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  1. #1

    8000 RPMs, 60-61 MPH? 2003 GTX 185, that can't be right.


    I have a 2003 GTX 185 that I have been upgrading trying to get to 260+. I know all the originals posters in this GTX forum are well past discussing mods on this old ski 2003 ski, but thanks to your old archived post, I'm another novice who has found your information some of the most useful and inspiring 4-tec info on the internet.

    I followed JPEConsults 2005 GTX thread from 2008. Read it like a book that I can now be quizzed on.

    I duplicated Pete's GTX 185 with an X Charger post upgrades and think all of you deserve credit for knowledge you were willing to share online.

    With that being said, lets discuss this 8000 rpms and 61mph. IT has me like wth? Before I discuss my issue, Let me give details about the ski

    Ski Condition:
    Hours: 122
    Compression: 130 all cylinders
    Oil Level: Middle of the stick
    Coolant: Full
    Plugs: Recently replaced OEM plugs
    Fuel: 91 Octane
    Supercharger color: Red
    Supercharger movement from hand test? NO.

    3" cold air to 4" Spectre filter
    ECU: 2005 RXP
    Knock Sensor Update: Yes
    RXP Aluminum Pump
    DIY OPAS Completion lock UP
    Prop: OEM 13/23
    08 mid pipe and waterbox
    Fizzle F1000 Intercooler
    Water Strainer
    Yellow Reducer
    Ride Plate Holes filled.

    (Upgrades I have that are not on yet:
    X Charger
    08 oiler
    215 Flywheel
    APR Bolts)

    I realize the only components I have on now to raise hp were the cold intake air filter and the intercooler. I didn't expect much from that but my results were actually wonderful! The ski was alot quicker but not much faster. Acceleration as bananas (good). Out the hole it would immediately jump to 8000 RPMS and would stick there with no inflections up or down. I thought this 2005 RXP ECU would give me 8100 as a limit but I am yet to see over 8000 RPMS. Not even 8020.

    The best speed I seen on the dreamometer was 66 mph for a split second. Some 63s and 64 as I started losing gas weight but no consistent speeds over 61mph. Maybe 62 for 10 seconds. This seems like my impeller right?

    Well, I have 2 OEM 13/23 "butterfly" impellers so my novice line of thinking went like this: I have 8000 RPM so I must need to repitch the impeller to get off "the limiter" and to get more speed. So I took 2 millimeter out of the trailing edge one of the impellers and the RPMS did go down but the speed did not go up. I was baffled. SO I went 2mm in the opposite direction with the other OEM impeller and got back to 8000 RPMS with no speed change still. And consider the 2mm of change on the second impeller represent 4mm of change from my first test run, yet I still did not see anything over 8000 RPMS.

    THe next day I went to test the ski with impeller #1 and the RPM would range from 7600 to 7900, with slow acceleration and a speed of 61mph.

    Following that I switched to the impeller with the decreased pitch and even took one more mm out to total -3mm and still did not see 8100RPMS. OUt the hole it hit 8000 dropped to like 7820 then crawled back up to 8000 and stayed glued there. At -2mm it went strait to 8000 and never came down. So what do you think is going on?

    Why is my ski only turning 8000 RPMS but is glued to it like its being limited. I thought the 2005 RPX ecu is 8100-8200 limit.

    Why am I only getting 61MPH out of 8000 RPMS even with the stock prop not modified?

    I have read other with the same ski getting 67mph at 7600 rpms.

    Any help would be appreciated.

    Last edited by Smashrockwell; 10-12-2020 at 08:40 PM. Reason: typos

  2. #2
    SplishSplash's Avatar
    Join Date
    May 2006
    Belle River Ont Canada
    Don't you have to change the gear on the flywheel to use an non 185 charger at full potential? Just asking

  3. #3
    JT jpt7779's Avatar
    Join Date
    Jul 2008
    Pittsburg, Texas Lake Bob Sandlin
    IMO, you would be better off with much less pitch on the trailing edge, which effects top end speed.

    Here is a 13/20R:

    Read my signature for a 05 GTX that is using a Solas 12.5/18 and runs mid 60’s at around only 7500 rpm.

    The root angle on the Solas impellers are different than OEM.

    You need to change out the flywheel gearing for the SC.

