They don't. My jump from 865 cams to 790 cams yielded 4 ft-lbs peak torque and 5 RWHP:I have the 790 cams. How do the 865 cams compare to these?
the lobs are built up then the whole thing is reground and reharden.They seam to last as long as stock.I guess that this is half on topic, if not I apologise in advance.
Presumably a 'performance' cam has more material in most if not all places, higher peek & fuller profile to give more lift earlier. How is this achieved using a stock cam? I can only imagine either material is added or the base circle is reduced
you do gain below 5000rpms with the right setup with 813 cams maybe all 813 cams arent like the ones you saw the spec for who knows.BUT to get any big gains in torque you got to go with more cc.At the risk of upsetting the "powers that be" I'll dare risk a comment on a cam thread. There are some potential benefits from having your original cams reground as opposed to doing a core exchange particularly if your engine has a few miles on the clock. An often overlooked factor in swapping cams is the straight cut gears that drive the cams, these gears "mate" over time just like any other break-in process and any mismatch between these gears is a potential source of valve train noise which usually presents as a high pitched whirr or whistle. Mismatched gears will eventually "mate" over time and the noise will reduce but if you use your original cams you know for sure that you are not going to experience this problem.
The above is a particular problem with Thunderbike cams as the billet material used to machine the cams from is very hard and the bedding in process between the cam gears and the OEM central driving gear is very slow. I've had Thunderbike cams fitted for over 30,000Klm's and the noise has just started to abate recently but when the cams were first fitted there was a definite high pitched "whistling" noise emanating from those gears that was very disconcerting.
I've measured Thunderbike cams against early 790 cams and yes there is not a lot of difference but the Thunderbike cams do have slightly more lift, slightly more duration and slightly wider lobe centres. Having seen the specs for 813 cams I would suggest that the Thunderbike cams are approximately halfway between the early 790 cams and 813's. I would also suggest that the only way you would tell any difference between these cams as far as performance delivery goes is on a dyno. The primary advantages of Thunderbike cams are that no core exchange is required (a privilege you pay for) and that they are machined from billet so they are much stronger than the OEM cast cams.
Regardless of what anyone tells you any gains in low to mid range performance from Thunderbike or 813 cams alone is minimal to say the least. Noticeable performance gains start at about 4,500rpm and rocket skyward from there. There is little point in adding any of these cams unless you raise the rev limit to take advantage of the increased top end breathing. Having said that a set of FCR carbs should be mandatory once you have fitted either of these cams.
If you are looking for increased performance in the mid range (3,000 to 5,000rpm) I would advise you look at a grind designed to increase mid range torque specifically rather than top end power. Neither the Thunderbike cams or 813's meet that criteria.
All of the above is my personal opinion based on my personal experience however YMMV. I'm very happy with the results:-
http://www.youtube.com/watch?v=r6vc0IEg5so
I'm not disagreeing with you but I'd like to see the before and after dyno charts.I run TPUSA; 813 cams, Plus-Pro Street Head, 903 Big Bore Kit w/Hyde Lightened Flywheel and 39CR Smoothbores. The single addition of the 813 cams, gave an honest 20% increase in hp/tq nearly across the board.
Where did you get this information from? Can it be verified?The original Thunderbike cam specs came from TPUSA. Then were slightly changed, so they wouldn't get sued.
That's about where the Thunderbike cams come "on cam" so I can imagine the 813's would behave in a similar manner however I'm sure that a dyno chart would reveal that the greatest improvement occurs higher in the rpm range. My experience is that that is the case with Thunderbike cams anyway.The gains from the 813 cams are most noticeable around 4500-5000 rpm
I don't want to argue with you Mike but I've been fooling with engines long enough to know that when it comes to cams alone you cannot increase HP at the top end without sacrificing the loss of some low end power. There's no magic in this, you simply rob Peter to pay Paul. Yes you can make other modifications that will increase volumetric efficiency at lower rpms and thus regain the power lost in that rpm range by altering the cam profiles but that increase is down to those mods not the cam.you do gain below 5000rpms with the right setup with 813 cams
Specs can be changed at a moments notice. I do know that the 813 specs I saw are no different to cam profiles that have been in use in the industry for years, even before Hinckley Bonnevilles were even thought of. No magic here the grind has been around for years.maybe all 813 cams arent like the ones you saw the spec for who knows.
Agree 100%.BUT to get any big gains in torque you got to go with more cc.
In this particular case you can't reduce the base circle by anything significant as this would require thicker shims to maintain correct valve clearances. Most reground cams are welded to build up the lobes then ground to a specific profile and then hardened. Done properly this process has proven to be very durable.I guess that this is half on topic, if not I apologise in advance.
Presumably a 'performance' cam has more material in most if not all places, higher peek & fuller profile to give more lift earlier. How is this achieved using a stock cam? I can only imagine either material is added or the base circle is reduced
Oh...okay. It's your story.The original Thunderbike cam specs came from TPUSA. Then were slightly changed, so they wouldn't get sued.
Lawrie,I don't want to argue with you Mike but I've been fooling with engines long enough to know that when it comes to cams alone you cannot increase HP at the top end without sacrificing the loss of some low end power. [/B].
Torque cams have less duration and tighter lobe separation angles than those for making peak RWHP. For our machines, my guess is that the 790 cams are the best torque cam grind for an off-the-shelf cam...though I didn't really give up anything down low when I went to the 813 cams. If I did lose torque, it wasn't noticable on either the dyno or in street use.So, if a person wanted a cam ground with mid range power in mind rather than top end,
what cam would that be, and what other mods would help achieve that? I know more
cc's will do it in terms of total torque: I'm thinking in terms of how to achieve the
maximum mid range power for a given displacement.
Thanks Mike, so they are metal sprayed (or something similar) then re ground and the base circle remains as per spec'.the lobs are built up then the whole thing is reground and reharden.They seam to last as long as stock.