924Board.org

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

just starting this thread for ideas that are coming up in the "Radical Head Surgery" thread .

simsport

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

another option might be to find a 16v head that's close enough to be adapted to the block.

The VW 2.0 head looks like it might be close, it would need galleries rerouted but if the cylinder spacing was right....

Here's a couple of pics to get you thinking:
http://www.wideopenwest.com/~xr4tic/headassy.htm
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

Geddy T · Joined: 10 Nov 2002 Posts: 149 Location: Bellingham, WA

woah, there, guys. Let me direct you to a website: http://dot.etec.wwu.edu/fsae/v30/v30pics.html

This is the site for the Formula SAE team at Western Washington University. For those who haven't heard of it, the VRI here has been heralded by Popular Science as "Quite possibly the best overall vehicle research institution in the country." Having said that, I'm about half way through the program and am taking a couple year break for financial reasons (hopefully can return this spring, but depends on a promotion I'm going for at work). I'm not on the Formula team, because I wasn't quite up to their level in time to make a real contribution (those boys had it quite handled), but I was always lurking around and a good friend of mine is now team captain. Therefore I know a lot about what it took to get that car built. Formula SAE is a 600cc formula that teams generally satisfy quite well with a 600 motorcycle engine in the back. A few years back, a couple of very talented guys decided they were going to shake things up a little. They designed and built from scratch a 553cc V-8 ENGINE!!! Welded up their own headers, designed and cut their own blocks and crankshaft and differential housing, and threw it all on a home-built carbon/aluminum honeycomb monocoque. Check out the pictures to see all of the custom parts. It was really the most gorgeous thing I've ever seen. Now, when looking at the picture, you'll notice one thing: they didn't touch the cylinder heads with a 40 foot pole. Even with the talent to design and build an entire race car from scratch in a year and a half, they understood that the effort involved in cutting a cylinder head was not worth it. Let's put into perspective: that team had spent over 30,000 dollars of rich uncles' money before they even had the engine running! And that's CNC machining all of the parts, not casting. With machinging, you just have to buy the materials and have access to a machine: free if you go to the school. And as long as the block of metal that you started out with was in good shape, you wouldn't have much to worry about. When you cast, you have to first build the "tool." I worked at a foundry for two summers. One of the parts that the foundry made were impeller blades for jet boats. They paid a toolmaker to make the tool (the compression mold that you fill with wax to form a positive of the part). It was a while back, but I swear that my boss said they paid $80,000 for that tool. It's not like a cylinder head is a simple part. Lot's of channels and undercuts (ports and oil and water jackets for example), that would require an immensely complicated tool. Then you have to get the pouring right. This does not happen on the first try. It's so easy in a casting that complicated to get voids and inconsistent properties and soft or brittle spots. Oh yeah, and you need access to casting facilities: "melters" (whatever the technical name is), big-ass furnace, wax, casting sands, crucibles, and a lot of electricity. Then you still have to finish machine it. So assuming that you have the skills and a really cool CNC milling station to make it even possible TO machine a head (I still say that I seriously doubt anyone here is pulling that off with machining), it would still probably cost a LOT more than 2 to 3000 pounds. That's the good news. The bad news is that casting the part would involve six figures at least and then may still suck. Not bashing anybody's ideas. Maybe somebody here is the CNC master, in which case there may be hope. But from what I've SEEN in people actually doing this, this kind of thing isn't even in the same league as a complete turbo conversion or even a new 968 (if you cast). It's much much more expensive.

As for modifying an existing head to bolt onto a 924... this is not something I haven't thought of before. And if the bore size and offset are the same, it may be possible with some clever machining...

Zuffen · Posted: Wed Dec 11, 2002 12:44 am Post subject:

with all the various castings available in the ford and chevy aftermarket we should look there for a blank. If one can't be found then maybe we should look at other four bangers that do have this available.

I'm not against the audi block but if we have hit a wall on parts and resources jumping to another supplier is not a sin. If Porsche outsourced we can too.

Another thing to look at is remachining the block to accept another head.

It would be alot easier to machine the block for new studs or bolts than totmodify a head with all the cavities they contain.

One other idea. Is cutting the upper valve side of the head off and having a upper assembly made, aka to the 944 head.

This may make having larger valves and a performace design to the cam bearings and springs.
_________________
Bob Dodd - 924turbo@cox.net
931 1982, 944 1982 euro, 924S 1988SE, 93 968 tip 06 Silver Cayenne S, 06 Black Cayenne S

I have Way too many cars, parts for the 931,944 and 951

Geddy T · Joined: 10 Nov 2002 Posts: 149 Location: Bellingham, WA

These are two more good points. One is that it is much much much easier to machine an entire bottom end than it is to machine a head. I like that Idea, just make a block that fits the 924's mounts and mates up to some super sweet head out there. Machining a head in sections is another thing that I've put a lot of thought into (one of the things that I would love to do before I die is cut an engine from scratch). I thought a lot about machining a head in sections that weld or bolt together to allow for the tough undercuts and coolant channels and whatnot. Would probably be a lot easier to do with a 2.5 or 3 axis station.

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

has anyone run across the process of building heads up from aluminium sheet? The process was mentioned in Richard Finch's Performance Welding.

Basically you design the part (head) with a 3D CAD program. You then "slice" the part horizontally into 0.100" slices. You then generate 2D CAD files from the slices and have them laser cut. The slices are then stacked with brazing flux and powdered brazing rod between each slice. The head sandwitch is then heated in a furnace to just above the brazing melt point but below the aluminium melt point and viola you got yourself a new head. Easy

I've searched around but can't find any more info on the process. Sounds like an amazing way to do prototypes and small runs.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

has anyone ever sifted through the headgaskets of other 2 liter 4's? it would be worth a try to see if there are any 16 valve audi or vw headgaskets that will match ours. much easier than building a new head!

-nick

Richard · Joined: 04 Nov 2002 Posts: 617 Location: Pacific N.W.

Geddy T, Thanks for the reality check. I am well aware of the complications of making an engine. A friend of mine has been trying to make and engine from scratch for a Beloit Indianapolis racer from the 1920's I think. Been at it for years. There are companies that will design heads for your special project, but like you said, ante up the $$$. That is why I'm most interested with working with the stock or turbo head and realigning the ports for better velocity. I really don't think larger valves or hogging out the ports is the answer, except for full out race gear. As Peter said many months ago, the engine already flows enough for it's size. My hunch is that same size or smaller ports, but with different shape, will speed up the flow. Also getting away from the stock fuel injection opens up a whole lot of possibilities. I believe the guys with carbs are getting 10 or more hp, some of which is due to richer ratio, but also because the air doesn't have to turn so much. I am interested in looking at an early head with D shaped port. Lots on the net about the virtues of D ports(flat floor). Maybe something to it? Not against looking at different heads though, but then you have to remake the pistons cause of the loss of CR. I did a dyno 2000 on this engine stock and the volumetric efficiency stinks. It gets as high as 83.2% at 5500 rpm. At 3500 midrange it is 78%. Modern cengines, I believe, get as high as 90 or more with impulse tuning. This is what needs to be adressed IMHO. For me, the less money the better.

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

finding a motor in the VW/Audi line with the same cylinder offsets might have the added bonus of finding a cheap stroker crank.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

Geddy T · Joined: 10 Nov 2002 Posts: 149 Location: Bellingham, WA

I've heard of really well-designed modern engines achieving HIGHER THAN 100% volumetric efficiency naturally aspirated using Helmholtz tuning (downside being the super narrow power peak and real drop off on either side, requiring lots of shifting). I'm with Peter. Let's find us a head. If you're willing to take on a project this radical anyway, I don't see why pistons or a stroker kit are completely unreasonable. I wish their was a table with the bores and offsets of all of the engines from all of the major manufacturers.

Joes924Racer · Posted: Fri Dec 13, 2002 10:38 am Post subject:

My car rerquires lots of shifting or at least very quick or as quicke -n-smooth as possible, with all my mods its a gas BTW research is being done almost daily though.Lets see what I know one guy here who has a cracked head around the journals from over tightend camshaft caps[my perception
being I dont see how that could of happend]I just sold him a head he might donate his broke one to be sliced up for you. Want me to ask.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

leadfoot · Posted: Fri Dec 13, 2002 3:32 pm Post subject:

no volkswagen heads would suit
largest bore from 1973 through 1999 is 82.5
larger stroke was used to make more power
highest cc was 2792 from 6 cylinder
next was 2324cc from golf/jetta 4, 5 cylinder
1984cc 2.0 litre crossflow 1993 - 1998 blocks used 82.5 bore 92.8 stroke
from "water cooled volkswagon performance handbook"
...Leadfoot

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

a quick search shows that the Mitsubishi Eclipse (4 cyl) and Galant and the Hyundai Sonata (Sirius II 4 cyl) have an 86.5mm bore.

No idea what the cylinder offsets are.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

Geddy T · Joined: 10 Nov 2002 Posts: 149 Location: Bellingham, WA

Joe, you're right. I totally forgot that I have that cracked head to sacrifice. It's up for grabs for free if anyone wants it. I'll post this on the "radical head surgery" string as well. BTW it's a '77 N/A

924_fan · Joined: 03 Nov 2002 Posts: 123 Location: Lompoc, CA; USA

Peter, I don't think that the bore dimension is as important as the bore center to bore center dimension. Within reason bores may be fly cut; but, basically you are stuck with the center to center size.
_________________
Skip Denton
1979 Sebring