Boost question from a noobie (first post ever) should be easy...
 

Im turboing a 250cc kawi, but thats not important.

I would like to run 4psi for cassual ridding and 8-14psi when I want to ride hard.
For this I will get the TURBOSMART Dual Stage MBC........BUT........

The wastegate spring is default @ 7psi, does this mean I would never be below 7psi?

I'm having a head-scratcher thinking about controlling the boost in that^ way if the wastegate will not release under 7psi.

-OR-

Would the setup likely only come out to around 4psi anyway due to plumbing and the intake plenum tank?
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Are there any boost controllers for the COLD(intake) side that would allow me to do this? Like a controlable BOV?

Im sure I will have more questions, but this one has me stumpped

if the wastegate is rated at 7 psi then it will produce boost up to 7 psi and hold 7 psi boost. it will not go any higher or lower than 7 psi. if you want 4 psi then you will need to replace the spring with a lighter one.

8-14 psi will blow that motor sky high. you will need to build the motor from the ground up and lower its compression. i doubt there are any stonger engine internals to do this on that motor.
the most boost i would go would be 6 psi. any more than 6 psi will require an intercooler or some sort of meth injection to cool the incoming charge.

also any more than 6 psi will drastically increase investment as you will need a stand alone engine control unit and an upgraded fuel system and a professional tune. a multiple stage boost controller will cost you a good amount of money as well.

Thank you busa4 for clearing that up. Too bad the built in WG spring leaves no way of changing it.. But from hearing from others about what they run on small engines, "8" is not too bad, I was just hoping I could run 4 as a daily charge to maybe increase life of the internals.

Yes I would also agree that 14psi on a stocker would blow the engine, but I have seen it work just fine(I suspect it was still not good). The least I will do when I start tuning, will be to add a second gasket...unless it is easier to remove some of the head(?). As of now I will NOT be replacing the piston. So what would you do in this case?

(I do not expect you to go into any details, you have already answered my main question)

Below is a link to a shop that sells turbo kits for the yamy wr250x. It is know to work well. The kit comes ready to push 40hp stock engine. But his own bike is pushing 53 or so.



http://www.mpfab.com/gallery/Album30.htm

if your using an internal wastegate then it can be modified to allow for psi adjustment. to make the wastegate adjustable you will need to cut the wastegate rod in the middle and thread both ends of the rod on the ends you just cut. go to the hardware store and purchase two nuts and a long thumb screw and install them on the threaded rod ends. this will allow for adjsutment. the longer the rod, the less boost. the shorter the rod the more boost.

it needs to look like this


http://image.modified.com/f/28355190...er_comparision

using multiple head gaskets will cause constant head blowout. removing some of the head will raise the compression. any of these mods will change valvetrain geometry and it is not recommended. the best way to lower the compression is with the use of dished pistons. i would advise not to boost the engine anymore than 6 psi. i had great success building turbo bikes with stock engines by limited boost to 6 psi.

wow thank you for the image. I will give it a try. If it does not work as planned, Im going to scrap the idea of 2 boost points, and buy an 8psi rated valve...(looks like a bov)

I have yet to find a piston made to LOWER compression for my engine. But I have not really looked very hard. I will try harder soon

your never going to find low compression pistons. you will need to have them custom made. if you do a google search for custom pistons you will find many companies that can make you forged pistons any way you want them. just send them your original pistons and they will make them. average price is about 125.00 per piston.

Im going to take your advice on only running 6psi busa4. I looked at the stock compression and thought about blowing the engine. I dont want to do that.
What do you think about a wastegate set to open at 6psi but on the charge side?
Something like this:
http://www.ebay.com/itm/UNIVERSAL-jd...item563fd74945

Is that practical?

Or would making that acuator arm extend be good enough?


I accually found out that I can buy a 6psi acuator like this:
http://www.ebay.com/itm/160484289659...84.m1438.l2649

Should I scrap the cutting and just buy that? It will fit, and I like how it cracks at 3psi and is fully open around 7


but please, tell me if a wastegate has ever been used on the charge side. lol

I should add that I say I want to use a WG on the charge side because I cannot find another one of these with a 6psi spring...

http://www.ebay.com/itm/400267906727...84.m1438.l2649

I choose the WG idea because these^ are all 8psi release.


Side note, I found info on "WG on charge side"...I guess it is used to keep boost flowing(compressor wheel spinning freely) and closes when the driver is ready to launch in a race.
Keeping this little turbo spooled on a small setup desnt sound like a bad idea, cuts out the chance of turbo lag, when the turbo is always at 6-8psi.