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Turbocharging my dirtbike.

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Turbocharging my dirtbike.

Unread postAuthor: SpudFarm » Thu Jan 14, 2010 11:39 am

Hello again Spudfiles, I recently decided to get a small turbo to get more out of my dirtbike.
The bike is a Suzuki RM-Z 250 2005mod.

I have talked to a guy in a swedish company that are specialized in turbocharging bikes and other "light" engines but he have never charged a single cylinder.
He have got a small mitsubishi turbo that he said was the right size that I will get for $510.
I think I am going for it since I will get an absolutely sick bike.

The questions I have at hand is:
Does anyone have experience with turbocharging? I will need some help since it is my first EVER modification at all to a four stroke.

Any unexpected problems?

Jetting since it should go real lean when the turbo is boosting, or does it drag extra fuel in aswell? its not injected OFC.

The guy I talked to said I would need to lower compression wich is no problem but I also need a stronger spring in the cluch. where can I get a spring that has the correct amount of resistance and dimensions?

I will tear through your brains deeper as I get comments :)

Thanks!
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Unread postAuthor: inonickname » Thu Jan 14, 2010 12:07 pm

I'm not hugely experienced in the art, but I may be able to help tomorrow (or later this morning) a little.

Though for $510 you should probably search around for a small import car in a wrecker yard to get a turbo from (unless of course you meant $150).

where can I get a spring that has the correct amount of resistance and dimensions?

The ideal place to look would be in a similar sized engine of a higher RPM output. Failing that, ask around at a few mechanics' places or check a DIY store (which will usually have a whole board os springs).

It shouldn't play with the mix (unless you do something wrong) as the turbo just increases the atmospheric pressure the engine has to use.

drag extra fuel in aswell

Hopefully
:P
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Unread postAuthor: SpudFarm » Thu Jan 14, 2010 12:28 pm

I would like to buy his charger since I can get help from him if he earns money on it. Fitting a turbo should not be that hard, just some pipework wich I am familiar with :P

Okay, I hope I get it right atleast. Mabe I manage to charge the exhaust in the engine ^^

I will wait for more input before I write more.
Thank you.
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Unread postAuthor: velocity3x » Thu Jan 14, 2010 12:51 pm

I've never had a bike with a turbo but, I've turbo-charged many cars (racing applications only). You should ask the vendor how much boosts (psi) the turbo will provide according to your engine displacement at a given RPM. Decide the maximin amount of psi boost you want to make available to your engine at a given (max) rpm and the turbo chambers must be sized accordingly to provide the pressure / volume required. If you are only considering 3-4 psi boost at max rpm, the performance will be disappointing to say the least considering the money you'll spend. If you lower the Compression ratio, you'll be countering the positive benefit of the turbo.

On my turbo installs, I always machined the heads (as many others do) to accept an o-ring between the head and top of the cylinder to prevent the head gasket from blowing out......then cranked up the boost.

General Motors states that for every additional atmosphere of pressure pushed into a normal asperated engine, the base horse power increases by 100% (20 base hp at 14.7psi = 40hp). On high boost the performance goes off the chart but, the engine life is considerably shortened.

It really depends on what you want......long engine life or serious engine performance. You cant have both but..... that's just my opinion.
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Unread postAuthor: jrrdw » Thu Jan 14, 2010 1:22 pm

So is it a 'Turbo Charger' or a 'Super Charger'. I'm guessing Turbocharger, all though I have seen Harley Davidson's with Super Charger's.

The thing with Super Charger's is you have to upgrade the entire valve train, everything from the crankshaft gear to the valve seats one end to the other. Also the crankshaft balancer, (changed to a hub)/crankshaft bearings/casing modifications.

Since both units do "basicly" the same thing, I would expect you to need most of the same upgrades, valve train/piston/crankshaft bearings and casing modifications.

The clutch in it's entirety, not just the springs would also need upgraded or you will be replacing it every other ride (that you test it's limits). Motor mounts are another concern due to the extra torque, particularly the rear lower mount is the engine casing, correct?
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Unread postAuthor: jeepkahn » Thu Jan 14, 2010 1:24 pm

Look elsewhere for power on that bike!!! How much power are you wanting??? And what kind of riding are you doing??? Turbos on dirtbike and quads aren't worth it unless you already have a built motor and are dragracing...

Throw in some cams, and a 14.25:1 piston, and maybe stick a flatside on it, fmf powerbomb or megabomb pipe, and go ride... If you need more than that, it'll be cheaper(in the long run, TRUST ME) to trade in on a 250 2smoker, or 450f....

I've only been in the powersports biz since 1990, so I know a little about it :D ...
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Unread postAuthor: ammosmoke » Thu Jan 14, 2010 3:40 pm

jeepkahn wrote:Look elsewhere for power on that bike!!! How much power are you wanting??? And what kind of riding are you doing??? Turbos on dirtbike and quads aren't worth it unless you already have a built motor and are dragracing...

Throw in some cams, and a 14.25:1 piston, and maybe stick a flatside on it, fmf powerbomb or megabomb pipe, and go ride... If you need more than that, it'll be cheaper(in the long run, TRUST ME) to trade in on a 250 2smoker, or 450f....

I've only been in the powersports biz since 1990, so I know a little about it :D ...


I'd say I agree with this guy... You can increase your power by at LEAST 20% by just doing simple upgrades. (Depends on the parts) Exhaust, jetting, revbox, intake, and maybe a piston. The clutch MAYBE would need an upgrade. But yeah, like jrrdw said, a stiffer clutch spring is just a bandaid. Get a better clutch if you really need it. If you REALLY wanted to go over the top, you could get a re-bore done. But that is kinda not necessary if you ask me. That bike has around 30hp I think stock. You will get about 40 by the time you do the above.

EDIT: In fact, you could remove the spark arrestor and get a better intake to start with, then see how that feels. Cheap test. You could even just try without the arrestor, though I've heard rumors that doing it is bad practice longevity wise.
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