  4. #4
    Quote Originally Posted by SplishSplash View Post
    Don't you have to change the gear on the flywheel to use an non 185 charger at full potential? Just asking
    Yes. I have an X charger and bought the 215 Flywheel gear but haven't changed it yet. Others with the same PWC have achieved 67+ before changing the flywheel. IF I'm getting 8000 RPM I got the power to make more speed than 61 mph but the ski won't go faster.

    GOtta be the impeller but other with the stock impeller on got to 75+ from threads im reading.

    Thanks for the reply
    Last edited by Smashrockwell; 10-09-2020 at 08:53 AM. Reason: typos

  5. #5
    Quote Originally Posted by jpt7779 View Post
    IMO, you would be better off with much less pitch on the trailing edge, which effects top end speed.

    Here is a 13/20R:

    The root angle on the Solas impellers are different than OEM.

    You need to change out the flywheel gearing for the SC.
    Thanks. Your 2005 GTX results are an example of what I am talking about. Mid 60s at 7500. I also presume my SPEED problem is the impeller like you said but before spending on a new one I wanted to get opinions from experienced guys like yourself on what the problem could be.

    I do not think the impeller is the RPM problem. Has anyone with an 05 RXP ECU been able to hit 8100 RPMS with 3" cold aid intake the standard SC and the 17 tooth SC gear? IF I am correct JPEConsults was posting 66mphs before changing the flywheel. I also bought the 185 SC rebuild kit in case I want to swap cog wheels and just run the X charger with the 17 tooth gear on it. This will create extra boost my cast pistons can handle, but I can't move to that stage yet cause currently my top speed is compromised by something unknown.

    Do you remember what results the solas 12.5/18 gave your boat over the stock impeller? The reason I am asking is I achieved 7600-7900 RPM and 61mph with a increased pitch OEM 13/23,then ran 8000 RPM with a decreased pitch OEM 13/23 at 61mph. I understand different manufactures have different pitch readings but will the root angle of the 12.5/18 provide for more top end speed than a OEM 13/23 at the same rpms?

    I also noticed I am running an 03 impeller, which is the first year they made these boats. I never seen a progressive pitch impeller 10 angles apart like this 13/23, seem ridiculously progressive. It works but I wonder if it is tuned for the 185, 7600 rpm ski and not good for the 215 build?

    Nothing I have done has gotten the ski to 8100rpms.

  6. #6
    Ok. Back from a quick run after switching impellers again. I went with impeller #1 (OEM 13/23), with the 2mm increased pitch on the trailing end. I measured leading edge to 4.1cm and took it down to 3.9cm taking 2mm of pitch out of the leading edge. This was just an experiment to see what she'd do.

    The results were top RPMS 8000, top speed 62. The changes from the leading edge were noticeable. No hole shot cavitation, which I only experienced a little on impeller #2. I also noticed the OEM impeller that I purchased fits the new blue OEM wear ring better that the stock original one.

    So while thinking, I came to the conclusion that my 2005 RXP 215 ECU is not limited at 8000 RPMs but my engine current is. This is what I propose;

    I have a 2003 GTX SC with 3" rear intake, 215 ECU, 58lb fpr and F1000 intercooler. Regardless of the other mods I have that are not on yet, that is the current powerplant. What is to be expected from these mods? Exactly what I have been reporting. Great acceleration through out the entire powerband with top speed limited at about 62mph. I am seeing 400 rpm over the stock GTX 7600 limit but what am I to expect from that with the stock 13/23 impeller? My conclusion after multiple test runs is; not much speed. Lets examine the affects my mods have on my powerplant.

    3" Rear air with 4" Spectre air filter

    How much horsepower do you think this mod makes on a GTX 185? Riva racing website says "Power Filter delivers greatly improved acceleration and a 1~2 mph (150~200 rpm) top speed increase by replacing the restrictive stock intake system."

    I would not credit this mod for more that 5-6hp just judging from my rider experience alone. Leaning towards 5hp. Hearing the supercharger gives an affect like your moving faster, and you are, but not much.

