Electric Fans, double nothing

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PlayingWithTBI

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What, BTW, does the data show - that the appropriate signal was received from the detonation sensor?
Here's an example from EBL but TunerPro RT has similar charts. In this example I was getting KCs at lower RPMs due to SA Launch Mode advancing spark too much. Once I lowered it, I got rid of all the lower KCs and then I reduced advance at higher revs in my SA tables.
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Sometimes you may get false KCs from things like exhaust pipe hitting the frame or something else loose. That's when looking at the plugs will tell you, they don't lie.
 

PlayingWithTBI

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Sorry @bobby v but I can't help it. Here's a great explanation of how spark knock works - just saw this on Gearhead-EFI.com, what a coincidence, ha ha.

Quote from @1project2many
"Knock is an audible event which indicates combustion pressure and temperature have risen too quickly and the energy which would be used to drive the piston is being converted into sound. Knocking can be caused by pre-igniton (before spark plug fires) or detonation (after spark plug fires). Triggers can include hot spots on the cylinder head or piston, lean air/fuel mixture, incorrect spark timing, incorrect octane rating, or a mix. During knocking the engine block, cylinder head, and piston top are heated above average temperature. As chamber temperature rises it becomes easier to light the air/fuel mix and the rate at which combustion occurs decreases. If knocking is allowed to continue there will almost always be damage.

Preventing engine damage using knock counts is really a dynamic process. Once knock begins the computer has to reduce spark advance below the value where it first occurred. Timing be safe to 43 degrees, knock begins at 44 degrees, then the knock sensor activity causes timing to drop to 39 degrees before knock stops. This is because the combustion chamber and piston top require time to cool off. A stock timing table and ESC system are programmed to advance spark to table maximum, and if knock occurs ESC will reduce advance until knock stops. It will then increase advance toward table maximum. If knock occurs during this process ESC will begin the cycle again.

Tuning with knock counts imo requires time travel. Tuning with knock counts is not simply a matter of reducing spark advance at the RPM and MAP where knock is occurring. The goal is really to prevent knock by decreasing timing by the smallest amount necessary. Properly tuning with knock counts IMO requires reading datalogs from a point in time prior to the onset of knock that indicate combustion chamber heating is causing or strongly contributing to knock. Changes such as afr increasing or rapid spark advance can begin a cycle of temp rise that results in abnormal combustion. I have seen cases where increasing fuel delivery at 2000 rpm prevents up to 6 degrees of spark reduction at 3000 rpm. I use the shape of the spark table as a guide. If I see a nice curve that generally seems to work, but requires a substantial change in shape (up to 4-5 degrees of timing reduction in one area) due to knock, I try to find a way to prevent knock in the first place.

In short: Drive the vehicle to obtain logs. Review logs for knock. Adjust timing tables to reduce advance and drive again. If you find you are reducing knock by more than three degrees in any three adjacent cells review the logs for changes that can be made elsewhere which could prevent heat in the combustion chamber from causing knock."
 

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Here's an example from EBL but TunerPro RT has similar charts. In this example I was getting KCs at lower RPMs due to SA Launch Mode advancing spark too much. Once I lowered it, I got rid of all the lower KCs and then I reduced advance at higher revs in my SA tables.
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Sometimes you may get false KCs from things like exhaust pipe hitting the frame or something else loose. That's when looking at the plugs will tell you, they don't lie.

OK, to drill down on the numbers.
If I'v understood correctly, then a 'count' is a detonation event in any one cylinder. At its worst in your case at 4800 rpm which is 80revs/second. To simplify the numbers, lets say it was 80 counts (not the 95 shown). If we assume detonation was confined to one cylinder (and remembering two revolutions between events) then worst case scenario is detonation is occurring for 160 revolutions which equates to 2 seconds. If all eight cylinders were detonating that would be 0.25s. In reality we could expect something in between so say four of the cylinders detonated then the duration of detonation is 1 second - which shouldn't be enough to cause damage or let the situation get out of hand (ie overheat the piston exacerbating the problem).

Am I correct in thinking the standard GM PCM will make the timing adjustment within the above time frames when it gets the appropriate signal(s) from the det sensor?

(I remember in the UK when unleaded gasoline was introduced (and before det sensors were fitted) it was common to hear cars as they accelerated out of junctions at low to mid rpms detonating for maybe 2-3 seconds and none suffered any lasting damage).
 

PlayingWithTBI

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If I'v understood correctly, then a 'count' is a detonation event in any one cylinder. At its worst in your case at 4800 rpm which is 80revs/second.
It's not just one cylinder plus these knocks are from doing one or more 0 - 60 MPH WOT (~7.3 seconds) run so, the engine is only running in that particular cell for less than 1/2 second.
 

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Sorry @bobby v
Preventing engine damage using knock counts is really a dynamic process. Once knock begins the computer has to reduce spark advance below the value where it first occurred. Timing be safe to 43 degrees, knock begins at 44 degrees, then the knock sensor activity causes timing to drop to 39 degrees before knock stops. This is because the combustion chamber and piston top require time to cool off. A stock timing table and ESC system are programmed to advance spark to table maximum, and if knock occurs ESC will reduce advance until knock stops. It will then increase advance toward table maximum. If knock occurs during this process ESC will begin the cycle again.

."

