 500rwhp now on a stock bottom end. What's your expectation for power increase in that last 2,000 rpms? It's really for longevity at that point because the fuel and spark are already tuned!

Detonation Kills. Stock $150 Junkyard Bottom End, $3,000 Forged Rebello Bottom End, or $?,??? Sunbelt Bottom (or Top) End!

[s30red240z]

And what is the limit for a L28 stock bottom end? when tune is almost perfect.

[Gollum]

Well even though the threads of the L31DETT all died I'd say it's safe to say the stock rods will reach 700rwhp. I personally think the pistons MIGHT survive that if the condition were right:

 

1. Cylinder temps need to be LOW LOW LOW.

 

2. Intake air temps need to be under CONTROL, sub 150F

 

3. Big aspect: The head needs to flow well enough that you're not needing to run 30psi to get to those power levels. The more boost you're running the more heat your fighting, and you'll already have enough heat from the horsepower to deal with.

 

So really there's two questions in that one you ask. 1. How much power will stock pistons take with the stock head? 2. How much power will the stock pistons take with a modified head, but let's add a 3rd just for the hell of it, 3. How much power will the stock pistons take in a theoretical perfect world?

 

The other huge question in all this is "what fuel"? Not all fuels burn the same and exhibit the same loading forces on the piston. It's a minor detail, but it's these minor details that kill you if you just guess and figure "well it's good enough"...

[Gollum]

Thought I'd offer something more on the initial topic here.

 

The thing about detonation is that it's poorly understood by most hot rodders, tuners, car builders, what ever you desire to call them. The mere fact people even car about the octane number of alcohol or LNG. It took me quite a lot of searching to find the answers I was looking for on the subject, but the most important thing I learned was that the whole octane rating system was NEVER designed to compare horsepower, or even compare gasoline to other fuels. It's SOLE purpose was to evaluate how different PETROLEUM BASED FUELS would run in comparable engines. Basically, it was to make sure you didn't damage your engine, and bought an appropriate grade fuel.

 

The most important thing to realize is that the octane rating was done in a test engine, just like an engine in your very car, only it's a single cylinder engine with adjustable compression ratio. There's two models of testing, the more prominent of the two you keep the ignition timing at one point and then increase compression till detonation is detected. In the other method you adjust timing with compression, but it's still a static timing setting for each compression level. If you've dealt with any alternative fuel to petroleum gasoline you should already see the issue. Not all fuel bases have the same burn rates, thus not all fuels have the same "timing requirements" to make peak horsepower. Remember, the goal of power is never to run as much timing as you can, but to place the peak moment of force just past TDC to allow as much energy as possible to be transferred to downward motion.

 

This test method then is ONLY useful to compare similar fuels against each other, or if you're checking a fuel for a wold in which you can't adjust timing of an engine.

 

Yet, for years hot rodders have thought "more octane means more power!" which couldn't be further from the truth. If this were the case, then petroleum based gas over 98 octane would be able to out perform E85, but that's not the case. In fact, even if you factor in the fact that E85 is lower energy density, but also factor in the extra fuel you're running to reach stoich or even "peak rich torque", E85 is still making even more power than it should in THAT calculation!!! This isn't to show how "great" ethanol is, but to show how broken our understanding of fuel, power, octane, and detonation is.

 

So, lesson #1. Detonation is a burn characteristic. Don't confuse it with a timing issue or a mixture issue. Even though both of those things in our world "SOLVE" the problem, that doesn't mean that's what detonation is.

 

#2. Detonation is NOT preignition. There IS a serious difference. If you compression gasoline vapors in oxygen enough it would combust all on it's own without any help from a spark. This is preignition. What we're talking about killing motors is detonation. Detonation is what happens when an even like preignition, where the fuel does combust on it's own accord, is started by a previous spark event. Detonation happens AFTER your spark plug fires, preignition happens before, or without the spark plug firing.

 

So, knowing just these two things, which you can go much further in detail on, you'll be able to deduce that what we're dealing with is chemical stability, or burn stability. When you start ignition in a sealed chamber pressures rise throughout the chamber, long before the flame reaches all the fuel molecules. This very pressure increase can be enough to send the another strain of fuel molecules into combustion. Now you have multiple flame fronts in one chamber. This is detonation.

 

Ask a chemist how to prevent detonation and they'll most likely say "remove the heat". This leaves us hot rodders saying "well... we... ummm... lower compression!!!" because even the beginner hot rodder understands that compression = heat. Hot rodders, especially of old, know that heat + HP and thus begins the never ending battle of HP versus compression versus timing which is the VERY thing we're actually talking about in this very thread, even though it hasn't been directly discussed much at all.