    In my case cold air intake improved acceleration but not top speed over the stock intake. I do not believe this mod alone will produce any more top speed on a GTX 185 but it might on a 215. Here is why. Unless I am incorrect, there is no "soft limit" on a GTX 185. The limit is 7600. On a 2005 RXP 215 it has been reported a rpm limit on 8100 soft limit, 8200 hard limit. If a rider with a GTX 185 was consistently riding on the limit (7600 rpms), what top speed is there to gain from adding cold air intake? NO RPMS or top speed to gain from this mod on a GTX 185 which normally runs at 7600. On the other hand, a 2005 RXP 215 has a soft limit of 8100. If you were on that limiter and added cold air you could get close to 8200 rpms with an increase in speed. No one wants to run on the hard limiter like that but in theory adding cold air intake works for skis with a soft limiter, or skis that are not build to ride the limiter from the factory. A GTX 185 can run 7600 rpms its entire life from the factory because that is far under what the engines internals can handle. So there is no space left to squeeze rpms out of this 185 set up if its running at 7600 wot from the factory. We may be able to squeeze some speed out by increasing the pitch on the stock impeller to get off the limiter but this hasn't worked for me.

    The RXP or Seadoo 215s have a soft limit and a hard limit. I presume this is because the powerband gets closer to the stock internals threshold, so the limits have to be programed so the ECU responds more reactively. For instance, there is no reason for a GTX 185 ECU to limit fuel when on the 7600 limiter. On the other hand, there is a reason for a RXP 215 to limit fuel when on the 8200 limiter.

    Stock Supercharger with 17 teeth and F1000 Intercooler affects
    I have read in threads the stock 185 supercharger makes 6lbs of boost stock. The 215 SC (same supercharger) makes 8lbs of boost stock. We know the difference between those SCs are the 17 tooth gear on the 185 and the 16 tooth gear on the 215s. We also know the 215 SC makes more boost because it spins faster due to the 16 tooth gear. So then my theory that adding cold air intake only to a GTX 185 will not increase top speed or RPMS may be consistent with the fact that a 185 supercharger is limited when the 185 engine is spinning 7600 rpms, and the 185 sc 17 tooth gear will not let the sc spin fast enough to get the engine go over 8000 rpms. The superchargers turbine is spun by the cog gear on the shaft which is spun by the flywheel on the engines crankshaft. It is not a turbocharger. The air from the cold air intake is not turning the SC turbine. It's being sucked in. The rate of air intake is determine by a combination of the unrestrictive air intake system, the engines rpms and the SC turbine. So what is to be expected when adding a 3 or 4" cold air intake to a supercharged engine on the rev limiter (GTX 185)? Acceleration increase but no top speed increase.

    This lead me to my second conclusion regarding a GTX 185 with the stock supercharger, cold air intake, stock impeller, and now let's add a 215 ECU. So, I added the 215 ECU expecting to get a new limit of 8100 rpms. And I started this thread because I was not able to pass 8000 RPMs. Now I return to get a peer review on what I think I have learned about these mods. IF you read this thread from the beginning you may recall me saying no matter how much I tweak the impeller, I cannot get past 8000 rpms. I do get all the affects of decreasing and increasing the impeller pitch except for more top speed over 62 mph and more rpms than 8000. It got to a point I started to question the impeller pitch science. Then after realizing what I think I've learned about the SCs maximum rpms, I want to suggest a GTX 185 with cold air intake, stock 13/23 impeller and a 215 ECU cannot spin higher that 8000 rpms because the 16 tooth SC may be at it's rpm threshold with the engine at 8000 rpms. Basically the 185 supercharger can't spin any faster to suck in more air to push the engine over 8000 rpms. Especially considering the 215 RXP is limited at 8100 rpms, this makes perfect sense for the 185s set up not to be able to touch 8100 rpms with the stock supercharger and stock impeller. I have not been able to test this but I am also willing to propose that changing to the 13/20r impeller would get me to 65/66mph with these mods but after this analysis I think that's just the wrong way get to that speed. I am willing to bet if I changed the flywheel and used the same SC with a 17 tooth gear and the stock impeller I would get 8100 RPMs and top speed of 67/68mph. This is because changing the flywheel and the SC gear makes the 185 more of a 215 that any other mod. I did the 215 ECU before I did the flywheel and I wish I would have put the money into the engine before the computer that controls it. My results are the 215 ECU, 3" cold air intake the stock supercharger, stock impeller and a F1000 intercooler; really quick ski. Acceleration great but top speed limited to 62mph and rpm threshold at 8000 with the 16 tooth gear on the SC. I consider how another impeller will change things but this research was done with the stock impeller for control purposes.