Taking this one paragraph - is it describing the GM PCM or an aftermarket one? And if an aftermarket one, does the GM PCM behave similarly and would it have a programmed ignition timing which is likely to cause detonation which it then uses the knock signal to row back from or would the programmed timings be compatible with the expected fuel quality and the ability to retard timing when detonation is detected be there as a safeguard only?
Or, to put it another way, will the GM PCM always look for the detonation threshold then take a step back? And, if that is the case - what octane rating might it be able to cater for?
 

PlayingWithTBI

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Taking this one paragraph - is it describing the GM PCM or an aftermarket one?
That's pretty much for all PCM/ECMs but GM uses a pretty mild tune to help eliminate KCs - that's why a tune on a stock engine will give you better performance. You play with fuel and timing to get to that precipice of knock then back down 1 or 2*

will the GM PCM always look for the detonation threshold then take a step back?
Yes, it will periodically advance timing to look for a working knock sensor. If it doesn't see any, it'll throw a code.

what octane rating might it be able to cater for?
For that, you'll have to play with timing/fuel and different octanes. I've seen one guy mix E85 with 91 to get better performance. BobR@dynamicefi put together a calculation for that on 3rdgen.org - too much work for me, I'm not running a fire-breathing monster where I need to get every little bit out of it. Someday, like @L31MaxExpress said, I'll try a cooler T-Stat and see what happens. I do know I need a summer tune and a winter tune here in the desert plus, I'm not running IAT or MAF, I'm strictly speed density (MAP vs RPM).
 

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That's pretty much for all PCM/ECMs but GM uses a pretty mild tune to help eliminate KCs - that's why a tune on a stock engine will give you better performance. You play with fuel and timing to get to that precipice of knock then back down 1 or 2*


Yes, it will periodically advance timing to look for a working knock sensor. If it doesn't see any, it'll throw a code.


For that, you'll have to play with timing/fuel and different octanes. I've seen one guy mix E85 with 91 to get better performance. BobR@dynamicefi put together a calculation for that on 3rdgen.org - too much work for me, I'm not running a fire-breathing monster where I need to get every little bit out of it. Someday, like @L31MaxExpress said, I'll try a cooler T-Stat and see what happens. I do know I need a summer tune and a winter tune here in the desert plus, I'm not running IAT or MAF, I'm strictly speed density (MAP vs RPM).

Thanks for all of that and the previous posts - it's really helped me understand what my GM PCM is capable of.
Going to try and delete the EGR and if it 'feels' right, stick with it. Longer term I might consider raising the CR to better exploit LPG's 112 octane #.
All a different PCM would give me is control over ignition timing - the LPG has its own control system. And I've no desire to be changing the cam or doing anything too radical tuning wise other than headers maybe - in which case ditching EGR would help. Depends though on the annual safety check which can get sniffy about removing emissions kit. I'll sound him out in advance though and I have two local testers (different garages) who by amazing coincidence are both into USA motors (one of them has Ford trucks but we'll forgive him that!)
Cheers!
 

fastfreddys454ss

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So if my temp situation doesn't improve to my satiisfction I guess the logical step is electric fans.
Here's my thoughts******
They say a BBC needs over 4100 CFM, tall order to be sure right
One big 16 incher or 2 12" ??????
Shroud or not ????
Will I have to upgrade my alternator ??
Any other words of wisdom ????
Thanks
Bobby V


Bobby


2 12” fan won’t get you to the 4100 cfm numbers your looking for. A single 16” if mounted in the center of the radiator will hit the water pump pulley and at the most a single 16” will give you 3500 cfm. With your trans cooler and a/c fan you won’t have enough room for a pusher fan in front of the radiator either. Another thing you have to consider is with a shroud you only you only have 4“ between the fan shroud and pulley surfaces (depending on how thick your radiator is). So you have to get slim fans. To optimize you electric fans you need a shroud. without a shroud you will have to run those plastic ties that go through your radiator.I recommend dual 16” fans mounted to the shroud.these fans are $99 each and would give you 3000 cfm per fan and are 3 1/4 thick. The next lowest cfm 16” fan is 2800 cfm but is 3.5” thick. I don’t think you will need a higher amp alternator because they only draw between 8 and 10 amps per fan. If they do cause your electrics to flicker you can always upgrade that later. But make sure you get a thermostatic adjustable on temperature off temperature fan controller with relays. I ran a Dakota digital fan controller with a bypass switch. It’s Bluetooth programmable, can hook up to most temperature senders, but it needs a second 70amp relay and has to be programmed to change some of the settings.


I would get:
2 16” 3000 cfm electric fans
1 dual champion 16” fan (34” shroud)
1 thermostatic dual fan controller with relays
1 bypass toggle for emergencies

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fastfreddys454ss

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Here is the wiring diagram I did for the Dakota gauge pac-2800bt. First pic is without a Dakota gauge using the a sender and toggle. Second pic is with a Dakota gauge with a BIM hookup. Just in case you were curious. Here also is what you have to do for dual fans in programming.

For dual fan setup you have to run two relays (RLY-3 70amp) one to fan high and one to fan low. In settings set to b. 2 fan mode. They will both run at high speed unless you have a 2 speed fans.


Fan type

1. Tap the INC switch until “FAN” is displayed.

2. Tap the SET switch. The display will show the current setting:either1, 2, or SPD.

a. 1 is for a single fan

b. 2 is for two fans

c. SPD is for a dual speed fan(for fans with two speeds only)

i. If the dual speed fan requires two powers at the same time for high speed, select 2

3. Tap the INC switch to change the selection. Tap the SET switch to save it.


When using BIM you don’t connect ground, sender or ignition. It is picked up through VHX instrument cluster

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