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Cheap-a$$ long rod + stroker + high CR pistons?
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BionicBalls  



Joined: 05 Jan 2009
Posts: 642
Location: Charlotte, NC

PostPosted: Tue Feb 28, 2012 12:27 pm    Post subject: Reply with quote

Stahl makes all their headers to order, wouldn't they be able to make a suitable header? The design they have for the NA is 35mm. I'm pretty sure you can order the headers "semi-complete" where you would have to finish welding on the manifold plate. Wonder if we could get a manifold plate cut and weld that on in the standard one's place.

Does that make sense?
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tyfighter123  



Joined: 19 Jan 2010
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Location: Colorado

PostPosted: Tue Feb 28, 2012 2:54 pm    Post subject: Reply with quote

Dan I was thinking the same thing about an adaptor for the N/A mani. Also what about moding a header for the N/A? It seems one could bend the individual pipes much easier than grinding out the cast iron.

What are your plans on your N/A build?
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Porsche 924 1977 N/A
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Porsche 911S 1976
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Raceboy  



Joined: 01 Mar 2004
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Location: Estonia, Europe

PostPosted: Tue Feb 28, 2012 6:05 pm    Post subject: Reply with quote

I had the exhaust manifold flange cut with the plasma-cutter for my 931 "Gulf" and it was something like 30 euros. Afterwards I machined the flame ring recesses to the flange also.

One could use this as an adapter to mount NA manifold or to buy some NA headers, cut the NA flange and weld the pipes to this flange. Of course the headers should be 37-38 mm diameter, not 32.
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
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ideola  



Joined: 01 Oct 2004
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Location: Woodstock IL

PostPosted: Tue Feb 28, 2012 9:21 pm    Post subject: Reply with quote

When I enquired about modifying the existing NA headers, Stahl and MSDS both said they would need to create a custom jig, which is where all the upfront cost comes from.

I did a bunch more measuring last night, and I think we may not be that far off from a solution as I first feared. After taking a second look at the 931's fire ring, comparing its inner diameter to the stock NA header, it only leaves about a 1mm or so that would have to be ground off of the header's inner diameter. The fire ring itself is 1.72mm thick. It's outer diameter is 38mm, and it's inner is ~34.5mm. The inner diameter of the NA header port is ~32mm, so roughly a 1.25mm lip around in the ID of the header would need to be ground away. Now the cool part. Since the fire ring is not really functionally required for an NA application, you could take one fire ring and cut it in half...they are 10mm wide, and 5mm is in the head, 5mm in 931 exhaust manifold. So by cutting a single fire ring in half, you would now have two fire rings to insert into two exhaust ports in the 931 head, which would then be flush mount to the NA manifold or header flange (i.e. two stock 931 fire rings would be enough to create four filler pieces). Of course, the NA mani/header bolt holes would have to be elongated and bored out to accommodate the larger diameter studs on the 931 head.

I am going to contact the header guys again today to see if they would be willing to redrill the bolt holes to a new bolt pattern without modifying the jig, and also to find out what the ID is of the material they're using for the header pipe.

The idea of a manifold adapter sounds doable as well...if it were 6-8mm thick, it could be possibly be designed with a taper to go from 34.5mm to the smaller diameter of the NA mani/header. I would probably have them made as 4 individual pieces rather than one big flange, as this would save on weight and material, and would be easier to make.

So good, all is not lost, some options available, even if it does add a little cost.

Hoping to visit the crank guy this afternoon.
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Raceboy  



Joined: 01 Mar 2004
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PostPosted: Tue Feb 28, 2012 10:40 pm    Post subject: Reply with quote

The flange I had made is 12mm thick in order to make it stronger for turbo application and accommodate the fire rings.
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
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ideola  



Joined: 01 Oct 2004
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PostPosted: Tue Feb 28, 2012 11:23 pm    Post subject: Reply with quote

Raceboy wrote:
The flange I had made is 12mm thick in order to make it stronger for turbo application and accommodate the fire rings.


Did you do one piece, or four individual pieces like the gasket?
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Raceboy  



Joined: 01 Mar 2004
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PostPosted: Tue Feb 28, 2012 11:30 pm    Post subject: Reply with quote

I did it one piece but it is easy to do separate sections. I posted a photo also in the "Gulf" thread.
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche
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ideola  



Joined: 01 Oct 2004
Posts: 15506
Location: Woodstock IL

PostPosted: Wed Feb 29, 2012 1:52 am    Post subject: Reply with quote

tyfighter123 wrote:
What are your plans on your N/A build?

Well, SONIC is due for a complete refresh. After going through two teenagers learning how to drive, he needs some body work. I have a complete front clip (fenders, badge panel, chin spoiler), and then a few minor dings here and there on the monocoque to sort out. Since I don't need him for a daily driver any more, I figured he'd make the perfect platform to experiment with this kind of setup.

