Tricks to keep an engine from pinging (predetonation)

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Tricks to keep an engine from pinging (predetonation)

Post by DjayS12 » Thu Nov 29, 2012 2:51 pm

So for those who are less familiar with pinging, this is when the fuel burn without control, meaning it does not need the spark to ignite. This ignition is caused by two factors: high heat and high pressure in the combustion chamber.

I'm building a KA24DE with a 11:6 compression ratio this winter. In my area, the highess octane is 91. Here's a run through of what the engine setup will be:

S14 head, ported and port matched
248/232 cams
S14 intake manifold
11:6 compression ratio ('90 SOHC pistons)
no egr, no catalyser
4-1 header with a 2,5'' exhaust
AEM uego wideband
AFC NEO
Fujita intake
nismo thermostat (62*C)

It have been documented a few times on many forums that octane boosters are not reliables.

I would like to run a such compression without adding a water/meth injection kit. So I started to think what else could be done to help the engine to be safe.

Here's a list of things that I found, from common logic and reading on teh net. I'll like if you guys could add some stuff to this list, and correct me if I got something wrong.

1. Colder thermostat, will keep the engine cooler.

2. Less ignition advance. Although, since our ecu are adjusting the ignition with the knock sensor, the ECU should manage this part on it own?

3. Colder intake air. Removing the heating line in the throttle body and having a nice cold air intake will help that.

4. Running a slightly rich fuel/air ratio. The unburnt fuel particle will catch some of the heat in the chamber... on the downside this mean worse gas mileage, black smoke and contaminating the oil, A S-AFC should be able to take care of this with a air fuel meter to monitor it,

5. Colder spark plug to keep the ignition cooler

6. Camshaft.. I read a few things on camshaft timing (if you have adjustable cam gears). Pressure in the combustion chamber is affected mostly by the overlap. More overlap usually mean less air for the intake charge and less pressure. It is known that a KA24DE have an hard time breathing through it stock intake manifold and MAF, especially at higher RPM, and the engine can benefit from a larger exhaust. Wouldn't having more overlap than stock cause the exhaust fume to rush back in the head from the exhaust backpressure being stronger than the intake air velocity?

7. Anything else?
Last edited by DjayS12 on Sat Dec 29, 2012 4:43 am, edited 1 time in total.
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Post by schmauster920 » Thu Nov 29, 2012 4:24 pm

You should set the timing low and tune the AFs to where you want them, then slowly add timing until you hear detonation with 91 octane.

It should be a fun project, everything else sounds good except the thermostat seems a bit cool. Ive heard a cooler thermostat can cause a lot of extra engine wear since things never truly get up to temp.
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Post by nismoautoxr » Thu Nov 29, 2012 4:52 pm

bigger cams help to an extent and go hand in hand with higher compression because of their tendency to lower compression due to the longer duration causing teh exhaust and intake valves being open at the same time . THis is why longer duration cams cause the idle to be rough .The overlap is allowing inversion of exhaust gases to the intake manifold and combustion chamber there by contaminating the intake charge with inert gases but the large overlap camshaft will usually not reduce your chances of detonation over a stock cam in my experience . Octane is your friend here . If I was building a motor with that much compression I think Id be leaning toward W/Minjection and or E85 . Cylinder head and combustion chamber design play a huge role in an engines tendency to have sparkknock also. Careful and tight spark timing controls are your biggest safeguard.
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Post by jholman05 » Thu Nov 29, 2012 7:06 pm

I'd say don't waste your time on the SAFC NEO and go straight to a programable ecu. My Nismotronic has a knock reading. You'll be able to adjust a/f, timing, keep an eye on coolant temp, diagnose potential problems, set rev limiters and all kinds of other fun things.
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Post by DjayS12 » Thu Nov 29, 2012 9:45 pm

thanks for the input. As for the cams, I have one 248, one 240 and two 232s. I'm drilling my spare cam gears soon to make them adjustable. Now I'm mostly hesitating between a stock S13 cams setup (240/248) or a hot cam swap (248/232).

