SE .575 Cams and SE .536 Cams

 

HD recently started offering a new set of XL performance cams, dubbed the "High Output" cams. Like all the modern XL cams, they fit all the way back to 1991 models when used with an appropriate pinion gear.

 

We were curious how these cams would stack up to the venerable favorite cam grind of the SE family, the SE 536. We've used the SE 536 with excellent results for many years and this new grind looks, on paper, like it might work a little better. The intake lobe is 2 degrees broader on each end, opening sooner and closing later, than the 536. The exhaust lobe is very similar, just advanced a couple degrees, which helps lower the troublesome TDC lift figure of the 536. But most interesting of all is the additional lift of this new grind. Head porting and larger valves tends to help heads more at higher lifts, and a relatively narrow, broad grind like this offers the possibility of more power across the spectrum.

 

The test mule chosen was a typical 100hp XL motor equipped with our Stage 2 head work and an NRHS/Axtell 1250 kit. Like all standard Stage 2 heads, these were set up to accommodate up to .600 valve lift and have moderate seat pressure suitable for typical street performance cams, along with Ti retainers and 10 degree locks. The rest of the valvetrain consists of stock pre-00 lifters, Hurricane fixed length pushrods, and stock rockers.  

 

We baselined the bike, swapped the cams, and dyno tested again within about a 3 hour time frame, on the same dyno with the same operator. No other changes were made to the bike except for a one-size jet change that the air/fuel monitor said we needed when we went to the new cams (the timing was optimized for each grind as well). Here's the result:

 

 

As you can see, the 575's give up nothing to the 536's at any rpm (don't read too much into that low rpm advantage, the throttle is being rolled on at that point and the repeatability is poor). But the 575's had a clear advantage on top.

 

The lobe shape is not particularly aggressive on these new cams. The chart above shows no signs of seat bounce despite the moderate spring pressure. Valvetrain noise is also very similar between the two grinds.

 

So it looks like SE has come up with an attractive new cam grind for XL's, one that's mild enough to not require an expensive cast of supporting components and yet offers a very real performance advantage over the 536's.

 

Both of these cam sets and many others are available from NRHS. See our camshafts page.

 

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