So this is what I'm envisioning for the power plant.

Stage 1: short block, consisting of knife-edged long-rod stroker + ~11:1 CR + lightweight flywheel
Stage 2: 931 big valve head + 931 S1 intake + Audi 5000 TB + Stage 1 Cam + MSDS header
Stage 3: EFI conversion
Stage 4: TWM style ITBs

On the one hand, it would be nice to do just the short block with an otherwise stock top end in order to get a good dyno baseline. On the other hand, I don't have a spare NA head sitting around, and even if I did, I wouldn't want to put money into doing even minor prep on it, only to pull it off later. If I had an unlimited R&D budget, it might be a different story...as you know, the head work is bloody expensive.

So all that said, I'll probably bite the bullet and do Stage 1 & 2 together. Completing the Club Sport is still my top priority, but I don't need to spend any more money for that, it's just having the time and warm enough weather to work on it.
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tyfighter123  



Joined: 19 Jan 2010
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Location: Colorado

PostPosted: Wed Feb 29, 2012 3:38 am    Post subject: Reply with quote

Im interested to see how this platform performs! What kind of power numbers do you think stage 1 & 2 will produce?
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Porsche 924 1977 N/A
Mustang GT/CS 2007
Porsche 924S 1987 (parts car)(cut up and recycled)
Porsche 911S 1976
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ideola  



Joined: 01 Oct 2004
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Location: Woodstock IL

PostPosted: Wed Feb 29, 2012 4:37 am    Post subject: Reply with quote

tyfighter123 wrote:
Im interested to see how this platform performs! What kind of power numbers do you think stage 1 & 2 will produce?

Yeah, I'm started to get sort of excited about it. The research I've done indicates that a CR increase from 9:1 to 11:1 should yield a minimum of 7% increase in BHP. The source where I got the "rule of thumb" from even indicated that their chart was conservative, and often greater increases would be seen. I would not be surprised at all because the 9:1 US had 120 BHP, while the 9.3:1 ROW had 125 BHP, which is almost a 5% increase from just .3 points of compression (OK, and maybe a few less emissions controls).

Reading up on CBass's old posts, if he truly had US-Spec S2 931 pistons in his NA, all else being stock, he should have been seeing very near to 11:1 CR. He seemed confident that is car was achieving near-931 characteristics, and that was with a crappy NA head and no cam.

All that said, adding more stroke, reducing weight in the rotating assembly (lighter rods, pistons, crank & flywheel), 931 big valve head, lightened valve train, header...it sure seems like 150 BHP should be attainable. I'm trying not to be overly optimistic !

##########

Now for some really good news on the exhaust header issue:

I've just confirmed that the I.D. of the MSDS header is ~34.925mm (1-3/8"). The I.D. of the fire ring is ~34.5. So right there, you have a very close match in port size, and no obstruction or restriction going from the 931 head to the header (as you would have when using the tiny 32mm ports on the stock NA manifold). This is fantastic news (IMO) because it means that the 931 head can be easily adapted to this application with minimal modification to the head or the header. Simply use the stock 931 exhaust gaskets, elongate the stud holes on the header, get two of the stock 931 fire rings, cut them in half to make four pieces for each of the ports on the 931, and Voila! you have a near perfect exhaust port match!
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tyfighter123  



Joined: 19 Jan 2010
Posts: 549
Location: Colorado

PostPosted: Wed Feb 29, 2012 5:30 am    Post subject: Reply with quote

Quote:
All that said, adding more stroke, reducing weight in the rotating assembly (lighter rods, pistons, crank & flywheel), 931 big valve head, lightened valve train, header...it sure seems like 150 BHP should be attainable. I'm trying not to be overly optimistic !



Im looking for similar gains on my build but now you have me rethinking everything! When are you thinking of getting this all put together?

Quote:
Simply use the stock 931 exhaust gaskets, elongate the stud holes on the header, get two of the stock 931 fire rings, cut them in half to make four pieces for each of the ports on the 931, and Voila! you have a near perfect exhaust port match!


That is great news! Now to get someone to do it.......
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ideola  



Joined: 01 Oct 2004
Posts: 15506
Location: Woodstock IL

PostPosted: Wed Feb 29, 2012 5:50 am    Post subject: Reply with quote

Just dropped the crank off for closer inspection today. The only question I have remaining at this point is which rod to use (the one with thicker or thinner big end). The crank guy will be able to tell me which one, but it's probably going to take him a week to get to it . I've identified two different rod configurations that will work, one with a 45mm rod journal and one with a 48mm rod journal, so the crank can be offset ground to achieve up to 6.6mm of additional stroke.

