Date: Sat, 19 Dec 1998 13:32:32 -0000 From: chrisnopsam-net.com (Chris Wilson) Subject: Re: Turbocharged Engine pings under boost
In article <36854b94.359059810nopsam.preferred.com>, NOSPAMnopsamAM.com says... > 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. Ok,here are some ideas.Turbo engines usually hit detonation problems at maximum *torque* where cylinder pressures are highest.Your CR is a bit high,unless you were to run a proper mapped ignition and fuel system. Ideal is to fit a fully mappable fuel/ignition system like a Motec...expensive! You could drop the CR,by machining the pistons or the head chambers...time consuming,maybe a full engine strip The most cost effective is to put an ignition only management on it,and map the ignition curve.It will want to be retarded considerably around maximum torque,but pull back up quickly as the engine reaches its less efficient top rpm peak.Ideally the ignition system should measure boost,so as not to retard when off boost,cruising. I assume you are in the US,so I can't recommend any makes of system available over there.The UK had a Micro Dynamics ignition retard device,that was switched in via a single stage pressure switch.Crude,but it worked ERL (http://www.aquamist.co.uk) used to do a ten stage 3D mappable ignition controller (I have one),that was boost aware,and it could be set using 10 pre set pots,no software involved at all.I don't know if they do them. Talking of the above URL,you might want to try water injection as a detonation suppressant.This works really well.Water and an intercooler *might* allow you to run the setup as is,depends on how much detonation you are seeing.Detonation can kill a turbo engine in seconds,don't let it ping if you can possibly avoid it. Hope this helps you. -- Best Regards, Chris Wilson http://www.f3.u-net.com mailto:chrisnopsam-net.com
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