Thoughts on some different engine configurations

[Shuie]

Wayne’s book gives good rundown of some engine configurations that are known to work pretty well. I know it’s impossible to cover every unique configuration, but there are a few I’m interested in knowing about that are not documented in either Wayne or Andersons books. I wanted to list them here to see if I understand how/if they can be put together and to see if anyone has any thoughts about any of them.

Short stroke 2.5 – 90mm bore x 66mm stroke. Early aluminum case 2.0 with spigots bored out to accept 90mm P&Cs. Including all of the case upgrades it seems like a lot of machine work, but still a very neat engine.

Grady Clay's 2.8 – 92mm bore x 70.4mm stroke. 2.4E MFI motor with 92mm P&C upgrade.

Short stroke 2.8 – 95mm bore x 66mm stroke. Type 930/02 early turbo or euro carrera case and a early 66mm crank with 95mm P&Cs

Short stroke 3.0 – 98mm x 66mm stroke Type 930/02 early turbo or euro Carrera case and an early 66mm crank with 98mm P&Cs. I’ve never heard this mentioned here and I don’t even know if it’s even possible. Seems like it should work the same way a short stroke 2.8 would. Any thoughts or opinions on this one?

Short stroke 3.2 – 98mm bore x 70.4mm stroke. SC motor with ‘bolt on’ 98mm P&C upgrade. This one is in both Wayne and Bruce Andersons books and is known to be a great setup. (Could also be built on a 930/02 case if you need to use an older 2.7 crank with a 6 bolt flywheel)

Short stroke 3.3 – 100mm bore x 70.4mm stroke. SC motor with 100mm P&Cs. Some machine work needed, but sounds like a great engine. (Could also be built on a 930/02 case if you need to use an older 2.7 crank with a 6 bolt flywheel). Any thoughts or opinions?

rdanes 3.4 – 98mm bore x 74mm stroke. SC motor with a 3.2 Carrera crank and 98mm P&Cs. 98mm Mahles used are the 23mm wrist pin version for the Carrera.

3.4 Carrera – 98mm bore x 74mm stroke. 3.2 Carrera with ‘bolt on’ 98mm P&C upgrade.

3.5 – 100mm bore x 74mm stroke. 3.2 Carrera with the 100mm P&C upgrade. Some machine work needed.

Please add any other interesting engine configurations that you been able to make work, or correct me if any of these cannot or should not be attempted.

TIA

[Henry Schmidt]

2.6 92mm bore X 66 mm stroke. good use for 2.8 RSR pistons. With the reduced stroke the compression ratio ( usually too high for 2.7 heads) is very usable.

3.1 100 mm bore 66mm stroke. This engine is built on a 3.0 turbo case with 100 cylinders. Revs high, huge power.

3.16 97 bore X 70.4 stroke. Quick revving engine config. for turbo aplication. Requires off set wrist pin in 3.0 rod or custom rods.

[Shuie]

Thanks Henry! Thats exactly the type of stuff I was looking for.

[Wayne 962]

Short stroke 2.5 – 90mm bore x 66mm stroke. Early aluminum case 2.0 with spigots bored out to accept 90mm P&Cs. Including all of the case upgrades it seems like a lot of machine work, but still a very neat engine.

Basically a 2.7 engine with the smaller crank. You could make this engine by using the 66mm crank and rods with the rest of the engine being a 2.7. This would give you a higher-revving engine.

Grady Clay's 2.8 – 92mm bore x 70.4mm stroke. 2.4E MFI motor with 92mm P&C upgrade.

As Henry pointed out, these are the RSR-sized cylinders from 1972. These cylinders are hard to find and I don't know if anyone is making aftermarket ones.

Short stroke 2.8 – 95mm bore x 66mm stroke. Type 930/02 early turbo or euro carrera case and a early 66mm crank with 95mm P&Cs

A better solution than the first one (2.5) because the case has all of the upgrades already, and you can use standard components.

Short stroke 3.0 – 98mm x 66mm stroke Type 930/02 early turbo or euro Carrera case and an early 66mm crank with 98mm P&Cs. I’ve never heard this mentioned here and I don’t even know if it’s even possible. Seems like it should work the same way a short stroke 2.8 would. Any thoughts or opinions on this one?

Yes, it should work fine, providing you have the proper pistons - I'm sure JE could make you a set. This engine would have big barrels and a very small stroke. I don't know of anyone running this engine, but I would guess with a high-lift cam, it would be very difficult to drive on the street.

Short stroke 3.2 – 98mm bore x 70.4mm stroke. SC motor with ‘bolt on’ 98mm P&C upgrade. This one is in both Wayne and Bruce Andersons books and is known to be a great setup. (Could also be built on a 930/02 case if you need to use an older 2.7 crank with a 6 bolt flywheel)

My personal favorite. Higher-revving, higher-performance engine, but only if you use carbs or EFI and a high-lift, high profile cam. I wouldn't really bother if you're going to stick with CIS and the mild CIS cams.

