Audible knock with new A/W intercooler

[A.J.]

I just tried something. My calculated timing at 15 psi and 3000 RPM was 17.5 before TDC. I brought the AdvanceFromMAPWarmPart 15 psi point from -15 degrees UP to the zero line and the calculated timing table jumps to 29 degrees BTDC. If I move it all the way down it moves to 5 degrees BTDC. If you look at the picture below you see a 10* BTDC. If you move the line up to 29* BTDC you are making the ignition event happen sooner. If you move the line down to 5* BTDC you're moving the ignition event later. Knock is two flame fronts colliding, pre-ignition and ignition. So you need to move the ignition event to before the pre-igntion. If my total timing is 17.5* BTDC and I'm having ignition before my spark plug fires I need to move to the other side of the knock, say 18, 19, or 20* BTDC. From everything I've read, the 2.4 turbo engine, because of the goofy pistons, like/love a lot of timing. By that I'm translating that into higher numbers BTDC 20*, 30*, 40*, etc. So I don't think I'm running enough advance timing. I just compared the calculated timing for a stock A139 cal and timing at 15 psi @ 3000 RPM is 15* BTDC. I compared the base cal I got from Brian Bucar from Sean (1FastCSX) and that cal is 17* BTDC. I'm not running enough spark advance. Am I right or wrong?

Have you chased down an SRT4 timing table yet? I know there has been at least one stock table posted on here in the past.

No I haven't. I posted on the SRT-4 forums (where i also have a build log) and nobody has responded yet.

[tryingbe]

I should be able to drop by tomorrow afternoon.

[zin]

Well, not exactly. Detonation and pre-ignition aren't really the same thing, though very similar. It is basically the difference between which flame front starts first, the uninvited one, or the intended one.

Pre-ignition is normally initiated by a hot spot, or incandescent (chunk of carbon or overheated metal/plug/exhaust valve), where detonation is the end gasses "going off" due to heat/pressure/mixture.

Either way, the flame fronts collide, and "ring the bell" of he piston.

Retarding ignition, be it for nitrous or boost, is an effort to place the peak cylinder pressure in the "sweet spot" of 15-20* ATDC, pretty much all engines respond this way, it's more to do with the geometry of piston/rod/crank than combustion chamber, etc. which is why I can state that with confidence.

Most engines like about 36-38*BTDC of total lead, at least for a 2-valve engine, the more efficient chambers of 4-valve engines don't require as much time, and can often run with a total of 24-28*. As boost is added, and combustion efficiency improves, less timing is needed (or desired) to produce peak pressure in the "sweet spot".

Normally, with nitrous, I'll get the engine dialed in on its own to find the total timing it likes, then reduce it a bit more than I think I'll want/need. This normally works out to be about 1.5-2* per 50HP of nitrous added, for boost it will be a bit different, we're not increasing the O2 content, just the density.

Taking "too much" timing away will never hurt parts, just power, as the peak pressure happens later as the piston is dropping away from the pressure. If not enough timing is taken away, peak pressure happens closer to TDC and much higher heat and pressure is developed, but at a point that the pressure is basically just trying to break parts. You can imagine what would happen if peak pressure happened at TDC! All that potential HP doing its best to push the crank out of the block!

Basically, what I'd advise you to do is back it off more than is needed/desired, then slowly add it back... pretty much the same thing the factory knock routine does, reduce it a bunch to "get ahead" of the knock, then slowly feed it back to what it "should be".

Mike

[turbovanman²]

The ski ramp pistons need LESS timing, that's why they used them. What Mike said is bang on.

[wheming]

This is what worries me if I get to the point to try and learn MPTune. I like starting safe and working up.
With our now ancient means of overriding the computer it was easy.
But starting off with a cal that is more agressive and trying to scale back still incurs alot of stress on parts when you are knocking alot. Those bearings and the pistons/rings eventually might say enough...

[tryingbe]

This is what worries me if I get to the point to try and learn MPTune. I like starting safe and working up.
With our now ancient means of overriding the computer it was easy.
But starting off with a cal that is more agressive and trying to scale back still incurs alot of stress on parts when you are knocking alot. Those bearings and the pistons/rings eventually might say enough...

Turbonator uses stock mapping for fuel and ignition, last I heard. MPtune provides us a way to use engines that never came on the car. AJ is having so much problem is due to 2.4L 16V was never used with SMEC, therefore no base fuel nor ignition timing for him to work with.

[Force Fed Mopar]

according to this i understand it that the LimitForHotMapAdvance is a maximum MAP timing not a minimum

http://www.turbo-mopar.com/forums/showthread.php?70764-Minimum-timing-still-have-knock&highlight=

All I know is, if you drop that table, it will allow lower total timing.

[turbovanman²]

Turbonator uses stock mapping for fuel and ignition, last I heard. MPtune provides us a way to use engines that never came on the car. AJ is having so much problem is due to 2.4L 16V was never used with SMEC, therefore no base fuel nor ignition timing for him to work with.

