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My porsche 944 S2 16 valve turbo project

 
Old 09-09-2013, 05:34 PM
  #46  
szabon
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Any updates on this?
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Old 09-09-2013, 06:12 PM
  #47  
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Yep Tim's giving me all the best bits off it, he just doesn't know about it yet .
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Old 09-15-2013, 06:30 AM
  #48  
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I'd heard on the grapevine that something went wrong and the engine is no more. Please say this isn't so
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Old 09-15-2013, 07:01 AM
  #49  
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The last time I spoke to Tim he was waiting for some new parts and it will be going into his car.
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Old 09-15-2013, 08:42 AM
  #50  
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Be good to get an update on where Tim is at with this motor.
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Old 09-15-2013, 01:44 PM
  #51  
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I'm fairly sure there will be less revs and boost involved in the future...
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Old 09-15-2013, 01:54 PM
  #52  
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Originally Posted by blade7 View Post
I'm fairly sure there will be less revs and boost involved in the future...
Had a failure?
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Old 09-15-2013, 02:09 PM
  #53  
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I think Tim pushed it on the dyno to see what it would do, running 500+ bhp on the road was unlikely.
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Old 09-15-2013, 10:35 PM
  #54  
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Sid and Shawn's route appears to be the way to go on these big HP motors for the street.
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Old 09-16-2013, 08:50 AM
  #55  
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Wow, I missed this back in spring - good to see people doing the 16v thing the right way!!
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Old 09-16-2013, 10:49 AM
  #56  
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Originally Posted by Chris White View Post
Wow, I missed this back in spring - good to see people doing the 16v thing the right way!!
Was it worth sacrificing 300cc for the rod ratio in your opinion ?
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Old 09-16-2013, 12:27 PM
  #57  
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Originally Posted by blade7 View Post
Was it worth sacrificing 300cc for the rod ratio in your opinion ?
depends on the goal. You can run higher RPM with the shorter stroke - but I don't know if the raised rpms make up for the lower displacement.

BTW - running higher RPM with less displacement is better for head gasket / head lifting issues. more firing events but less peak pressure in each event.
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Old 09-16-2013, 08:06 PM
  #58  
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Originally Posted by Chris White View Post
depends on the goal. You can run higher RPM with the shorter stroke - but I don't know if the raised rpms make up for the lower displacement.

BTW - running higher RPM with less displacement is better for head gasket / head lifting issues. more firing events but less peak pressure in each event.
I'm going to throw my thoughts in here on this, as well. To answer Chris' "does it make up" question, displacement was a secondary question to me relative to valve area. A few examples of produciton engines when I was at Ford were the 4.6L and 5.4L engines. They made very, very close to the same power with the same heads, be they 2V, 3V, or 4V. The differences could be accounted for with induction and exhaust losses, for the most part.

But it all boils down to somethign called "Z-Factor" which is similar to the average port velocity during an entire intake event divded by the speed of sound. And the port doesn't care what is below it. One of the first rules of thumb I'd use is 1#/min of airflow is equal to 10 horsepower. That's rough. More clarity is ISAC - indicated specific air consumption. Again, units are pounds of airflow (per horsepower-hour).

So what that all means is that you have roughly the same horsepower potential with a 3.0L as a 2.7L with the same head. It just happens at a different RPM point. This is very rough, there are a great many other factors that come into play - cam events, intake and exhaust tuning, and internal friction.

I am not a fan of oversquare engines, unless it is a 2V chamber. On our engines, you've got GOBS of potential for valve area. In this case, a 968 head may be a better choice, as the 37mm intakes are probably best sized for a 2.5L, whereas the 39's are best for a 3.0L, for the RPM ranges mentioned in the initial parts of the thread. Well, with a 104mm bore, you've got room for even bigger valves.

What it boils down to in my mind is that with a smaller bore, you are going to be more robust to detonation, and can run a higher compression ratio. Yes, your friction will go up a little, but in my mind it is a worthwhile tradeoff.

So if I had my druthers, moving from a 2.5L to a 3.0L, in this specific case, I'd rather do it ALL with stroke (or a 2.7/2.8 if doing one, but not the other). You need the same valve area to do it, regardless. But in doing it with bore, you are going to run into mechanical issues trying to hit an RPM point before you run out of airflow. I'd rather run out of airflow before oiling capability of valve float.

Agree with Chris on the cylinder pressure, but countering that is the dwell. Again, when you get the piston further from TDC more quickly, you'll be less likely to detonate. You have a more favorable (i.e. smaller) surface area/volume ratio.
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Old 09-16-2013, 10:53 PM
  #59  
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Harry:

As always, pleasure to read your insight!
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Old 09-16-2013, 11:01 PM
  #60  
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Originally Posted by URG8RB8 View Post
Sid and Shawn's route appears to be the way to go on these big HP motors for the street.
BTW, fundamentally Duke's new race motor is a Hybrid Stroker
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