The 87' 5-speed is home
04-13-2009, 11:03 AM
#46
Nordschleife Master
Thread Starter
Greg:
So is your opinion that one should use the GTS crank for an engine with redline at about 7300? I get your point about the rod-to-stroke ratio, but I am worried about the piston speed and the rod bearing loads. Are those not a problem? Porsche did significantly lower the redline for GTS relative to GT, did they not?
The GTS crank would allow one to use lower compression height pistons. The compression height would go down from 42.6 of S4 to about 35.6 of GTS. This in turn would mean lighter pistons, which would be good. But I doubt that the lightening can fully offset the increase in loads which go up by the factor of (85.9/78.9)^2. Is this correct?
Thank you very much for the GTS head info! I'll see what I can learn from the printed material and the GTS head gasket.
So is your opinion that one should use the GTS crank for an engine with redline at about 7300? I get your point about the rod-to-stroke ratio, but I am worried about the piston speed and the rod bearing loads. Are those not a problem? Porsche did significantly lower the redline for GTS relative to GT, did they not?
The GTS crank would allow one to use lower compression height pistons. The compression height would go down from 42.6 of S4 to about 35.6 of GTS. This in turn would mean lighter pistons, which would be good. But I doubt that the lightening can fully offset the increase in loads which go up by the factor of (85.9/78.9)^2. Is this correct?
Thank you very much for the GTS head info! I'll see what I can learn from the printed material and the GTS head gasket.
Tuomo I will try today to email you the info your require, I am on a slow wireless connection at this time. As to needing a smaller stroke for the higher revs, I can't agree and Darin Morgan certainly wouldn't agree either. Let me elaborate. The 928 has a very high rod to stroke ratio as it came from the factory.
What is becoming evident is certain rod to stroke ratios work better at certain rpm ranges. This is why in the Engine masters challenge, the winners always have low rod to stroke ratios. Their competition is limited to 6,500 rpm and they have rod to strokes around the 1.5 to 1.6 range. The standard rod to stroke is 1.9, the GTS is less, as the stroke is longer and the rod length the same therefore around 1.75
As such the standard rod to stroke is suitable for a 9,500 to 11,000 rpm engine. The GT3 engine has a 1.75 ratio and my stroker engine the same. This allows for an engine to be built for around 7,500 to 8,500 rpm. I would have thought that is the area you would want to operate in? Although I would keep it in the lower part of the range due to the heavy nature of the GTS crank.
Also the GTS pistons are a bit lighter than your S4 and will be higher comp, so all good there. The rod to stroke ratio issue is a relatively minor issue not a deal breaker as such but there is evidence to support correct piston speed relative to valve timing, i.e draw on the cylinder heads and turbulence as the piston approaches TDC, complete cylinder filling etc to support doing things this way. There has been some abandonment of the Smokey Yunich practice of putting the longest rod you can in there.
Mind you there has been considerable improvements made in material technology and design to support higher mass forces, so I am not being critical of Smokey.
I don't have any affiliation with the seller although he is one of the true original 928 pioneers and will be well known to many members of this board.
Greg
What is becoming evident is certain rod to stroke ratios work better at certain rpm ranges. This is why in the Engine masters challenge, the winners always have low rod to stroke ratios. Their competition is limited to 6,500 rpm and they have rod to strokes around the 1.5 to 1.6 range. The standard rod to stroke is 1.9, the GTS is less, as the stroke is longer and the rod length the same therefore around 1.75
As such the standard rod to stroke is suitable for a 9,500 to 11,000 rpm engine. The GT3 engine has a 1.75 ratio and my stroker engine the same. This allows for an engine to be built for around 7,500 to 8,500 rpm. I would have thought that is the area you would want to operate in? Although I would keep it in the lower part of the range due to the heavy nature of the GTS crank.
Also the GTS pistons are a bit lighter than your S4 and will be higher comp, so all good there. The rod to stroke ratio issue is a relatively minor issue not a deal breaker as such but there is evidence to support correct piston speed relative to valve timing, i.e draw on the cylinder heads and turbulence as the piston approaches TDC, complete cylinder filling etc to support doing things this way. There has been some abandonment of the Smokey Yunich practice of putting the longest rod you can in there.
Mind you there has been considerable improvements made in material technology and design to support higher mass forces, so I am not being critical of Smokey.
I don't have any affiliation with the seller although he is one of the true original 928 pioneers and will be well known to many members of this board.
Greg
04-13-2009, 11:29 AM
#47
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Also, it looks like, if the hole in the bumper cover is, to you, unsightly, that if you rotate the stock rear license plate frame by 180 degrees the license plate will move "up" and closer to the top of the cavity in the bumper cover so as to cover up the hole for the tow eye.