As far as engine control, I got a sweet deal on the safc neo, and I wanna keep the costs as low as I can. The stock ECU does back up the timing when it detect a knock as far as I know.
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Post by Freise » Fri Nov 30, 2012 12:03 pm

The stock ECU will not retard timing enough to handle predetonation, the knock sensing system is rather crude, nothing more than a microphone that converts a signal to a voltage, and in higher rpms it has difficulty picking up knock from engine sound... and even then the the ecu's solution is to switch to a knock map which dumps fuel and retards timing to allow you to limp the car home.
You will need some form of correction for timing, either some form of chipped ecu or at the very least to retard timing at the distributor

Not 100% sure on this part so maybe someone can chime in on it but I've also heard that running fuel control like an safc that just manipulates the signal to the ecu will actually cause the ecu to add timing to compensate for the rich conditions, thus increasing chance of knock
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Post by p00t » Fri Nov 30, 2012 6:37 pm

Pinging is otherwise known as knock and it is effected by ignition timing so start very conservative with your timing when you first get it running.

Having high compression is tougher to tune because if you knock you have less combustion chamber volume to absorb the shock, also there is more pressure so the strength of the shock is higher.

I recommend getting a chipped ECU that you can tune yourself like a Nistune. The stock map will not work well for you and you will have flat spots in how the car feels. Take it to the dyno with a tank spiked with octane booster and see what the car needs in different areas.

If you keep EGR you will keep your combustion chamber cooler when cruising.

Good luck.
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Post by 8-bit » Sat Dec 01, 2012 2:15 pm

Cold thermostats are a bad idea unless you know your oil will be performing as expceted at those lower temps. Most oils are not designed to run at lower temps than normal and have abnormal viscosity and do not work correct when at other-than-expected temps.

Also, you should know that pinging/knock/det in the KA can be happening pretty badly and you won't even hear it. Something about the way the motor is designed makes it so that you can det and not hear it ---- obviously really bad det is noticeable and sounds like pebbles hitting the bottom of your car or at its worst like rocks in a blender.
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Post by DjayS12 » Sun Dec 02, 2012 7:56 pm

mmh.. your last statements make me wanna buy a knocklite.

As far as a tunable ecu, it's really not in my plans.. it's not that I am afraid of playing with a tunable ecu, but I wanna keep the cost LOW.

I went to a local machine shop that does nothing but engine head (mostly domestic V8 drag machine.. but well an engine head is an engine head).

I asked him about playing with the cams overlap.. he've been honest and told me he isn't very comfortable with setting cams for a twin cam.. pretty much all the performance engines he've worked on were big V8 with pushrod.

He agreed with my thought about running a thicker headgasket. He checked what he could get for my engine. Cometic sell different thickness up to 0.140''... I told him I didn't really wanted to get the block and head machined for a metal headgasket...he told me since his shop is open, he use paint to seal the headgaskets (that's right, PAINT!) and never got any complains... the trick seem iffy but he have been in this business for about 20 years and built a fair amount of car in the area.

Thought on that?.. maybe I could lower the compression to something more reasonable.. 10,5:1?
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Post by redpotatoes » Mon Dec 03, 2012 10:36 am

Water injection would do what you need. I know you don't want to run it but it is still the best thing to reduce/prevent detonation. No need to run meth, only water. Cheap, effective, what more could you want ?
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Post by p00t » Mon Dec 03, 2012 4:32 pm

DjayS12 wrote:...he told me since his shop is open, he use paint to seal the headgaskets (that's right, PAINT!) and never got any complains... the trick seem iffy but he have been in this business for about 20 years and built a fair amount of car in the area.
Epoxy would work even better...
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Post by DjayS12 » Tue Dec 04, 2012 5:22 pm

yeah the more I think about it the more I think I'll run a water meth kit.

Some windshield fluid are a mix of water/meth already.. I think I'll use one of these kit that use the same tank than the windshield washer.

Seriously? epoxy? I was about to weld my block and head together,.. :P
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Post by DjayS12 » Wed Dec 26, 2012 8:16 am

I thought I will update this a little bit.

I scored a AEM water meth kit with the flow gauge for very cheap. Only thing is the controller have a built-in 3 bar MAP sensor... well this suck because I am not boosted.

