Head gasket and fresh head before turbo?
 

are you still on the original gasket? then probably worth doing proactively simply due to degradation by age.

if not...leave it alone.

With the right turbo these engines will do 330 whp on a mustang dyno with a stock head and cam fairly easily. You have to decide, is the last 20 hp worth whatever the head costs? for me, I would probably say no. You could contact David Brabavitch (I always spell his name wrong, sorry david) and get one of his modified intercoolers for around, or less than $300 off the top of my head. That is worth 10 hp on a dyno with a bone stock 951, so it would probably do 15 or 20 on a higher strung package. The turbo is the key to making the package work. hitting the numbers is one thing, but crappy spool makes the character of the car suffer. You don't know what you're missing out on until you drive one that has been spec'd properly. Right now Emanuel Galosson (rennlist Eman930) is the only person I would trust to size a turbo for me. He works with tim's turbos and has the best stuff I've been exposed to in 15 years of 944 work.

For a head gasket, the best bet is the cometic MLS gasket, but that's ONLY IF you can get the surface prep right on the block and head... The block is tricky to do in the chassis. Don't forget raceware head studs while you're in there.

no need to change the studs - stock are excellent quality and more than sufficient.
i suggest you find somebody near you who has a modded 951 and drive it to feel power...350 is a nice round number, but a stock 951 with a freer exhaust and a MAF/MAP conversion is already a very quick car regardless of what the HP number says.

It all depends on how much hp you want in the end, if you are looking at a lot of boost then yes replace the head gasket. I would go with the standard head gasket, the widefire is more set up for an o-ringed head. The MLS gasket is a good gasket but it may throw your timing off if you get one too thick.

Any change to your turbo charger and it is not a rebuilt KKK, then it is going to require modification to your car or an adapter plate to mate the turbo to the engine carrier. The bolt pattern to the KKK turbo is fairly wide. If the car is basically a stock 2.5 l there are a lot turbos out there that will give you significant power, just by updating the turbo presently on your car you will be amazed.

One of the major problems is putting too large a turbo on your car. Do not fall into that trap.

Well, yes, hes going to have to decide whether he wants a 951 with a muffler and a chip, or a reliable 350 rwhp... One of those things is not what he inquired about.

Dkritz,
The billet compressor K26/8 that Emanuel built me out spooled my k26-6 on the same car same dyno, did 370 ft lbs at 3500 RPM, and 330 whp at 18psi, all on stock block, head, cam, intake, IC pipes, TB, and intercooler. I don't think there is a KKK plain bearing based turbo in the world that will out perform his packages. By the way, I have a Super 61 spec'd for a 2.5 liter that has ~4000 miles on it, and is in perfect condition that I would sell you for 1/2 price of new. It's still installed on my car, and will take a minute to remove, but it will be available soon..........I'm removing it for another turbo that I bought from Emanuel......

Sorry I had his screen name wrong: e-man930
https://rennlist.com/forums/944-turb...rid-turbo.html

or www.timsturbos.com and ask about getting one of emanuel's voodoo turbos.
My guess is they wouldn't spec something in a K27 or larger cover. Tim has built a 350whp all day long turbo for me already. Mine is K26 based, ill try to include a picture. It seems like the larger turbos are holsett covers.

the super 61 was all around more enjoyable to drive than the stock K26-6. I lost a little spool at slower respool at transient throttle compared to stock. I'm getting full boost by 3400 rpm in 4th, which honestly isn't bad, but it ultimately is 10% to 15% down on power compared to the turbo from emanuel, at same boost levels. So The voodoo turbo puts up better peak numbers and better spool numbers, it's just better all around than stock or super 61 on any metric. https://cimg4.ibsrv.net/gimg/rennlis...939798d90.jpeg
https://cimg5.ibsrv.net/gimg/rennlis...0761d28da.jpeg

It bolts up to the stock crossover pipe. Mine has that taper machined into the hot housing, so it is basically a necessity to run a 3" down pipe. The turbo could probably be made for the stock down pipe, but that's certainly not going to help spool.