Jeep Strokers

Tired of waiting for the custom pistons, the engine was assembled with the supercharger. the characteristis are as follows:
Deck clearance about .0028
Combustion chamber about 58 cc
MLS Victor reinz head gasket
Silvolite 3241HC pistons +.040
4.2 Connecting rods (707 casting number)
Supercharger MP 90, boost "only" 4.5 psi
98 0ctane gasoline
32 lib/h ford injectors
CR about 10 to 1

Test on the higway, a few minutes (WOT), and that happened. [/attachment] causes of damage?

Just to make sure you covered all your bases:

You have a 2 bar map sensor installed?
flashed the ECU with a boost map (so it doesn't run lean in boost areas?)
Turned off baro relearn in the ECU?

or, if you dont' have a tuner for the ECU, then some form of piggyback? (Still need the 2 bar map sensor)


If you were running boost on the stock ecu with *just* injectors changed, it melted a piston because that is what happens without anything to manage fuel in boosted situations.

Look like detonation or extremely lean. How do the other plugs and pistons look? Maybe a partially clogged injector?

What are you doing for fuel management? Do you have a wideband installed?

The Stroker was running with all original components, except 32 lib/h injectors (wich were new).
The rest of the pistons are fine.I see no more damage.

I have bought a FCT1-019B (with 2 bar MAP sensor), MSD Knock alert and a wide band O2 sensor (I´m thinking to put two, one for each 3 cylinders).
I am also waiting for the Bulltear custom pistons (dish 34 cc, CR about 8.6 to 1).
Is it enought with all this?
I hope so

all you technically need is the 2-bar map sensor and proper fuel injector control. With a good ear and the ability to read spark plugs, it will live a long, healthy life.

Wideband and knock sensor are both very valuable tools to make that tuning process more efficient.

One question.
Does the rod will be damaged by heat, doubled or has been twisted?
A simple view is not seem nothing, excep for a color more "roast" (overheat?) near to the pin.

That piston has been burnt through due to detonation. Could have been due to the engine running lean, too much timing, or too much compression. If you had a wideband O2 sensor you could at least rule out the first.

Some things I wonder at here... not the fuel management or piggybacks, but the 10-1 cr which is high in aluminum block ricers. The supercharger is pulling ambient air and heating the shit out of it before compressing it, before compressing it further and detonating it with a likely stoich mix (if you are using such large injectors on a stock regulator, starting out rich but balancing out somewheres...) perfect stoich is the hottest mix. rich is cooler & lean is cooler. You melted through your piston, not just blew through it with compression. even with forged everything do you think the temperatures obviously being reached in your combustion chamber are manageable? I drilled all my water passages out on my head gasket to get better cooling & it did wonders. no clutch fan, electric fan never kicked on since I have been trying to work it out & my temp is a beautiful 210.

yea, that is a melted piston, not a detonated piston. It ran too hot and too lean for safe combustion.

In this particular case, the compression isn't the problem, the "supercharger" isn't the problem, even the heat isn't the problem. The problem is improper fuel management. Without the ability to see boost and properly enrich the combustion process, damage occurred. @ 7-10 psi, these engines would have no problem at 10 or 11:1 cr, with proper fuel and spark control (you have to pull so much timing and run so much fuel through that it would probably run like a turd, but it would be "safe", nonetheless....)

when it goes back together, get the engine setup with big injectors, a proper 2 bar map sensor, and NO supercharger. get it tuned and running smoothly & strongly,. then bolt the supercharger back on.

Strapping boost to an untuned (or untuable) setup is just not the way to do this.

lafrad wrote:yea, that is a melted piston, ....... . .. ..Strapping boost to an untuned (or untuable) setup is just not the way to do this.

That is the ONLY way to do this

lafrad wrote:yea, that is a melted piston, not a detonated piston. It ran too hot and too lean for safe combustion.

In this particular case, the compression isn't the problem, the "supercharger" isn't the problem, even the heat isn't the problem. The problem is improper fuel management. Without the ability to see boost and properly enrich the combustion process, damage occurred. @ 7-10 psi, these engines would have no problem at 10 or 11:1 cr, with proper fuel and spark control (you have to pull so much timing and run so much fuel through that it would probably run like a turd, but it would be "safe", nonetheless..

Yup, Lean Condition.

Maybe someone can clue me in what guys are doing on EFI 4.0's but in a parallel universe we use return style fuel regulators that increase fuel pressure as boost increases and boost timing retard ignition boxes. I've read some posts here from guys that seem to have it pretty well figured out on the Jeeps.

I agree, detnation, if you're running the stock spark plugs that has a lot to do with it, my dad found that out in his race car, can the projected tip plugs! and probably the engine mangment like the others have stated.