Carpokes Porsche Forum

michaelmount123 wrote: Fri May 19, 2023 12:11 pm I won't get into cost estimates since it may be parts only, or may need to include labor. Your 140K mile 968 engine is tired, and even with good looking bores piston/ring wear is compromising good seal. Can (should) you move ahead with it? Ideally, no. Can (should) you freshen the bores and install new pistons? Ideally, yes. If it were mine and I had adequate funds, I'd at a minimum have Millennium Nikasil the bores and install a fresh set of pistons and rings. Now you're looking at 300fwhp with the proper cam. That's a significant increase in power. You'll also be confident to have created a long-lived engine. I can help with piston specs if you like.

Does Millennium supply pistons and rings matched to their coated bores? If not, what pistons/rings would you recommend for a stock/street motor to go with their Nikasil? I still have the motor that came with my car (scored cylinders) which has been sitting since I did my 3 liter, and I'm thinking I might rebuild it and return the car to stock (maybe a cheater k26 and chips, but otherwise stock, smog friendly, with AFM/snorkel, original injectors, etc.).

Tom wrote: Fri May 19, 2023 12:37 pm

michaelmount123 wrote: Fri May 19, 2023 12:11 pm I won't get into cost estimates since it may be parts only, or may need to include labor. Your 140K mile 968 engine is tired, and even with good looking bores piston/ring wear is compromising good seal. Can (should) you move ahead with it? Ideally, no. Can (should) you freshen the bores and install new pistons? Ideally, yes. If it were mine and I had adequate funds, I'd at a minimum have Millennium Nikasil the bores and install a fresh set of pistons and rings. Now you're looking at 300fwhp with the proper cam. That's a significant increase in power. You'll also be confident to have created a long-lived engine. I can help with piston specs if you like.

Does Millennium supply pistons and rings matched to their coated bores? If not, what pistons/rings would you recommend for a stock/street motor to go with their Nikasil? I still have the motor that came with my car (scored cylinders) which has been sitting since I did my 3 liter, and I'm thinking I might rebuild it and return the car to stock (maybe a cheater k26 and chips, but otherwise stock, smog friendly, with AFM/snorkel, original injectors, etc.).

Millennium does not provide pistons nor rings. I would use JE or CP with their Nikasil compatible rings. Millennium offers .0002" tolerance upon request, so piston to wall clearance should not be a problem. Turbo??? I thought you were doing a NA engine. Perhaps your car is a 951 with a 968 engine at the moment. If so, I understand your post. Millennium can work with scored walls but I recommend discussing with them and perhaps sending photos.

michaelmount123 wrote: Fri May 19, 2023 1:41 pm

Tom wrote: Fri May 19, 2023 12:37 pm

michaelmount123 wrote: Fri May 19, 2023 12:11 pm I won't get into cost estimates since it may be parts only, or may need to include labor. Your 140K mile 968 engine is tired, and even with good looking bores piston/ring wear is compromising good seal. Can (should) you move ahead with it? Ideally, no. Can (should) you freshen the bores and install new pistons? Ideally, yes. If it were mine and I had adequate funds, I'd at a minimum have Millennium Nikasil the bores and install a fresh set of pistons and rings. Now you're looking at 300fwhp with the proper cam. That's a significant increase in power. You'll also be confident to have created a long-lived engine. I can help with piston specs if you like.

Does Millennium supply pistons and rings matched to their coated bores? If not, what pistons/rings would you recommend for a stock/street motor to go with their Nikasil? I still have the motor that came with my car (scored cylinders) which has been sitting since I did my 3 liter, and I'm thinking I might rebuild it and return the car to stock (maybe a cheater k26 and chips, but otherwise stock, smog friendly, with AFM/snorkel, original injectors, etc.).

Millennium does not provide pistons nor rings. I would use JE or CP with their Nikasil compatible rings. Millennium offers .0002" tolerance upon request, so piston to wall clearance should not be a problem. Turbo??? I thought you were doing a NA engine. Perhaps your car is a 951 with a 968 engine at the moment. If so, I understand your post. Millennium can work with scored walls but I recommend discussing with them and perhaps sending photos.

My car is a 951. The motor in it now started life as an '89 2.7 motor, but I built it with an 88mm crank and Andial/Mahle 3 liter turbo pistons back when they were selling those. The result is a 3 liter turbo street motor with larger turbo, etc. It made 500/500 on a dynojet back in the day, but I got tired of breaking things, so have toned it down quite a bit. Scott Gomes did the machining if you remember him, and I assembled it, and it's held up great over 15 years and maybe 40k miles. As I get older, I'm starting to think a tinker-free stock-ish motor with maybe 275 dynojet horsepower or so would be ideal. I have the 992TTS now, which is hard to compete with, and would be nice to restore a little of the overall balance to the 951. 500hp was a blast, but kind of overwhelms the overall 951 experience in a street car...

I found that 350-400 rwhp is a sweet spot for Steet cars, more that that and you have to stiffen up the suspension and other chassis upgrades that take some of the smoothness out of the car. Drove a 370 rwhp on Steet / DE for many years with out issues- and that was a 2.5
I’m a fan of Mahle pistons, they are good people to work with on custom parts and very precise. The pistons come with actual measurements out to tens of thousands. Typically with in a couple tenths of a gram (other custom pistons have been +/- 2 grams

michaelmount123 wrote: Fri May 19, 2023 12:11 pm I won't get into cost estimates since it may be parts only, or may need to include labor. Your 140K mile 968 engine is tired, and even with good looking bores piston/ring wear is compromising good seal. Can (should) you move ahead with it? Ideally, no. Can (should) you freshen the bores and install new pistons? Ideally, yes. If it were mine and I had adequate funds, I'd at a minimum have Millennium Nikasil the bores and install a fresh set of pistons and rings. Now you're looking at 300fwhp with the proper cam. That's a significant increase in power. You'll also be confident to have created a long-lived engine. I can help with piston specs if you like.

I read a recent thread on the other forum where the owner got the Nikasil treatment for his block. It seemed involved and expensive. Is it a reasonable option to have the Alusil bores lapped and get compatible pistons and rings? Question is, are there verified compatible pistons and rings available today? Heard some anecdotes of people learning the hard way when their cylinders got scored up.

I've had many 944 blocks done at Millennium, and 911 cylinders too. Since it was years ago, I haven't kept up with pricing. I did have very good results, however, with both Goetze (factory Nikasil) rings, and Nikasil compatible rings from JE and TotalSeal. Certainly you have to understand that specific rings must be used, and the piston manufacturer must know that the piston is for a Nikasil bore.

Chris White's comment above about Mahle is spot on. I've used them for water cooled flat sixes with good results.

Here's a tip: Have your 2.5 block Nikasil coated, then use the Porsche (Goetze) 964 100mm rings. It's worked out very well on several 951's I prepared for Club Racing.

Hi Michael,

Do you measure the bearing crush when you assemble your engines? I'm in the process of building an 3.0L (new 968 block, crank within std specs, glyco main/acl rod bearings) and my mechanic is very hung up on finding out what this measurement should be ATM.

Bergerac wrote: Sat Jun 03, 2023 7:54 pm Hi Michael,

Do you measure the bearing crush when you assemble your engines? I'm in the process of building an 3.0L (new 968 block, crank within std specs, glyco main/acl rod bearings) and my mechanic is very hung up on finding out what this measurement should be ATM.

Bearing 'crush' is a design feature that secures the bearing in the rod big end, or the main bore. It doesn't occur until the rod cap or crankshaft girdle is bolted and torqued. There's no simple way to measure it, but more importantly it's not a critical measurement as long as the connecting rod big end meets size spec. What is critical is the oil clearance. This should definitely be measured by your machine shop. Main bearing clearance is typically fine, but rod bearing clearance varies with the rod. Measure it and put it in spec. Rod oil clearance of .0025" is a good target. Pay particular attention to your cylinder head. Reconditioning and upgrades are pretty straight forward as long as your machine shop is familiar with them, or is performance oriented. Both will need the proper equipment. Seek a cylinder head specialist if there's any question. A good cylinder head benefits both a NA and boosted engine.

Any interest in higher HP builds for 2.5, 2.8 or 3L? I have my old engine files and can share detail if it would be of interest. I won't ask about air cooled 911's, but could go there too. 2L, 2.4L, 2.5L, 3L, 3.4L.

michaelmount123 wrote: Sat Jun 03, 2023 8:24 pm Main bearing clearance is typically fine, but rod bearing clearance varies with the rod. Measure it and put it in spec. Rod oil clearance of .0025" is a good target.

To build on this / ask about this a little bit: I had to get a set of +.001 (4B2475HX) oversized ACLs to get clearance up to 2.5. I think I ended up with a little shy of 2.5 - closer to 2.25 (with generally one of std, one of std+.0005). Is it generally wiser to err on the higher or lower side of this sort of thing?