    Lastly, a stock 2004 GTX 155 with no supercharger is limited at 7600 RPMS. A Supercharger 2004 GTX 185 is limited to 7600 RPMS. They use the same 13/23 impeller. Why is the supercharger model faster? We know it is because the supercharger is supplying the engine with more air faster. The speed between these two models is gained in engine efficiency. The difference between slamming the limiter or crawling up to it. Also, by Seadoos numbers, the 5-6lbs of boost the 185 sc provides the 185 engine is worth 30hp. Horsepower increases 5-6% per lb of boost. On a 155hp engine 5% would be 7.75hp per lb of boost. Take a 155 seadoo and add 5 pounds of boost at 7.75hp each and you got 193hp. Now, if it is true that the flame restrictor in the intake manifold reduces boost by 1lb we would have to take 7.75hp off of 193. Subtract 7.75 from 193 and you get 185.25. This is the correct horsepower for the GTX 185 so we know each lb of boost is worth 7.75hp and the 185 SC only makes 5lbs of boost.

    The X charger is the standard supercharger for 255/260 seadoos so lets test this math. It is said to make 9lbs of boost at 8100. Take a seadoo 155 and add 9lbs of boost each worth 7.75 hp and get a 224.75hp. IF this math is consistent the 255/260 seadoos get the additional 30hp from another source. A main difference between the 215 and the 255/260 are the fuel injectors an external intercooler. So then the external intercooler and 42lb injectors are worth 30.25 hp.

    Three 38# injectors divided by a BFSC of .5, with a 100% duty cycle can handle 228 hp. The 185 and 215 skis have 38# injectors.

    Three 42# injectors divided by a BFSC of .5 with a 100% duty cycle can handle 254HP.

    Three 48# injectors divided by a BFSC of .5 with a 100% duty cycle can handle 288 HP. The newer 260s have 48# injectors.

    These numbers confirm our supercharger research is quite accurate. So the intercooler must account for heat reduction that will allow the engine to produce close to 30 hp.


    My conclusion is I should have started with the flywheel upgrade. That is the most important upgrade. I do want to try a 13/20r impeller but I have already purchased a 215 driveshaft, carbon seal, bellow and have two 215 and two 185 impellers already. I don't need another 185 impeller. I am happy I stopped to think about the maximum RPM threshold for a 185 ski. I believe from my experience what I wrote is true.

    The stock 13/23 impeller is good for the stock application but I was not able to squeeze any speed out of it. Maybe that's just me.
    Last edited by Smashrockwell; 10-13-2020 at 03:10 PM. Reason: typos

  7. #7
    Ran the ski yesterday with impeller #2. Top speed 62mph, constant 61mph. 8000 rpms. Decrease the pitch on the leading edge -2mm decreased pitch on the trailing edge -2mm to total -2mm on the leading edge and -4mm on the trailing edge. The hole shot was impressive. No cavitation and great acceleration. Out the whole it nailed 8000 rpms and walked back a little then climbed back up to 8000 rpms and stayed there.

    I did more research and read Pete's GtX 185 with an X Charger thread and confirmed that even with an X charger a GTX 185 cannot spin over 8000 RPMs. Just read Pete's signature;

    This confirmation has me ready to pull the engine this morning to change my flywheel. I have the flywheel, driveshaft carbon seal and bellow from an RXP and will do those with the flywheel so I can get over 8000 rpms. I do not have the driveshaft alignment tool but I think I may not need it.

    The order of operations for performing mods to make a GTX 185 to a 260+ should go as follows IMO. This list does not consider engine internals. Keep in mind I have only owned a ski for two years, so this is in no way an expert opinion. This is just what I would do if I could do It over and the logic behind it;

    1. Flywheel change to 215 flywheel
    This is the most important mod. A GTX 185 will not be able to breach 8000 rpms without it. This will require a supercharger rebuild to change the SC gear. After this mod you will still be stuck at 7600 rpms but the ski will have 2 or 3 more lbs of boost than stock, adding 15 to 22 more horsepower to your stock 185.

    2. 215 ECU
    You can do the 215 ECU first. This will let you unlock 400 more rpms over the stock GTX 185 7600rpm limit if you do this first, and 500 to 600rpms if you do the mod after the flywheel change. The 215 ECU has a soft limit of 8100rpms and a hard limit of 8200rpms. The problem is the 185 sc gear will not let the 185 motor reach 8100 rpms. Also those additional 400 rpm for the GTX 185 with the 215 ECU changed before the flywheel are on 5lbs of boost. 8000rpm on 5lbs of boost will not be as fast as 7600rpm on 7lbs of boost (which you will have from changing the flywheel). The additional 400rpm from adding the 215 ECU will not make substantially more horsepower. Especially with the stock impeller. Might be a good time to change the fuel pressure regulator to 58lbs or whatever we will run.

