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Discussion Starter · #1 ·
Please take a look at these pics. I'm looking for insight as to the root cause of this damage. E85 car. 03/04 cobra heads, 5.4 iron block +.020" bore, gibtec pistons, twin turbo running around 10psi and 16psi max.

Ect is usually around 175-180*f
Ptw clearance was set to .005"
Piston coating was applied by Gibtec
Ring gaps were set to .030" top and .028" 2nd
Oil pressure hot was 35psi at idle, 85-90psi wot.

This build only has arpund 3000 miles on it.

These pics were all of cylinder #2. The other cylinder followed suit, some not as bad. It appears the pistons were rocking in the bores?


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Matt,

Something went afoul in either the fueling system or the cooling system. The pistons overheated and swelled up larger than the PTW clearance and subsequently scuffed the pistons and the bore.

If the cooling system is OK then I would look for a whoops in the fuel system. Perhaps an electrical ground gone bad or a pump gone bad. You guys have been doing these engines too long to experience one of those failures without an accompanying fueling or cooling system failure — and I know you don't make tuning/fueling mistakes that could do that.
 

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Discussion Starter · #4 · (Edited)
Thanks Ed. I know the cooling system is a non-issue. Temps never got hot and it's never out when ambient temps are real high. I'll pass this along to my brother as it's his build. He's running a Holley EFI system and tuned it himself. Time to double check everything.

What are your thoughts on fuel washing the cylinders? Possibility? It was a fresh build when he installed the Holley ao there was a lot of afr tweaking initially.

Matt
 

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Fuel washing a cylinder is one of those urban legends that sprang up in the street racing and drag racing circles decades ago. A typical blown alcohol engine will use a 20 gpm (or larger) furl pump and literally put 90 to 95% of that into the engine. 20 gpm is the equivalent of 4542 lph! None of our engines even come close to this number. A nitro car uses a 110 gpm fuel pump and they don't wash cylinders. We definitely are not washing cylinders with a 1000lph fuel system, if it even gets that big!

The engine went lean. The pregnant question is why. If your brother has not tuned these Holley units before have him try using the Holley self-learning capability to get the system close and then finesse the last few hp manually. Make sure the injectors are large enough and the fuel pumps are big enough. BTW Line-2-Line can almost certainly salvage the pistons for you!! The cylinders are a different story.

While it is not the cause of the scuffed bore and pistons a 0.020" overbore is getting pretty thin for a blown ModMotor ...
 

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Discussion Starter · #6 ·
I agree with the +.020" and he's going as small as possible this next time. My 5.4 iron block is +.002" with line-2-line Gibtec pistons.

On to find the cause of damage. Thanks Ed

Matt

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Matt,

When you scuff the piston in the ring lands, you need to get it really hot to do that. The piston is much smaller in the land area than anywhere else. That kind of scuffing frequently points to a lean condition at part throttle around town-style driving and part throttle cruising on the highway. This is a timing map from a tuning article for an MS3Pro. While intentionally done with a bit of flair and tongue-in-cheek humor, it is still a pretty good idea of the various regions on a timing map and what happens if they are misused.
Font Screenshot Rectangle Terrestrial plant Parallel


Clearly a little tongue-in-cheek humor in the naming conventions but overall spot on with respect to the significance of each region. For example, the 700 to 2600 rpm range at a load factor from 70 to 150 is where you will ping the engine mercilessly if you get frisky with timing (or cheap with the fuel).

Another thing that could impact fueling and engine temperature would be a misbehaving O2 sensor. On balance, I think that if you take advantage of the self-tuning capability and then hand-finesse the final tune, you will be pretty good. There are some things that Holley may not do as nicely or as pretty as some others, but they do provide the capabilities for the tuner to take advantage of. The one thing they do that is very likely the best in the industry, right now, is their self-learning, auto-tuning, or self-tuning capability. I think their approach may well be the best commercially available today.
 
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