A stock 8 valve map should be damn close. If he wants to compare, there is the Masi cal in there which has way less timing than an 8 valve so maybe he should try that one for a base.

[johnl]

Wowser.

[cordes]

Well, not exactly. Detonation and pre-ignition aren't really the same thing, though very similar. It is basically the difference between which flame front starts first, the uninvited one, or the intended one.

Pre-ignition is normally initiated by a hot spot, or incandescent (chunk of carbon or overheated metal/plug/exhaust valve), where detonation is the end gasses "going off" due to heat/pressure/mixture.

Either way, the flame fronts collide, and "ring the bell" of he piston.

Retarding ignition, be it for nitrous or boost, is an effort to place the peak cylinder pressure in the "sweet spot" of 15-20* ATDC, pretty much all engines respond this way, it's more to do with the geometry of piston/rod/crank than combustion chamber, etc. which is why I can state that with confidence.

Most engines like about 36-38*BTDC of total lead, at least for a 2-valve engine, the more efficient chambers of 4-valve engines don't require as much time, and can often run with a total of 24-28*. As boost is added, and combustion efficiency improves, less timing is needed (or desired) to produce peak pressure in the "sweet spot".

Normally, with nitrous, I'll get the engine dialed in on its own to find the total timing it likes, then reduce it a bit more than I think I'll want/need. This normally works out to be about 1.5-2* per 50HP of nitrous added, for boost it will be a bit different, we're not increasing the O2 content, just the density.

Taking "too much" timing away will never hurt parts, just power, as the peak pressure happens later as the piston is dropping away from the pressure. If not enough timing is taken away, peak pressure happens closer to TDC and much higher heat and pressure is developed, but at a point that the pressure is basically just trying to break parts. You can imagine what would happen if peak pressure happened at TDC! All that potential HP doing its best to push the crank out of the block!

Basically, what I'd advise you to do is back it off more than is needed/desired, then slowly add it back... pretty much the same thing the factory knock routine does, reduce it a bunch to "get ahead" of the knock, then slowly feed it back to what it "should be".

Mike

Not from detonation, but retarding the timing will raise EGTs and melt pistons eventually. The point at which you can't pull enough timing without things melting is the point at which you're octane limited for that boost level. You'll have to up the octane rating or lower the boost.

I'm glad that Simon mentioned the fact that the piston design of the SRT4 required less timing. IIRC they run much less timing than what we do. I didn't want to throw out bad info based off of a brief look at a timing table a couple of years ago.

[A.J.]

I was wrong wrong wrong. I was moving the points up and I should have been moving them down. Harry came by and helped. We moved the points down, no knock. We moved them up 2 points at a time until we got knock and moved them back down again. We adjusted both AdvanceFromMAPWarmPart and AdvanceFromMAPWarmFull. Once I get my rebuild kit (and adjustable spring assortment) for a Forge wastegate that I have for an SRT-4 made to work with my Garret I'm going to hit the dyno.

Thanks for all of your help. I'm still having a hard time wrapping my brain around this timing thing. I have a friend who's an automotive instructor who's really good at breaking things down and explaining them. I'll see if he can get it to sink in.

[cordes]

I was wrong wrong wrong. I was moving the points up and I should have been moving them down. Harry came by and helped. We moved the points down, no knock. We moved them up 2 points at a time until we got knock and moved them back down again. We adjusted both AdvanceFromMAPWarmPart and AdvanceFromMAPWarmFull. Once I get my rebuild kit (and adjustable spring assortment) for a Forge wastegate that I have for an SRT-4 made to work with my Garret I'm going to hit the dyno.

Thanks for all of your help. I'm still having a hard time wrapping my brain around this timing thing. I have a friend who's an automotive instructor who's really good at breaking things down and explaining them. I'll see if he can get it to sink in.

Hey, you're doing great! The cal stuff is a pretty steep learning curve. Let's all just be thankful we aren't adjusting tables in a hex editor any more.

[turbovanman²]

I was wrong wrong wrong. I was moving the points up and I should have been moving them down. Harry came by and helped. We moved the points down, no knock. We moved them up 2 points at a time until we got knock and moved them back down again. We adjusted both AdvanceFromMAPWarmPart and AdvanceFromMAPWarmFull. Once I get my rebuild kit (and adjustable spring assortment) for a Forge wastegate that I have for an SRT-4 made to work with my Garret I'm going to hit the dyno.

Thanks for all of your help. I'm still having a hard time wrapping my brain around this timing thing. I have a friend who's an automotive instructor who's really good at breaking things down and explaining them. I'll see if he can get it to sink in.

Awesome, glad you found it. When they changed the templates 2 years ago, I couldn't for the life of me get the cal to change, didn't realize I had to save the tpl and bin after every change vs you didn't do that before. As long as we learn, its all good,

Timing is simple, we want the spark to occur BEFORE TDC, as the flame front needs time to move and do its job. If we have timing too late, the flame front has no time to travel and we get a poor running engine, so we want to move the timing so it happens earlier, which is advancing it, or BTDC. Engines have a sweet spot and when go passed that, the engine want's to detonate and run like crap.