 

But, as you might know, there's a plethora of ways to remove heat from the chamber, all of which are things attended to by real race teams, especially formula 1. First and foremost is cooling your cylinder head which forms a good portion of the overall chamber. Next you want to cool the piston as much as possible. There's two ways to cool each. The piston is cooled by oil, it's very lubrication, and the cylinder head is cooled by water, and also oil to a minor extent. The block is cooled by water as well, and there is heat transfer there between the piston and block, but I'd argue it's insubstantial, ESPECIALLY when we consider the other main contributor to temperature control....

 

...Atomization!!!!! What's the biggest difference between a cold engine and a hot engine? One runs absurdly rich, and one can run a wide range of fuel ratios. A cold engine needs to run huge excess amounts of fuel because it's gasoline VAPORS that burn, not liquid and the liquid needs HEAT in order to atomize and become vapor. Until the engine is warmed up a bit we need huge amounts because so little atomizes. But there's another factor at play here. Basic physics: Every action will cause an equal and opposite reaction. Just as it takes heat to atomize fuel, the atomization process actually REMOVES heat through "latent heat transfer". This is a huge reason direct injection motors can be more aggressive with timing and compression, as they can remove more heat from the chamber. When you inject fuel pre-valve you're removing heat from the air, and also the intake and intake valve itself, which hardly matters at all. The extra heat that's being removed from the intake can be removed from the piston and cylinder head when utilizing direct injection.

 

Besides just those basic cooling aspects there's also other forms, such as material engineering. Using a material that can handle heat better and has a higher transfer of heat will reduce detonation tendencies. Why do you think that though iron heads can handle detonation nicely, they also tend to not allow as aggressive of timing? Let's not also forget about another huge area of breakthrough: Coatings.

 

I'm actually out of time and will continue this later.

[bthomp]

Not all fuels burn the same and exhibit the same loading forces on the piston.

 

One thing I would like to add about pump gas that I was informed about was that oct 87 is never really that rating. A test was done on the different octane ratings from different gas stations. The results from 87 were crazy. It was found that some stations had gas that had an actual rating of 12 less than 87!!! On a side note, the test also showed that the higher octane rated gases were closer to their real rating.

 

Anyways, back to the real discussion at hand

[s30red240z]

Well even though the threads of the L31DETT all died I'd say it's safe to say the stock rods will reach 700rwhp. I personally think the pistons MIGHT survive that if the condition were right:

 

Therefore is you have ideal conditions, stock (pistons, crank and rods) will reach 700whp nearly safe?

Edited November 5, 2012 by s30red240z

[Gollum]

Ideal conditions don't include a heat that will be having massive heat management issues at 700rwhp. Ideal conditions don't include intake temps over 150F, nearly impossible on most 700hp setups. Ideal conditions don't include imperfect cylinder to cylinder tuning, which I've seen few people account for.

 

Ideal conditions are just that, fantasy that few will ever see into being a reality. Another factor that people don't talk about is "under what stress" and "for how long?". There's quite a many 1000+ HP 2JZ motors out there, but how many of them will LIVE at WOT? I've seen motors making 300+HP per liter that do it all day long without breaking a sweat, while other 150HP per liter motors blow up on a hot day. Ideal conditions rule out this factor, since the question is just "how much power can the stock pistons make". It's a fairly arbitrary question but yet it seems to be the one everyone tends to ask, as it makes something "real" in our minds and gives us something to talk about.

 

I'm honestly not surprised that Jeff is making about 500 to the wheels on a stock bottom end. I'm somewhat surprised more people haven't done it. It's obviously quite possible. I don't know of anyone who's broken the 600hp mark at a stock bottom end, but I don't think Jeff's setup is the most exotic ever seen and I think it's certainly a goal worth shooting for.

[Lazeum]

When I tried to explain to some of my friends how they should think about tuning, I've made a small sketch to explain them the relashionship of detonation versus torque & timing.

I come up with the following chart:

 

 

I've seen this chart in many tuning books & I believe it is easy to understand the concept of MBT & why more timing isn't always good.

To avoid detonation we can clearly see that timing can help but we also see that some torque/power are left on the table.

The smart move is then to alter the physics behind detonation to push the detonation threshold above max torque achievable: with quench, gas quality/properties, cooling, head shape, air flow, vaporization, etc.

Some of the item from the list above also change max torque achievable so everything is linked together.

 

If detonation threshold is above max torque, it also shows that some engine will never ping no matter what since they are designed conservatively

 

Since the chart above is showing only one state of the engine (given RPM, Temperature, engine load, etc.) , it also helps to understand why tunable ignition is a nice thing to have.

 

The main question to me how to tune an engine & to avoid detonation? how to do it without having to get he engine to detonate "a little" to know the limits?

