Question for the engine builders : synthetic vs Mineral oils

[spyerx]

Ok this isn’t meant to be an oil debate. I’m interested in recent experience from the builders on mineral vs synthetic oils. Specifically in the older mag case motors that have fresh rebuilds.

I have 2 new motors.
One is a short stroke 2.5l built off a 70 914/6 case - this is a more conventional build. Builder said “ motul mineral break in, total classic mineral to run it”

The other is a 2.8 monster built off a 77 7r case. This motor is modern everything inside. Bearings crank pistons rings rods rockers etc are all modern materials many from water cooled gt cars.

The 2.5 just completed break in and is getting dyno tuned and jetted next week.

The 2.8 is getting run in next week.

I’ve had a 3.2 and 964 that i always ran synthetic in, they did not leak.

The 914 and 2.7 mag motors had mineral oils in them, neither one leaked usually. Once in a while the 2.7 would drip a drop

What I’ve been told is “mineral high zinc in the older motors, synthetic high zinc in the later aluminum case air cooled motors”. “Switching to synthetic can cause leaks”

Im familiar with the benefits of high quality synthetic oils, i tried a few different brands in my gt3rs when i was tracking it extensively and ran oil tests at every change. It became clear which brand sheared less and maintained its performance, viscosity, and additives after heavy use. Sometimes i was driving this car in 100 degree weather with dash oil temps over 250 and the oil (motul 300v) tested fine.

Anyway, my preference would be to run synthetics (like a high zinc motul or m1 or driven etc) but if there is hard experiences as to why not would love to hear the perspectives.

Fwiw neither car will be tracked but both are driven aggressively and as intended in the canyons. And it does get warm here in SoCal.

Again not looking for a debate On oil brands here….

Thanks.

[otto_kretschmer]

ok,

I do have a 76 911S but I have not (yet) rebuilt it.

but..

I do have 2 BMW motorcycles from the 70s, both Airheads, one is a 1970 R50/5 and the other is a 1975 R90S. I have rebuilt both Airhead motors. I'm making an assumption that the materials and tollerances for the BMW and Porsches are similar. Both are aircooled, both were designed and manufactured in the same country.

The rockers of both are forged with bronze bushings, except the R90S. It has needle bearings. The rods are about the same. The Airheads have iron cylinders and the 911 have plated aluminum.

I think I'm comparing apples to apples here. Maybe apples to pears but definitally not apples to escargot.

I broke in the bikes engines with the proper dino oil, SG or SH rated motorcycle oil that is available on the shelf at AutoBone. I rode the bikes about a 100 miles and changed the oil and filter. I think I used the same oil again and rode the bikes to 600-700 miles and changed the oil and this time I used the good stuff, either Redline motorcycle 20w50 or Mobil 1 Vtwin 20w50.

My 911 is on jackstands with gear oil leaking past the shift rod seal. My R90S is in my shed waiting for me to restore it back to its original Daytona orange/silver (starts this year?) and I ride the R50/5 every now and then.

here is a leak down I did on the R50/5



If you want to use special break in oil, go ahead but I don't think its necessary. I'm generous with the assembly lube when I put a motor together. I pack the oil pump with assembly lube. I coat the cam lobes and journals. I coat the lifter faces and sides. Both ends of the pushrods get lube. The cam chain and sprockets get lube.

If Henry is a master chef, then I'm a short order cook at Waffle House. But sometimes all you need is a stack of flap jacks and cup of coffee.

[gled49]

Use break in oil, then what ever u want. I have a 35year old rebuilt 2.4 with 20/50 mineral oil, still no leaks. And a recent 2.7RS spec with a big oil pump and a little more oil pressure cold than I would prefer, so I run Synthetic 5/40 in that, no leaks no problem.

[lvporschepilot]

This is actually very timely! We just completed running in a 2.9L twin plug that I rebuilt over winter. Mod-S cam, PMO 46 carbs w/38mm chokes, 964 oil pump, fantastic little engine. Client ran it in for a good 400 miles on mineral oil, then changed to synthetic motul 20w/60 and sure enough after a couple hundred miles it leaks just a tiny bit from somewhere near the flywheel.

[996AE]

My 3.2 build ran breakin oil for first few in shop heat cycles. Full bottom up build.

Then changed breakin oil for dino oil and gave me car.

RPM limits for 500 miles. Then oil change, valve check and synthetic. Then, go find redline!

All good here.