Turbo Seadoo 2 Stroke

Royal Motor Works · Dec 9, 2007

Hey Guys I Am New Here, I Have Built A Turbo 800cc Rotax Rotory Motor. I Am Having Problems Getting Enough Air Flow To The Air Box At Low Rpm's. At The Crack Of The Throttle It Will Fall On Its Face And Barely Idle Until It Bounces Out Of The Water And The Pump Unloads. Right Now I Have A Custom Built Pipe From Cpi And A Mitsu Turbo Tdo516g. I Have Already Put Reedcages In The Airbox But It Is Still Not Enough For The Boat To Leave The Line Hard. Once The Boat Bounces And Revs Up The Reduced Load On The Pump Lets The Turbo Spool Up And The Thing Runs Like A Raped Ape. Does Anyone Have Any Good Ideas To Get Almost A Fully Open Carb/airbox At Low Rmps And Low Load To Get This Thing To Respond? What About Going To A Aerocharger??? I Think That Will Help Alot. It Acts Like It Wants No Airbox Until About 3500-4000rpms Then The Motor Has Enough Natural Power To Spool Up And The Thing Will Run Great All The Time As Long As You Dont Come To A Stop And Try To Take Off Again, It Will Just Gurrgle And Idle Till It Comes Unhooked Again. Any Help Would Be Great This Is A Great Forum And Look Forward To Getting To Know You Guys. Thanks Mark :d

MEDIUMPIMPN · Dec 9, 2007

try installing reedcages in the exhaust and on the battery and if that doesnt work youll just have to give it more airbox!!

TravRMK · Dec 10, 2007

Sounds like your exhaust side of the turbo is too big. What are your turbo specs? Like how big is the tubine housing and wheel?

Royal Motor Works · Dec 10, 2007

yea that is what I thought also, but the more restrictive small a/r then the motor starts to deto. these motors have so much load on them at all times it is like running 10 extra grams of clutch weight. Thats why I was wondering about the areocharger. Thanks four your insight..

allblowdup · Dec 10, 2007

You can set up nitrous to spool up your turbo for you very quickly. It works great and the nitrous lasts a long time because you are only using it for .5 second bursts.

Royal Motor Works · Dec 10, 2007

unfortunatly, using nitrous is not legal for the races. what about just using o2?? in the stinger going into the housing?

brycter · Dec 10, 2007

there is a tons of stuff that needs to be talked about here, what prop and degree are you running? is it straight cut? do you have a good vented hull or are you pulling hot air? What head are you running? have you lowered your comp? Have you changed you pump? Are you adding fuel through power jets? are you fueling the turbo? What fuel reg are you running? what is it set at? are you running two fuel pumps or one? How are you oiling your turbo? Just give a call or email us. www.turboboyz.net

Royal Motor Works · Dec 11, 2007

BRYCETR
Ok, gone all over the place with props and pump sizes, from a 144mm 14 vein set back pump 18-27 prop it went 74mph. with amazing acceleration once spooled up, to a 140mm 14 vein setback pump and a 14-24 prop and it only went 61 mph and felt like a normal race boat, tried every combo on prop pitch and nozzle sizes. The hull has plenty of air flow, no hot air, has fresh air intake.As for heads, I have tried everything from .030 squish with wide squish area and 200 cranking comp to .100 squish and 110 crank comp. I have 4 different heads and about 20 sets of domes to work with. Yes I have power jets(CPI), they are running off of a pressurized remote fuel bowl (Thunder Products), They are Mikuni BN watercraft carbs, modified by NOVI to 44mm special booster etc. also mikuni bn modified by Full Spectrum to 48mm. The carbs diaphrams are pressurized to ballance the internal pressure. As for fueling the turbo I am not sure what you mean by this. It is a blow through settup. Using a Mallory bypassing reg, also tried aeromotive, and also a std mikuni pulse pump for inital startup, Holley electric pump that turns on at 1500rpm's. gone all over the place with fuel pressure, from static at 1psi to static at 15psi with the rising rate. Using a electric oil pump from CPI. I have a dyno and I have tried every timing curve and every jet combo you can think of. The taller the prop and pump, the faster this thing will go, smallest and lightest pump prop combo makes not much difference on throttle responce, I simply think I cannot get enough air into the motor at idle. It would be like running a turbo sled and having the clutch engage at 800rpm and then trying to hammer the throttle and expect to launch like normal. I have over 150 hours of tuning already and just cant get it better. What do you guys think? Thanks for the help

brycter · Dec 11, 2007

I need to think about this for a bit. Can you send us some pics of the boat and set up. abkendrick4@msn.com or turboboyz.net

