Hey guys, i have a kachina labala 22.5ft jet and tryin to get the most out of my topend,  i have a grade on the intake and was told to take it off and dont put any kind of grade in it and just leave it open.  The grade has 2 El channels on either and and strait stock in the center of the grade, should i purchase a after market grade that directs water at the top of the impeller?  Im running a AA impellar  and pump was just redone.  Can give more detail if asked, any help would be grate.

Thanks.http://

What your describing (can't see the pics) sounds like a "river racer grate" (angle iron type) , Truthfully on that particular boat as currently set up and depending how/if the grate is trimmed to keel it may be actually hurting your performance call or post up if you need help Tom

X2, and NEVER run without at least a rock grate. Stock rock grates, I'd be willing to bet there are at least a hundred of 'em laying around members garages they'd trade ya. 

I think Tom is right, check for proper install and leave it alone if it is set up right. You can get more speed elsewhere, and spend less time digging rocks out of the impeller! 

Ray

thanks, ya i thought i should have something protecting the impellar, i just rebuilt the motore and made many changes this time, lol.  The motor is a 454 bored 60 over, oval port heads that have been ported exauhst and intake, i also installed a bigger exauhst valve in heads,643 lift cam, rocker roller everything, air gap manifold, flat top Keith black pistons, 830 holly, Kodiac exauhst.  I dont know what the horse power is, i built the motor myself, but it pulls hard from bottom threw mid rangs that seem like it just flattens out, should i cut the impellar to an AB?  I dont know if the grade is trimmed at all, looks like its just bolted in, in 4 places, also i hear that that type of grade is dangerous and dont get why that is?

Not enough information to be honest..

What Camshaft? what heads (or better yet C/R)? When you say flattens out, at what RPM?, the motor could just be clean out of torque.

Cam timing, ignition timing, carb jetting, synchronization and linkage adjustment have a lot to do with it too...

The loader grate you are using work OK for keeping the pumps loaded to a point, but are totally under built IMHO (if it is what I am thinking it is) and if it fails, can cause catastrophic events to occur..If part of the loader gets sideways, or worse breaks completely off, it would be like throwing an anchor off one side of the boat while running flat out. 

If the motor runs up to say 5,000 and simply stops accelerating (stupid common BTW) you are more than likely just out of torque to continue accelerating...(could also be read as lack of HP)..

If the motor runs up to the 4500's, and hits a wall, could very well be overloading the pump (doubt this seriously)..Or something is amiss with the tune.

Simply saying "cut the impeller down" would the a perfectly wrong answer....

Get some running condition information and post it up....Vacuum gauge reading would be most informative at WOT...

GT

thanks, i re-updated my last post and will tell you rpms, but it tops out at 4800. it just seems like for what ive done to the motor i should be getting more, i havent been in any other jet boats but mine so i have nothing to compare to. Cam 643 lift, 115 separation, cam from merc, all rocker roller.

Sorry to say this, but either advance the cam timing a touch or start over....I/O cams are as close to an automotive grind you can find and still be considered marine...

Any idea what the compression ratio is?

With flat tops they would be fairly small combustion chambers to be even close, do you know the casting number on the heads?.

It's not necessarily that you don't have have "good" parts, I'm thinking you have the "wrong" parts. 

By advancing the camshaft, you may be able to gain some much needed high rpm range torque, you will lose it at the bottom, but jets don't need torque until the high 3,000's...May be a good band aid..

I have a Merc 454 Magnum in the garage at my pops, supposed to be 375 HP, but at 4800 RPM, really nothing special about it.

4,800 RPM is pretty good IMO, you will need more RPM if that is what the engine is looking for, which is why I asked the camshaft question, I'm going to go out on a limb and say too much cam and quite possibly to low of compression...

In all honesty I would feel more comfortable with an A impeller, but with the amount of boat you are trying to get moving, it's a crap shoot...

At this point, playing with cam timing, rocker ratio and the tune are the only viable options to make sure you're not leaving a little something on the table...I guess that's why dynomometers were invented...

Cutting the impy (or buying an A, keeping the AA in tact) may be the ideal fix, just hate to see you find the missing HP later...

GT

thanks, i re-updated my last post and will tell you rpms, but it tops out at 4800. it just seems like for what ive done to the motor i should be getting more, i havent been in any other jet boats but mine so i have nothing to compare to. Cam 643 lift, 115 separation, cam from merc, all rocker roller.

You certainly spent some time on the motor, but as Glenn said, Final C/R, actual cam specs are really needed (MAybe a pic of the cam card).

The other thing Glenn touched on, and beleive me, not such a big deal on rebuilds and mild motors, but absolutely CRITICAL on high performance builds, is cam timing. They need to be degree'd in correctly. Most all timing sets have multiple keyways these days for this, but beyond that, there are offset keys available to make the shortblock dead balls on accurate before you go any further! It's also never a bad idea to check, again, using another method, after the valvetrain has been installed. I've never personally seen a properly degree'd in cam NOT use an offset key. Had a friend (engine builder ) explain it to me this way many years ago.

