98mm Athena vs 100mm Vertex

I have made the decision to try a big bore kit on my new 450. I have found good buys on both the Athena 478cc kit and the Vertex 500cc kit. I have not been able to find any feedback on the Vertex kit at all, and have found minimal feedback on the Athena kit. Is there anyone that has any experience with either or both kits?

Nope I did a 472cc kit from Langcourt on my 03......

Athena has lots of fans but I am also curious about the Vertex...500 kit.....:prof:

I am also in the same boat. I am looking for a big bore kit for my 2007 Yamaha YZ450. Max Power RPM's is another option that I am considering. Here is an email I sent them last week and their reply:

Please send me the latest dyno chart for the YZ478F big bore kit. I am

considering this kit for my 2007 Yamaha YZ450F.

I have the following questions:

- Do I have to make any jetting changes with this kit? If so, what?

- How does this compare with the Vertex big bore kit? The Vertex kit is a

little cheaper, $580, when you consider that you do not have to send in

your cylinder. It is also a little bigger with a 100mm bore.

- I also currently have a 2005 KTM 525SX with a 540 kit in it. Will your

big bore kit make the Yamaha motor feel like the big bore Katoom? I put

the Katoom in 3rd and I never have to shift it.

Here is their reply:

Thanks for the inquiry Ben.

We include jetting specs on every kit that we offer. Max Power does more

big bore kits that anyone, period! We have the best products and customer

service that money can buy.

When we originally tested the YZ 450, we used every bore from 95-102mm.

The 98mm is the sweet spot. If you get bigger than that, vibration gets

pretty bad. The pistons we tested that were larger than 98/99 on the bike

robbed the bike of its top end pull as well.

I can't really compare the kit to your Katoom. We don't work on this

model so a direct comparison is virtually impossible.

The 478cc is a instant +8hp everywhere on the RPM range on the dyno.

I don't have the charts in a emailable file at the moment. I may be able

to fax them to you?

I will try and get the dyno charts and post them.


8 hp !?????? Seems to be a pretty big increase.

8 hp !?????? Seems to be a pretty big increase.

+8hp gives me wood:crazy:

Thank you for the feedback. I do not think that the bottom end on my new 08 will be an issue with my 98mm big bore kit installed. Plus it will be cheaper than a pipe.

I wonder if some HotCams would do anything for it.

hot cams would definatly help use the extra CCs and really get out some more power...

and while im sure that the increased bore greatly helps low end... i highly doubt 8 hp increase though...

8 hp !?????? Seems to be a pretty big increase.

I remember MXA did a 470cc RMZ project bike and that thing got 7hp just from the different bore! :ride:

I am not sure if the 8 hp increase is measured at the crank, the rear wheel, or the brochure! :ride:


did you ever manage to track down that dyno graph?


i got a 478 kit and it works wonderfull

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