Royal Motor Works · Dec 11, 2007

Sure, this is a thought that I had, have the top lid of the airbox hindged and sealed so it will open completely form start up and then have a boost sensing or rpm switch that will send a signal to a co2 powered air ram, and the top of the box closes when it starts to build air voulme, then hopefully it will run from there. get below a certain boost pressure or rpm point and the box opens back up. What do you think about this idea?? I just dont want to spend a bunch more money and time trying things that wont work, so I thank everyone for their input..

BIGDADDY · Dec 11, 2007

Leave everything hooked up except for pipe to turbo, (vent it out,going to be loud)and the tube to the air box. So it runs as a normally aspirated sled. It should run on the bottom end like this. If it does not run at all this way, then it is not the turbo set up. Sounds like carbs are to big if you ask me. BD

EventsInTheChamber · Dec 11, 2007

A few more questions to add into the mix...

-What size plenum are you using?. (Should be 110% - 120% the engine displacement)
- Do you have your power jets in the correct location?
- Where are you running your lines from to the "presurized remote fuel bowl" that is suplying the powerjets?
- What size carbs did this engine use stock?
- Are you running the proper fuel pressure and not dumping large amounts of fuel when just off idel? (Super rich untill the motor can overcome this)?.

Royal Motor Works · Dec 11, 2007

I believe the stock carbs are 38mm, our race boats will never have good mid to top with that size carbs being N/A. This is why everyone is using such big carbs. I have thought that also. The remote fuel bowl is boosted by the air box. I have also tried it in the primer fitting on the carbs so it is just like the exact pressure the power jet has.
As for unhooking the turbine, I do not believe it will run like that, I opened the wastegate and tried it it was the same. It acts like the choke is on. I think some of the problem is the airbox inlet is only 2in and it is feeding two carbs that total 3.5 in total combined size. Too me it just seems like it is not possible to draw enough air through that size hole and through the intake tube and turbo to flow what the motor is demanding.
I never have figured out the cc's of the airbox, I will do that.

Thanks Guys, everything is helping..Mark

EventsInTheChamber · Dec 11, 2007

If you think your engine is not pulling enough air when connected to the plenum and charge tube, take the plenum right off the carbs and fire the engine up. See how it reacts to this.

If your still have your bog (but not as bad) and the motor still stumbles your carbs are too big.

I'm still on the fact you are trying carbs which are 6-8mm larger then the stock ones. If it was me I would throw the stockers on there and try that. If the problem was solved I would look for other ways to increase top end, as I'm sure there are things that can be done?.

Anouther thing you can play with once you get your initial setup fixed is your A/R ratio. May be beneficial to your application.

BIGDADDY · Dec 11, 2007

A couple pics would say a thousand words....BD

Royal Motor Works · Dec 11, 2007

Events,

If I pull off the air box, and rejet to smaller mains. I can get the boat to go 5-60mph in 2.3, this is my best 0-60 times this year, usually on any given day it goes 5-60 in 2.4 to 2.6sec. So in N/A form the carbs are sized correctly. But I have not tried using stock carbs, I dont have any.

EventsInTheChamber · Dec 11, 2007

Check your PM's, and like BD said throw a couple pics up...

Ratherbeflyen · Dec 12, 2007

I'm kinda skeptical about you not getting eneugh air at idle. Unless your getting fresh air underway and your sucking you hot exhaust at idle, you should be using more cfm at rpm than at idle. I'm guessing that your problem isn't air supply but more likely fuel, or turbo backpressure or spool lag.

Pictures are worth a thousand words put some up here.

Royal Motor Works · Dec 12, 2007

I will try to get some new pics up, all the ones I have tried to are all too big to upload. Not sure if I am uploading them right. Thanks again for all the input guys, this is a great forum.
Mark

geno · Dec 12, 2007

imo, your problem doesn't lye in the intake side of the equation, but the exhaust side. Not only is this a watercraft, but turbo'd. You have a huge exhaust restriction, at low rpm's, because of the nature of the beast. Have you tried leaning the mid, way down? I know it's dangerous. What is the pop off pressure set at?

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