All that said, as long as the rod / crank situation checks out, I am definitely going to build one of these setups this spring. I have the budget already set aside. As soon as I get an answer on the rod, I'll start acquiring the bits and prepping the short block. The first task will be to prove that the lower end can be assembled with the additional stroke, aftermarket rod, and aftermarket pistons with no interference in the cylinders or crankcase. Once that checks out, then I can finish building the top end, maybe have it ready to swap in by summer/fall. One of my goals is to verify the short block build as soon as possible so I can start offering a turn-key solution.

Regardless, Tyler, you're going to have a very nice setup with what you've been working on. This bottom end will still be more expensive than your pistons, although with added benefit of more stroke, so perhaps marginally more power. But all things considered, your engine should really sing when you get it together.
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Martijnus  



Joined: 29 Dec 2006
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PostPosted: Wed Feb 29, 2012 7:22 am    Post subject: Reply with quote

Haven't read the whole thread but I'm interested.

I've got access to a grinding machine which can grind offset, and we've inquired nitriding which was a fraction of the quoted 170... it would be about 50eur.

I'm pretty sure the stock 924 crank is NOT nitrided. Nasty thing about it is that you need to grind, nitride and regrind (because the journals do actually deform/change size by nitriding) again. Labour intensive...

I'm pretty confident it can be done. A lot of material is removed and I'm also sure the crank will be prone to cracking right next to the journal. Not only because of the removal of material, but mostly because the margins and dressing of the grinding stone will be very very very important. When the grinder does his job perfectly I'd say it has a chance to work.

Recently I read that VW decreased the journal diameter a bit to reduce friction. Has some downsides, but our engines have a surplus of oil pressure/volume to prevent most problems.

Any estimates on how much power you'd get if you do these modifications, but also put on a 16v head? With/without turbo.
The 16v part is possible, the alternative parts also. Completely different engine, but the stock base. That's my current goal.

I'm pretty sure I can go beyond 100hp/liter that way, so how about 200+ N/A.... would be an easy 300 when blown.

Dan, I've been (not actively) searching for alternative parts, so I'm very curious about the models you found parts from . Pistons won't be a problem, rods don't have detailed information (I've got access to many many different catalogs of pistons, but not rods...).

Not only performance is interesting, I always like 'off the shelf' solutions.

I like these threads. They don't cost money. yet.
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"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment
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ideola  



Joined: 01 Oct 2004
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Location: Woodstock IL

PostPosted: Wed Feb 29, 2012 9:04 am    Post subject: Reply with quote

RE: nitriding, my crank guy says it really depends alot on how the original crank was manufactured. There are some processes such as chill casting that were historically used in Europe that are now banned in the US due to environmental concerns. I would be shocked if the Porsche cranks were not hardened, and it would not surprise me at all if it turned out to be an integral part of the casting process as opposed to a post-casting treatment like nitriding. My guy says there is no way to know for sure without blasting the crank, which compounds the issue because it will affect the main journals, which as we all know you do not want to tamper with because of the NLA oversized bearings.

All that said, he is going to let me know how critical he thinks nitriding should be after taking a closer look at the crank. While he may not specifically remember it, when we asked him earlier about nitriding the stroker crank, he said it wasn't required, so we didn't have it done. We shall see.

As for your comments about a 16v head, I am highly skeptical that such a possibility exists. I have scoured this site and others for information that might give a clue to a possible 16v conversion, and nothing comes to light..the big issue being the bore spacing. There are some tantalizing possibilities, but so far, they have all turned out to be non-starters because of the bore spacing. So if you've found a potential solution for that, of course we'd all be keenly interested to hear!

As for power possibilities, I don't think there's any question that the high water mark for an NA is the 180BHP figure frequently cited for the D-Prod engines. What we're attempting to produce here is essentially equivalent to the D-Prod approach, using off-the-shelf components on a (relatively) shoe-string budget, so I have no illusions about the slim chances of exceeding the 150 BHP range.
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Martijnus  



Joined: 29 Dec 2006
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PostPosted: Wed Feb 29, 2012 10:09 am    Post subject: Reply with quote

Actually my estimates were unfair. I calculated heavy modifications to the crankshaft (extreme milling etc.) which could kick the performance up a notch. Also I reckon, whether it will be realizable or not, that with a 16v head 100hp/liter isn't a crazy thought. But keeping the 8v won't do it, I totally agree.

The reason I'm interested is because, let's say I know a guy that knows a guy that has an uncle with a friend who thinks he has found the right candidate for the 16v stuff, I'd like to build an engine which has some improved off the shelf stuff besides only the head mod.

I do not intend to spawn all 16v ideas in this thread, so I'll shut up about it.

Great plans though. 150 hp with such a mod is a great result imho.
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment
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