| MayanArch |
Posted
Friday, Jan 21st 10:45pm [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 76
Florida, USA
Baur E21 2.7 1982, Baur E30 318i 1985, 323i 1978 |
At what point does the cam start to produce a rough idle in the baby six? 288? |
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| Marquis_Rex |
Posted
Saturday, Jan 22nd 3:51am [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 180
UK
BMW 323i 2.7-as featured in Total BMW Nov 2002,Porsche 911/993TT |
According to Schrick themselves- the amount of lift you should NOT exceed at TDC to avoid rough idle speed running is 2.3 mm.
This is the figure they quote for a 2 valve engine with "solid lifters"- which ours strictly speaking isn't- but I don't think the valve actuation makes that much difference.
Now the Schrick 284 duration cam is quoted as having 2.2mm lift at TDC and the 288 period is quoted as having 2.8 mm of lift.
My current 2.7 litre engine uses a Schrick 284 camshaft and the rev counter needle at 850-900 rpm is steady but you can definately feel reverberations in the seat- although some of this is because I run my car quite lean at part load operation.
This is a general guideline though and I've heard of a few people using 288 period cams successfully with a slightly lopey idle. I wouldn't go above 288 period and retain K jetronic and our current design or intake manifold- as the K jet metering baffle is likely to get unsteady from reverse flow pulsations.
Good tubular tuned exhaust manifold design combined with low back pressure exhaust helps smooth out idle too.
You can go for a higher TDC lift figure/longer duration if you use port throttles, but then again typically port throttles aren't compatible with K Jetronic Fuel injection. |
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