Crazy idea ... 8 cylinder 911 motor
 

So here's a wacky idea that has been bouncing around in my head for a few months... more cylinders.

The interest in "7R Aluminum cases" got me thinking that there might be interest in something a little stranger...

There are some fundamental limitations in the ability to dissipate energy which are more tied to the number of cylinders rather than the displacement. So how about a 8 cylinder motor?

Obviously Porsche has already been down this path (the 908), and replicating that exactly would likely be just slightly cost prohibitive. Assuming you had completely accurate measurements, there was a lot of unique technology in that twincam variant.

So... I started considering how to maximize the off-the-shelf content of a custom 8 cylinder horizontally opposed 911-style motor:

1. engine case - no way of avoiding custom here... given low quantities simply CNC milling from billet might be the best approach (I'm assuming that the setup cost for die casting would be high).

2. crankshaft - Ideally you could keep the same geometry in stroke and cylinder spacing. So I considered a number of options. As significant changes in stroke would have major impacts on rods, pistons, heads, ... so my suggestion is a Ford SB 302 crank @ 3" (76.2 mm) stroke and 4.38" (111.2mm) bore spacing. An alternative would be a custom BB Ford crank which has a 4.63" (117.6mm) bore spacing.

3. rods - you're only $ away from custom rods, but Ford 302 rods are strikingly similar in dimension to 964 rods. Just a hair long, but can make a little up in the piston maybe? You can get a set of h-beam billet rods for a 302 for ... about the price of one custom 911 rod.

4. cylinders - who would use anything but Nickies? you could also probably coopt spare mahles into use. My thought is that if Porsche could use 100mm cylinders with a 118mm bore spacing that you could get away with 95mm cylinders on a 111.2mm spacing, right?

5. heads - used porsche heads, obviously with some minor machine work to accomodate the 111.2mm spacing (shaving 3.4mm = ~1/8" off each side of the head).

6. cam towers - custom, obviously, but otherwise basically just longer

7. cams - custom, w/964 lobe profiles, longer and with 8 lobes per cam. I would think you could get something like this from Dougherty Racing, right?

8. pistons - JE should have something close enough (3.2 9.5:1?)

9. camshaft drive - as the engine shouldn't be growing significantly in width, I think you could make the stock cam drive work. Of course there is a little detail of changing the offset between the banks as the crank has two rods on the same throw... but that's just a matter of reconfiguring the...

10. intermediate shaft drive - reorder the stock gears such that the two sprockets are together.

11. oil pump - pick your favorite porsche pump. The flow might be a little more, but then again you only have 5 main bearings.

12. cooling - big external oil cooler. Maybe overdriving a 3.6 fan would flow enough air?

13. flywheel - custom for 915, several sources of custom flywheels.

14. intake - individual EFI throttle bodies (TWM?)

15. exhaust - custom tubular headers...

16. ignition - aftermarket ECU, coil-per-plug - several choices

Plus a bunch of other little details...

There are a few interesting things to consider:

length: the 908 case is necesarily about 4" longer than a 911 case, so it's obviously beyond a tight fit in a 911 chassis. Of course if the cylinders are offset by 23mm rather than 59, you've gained 36mm. If you save 6.8mm on each cylinder, that's another 27, so it would only be (118-36-27) = 55mm longer than a 911 case. Certainly you could use a short bellhousing tranny and move the engine forward to gain a little... and it just... might... fit, right?

So whattaya think? Impossible?

--
Joe

Cams could be done.
I made a set of flat 8 cams for a ZR-1 Chevrolet project once before.

There's room in there. You can get away with using stock parts, and you'd need custom:

- crankshaft
- case
- cam towers
- camshafts

Not too much more than that, except probably some 2-barrel Webers...

-Wayne

.....and a lot of money along with a bunch of development time.

Sherwood

Some things you're over-complicating.

The intermediate shaft gears are fine, and so is the oil pump. Leave them alone. Just install a longer drive shaft between the two. So you'd be adding the extra 2 cylinders in the middle.

Also, as far as engine length, remember the '78-'89 911 Turbo has it's engine sitting 1.5" farther back in the chassis, and the rear portion of the 930 chassis near the reflector panel is recessed to clear. So there's 1.5" of the needed room right there if you use a 930 chassis.

