Fact or Myth


30 replies to this topic
  • Yamaryder29

Posted December 30, 2011 - 07:49 AM

#1

I know this has been talked about many of times, but I haven't really found the answer I'm looking for.

I have a stock 2008 yz450f with a full fmf system. The bike produces tons of power and handles very well. I'm very happy with it.

I have recently heard that swapping the cams out for stock 06 cams will increase the power. Is this true? or does it just change the power output? As far as I can tell my 08 with the full fmf puts out more power than an stock 06

Another question I have is... will swapping the cdi or coils with the 06 do anything?

Any input is greatly appreciated.

  • 2grimjim

Posted December 30, 2011 - 07:59 AM

#2

The CDI from the '06 will add a little more low end. The cams were also a different part number on the '08. You should see a little gain in bottom end with a cam swap too.

  • grayracer513

Posted December 30, 2011 - 08:16 AM

#3

The fact is...

Swapping '06 cams will not increase peak power, and in fact, doing so will cost you about 1-2 HP at peak. It does, however produce a wider power curve with a stronger lower mid range. The '06 (and '07) cams were the same lobe profile as the 5TA cams used in the '03-'05 YZ450, but each of the two later cams were retimed with slightly narrower lobe centering than the previous year. A compromise move on the cams is to use only the exhaust cam from the '06. This retains more of the peak power while still increasing power at the lower end of the curve.

As to the coils or CDI, the coils are the same so there's nothing to be gained by replacing them one with the other. Coils won't increase power or performance beyond the point where they are strong enough to reliably provide ignition anyway, regardless of claims to the contrary. The CDI, however, contains the information by which the ignition timing advance curve is controlled, and there is a definite difference between the '06 unit and the later ones.

In fact, swapping to an '06 CDI by itself will do more for the low and mid range of the '08-9 models than either cam swap by itself (swapping cams without changing the CDI would be a disappointment). This used to be THE low cost mod for the '08, but the price of used units went up quite a bit as the mod became more popular and the supply went down. An alternative is an aftermarket multi-mapped or programmable unit like the Dynojet Power Commander.

  • Yamaryder29

Posted December 30, 2011 - 08:26 AM

#4

I was hoping I would hear from grayracer. You answered any questions I may have had. Thanks man!!

  • Yamaryder29

Posted December 30, 2011 - 08:42 AM

#5

One more question for you. How would the effect of installing a hotcams exhaust cam compare to a stock 06 exhaust cam? any thaughts?

  • grayracer513

Posted December 30, 2011 - 08:57 AM

#6

A HC stage 1 cam for the '03-'05 would, it seems to me, cross over the the "curve" from the '03 to the '08 OEM cams. I believe that the original Stage I cam is less aggressive than what you currently have in the engine, and would "probably" be something like installing an '06 cam in your engine. But before I made that statement as hard info, I'd need to see grind info, etc. At this point, that's just a guess, and you'd be better off checking with the cam grinder themselves, or with someone who's tried it.

  • 2grimjim

Posted December 30, 2011 - 09:27 AM

#7

Swapping '06 cams will not increase peak power, and in fact, doing so will cost you about 1-2 HP at peak. It does, however produce a wider power curve with a stronger lower mid range. The '06 (and '07) cams were the same lobe profile as the 5TA cams used in the '03-'05 YZ450, but each of the two later cams were retimed with slightly narrower lobe centering than the previous year.


So the lobe centers are closer on all the 5TA cams than the 2S2 cams? (lower number). There were 2 revisions of the 5TA cams; '03-'05 (original), '06, and '07. I know that that Yamaha tinkered with lobe centers to work with the corked-up exhaust (the '07 wasn't too bad, but the '08-'09 exhausts were horrible). Opening up the lobe seperation would be the obvious change to deal with a restrictive exhaust and would explain a lot why the '08-'09 get better peak numbers when the exhaust is opened up.


A compromise move on the cams is to use only the exhaust cam from the '06. This retains more of the peak power while still increasing power at the lower end of the curve.


I'm not really sure that that this would be a cost effective mod. Probably the easiest and cheapest way is to press off the intake cam sprocket and reduce the lobe center. Of course, this would require access to a hydraulic press, a degree wheel, and dial indicator.

In fact, swapping to an '06 CDI by itself will do more for the low and mid range of the '08-9 models than either cam swap by itself (swapping cams without changing the CDI would be a disappointment). This used to be THE low cost mod for the '08, but the price of used units went up quite a bit as the mod became more popular and the supply went down. An alternative is an aftermarket multi-mapped or programmable unit like the Dynojet Power Commander.


I checked Dynojets website and didn't see any progrmmable CDI's, just stuff for FI bikes.