"I've never seen, even a BBC crank, where the keyway was EXACTLY where it was supposed to be. All in tolerance, but not even one exactly where it was designed to be on the spec chart. Then figure the tolerances at the cam grinder that bored the cam gear bolt holes at THEIR plant, the timing gears tolerances at theirs......... They're expecting their aftermarket stuff to be installed properly, so those particular holes are given a lot of tolerance in most cases"

Pat (ibhz), Ralph Brunt and Dave (Enginedoctor) are without doubt far more hyper-critical on measuring dimensions than I am, on everything, but this is one area I think we'd all agree on. I've kinda adopted their theory of measure, measure, measure, assemble, dissassemble, measure again, assemble, and if it's right, then repeat...........

Ray

Wow, looks like i have a couple things to look into, the only thing i did as fare as timing is concernd is, made sure i had #1 top dead center and remarked the dampner for 0 and timed it that way.  As fare as dialing the cam in, that wasnt dont and yes kick myself for not doing so.  I was told to turn the impellar to get up on the rrr's and motor would pull through the top end, wanted a couple ofopinions.  Im not sure how to accualy dial the cam in, could you give me some hints?  Can i dial the cam in buy just pulling the back seat out to get to front of motor, and do i have to pull the dampner off?  How much would a ride plate help me for top end?

There is something you guys need to understand.

The pump will continue to accelerate until the engine has no more to give. The impeller curves show how dramatic the requirements are. It's not linear and to get that extra 200-400 RPM requires a butt load of HP.

This may help shed some light...

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BTW, just because the impeller chart says you need 400 HP to turn an A impeller X rpm, does not mean you have 400 HP, you have to read the curve as "an A impeller can absorb a max of 400 HP at X rpm".

Why? it's simple, lets say you have ridiculously large clearances in the pump, the pump will slip allowing the engine to rev higher than normal, so does that mean you gained 100 HP?, no.....It means your not getting the HP to the water... 

You need to be sure the tune is dead nuts and you have achieved maximum potential before cutting the impeller...

Hope this helps...

Well, i think i should start by making sure the cam is dialed in  for starters.  I could be that i just dont have the HP, it is a big boat for a jet but after all the motor work i jjust thought i would have more top end.  You guys have benn a great help on many levels, i need to start with just motor timing first i think.  Ater im done with that ill  hit you guys up again, you guys been a great help and think motor tune and set up is the starting point.

Now i was told to get a longer droop, and big ported heads, any truth to that?  and  whats wrong with the oval ports i have that were ported intake and exauhst with a bigger exaust valve?

I do not recommend rectangle port heads until above the 5200 RPM range, IMHO ovals make better mid range grunt...

Stay away from bolt-ons until you have everything else ruled out, I think your setup is really close, you're trying to get things ruled out at this point, just throwing money at it will just cost more money and you will be chasing your own tail...

I would doubt seriously that your hull could benefit from some bow lift at this point and time, it takes more HP than what I believe you are making (maybe low to mid 400's) to get that big fugger to lift (in the mid 600's if I had to guess)..

Be patient and methodical and the answer will find you....Still say your close. I would sure like to see what an A impeller would do...

GT

KInd of read down thru the middle since my post re the "RR" grate , and  possibly whats ahead here is redundant and maybe irrelevant , but some things to think about , many 80's 90's OEMs built thier boats with 350 to 375 ish HP production BBCs and used AA Impellers and trim to complete their "package"  , the logic is/was (as I was told) to get thier advertized and "wet tests" jet drive boat offerings fuel consumption numbers closer to the IOs and they were somewhat succesfull (I have Old issues of HB) , these medium and bigger cruisers would typically turn that AA around 4400 to 4600 WOT and speeds of around 55 to 60 (normally loaded) . To get much more out of that type set up requires alot more HP (small HP and performance increases in jet boats  are realized in "baby steps" ) Big boats IMO dont typically "Like" smaller impellers (b's etc) , the AA for example will help get the bigger boat up and out of the water better , to make a 20-21 run 65-70 will likley take a true 500 HP + and 500 will turn an AA around 5k + or - , 500 HP from a BBC is improved heads, mild cam (2500 to 5000) , improved ignition , greatly improved intake and exausts and tuning ,just my 2 centsTom

Thanks, Mr jet boat performance ( dont know your name)  I think i have to be around 550 or 600hp.  Look back at the beginning of my post and will tell you the set up im running.

Would be willing to bet less than 500 HP...(at the present 4800 RPM)..

GT

You really think so? Dam ive make so many changes in heads, bore, cam and so on!

Maybe I should re state my post....Keeping the engine limited to 4800 RPM I would bet your current setup has more in it, it just can't get there....

It may very well make 550-600 HP on a dyno (still bet your in for an unpleasant surprise), but keeping it lugged down is hurting you.


Cam could be the wrong grind for the application. (very often are...)

Do you have the model number of the cam, or the cam card?

Don't mean to offend. Dyno tests have humbled many...

GT