Friday, April 18, 2014

Lift graph for 4V Desmoquattro cams using strada inlet cam as exhaust cam

I thought I'd post a graph here for a conversation that I've been having with someone about using the 4V Desmoquattro strada inlet cam as an exhaust cam.  I haven't tried this personally, but have been told it works well.

In the graph, you can see the exhaust cams on the LH side.  The yellow curve is the G, the corse exhaust cam used from 1992 (888 SPS had it too) until the last of them in 2000.  They obviously liked it.  The 916/999SPS exhaust cam (blue), while having much less duration, has a fairly similar shape and compared to the pink strada exhaust curve, is completely different.  The strada is much slower opening, with what is called an asymmetric profile.  The point of this graph, the red line, is the strada inlet cam being used as an exhaust.  Profile wise it is very similar to the SPS up to peak lift, although it doesn't hold the peak or closing profile as long.  But much better than the strada exhaust, and the SPS cam set does work very well.  It's not a straight fit, the closing lobe needs to be narrowed and the opening rockers need some grinding at the feet.  But well worth the effort given the cost and complete unavailability of the SPS cams.

How much input the SPS inlet has over the strada inlet in comparison I don't know.  The extra high lift duration of the SPS inlet is something the specs don't show on their own, and that sort of extra area under the graph can only be good.  The orange curve is the 748RS '506' cam, shown because there's some on Ebay at the moment and duration wise they only have 5 degrees more than the SPS and 11 degrees more than the strada.  They do have a lot more lift, and are quite aggressive acceleration wise.  But if you kept them to around 10,000 rpm, not the 13,000 or so they would have seen trying rather vainly to keep the Japanese 600's in sight, they won't be too destructive I'd think.

Doug Lofgren's cam page has more info on them too, with cam doctor graphs.

No comments: