DRZ400S 440 Big Bore kit

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DRZ400S 440 Big Bore kit

Post by 4Strokes » Mon May 23, 2016 9:17 am

Topic: 440 Big Bore kit (DRZ400S)
Author: tomass
Posted: 04/12/2007 6:07:41 PM

I have an 02 Suzuki DRZ400-S with a Big Gun exhaust, KnN filter and Dynojet needle and spring. Well, I'm thinking about getting an Athena Big Bore kit. It comes with the 440 cylinder with larger-than-stock water jackets, piston, gaskets, and all the goodies needed to bolt that baby on. No resleeving needed. My question is this: Can I do this without getting a whole new carburetor? $600.00 is a lot of money and a new carb would be that much more. Can I get away with keeping my Mikuni BSR36 carb and just jet it up? It's such a reliable carb. My bike starts so easily, regardless of engine temperature. I don't know if the Keihin FCR 39 is as reliable. Also, if I got a new carb, would the stock front and rear boots fit it right? I would hate to have to change everything just to put on a new carb. Thanks for any help you can give me.

Reply by Admin on 04/19/2007 4:42:24 PM
Hi Tom, I did a little research for you. Everything that I could find showed the BSR36 carb working well with big bore kits. I found lots of LTZ/KFX 400 quads still using the BSR36 carb with 440 kits. Additionally, both Thumper Racing and Yoshimura's Websites do not mention anything about having to use a different or larger carb with the additional bore size. If you want my vote, I say use the BSR36 carb. This way hopefully you want have to deal with fitment issues. Please let us know what you decide and how you make out.

Reply by b_king on 04/19/2007 6:04:59 PM
Simply as a different opinion, I would opt for the FCR if there is a kit available that will bolt directly on with no modifications to the bell or spigot. The FCR is probabely by far one of the best carburetors out there. Excellent throttle response and top end power, easy to jet. The FCR will be just as or more reliable only if properly jetted. The same can be said about any carburetor. Most people who have starting issues have modified their bike in some way to cause this and have not properly sorted it out. Good luck!

Reply by tomass on 04/19/2007 7:11:14 PM
Thanks guys. That gives me a lot to think about. With two options, I can start out with the stock carb, and eventually (after a small loan)advance to the Keihin later, if and when I'm ready for another upgrade. Would the difference be that obvious? Is it that it can handle more air and fuel than the Mikuni can, therebye producing more power? Or is it something else that's giving more power?

The Athena Big Bore kit costs around 500.00 to $600.00. What does a Keihin carb cost?
When I get the kit, a friend and I will attempt to put it on. It looks simple enough, but looks can be deceiving. Have you heard anything about simplicity or difficulty of bolting this thing on?

After it's on, what size jet would you recommend for the Mikuni, and also for the Keihin. Here are my thoughts about jetting my stock carb. If this kit gives me 40 more cc's, that's exactly one tenth of my overall cc's. So, if I take one tenth of my jet size (142.5) that would be approximately 14.3. Add that to 142.5 and you get approx. 157, give or take. Maybe round it off to 160 for good measure. What do you think of this? I definately don't want to be lean. Also, the kit would put me at 12.4:1 compression. I mention this as it may help you to determin if my calculations are near the mark.

Please excuse all the questions. There is so much to learn. Thanks a lot Admin and b_king for all your help.

Reply by b_king on 04/20/2007 6:37:11 PM
If everything in the kit is ready to go, it is as simple as bolting everything on together. There are many things to remember when assembling a top end. Things like offsetting the piston rings , where to put the clip that holds the piston pin in, how to time the engine properly, how to adjust the valve clearances, etc. If you do not have a manual, I would make sure either you or your friend have a very good understanding of how all this works. I've seen to often people attempt to assemble top ends and end up blowing motors and such, which is a pain because I end up having to fix it and it costs them alot more money.

You will notice the FCR with all the other modifications. The problem is most people think hey, boring out will give me tons of bottom end and more power overall. Yes, that is correct only if you take into consideration all the modifications work together to create the overall power increase. So by simply boring and keeping everything else stock you won't notice a huge difference. By boring, increasing the compression, installing oversized valves, porting the intake, a performance cam, installing a complete exhaust system that flows more, a larger and better carburetor that is properly jetted and a performance air filter you will notice a significance increase in overall power and either more torque, top end of mid range depending on the types of mods you did.

I'm not trying to make you feel stupid, it just kills me too see guys spend all this money trying to make their bike their own by modifying it and they are unhappy with the results. Good luck!

Reply by Admin on 04/21/2007 09:52:14 AM
tomass, please don't let b_king discourage you. I think you are on the right track. Here's a small article on a Suzuki 400cc engine that shows some differences between a piston (big bore kit), cam, and proper jetting. I'm assuming they used the stock carb but you may want to email them to be sure. By looking at the dyno sheets, you can expect a sizable increase in horsepower. On their 400 to 440 project they gained 5-6 horsepower with a piston alone. Not too shabby!

In searching for main jet sizes for carbs on 440cc Suzuki engines, I found mostly 155 and 157. I would go a little fatter, as you speculated, then fine tune from there. That's how I do mine.