I've made a detcan, ping noise is not always obvious...

 

This is theory however, I have yet to play on a dyno & play around with it to destroy engine

Edited November 5, 2012 by Lazeum

[johnc]

Therefore is you have ideal conditions, stock (pistons, crank and rods) will reach 700whp nearly safe?

 

No. Conditions are NEVER ideal. What is true on an Internet message board fails when you move into the real world.

[s30red240z]

No. Conditions are NEVER ideal. What is true on an Internet message board fails when you move into the real world.

Yes i understand about this, my question is about how much WHP can achieve a stock L28 bottom end turbo or NA, because a friend of mine is afraid of destroy his engine with a hybrid HX40, i know if detonation is present at 200whp would destroy, but is we are carefull of detonation how much WHP will can reach on nearly safe mode.

Edited November 5, 2012 by s30red240z

[Gollum]

Well then consider 500rwhp the foreseeable limit until you guys prove otherwise!

 

Lazeum ~ For one, the detonation threshold should read reverse color. You get softly into detonation, often without knowing it, until it becomes more aggressive and becomes obvious.

 

The other issue I have with that chart and what you said is that it assumes max potential achievable torque doesn't move. It DOES move!!! That's what I'm saying about comparing different fuels. They all have their own independent chart curve with different limits. And there's a heck of a lot you can do to raise the detonation threshold without changing your fuels. Detonation has to do with HEAT. I've seen guys who once they traced their root cause of detonation found that their fuel was getting super-heated because there was so much unused fuel being pumped through their lines that the fuel in the tank would slowly rise in temperature. They added a fuel cooler past the pressure regulator and the problem was solved.....

 

That's what I mean when I say this isn't as easy as "run less timing" of a subject. It's extremely complex and requires looking at the WHOLE PACKAGE.

Edited November 5, 2012 by Gollum

[Leon]

Well then consider 500rwhp the foreseeable limit until you guys prove otherwise!

 

Lazeum ~ For one, the detonation threshold should read reverse color. You get softly into detonation, often without knowing it, until it becomes more aggressive and becomes obvious.

 

The other issue I have with that chart and what you said is that it assumes max potential achievable torque doesn't move. It DOES move!!! That's what I'm saying about comparing different fuels. They all have their own independent chart curve with different limits. And there's a heck of a lot you can do to raise the detonation threshold without changing your fuels. Detonation has to do with HEAT. I've seen guys who once the traced their root cause of detonation found that their fuel was getting super-heated because there was so much unused fuel being pumped through their lines that the fuel in the tank would slowly rise in temperature. They added a fuel cooler past the pressure regulator and the problem was solved.....

 

That's what I mean when I say this isn't as easy as "run less timing" of a subject. It's extremely complex and requires looking at the WHOLE PACKAGE.

I think the biggest issue with that chart is that the detonation threshold should be a vertical line, not horizontal.

[Gollum]

I think the biggest issue with that chart is that the detonation threshold should be a vertical line, not horizontal.

 

Ah again!!! So true! I didn't think about it but detonation is more a product of the pressure fluctuation of timing, not torque, therefore it SHOULD be a vertical line. I still think it should start as a soft red, not hard, then work into a deep red.

[Lazeum]

Gollum,

the color I've chosen for detonation has nothing to do with its severity, I've done it this way because it looks nicer Color transition brings confusion, I did not think about that. My bad.

The chart is true at one only specific condition. When I said: "Since the chart above is showing only one state of the engine (given RPM, Temperature, engine load, etc.)" I meant that one particular chart exists for each unique condition (i.e. every cell in a timing map for instance with defined AFR + all the intermediate conditions in between cells).

 

Do you suggest also that torque or detonation value would not be so repeatable? it will hardly be repeatable since other inputs might affect the reaction. That's why, I believe, modern car such as Evos (the only modern EFI car I've played with) for instance have a complex formula for engine loads.

 

Looking again at my chart, I still think detonation threshold should be horizontal, here's how I see the physics behind:

1- going from low timing to higher one before detonation, pressure will increase with ignition timing

2- ...until it reaches too high comp to avoid detonation

3- too high timing, past max potential torque, ignition occurs too early; pressure from ignition increases + additional pressure from piston motion is enough to create compression & detonation. Still, energy from combustion will try to slow down the piston. As a result, you loose work & gain calories for the engine.

4- too high timing, past detonation threshold, ignition occurs way too early, pressure from ignition will increase but additional pressure from piston motion is not enough to create enough compression. Energy from combustion will try to slow down the piston even more. As a result, you loose more work & gain more calories for the engine.

 

This is how I see the chart. If what I'm saying is wrong, I'll be glad to hear a different version (even if Tony is the one doing it )