Short stroke 3.3 – 100mm bore x 70.4mm stroke. SC motor with 100mm P&Cs. Some machine work needed, but sounds like a great engine. (Could also be built on a 930/02 case if you need to use an older 2.7 crank with a 6 bolt flywheel). Any thoughts or opinions?

Steve Weiner doesn't like 100mm - too thin. Not too many people run these sizes

rdanes 3.4 – 98mm bore x 74mm stroke. SC motor with a 3.2 Carrera crank and 98mm P&Cs. 98mm Mahles used are the 23mm wrist pin version for the Carrera.

This is essentially a 3.2 engine with a big bore kit bolted on. I would make sure that you run a good cam with this setup to extract the most out of it (also programmable EFI is really the only true way to go here.)

3.4 Carrera – 98mm bore x 74mm stroke. 3.2 Carrera with ‘bolt on’ 98mm P&C upgrade.

Exact same engine as above

3.5 – 100mm bore x 74mm stroke. 3.2 Carrera with the 100mm P&C upgrade. Some machine work needed.

Again, 100mm may be a bit too thin for reliable street use

Please add any other interesting engine configurations that you been able to make work, or correct me if any of these cannot or should not be attempted.

TIA

Important: Pistons, cylinders, cranks and rods, are only one part of the system here. A big bore engine with CIS and a mild cam seems to me like the equivalent of a 42" plasma screen with rabbit ears attached. You need to design the whole package as a unit in order to extract the most out of your engine dollars.

-Wayne

[jluetjen]

Some of the things to consider...
* Aside from the cylinder wall concerns with really Big Bore configuration, keep in mind that as the cylinder walls move away from the spark plug, it takes longer for the flame front to reach into the corners. This can cause all sorts of combustion and drivability issues.

* Mixing short strokes with really big bores can make it hard to achieve a high enough CR without making the piston crowns taller. If they get too tall, you wind up with the issues that the 2.0S and 906 pistons had.

The solution to both of these issues is to twin plug, but that means more money. You could get an engine with the same performance without twin plugging in many cases by making the stroke longer and the bore narrower as long as your piston speeds don't go over the top.

According to Frere and others, Porsche's engine design engineers were always concerned with the thermal efficiency of the motor. Having a larger bore then you need to keep the bottom end together increases the surface area of the combustion chamber which is apparently not a good thing because more heat is lost to the head and cylinder walls. I'm guessing that the results might include insufficient combustion, poor low speed running, insufficient cylinder filling, a low mpg number, and things like that. These things are especially challenges for hemi engines. The designers were also very concerned about the robustness of the design - which has always been a Porsche hallmark. For example they would routinely run dyno tests for extended periods of time to measure the drop-off in performance of an engine after breakin.

If you were talking about a modern 4 valve head with narrow valve angle, a compact combustion chamber, squash areas and flat topped pistons (as defined by the Cosworth DFV and copied by all of the modern multi-valve street engines), these same issues wouldn't exist.

Since all of the configurations that you described are based on the 911 engine, I doubt that any of them would be complete dogs, but I'm sure that with use over time, some of the more extreme variants will develop more issues compared a factory configuration. Using the 100 mm cylinders for example, they may work great to start, but as they wear and distort you will most likely find that the engine develops ring sealing problems which lead to excessive oil consumption, fouled plugs and a significant HP drop over the life of the engine.

[Wayne 962]

Well said. In summary, the engine configurations that are most popular and most widely used, are often used for a reason - they are the best proven ones out there.

-Wayne

[Shuie]

Great info, thanks guys.

I failed to mention that I was assuming twin plug on all of the engines I listed since they would all be relatively high compression. I will only be allowed to buy the reformulated gas that everyone loves so much here within the next month, so twinplug will most likely be a reality for me no matter what I end up putting in my car. I didnt want to think too hard about induction or cams until I was sure the longblock would bolt together.

I accept idea that the configurations that are documented are probably documented because they work well. The people that designed and built these cars were definitely on their toes. The factory setups are surprisingly hard to improve on.

[Henry Schmidt]

Originally posted by Wayne at Pelican Parts
Well said. In summary, the engine configurations that are most popular and most widely used, are often used for a reason - they are the best proven ones out there.

-Wayne

What is more likely true is that people build the safe, easy engine, not necessarily the best engine. A 911 engine is, for most, a huge undertaking and gambling on the unknown can cause many sleepless nights.
The engine I mentioned 97 x 70.4 is built for more than people tend to believe and yet you rarely hear about this configuration. I was skeptical, but visiting mechanic to my shop built one and the end result was amazing.
Also when built properly, the 100 mm engine will also offer tremendous results. We just built a 3.5 MFI single plug engine that amazed us on the Dyno. 369 RWHP @ 7660 rpm.

[jase007]

We just built a 3.5 MFI single plug engine that amazed us on the Dyno. 369 RWHP @ 7660 rpm.

