Need more speed!

9 replies to this topic
  • Aspenrt14

Posted July 17, 2008 - 06:38 PM


I've got an '05 yz450f and have read about different mods I can do to increase my speed. I've dropped my rear sprocket to a 48. I've ordered, but haven't installed The Big Gun Rev Box. I've read about swapping to a 5 speed tranny as well.
I ride the dunes and trails only and just don't have the top-end speed I want. (mostly just in the dunes) What should I do?
As far as swapping trannys goes, does anyone have a parts list?

  • grayracer513

Posted July 17, 2008 - 07:42 PM


I ride the dunes and trails only and just don't have the top-end speed I want. (mostly just in the dunes) What should I do?
As far as swapping trannys goes, does anyone have a parts list?

Have you looked in the Common Threads Sticky? It's in there.

Your '05 should pull about 80 in the sand. If that's really not enough for the dunes, bump the front up to a 14.

  • Aspenrt14

Posted July 18, 2008 - 10:24 AM


Thanks for the advice in bumping up the front. I did check the Sticky thread and saw a parts list, I just didn't know if that was the same list for my '05. I'm not sure what size the front sprocket it, but 11 or 12 sounds familiar. If I go with a 14, how much am i gonna lose in the bottom end? I'm thinking about going with either the power now plus system and/or the ready racing rapid response R4; will that make up for changing the sprockets?
My biggest concern isn't based solely on gaining speed, but the fact that I'm having to run at such a high RPM and keep it there for long periods of time. I'm not wanting to add to the wear of the engine more than I have to.

  • grayracer513

Posted July 18, 2008 - 12:40 PM


The parts list is for all 4 speed YZ450's.

Stock gearing on an '05 was either 13/48 or 14/51, usually the latter. Both come out to roughly 3.66:1. I used to run my 4 speed one two higher than stock almost everywhere, and it was fine. On your bike, that would be 14/49. But mine was an '03, which had more low end grunt than an '05.

The Rapid Response system is an expensive substitute for the accelerator pump wiring mod, and I recommend neither of those. IF you really have an issue of bogging on throttle opening that is really related to weak delivery by the AP, then the O-ring mod, or the stiffer AP linkage spring from Merge Racing is a better choice. However, none of this will increase low end power, only throttle response, and only if the AP is the source of a problem.

Likewise, since the problem with the '05 is not the carb, the Power Now won't help, either. If you want more low end, use the CDI unit from an '04, or buy a Vortex unit. The timing map is the main difference between the '05 and the earlier engines. The cams are the same.

  • Aspenrt14

Posted July 18, 2008 - 01:23 PM


I don't really have any issues with bogging down and my throttle response is fine. The only problems I have are when I'm either not giving it enough gas on take-off, or when I'm in too high of a gear and just need to downshift. I was just hinking that with those mods, it might compensate for changing the gearing of the drivetrain. if not, then i probably won't them.
It's just hard to decifer sometimes when some reviews say it's the best mod you can do and others say the opposite.
As far as going with an '04 CDI and/or Vortex unit goes, I'm not sure what those are, or what they do.

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  • grayracer513

Posted July 18, 2008 - 01:43 PM


The key to knowing whether a mod or a add-on part will benefit you or not is to understand what the true function of the item is, and how that will play in with your engine.

The CDI control module in any bike is the heart of the ignition system; the ECM, the "computer", or "black box" if you will. The primary function is to watch for the signal from the trigger coil near the flywheel, and send a jolt of electricity to the ignition coil in response, causing the spark at the plug. The secondary function is to control the ignition timing, and adjust it as conditions change. 40 years ago, bikes had just one timing setting, so they had to be set to be right at full throttle at lower rpm. Now, however, the CDI takes information from the trigger coil and from the throttle position sensor, and adjusts the timing over a wide range to optimize performance at any given moment. The set of programming rules by which the CDI does this is called the "ignition map".

The power delivery of the engine can be and often is controlled by modifying this map. You can increase or decrease the output in a specific rpm range by modifying the ignition timing in that range. This is what was done with the '05 in response to feedback about the low/mid range power output of the '03 and '04 models. By using an earlier CDI, you can get the performance of the earlier engine, e.g., more hit off the bottom. By using a Vortex, you can pick between about 7 different programs and select the one you like. The OEM units are more reliable, the Vortex is more versatile.

  • Aspenrt14

Posted July 19, 2008 - 09:27 AM


Thanks for all the help and insight!
I'm 26 and have been riding for about 20 years, but have just started working on my own bike, so as far as installing such mods as a new CDI; is that something a new-jack can get done, or is that something I should take to my Yamaha dealer to get installed?
You're the best man!!

  • lluks252

Posted July 19, 2008 - 07:46 PM


Yes, grey is right, this man knows tons about YZF's, My '03 has tons of low & mid range power, however my friend has an '05 and personally I don't like the power delivery on it. The low end is toned down alot compared to mine, however I believe he has a little bit more mid range punch. I'm running a 14/48 (stock) when I go ride in trails(sometimes I use a 49 for trails) or sand. However, when I'm riding on Motocross tracks I either put on a 49 or 50 depending on the track...Hope this helps you some

  • grayracer513

Posted July 19, 2008 - 08:25 PM


When you compare gearing between '04 and earlier models with the '05 and later models, bear in mind that in '05 Yamaha changed the primary drive ratio from 2.818:1 to a higher gear ratio of 2.652:1. This change is almost exactly equal to going one tooth larger on the front sprocket, so the '05 rear gearing is lower to make up for it.

An '03 with 14/48 is geared exactly the same overall as the '05 with a 14/51.

  • mule21

Posted July 19, 2008 - 09:30 PM


running a 15/45 .... switch to the 14/45 when in the tighter trails

04 450

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