10 replies to this topic

[hhhh]

Has anyone produced dyno curves of the RS vs. the RS+ camshaft on the same motor? I'd really like to see a direct comparison. I'm going to be building a 1293 for the street and am torn between the two.

 

I used to a run a 1380 with a 731 that actually turned 8000 RPM and went very well, but have concluded that kind of RPM is not the best for the road. I'm going to have a hard time getting the high RPM out of my system so I'm tempted to go with the RS+, but on the other hand I could always fit 1.5 rockers down the road if the RS isn't enough. 

 

Thoughts or comments?

[carbon]

Timing for a 731 cam advanced 5 degrees: 29-59 in, 64-24 ex. Lift for both in & ex at lobe = 252 thou

 

Timing for RS+: 29-59 in, 64-24 ex. Lift for both in & ex at lobe = 314 thou

 

So if you were previously running a 731 with 1.5 rockers, then the RS+ with std rockers might give fairly similar performance?

[hhhh]

Thanks! Interesting comparison. Actually I was running 6% offset rockers, so 1.3 at best maybe on the 731. Vizard didn't have much good to say about the 731, but maybe it's just suffering from lack of lift. It never should have performed up to 8000 RPM though. Not sure what to make of that. That 1380 was a real screamer with a DCOE45, LCB, and around 10:1 and enlarged valve 12G940.

Edited by hhhh, 04 December 2017 - 08:47 PM.

[Cooperman]

Even in 'the day', the 731 was not a very good cam. It seemed to destroy a lot of bottom end whilst not doing much for the top end. Personally I preferred the old 510 Cooper 'S' cam which gave great torque at mid-range.

 

For a road cam you won't notice much difference between cams such as the RS+, the Kent 266 or one or two others (despite what others might have to say about it!). Go for good torque at mid-range as that is where you will be driving the car most of the time. Just build a nice smooth engine with good torque.

[hhhh]

I have a feeling modern cams have quicker lift and slower drop at the tail end, i.e., fatter, less pointy lobes which account for the better low RPM torque while still working at higher RPM.

[whistler]

If memory serves the 731 cam was used in Formula Junior Racing in the late '50's early '60's. As Cooperman said, not a very popular cam for the Mini. Before the 510 'S' cam most Mini's I knew of either ran the 649 or the milder 544. Those engines were running on low final drives for Rallying in the lanes.

[Cooperman]

The 544 was good in its day when the transmission had a SC CR gear set and a low FDR, like 3.9:1. 

 

It is easy to go OTT on a cam for a road car, but in all honesty, unless you are doing timed runs or laps of a track, in normal driving the small differences won't be noticable. In fact, it is build quality which is important.

[ACDodd]

The rs+ Is much more 'cam' than the RS. The RS has a smooth idle and pulls from idle up. The RS+ needs 2krpm to get going and has a lopey idle. The rS+ is much faster opening rate and moves the inlet valve 20% more than the old 731. Nothing like that same rate of movement and not in the same league the reason the 731 is a lame duck is that it moves its valves less than a stock 850 cam, from the overlap point to full lift!! The RS cam actually has a faster opening rate still, and is the cam I use in road based engines, where average torque between 2 and 5krpm is needing to be maximised. Best used with 1.3 rockers for maximum average torque.

Ac

Edited by ACDodd, 04 December 2017 - 11:18 PM.

[hhhh]

Thanks for chiming in AC. So the RS cam is a faster opening rate than the RS+?

[ACDodd]

Yes.

Send me an email, and I'll send you some info.

Ac

[ACDodd]

Email info sent.

Ac