Henry, assuming 15% drivetrain loss that is 424hp from a 3.5.

Which is 121 hp per liter? Seems high for a normally aspirated engine. Many a 3.4 I have seen coming from Dawes Motorsports and other "tuners" that are twin plugged, ceramic coated high compression JEs, titanium valvtrain, etc ... only get 360hp +/- at the crank.

Dawe Motorsports 3.4L twin plugged.


How'd you get there?

Jason

[Henry Schmidt]

Hi Jason
I can't explain it. Our goal was 320 and we built the engine with that result in mind, so we were surprised with the result. At first we thought it was the dyno so we used a control vehicle, a 1972 CSL BMW that had plenty of dyno time on other dynos and the dyno actually seemed a little pessimistic on that car.
We don't usually quote HP because who wants that conflict. What I was saying in the post was that you can find hp in unusual places.

[jase007]

What I was saying in the post was that you can find hp in unusual places.

I agree with that entirely. I was just curious. To be honest, we rarely dyno our engines besides getting them set-up.

Lap times at the track and whether it is to be P1, P2, P3, .... are what matters to the driver

Cheers,

Jason

[rdane]

http://www.andial.com/

Andial has done more CIS/Motronic, big bore motors than anyone in the country I suspect. Lot of speculation on what will and won't work has been posted on the Max Moritz conversions on Pelican. Much of it has been incorrect. (appropraite wrist pin sizes, compression ratios and pistons styles come to mind)

I have to agree there are any number of great engine set ups available that don't typically get built. From my experience it is because either the owner or the builder is unaware of them or afraid of them.

The Andial Motronic 3.7 is a good example, as is my CIS 3.4. Mine will eat a new Boxster S (a good 3.2 Carerra isn't even in the game anymore) if last weekend is any example. Until you have built and driven some of the more esoteric combinations I would be very careful judging their worth.

Having been in two 3.6 conversions (varioram and the older 3.6) I can easily say I am happy with my end results on the CIS 3.4.

I am impressed with my 3.4 enough that the next project I am starting is a 3.8, Motronic, again with a mild cam like the 20/21 or something very similar. The big bores fit the way a majority of us drive on the street and give you plenty of thrills and power. Almost scary

Henry,
What else was done to the 3.5 to extract that much HP? Also interested in the torque#'s.
Thanks,
Mark

[Henry Schmidt]

Originally posted by Mark Wilson
Henry,
What else was done to the 3.5 to extract that much HP? Also interested in the torque#'s.
Thanks,
Mark

3.2 case, Carrera II oil pump
Mahle 100 mm Ps & Cs 10.8 to 1
3.3 turbo crank with 962 journals / 3.0 rods, titanium 935 rod bolts.
3.3 turbo heads ported & flowed by Supertec 41 mm in 38 mm ex. Aasco springs, ty retainers
1 and 7/8 header
Elgin cams 320 / 304 set @ 6.2
Recurved Dist by Supertec 36 degrees total advance 100 octane unleaded
Taylor wires, MSD ign box 7800 rev limit
Custom MFI 41 butterflies, stacks, custom MFI pump, Fuel lines and enrichment by Supertec
Dyno was a Dyno Jet @ Pecora Dyno Service, Costa Mesa
369 @ 7660
326@ 5300

[Wayne 962]

Originally posted by rdane
http://www.andial.com/
The Andial Motronic 3.7 is a good example, as is my CIS 3.4.

It would most certainly be quite a bit better without the CIS, as that would allow you to run a more aggressive cam. CIS is just not a performance injection system. It's better suited for things like VW Jettas.

-Wayne

[rdane]

CIS is just not a performance injection system. It's better suited for things like VW Jettas.

You certainly have a sense of humor Wayne. Bring your Ferrari or a Jetta along for a drive with us. My point is a more agressive cam is fine many places...like a track for example. On a street car, aggressive cams aren't all that practical. Fun, yes but practical..no.

CIS continues to get a bum rap no matter the evidence to the contrary. Perfect? No. Decent? You bet for a street car. We can continue to disagree but then I have both a 911 and a 3.4 Wayne, and you don't

Any flat six 911 that gets 275 to 300 hp is pretty fun no matter what induction you have. You can do that with CIS or Motronic.

Thanks Henry. Congrats on that beast!

[Shuie]

3.5......MFI.....drool

Henry, that is spectacular. There was obviously a lot of thought that went into designing and building that engine. I have to ask why you guys didnt twin plug it or run engine management instead of the MFI? I thought the twin plugs were bascially required on anything that size.

3.4.....MFI....twin plugs...drooling again

Jason, any more details on that monster?

[rdane]

and here is a couple of pretty quick ways to get a few extra HP

Custom MFI, 3.3 turbo heads ported & flowed, 100 octane unleaded, MSD ign box 7800 rev limit

for :369@ 7660 and 326@ 5300

Awesome engine! I want one

I also. Hmmmm, a 400HP Duck.......