Recommendations/tips on building an X4 monster :)

[IDoSeaDoo]

I can't believe it's taken me THIS long to do this, as I've had the parts for a while now... but I'm finally getting around to building my dream jet ski: I have a 96 hull with 95 wiring and the following mod parts:

Bored NOVI carbs with large jets (mains in the 160's I think)
R&D Flame Arrestors
Spec I Factory Pipe
MSD ignition enhancer
Water Injection
Stock head off a 95xp 800 which magically boosts my compression to 180 (or maybe 185, I forget)
R&D intake grate
17/23 Skat Trak impeller

The motor I'm working with I pulled apart last year and replaced the outer crank bearings, as well as the Counter Balance shaft bearings. I did not get a new crank so the connecting rod bearings are stock. I will be replacing the top end as well as new wrist pin bearings.

My question is: what do people mean when they say that I need a "fresh" motor to mod? I plan on building this one up and making sure that it does not have any air leaks and has good (if not REALLY good) compression. With compression numbers as high as 180, do I need to run 100octane fuel or will I be okay with pump gas? Is it compression or RPM's that necessitate higher octane? Should I bore the motor past 82mm? Has anyone hooked up an MSD enhancer on one of these babies before? Were there any particular hints/settings you recommend? People say to find a good tuner to mod these up. Well, I want to become that good tuner. I have a few years rebuilding/diagnosing seadoos, how do I learn more about tuning?

All feedback is greatly appreciated. I'll follow up with details as I progress with this project.

 

[Dr Honda]

With the parts projected... you could be into the 150 hp range. Because of that... yes... it's recommended that you have a "Fresh" engine. If you try to use a 15~16 year old crank, with old rods, and bearings... the new found power could be the nail in the coffin. Even if the rods/bearings feel OK... they have a lot of time that has beat on them. They could be full of small fractures, pitting, and general wear. The higher HP will cause those normal wear points to disintegrate.

Also... old pistons start to die. Basically, the aluminum will break down and get internal fractures. This is why sometimes piston skirts shatter, or crowns fail without warning.


Now... one thing that worries me is you saying that the 95 head magically gives you 185 psi static compression. It shouldn't. The only difference with the 95 800 engine, and the later years was the pitch of the gears on the counter weight... and the threads on the end of the crank for the PTO. Before you commit to that head... check it !! Make sure if it was cut... the squash gap is set correctly. With 92 octane fuel... you can support 180 ish PSI compression... assuming that everything is PERFECT !! If your timing is a tad high... or your mix is just a little lean... you will get detonation, and eat the engine.


With that said... even if you go up to 100 LL or Race fuel... you still have to make sure EVERYTHING is perfect. The Rotax seadoo engine is already putting out +140 hp/l... so pushing that up to 180 hp/l means you have to be even MORE PERFECT. So... that means........

1) Piston clearance
2) Ring gap
3) Bearing end play (rods, wrist pin, outter)
4) Squash Gap
6) RV timing
7) Ignition Timing
8) Water being injected into the pipe.

And finally... what the "Tuner" is responsible for... the fuel mix.


A proper (slightly Rich) fuel mix will keep the engine running cool, and make the best power. On a 2-stroke... 12.5:1 at full throttle is ideal. If you go too rich, using high octane fuel... then you will be passing too much, un-burnt fuel out the exhaust port... and you will overheat the piston crown, and melt it. A lean mix will cause detonation... and melt the center of the crown. (or crush the ring lands, or rod bearings) The more HP you are looking to make... the smaller the window.

Now... regardless of the time you've put into working on these things... you are still and amateur "Tuner." So... my advice to you would be... use a MUCH lower compression head, and run the ignition timing a little low. (about 5 degrees) That will open that window... and allow you to make a little error in the mix, without killing it. Then.... Once you get it tuned... bring the compression up, and re-adjust the fuel. (if you are spot on... you may not need too) then, bring the timing up to spec.


There is only one way to learn to tune... and unfortunately... Sometimes.... that means loosing a couple engines.

 

[Spimothy Leary]

There is only one way to learn to tune... and unfortunately... Sometimes.... that means loosing a couple engines.

doc your entire post is worthy of quoting, but this is important, granted with the wealth of info out there these days the likelihood drops quite a bit if you follow instructions carefully, back in the "day" tuners had to learn the hands on way.

I'd also invest in a new crank, i wouldn't recommend putting an old "good used" crank in a high performance ride, that should be sold and move into a stock ski to finish its life in a normal environment.

 

[Stunnerable]

Doc your post is perfect except with those mods he's going to be closer to 130hp. It takes 945R or VE cylinders to get near 150. Look at the new open spec runabout class this year. You can either run an all out super stock 787 or a 951 conversion with a stock pipe and no porting, boreing etc. 150hp in an X4 is absolutely bonkers! Scary fast.

 

[northshorerider]

First off with that head at 180 psi and your compression gauge is spot on coupled with the spec 1 you need to run at least a 50/50 mix of av fuel and 92 or 93 octane(ethanol free of course). I have a heavily modified 95 xp800 and i can help you out in getting it tuned just send me a pm.

 

[IDoSeaDoo]

Hmm, that may be a problem. I might just want to build it for 93 octane... I have no idea where to get AV gas, or ethanol free gas. What do those cost per gallon where you buy it? Do you use an EGT gauge? I def appreciate the help. I'm so behind on all my projects... life keeps throwing one thing after another at me while all these parts just sit and gather dust. (not really, they're boxed up )

 

[northshorerider]

The ethanol free gas is about 10 to 20 cents higher a gallon and most of the gas stations around where i live carry it. I don't run av fuel because I couldn't get any airport to sell it to me. I run 93 and a 25% mix of 110 race gas which is $9 a gallon. I haven't been running egt's but i just bought a racepak hottach 2 kit but I'm waiting on specs where to drill my spec 2 manifold to accept the egt's.

 

[IDoSeaDoo]

There are several threads on the topic of EGSs in X4's. When I mounted mine, I shaved down those rectangular protrusions on the side of the Y-pipe and drilled right in the middle of what was left. That put the probe somewhere like an inch from the gasket surface. I seem to be getting a good reading there. Caught my EGTs creeping into the 1100's today and enriched that carb. Melting point of aluminum is 1218F and I want to stay well away from that! I hope you get yours mounted soon because I want to know the temp. difference you see on yours. I'm getting around 100degF difference between MAG and PTO, and everyone keeps telling me that's normal due to the difference in exhaust design and how it affects scavenging. I'm about to build a couple more X4's and put EGT sensors on all of them. Going to start building my own EGT sensor systems using cheap micro controllers. I have a KOSO gauge that I'm using now and will use to calibrate my future creations. I had an engine die on me for no apparent reason. Engine just cooked the head O-rings which let water in, which ruined the crank as it was turning in at 7000rpms. The engine had maybe 30 hours on it :/

 

[1995hx]

I run a ported 787 with 195 psi head squish is wide which is what you want I don't run egt's but I do run a 50/50 mix of av gas and 93. I turn 7450-7500 rpm's and have over 100 hrs on this set up I run a spec 2 pipe west coast mikuni 44mm carbs and a custom cut rotary valve. I have be told this setup can make 140hp. Your setup for 93 should be compression no more than 175 with a wide squish,your spec 1 pipe, no timing advances at all, stock carbs at 75 pilot jets and 155 mag main jet and 157.5 PTO main jet low speed adjusters at 1.5-1.75 out to start and high speed adjusters at 1.25-1.5 to start tuning is gonna be necessary. Carbs should have a 2.0 needle and seat with a 80gram spring (black in color) pop off in the mid 20's. With a supporting prop your ski should be about 61-62 mph turning 7200-7300 max rpm's on pump gas. If not using water injection on the pipe make sure you hard jet it with a spray bar with a 120-130 main jet if using the water injection use a 120 main jet in the spray bar on the mid pipe and a 125 in the spray bar for the water injection. I like a 135 main jet at the water box. Hope this helps. Also if it was me and the engine runs great now I would mod it just my opinion.

Sent from my C771 using Tapatalk 2

 

[northshorerider]

What he said ^^^^^! Like I said I am waiting on specs where to drill my spec 2 manifold I don't want to just go drilling an expensive part that is not made anymore.