difference between cams

[Czekus21]

What is the difference between cams from the XJ and the SF??
Will one work in the other? Are they the same size? Will a rejetting need to happen by switching one for the other?? Are there any benefits by switching one to the other??

[TopCatGr58]

Hey Steve,

I remember XSDAN posting a great discertation on the differences between the early model cams and the later ones.

IIRC, the later ones have a slightly lower cam lift, and shorter duration. You've got the hotter earlier cams in your 79SF, I don't think you'd get any performance boost from the XJ's cams!

Would be good to do a search for cam differences, might find the post, makes great reading, I should have saved it for inclusion in the tech tips?!
T.C.
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I found it, was 2nd page of Maximan's Mega Hot Of the Dyno thread!
Dan Hodges spake this!

I have several set's of cam's both early and late and the cam journal's are all within one thousand's of one another.You can check the shop manual to verify this. I also have three set's of pristine head's and the journal's are within spec from journal to journal.The 78-79 cam's will make 3-5 hp more in the 5000 rpm and up range vs the 80 and up cam's.I used 78 cam's in my 81 for sometime before I bought a set of hardweld cam's.I sent a set of used cam's from a 79 motor to have the cam's hardwelded and reground.I installed them and they have over 5000 mile's on them at this time and are perfect.I bought a ton of part's just so I could compare all this stuff because the dealer was too stupid and could not answere all these question's.Yamaha went to the big valve head's because when they removed the big cam's for emission's purposes they gutted it.The head's got some of it back,but not all.The early cam's have 12 degrees more duration and tighter lobe centers than the late one's and will definately help the top end,but no they are not as strong from 4000 rpm rolls in high if you do that sort of thing.An eleven has lot's of midrange to begin with but need's top end,so a cam change is in order for you, especially with the 1180 motor.More cubic inches without better breathing will only make more low and midrange,but little if any more on top.

[Czekus21]

Thanks. That's what I thought but wasn't sure. I did put a dial caliper on them and they showed a little difference. I'll check the 79 cam with a better dial caliper and put those numbers agianst the book for max run out.