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Engine Detonation/destruction at Daytona


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Just curious if anyone else lost an engine at Daytona due to lean detonation?  I was with Rhino Racing 1993 Mustang #288.  We ran fast until lap 67 when we detonated two cylinders and trashed the engine.  If anyone else experienced this, please let me know.  I have questions about fuel source/octane, and ECU setup.

 

 

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Yes, we did.

 

fuel came from buccees, but it wasn’t the fuel.

 

the duration at WOT caused engines to be highly prone to knock.  Need to pull timing To get them to survive If you run a aggressive timing map

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Our engine was set up on the dyno at 12.5 A/F with O2 sensor adaptive loop defeated.  I call it a fancy carburetor.  Ignition set at 34 degrees constant above 3500 rpm.  Engine geared to run between 3500-5500 rpm.  Fuel pumps sized and tested to have 70+% excess flow at peak power.  However, fuel injectors at 92% duty cycle.  93 octane fuel came from the Sunoco station on International Speedway Drive close to the speedway.  Clean, capped 5 gallon fuel jugs.  We have tested fuel pumps fuel pressure, and set an adjustable pressure regulator at 12.1 A/F for next race.  Also installed wide band O2 sensor and readout on instrument panel.  Ran two days SCCA sprints in May-no trouble.  Heading to Nelson Ledges in July and I am still worried.

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We had a problem when we first got the car together.  We went through 2 motors with broken pistons due to detonation.  To correct it we changed our tune to pull more timing out and bumped our AFR a little more.  Then we also got real paranoid and added knock sensor along with EGT probes for each cylinder.  

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Yeah I’m no mustang expert but just applying some general stuff-

 

13.5:1 static comp and pump 93, nope. Timing locked in mid 30’s with that combo, nope.  On top of that fuel injectors at 92% duty cycle… nope. 

 

Won’t last long even if you see a nice low 12’s AFR which is sorta different.

 

 

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41 minutes ago, drgrumpus said:

Compression ratio NOT 13.5.  We run 9.4, just a tenth over stock.  34 degree advance at high rpm was optimum on dyno.  


Gotcha, saw 13.5 from another and thought “maybe he’s on the team”. Glad that’s not the case!  
 

Still, I’d find max power on the dyno and bring it back a few degrees for our purposes. You’re gonna see higher intake temps and slightly varied quality of fuel.  You want some cushion for less than ideal conditions. 
 

I’d also get the duty cycle down with larger injectors.  Running that high will affect their reliability and could result in a suddenly lean condition. 

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28 minutes ago, ETR said:


Gotcha, saw 13.5 from another and thought “maybe he’s on the team”. Glad that’s not the case!  
 

 

 

Oh, I'm quite familiar with the car, but was curious to see who would bite at the idea that a mostly stock EFI system of that age could cope with a number like that and still run 93 octane.  Or if the car was running like that why someone would bother to ask for opinions on why it blew up.

 

 

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2 hours ago, MMiskoe said:

Oh, I'm quite familiar with the car, but was curious to see who would bite at the idea that a mostly stock EFI system of that age could cope with a number like that and still run 93 octane.  Or if the car was running like that why someone would bother to ask for opinions on why it blew up.

 

 

The EFI system, mostly stock or otherwise, doesn't care what the compression ratio is and can run whatever AFR the injectors can handle. Not really a notion to "bait" with but whatever floats yer boat.

 

The octane requirement depends on a lot of things, with combustion chamber design being one of the more significant ones. A mid-90s Ford V8 isn't cutting edge so compression ratio is worth asking about as a starting point when talking about octane sensitivity. 

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on a roller dyno or a eddy current dyno?   The load the car sees at daytona is way higher than most roller dyno's can simulate. 

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Chris, very true.  We run on an inertial "roller" dyno.  True, not a good simulation of WOT, constant speed like banking at Daytona, but we use it for back-back testing.  I think we will pull back to 32 degrees total advance and keep A/F at 12.1.  We'll go with bigger injectors to get the duty cycle back to about 80%.  Maybe re-activate the O2 adaptive function in the ECU.  

 

BTW, I have built 13.5 CR engines for sprint racing(not ford small blocks) and had to use 112 octane fuel.  At $10 a gallon or more these days, that is not an option for us cash concious endurance guys.

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34 degrees sounds like a lot to you modern fast burn chamber guys, but nearly all the domestic v8s especially pre vortec sbc stuff is 35-42 degrees. Cylinder fill and burn speed is so much better on most 4v motors they seem to usually be in the low 30s. Look how much timing an m20 takes compared to an m50.

You should be nervous about the problem, thankfully you have megasquirt so you can log some data and do some diagnostics. Do other cylinders show signs of preignition? What was the failure mode of the 2 cylinders?

 

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3 hours ago, drgrumpus said:

No Megasquirt. We use stock ECU with custom card to customize fuel maps at WOT.  The O2 sensor trim is deactivated.  Spark plugs showed all 8 cylinders lean.  Two plugs had tips blown off.  

Fuel delivery at extended WOT would be my suspicion. Filter, small or failing lift pump, etc. 

I was going to suggest checking for spark scatter as well, a couple of degrees when hot can tip the balance on long hard pulls. 

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10 hours ago, mender said:

Fuel delivery at extended WOT would be my suspicion. Filter, small or failing lift pump, etc. 

I was going to suggest checking for spark scatter as well, a couple of degrees when hot can tip the balance on long hard pulls. 

Agreed, this is a fueling issue, not ignition. 

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On 6/25/2021 at 5:52 AM, drgrumpus said:

Our engine was set up on the dyno at 12.5 A/F with O2 sensor adaptive loop defeated.  I call it a fancy carburetor.  Ignition set at 34 degrees constant above 3500 rpm.  

 

  However, fuel injectors at 92% duty cycle.

Do you datalog knock or afr and can see it ? A quick google search showed a map with 30 at WOT and another 28 at WOT.  The extra degress of timing, when close to maxing it out, does not gain a ton of hp.  The 92% duty cycle does scare me with the combination of that much ignition advance. At that point you are basically going static with fuel and at max fuel amount. I would think your afr would have gone from 12.5 to who knows how high.

 

How does the stock ecu control detention? Can you adjust it at all? I am not sure what your engine, but if an older mustang v8 and it has knock it might be a single wire sensor. Is there a way to convert to a newer Bosch style, though you might have to

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On 6/27/2021 at 6:36 AM, drgrumpus said:

No Megasquirt. We use stock ECU with custom card to customize fuel maps at WOT.  The O2 sensor trim is deactivated.  Spark plugs showed all 8 cylinders lean.  Two plugs had tips blown off.  

Sounds like you have it figured out. AFR gauge my be suspect. Maybe add an EGT gauge, bigger injectors, and a new tune. 

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4 hours ago, Hurljohn said:

Knock showed up in 5th gear pulls, don't just tune in 4th gear.  

 

 

 

Long time ago, I kept knocking rod bearings out of my Pontiac engine but only after doing a top end run. Fuel system wasn't keeping with the demand and went lean. Hard to hear detonation in a convertible going 130+ mph...

 

Long hard pulls will point out problems. 

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40 minutes ago, mender said:

Long time ago, I kept knocking rod bearings out of my Pontiac engine but only after doing a top end run. Fuel system wasn't keeping with the demand and went lean. Hard to hear detonation in a convertible going 130+ mph...

 

Long hard pulls will point out problems. 

QJet?

 

That small fuel bowl is a pain on large bores.

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