More POWER (YZ450F -03)


My dad has a -03 YZ450F (as do I) and he wants more power. He also does not want to lose any of the hit. We are considering everything including cams, larger displacement cylinders/pistons and exhaust systems. The new gases with high oxygen content are not an option, since they are not available around here.

I would like to invite all experiences and suggestions. The top priority is horsepower/money and ease of installation.

Some questions I have:

Do big-bore kits require head-work if they increase the bore? How about the once that increase the stroke? Obviously the once that increase the stroke require the cases to be split in order to fit a new connecting rod?

Does larger displacement require other changes to the intake or the exhaust?

To pre-empt the inevitable:

Yes, the bike is running perfectly.

No, he doesn't necessarily want to be faster, just more fun.

Yes, he can handle it.

Thanks for all responses.

1. port the head

2. a hotter camshaft

3. a *good* exhaust system (not your typical canister...) -RHC here on the forums....this is the guy that did my motor...

or -Rich_Rohrich on the forums...these guys did davbrucas' CRF450

Both do great work, depending on what and how much power you are after...

Just give 'em a call....

DOH...I see you are in Finland.... :)

DOH...I see you are in Finland.... :)

Yes, that does limit the options a bit.

How about contacting Renaldi. They build Everts Yamaha's for FIM.

DOH...I see you are in Finland.... :)

Yes, that does limit the options a bit.

Eric Gorr would be happy to help you out and has a solution so you don't have to send your cylinder back and forth. He has a complete package with a big bore cylinder, higher compression forged piston and gaskets at a good price. He might also mention to you that his family not long ago came not far from where you are :D

I sent my cylinder to Eric and Rich for the 470 treatment and I could not be happier with the performance. That thing is an absolute tractor now. I ride in the woods and I was able to drop three teeth off the rear sprocket due to the power increase.

Thanks for the replies guys. The Rinaldi tip and link were real eye-openers since I'm not really used to looking towards Europe for this kind of stuff (my German is lousy and Italian nonexistent).

Did you get the higher or lower compression piston for the 472, Stumpy? Just asking because you mentioned the thing becoming a tractor and we want the bike to be more of a dragster like it is now, just more power everywhere.

That kit from Eric Gorr is looking real enticing, but I think we'll have to go for the lower compression since there's enough low RPM torque already.

Does anyone have any experience with re-sale of a over-sized bike? Would a YZ470 go for more, the same, or less?

I honestly don't think I'd buy a used over-bore. I've heard they have problems starting and running cleanly. And I'd wonder what they guy that did that was thinking and how he rode.

Yet I'm considering doing it to mine. If the '05 YZs just have some minor mods (I've heard new carb and airbox), I'll keep mine. But I don't want to be at a disadvantage, so maybe the YZ470 thing is the way to go.

But I'd hate to spend $1000 to then torpedo resale. Used bike buyers think aftermarket exhaust or suspension is cool. What do they think of over-bores?

Any thoughts on that?

The 470 kit from Forward Motion (Gorr) is, I assume, a drop-in replacement, i.e. you keep your stock cylinder and piston and nothing is modified. It's only $499. I don´t think a lot of buyers will argue with extra parts.

I have the 470 kit with head and valve work, the bike rips. I have about 30 hours since the rebuild with no problems, tons of power

It is kind of scary to dump money in to aftermarket performance parts without witnessing or hearing some success stories. Last weekend we were hillclimbing on the sand dunes with five CRF 450's. Two of them had head work and pipes and didn't have a bit of advantage over the stock CRF's. Of course the YZF beat them all. The point is, there were some unhappy customers and I don't want to be one of them. You also run in to riders who claim their mods to work just to save face. I know there are some good products our there, but what REALLY works?

Any other success stories??

I think that if a big bore kit isn't completely screwed up and retains the stock(or close to it) compression, there's not much that can go wrong (two-strokes are a different matter with all the porting).

