When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Wouldn't you have noticed if it were detonating that much?
How would you tell?
Under WOT with a helmet on, open exhaust etc... if it were pinging loud enough to hear in such conditions, he would have left a trail of engine debris back to the paddock.
Originally Posted by bureau13
Also, would a wide-band in the car tell you if you were going too lean (assuming you don't have one already)? I would think there were acceptable ways to test your theory that don't involve losing the performance gains from the chips...
It's not just lean conditions which cause engine damaging detonation. Excessive ambient / engine heat effecting timing is a more likely culprit here. You can be running fat rich with a hot engine on a hot day and still detonate enough to damage an engine. The modified chips only add to this theory.
This could be a moot point, the heat could have adversely affected the motor oil too. As I spoke with Andrew last night, maybe it's time to install an oil temp sensor (or two).
Years ago Jim Page noticing high oil temps even when engine temps were "normal" and he installed a bright red warning light which is triggered when oil temps reach a certain threshold. It's something I plan on adding to my 79 if I ever get back to the track:
...I'm really starting to "like" my theory of detonation hammering my rod bearings.
I'm liking this theory also. Detonation is certainly hard on rod bearings, especially the relatively soft 928 bearings, and especially when the oil is very hot. Amsoil is a good high-strength/high temp oil but everything has limits.
Originally Posted by AO
If that is the case, (and I have experience seeing this in boosted motors), then I will probably return to a stock EZF chip rather than Ken's and see if that keeps everything in place.
For sure go back to stock timing, but I also think a knock-lite of some sort is a necessity. I would also consider an auto-retard system, either something like the J&S Vampire or retrofit a LH2.3/EZK-- a big job but you need some way to monitor detonation and tweak timing.
Or do what the factory did, and use a conservative (i.e. stock) timing map.
I'm liking this theory also. Detonation is certainly hard on rod bearings, especially the relatively soft 928 bearings, and especially when the oil is very hot. Amsoil is a good high-strength/high temp oil but everything has limits.
For sure go back to stock timing, but I also think a knock-lite of some sort is a necessity. I would also consider an auto-retard system, either something like the J&S Vampire or retrofit a LH2.3/EZK-- a big job but you need some way to monitor detonation and tweak timing.
Or do what the factory did, and use a conservative (i.e. stock) timing map.
I am really hoping it is just rob bearings!
Hi Jim,
Thanks for backing up my theory. I can add a knock lite, but if I go to knock control, I think it's cheaper for me to move to a complete aftermarket ECU like an AEM Infinity system or Megasquirt.
I tried, but it's a different filter that comes with the Accusump. In the end, not sure it makes a difference at this point. Need to dive in and see if the journals are scored, and which rods are the offenders.
Thanks man!
I did not drop any pennies (but I wish I had). But if everything works out and it;s just a bearing replacement, then yes, I think I will start logging time and doing preventive maintenance like this. May also start doing used oil analyses to predict when they are due.
BTW, one thought occurred to me last night. This car has Ken's S3 chips in it, and it was VERY hot at Pitt Race. Because this car does not have knock sensors, I think it is possible that the timing chip is too aggressive and causing knock that the engine cannot handle (in extreme situations). Does anyone have any corroborating theories?
I've written volumes about 928 rod bearing failure sources, on this Forum.....you can probably go back and search for these discussions.
You can feed one of these engines will ample oil of the very best quality and still have bearing failure.
Any significant "push back" of the piston in the opposite direction of its intended travel will quickly ruin the super soft stock rod bearings. The bearings are simply too soft to absorb much/any pounding. A few degrees too much ignition timing and engine life goes down very quickly. On a "knock sensor" controlled engine, these engines will suffer from the bearings being pounded when knocks are as low as 75 per 10,000 cycles.....a very low threshold.
Without knock sensors, timing maps need to be very conservative.
You will find that some of the bearings will have lost their "crush" in the rods and will just fall out. This is the very first step as a result of "push back". After the bearings loose their crush, there is nothing to keep them from spinning in the rod journals.
Your engine will have progressed to this point, minimum.
Running Ken's chip in a boosted engine is a very bad combination. The early low boosted 85/86 32v cars ran about 6 psi boost and as the stock chips were so conservative they survived.
Ken's chip probably uses all that safe margin and more, so you were certainly living dangerously with that combination. How much boost are you running ?