Now I was thinking about a diy MS1 V3.0 megasquirt kit ( I know.. I'm far from the original cheap n easy build :P ) but it looks like even their water injection controls work from a boost setpoint in the program.. so still no good for me. I asked on the MSextra forums anyway to see if it is possible to put a negative boost value (-10psi would be 30Kpa.. roughly the idle vacuum IF the psi was a valid vacuum unit). I'll see what they will tell me.

another avenue I was thinking about is maybe modifying the AEM controller, but I will start another thread for this.. if this doesn't work I'll just get a MAF controller.
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Post by schmauster920 » Fri Dec 28, 2012 4:48 am

I think software should be your first venture, like you are trying to do, but if it doesnt work out there might be other options

Maybe use a hobbs type pressure switch but one made for vacuum and keep the ECU out of it

There are a bunch of different pressure/vac switches available.. lots of things like dishwashers, jacuzzis, etc use things like that, the hard part is finding out which ones do what we need.

Another option would be throttle activation like nitrous systems use. This might be the easiest and do a good job since it is NA and you dont have to worry about different boost levels at the same throttle position.


I say +1 on the megasquirt too, lots of options and so much future expandability.. not to mention using cheap and available GM/Chevy sensors.

Everytime i see your sig it reminds me of how much i want an S12 lol
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Post by DjayS12 » Fri Dec 28, 2012 5:57 am

I can't agree more with megasquirt being optimal, but the thing is I already have a lot going on for the car already and I would like to have more seat time next summer rather than spending my time in the garage fixing/tuning it...the more I think about it, the more I believe that I should wait until next year.

As for the water injection, the best is to have it proportionnal to the fuel (8-12% on a N/A from what I read on the subject). The fuel is injected depending on the airflow...The issue I see with using a signal from the tps is that it will inject the same amount of water no matter if I am at WOT at 2000RPM or WOT at 6000RPM... so it will be either a compromise of too much water at low rev or not enough at high rev.

I found this pressure sensor: http://www.phidgets.com/products.php?product_id=1141

they give the formula and all the spec for it. It looks like it could replace the built in MAP of the OEM controller... but I also wonder if I should just sell the 3 bar controller and buy a MAF controller (200$ new)...seems like the easiest path.
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Post by 8-bit » Fri Dec 28, 2012 4:45 pm

DjayS12 wrote:thanks for the input. As for the cams, I have one 248, one 240 and two 232s. I'm drilling my spare cam gears soon to make them adjustable. Now I'm mostly hesitating between a stock S13 cams setup (240/248) or a hot cam swap (248/232).

As far as engine control, I got a sweet deal on the safc neo, and I wanna keep the costs as low as I can. The stock ECU does back up the timing when it detect a knock as far as I know.
You could save a lot of money on a gun for hunting and go out with a plastic knife from burger king....

Get a clue. You could throw a million parts in your engine bay and they won't run without a brain. This isn't a 1960s car with a carbourator. EFI is a big deal and all of the benefits we see from EFI are brought with the tuning.

AFCs are trash and that point has been made and echoed dozens of times. It's now your opinion that you want to make a nice car and put stupid tuning in it.

Good luck with your bad choice.
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Post by nismoautoxr » Fri Dec 28, 2012 8:11 pm

I can give you some insight on the cams . I have run all 3 or 4 combinations of each and for all the effort ....240 intake and 232 exhaust gave me the best all around performance . Then you get to skip all that cam degreeing crap and link/pin counting and best of all there are no compromises .

Call me crazy but I really dont think you are going to have a big det problem unless you do something dumb like try to boost it or run huge timing . The quench will already be super thin which is important ...the combustion chamber is fairly conducive to a higher compression ratio and so long as you use your head and dont over reach in the timing department itll probably be OK.

I mean come on ...looks like to me all your doing is throwing a franky motor together using mostly used OE parts ...not like you gonna throw a ton of money up a hogsass.

If you end up with a det problem then you gotta deal with it .

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Post by DjayS12 » Sat Dec 29, 2012 2:22 am

8-bit wrote:You could save a lot of money on a gun for hunting and go out with a plastic knife from burger king....

Get a clue. You could throw a million parts in your engine bay and they won't run without a brain. This isn't a 1960s car with a carbourator. EFI is a big deal and all of the benefits we see from EFI are brought with the tuning.