Now dad is having second thoughts about the whole thing and is thinking about getting a -05 before doing any mods and _I_ am so excited about the kit that I might have to get one for myself.

Man, there is so much truth to what you said, Stroken!

I've spent quite a bit of money on stuff that didn't work. At first it was because I believed the ads. Then I got a little smarter. But still naive enough to believe the magazines. Either those guys are a LOT more sensitive to changes than I am or I'm not sure how they live with themselves. I bought a 2002 CR250 because the handling/suspension were supposed to be so great and the motor was supposedly competitive. I later rode a YZ250 and understood why I couldn't get a start and got killed on the uphills. :D

So I started relying on personal recommendations of people that used the product. Once again, perhaps I'm just not sensitive enough to change because I've spent money on surefire ways to improve performance and come away scratching my head. I put a FMF SST system on that CR250 based on the advice of a guy who had one. He must have done the exhaust at the same time as porting because the pipe by itself was too subtle of a difference to be worth $50, let alone the $300 I paid for it.

Same thing with some guys on TT - some have claimed a PowerNow gets them over a double or triple they've never come close to clearing before. That really baffles me. I got one and found that it makes the bike a touch more eager when you first crack the throttle, but it isn't going to give you a lot more distance on a jump. I even removed and drilled the hole in the PN2 because people on TT said it made a noticeable difference. Not to my backside!! :D

A 50 tooth sprocket made a significant difference. A Jardine exhaust made a significant difference. :) The PN was noticeable but slight.

How much difference does 20cc make? Is it worth a bike length on a medium length start? 2 bike lengths on a long uphill?

And are there any disadvantages? Hard starting? Over heating? Jetting nightmares? Requirements for better gas?

Mine runs strong, though I always want more power and always want to improve it. But I'm tired of wasting money!

Thanks for the info, Rippin. We can't do anything about slanted editorial or advertising claims, but as consumers we should tell it how it is. If I buy a product that doesn't work, why would I want other fellow riders wasting their money on it?

I agree with you guys...hence I was apprehensive about spending @900 bucks to have my engine modified...I narrowed it down to 2 companies, Ron Hamp and Eric Gorr/Forward Motion/Rich Rohrich. Both of them were willing to talk (at length!) on the phone and treated you as if you were a valuable customer. Try that with some of the other companies...or even try to talk to the actual guy that will be doing the mods!

I decided on RHC porting, cam, and springs for personal reasons and partly because of the exhaust system that matched, not to mention the fact that that FFRacing actually sent me a full exhaust system, overnight shipping and all, for me to test. I liked it so much I bought it from him.

My buddy went with Forward Motion...that is great because now we are able to test both bikes back to back, etc.

I have to say, both bikes haul major booty, Dave's is a bit more low to mid oriented while mine takes the mid to top category. The biggest differences lie in the porting spec and to some degree, the camshafts we are running. I have not ridden Dave's bike with his new Jemco, but I know what to expect since I got to run it a couple of motos last weekend on my own bike.

I have to give a big :) up to both builders, I know the money DID something worthwhile, and I can offer an unbiased opinion on one of them because it's not my bike...

Besides, how often do you actually see the guy that does the mods actually posting on a big public forum, i.e. RHC and FFRacing, and Rich_Rochrich. I hope you appreciate all of the info these guys have parted with here on TT and ATM and over on DRN forums as well.

You can't go wrong with either of these builders, both build some of the fastest, winningest bikes in the country. :D

I really think that the Power Now increases torque during roll on and that it does not increase peak horse power.

I feel like I can get on the gas earlier with less clutch and the bike moves with less effort from the bike or the rider. Also adding the TPS mod really wakes the bike up off the bottom. My bike seems more like an open 2 smoke now.

It is real simple if you ride the bike near the horse power peak you may not notice the power now if you ride it in the torque peak you will.


Is the TPS mod you are referring to simply disconnecting the TPS?

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