Thanks for backing up my theory. I can add a knock lite, but if I go to knock control, I think it's cheaper for me to move to a complete aftermarket ECU like an AEM Infinity system or Megasquirt.
But yeah... fingers crossed.
I think you will find that most all of the aftermarket ECU systems depend on you telling the system what an actual knock is....for your individual engine. This is extremely time consuming....you can/will wear out a couple of engines trying to "teach" these systems what a knock actually is.
And then there is the elephant in the room.....the offset piston problem.
For all the 928 engines, Porsche used pistons with offset pins....a traditional "German" piston thing. The idea of offset piston pins is that it is possible to improve the angle of the connecting rod to the crankshaft, with pins that are not centered.....or make it worse, depending on which way the offset faces. The downside of offset pins is that in one direction, the pistons are quiet (minimal slap) and in the other direction, the pistons are very noisy (maximum slap). Unfortunately for us, on all the 928 engines prior to 1987, they installed one side of the engine with the piston pins in the "quiet" direction and the other side of the engine with the pistons in the "noisy" direction.....1/2 of the pistons face one way and the other half face the other direction. Not very "solid" engineering. [They had been doing this for so many years (all though the 356 and 911 engines from the beginning of time), that I guess no one paid much attention.]
However, when they went to active knock sensors in 1987....the "slap" from the pistons on the "noisy" side of the engine completely confused the knock sensors....making them totally useless. To "cure" this problem, in 1987-1995, the pistons are symmetrical and can be installed so the piston pin offsets all face the same direction (the quiet direction.) After this change, it was possible to "teach" the knock sensors what a knock sounded like and then have the knocks remove ignition timing.
Long story short....On an '85/'86 engine, you will never get a knock sensor to differentiate the difference between piston slap and an actual knock. (Let me reword that statement....Bosch, with all their engineering experience, couldn't do it.)
The really smart people, out there, will quickly realize that "aftermarket" American forged pistons always slap, because of the high piston to wall clearance required by the aluminum they use. And yes, knock sensors using these pistons are almost completely useless.
Trust you have not forgotten how to install hard Clevite CB1628HX rod bearings for high performance applications. I have posted about the Clevite rod bearings several times before.
Åke https://rennlist.com/forums/944-turb...aring-fix.html
Last edited by Strosek Ultra; 07-27-2017 at 05:19 AM.
This could be a moot point, the heat could have adversely affected the motor oil too. As I spoke with Andrew last night, maybe it's time to install an oil temp sensor (or two).
Years ago Jim Page noticing high oil temps even when engine temps were "normal" and he installed a bright red warning light which is triggered when oil temps reach a certain threshold. It's something I plan on adding to my 79 if I ever get back to the track:
Exactly what I've experienced .... coolant temp tells you when it's already too late.
On race motors I've thrashed, I always found that oil temp was first to rise, followed some time after by coolant temp. For that reason I believe an oil temp gauge (and idiot light) to be essential in a race motor, and a much better indicator of actual engine temperature. By the time a coolant gauge is showing high temp, the oil is already like water, and the oil temp is sky high. Control of oil temp (coolers), and therefore viscosity, makes a huge difference.
Hey guys I really appreciate the input. Unfortunately life got in the way last night and I was not able to get the oil pan off, so no real updates.
To be clear as DaveK said, this is a NA motor. Crank was drilled (Taylor) according to Abby, but I've not seen it yet so... but let's say it's drilled. for the sake of argument.
I reviewed the footage yesterday, and the car seems pretty rich at high RPM (upper 10's mid 11's). It's really hard to see becasue the way the LEDs light up in the display and the "shuttering" effect of the CMOS in the camera. Anyway, at no time did it seem lean. Since i can't datalog the other inputs easily, if this car lives, I may take a tiny camera and have it monitor the instruments and add an oil temp gauge.
Anyway, nothing really to report. Sorry. All in due time.
Andrew, analog oil pressure/temp gauges are easy to install if you don't have both, and easily picked up by your camera. While you're at it, a water and tranny temp gauge too.
The trans temp sender can be tapped into the center of the diff fill plug.
Erik's gauge layout looks very nice. A slight variation to consider would be angling the gauges towards you.
Finally, install an external oil cooler over the winter. I have all the specs as my car came with one which is Ronn's yellow racer from 928 Intl.
07-25-2017, 01:23 PM