Reply by tomass on 04/21/2007 1:08:06 PM
I must admit, b_king's comments did make me stand back and question whether I should do this at all. It sounds like a monstrous undertaking. A large chunk of change just to get a nice boost out of that kit. The kit alone is 5-$600.00. Then there's the valves, cam, carb, and porting the intake. I have the exhaust. And I have no doubt that all that b_king suggests would give even that much more power, but I don't have that kind of moula. That's why I'm glad that I can still get a nice boost in horsepower, (5-6 horsepower is excellent) without spending an arm and a leg.

I guess that a cam change would be necessary in the power gain. Would you recommend a Hot Cam? And would it be the exhaust cam that gets changed? I see Hot Cams mentioned often. Are they proven reliable? I've heard that some aftermarket cams are made from less agressive cams. Metal is added onto these cams until they get the desired size. This metel isn't as hard as the metel it's coming in contact with, so it wears out faster. When I do this, top quality is paramount.

Thanks again for all your help.

Reply by b_king on 04/21/2007 3:41:07 PM
Tomass, where did you find out the bore kit would give you 5-6 HP?

I find it hard to imagine a huge gain like that, approx 17% increase, from simply boring. I think maybe 1 or 2 horsepower. The amount of effort that people go to turn get extra power out of motorcycle motors is very in depth. Unfortunately alot of people on this site claim to have gained upwards of 6-8 HP from their at home mods. This really astounds me when trained professionals who have been in the business for mainy years struggle to get 2-3 HP out of their engines. There is alot of misinterpretation on the internet about this kind of stuff. Single cylinder motorcycles like DR-Z's and XR's, old school 4 stroke technology, are no where near as capable as the new 4 stroke offroad bikes in terms of power production.

I personally would think from all the modifications I have done to my motor have probabley gained 2-3 HP if that.

I saw an add for an XR400R for sale which had these modifications:

Here is my 2003 Honda XR4 which was bought new in the spring of '05 (I'm the only owner).
There is a huge list of aftermarket parts so hold on:
  • Xr's Only Stainless oversize pegs($150)
  • Utah Sport Cycle Aluminum skid plate($100)
  • SRC fork brace ($300)
  • Clarke oversize fuel tank (one ride) ($250)
  • GPR steering damper ($700)
  • Oil temp dipstick ($50)
  • Complete FMF "Q" exhaust system (header and pipe) ($700)
  • XR650L glass headlight and H3 bulb upgrade ($100)
  • HD clutch springs ($50)
  • XR's Only built 430cc kit, JE 11:1 piston, new valves and guides at the same time for the heck of it, with intake manifold matched to head and port work(about $2000)
  • Stage 2 Hotcam ($200)
  • Brand new EBC wave rotor ($250)
  • Xr's Only rear shark fin ($50)
  • Motion Pro needle bearing clutch with quick adjust ($150)
  • Mikuni Pumper carb ($400)
  • RaceTech springs and revalved forks new seals ($500)
  • Full gripper seat cover($90)
  • New FMF graphics ($100)
  • Renthal CR high bend bars and new grips ($150)
  • EE hand guards and deflectors ($100)
  • Sidewinder TI chain and tool steel sprockets ($400)
  • Excel front rim and stainless spokes ($300)
and I'm sure there is way more stuff that I'm forgetting to list. What I did remember totals $6640 and that is before the bike!!!

This is likely one of the sweetest XR4's out there with no expense spared for the most part. I would love for it to go as a complete package. I have almost every stock item still which will be included with the bike (stock tank, cam etc). Almost everything is new or almost new. The motor and 90% of the aftermarket parts have only about 10 hours tops on them as well as a new set of Michelin S12's. Hard wired for Garmin GPS. Oil changed every ride with Motul 5100 since new.
Selling because I just don't ride this bike enough to keep it. I ran it maybe 3 times last year, looking to clean out the garage and have only one off-road bike.

I may start to put the bike back as close to stock as possible in a few weeks if there is no interest.
Blue plated (street legal)
Price? try me.

Then wait for it...

XR's only tells me that similar bikes on thier dyno are in the 43hp range, which is likely close. It is not crazy HP power either closer to a train engine then a rocket. Very controlable. On a fire road just open it up and she will fly, in single track just ride 2nd or 3rd gear all day and the torque will pull you along.

43! HP! Ok, for a bike that has a stock HP of around 31-32, an increase of around 11 HP is outrageous. That is an approximate increase of 34.5% Ok, yeah right buddy. Unless he through an Unicam motor from a CRF450R in there, there is no way he's making that kind of power with that kind of engine.

Again, I'm not trying to belittle you or seem to lecture you, I'm only trying to bring out the facts.

Reply by tomass on 04/21/2007 4:35:34 PM
Admin mentioned in his last reply that the site he was at, showed a 5 to 6 hp increase.

I understand what you're saying. You're in the business of working on motorcycles and all your experience tells you that 5 to 6 horsepower is an exageration. I wouldn't argue with you and I believe you.

