DRZ-400 Rally Raid Big Bore Engine Build (Under 450CC)

I'm currently looking at moving with work to Andalucia in Spain, just across the water from Morocco and am looking at building a new DRZ-400 into a Rally bike to take with me.

I looked at getting a KTM or Husky or other 450cc, but the maintenance would be a killer, so my intent would be to build a DRZ-400 engine under 450cc which can put out a reliable 50+HP. The only must have's on this beast would be kickstart, a capacity smaller than 450cc to stay in the lightweight class and ability to work in hot n high environments.

I'm guessing I'd build it using a set of wide gears?

I get that the DR Rally bike will be heavier and I'll have to change a lot of the components like brakes and suspension to make it onto the same playing field as a KTM 450 EXC, but the key for me, is having a bike which means I can actually focus on the riding during a 4/5 day event and self deploy to the event, meaning I can start racking up experience.

As well as Morrocan based rallies, I'd be looking at competing in the Rally Albania and Greek rallies and maybe getting off-road in the Sierra Nevada's.

Thumper Hive Mind, hit me with your opinions and suggestions on how to achieve this goal.

As I've come to find out, the old posts claiming that a bigbore will make 50 horsepower is bs,(unless your Dyno is really generous. You can get close though. To hit 50, you'll need to stroke it as well and still use the right combination of carburetor, cams, and exhaust.

 

You will also need to machine the head for manual decompression if you want to kick start a true 50 hp DRZ.

 

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2 minutes ago, ohiodrz400sm said:

As I've come to find out, the old posts claiming that a bigbore will make 50 horsepower isn't bs,(unless your Dyno is really generous. You can get close though. To hit 50, you'll need to stroke it as well and still use the right combination of carburetor, cams, and exhaust.

 

You will also need to machine the head for manual decompression if you want to kick start a true 50 hp DRZ.

 

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Brilliant, thanks, near enough is good enough, having enough power to keep in the stream would be my aim.

I think stroking would be out as that puts you at 470cc which according to the rules moves you into the same class as the 600cc singles and didn't realise you could machine the head for manual decompression at higher hp's, that was one of my primary worries.

 

 

 

I corrected my original post. Is'nt should be is.

The cam choice with auto decompression function limits you to a low to mid range only powerband, unless you go with Mega Cycle. I'm not sure of their current status. I know Web, who makes top end orientated cams, doesn't offer exhaust camshafts with an automatic decompression function. That's the reason for my statement about machining the head for a manual release.

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OK, I think that if I can get over mid-40's, that should be enough power, so, if we can machine for manual release, which gives a better choice of cam's and go to a 440cc bore etc, we're working in the realms of possibility?

I'm guessing that most riders in the under 450cc class will be on KTM's or Honda's, which whilst weapons, need a lot of work to make sure they work properly, I'm also going to state the obvious and say if you can use all that extra HP on the wonder machines, you're probably a better rider than me, so would have beaten me anyway :D

You can get mid 40's using 434cc ,Hotcams stage 2, fcr 39mm carburetor and an MRD exhaust You can squeeze a couple extra if you go to the larger cams without the auto release and use a 41mm carb.

 

 

 

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Hotcams stage 2 have the auto de-compression release. You can use a kick starter with them.

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Perfect, this looks like a go-er then, I guess the only if or but is how will machining the head so you can use larger cams and kickstart affect reliability?

In the long term the larger cams could cause wear to the valves.

All the cams available have been used in the ATV version of the motor and proven to be reliable.

 

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way not using a rmx450f or husaberg/husqvarna or swm or a beta any of this compains have a good light 500

Well, a DR can be road legal in Europe, huskies some countries only, rmx, just no and swm/beta no experience of those bikes and of course, light 500cc bikes would be over the 450cc or less race category I'm targeting.

 

16 minutes ago, ohiodrz400sm said:

In the long term the larger cams could cause wear to the valves.

All the cams available have been used in the ATV version of the motor and proven to be reliable.

 

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Yeah, this I think is going to boil down to whether there is a tangible benefit from chasing a couple of extra horses? Not really worried about long term maintenance, it's the mandatory valve clearance check at the end of every competition day on a KTM that worries me as a single competitor. No drama's spending a couple of evening's after race week doing a tear down in the garage, but that could sap the enjoyment out of racing if I have to do it every evening in the paddock. Whilst I want to try and be competitive, it's more important to enjoy the time I'm spending out of work at the moment, that could all change if I discover hidden riding talents, but...

swm is the old husqvarna and it is vary reliable its on the cheap side chse it an old design but it is newer the the drz 

a modified drz will be losing its reliability and will cost a loot of money to do right you will end up spending moore time

waiting for parts and fiddling with the bike then riding it . i have been thro the same thing with my old dr( i am going to de mood it

wane i have sam money it is still wane of my favorite bikes ) i have a huski know 


a modified drz will be losing its reliability and will cost a loot of money to do right


You made some fair statements in your post expect for the above which I have quoted. With a little searching, the parts to build a 45 horsepower 434cc DRZ that will run for 20 thousand plus miles without a single valve adjustment. The list of modifications is simple and short. An 39mm Keihin FCR carburetor, and MRD ZPro exhaust system, Hotcams stage 2 cams and a 434 big bore kit.
Sourced wisely it could be accomplished for approximately 1500.00 USD or so. Peanuts really.

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Check out Myer's Racing Engines. 
 

If you've got the money to burn, that's what you need to hit those kinds of numbers. 

this 

6 hours ago, ohiodrz400sm said:

 


You made some fair statements in your post expect for the above which I have quoted. With a little searching, the parts to build a 45 horsepower 434cc DRZ that will run for 20 thousand plus miles without a single valve adjustment. The list of modifications is simple and short. An 39mm Keihin FCR carburetor, and MRD ZPro exhaust system, Hotcams stage 2 cams and a 434 big bore kit.
Sourced wisely it could be accomplished for approximately 1500.00 USD or so. Peanuts really.

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this is a waste of money even if its thro the power band won't work well with gearbox 45hp out of 434cc is not impressive and the suspension will also need lots of work done to it for the much money you are better of getting a better bike to start with iven a wr or crf or klx are much moor suitable 

ps i am not trashing on the drz its a good dualsport bike 

2 hours ago, motodr441 said:

this 

this is a waste of money even if its thro the power band won't work well with gearbox 45hp out of 434cc is not impressive and the suspension will also need lots of work done to it for the much money you are better of getting a better bike to start with iven a wr or crf or klx are much moor suitable 

ps i am not trashing on the drz its a good dualsport bike 

Thanks for your input into this conversation, as you rightly point out, there might be better options, however, only by asking specific questions and getting the answers can I make a value judgement, so if we could keep focused on answering the questions asked about the engine build rather than going down the buy a husky or buy a honda or buy a KTM, that would be great.

i you want reliable power from a drz i wolde say you your best option is air box mood and fcr a good pipe and maybe a drz400e cdi it won't be a monster 

but if are not going to spend a loot of money on suspension which is one of drz weakest points along with wagith the biggest bang for bucks  and differences 

is the fcr big bore kits create a lot of reliabilt problems and cost . looking for a cam that makes moor turq is allso a good idea do you know the speed range

you are going to be doing if you are planning on going over 100 kmh for long periods you will need turq more than hp for higher gearing and maybe better radiators 

5 hours ago, LuckyLucky said:

Check out Myer's Racing Engines. 
 

If you've got the money to burn, that's what you need to hit those kinds of numbers. 

That's really interesting, thanks, have asked what displacement that engine is, unfortunately the upper limit is 450cc and with the bore and stroking I cannot see how this beast would still be under. Have asked the question and will post the answer.

Reliability, it's a question of whether you can get away with oil changes whilst in the field for the 4-5 days of a rally, followed by a tear down at home base, or whether at this HP you've just moved to a KTM type maintenance regime.

Finally, burning money, maybe, I was about to buy a new r1200gs adventure before news of my new posting hit, so I have a reasonable budget, I figure I can pick up a cheaper 2nd hand gs in europe for highway mile munching...

5 hours ago, LuckyLucky said:

Check out Myer's Racing Engines. 
 

If you've got the money to burn, that's what you need to hit those kinds of numbers. 

And, through my ninja like google-foo (https://www.facebook.com/MyersRacingEngines/posts/466410233745083), Myer's racing are claiming the following HP/Displacement numbers off the same dyno:

Myers Racing 462cc Drz - 64.66hp

Myers Racing 434cc Drz - 59.2hp

stock Drz - 29.65hp

Now, if they can work the 434 magic with a kickstart and reliability, that's almost too good to believe, but they'd get my money...

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