  • Yamaryder29

Posted December 30, 2011 - 10:34 AM

#8

I think I'll just try the 06 cdi as I really don't have a problem with my bike now. I was more interested in the knowledge. For $65 plus shipping, I can get a 06 cdi. From what I've read from other TT testimonials, this seems like a nice low end improvemnet for the cost.

Thanks for the info guys. Very helpful as always.

  • grayracer513

Posted December 30, 2011 - 01:43 PM

#9

So the lobe centers are closer on all the 5TA cams than the 2S2 cams? (lower number). There were 2 revisions of the 5TA cams; '03-'05 (original), '06, and '07. I know that that Yamaha tinkered with lobe centers to work with the corked-up exhaust (the '07 wasn't too bad, but the '08-'09 exhausts were horrible).

No. The lobe centers on the '08 stand at 100 degrees, whereas the '06 was 105 degrees. The reason Yamaha closed up the lobe centers was to squeeze more top end power out at the expense of low end.

Opening up the lobe seperation would be the obvious change to deal with a restrictive exhaust and would explain a lot why the '08-'09 get better peak numbers when the exhaust is opened up.

But, as I said, they closed the lobe centers in '07 and again '08 (in addition to changing the grind), and the '08-'09 does not get better peak numbers from changing to a more open exhaust in most cases. It's the mid range that improves. Only when a full system is used with a smaller header is there a chance to gain on top.

As far as pressing off the cam sprockets to alter timing, that's a simple process on the intake (although it should always be tack welded once reinstalled), but it's a considerably more complicated exercise on the exhaust with the auto decompression system in place. The assembly itself isn't too bad, but the timing change can require correcting the decomp pin length, which in the case of moving from 100 to 105 (advancing the cam), would mean adding material to the pin.

  • 2grimjim

Posted December 30, 2011 - 04:03 PM

#10

No. The lobe centers on the '08 stand at 100 degrees, whereas the '06 was 105 degrees. The reason Yamaha closed up the lobe centers was to squeeze more top end power out at the expense of low end.


But, as I said, they closed the lobe centers in '07 and again '08 (in addition to changing the grind), and the '08-'09 does not get better peak numbers from changing to a more open exhaust in most cases. It's the mid range that improves. Only when a full system is used with a smaller header is there a chance to gain on top.

As far as pressing off the cam sprockets to alter timing, that's a simple process on the intake (although it should always be tack welded once reinstalled), but it's a considerably more complicated exercise on the exhaust with the auto decompression system in place. The assembly itself isn't too bad, but the timing change can require correcting the decomp pin length, which in the case of moving from 100 to 105 (advancing the cam), would mean adding material to the pin.


You have my curosity piqued now.

If you're referring to the data from MXA's website, I'm not sure that their reference to "event angle" has anything to do with lobe center.

http://motocrossacti...tting-5584.aspx

I'll confess that I haven't put a degree wheel on a stock YZ cam (at least '07 or newer ones), but I have access to an '09 and '07 that I will be taking notes from when I get the chance.

From all of the tuning I have ever done and published information I've read, as well as the reccomendations from every cam manufacturer I've dealt with, reducing the lobe center (mostly on the intake) improves mid range power and increasing the lobe center sacrifices low end for top. Reducing the LCA on the intake is referred to as advancing the cam and increasing the LCA is retarding the timing.

http://www.lunatipow...mSpecTerms.aspx

As far as a smaller header is concerned, throttle response and midrange power will be helped. But for a builder just looking for peak numpers, a larger diamater is always going to produce better peak numbers assuming the engine has apropriate matching components (I'm refering to an engine that is not stock).

Yamahas main reason for going to the giant header was to increase exhaust volume and recover some of the lost performance from the corked-up muffler (didn't work). A smaller header just happens to work well with an aftermarket muffler with OEM cam grinds and stock porting.

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  • grayracer513

Posted December 30, 2011 - 07:39 PM

#11

If you are thinking of "lobe separation", the degrees of crank rotation between the intake, then that's not what I'm talking about, nor what MXA is talking about. I'm speaking in terms of the lobe center relative to TDC. It's not a particularly good way to compare one cam to another, but it's useful as a reference when changing cam timing on the same grind.

You're correct about the reason for the larger header, except that it did work in the sense that the bike was able to produce 52 HP with a rag stuffed in its backside, but the smaller header/freer muffler works well in combination with a lot more cams and port setups other than stock. That said, the three valve intake port is far easier to screw up than it is to improve, and porting one is a job best left to those who have found the right combination with their own money.

