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My main issue is trying to figure out what to do with the motor. What parts do I choose and why? Should I also switch out final drive to Shep's 4.30 while I'm replacing diff pins? I'm not going to huge power and prefer not to be laggy. The MHI 18K has been great so far. I'll be doing all the work myself outside of having the machine shop deck the motor. I'm fairly happy with the current power (~450whp/370tq) the car had prior to loss of compression, stockish spool as well. I'm debating about bumping up to the 500-600whp range. While this is considered my DD, I WFH and I mainly cruise around town or get on the highway or an occasional AutoX. I run e85 99% of the time and if I need to drive over an hour I'll switch to 93 if I feel like it.
A few months ago my car randomly had a bad misfire after getting on the highway. Pulled over immediately and had a friend tow it back home. After trying to diagnose it and hoping for something simple I decided to just pull the motor. I had no compression in cylinders 3 and 4. I wanted to clean up everything, do the timing chain and overall refresh the motor/engine bay. From what I can see I got incredibly lucky that two exhaust valves, one for cylinder 3 and one for 4 chipped away. I suspect most of that chipping had been done prior to me owning the car though. The original turbo's exhaust turbine was badly damaged. I never drove the car when I first bought it and in the process of fixing it I went ahead and upgraded to a MHI 18K and it is still in perfect condition. And I don't see any loose metal.
Options I'm considering:
Build head / stock block / keep MHI 18K and stay around the same power just added reliability
Build head / build block / keep MHI 18K and stay around the same power just added reliability
Build head / stock block / GTX gen 2 3576 or similar spool to MHI 18K
Build head / build block / GTX gen 2 3576 or similar spool to MHI 18K
First things first, I have no experience on the X but I'll still toss in my opinion.
If the stock bottom end is good; no bore scratches and stuff, I'd clean it up and use that. Its impossible to compete with stock for reliability. Then I'd upgrade the head with some valves, springs and small cams to keep the turbo spooling fast while adding a bit out top and I'd run it.
I had a something like this happen on my 9 but my timing tensioner failed and it broke off heads of the valves and scratched the bores badly. I built the engine and stuff and its great, don't get me wrong but the extra 100whp is kind of whatever. The 500 it made on the stock motor was plenty and the 600 it makes now is more than plenty lol.
As for the head build you listed, thats exactly what I went with on my 9.
If the bottom end is in good shape you could clean it up and reuse it. If you have the budget I’d go with rods and pistons and fresh hone & deck. As for the top end I love the GSC S2’s in my X but prefer Ferrea valve train components.
the burnt valves are likely from the valve lash tightening up over time and not allowing the exhaust valve to cool properly when seated.
