Engine Temps & Detonation Resistance

I recently came across the following graphic on this forum:

My take-away is that if I start to see detonation in the summer when the air is warmer, can I simply either tell my EFI to run the fans sooner to keep my coolant and therefore engine temps down and or install a lower temp thermostat? --If so that's a fantastically great option.


My engine build has a static 10.2:1 CR planned and I'm bouncing between a couple different CAMs but the dynamic compression calculators estimate between an 8.2 and an 8.5 dynamic CR for the cams that I'm looking at. I live in Washington State where 91 and 92 octane premium are readily available but 93 octane is pretty rare, so I'm wondering if I can use a lower temp thermostat and turn my fans on early to reduce the risk of detonation.

I know that dynamic compression calculators really only take a static compression calculation and adjust it to be more accurate based upon the intake close event- it is missing many, MANY other aspects that would be useful in predicting detonation, so I again feel like I need added detonation insurance.


-I'm also looking to use a long-runner FIRST intake and a build that maximizes the VELOCITY of the flow so my fear is that I'm going to pack extra air into the cylinder and my cylinder pressures (and therefore actual detonation risk) is going to be higher than the dynamic compression calculators estimate.


As far as I can tell, 3 easy forms of detonation insurance that don't significantly impact performance are: 1. use a cold air intake (done) and don't use an intake with an exhaust crossover or block it (done) 2. lower engine temps (I think) 3. Add octane booster during the warm months of the year- EXPENSIVE insurance option so therefore my last one.



Adam

detonation is the result of the fuel/air self igniting due to a combination of HEAT and compression or the fuels heat and cylinder PSI threshold reaching the fuels octane ignition limits,
yes you have the option of changing the way the engines cooled, or reducing the coolant temperature, this will TEND to reduce the combustion chamber temps thus in theory keeping the ignition threshold below the combustion ignition point.
here in florida alot of guys buy and install kits that spray E85 fuel into the carb to change the effective octane limitation on performance engines to eliminate detonation issues.
be aware that, the fuel octane, being used, alone is not the only factor here!
iron heads hold heat and transfer heat to coolant at a lower rate!
running a 180f -190f t-stat and use of a 7-8 quart oil pan, an oil cooler will tend too lower the effective operating temp.
both the coolant and oil temps, and ignition advance curve, will effect the range where detonation will occur,richer fuel/air mixtures (12.5:1-13.5:1) tend to burn a bit cooler than lean mix ratios,(13.5:1-15.5:1)
aluminum heads, transfer heat much faster, and benefit from, some, simple mods , like keeping the quench in the .040-.042 range, polishing the piston deck surface and combustion chamber and rounding the edges on the combustion chamber and piston valve notches, will reduce the tendency to get into detonation

well I'll assume you previously read the links on engine building,and quench, and you have at least tried to build a well balanced combo with reasonable quench,and tried to match the cam duration and lsa to the engines compression and intended power range, and you selected a fairly well matched cam timing and reasonable compression, but at this point in the tuning ,your still having indications your getting into detonation.
keep in mind that keeping reasonably consistent and as low as practicable , combustion chamber temps are a huge factor in avoiding detonation issues, having an auxiliary oil cooler and a trans fluid cooler with a powered fan, and the proper fuel/air ratio and ignition advance curve along with matching your cars engine dynamic compression ratio to the available fuel octane can go a long way toward avoiding detonation issu

http://garage.grumpysperformance.co...ow-to-reduce-its-likely-hood.9816/#post-37278

http://garage.grumpysperformance.com/index.php?threads/port-speeds-and-area.333/

http://garage.grumpysperformance.co...mble-and-swirl-quench-squish.4081/#post-35069

http://garage.grumpysperformance.co...octane-for-compression-ratio.2718/#post-35581


http://garage.grumpysperformance.co...-into-gen1-chevy-small-block.4484/#post-11815

http://garage.grumpysperformance.co...g-e85-in-your-old-muscle-car.2141/#post-25201

If you have EFI tuning software and can write you own SA and VE tables... you might have some other things you can play with if you are going after emissions compliance and/or maximum power.

If you aren't running cats- you can adjust the AFR too. Run just a little richer and that should help avoid detonation.

And you can turn the fans on earlier too.

You can real complex in tuning I have read up on allot of it lately but be careful running to cool not good for an engine either

Kane said:

If you have EFI tuning software and can write you own SA and VE tables... you might have some other things you can play with if you are going after emissions compliance and/or maximum power.

