From: mlschmidt@sprintmail.com Sent: Tuesday, October 08, 2002 10:31 PM To: 928 Subject: [928] Dyno Results I finally got around to getting my car on the dyno to see the results of the changes that were made. These included changing the cam timing, changing the engine breather system around, and making a full sump baffle and crank oil scrapers. The car is my 1988 928S4 with an automatic transmission. The best SAE rear wheel corrected numbers I ended up with were 300.9 hp and 317.2 ft/lbs. The uncorrected numbers were 309.8 hp and 326.5 ft/lbs. Those are the best horsepower and torque figures I've gotten to date. I'm thinking that's about all I can do without going into more involved stuff, like different cams, head modifications, a different intake, stroker motor, or supercharging. Mike Schmidt '88 928S4 Auto Black/Black "PORSCHE" cloth 928 Owners Club Charter Member PCA Chicago Region From: mlschmidt@sprintmail.com [mailto:mlschmidt@sprintmail.com] Sent: Wednesday, October 09, 2002 6:25 AM To: 928 Subject: [928] Re: Dyno Results >..Would you mind explaining to the class how you have rerouted the >breather system for your vehicle Mr. Schmidt? Those, my good old Chi-Town >friend, are some damn fine numbers. >This Does, of course, include your Dastek piggyback computer? > >Thanks Mike, for the info, >Brendan Campion >San Diego Yes, I do still have the Dastek on the car for tuning with the stock chips and stock fuel pressure regulator. For the breather system I put one of the metal oil filler necks on the car when I had the intake off. I added a fitting to each side of the oil filler neck for a 5/8" hose, and plugged the two stock fittings at the base of the filler neck. I made two air/oil separators and mounted one on each side of the intake manifold's side plates. A short piece of hose runs from each of the fittings that I added to an air/oil separator. Another short piece of hose runs from each valve cover up to the air/oil separator on that side of the engine. A 5/8" hose runs from each of the separators to a fitting that's welded into the header collector on that side of the engine. The rear fitting in the passenger side valve cover and the hole in the rubber elbow between the MAF and throttle body are both plugged, and so is that small hose attached to the driver side of the oil filler neck. The fast moving exhaust gas flowing through the header collectors causes a low pressure, and draws the blowby gasses out. I get a 3"-4" Hg vacuum in the crankcase like this. Vacuum in the crankcase is supposed to be good for some power because of better ring sealing, a reduction in the amount of oil spinning around with the rotating assembly, and thinner air for the rotating assembly and pistons to move against. I also don't have the blowby gasses going into the intake. That means more room for fresh air/fuel mixture, and also no more oil going into the intake. Oil going into the intake lowers octane, and also takes up space that could otherwise be fresh air/fuel mixture. As those that drove behind me at the Fall Sharks in the Mountains drive could tell you, the current system does have at least one drawback to it. The air/oil separators are too horizontal the way that I have them mounted now on the sides of the intake. When flooring the gas pedal while going up a good hill, a little bit of oil can run towards the back of the separator and end up going into the exhaust. It's only a very very small amount of oil, but it doesn't take much to make a very very big cloud of smoke. I'm going to be changing the air/oil separators so that this doesn't occur anymore, and may also try something else I have in mind to try and get more vacuum in the crankcase. Mike Schmidt '88 928S4 Auto Black/Black "PORSCHE" cloth 928 Owners Club Charter Member PCA Chicago Region From: Wally Plumley [mailto:wplumley@bellsouth.net] Sent: Wednesday, October 09, 2002 8:27 AM To: 928 Subject: [928] Re: Dyno Results >Vacuum in the crankcase is supposed to be good for >some power because of better ring sealing, a reduction in the amount of oil >spinning around with the rotating assembly, and thinner air for the >rotating assembly and pistons to move against. I also don't have the blowby >gasses going into the intake. That means more room for fresh air/fuel >mixture, and also no more oil going into the intake. Oil going into the >intake lowers octane, and also takes up space that could otherwise be fresh >air/fuel mixture. > and may also try something else I have in mind to try and get more >vacuum in the crankcase. One warning: The crank and cam oil seals are lip seals, designed to hold the oil in. If you put too much vacuum in the crankcase, the seals will be pulled away from the sealing surface, allowing dirty air to dump grit directly into the bearings. This is NOT a good thing! Possible (non-trivial) answers include changing to O-ring seals, or adding reversed seals to the outside of the existing seals. Just one more complication to add to your much higher exhaust emissions .... Wally From: mlschmidt@sprintmail.com [mailto:mlschmidt@sprintmail.com] Sent: Wednesday, October 09, 2002 2:46 PM To: 928 Subject: [928] Re: Dyno Results >One warning: >The crank and cam oil seals are lip seals, designed to hold the oil in. If >you put too much vacuum in the crankcase, the seals will be pulled away >from the sealing surface, allowing dirty air to dump grit directly into the >bearings. This is NOT a good thing! Too much vacuum in there is no good for a few different reasons. The optimum is supposed to be about 12" Hg on a wet sump engine. I'm at 3"-4" Hg now, and can't imagine I'd get to even the 12" Hg level unless putting on a dedicated vacuum pump designed for that purpose. > Those are some pretty good (great) dyno numbers. coupled with the fact > that the auto trans cars always seem to produce less rear wheel hp do to > inefficiencies, your motor is right up there at the top!!! > what else have you done to the motor. > cam timing: Hp gains? > headers: > intake mods, what type? > etc I retarded the cam timing by 3-4 degrees. This doesn't really increase overall power, but kind of tilts the power curve to provide a little more top end at the expense of some bottom end. Peak torque occurs at about 3,000 RPM. When the transmission shifts, the RPMs never drop back down that low in the next higher gear. At full throttle the only time the engine sees peak torque is in first gear. I had plenty of torque down low, so I retarded the cam timing to get a little more torque at the higher RPMs, where it would potentially be able to be used in three gears instead of just one. Realistically it's more like two gears though, and not even that in everyday use. On the dyno third gear was enough to go more than 145 mph, so full throttle fourth gear isn't exactly something that's going to occur too often. Shifting the torque curve would also reduce the wheel spin I was having when flooring it from a dead stop. The two humps of the torque curve are closer to the same level now. I don't know if that's from the second hump being increased, or from the whole curve being higher, and the first hump being decreased in relation to the whole curve in general. Just stating maximum numbers might not really give the whole story a lot of the time because of the shape of the curves. Mine is actually pretty flat. Even when starting dyno runs as low as 1,000 RPM, the torque curve never drops below an SAE corrected 285 ft/lbs until over 5,000 RPM. On a couple of runs where I went that high, it's still making more than SAE corrected 280 hp at over 6,600 RPM. I have the Devek stage2 headers. The exhaust is all 2.5" mandrel bent pipe, an "X" pipe, Bullet brand mufflers in the center muffler locations, and two resonators in the rear muffler location. There have been no real intake modifications except for the modified airbox I made. Those airbox modifications included making a spacer to raise the air filter slightly, and increasing the radius of the hole in the base of the airbox. Those are things that have been on the car for quite a while. The new modifications were the cam timing change, breather modification, and the full oil pan sump baffle and crank oil scrapers I made. Mike Schmidt '88 928S4 Auto Black/Black "PORSCHE" cloth 928 Owners Club Charter Member PCA Chicago Region