Better yet, put it in an '89 Turbo chassis, and do the short bellhousing mod to a G50-50.

Actually I was thinking that you really could use a Ford 302 crank (or some appropriately strong forged aftermarket variant). Custom crankshaft sounded expensive to me, but then again it's all gonna add up eventually, right?

--
Joe

The problem with the stock intermediate shaft is that it's designed for the left and right banks to be 59mm apart rather than something closer to 23mm that would be dictated by using a crank with 2 rods per throw... of course it might be easier to just add a spacer to the front of the cam tower and make the custom camshaft longer.

Either way, there would be a good bit of planning involved in getting the sprockets to line up.

--
Joe

O.K., now I see what you were worried about. The offset of the banks. Yeah, I'd definitely just use a spacer between the sprocket and cam on one side. Or like you said, have it built into the custom cam.

For the throttle bodies, you could cut the rear TB off of two sets of MFI throttle housings, so that you have 4 sections of two. Then you just need a second pair of throttle rods joing them on each side. Then an engine management system and some custom injector blocks, and you're good.

For that matter why not go to 12 cylinders, with the drive from a gearbox in the middle of the engine and then you could use std camtowers and camshaft blanks, carbs or MFI etc, I believe the crankshaft would be a challange

Neven

Why not just balance two regular engines together with a coupler of some sort?

12 cylinders does sound interesting, but the appeal of 8 to me is that it could be made to fit in the 911 I have in the garage...

--
Joe

Can't you use VW parts? Building a flat 8 like Porsche did the 917 engine?

Would you add more oil and would the oil pump work well enough?

Not to discourage you if this is an engineering exercise. By all means do it.

However, as blasphemous as this is sounds, an off-the-rack lightweight V8 might be at least equivalent and maybe lighter than CNCed aluminum pieces. How heavy can a full aluminum SBC or Buick be? I know, they use that liquid stuff.... coolant, but I'm guessing the cooling requirements of an air-cooled flat-8 will exceed the number of oil coolers you can install.

Sherwood

Forget about using a 'murican V8 crank.
The Porsche flat 6 engine has a throw for each cylinder, the fords and chebbies have two cylinders per throw.
The 917 was the same way but no reason to do it with a flat 8 cylinder engine.
You will have to start from scratch on the crank. You can't even modify a stock 6 crank because the cylinder firing timing would be off so you wouldn't be able to balance the engine.

I love the idea. It has been kicked around Pelican a few times before. There was an article in Excellence about a guy named Populos (?) who cut down a 911 motor from six cylinder to just four...you could do the same and weld the two fours together - thus saving development costs...but then you'd have to use the sawzall on your 911 to make it fit...I've seen some articles on the internet about VW fours bolted together to make flat 8's used in aircraft (can't find the links now)...if you're gonna use a custom crank, have you considered using a modular crank? It isn't a new idea...been done before...and may make your life easier...

You're not crazy...or at least no crazier than the average around here...be sure to post pics if you get this project off the ground!

Easy induction: a set of 4X2 V8 Webers or Englese injection.

I mocked up a case half based on the dimensions of the SBF crank and 95mm cylinders (103mm spigot, 83mm head studs, right?).

http://forums.pelicanparts.com/uploa...1138422328.jpg

http://forums.pelicanparts.com/uploa...1138422349.jpg

http://forums.pelicanparts.com/uploa...1138422373.jpg

By the way... I'm using a 3D drawing package from http://www.emachineshop.com/ I posted the drawing at http://www.deblaquiere.net/machine-minimal-1.ems if you want to look at the drawing in greater detail...

--
Joe

somehow i think it's not a straightforward as thinking it up and milling some aluminum... wouldn't a milled crankcase be seriously less strong compared to a cast crankcase (which is the factory style if i'm not mistaken)?

then there's crankshaft design
camshaft design

things flexing, heat expansion, torque going where it should instead of where it should not.... etc etc

don't get me wrong , it's a nice little brainstorm
but if engine design was so simple , i'm sure more people would be designing engines themselves...