    3. 3 or 4" air intake and free flow or thru hull exhaust
    Once you have the ECU and the flywheel in place removing air restriction could be beneficial. I think I've learned a gtx 185 can't do much with the additional air. An RXP can. You will see acceleration gains on a GTX 185 but not much top speed gains. It is because we are supplying addition air that the supercharger is not sucking in at the 7600rpm limit. Example, you have a stock GTX 185 running 7600 rpms 61mph. You add a 3" rear air intake. How many rpms will you gain? 0. You will get to 7600rpms faster but you will not see rpm gains over the stock 7600rpms with the stock ecu. You have two GTX 185s one with 3" rear air and one without. The one with rear air will accelerate faster and will win all races but will not have a much higher top speed. Maybe .5-1mph.

    X charger 42lb injectors, intercooler, 08 exhaust and all the other mods
    Next I would do the intercooler and x charger or whatever charger you desire. I have the X charger and am contemplating on the et137 wheel. I did the exhaust and intercooler before the X charger and flywheel just to be able to ride this summer, or just from newbie inexperience. Now I wish I did the reverse.

    Today I am pulling the engine to add the flywheel and 08 oiler. It's 6:24 in the Cali delta. About to grab a coffee and get it poppin!

  8. #8
    JT jpt7779's Avatar
    Join Date
    Jul 2008
    Pittsburg, Texas Lake Bob Sandlin
    Was going to suggest an external IC, but reading back I see you have that already.

  9. #9
    So, today I got the engine out. Didn't have the time to work on it over the weekend. I copped a Supertech Light Weight Valve Set and Supertech springs and retainers, new head gasket too from greenhulk. I live in California and we're still getting 90 degree days in the Delta but I figure I will make this a slow winter project and come out next spring acting up. You can see photos on instagram, @casualrapgod

    Next it's cp pistons and Carillo rods. Then a Gato manifold. Thinking about the Riva Cam too.

    I know I don't need all that to run an X charger with an et137 wheel but I want to experiment with new set ups on this boat. I also want to run 8600 to 9000 rpms once done. This should give me about 16lbs+ of boost on that et-137 wheel. I'll run an RXP 260 12-15 stage 4 tune at 8900 or just do a custom flash to 9000rpms. The only thing I need to run that tune now is vt1100s and a bunch of monitors. I just want a super fast recreational ski. About to do some more piston research but it 9:5:1 cp or diamond pistons.

  10. #10
    Update: I wish I would have done more reading which would have amounted to less spending.

    I got the engine tore down, don't have my Carillo rods yet but its a matter of time/budget. Still need all the ARP bolts too. Thinking about sending the head to Eastside Powersports for a port and polish, but I can't find anyone posting results. Wondering if I need that. The cam is going to Schniedlers Racing Cams in San Diego for a Stage 2 Supercharger grinding. Only $224 and the specs are on the website.

    Here is what I want to write for anyone with a old school 4tec GTX like me who's researching old post from legends of Green Hulk to find how to upgrade their old 4tech.

    I'd skip the X charger + 215 flywheel build and go strait from 185 to 300 hp.

    Get a 300 PTO or modify your PTO. To modify your PTO see here;

    I do not know if it is mentioned in the above post but there is also another oil jet that may need to be removed from the top of the Cylinder block/crank case. Confirm that yourself.

    Now the build is the XXX Charger on the 300 PTO. This xxx charger should provide 23 lb of boost at 9,200 RPMs. by my calculations that should be worth 178 HP.

    My equation is; natural aspirated 155 HP +(178.25 HP= 23 lb of boost at 7.75 HP per LB) + external intercooler efficiency rated @ 30 HP + cold air intake rated @ 5hp + flame arrestor removal rated @ 1lb boost or 7.75 hp= 376 HP.

    I believe these number to be fairly accurate. If you take any Seadoo 4-tech model number, from 185 to 300 and run this equation (NA+(B*7.75)+ intercooler @ 30hp + B -1 lb for flame arrestor, you will be within 1 HP of the model number.

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