911 ST Engine Specs
 

I am researching building one of the ST engine variants and am looking to the collective knowledge of this board to fill in the blanks...This is what I think I know based on Bruce Anderson's Performance Handbook and Patrick Paternie's Porsche 911 Red Book...

2.3 - 2247 cc
Bore - 85 mm
Stroke - 66 mm
Compression ratio - 10.3
Twin plugged heads ???
Intake Valve - 46 mm ???
Exhuast Valve - 40 mm ???
Cam - 906
Case - Magnesium or aluminum ??
Cylinders - Biral or Nikasil ??
Rods - S ??
Fuel Injection or Weber 46 IDAs

2.4 - 2380 cc
Bore - 87.5
Fuel injection
Everything else same as 2.3 ??

2.5SS - 2466 cc
Bore - 89 mm
Cylinders - Nikasil
Everything else same as 2.3 ??

2.5LS - 2492 cc
Bore - 86.7 mm
Stroke - 70.4 mm
Mechanical injection
Everything else same as 2.3 ??

Any comments and recommendations are welcome

TIA...SmileWavy

The 2,3 and all of the other ST engines were Magnesium crankcase.

They had Biral cylinders until the 2,5 liter with 66mm stroke was introduced as the very last variant. This was made possible by the 89mm Nickasil cylinders. The 66mm stroke revved faster and lessened the vibration problems in the crankshaft on the 70.4mm stroke crankshaft, which had caused flywheels to come loose.

ST engines all had 10,5:1 compression ratios, though there may have been some special factory cars (916 engine?).

According to Paul Fere's Porsche 911 Story:

911/20 and 911/22: 2,247cc (85mm bore x 66mm stroke)
power: 230 PS @ 8000 rpm
valve diameter intake/exhaust: 45mm/39mm
valve lift intake/exhaust: 12.1mm/10.5mm
911/20 = injected 911/22 = Webers

911/21: 2,380cc (87.5mm bore x 66mm stroke)
power: 250 PS @ 8000 rpm
valve dia. intake/exhaust: 45mm/39mm
valve lift intake/exhaust: 12.1mm/10.5mm
injected

911/70: 2,494cc (86.7mm bore x 70.4mm stroke)
power: 275 PS @ 8000 rpm
valve dia. intake/exhaust: 46mm/40mm
valve lift intake/exhaust: 12.1mm/10.5mm
port diameter intake/exhaust: 41mm/41mm
injected

911/73: 2,466cc (89mm bore x 66mm stroke)
power: 275 PS @ 8000 rpm
valve dia. intake/exhaust: 46mm/40mm
valve lift intake/exhaust: 12.1mm/10.5mm
port diameter intake/exhaust: 41mm/41mm
injected

86.7 and 87.5 mm bores were nickasil cylinders. The earlier 2.3 may have been either nickasil or chromal. I would have expected most of the ST's if not all of them were twinplugged.

Are you thinking of building one?

Aaron,

I am thinking of building (more like have one built for me) one of these motors; either the 2.3 or the 2.5SS...The 2.3 is more correct for my car since it's a 1970 tub but the 2.5 has more power and that's very tempting...:rolleyes:

Don't know what the cost differential is between building the 2.3 vs 2.5 but at the end of the day I want to remain FIA legal...

SmileWavy

Either way, the price will be about the same.

2380 st motor from armando's wonderful site.
Note early cam towers on 2.2/2.0 mag case
http://forums.pelicanparts.com/uploa...1222032053.jpg

According to Fere, 87.5mm and 86.7mm cylinders were Biral. He says that 87.5mm was the maximum Biral cylinder diameter the factory could use with enough reliability.

For the 2380cc engine, 87.5mm bore Biral cylinders were used with the 66mm stroke crankshaft. For 2494cc, 86.7mm with a 70.4mm stroke crankshaft was used.

Porsche wanted to use the short stroke 66mm crankshaft for better revving and less vibration so they used the Mahle Nickasil technology already tried on the 917. This was the 89mm bore cylinder with the 66mm stroke crankshaft.

Here is an early document stating the use of chromal...
http://forums.pelicanparts.com/uploa...1222041425.jpg

FWIW I also have sets of 86.7 and 87.5 Mahle cylinders that are nickasil.

I am not arguing that Biral was not used because I wasn't around at the time. But all of the factory documentation that I have come across stated the use of either of these two types.


Also, Nickasils were introduced in 1971 which would put the use of them close to when the ST's were being actively raced.

Interesting. Thanks for the document.

I know Mahle now makes Nickasil cylinders smaller than 90mm. I thought that when Porsche used Nickasil on the 917 with great performance, they decided to solve the 911ST problem at the same time. I would think they would not bother with the smaller bores and would go straight for the 89mm 2500cc short stroke which they knew offered the best performance.

Do you have a time period for the smaller Nickasils or was this something done after the 911ST had been developed and replaced by 911 Carrera RS/RSR?

I wish I did, but my guess is by 72. I suspect they were offered as replacement p/c for the factory/customer racing effort. Now Birals may have been used if Chromal cylinders were unavailable or customers did not want to pony up for the Nickasil replacements. I'll ask some of the old timers to confirm.

I suspect chromal means a Biral cylinder with a chrome coating. That has been used on aircraft cylinders that are steel. I don't think you could make an aluminum cylinder with chromal coating.

-Andy

Chromal cylinders are identical to Nickasil cylinders with the plated surface being the only difference.

Chromal cylinders from a Fuhrmann 547 engine:

Aluminum with Chromium plating, dimple honed to retain oil. Nickel is more oleophillic and does not need the dimples to retain oil.

http://forums.pelicanparts.com/uploa...1222058532.jpg

Hmm, Frere p. 36 specifically confirms what Max said above e.g. "as the 87.5mm bore used for racing was the maximum that could be accomodated when the Biral cylinders were used." Starkey 14-16 inconclusive on the point.

I think of Chromal as being a very early sixties concept, is it not? When was the last time they used it, did any of the prototypes have it? (other than in an airplane engine?) :)

John, the 914/6GT, 911R, 917, 908/2 all list chromal in their engine specs.(like the ST submitted above)

So the last ones to get Chromal seem to be the 917 and the ST.

Really interesting, that would put it as late as 1971. No wonder they greeted the Nikasil with such enthusiasm, I have heard of the chrome plating flaking off (but in the airplane world).

Learn something new all the time here!

Flieger, Aaron and John, this is great information !!!

Thanks for your contribution...I'm learning alot...

Porsche factory cars are known to try new technology between different chassis and different races. The factory would develop the technology and always stay 1 step ahead of the privateers in speed. When the factory moved on to something faster, they would sell the technology to the customer racers in the next model or race equipment package.

Anyone have an original, untouched 911ST motor lying around to inspect?;)

Wrong guess on my part. Thanks for the explaination.

-Andy

Aaron,

Do you have this type of document for the other ST motors we are discussing ??

If so, can you post them...

Does anyone know what type of work the factory may have done on these cases ??

TIA

Interesting that it specs Platinum Bosch spark plugs.

Most on this board say Copper is the way to go for MFI.