(Pull up a seat and grab a drink)
Karl,
As you know from our discussion back in February, this is the third engine to go bad in this car (two with me in 12 months) The first two can be directly attributed to drag racing with high-horsepower, supercharged setups, I am not sure about this one. The second owner of the car blew the first engine at a drag race in Texas. He cracked a ringland on the #7 piston when the car was supercharged with the stock engine.
I know for a fact the second engine to blow was in part due to a faulty coolant flow design by Ford in the 4-valve Cobra engines on the driver's side head. On the passenger side, hot coolant flows from the front of the head to the coolant crossover tube to the radiator and from the rear of the head to the heater core. On the driver's side head in the factory configuration, the only outlet is from the front to the crossover tube. The end result are hotter than normal temperatures in the water jackets surrounding the rear two cylinders in the driver's side head (#7 and #8 ).
When I blew the second engine, I was foot-to-the-floor at 1000' at a drag strip in Augusta. When we pulled it apart, none of the pistons exibited any signs of detonation or undue wear, yet there was hole the size of my thumb through the #8 piston (this was a fully forged engine). The hole appeared almost as if it was melted through the piston, but 14lbs of boost can do that I guess. The only thing I could figure is that we may have damaged it on the dyno when we were tuning it a couple of months before it happened (554rwhp). The engine never overheated from what I recall, but without air flow around the engine, #8 may have localized boiled and did some damage. When we built the new engine (new block, new forged internals, reworked heads), I put on an LDC Cooling Mod to hopefully overcome this issue. The cooling mod attaches to the rear of the driver's side head and allows coolant to flow from the rear and "t" up with the coolant from the passenger side head and then on to the heater core.
The third engine to blow (this one) was completely out of the blue. We detuned the car significantly (down to 498rwhp), reduced timing, added fuel, etc back last September. When we were at Rockingham for the THSCC event in October, it was pretty hot that weekend. The car would get warm after a couple of hard laps, I would back off and short shift for a couple of laps and the temps would cool down. Over the winter, I replaced the radiator with a much larger LFP unit and I replace one of my twin fuel pumps (I think one was going bad and this could have been causing a lean condition in the heat). We put it back on the dyno in January and everything checked out great (A/F. power, etc)
Thinking everything was good to go, I drove the car very hard at the February THSCC VIR event. The engine never gave me any issues at all and I drove the car hard enough to overheat the IRS (this is a common issue with IRS Cobras and high speeds). So, I spent the rest of February and March with the rear out of the car fabricating an IRS diff cooler and pump as well as replacing some bushings that melted.
Literally the Sunday before the April VIR event, I took the car for a spin around the block to check out the rear-end reinstall and noticed it was smoking on acceleration, but there is still plenty of power when you get on it. There is oil on the #7 spark plug and a leakdown showed 50-80% loss on #7. So, I am thinking that I either have a broken ring or a broken piston ringland. This was completely out of the blue as I didn't have any issues with it at the track nor after I got it home. The only smoking that I had at the track during my last session was due to the fluid boiling out of the IRS (which, btw, smells awful).
Was this yet another victim of the #7/#8 coolant flow issue? Was it due to a bad tune? We built this engine over the course of two weeks last Spring in order to make it to a Muscle Mustangs and Fast Fords drag race in New Jersey (August issue btw,
) and took it straight from the dyno to the drag strip. Did we do something wrong during the build? Did the rings not properly seat? I have no clue.
So, I have decided to listen to my own advice I have been giving other Mustang owners and get rid of the blower and high-horsepower numbers. I pulled all of the supercharger related parts off the car last night and they are for sale. I'll definitely miss the extra 150-200hp, but if the car won't stay together, I can't get seat time. For this build, I am aiming for around 350rwhp, with a preference towards longevity and reliability than any semblance of peak numbers. I am looking for a new engine builder as well as a new tuner (I think I have located one of each that I am willing to try).
If I didn't have so much already in this car, it would be for sale and I would be looking for something else entirely. I am not quite ready to "cut my losses", but I have thought about it a LOT for the past month.
So, to answer your question, yes and no. DOHC (4-valve) Cobra engines are well known for blowing #7 and/or #8 pistons in supercharged setups. These two pistons go bad more often than any other in the engine. I have seen many factory supercharged 03/04 Cobra and 07 GT500 cars live for many miles on the road couse at WOT. There may be something else to my failures (something in the tune maybe).
So there you go, the whole saga.
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