  • 2grimjim

Posted December 30, 2011 - 08:09 PM

#12

I understand the difference between lobe seperation (LSA) and lobe centerline (LCA). If what MXA is describing is LCA then it is contrary to everything I have ever learned on the subject over the last 30 years.

Like I said, I'm intrigued. If that is the case, I'm going to dust off the degree wheel and do a little checking.

It's too bad Yamaha doesn't put part numbers on their cams. I have 5 sets of OEM 450 cams in boxes and no way to id them..... Dammit!

  • grayracer513

Posted December 30, 2011 - 09:30 PM

#13

You're most likely aware that a common trick with the original non-auto decomp cams in the WR426's and pre '03 WR250F's was to retard the exhaust cam (NOT the intake) a full tooth to convert to YZ timing and pick up more high end performance, right? What does that do to the exhaust lobe centerline?

Yep.

  • camman

Posted December 31, 2011 - 09:55 AM

#14

Lobe separation angle doesn’t really apply to a twin cam engine as the intake and exhaust lobes ARE NOT on the same shaft. LSA is typically used on cams that have both intake and exhaust lobes on the same shaft. Also, LSA is really just a quality control measurement for cam grinding. I should also point out that valve centerline is nothing more than splitting the valve open and valve closing point (typically .040") in two. There is nothing magical about centerlines. Your engine doesn’t breath off centerlines. It breathes off opening and closing. Centerlines are convenient for describing whether the cam was advanced or retarded - that is pretty much it.

  • grayracer513

Posted December 31, 2011 - 11:24 AM

#15

I should also point out that valve centerline is nothing more than splitting the valve open and valve closing point (typically .040") in two. There is nothing magical about centerlines. Your engine doesn’t breath off centerlines. It breathes off opening and closing. Centerlines are convenient for describing whether the cam was advanced or retarded - that is pretty much it.

That, of course, is correct, and is what I was getting at. The lobe center in fact may not even split the opening and closing points in two even halves in the cam was eccentrically ground, although that sort of thing is not very common. It's a much easier reference to use in adjusting the cam timing than the opening/closing points are because it takes the quieting ramps out of the question.

As you and I have both essentially said, it can't really be used to compare one cam to another that is differently ground, so it's a little bit suspect even in the case of the comparison between the '08 and '07 cams.

  • 2grimjim

Posted December 31, 2011 - 03:25 PM

#16

You're most likely aware that a common trick with the original non-auto decomp cams in the WR426's and pre '03 WR250F's was to retard the exhaust cam (NOT the intake) a full tooth to convert to YZ timing and pick up more high end performance, right? What does that do to the exhaust lobe centerline?


Retading the the exhaust cam is the same as reducing the LCA. What most people felt was an increase in "hit", or how hard the power came to life as RPM's came up.

A textbook example of what reducing LCA does.

Reducing LCA widens the RPM difference between peak HP and peak torque, increasing the LCA closes the RPM difference between peak numbers.

Edited by 2grimjim, December 31, 2011 - 03:48 PM.


  • 2grimjim

Posted December 31, 2011 - 03:47 PM

#17

The lobe center in fact may not even split the opening and closing points in two even halves in the cam was eccentrically ground, although that sort of thing is not very common.


Correct. These are refered to as asymetric grinds and not very common.

It's a much easier reference to use in adjusting the cam timing than the opening/closing points are because it takes the quieting ramps out of the question.


Correct. No cam maufacturer recommends using the open or closing event to index a cam. All of them use LCA for establishing correct timing.

Maybe the confusion is from the fact that reducing LCA on the intake is the same as advancing the intake cam timing, and reducing LCA on the exhaust is same as retarding the exhaust cam timing. Reducing the LSA advances the intake and retards the exhaust at the same time (increasing overlap).

  • camman

Posted December 31, 2011 - 04:23 PM

#18

The reason that .040" is used for calculating centerlines and installation is that this location of lift is getting close to max acceration of the valve lift profile. Therefore, small changes on the degree wheel produce big changes on the dial indicator - increasing the accuracy of installing the cam.

  • camman

Posted December 31, 2011 - 04:44 PM

#19

UhOh! Camman misspoke - please replace the word acceleration with velocity in the above post!

  • grayracer513

Posted December 31, 2011 - 08:41 PM

#20

Maybe the confusion is from the fact that reducing LCA on the intake is the same as advancing the intake cam timing, and reducing LCA on the exhaust is same as retarding the exhaust cam timing. Reducing the LSA advances the intake and retards the exhaust at the same time (increasing overlap).

That's the reason people start referring to as widening or narrowing the lobe centers. It gives a picture of what you're doing, whichever cam you do it to.

How much confusion do you suppose the reversed port head on the Gen3 YZ450 is going to cause people when they see the lobe position at TDC?





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