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The 928 guys like to get 944S2 and 968 pistons, bore their blocks to 104mm, and make a 5.4 or 5.8 engine, depending which crank they have (78.9mm/5.0L or 85.9mm/5.4L)
You could also regrind 928 cams to work on a four cylinder. I know its a little pricey to do a 968 or S2 regrind so it may be more costly to completely change the lobe locations. See if you can get a quote at a few cam grinders. It could be cost prohibitive but it may be worth a look.
I don't think I need to regrind the 944S camshafts. I was thinking if I just retard the cam timing that would work for a turbo set up. That's only because I thought I
had seen that the 944 and 944 turbo have the same camshafts, but the turbo's is retarded in timing. So if I retard the 944S camshafts timing it would have the same effect as the turbo camshaft timing needs to be. Right?
Consider investing into a paid membership on Rennlist, likely a better investment vs purchasing a top tier CNC or paying for the machine work/expertise building a reliable 951 using a 928 head. I'm at least honest. Trust me, this can be done:
If you can do this, God Speed, and I'll be smitten with your skillz.
Regards,
G
Originally Posted by Humboldtgrin
It seems Thom has a funny side. Sorry not into bending valves right away. The "S" cams fit perfectly from the 944S. The turbo intake is a little off and has much smaller holes. But with a little fabrication, some 928 flanges with custom intake, or cut off the runners on the turbo manifold a use the plenum, looks like it will work just fine. looks like the 944S fuel rail will fit with minor adjustments if any for mounting as well. Looks like I'm going to biuld myself a 928 DOHC turbo head set up for the 951 2.5L block. Just to show it can be done. Wonder why no one has done this before? I'm still not seeing the "big waste of time and money". I'm seeing a very possible, and most likley huge power gains thou. I will keep all posted. May take a while to put together due to funds. But I will.
False: Also not all 928 32 valve heads were 100mm. The 928GTS DOHC has the 104mm bore block. Making it a 5.4L not a 5.0L.
Why would you want to retard 944S cams? I have 2.5liter 16v turbo with S2 cams and I needed to advance the cams by A LOT from factory timing to move powerband lower, otherwise it would not have any torque until 5k rpm. Not sure about 944S cams (they have different timing from the factory), but for sure no retard needed if you want to have lower powerband, you need to advance the cams a bit.
The 944S cams have a more aggressive overlap which doesn't lend itself well to turbo applications. The exhaust cam is the more extreme difference between S2/968. Sourcing a set of cams shouldn't set you back more than a few hundred dollars.
I'm exceptionally interested to see where this goes, the largest hurdle to 16V turbo builds is solving the intake and exhaust manifold problems. Before we say the 928 heads will work with the 8V exhaust manifolds, you really should mock up the entire exhaust to the turbo to ensure it will still reach.
You might even be able to get away with using 944S pistons if you use a thicker HG to drop the CR. The 16V head is much less prone to detonation because of the combustion chamber design so you can get away with a 9:1 compression ratio on a street motor or higher if you're running e85.
I'm exceptionally interested to see where this goes, the largest hurdle to 16V turbo builds is solving the intake and exhaust manifold problems.
I'm genuinely curious why no vendor or person with machinery has taken the step of making a simple adapter plate between the 951 intake manifold and the 16v head bolt pattern.
When I had an "S" head and a 951 head side by side, and overlaid gaskets and stuff, it looks like it'd work no problem. One bolt hole appears to even line up, maybe that one should get a long stud installed in the head to align the whole assembly.
It wouldn't be ideal with the 951 runners versus the 16v port size but it'd work and be cheap...
I'm genuinely curious why no vendor or person with machinery has taken the step of making a simple adapter plate between the 951 intake manifold and the 16v head bolt pattern.
When I had an "S" head and a 951 head side by side, and overlaid gaskets and stuff, it looks like it'd work no problem. One bolt hole appears to even line up, maybe that one should get a long stud installed in the head to align the whole assembly.
It wouldn't be ideal with the 951 runners versus the 16v port size but it'd work and be cheap...
Spencer, I think the issues are cost and production volume. I have the solidworks file for a 16V adapter flange that could be welded to a 951 intake but the cost in getting them produced has kept me from getting it done. And it wouldn't even be hard, have a machine shop mill the old flange off of the 951 intake and then TIG weld the new flange in place. You could make a wooden jig and have the whole thing done in an afternoon. But it comes back to the difficulty in manufacturing the flanges.