If you aren't running cats- you can adjust the AFR too. Run just a little richer and that should help avoid detonation.

And you can turn the fans on earlier too.

Click to expand...

Luckily, no cats and no emissions checks required for me. Can tune to my heart's content.

Fuel economy is important to me, so I'd prefer solutions that don't involve running richer. I'm happy to focus on reducing temps and increasing octane via "poor man's octane booster" as methods of avoiding detonation, while still maintaining good fuel economy and power.

keep in mind if your driving the car for best gas economy youll rarely exceed 3500 rpm and part throttle,
fuel air ratios in the 13.9-14.7 range for economy will be fine under light loads,
under high rpm and loads well above 4000 rpm is where running a f/a ratio closer to 12.8:1 pays off in reduced detonation

http://garage.grumpysperformance.co...octane-for-compression-ratio.2718/#post-68131

When tuning efi what system are running can you tune using tps I am all new to tuning efi but the system I have is real indepth

Why is detonation so bad for an engine, anyway?
-I've been meaning to ask this for quite some time; I honestly don't get it.

If you explode the gas with a spark or with compression -why should it matter? Diesel engines work by creating heat-pressure induced "detonation" and they're fine, right?


Is it simply that when spark ignites the fuel-air mixture that it's actually burning and not exploding and doesn't occur as quickly / violently as an actual explosion, but when you ignite the mixture via pressure ala detonation/pinging it's an ACTUAL explosion?

--If so it still seems exactly like how diesel engines work and I'd think that explosions like this would actually be more efficient so I'm still confused at why this is bad and we don't just build engines to harness this...



Adam

Adam, you hit the nail on the head!!

In layman's terms:

The air/fuel in the combustion chamber must burn rapidly.

It must not explode, if it explodes that is detonation, when something detonates, it explodes.

Detonation, spark knock and pinging are basically interchangeable terms and occur after the spark pug fires .
Pre ignition is totally different.

The ping one hears is like the noise when metal is struck with say a big hammer. It gets muffled to a ping through the assorted Engine components.

In simple terms, higher octane fuel burns slower than low octane, so is more detonation resistant.

Excessive heat and or pressure in the combustion chamber leads to detonation, in relation to the given octane.

Hot Engines detonate easier than cold, its basically impossible for a cold Engine to detonate.

Advanced ignition timing can lead to detonation as the A/F mixture starts burning too soon and the pressure before TDC overcomes the octane.

Detonation is bad for an Engine as the shock of the explosion can crack ring lands instantly, flatten rod bearings, and worse.

This is one reason Forged pistons are preferred in a high performance Engine, they can absorb much more detonation than a cast piston.

The thing is, Engines run the best and give the best economy when they are on the verge of detonation, that's why tuning is such an issue.

Otherwise Engines could just run retarded timing, but they would be slow and hard on fuel.

Ever heard an older gas powered dump truck, they run retarded timing so they can haul very heavy loads all day on low grade fuel.

If you ever have the opportunity to Experiment with an older carb Engine you can learn a lot by advancing and retarding the ign timing.

With a warm Engine idling, slowly retard the timing and you will see the Engine slow down and the exhaust sound labored, eventually stall.

Advancing will speed up the idle and the exhaust will sound crisp, over advancing makes the Engine idle erratically.

Many of us old timers can set idle ign timing by ear to perfection, even WOT timing, and then establish an advance curve between the two.

Diesel Engines actually run on detonation, only the heat of compression initiates the explosion when the fuel is injected in the combustion chamber.

Modern Diesels are constantly improving by injecting fuel at a regulated rate, allowing for a less severe but longer lasting explosion.

Thanks
Randy

Why is detonation so bad for an engine, anyway?
-I've been meaning to ask this for quite some time; I honestly don't get it.

Click to expand...

if your experiencing detonation issues that are cured by swapping to higher octane rated fuel, and you would prefer to use the lower octane , less expensive fuel, you should adjust your cars ignition advance combination , so that its advance curve has either less initial timing, or delaying the mechanical advance vs. rpm with some stiffer springs, or a combination of both might reduce the pinging under load at 2500-3500 rpm where its most commonly seen,. Does this detonation or pinging, only occur at WOT? If not, limiting the vacuum advance with a stop, or using an adjustable vacuum advance unit and raising the amount of vacuum required vs. the amount of vacuum advance might be warranted also and installing a lower temp rated t-stat and adjusting the engine fuel/air ratio a bit richer may also help..



the guys have a point, best power and in many cases durability, is generally found at nearer 12.7:1 f/a ratio, I don,t ever remember your engine getting near that lean while we discussed getting it tuned up?

well I'll assume you previously read the links on engine building,and quench, and you have at least tried to build a well balanced combo with reasonable quench,and tried to match the cam duration and lsa to the engines compression and intended power range, and you selected a fairly well matched cam timing and reasonable compression, but at this point in the tuning ,your still having indications your getting into detonation.
keep in mind that keeping reasonably consistent and as low as practicable , combustion chamber temps are a huge factor in avoiding detonation issues, having an auxiliary oil cooler and a trans fluid cooler with a powered fan, and the proper fuel/air ratio and ignition advance curve along with matching your cars engine dynamic compression ratio to the available fuel octane can go a long way toward avoiding detonation issu

so what your trying to do is reduce combustion chamber temps,increase your fuels octane, reduce your fuel/air temperatures, or reduce your combustion chamber pressure or speed up combustion
http://garage.grumpysperformance.com/index.php?threads/carb-tuning-info-and-links.109/

read these threads and pay attention to the pictures
http://garage.grumpysperformance.com/index.php?threads/detonation-damage.2883/#post-31942

http://www.contactmagazine.com/Issue54/EngineBasics.html

http://garage.grumpysperformance.co...octane-for-compression-ratio.2718/#post-35581

http://garage.grumpysperformance.co...ow-to-reduce-its-likely-hood.9816/#post-37278

http://www.contactmagazine.com/Issue54/EngineBasics.html

https://www.ms-motorservice.com/en/technipedia/post/piston-damage-and-causes/

https://mcbperformance.com/p-25418-piston-failures-causes.html

http://www.madsens1.com/saw_piston_fail.htm

https://www.hotrod.com/articles/0606em-understanding-compression-ratio/

http://blog.wiseco.com/everything-you-need-to-know-about-ring-gap

https://www.memoparts.com/img/cms/Documents/Piston Failue.pdf

GLHS60 said:

Adam, you hit the nail on the head!!
Many of us old timers can set idle ign timing by ear to perfection, even WOT timing, and then establish an advance curve between the two.

Click to expand...

Hahaha! Now THAT'S impressive!

What I still don't understand is why don't we just build gas engines as "tough" as diesel engines so that they can not just survive but actually work with compression-based ignition. Let's put awesomely efficient 4 core radiators in a car, CAI, an oil cooler, and a separate trans cooler, coated headers+a tuned exhaust to pull heat out and run the stupid thing up to a 14:1 CR and just make detonation how to runs. -You'd get stupid torque and amazing fuel economy, right?

(It's my understanding that this is roughly what the Mazda Sky-Activ engines due except they still avoid detonation and use spark at stupid high CR's - 13:1 on the US gas configuration, 14:1 on premium european gas.)


Why haven't we harnessed detonation instead of trying to avoid it all the time?


Adam

Engines loose considerable power when detonating, typically max power and economy are at the point just before.

There is no point in harnessing it when the result would be a more inefficient, and much heavier Engine.

Compression ratios are sneaking up, but still avoiding detonation.

Even diesels and their totally different fuel, are moving away from the harshness of detonation to a smoother longer burn.

Contrary to popular belief, Turbochargers raise cylinder pressure only slightly, instead make much more power based on ..................

Thanks
Randy

NewbVetteGuy said:

Why is detonation so bad for an engine, anyway?
-I've been meaning to ask this for quite some time; I honestly don't get it.

Click to expand...

Adam, read this wikipedia explanation!
https://en.wikipedia.org/wiki/Engine_knocking

Grumpy said:

read these threads and pay attention to the pictures
http://garage.grumpysperformance.com/index.php?threads/detonation-damage.2883/#post-31942

http://garage.grumpysperformance.co...octane-for-compression-ratio.2718/#post-35581

http://garage.grumpysperformance.co...ow-to-reduce-its-likely-hood.9816/#post-37278

http://www.contactmagazine.com/Issue54/EngineBasics.html

Click to expand...

These links were A-MA-ZING! EXACTLY what I was looking to learn. Thanks Grumpy!


Adam

Bang happening while still compressing fuel air is counter productive two opposing forces fighting each other.