Anyone ever built a 1760cc engine or have any info on one?
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Re: Anyone ever built a 1760cc engine or have any info on on
When you say the cam comes with a 4 crank degrees advance built in what does that really mean?
- Marc
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Re: Anyone ever built a 1760cc engine or have any info on on
As a rule, "straight up" cam timing (for conventional cams with symmetrical lobes and identical intake & exhaust duration) comes when the intake-opening event occurs the same number of degrees before TDC as the exhaust-closing event occurs after TDC...the first link I gave you on degreeing a cam covers that pretty well.
If you'll look at the cam card for the FK65 (the second link above), you'll see that both events occur 4° sooner than they would with "split overlap" timing (for this cam, that would be I.O. at 10°BTDC and E.C. at 10°ATDC)
The most significant event is the point of intake closure. At lower speeds, the sooner the intake shuts the sooner the compression of the fuel/air mixture can commence, which raises peak cylinder pressure and therefore power output. Conversely, at higher RPM the cylinder will fill more completely if the intake closure is delayed, to take advantage of the momentum of the incoming charge...retarding the cam lowers the amount that the mixture is compressed, but since it allows more to get in there'll be more power produced anyway (at higher RPM - at low RPM a retarded cam results in "soggy" response).
When a cam is ground so that the valve events come sooner in relation to crankshaft position, it's done to enhance low-end performance with some sacrifice of top-end.
4 crankshaft degrees isn't a lot and generally won't make a dramatic difference, but if one were to advance the timing even more with an adjustable gear it could conceivably cause the condition you report....but inadequate valve springs are a more likely cause. Springs have harmonic frequencies where they lose a significant amount of their strength; with dual springs the harmonic of the inner and outer will be at different RPM so they can cover for each other, but with singles it's not unusual for the weak point to occur at a relatively low RPM. My son had a 1995cc engine in his bus with an Engle W-100 (a stock-rocker cam with similar characteristics to the FK65) and it had no problem at all reaching 6000 RPM using dual springs - that's why I expect more from your cam, even though they're both intended for ~5000 RPM applications.
If you'll look at the cam card for the FK65 (the second link above), you'll see that both events occur 4° sooner than they would with "split overlap" timing (for this cam, that would be I.O. at 10°BTDC and E.C. at 10°ATDC)
The most significant event is the point of intake closure. At lower speeds, the sooner the intake shuts the sooner the compression of the fuel/air mixture can commence, which raises peak cylinder pressure and therefore power output. Conversely, at higher RPM the cylinder will fill more completely if the intake closure is delayed, to take advantage of the momentum of the incoming charge...retarding the cam lowers the amount that the mixture is compressed, but since it allows more to get in there'll be more power produced anyway (at higher RPM - at low RPM a retarded cam results in "soggy" response).
When a cam is ground so that the valve events come sooner in relation to crankshaft position, it's done to enhance low-end performance with some sacrifice of top-end.
4 crankshaft degrees isn't a lot and generally won't make a dramatic difference, but if one were to advance the timing even more with an adjustable gear it could conceivably cause the condition you report....but inadequate valve springs are a more likely cause. Springs have harmonic frequencies where they lose a significant amount of their strength; with dual springs the harmonic of the inner and outer will be at different RPM so they can cover for each other, but with singles it's not unusual for the weak point to occur at a relatively low RPM. My son had a 1995cc engine in his bus with an Engle W-100 (a stock-rocker cam with similar characteristics to the FK65) and it had no problem at all reaching 6000 RPM using dual springs - that's why I expect more from your cam, even though they're both intended for ~5000 RPM applications.
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Re: Anyone ever built a 1760cc engine or have any info on on
E10 doesn't have much to do with the compression ratio - that's related to the octane number which can be obtained with or without Ethanol, but it more to do with the age/composition of the rubber etc. The older rubbers and seals were not designed to resist alcohol (Ethanol), but the newer stuff is. Even then, E10 doesn't usually cause many problems for the older rubber, but E85 certainly can be a problem (85% Ethanol).advinnie wrote:Cheers for the reply here in the UK I don't believe that they tell you if the fuel your using is E 10 or not. I've heard bad things about E10 it's fine in a high compression system but in a low compression system it can do some bad things like eat away at the fuel lines, destroy carbs and there gaskets and so on
I tried to remember whether the UK listed E10 on the pumps - my wife and I had a great holiday there last year but we had a diesel motorhome (Elddis/Renault), so we weren't looking at the petrol pumps - only the diesel.
Here in Aus all E10 pumps are clearly marked, and the sign board at the servos/gas stations/garages (pick your language usually list the price of E10 separately - it's usually about 2c/litre cheaper than similar octane straight petrol.
Regards
Rob
Rob and Dave's aircooled VW pages
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Rob
Rob and Dave's aircooled VW pages
Repairs and Maintenance for the home mechanic
www.vw-resource.com