HPR states -

"HR3 TT/aggressive trail/Race cams. $395. This is where other camshafts get left behind! fast accelerating all around camshafts improve power 3-5hp throughout the rpm range on a stock ds650. Gains are amplified on modified motors. Gains are concentrated on the mid range, top end and overrev. A good cam even for stock engines, but designed for single carb, higher compression stock bore pistons, with or without porting. Also ideal for big bore trail engines with lower compression and/or heavier riders. Heavy duty valve spring kit and shim under bucket conversion kit required $415. Total kit price $745"


I was wondering about the statement for HR3 cam, "Gains are concentrated on the mid range, top end and overrev."

Cams usually effect 3K rpm range, and these sound like they will help 2K to 8K range. Are they just moderated over a longer range, or accented on 2.5K to 5.5K and the momentum once going seems like it will help in overrev? I was wondering for a street bike if they would run out of gas on top end. The mid range sounds good, and maybe you can only expect one or the other but the ad sounds almost like everything above idle would be affected.

It would be hard to tell on atvs maybe because your guts are being bounced so hard at top end, it may be hard to hold it there for any period of time to truely wind it out completely (an assumption).

A comparison with the stock cam would be nice on similar bikes around stage 2 development to understand how the output would be different and at what rpm ranges.


Thanks

 

First I will say that I have no personal knowlege of this cam... so I will just kind of think out loud, or on paper, or keyboard, or whatever. So here goes. The add does say that it is for aggressive trail. That tells me that the it is not ALL about the top end power.. that would be the HR4's. If you are looking for pure top end I would look there.

Second there are many situations where ATV's operate in mostly top end... specifically the wide open dunes. That is why so many "duners" actually seek products designed for drag racing. WOT is what we are working with most of the time in the dunes. I rarley use only partial throttle... in the dunes its all about pinning it, all or nothing. On the trail a better low end and mid range would be the ideal. IMHO your assumption about truley "winding out" the engine is not accurate. Many duners spend their whole day "wound out," in huge bowls where top end power is the key. I assume that is why HPR makes the different grinds that they distribute. The aggressive trail cams would have a different focus than the drag race cams.

I am not sure what you are looking for but the description of each cam should lead you in the right direction. It all seems fairly logical.

I think your question about "running out of gas on the top end" is more a question about what you are working with currently. If you are feeling that you fall short on your top end then maybe you should have a look at the HP4's... but I really think that all depends on what type of riding you are doing. Some riders want the low and mid range power to get up to speed, and some want the top end power to hit hard when you are already at speed. I think when you said "maybe you can only expect one or the other" you were right. While I would expect small gains at a larger range of RPM's the true focus of the cam would be in a specific RPM range.

Thanks for reading my ramblings.

 

Thanks Fatholly,

that makes sense.

Wouldn't it interest you to see a stock cam stage 1 bike vs HR3 dyno comparison? Its almost legendary in my mind,
and I have nothing to realistically back it up yet.

And then to show the capability range, maybe a stage 2 bike stock cam vs HR3 comparison?

4 dynos assuming perfect runs and that would show the world what all the talk is about.

(and then HR4 cam could be with Stage 2 and Stage 3 bikes - 4 perfect tests).


Thanks

 

You said you are into statistics in another thread so I will take it one step further... I would like to see these tests run on at least three different dynos with a minimum of four runs per dyno. That should give a good statistical range and provide a statistically relavant sample. We could then figure a standard deviation to guage the true average and accuarcy of each dyno and bike. Will that ever happen... probably not, but I'd love to see the results if it did.

 

It would n't be an exact partial factorial design, but with those 8 runs, you could have a great deal to compare with and validate.
HPR's dynos are the best and their repetition in experience makes their runs good as gold. In total 3 different stages of bikes and 2 cams. You would know them inside and out as far as how robust they are.

People want to know(!), what will it do for me now, and what will it do for me later???? :-o