I can't afford to go the whole nine yards as far as upgrades. Besides, unless I was in competition, it wouldn't make sense for me to go to such extremes. Not for my kind of riding. Unless I win the lottery or some distant relative leaves me a bundle, I need to keep it simple.

So, with this kit, a cam, and good jetting, I can only expect to get 1 or 2 horses from it? 40 extra cc's only yields 1 to 2 horses? If that's the case it's hardly worth doing. 3 or more hp would be more motivating.

I noticed you mentioned boring out several times and I just wanted to let you know that, with this kit, there's no boring out at all. This kit is a larger cylinder head and piston, replacing my stock ones. There will be no boring or resleeving. Just more cc's bolted on.

Thanks for your help b_king. Your knowledge and input are always welcome.

Reply by Admin on 04/22/2007 11:30:04 AM
If an "old school" ('98/'99 XR400R) four-stroke bike can gain up to 2.3 HP with just a pipe alone, it doesn't sound unreasonable to me to gain 5-6 HP with a 40cc big bore kit. There are Websites out there claiming 4-6 true HP gains at the real wheel with a pipe, jetting and intake derestrictions.

Isn't it all about the seat-of-your-pants feel anyway? If tomass can't afford a new high technology four-stroke and wants a little more power out of his DRZ, I say have at it! Personally I think it would be fun to do the work and be proud of the accomplishment. Besides, I think I would rather drive a DR-Z on the street and trails than an RM-Z.

Reply by b_king on 04/22/2007 4:45:01 PM
I'm not ranting at all, I'm just trying to help out a fellow rider. Yes, seat of the pants feel is the ultimate opinion. If he wants to go ahead with it, by all means do so. I was just trying to point out some facts.

Tomass, if you want to make the engine modifications that you are looking into, please do so. I am actually contemplating a DR-Z400S as my next bike. I am quite interested in what types of power increases are available, so let's see how it turns out shall we?

Another thing, if you can't afford to go all in at once, there is no harm in slowly accumulating the different modifications. I mean, that's exactly what I did. Take a student's budget and see how far you can go in a month. It's a actually kinda cool to add on something else and see what kind of power that releases. I'm in a different situation now where I can actually afford something, so if I was to purchase a new bike, I would simply dump everything into it.

I'm also not suggesting that you should be looking at RM-Z's or any of the new 450's. I personally think those are solely for racing. I really dig the old school simple idea 4 stroke engines. Sold power and reliability.

So all in all, I say go for it. I also want to apologize for sounding argumentative and rude. I never intended for it to come across like that. I was simply trying to join a discussion and contribute and learn from it. I truly value the opinion of others because I, as everyone else, am still learning.

Reply by tomass on 04/23/2007 4:00:22 PM
No apology needed. Giving your opinion is what a forum is all about. And I'm slowly learning.

It will be interesting to see what each mod does toward the performance of my bike. I hope the first one makes a nice impression. I don't want it to be subtle. I want that feeling to be obvious. But we'll see.

If you do get a DRZ400-S, the Big Gun exhaust system made a nice difference on mine. Coupled with a KnN filter, opened airbox, Dynojet needle and spring, and an icat.

A buddy of mine just got an 04 DRZ-S, with 3500 miles. Switching from his bike to mine or vise versa, you can feel an obvious difference in power. One test was to see if his bike could do a roll-on wheelie in second gear like mine can. His front wheel was coming up ever-so-slightly. Mine, it just snaps up. Much better low-end grunt. But, I don't really know what kind if horse power gain I got from my set-up.

Reply by b_king on 04/23/2007 8:43:05 PM
I'm also curious to see how the 440 kit fares in terms of cooling. The DR-Z400S being a liquid cooled bike should be able to handle it. I don't know of any companies that make larger radiators, but that might be an idea if you start seeing abnormally high temps while offroad.

Reply by tomass on 04/24/2007 11:57:34 AM
I'm hoping that there won't be an issue with
cooling. I don't think it will. The Athena 440 kit has wider water jackets so maybe that will do. Here's a description of that kit:
  1. Aluminum cylinder with a nickel carbide coating designed with wider water jackets
  2. Forged piston with a moly coating(kit includes rings, clips, piston pin, complete kit)
  3. Top End Gasket kit
  4. Complete instructions
I'm glad it has complete instructions because were gonna need em. If there's shimming involved (valves), that's gonna be tuff.

Reply by Admin on 05/10/2007 09:46:05 AM
This might be a little more than what you're planing to do with your DRZ, but should be a good reference article nonetheless: 2004 Suzuki DR-Z440 - Reverse Psychology

Reply by tomass on 05/12/2007 09:26:03 AM
Interesting article. Thank you.

Reply by live2offroad on 05/27/2007 11:44:44 PM
Originally posted by Admin
This might be a little more than what you're planing to do with your DRZ, but should be a good reference article nonetheless: 2004 Suzuki DR-Z440 - Reverse Psychology
Thank you for posting that article.. I, just today, took delivery of my DRZ400E and had been dealing with a bit of buyers remorse at not getting into one of the hotter 450's (CRF/WR). That article put everything back into perspective for me.. -Peter

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