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Date: Sat, 19 Dec 1998 11:08:03 -0800
From: Stan Weiss <srweissnopsams.com>
Subject: Re: Turbocharged Engine pings under boost


One thing that you have not looked at is camshaft timing, even without the turbo on a compression gauge with 8.0:1 cr different intake duration/opening events will show different pressure. Stan Chris Wilson wrote: > 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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