2.4e freshen up
 

I just finished a 2.4E engine.Cylinders were bored from 84 to 86mm.Nicasil plated with CP Pistons.Using a needle beam style torque wrench the engine turns over at 15 lbs. of effort without the plugs.CP Pistons do have thinner rings than standard but very little effort for a complete motor.Ciao Fred

turning effort for new motor
 

As per many of my posts I do not get a lot of response.I think very few people have assembled an engine and checked drag to turn over.If you use the stiffer springs from AASE it is 45-55 lbs. to turn over one revolution.Now that is called parasitic drag.Otherwise known as hp loss.Cmon guys I can not be the only fool who checks these things.When Grady Clay and I used to talk he had a 906 engine he had worked on.This was 1979 and I had just finished a 911R for #013 for Michael Green and it turned over about 6-7 lbs.of drag.His turned over at 5 lbs.but had way more hours on it.Back then the bores were chrome and had tiny perforations to hold oil and lubricate the rings.I have a 906 factory hillcimb piston I will take a pic and show tomorrow.It is from a 910 I bought in 78 or 79.Ciao Fred

Noted.

I used to measure and track the rotating torque on all of my circle track engines. Rings are the main cause of drag, and the modern skinny rings can reduce the rotating torque quite a bit. (Main and rod bearing rotating torque we measured in inch pounds, so there's not much to improve on there, unless you count the garter springs on the crank seals or the line boring is off or the crank is bent)

Now, where does this all lead us?

Dyno results?

Early on, thinking it was the holy grail of free horsepower, we assembled a few engines with different ring packages. While the skinny ringed engines did produce more power, it was nowhere near what we thought, so we tried it again. The result was the same. We even quantified it. A reduction in rotating torque of 10 lb ft resulted in a net torque output gain of right about 3 lb ft of engine torque. If your class of racing requires you to squeeze every last hp out of the engine, then go for it. Wanna really see the rotating torque drop? Omit the second ring. We've built and ran engines like that before when every last bit was needed. Mostly NHRA Stock and Super Stockers, but you run the risk of getting thrown out if its torn down, but they very rarely ask to see a piston.

YMMV, but that's what our testing revealed.

What did we get out of all of this? If you need to replace the pistons anyway, go for the skinniest ring package available. It's what modern day production engines use. If your old pistons and cylinders are still in good shape, just run what you have.

With respect to valve spring seat and over the nose pressures, you're at the mercy of the action of the cam lobe, engine speed, and if it has boost on the backside of the valve. More modern fast action cams will open the valve at a faster rate, necessitating higher spring pressures. Early Porsches have pretty gentle ramps compared to modern cams, so not much spring pressure is required unless you want to buzz it up. Got boost? By physics, the area of the intake valve subjected to boost will cancel out your seat pressure. It is common to "do the math" on the area of the valve multiplied by the boost and increase seat pressure by that much. Porsche did it on the 930's. (If you look in the factory service manual you will find the installed height spec of 930 springs 33.5mm instead of 34.5 on the NA cars). That extra seat pressure is there for a reason.

Fred, please keep posting, there are still people interested in these sorts of things!

Friction posts are the best.

Dropping the second ring was common in production racing 4 stroke motorcycles years ago. Rules said you had to have all the factory parts (but not where installed) so you safety wired 2nd set of rings inside the oil pan so it would pass tear down. Then you ran as much two stroke oil as possible avoiding detonation inducing oils. Cycle World dyno tests showed engines making more power up till 24:1 ratio due to increased ring seal. I still run my MFI car today at 100:1 if only for the smell.

Always interesting information from the guys who have built and developed hundreds of engines, in the search of those extra bits of power or longevity

Thanks for sharing the tricks of the trade us engine “assemblers” are still learning

Fred, I'm glad you added your second post so I understood the context. Your post sparked some interesting additional information I'm not sure I would have learned any other way.

Good morning Fred.
Your assembled rotational resistance when cold was never a measurement I considered important. It just shows, there's always something to learn.
We do a rebuild service on 911 (2 valve) rockers that includes dry-film contact pad, cryo and a DP-4 bushing. During our in-house testing we discovered a huge (I know....not a scientific number) reduction in friction at the pin/rocker intersection.
Our test measured heat under extreme but not excessive loads. The dry-film speaks for itself. I would be willing to donate a set of cast rockers just to see if you can measure the drag reduction (if any).
Our process is performed on all types of cast as well as forged rockers. Our experience tells us cryo has little affect on forged steel so we skip that process on the forged rockers.
Our research suggests that the early non-bushing cast rockers are made with the best materials.

http://forums.pelicanparts.com/uploa...1617707742.JPG

http://forums.pelicanparts.com/uploa...1617707769.JPG

new rocker techniques
 

You have told me about the new bushing and dry film.The bushing looks great.I have some forged rockers to send to you.Your innovations are always appreciated.Fred

new rocker techniques
 

Henry,I have to say with the black gloves it looks like Darth Vader is the tech.Ciao Fred

It’s really cool to be able to listen in when the experts talk shop. Thanks

Love the stories Fred, please keep 'em coming

I’d think a friction test done at operating temp would also be interesting.

I was thinking the same thing.
Back in the late eighties, NPTI was building some pretty impressive GTP cars.
I ended up owning a number of those engines. When cold they would barely turn over.
My understanding is that the tolerances were so tight, that the engines had to be warmed via oil heaters in order to start them. Something like a 45 minute process.

I also had a chance a few years back to run some of my 911 engine on an engine stand (Spintron) that would spin the engine (without running) at 2000-3000 rpm. The stand measure torque based on watts and you could actually watch the motor load drop as the process continued. 4 hours in and the engines were making oil pressure and spinning much freer.

low drag hill climb factory
 

In the later 70,s bought 2 hill climb cars.A 907 with the roof removed with a 2.9 High Butterfly MFI for a customer and 910 with 2.0L 906 motor.The 910 came from Europe and was advertised as sound chassis but engine was smoking.Price was $8,000.00.Here is one of the 3 pistons that look like this.This was a factory build with a one compression dykes ring like for a motorcycle.So when it revs the pressure forces it to seal.A few years later a customer of mine named Ken Williams bought a 72 2.4 911S from Al Holbert.At that time Al had that car built by Porsche because he was running a CP SCCA car.The car came from Porsche with a 2.4 WITH these 85mm slipper one ring pistons at 12.5 to 1.Also had 906 Cams with injection pump to match.It made 263 hp. on my dyno.Kenny sold it to an attorney from Eastman -Kodak in Rochester a few years later.It was bright green in color.That car is still out there.I installed 2.8 P & C before he bought it.The mechanic who looked after it up there was named Bill Siegal but that was 40 years ago.http://forums.pelicanparts.com/uploa...1618014014.JPG
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2.4 Al HOLBERT 911S
 

The color was Kelly Green.I will call call Bob Russo who was taking care of parts at that time for Al Holbert to see what he remembers.Thanks Fred

Did the autopsy reveal why it holed the pistons? Ignition timing off? Distributor problem? Did it run lean? Or did someone just run pump gas in it? Dr. Dykes rings were popular for awhile. Now they're pretty much museum pieces, unless you're racing Top Alcohol Drag Racing or rebuilding Mopeds.

Neat stuff, Fred.

reason for the engine demize
 

The points were not set correctly for the twin plug and timing was advanced a bit.The fuel may have been suspect as well as Danno suggested.Initially put in a spare SCCA CP 2.5 motor as the parts for the engine repair took a year to accumulate.The 2.5L was 66 x 91 making 2575cc.Fun package for a light car.I had Dealer plates back then so of course it needed to be road tested.I have a picture of the 907 and I will look for the 910.It was white.Light and fast is what Porsches were back then.Local cops were not fond of me.Fred

Fred snuck a pretty rod in there too- Pankl!