04-13-2009, 11:50 PM
#48
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Tuomo and I spent almost four hours tonight crawling around his new 5-speed. Given the age and mileage I'd have to say that this is the best preserved '87 I've seen. While it has a few of the afflictions that are common to 928s of this age, it does not feature most of them. All the rubber and harnesses are in good shape both under the car and in the engine compartment. Suspension in good shape. With one exception all the engine bits and pieces are working perfectly and are serviceable.
It looks like this car, despite growing up in Michigan, didn't see very many cloudy or rainy days and didn't get out into the cold often either.
Definitely a well-purchased 5-speed. And I've seen folks start out with a lot worse for the same or more money.
It looks like this car, despite growing up in Michigan, didn't see very many cloudy or rainy days and didn't get out into the cold often either.
Definitely a well-purchased 5-speed. And I've seen folks start out with a lot worse for the same or more money.
04-14-2009, 07:54 AM
#50
Nordschleife Master
Thread Starter
Option codes
Doing all the checks with Dave C was a lot of fun last night. I think I learned a fair bit, and there's definitely a lot more to be learned.
Dave just emailed me the photo of the option codes, in case anyone is interested. I understand that most people probably aren't! ;-)
139 Seat Heating - Left
158 Radio "Monterey" - 86 "Reno" - 87
220 Locking differential
302 Type designated on rear end
340 Seat heating - Right
347 Platinum anodized wheels
418 Protective side mouldings
474 Sport shock absorbers
481 5 speed manual transmission
490 Hi-Fi sound system
494 2 speakers on back shelf
513 Lumbar support - right seat
533 Alarm system
537 Left seat with positrol and lumbar
538 Right seat with positrol and lumbar
570 High output air conditioner
586 Lumbar support - left seat
650 Sunroof
C02 Equipped with catalytic converter
Dave just emailed me the photo of the option codes, in case anyone is interested. I understand that most people probably aren't! ;-)
139 Seat Heating - Left
158 Radio "Monterey" - 86 "Reno" - 87
220 Locking differential
302 Type designated on rear end
340 Seat heating - Right
347 Platinum anodized wheels
418 Protective side mouldings
474 Sport shock absorbers
481 5 speed manual transmission
490 Hi-Fi sound system
494 2 speakers on back shelf
513 Lumbar support - right seat
533 Alarm system
537 Left seat with positrol and lumbar
538 Right seat with positrol and lumbar
570 High output air conditioner
586 Lumbar support - left seat
650 Sunroof
C02 Equipped with catalytic converter
04-14-2009, 08:43 AM
#51
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Heated seats, I'm jealous!
Seriously, Dave is **** and if he says your car is one of the nicest he's seen then you really did well. Looking forward to seeing it this spring/summer.
Seriously, Dave is **** and if he says your car is one of the nicest he's seen then you really did well. Looking forward to seeing it this spring/summer.
04-14-2009, 11:04 AM
#52
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Oh man 87 5 spd with Lsd. Rare bird indeed. Once again, does the rear wing flip and what are the engine numbers as well as the last 4 of the vin? There weren't many of these if you have these things as well.
04-14-2009, 11:21 AM
#53
Nordschleife Master
Thread Starter
No flipping wing and yes plastic oil filler neck. Oil squirters uncertain.
04-14-2009, 11:50 AM
#55
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04-14-2009, 12:11 PM
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I am ****. That is why I wrote "the best preserved '87 I've seen." Tuomo's '87 has been very well treated. Better than most of this age and doesn't need, presently, tons of work. However, there are '87s that are nicer because they have undergone extensive restoration work.
04-18-2009, 06:37 PM
#59
Nordschleife Master
Thread Starter
Base case dyno runs
I did pulled some quick dyno runs this afternoon. The car has a "chip" and RMB, which amounts to being basically stock. The only known engine problem is that the flappy only operates about 50 degrees and doesn shut down completely. The flappy problem increases the the valley in the torque curve a bit. The runs show about 265hp and 276 ft-lbf. In my judgment, this is about normal for a 67k miles car that originally produced about 318hp at the crank. Anybody disagree?
Last edited by ptuomov; 08-27-2009 at 08:25 AM.
04-18-2009, 07:30 PM
#60
Race Director
I did pulled some quick dyno runs this afternoon. The car has a "chip" and RMB, which amounts to being basically stock. The only known engine problem is that the flappy only operates about 50 degrees and doesn shut down completely. The flappy problem increases the the valley in the torque curve a bit. The runs show about 265hp and 276 ft-lbf. In my judgment, this is about normal for a 67k miles car that originally produced about 318hp at the crank. Anybody disagree?