908 Engine on the Dyno at Rothsport

Britain Smith · 01-04-2011, 09:24 AM

Check out this cool video of a 908 engine on the engine dyno at Rothsport Racing in Tualitin. I had the privilege to not only see this engine during its assembly phase, but they recently had another 908 engine under assembly and on the dyno that I got to see at several phases of the rebuild. Those engines are remarkable in the engineering detail from that era. Every nut, bolt, and stud was titanium and the exhaust layout was impressive.

Welcome to Rothsport Racing - Engine Dyno Tuning - Porsche 908 Engine

-Britain

T77911S · 01-04-2011, 09:48 AM

so what are the plans for the motor?

i like the end, "that is the fastest i have ever turned any motor on this dyno"!

come on man! details!!!

Bullet Bob · 01-04-2011, 09:54 AM

The motor is from Germany and I believe it has been shipped. It is pretty cool to see those go together.

daepp · 01-04-2011, 11:11 AM

Wow - so awesome and so many questions.

What was the max HP? Torque? Speed?
Why is the alternator off to the side?
How will the motor be used?

I never realized it was an DOHC engine! Stunning!

Superman · 01-04-2011, 11:19 AM

What RPM, do you suppose? At what RPM did these motors redline?

daepp · 01-07-2011, 09:15 AM

Britain Smith - no additional info?

Britain Smith · 01-07-2011, 09:35 AM

The engine shown in the video was from an early 908 coupe. The motor made somewhere around 350hp and I believe spun to around 8900rpm if I remember correctly.

Now, the most recent motor that I got to watch during the rebuild was a very special one off engine from the 1968 Le mans 908/3. It was very cool as it had an oil fed cooling fan which I presume operated a clutch type dampener to prevent the fan from putting stress on the crank during the 24hr race. I just remember that when the motor was shut off, the fan continue to spin freely until it coasted to a stop. That motor made just under 400hp and was simply amazing. The MFI pump and plumbing was a work of art and probably worth it's weight in gold.

-Britain

Wil Ferch · 03:43 PM

The alternator on 908 was off to the side, because....well....that's how 908's were built....

Vertical fan ( at least up to 908/2) and dual fan belts. Double-overhead cam owing much of its design heritage to the 2 liter DOHC 916 motor that was tested around 1966 or earlier.

I'd like to hear details of the oil-damped 908/3 fan drive. Pics?.....details?....

Bullet Bob · 01-07-2011, 10:44 AM

I spoke to Jeff this morning and while I had him on the line I asked him about the 908 engines. They both produced 393Hp @ 8200 rpm and the dyno run peaked at 8600 rpm. The funny thing about the fan is that it will not spin until there is oil pressure so the fan doesn't spin when the engine is cranking. It begins to spin once the engine starts up. When the engine was on the stand I played around with the fan a bit and it spins freely with little drag. It is quite a setup.

I believe the engine in the video went in this car.

911pcars · 01-07-2011, 11:23 AM

..."It was very cool as it had an oil fed cooling fan which I presume operated a clutch type dampener to prevent the fan from putting stress on the crank during the 24hr race."...

Perhaps Porsche chose to eliminate the mass and inertia of the alternator shaft and rotor from the fan assy., and probably related to their fan drive/crank issue.

The fan drive described sounds like a variation of an A/T fluid drive coupling.

Sherwood

Jon B · 01-07-2011, 11:29 AM

The 908 engine had chain-driven cams like a 911, unlike the smaller 8-cylinder 753/771 or 912(917) engines. By the late 1960's, very few racing engines still ran chain-drive cams.

AlfonsoR · 01-07-2011, 12:39 PM

I wonder if an engine like that can fit into a 911?? The flat 8 sound must be amazing!!

Britain Smith · 01-08-2011, 11:05 AM

They fit one in a 914 so I am sure it could be made to fit a 911

-Britain

T77911S · 01-08-2011, 11:40 AM

perhaps the oi fed fan was to keep from wasting HP on driving the fan

Jim Horton · 01-08-2011, 03:57 PM

Quote:

Originally Posted by Britain Smith

The MFI pump and plumbing was a work of art and probably worth it's weight in gold.

-Britain

One of the techs there told me that it was a "$1/2 million motor". Explains why Jeff was a bit distracted last week. That and the fact that it came over with a tech in tow. Gee; wouldn't you have thought that maybe someone in Germany could have worked on it? Just goes to show the reputation that Rothsport has in the community.

daepp · 01-08-2011, 04:18 PM

What drove the cams on the 917 engines?

Jon B · 01-08-2011, 05:57 PM

The 917 engine (type 912) used a train of spur gears to drive the four cams, from the center of the crankshaft. Some engines used a combination of steel, aluminum and titanium gears...

jcge · 01-09-2011, 12:24 PM

Werkstatt / Jon - I have not seen that 912 gear diagram before - where is it from ??
Regards
John

Jon B · 01-09-2011, 05:04 PM

John,

The gear train photo is from a 912 engine development article by Hans Mezger in Christophorus magazine, No.121/Feb 1976. The color photo of the 908 engine is my own, from the pre-digital early 1990's.

m110 · 01-09-2011, 05:49 PM

Quote:

Originally Posted by Werkstatt

The 917 engine (type 912) used a train of spur gears to drive the four cams, from the center of the crankshaft. Some engines used a combination of steel, aluminum and titanium gears...

This photo is outstanding...truly marvelous