Yamah suv 1.8 conversion

[ERICSUV1.8]

Converted my SUV to a 1.8 vxr motor. Having trouble getting the ski to stop proposing over 57mph. Current mods are XLT1200 R&D ride plate. XLT1200 Worx intake grate. Ski is running a vxr pump with solas impeller and new oem wear ring.

I have read up on the old school shimming ideas so that is this weekends test. Any other insight would be greatly appreciated as I am also in the process of converting my other SUV into a 1.8 supercharged swap.

[steve45]

Welcome aboard, Eric!

Perhaps a pump wedge would help.

[ERICSUV1.8]

Sorry not familiar with what a pump wedge is. (I forgot my other account name I made many years ago so I just made a new one today!)

[steve45]

It fits between the hull and pump, changing the output angle of the pump a degree or two.

[TimeBandit]

I'm in the middle of a SUV 1.8 conversion myself . . . not even close to being done currently.
That said, I can already tell that the SUV ride plate is ... well ... short. I wonder if lengthening it some might help?? Depending if one left the VXR's pump housing as-is (aka set the motor 2" back) or butcher'ed the housing to add offsets to the mid-shaft bearing (aka engine fwd 2") would dictate the pump sticking a little further out the back from OEM, thus getting a longer ride plate fabricated. Personally, I think the 2" more rear set-back is the way to go - just worried about the control cables reaching. Not sure yet if I'll attempt to extend the OEM plate, or re-fab a new design from leftover carbon fiber.

Another aspect I hope to address in my conversion, are the sponsons. I've pre-fab'ed new ones, and slightly longer using aluminum "L" channel and 2" HDPE spacers. Also glassed-in permanent nuts inside the hull for the mounting.

[K447]

The engine is the heaviest thing inside the hull. Shifting the engine forward or rearwards will affect the hull center of gravity and therefore the hull balance when on plane.

Longer ride plate tends to shift the center of balance forward. Ride plate angle is also a factor of course, but generally a longer ride plate tends to help the bow stay 'planted' in rough water and reduce bow lift during hard acceleration. Overall the bow tends to stay in the water more.

Engine weight forward has similar effects to longer ride plate.

Moving the engine rearward would tend to allow the hull rear to ride lower and the bow to rise.

All this would be for when when the hull is fully on plane.

[ERICSUV1.8]

I have adjusted that and still jumping. this is a issue many of us who have converted are facing. Will be adding riva pump kit as well as starting back with a standard xlt tide plate.

[ERICSUV1.8]

If you have a facebook join the yamaha suv group. Plenty of information on how to do the swap and would love to seee the sponsons!

[TimeBandit]

If you have a facebook join the yamaha suv group. Plenty of information on how to do the swap and would love to seee the sponsons!

Thanks for the FB group tip!


"My" theory for the SUV prone to jumping/porpoising:
So as you said, this is an issue that plagues this specific craft, especially after the conversion. Conventional wisdom points to the heavier engine and change in center of gravity, and more speeds. I think there is merit to all that but I think there is more at-play here... or rather, there's a way to tie this together :

Right now, in my workshop, I'm comparing the hull-shape of the SUV right next to my FX HO hull. The SUV's ride-plate is not only shorter, but it retains the overall "V" shape of the entire keel <-- remember this observation, will get back to it.

The FX ride-plate has a flattened section, as if one took-out a cross-section of "V" at the lowest-point. It can do that, because the FX hull is generally "V" shaped up until it approaches the jet intake. Then, anything from there aft, is transitioned to this keel-less flatten contour. I'll use the word "missing" a keel definition for anything aft of the intake. <-- truth-be-told, I think that is an improved hull-design concept, because (in my mind) this accounts for the "hole" or cross-section of water column which is now "missing" as it has been diverted/sucked up and into the pump. Relatively-speaking... if you picture the hull stationary while envisioning the entire water underneath moving aft-ward, on the FX, the ride-plate's flat area complements the missing column the jet took. On the SUV, the ride-plate maintains the keel aft of the jet intake and therefore collides with the replacement water column coming upward from the bottom of the column that was jet taken by the jet intake. I believe this "hits" the intake-grate's most extreme bottom and subsequently the ride-plate. It is this dragging-effect that I believe causing a type of feedback loop, thus porpoising. And I think this flaw has always been a part of this craft, it's just that the slower 2-stroke never got it fast enough where this hydro-dynamic starts to reverb with the hull. In-short, I think the SUV's hull-design is not ideally suited for 55+ MPH speeds.

Can something be done ... possibly, but to what degree and effort. One could hull-shave the keel "point" just ahead of the intake a bit (add glass to the inside hull) to reshape a better transition, but it would be hard to transition to a flat ride-plate because, again, the SUV's intake grate bottom section is still V'ed to match the entire keel-run.

Not easy to put this into words.... but I tried. Apologize for the generalizations.

[scittb]

Well the xlt's used to do what your describing. The fix was the r&d plate/intake grate that you have but then milled the rideplate by Jims performance. Pump wedge and set of sponsons. world of difference with that combo. Riva sponsons or beach house they were identical. For the xlt it helped track in the chop and got rid of the side to side chine walking. When all set up we used fenderwashers to shim the rideplate to get rid of the porpoise. We had the xlt's doing mid 70's back in the day on 1300 cylinders and Novi's was a breat combo! If you have the money try getting the plate milled and get a pump wedge amd then shim the plate accordingly. I bet the hull will behave much different even for the size it is.

[ERICSUV1.8]

I am willing to send my plate to be modded. I am unsure of where to find a pump wedge my internet searches are coming up blank. As for sponsons no one makes one for the SUV but the side to side walking motion was fixed by replacing the intake grate with the WORX xlt grate. I have inched the ride plate down 1/8" at a time and have only had minimal effect. Good thing I have all winter to keep up with the testing.

[ERICSUV1.8]

The guy who does most of the conversions in south fl including mine has shaved the hull on one and it did correct the issue so in fact you are correct with your statements. Multiple people have corrected it with ride plates and shims but each craft is a different hull due to the hand lay fiberglass. I have a 1.8sho swap starting next week in another of my SUVS and will see how that one rides in turn to the n/a. A friend of mine has a n/a and it does not porpoise much even with a standard suv plate which is crazy.

[scittb]

I am willing to send my plate to be modded. I am unsure of where to find a pump wedge my internet searches are coming up blank. As for sponsons no one makes one for the SUV but the side to side walking motion was fixed by replacing the intake grate with the WORX xlt grate. I have inched the ride plate down 1/8" at a time and have only had minimal effect. Good thing I have all winter to keep up with the testing.

https://deansteam.com/collections/best-selling-products/products/yamaha-2-degree-pump-wedge-for-sho-svho

[TimeBandit]

Thinking out loud again...
how different is the SUV pump shoe compared to, say, a 2004-08 FX pump shoe ??
If you follow where I'm going here ... if the FX HO pump shoe can be mounted onto the SUV, it would then complement the "flat-bottom" transition needed to then mount the FX HO ride plate. So forget about the mounting fasteners in the hull (as they can be relocated) ... just asking if the FX shoe & ride plate would rest into the hull pockets of the SUV?
Getting ahead of myself here... "if" these do generally fit, it certainly opens the door to a better ride plate. Also, since the 08-11 SHO plate is a direct-swap for the 04-08 HO plate, not to mention any other aftermarket plate/mod for the old SHO's.

Does anyone have one have any FX parts laying around from a previous donor ski? Can we compare general dimensions?

Here are some rough measurements of the SUV shoe :