i am pretty pleased - new motor coming together |
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i am pretty pleased - new motor coming together |
Scott S |
Apr 8 2010, 07:51 PM
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#1
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Small Member Group: Members Posts: 1,697 Joined: 30-April 03 From: Colorado Member No.: 633 |
I just finished the final grinding on the new fan shroud for the intakes today. Then I had to take everything apart to clean up the dust (that took another hour and a half - sheesh). Just as I was finishing up, the fed ex guy showed up with what became my intake screens. I am really pleased with the end result!! I am just a flywheel and a throttle linkage away from being all done - then I get to start on the chasis....
Attached image(s) |
J P Stein |
Apr 9 2010, 08:55 AM
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#2
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Irrelevant old fart Group: Members Posts: 8,797 Joined: 30-December 02 From: Vancouver, WA Member No.: 45 Region Association: None |
Here's something you may find interesting.
A dyno graph with back to back runs with different intake set-ups above the carbs. The blue line is with open stacks. The red line is with a stock 911 airbox with a bellmouth mounted instead of the snorkle and a K&N replacement filter rather than stock. I wouldn't have believed it. Attached thumbnail(s) |
ArtechnikA |
Apr 9 2010, 07:15 PM
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#3
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rich herzog Group: Members Posts: 7,390 Joined: 4-April 03 From: Salted Roads, PA Member No.: 513 Region Association: None |
Here's something you may find interesting. A dyno graph with back to back runs with different intake set-ups above the carbs. The blue line is with open stacks. The red line is with a stock 911 airbox with a bellmouth mounted instead of the snorkle and a K&N replacement filter rather than stock. I wouldn't have believed it. The discontinuity betweenn 5500 and 6000 is unfortunate. The peak numbers are really close. I need to look at things more closely but what jumps out is that the open intake is just a bit too rich for max power. But the plenum effect is not news. Air has a lot more mass than you think of at first, which is why wind power is so attractive... And at intake velocities (about Mach 0,5) there is significant momentum to the airstream. It's be _really_ interesting to see manometer readings comparing airbox pressure to atmosphere. Once you get a stream of air moving into the plenum, it tends to keep moving, so even when one intake valve closes, another is opening (and this is one reason why 6's are so much smoother than 4's - you make power over about 120º of crankshaft rotation...). With 6 individual throttle bodies, the best any can expect is to gulp in from atmospheric. In a plenum, each cylinder can take advantage of the momentum generated by the previous cylinder's intake airstream momentum. Sizing is critical, but I believe this graph is evidence that Porsche got it right. BTW - if you compare the Inglese photographs with the others, and cross-reference 'Prepare To Win' you will be reminded that Carroll Smith observed 25 years ago that the intake stack must have a full radius on the entry, and that 'only Porsche and Ferrari' really grasped the concept. |
J P Stein |
Apr 9 2010, 11:11 PM
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#4
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Irrelevant old fart Group: Members Posts: 8,797 Joined: 30-December 02 From: Vancouver, WA Member No.: 45 Region Association: None |
[The discontinuity betweenn 5500 and 6000 is unfortunate. The peak numbers are really close. I need to look at things more closely but what jumps out is that the open intake is just a bit too rich for max power. I'll wager about any amount that if you run carbs on your motor, you will run as rich as I did.....it is purposeful.. Theory is all well & good, but real life tells the tale. The AF ratio on the graph ain't worth printing. Bad location on the probe...it runs way richer than that down low and again, there is a reason. he real average is pretty flat at around 12:1 from a previous test with a better sensor set up. Wide guts ar 16:1 will make your motor make *very* rude noises. |
ArtechnikA |
Apr 10 2010, 04:45 AM
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#5
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rich herzog Group: Members Posts: 7,390 Joined: 4-April 03 From: Salted Roads, PA Member No.: 513 Region Association: None |
The AF ratio on the graph ain't worth printing. I agree the numbers are cr&p - i wasn't buying 16:1... But something (efficiency...) has to account for the HP differences so the AFR curves might be useful for comparison, numbers aside. In a lot of ways, it does show what we've felt intuitively - a street airbox improves driveability in street rev ranges ( <5000 ). Over that, it starts to hold you back, compared to open intakes. I believe you could make a plenum sized for 6000-8000 rpm, but the factory one isn't it. I also believe that if Porsche's dyno testing showed they could get more HP on the RSR engines using an air filtration system, they'd have run them at Daytona and Sebring especially, but LeMans and Nürburgring too. |
J P Stein |
Apr 10 2010, 09:43 AM
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#6
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Irrelevant old fart Group: Members Posts: 8,797 Joined: 30-December 02 From: Vancouver, WA Member No.: 45 Region Association: None |
The AF ratio on the graph ain't worth printing. I agree the numbers are cr&p - i wasn't buying 16:1... But something (efficiency...) has to account for the HP differences so the AFR curves might be useful for comparison, numbers aside. In a lot of ways, it does show what we've felt intuitively - a street airbox improves driveability in street rev ranges ( <5000 ). Over that, it starts to hold you back, compared to open intakes. I believe you could make a plenum sized for 6000-8000 rpm, but the factory one isn't it. I also believe that if Porsche's dyno testing showed they could get more HP on the RSR engines using an air filtration system, they'd have run them at Daytona and Sebring especially, but LeMans and Nürburgring too. It's all in what you want for your application, IMO. The motor was built for mid range torque which, IMO, is the cat's ass for autocross. (street driving also) You spend little time at the top end but nearly all the time in mid range. Picking up 5-8 ft lbs in mid range was a pleasent surprise. I'd gladly trade that for an equal of HP loss at top end. For bragging rights, HP sells but torque wins. (IMG:style_emoticons/default/biggrin.gif) As for air filtration, Porsche's racing applications are meaningless for the rest of us.....unless you rebuild the motor after each race....and/or sell the car after one use. |
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