AFCs are trash and that point has been made and echoed dozens of times. It's now your opinion that you want to make a nice car and put stupid tuning in it.

Good luck with your bad choice.
Lol that was a harsh input. I sadly I do not hunt so I won't miss not having a rifle.

The AFC is just there to keep the afr within the range.. I'm not even sure if I'm going to use it if..it's really gonna depend on my afr once the engine is put together.

I know the AFC throw off the ECU and make him think that he have a different load value, and the ECU change the timing map consequently. But isn't this mostly true when you try to use a piggyback to compensate for differente sized injectors or maf? slight adjustments shouldn't cause a lot of change in the timing. I espect the VE to be somewhat different since the CR and cams are changed and the car have an intake and exhaust.

Maybe I sound like I'm making a big deal of it, but it is just an engine that would be put together for cheap and that would give me some decent power over the stock engine (not dreaming about 200whp at all here!). But I'll hate to blow it because I overlooked something.

Water/meth + stock timing + 91 octane + 240/248: that's where I'll start. If the AFR is too rich or lean for my taste, then the afc will go in.

@nismoautoxr: mmh never though of this cam setup.. will be worth a try. But I have a set of hand made adjustable gear (made with a rotary table, so the drilling is precise). So I will get a proper cam timing whatever the cams I choose.

And with the water/meth I don't think I'll have a det problem anymore. I could probably run more timing than stock but I'll wait until I have a proper tunable ecu before doing this.
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Post by turboholic » Sat Dec 29, 2012 9:10 pm

Have you checked to see where's the nearest e85 gas station? Im running 11:1 and was able to get aggressive with the timing because of e85.

Good luck with your build.
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Post by DjayS12 » Sun Dec 30, 2012 2:14 am

no such thing around here. usually we have 87,89,91 and if I get closer to montreal there is some 93..but that is like 500miles away.

How does the engine feel at 11.1:1 vs stock compression?
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Post by turboholic » Sat Jan 05, 2013 6:03 am

feels amazing. lots of torque.
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Post by duncan351 » Sun Jan 06, 2013 3:00 pm

This is a great subject to bring up. One thing I did to my engine when I built it was I had 1.5cc's added to each cylinder in my head and entire cylinder smoothed out. By doing this it lowers chances of detonation for me under boost. It definitely worked too. I push more boost on pump gas easily without detonation.
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Post by adamky » Sun Jan 06, 2013 7:31 pm

duncan351 wrote:This is a great subject to bring up. One thing I did to my engine when I built it was I had 1.5cc's added to each cylinder in my head and entire cylinder smoothed out. By doing this it lowers chances of detonation for me under boost. It definitely worked too. I push more boost on pump gas easily without detonation.
Interesting. You don't happen to have any pics of this, do you? I'll be building my head next year and would love to do something like this while I've got it apart.
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Post by duncan351 » Sun Jan 06, 2013 7:43 pm

I don't have any pics anymore but you can PM titec2. Jay is the person who set my head up and did an AWSOME job on it. He ported and polished it along with balancing each cylinder adding 1.5cc. Hit him up and ask him for his services. Money well spent.
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Post by adamky » Tue Jan 08, 2013 8:59 pm

Cool, thanks.
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Post by emo_tactical9 » Tue Jan 08, 2013 10:19 pm

nismoautoxr wrote:I can give you some insight on the cams . I have run all 3 or 4 combinations of each and for all the effort ....240 intake and 232 exhaust gave me the best all around performance . Then you get to skip all that cam degreeing crap and link/pin counting and best of all there are no compromises .

Call me crazy but I really dont think you are going to have a big det problem unless you do something dumb like try to boost it or run huge timing . The quench will already be super thin which is important ...the combustion chamber is fairly conducive to a higher compression ratio and so long as you use your head and dont over reach in the timing department itll probably be OK.

I mean come on ...looks like to me all your doing is throwing a franky motor together using mostly used OE parts ...not like you gonna throw a ton of money up a hogsass.

If you end up with a det problem then you gotta deal with it .

my .02
Any more detailed input on the 240/232 cam swap? I have these lying around and I think I might do it.
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