Wayne's Engine Picks: short stroke 2.8

[gridgway]

So there I was reading my fav bed-time book...Wayne's engine rebuild book and it fell open at the Wayne's picks page.

So I thought I would ask if anyone has built or experience of the short stroke 2.8 built in 3.0 turbo cases with a 66mm crank and fat (95mm?) pistons?

I really fancy building one. Although I assume it's going to be hard getting the bits?

Graham

[Alan @ CanfordClassics]

We are building one right now. I have mentally been building this motor and collecting parts for some time. Works on the cases started last week. Starting with Carrera 3 cases I bought in Italy.

It will be a high rev'in monster.

Alan

[IanM]

Wise words from YTNUKLR:

No ego in this game, just curious. Defensive much?

Numbers: We got 266hp/196lb.-ft. out of this engine on Randy Aase's dyno.

Specs.
3.0 930 case
2.2 S Crankshaft
3.3 930 oil pump
Carrillo rods
ARP head studs
CP Pistons - 10.3:1
Mahle Nikasil 95mm Cylinders
Goetze rings
SC Heads; 40/38mm ports; 49/41.5mm(stock) valves
Ti retainers, Aasco Springs
DC80-102 Cams
RSR Spec. MFI Pump based on '69 S core
NOS RSR High Butterflies
226mm 78-79 SC Fan assembly, early fan pulley, RSR crank pulley
Series900 fiberglass, RSR German Twill
Supertec Twin Plug Distributor, Moroso wires, Single MSD-6AL ignition box
1-5/8" Alex Job Headers and 'phones

Honestly, I was completely underwhelmed with this configuration. Perhaps it is the builder, but I didn't deviate much from the 'recipe'. . .

-I wish I could have done a custom MFI space cam or run this motor on plain old PMO 46's because we got a flat spot right in the power, because of the MFI pump not quite designed right for this engine. The AFRs go lean to 13.5 from 5200-6000 and it flatlines the power right there.

-I think the RSR High Butterflies in stock configuration are much too big for a 2.8 that even dreams of streetability. They are much more suited to something like a 3.4-3.8L, but the owner wanted to use them anyway. I am sure we lost power over standard smaller throttle bodies.

-I think the ports are a little too big, or the valves are a little too small, for this particular engine. Bigger valves or smaller ports (along with std. throttle bodies) would undoubtedly make this engine better on the street and probably not hurt top-end at all.

-It is difficult to get real compression out of this engine. We got 10.3:1 after much fuss. The combination of short stroke (smaller swept volume) and large dome volume in the head conspire against you. I think the 76cc or so on a standard 2.8 is a better fit for the displacement...a better balance of valve size, dome volume, stroke, and displacement. The large combustion chamber is inherently lazy in its swirl and combustion characteristics and more suited IMO to a 3.2L+ . To get compression out of this engine you have to build a mountain of a piston that is both relatively heavy and compromises optimal combustion chamber design (divides the chamber). So much so that you have to run more advance than is really optimal which is really bad for power.

I am now of the opinion that it was probably intelligent on Porsche's part that they never built this engine.

Why? Because the advantage seems to be durability in displacement-limited (2.8L) classes, where the ability to spin it another 500-1000rpm beyond a long stroke 2.8 makes the difference. And everywhere under 8000rpm the engine is only equal to or less than a long-stroke (standard) 2.8 RSR style motor. And these days, Porsche can spin its much larger and more powerful 4.0 GT3 to 8800, or higher if you want. . .

The complication and expense of a 2.8SS does not seem warranted given that a long-stroke 2.8 or standard 3.0 will probably serve the majority of Porsche drivers better. For the 1% of guys where a 2.8SS is better than a 2.8LS in a 2.8 class (like GT4), because you can turn 9000rpm instead of 8000, it seems to make sense. The economics certainly do not make any kind of reasonable sense with this engine. The torque of a 3.0L is better everywhere and if the engine is kept under 8000 and/or driven on the street, can't argue with that. For raw numbers, displacement is king.

Granted, numbers only tell part of the story and I can see why a little high-revving banshee is a blast in the pants. I was hoping the new owner would chime in and say that, because feel is ultimately more important than the raw numbers, anyway.

And, now that I have posted a searing indictment of the 2.8SS, I will qualify that and say that I have nothing against short-stroke motors in general. I would say a better short-stroke motor is a 2.7SS with the smaller dome chambers, etc. If you want more power than a 2.7SS (which is very close to a 2.8SS and lighter by 22lbs. if you use a mag case), build a 3.0L or. . .go all the way to a new GT3. . .

My 2¢!

http://forums.pelicanparts.com/911-engi ... ilt-3.html

[Alan @ CanfordClassics]

It will be a while yet before mine is done but I will report back. We have quite a few other mods that we are doing above and beyond the above and will be doing a lot of testing on the engine Dyno. I don't have a car for this motor yet it's more about just doing it and for fun, the fact the crank is already done and I have many of the parts such as nos high butterfly, new gt3 oil pump and rods and we make quite a lot, such as twin plug dizzy, all the machining, valve guides, fly wheel, and will soon be looking into making our own barrels, that make the build economic.

Besides we have done quite a few 2.8 around long cranks, lets build one around a short 66mm crank.

Thanks

Alan

[Nick Moss]

Give me a TBed 3.5 any day. Similar or lower costs, a flat torque curve and plenty of power.

[PhilipB]

Didn't the larger capacity short stroke motors have all sorts of vibration issues in period?

[gridgway]

That all looks very interesting then and quite a few challenges to overcome, be fun to see how you get on Alan.

I have been musing for a while about starting a project to do an engine rebuild just for fun. This caught my eye as the antithesis to what's going to be in my (ahem) 89 hot rod...a whopping great 3.8.

I thought there you go, just knock up a 2.8SS and I can just choose which engine to run for a particular blat!

But, on reflection, I think that rebuilding a worn stock engine with a few tweaks might be a better start!!

Graham

[Mike911scrs]

2.8Lt short stroke, has now been up and running for over a year, and now due for upgrades this winter, has no vibration/balance prob's



regards mike

[gridgway]

Obviously no problems with combustion only having 1 sparky-thing per uppy-downy-thing then Mike! Can you tell us more about it? Spec, performance, revviness?
Cheers
Graham

[Highfield]

Dumb question but what the heck. What are the driver differences between a SS 2.8 and a 2.8RSR which I assume is an overbored 2.7 (i.e. a long stroke ???).

i guess it is like asking what is the difference between a big block 400ci Chevy and a 415ci small block Chevy. Does one rev fast and fragile whilst the other is less revvy and more turquey ? Does one cost a lot more than the other ?

Ian

[Mike911scrs]

HI Graham

"Can you tell us more about it? Spec, performance, revviness?"

the engine has a 66mm NCW crank, Std 2.0lt rods, lightweight flywheel, JE pistons for single plug

as for the,performance, it has been fitted and run, no dyno or rolling road

you will have to ask the driver (Brembo) how it runs

some of you may remember the engine, as it was stripped on the engine class with me,

regards mike

[IanM]

the engine has a 66mm NCW crank

What are the main reasons you've chosen that?

It's not very often you hear a 911 engine builder using a non-counterweighted type crank. I know it's lighter but I would have thought balance is more important...

[Mike911scrs]

HI Ian
the crank is even lighter, at 0.50mm Under Size on all bearings, the crank and rods where just handy when engine was being built, there is a counter weighted crank now waiting to go in, when the engine comes back in the shop.

regards mike

[brembo]

the engine has a 66mm NCW crank

What are the main reasons you've chosen that?

It's not very often you hear a 911 engine builder using a non-counterweighted type crank. I know it's lighter but I would have thought balance is more important...

Have covered approx 3k, (very enjoyable), miles with this engine, and have had no vibration issues whatsoever, in fact, no problems at all, (I suppose having to give Mike his engine back could be a problem ).
I can only compare it to the engine I had in the car previously(3ltr on Webbers},and it feels more powerful, and seems to have a lot more torque. I have never driven an mfi engined car, so it would be interesting to compare the two.

[Mick Cliff]

.... I have never driven an mfi engined car, so it would be interesting to compare the two.

Next time we meet up Dougie