A friend laser cut some 16V exhaust flanges as a test for me to see if it's feasible to adapt to the OEM exhaust components. I'm happy to report that with very little effort (use a die grinder to remove the welds on the factory crossover flange) you can replace them with a flange that mates up to the 16V headers. Unfortunately, the cost in going from mild steel flanges to 304/321 stainless is exponential and doesn't lend itself well to a cost-effective solution for most. In order to make it cost effective to produce, the modified factory crossover would have to sell for $600+ and that leave a profit margin of around $100 which isn't much. Machine shops in the DC area aren't inclined to take on a small volume project for their CNC mills without charging a massive setup fee.
This probably isn't the right thread for all of the above information but it's a topic I've been researching and exploring for the last few years.
Spencer, I think the issues are cost and production volume. I have the solidworks file for a 16V adapter flange that could be welded to a 951 intake but the cost in getting them produced has kept me from getting it done. And it wouldn't even be hard, have a machine shop mill the old flange off of the 951 intake and then TIG weld the new flange in place. You could make a wooden jig and have the whole thing done in an afternoon. But it comes back to the difficulty in manufacturing the flanges.
A friend laser cut some 16V exhaust flanges as a test for me to see if it's feasible to adapt to the OEM exhaust components. I'm happy to report that with very little effort (use a die grinder to remove the welds on the factory crossover flange) you can replace them with a flange that mates up to the 16V headers. Unfortunately, the cost in going from mild steel flanges to 304/321 stainless is exponential and doesn't lend itself well to a cost-effective solution for most. In order to make it cost effective to produce, the modified factory crossover would have to sell for $600+ and that leave a profit margin of around $100 which isn't much. Machine shops in the DC area aren't inclined to take on a small volume project for their CNC mills without charging a massive setup fee.
This probably isn't the right thread for all of the above information but it's a topic I've been researching and exploring for the last few years.
If you look back a few months Tom MGuinn shared something called "Big Blue Saw", a waterjet service that you send them your CAD file and they waterjet the piece out of whatever material you want for a good price.
Spencer, I think the issues are cost and production volume. I have the solidworks file for a 16V adapter flange that could be welded to a 951 intake but the cost in getting them produced has kept me from getting it done. And it wouldn't even be hard, have a machine shop mill the old flange off of the 951 intake and then TIG weld the new flange in place. You could make a wooden jig and have the whole thing done in an afternoon. But it comes back to the difficulty in manufacturing the flanges.
A friend laser cut some 16V exhaust flanges as a test for me to see if it's feasible to adapt to the OEM exhaust components. I'm happy to report that with very little effort (use a die grinder to remove the welds on the factory crossover flange) you can replace them with a flange that mates up to the 16V headers. Unfortunately, the cost in going from mild steel flanges to 304/321 stainless is exponential and doesn't lend itself well to a cost-effective solution for most. In order to make it cost effective to produce, the modified factory crossover would have to sell for $600+ and that leave a profit margin of around $100 which isn't much. Machine shops in the DC area aren't inclined to take on a small volume project for their CNC mills without charging a massive setup fee.
This probably isn't the right thread for all of the above information but it's a topic I've been researching and exploring for the last few years.
Would you share the file? Is it just a cutout design from a stainless steel plate, or is it 3D requiring CNC? If it is only cutout, I could probably have a batch made on water cutter.
I just bought 400V 350A water cooled AC/DC TIG welder and will try to produce my own 16v stuff.
We make custom manifolds all the time for all kinds of applications, it is the easiest part. And usually the less expensive way.
Regarding S cams, when you say it has overlap, then retarding it won't give you anything good. You should try to set LSA to acceptable level, but trust me, stock NA cams are usually 95% the best cams you could get for a turbo car. Todays modern turbos have good efficiency and you can use quite big turbo and still have excellent response, that means you have less backpressure and can have more overlap. It's a huge number of choices that will make for satisfying (for specific owner) result and what works for some, may not be good enough for other.
Check out the exhaust set up with a 86 944 8v head and a 928S 16v head from 85,86. I'm thinking the turbo exhaust will bolt right up without any issues.
The 944 NA head and the turbo head are the same head design. Don't know how a turbo head on a NA Car would give any less power.
For one thing the ceramic coating (Liner) and lower CR. 944 NA motors either have 9.5 -1 and 10.2 -1 vs the turbo head with 8.0 -1.
Lowering the CR and restricting the internal volume = loss of power on a non forced induction motor. Feel a tad silly posting this, but saying they're the same forced me to respond.
I'm sure I'll hear, "It's the piston, not the head that changes the CR." Well, this is definitely part of the equation. If these engines were easy to make power, we'd all have 400whp reliable cars like the EVO folks with just a flash and exhaust.
08-20-2015, 11:30 PM
Trust me, this can be done:
