Date: 20 Dec 1998 08:49:59 GMT From: Bob Noble <the.nabobnopsamdnet.att.net> Subject: Re: Turbocharged Engine pings under boost
In one of my previous lives I played around quite a bit with Corvairs - the poor man's Porsche. Blowing was native to the cars and we all had to try and do it better. While this was in the bad old days of decent gasoline (leaded), the only effective way to avoid trouble was with water injection. This was used a lot on aircraft engines in WWII - both before and after. Usually a 50/50 mix of water and alcohol. The whole idea is to increase charge density, a quick fix to preignition problems. We used mini beer kegs (about one gallon, I remember) and managed the injection rate by having the blower pressurize the tank as it blew into the engine. Blow against any convenient "nozzle" that's no more than a cap on your injection tube, which runs into the intake line at almost any point upstream of the blower itself and after the air cleaner. With only 7 psi, you could likely start really small - say .010". We had one Corvair Club member that was running higher and higher with his engine on a stand when he hit 30 psi and melted an exhaust manifold. Messy, but engine and owner came back for more eventually. bob noble Reno, NV Firestarter wrote: > > I recently installed sort of a home grown turbo system on my car. It > really runs great but it starts to ping when it reaches maximum boost. > > The reason I am posting this message in the Saab and Volvo newsgroups > is because they are two of the most popular turbocharged makes sold in > America. > > Here's the specs: > > Car: 1980 Fiat 2000 Spider > Engine : two liter twin cam > fuel delivery system: Bosch L-jetronic FI > Compression ratio: 8.1:1 (stock C/R) > Maximum Boost: 7 pounds > Turbo: Rayjay 301F > Fuel enrichement device: rising rate fuel pressure regulator > engine managment system: J&S Safeguard knock retard device > > First of all: > > I retarded the static timing to 5º BTDC which is 5º below factory > spec, put some octane booster in the tank and even cranked up the fuel > pressure a bit but it still pings. > > I installed a $400 J&S knock sensor to prevent this but I can't seem > to get it adjusted properly. > > If I turn the sensitivity dial all the way down, it doesn't pick up > the ping (I've got a meter that tells me how much the timing is being > retarded). > > if I turn it up even just a bit, it picks up all kinds of weird noises > under slight acceleration and starts backing off on the timing upto > 20º long before I reach any boost. > > So either it's picking up false noises or my engine pings under even > slight accleration and I really have problems that I don't know about. > > Here's what I want to know. > > What kind of C/R and boost pressure do Saab and Volvos run? I do > realize that these cars use a knock sensor. > > According to several sources, an engine with a C/R of 8.1:1 using 92 > octane gasoline should be able to handle 7 pounds without an > intercooler with no problems of detonation. > > From what I remember, the engine doesn't start to ping until I hit > maximum boost which means I can turn the wastegate down to 4 pounds > (it has a range of 4 to 7 pounds) and it would probably be OK. > > But I really want to run 7 pounds because more pounds = more power but > on the same token I don't want to burn my engine up. > > Then again it's been in the 50s today so 4 pounds be OK in this > weather but in the summer when it's 95ºF, I don't know what is going > to happen. > > I've got an adjustable (0.5 to 24 pound) pressure switch, which I am > thinking about using to trigger the cold start valve which will dump > fuel into the engine under boost. > > I've got it already mounted after the throttle body. > > I did a test before the turbo installation and triggered the cold > start valve under wide open throttle with my fog light switch and it > tended to flood the engine out but it may work fine under boost. > > I also have an air fuel meter guage and can say that the ping is not > caused by an overly lean mixture. The mixture is around 14.1 under > maximum boost. > > Seems like I read somewhere that under boost, a mixture of 12.1 to > 13.0 is the right range under boost so maybe that is the trick to > getting rid of the detonation. > > Sorry for posting all of these figures in pounds per square inch but I > am not familiar with BAR because I live in America. If someone knows > the formula to convert PSI to BAR, please post so I can convert these > figures. > > Any ideas to stopping detonation are appreciation. > > Due to the overwhelming amount of SPAM I receive, send replies > via email to mailto:firestarternopsamcron.com > > ------------------------------------------------------------ > > 1980 Fiat 2000 TURBO Spider (Fuel injected) Summertime daily driver > 1981 Fiat 2000 Spider (Dual 40 webbers) Growl! > 1981 Fiat X 1/9 (Fuel injected) Slot car like handling > 1994 Jeep Wrangler (2.5 liter) Wintertime daily driver > > Get your own Forwarding address : http://www.netforward.com/ > > ------------------------------------------------------------
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