cam or case differences 69 vs.71

[ThumpStreet]

Need some IronHead education from the community.As I dive into the engine overhaul of my 69 XLCH,which cams I'm going to use comes to fore front of build planning.Sifting through the droves of available cam shafts available on the market,I start noticing that cam application have differences between 1969 and 70-71 models stated by the suppliers.I would much appreciate some input from members experience as to what these differences are.Is it the cams themselves? Is it in the timing case cover or the crankcase? Is there reasonably easy modification to make any cam set work from say years 1966-1976?Lastly,any opinions as to what cam set up was found to work best for street application utilizing stock bore/stroke,Tillotson carb,lightly modified heads, dynamically balanced crankshaft,stock air cleaner and stock independant dual exhaust.Thanks in advance for any replies and information.Peter

[sportsterpaul]

For me the best cam is a stock P-cam. Any other choice involves sacrificing low-end to get more horsepower at the top, while making the idle, off-idle, and driveablity worse. When you go high-lift you also reduce reliability and insure you will be doing more valve jobs.

If the factory could make the bike "better" by changing the shape of the cam, it would, its a no-cost change. The cams they have, (once Sifton taught them) are pretty good. If you like keeping the bike at 6000RPM and don't mind it takes longer to get up to that speed, then put in some "horsepower" cam.

My engine shop buddy talked about how Ford would put in bigger valves and wider ports, just so they could advertise a few more horsepower than Chevy. But horsepower is a stupid number, and has little to do with how the engine runs in all regimes in all conditions. Heck, it was Jerry Branch that had to teach the factory that smaller high-velocity ports can be far superior.

Now do bear in mind that Harley's sloppy manufacturing means no P-cam will act the same. The rocker box gasket affects valve geometry, and there is a reason engine builders have a cut-open rocker box so they can put an indicator on the valve tip to see what is really going on. If I remember right-- the P-cam was based on a Sifton grind, so I am sure Sifton still sells that grind and I am sure the cams at least are more uniform, although there is no way to compensate for all the other sloppiness in an Iron Sportster engine.

[ThumpStreet]

Thanks Paul,Makes perfect sense that stock is best all around if the bike is to be ridden in street conditions.I had been thinking about Andrews R5 cams as they advertise more torque through higher lift and shorter duration.I believe you are accurate in stating there is always compromise with changes made.Pete

[EKHKHK56]

Cams are like the bowtie that finishes the tux you wear. It ties the engine package together and sets the tone for how the engine runs. Cams change engine characteristics in two ways. They set the rpm range for where the engine spends most of its usable HP time and they set up the usable torque curve of any engine. Cam selection is based on what rpm you want your motor to run efficiently taking into account valve and port size and static compression ratio. The cam is the most important selection of all the engine components. An engine tuned to run 6,000rpm + constantly will be set up camwise quite differently than one that needs to accelerate smoothly from 600 rpm. Regardless of other engine components the cam sets the tone for engine efficiency at the rpms you choose. You can have big valves and ports and and still have a smooth running engine that pulls strong from idle by limiting the duration, regardless of lift. Or with same specs but long duration you will move the usable powerband much higher which is great for racing. You can wake up a small valve motor with bigger cam lift and duration but it only helps if run at high rpm and will not be happy idling or off idle. Any duration increases lower the compression ratio. This can be good if you have high compression pistons and need to lower the numbers say for pump gas. On the other hand if you have long duration and high lift cams you need to raise the compression to compensate for effective performance. Cam selection is based on balancing what rpms do I want to use with this engine normally and what size valves, ports, and compression do I have to start with. It cam be camfusing at times yes. P cams work great for all around riding with a stock Sportster engine. Erik K

[ThumpStreet]

Thank you gentlemen for the information and recommending that P cams are indeed a good all round choice.For my situation also the most economical as the cams that were installed as received are stock P cams in good shape.Quick question...Has anyone any experience with the Andrews R5 cams in a pre 70's Sportster with mildly ported heads(accomplished by previous owner)?I've got more investigating to do on what has actually been done to the heads.I'll be there soon,for now I'm prepping the crankcase for all things that rotate.

[8ball]

i didnt notice this part answered... you want the early set in any case wether you keep stock p's or other. "nose cone" cover cams wont fit mag/timer cam covers... actually i think its really just #2 and 4 that differ but you get the idea

[ThumpStreet]

Thanks for the verification of that cam detail.I'd been thinking the magneto drive was the difference but experienced knowledge defines what works,what can be made to work if there benefits to be found,and what flat out does not work. Peter

[DaveC]

Regarding cams, Jerry Branch recommended the Andrews V-9 cams, which are hotter that the R-5's for all iron Sportster applications. In his XR-1000 hop up booklet, he shows dyno data for a stock 1000cc XL and a modified (ported heads, big valves, straight pipes and V-9 cams, S&S shorty carb) XL. The RWHP jumped from 50.2 to 62.1 @ 6750 RPM with those mods. I have the V-9's, bored out carb and big valves in my stroked XLCR and it pulls very well. A modified XR-1000 pulled 95.7 RWHP and 75 ft-lbs. of torque at that RPM. That is why I ride the modified XR-1000. Twist and shout.

[ThumpStreet]

Dave,Will Andrews V9 cams work for a magneto Sportster?The application chart I have shows the X grind as the most radical Andrews has available for 1957-1970 XL engines.Can the V9 cams be modified for use?All very interesting.Thanks for the responses.Peter

[DaveC]

The V-9's have slightly more lift and less duration Than the X grind. I have ridden both and the V-9's provide more low and mid range torque than the X grind. Check with Kirk Kelly at Sporty Parts for availability as I belueve he is amn Andrews dealer.