Short Stroke 2.8

[Wayne 962]

The one with or without advance?

-Wayne

[Steve@Rennsport]

Those units made by Dick have no advance,......

(I've used them for 15+ years when he was making them right here in River City)

[Henry Schmidt]

This distributor has a very nice fully adjustable advance curve. This is the second one I've used (strangely enough both in SS 2.8) and both of them had nice advance curves .
If you say the distributors that Dick builds have no advance curve then someone else built this distributor.
In that case I don't know where they came from.

[Steve@Rennsport]

Dick's units all used a GM HEI trigger and no advance whatsoever. We used them with MSD ignition systems and MSD retard box for starting.

LOL,..I watched him build the majority of them,...

[blue72s]

Henry,

What's the overall weight of the engine?

[Henry Schmidt]

shipping weight was 350.
We have no real weight on the engine alone.

[blue72s]

Henry,

Sorry if it's a strange question but are the exhaust valves sodium-filled like the pre 74 ones?

[Henry Schmidt]

The core heads used in this project were 930 Turbo. 930 exhaust valves were used in this engine. Turbo exhaust valves are sodium filled.

[Speedster94]

hallo
Very nice work , i love the old Twin plug Distributors , are they still available in the US ? i havent seen them here for sale for the last 10 - 15 Years .
harald

[blue72s]

Thanks Henry,

Would you say a 2.8SS is a better engine than a 2.6SS?

[kenikh]

Originally posted by blue72s
Thanks Henry,

Would you say a 2.8SS is a better engine than a 2.6SS?

I know my opinion wasn't asked but we aren't shy here right?

The strength of the turbo case, coupled with the fact that you have to do less machine work to it (no need to add oil bypass or squirters), plus the additional displacement says a lot. Even if you build a 2.6SS on an early Al case, it won't be as strong as the 2.8 and it needs a LOT more prep. Last, you can build the turbo case all the way to 3.1 liters on a 66mm crank, so you have room to grow if you are truly insane.

Better, maybe. It is a lot more extensible, though.

[Henry Schmidt]

Originally posted by blue72s
Thanks Henry,

Would you say a 2.8SS is a better engine than a 2.6SS?

The true magic of the short stroke 2.8 is the bigger valve heads.
I have tried to make big valve heads out of the 2.7 head but all we could do was 48mm in and 40mm ex.
The 3.0 heads have 49mm in and 41.5mm ex and they have a better valve angle.
The strength of the 3.0 allow case is also a bonus for longevity and it weighs more so that might be a toss up.
92x66 is nice but 95x66 is great. I believe it's the best of all 911 air cooled two valve engines.

[blue72s]

Henry, What's the fuel consumption like of that 2.8SS? How many miles to the gallon?

[Henry Schmidt]

At 8500 this gets fuel yardage not mileage.
Joking aside, this engine like all other MFI engines is very thirsty.
I don't have any real fuel consumption numbers but I would guess 8-12 depending on right foot flexibility.

[safe]

Originally posted by Henry Schmidt
The true magic of the short stroke 2.8 is the bigger valve heads.
I have tried to make big valve heads out of the 2.7 head but all we could do was 48mm in and 40mm ex.
The 3.0 heads have 49mm in and 41.5mm ex and they have a better valve angle.
The strength of the 3.0 allow case is also a bonus for longevity and it weighs more so that might be a toss up.
92x66 is nice but 95x66 is great. I believe it's the best of all 911 air cooled two valve engines.

If you don't have to comply to any displacement regulations has the 2.8SS any performance gains (hp) over a 3.0?
I mean if you just switched the crank 66 -> 70.4.

[Henry Schmidt]

If your only criteria is horse power, the answer is no. It is reasonable to assume that a larger engine (all other things being equal) will make more horse power.
The benefit of the SS 2.8 over the 3.0 is that the engine will spin at a higher RPM safely.
The rod length to stroke ratio is better.
A relatively low conrod-to-stroke ratio such as the 3.0 produces greater rod angularity with the cylinder’s centerline as the crankshaft turns from top dead center (TDC) to 90 degrees after TDC than that of engines with higher conrod-to-stroke ratios. (Note: conrod-to-stroke ratios in Porsches range from about.1.66:1 [3.3 - 3.8] to 1.97:1. [2.0-2.8 ss] As rod angularity increases, the piston accelerates away from TDC more quickly than in an engine equipped with a longer rod; engine designers refer to this phenomenon as “piston dwell.” Short rods generate abbreviated piston dwell; long rods have prolonged piston dwell. The trick for designers is to match piston dwell with the fuel’s burn speed to produce an acceptable increase in cylinder pressure without introducing detonation (a destructive, power-sapping combustion defect). Many experts believe that the most important benefit associated with long connecting rods is the reduction in piston side thrust, which increases friction and promotes cylinder-sleeve distortion.

[kenikh]

Isn't there also theory regarding ideal bore to stroke ratio? If so, do you know how the 2.8SS measures up?

[safe]

Henry: conrod-to-stroke ratio, I haven´t heard that before, obvious when you think about it for a while

Different question on the same subject: If you have an SC engine and you have a goal of making 250 N/A hp at the wheels.
If you want to do it as reliable and cheep (the wrong word maybe) as possible. How would you go about it?
What displacement (2.8, 3.0, 3.2, 3.4) and induction would best suit the criteria reliable and least expensive?

[safe]

Originally posted by kenikh
Isn't there also theory regarding ideal bore to stroke ratio? If so, do you know how the 2.8SS measures up?

If I understand Henry right the bore/stroke ratio has little to do with conrod-to-stroke ratio. It´s the legth of the conrod that makes the engine rev better or am I wrong?

[Henry Schmidt]

Originally posted by kenikh
Isn't there also theory regarding ideal bore to stroke ratio? If so, do you know how the 2.8SS measures up?

In general short sroke / big bore are used for high RPM (big ratio). Long stroke / small bore work well for engine torque at low RPM (small ratio).
3.6 engine have a 1.3 to 1 ratio. Good low end torque.
2.5 engine IMSA race engine 1.36 to 1 well proven hi RPM race engine
2.8 short stroke engine 1.44 to 1 My favorate
2.8 959 Super Car 1.42 to 1 Dream car
3.5 Benetton F1 engine 1.90 to 1( 16000 rpm 95x50)

Remember that there are many factors that effect torque and rpm. This is just a general rule.