Help with restoring Kona jet

[DrGoodfella]

I was just given a 1978 kona jet with a rebuilt 454 motor. It has original cam , holley carg, panther exhaust manifolds. Its starting to tick, knock, backfire etc. :crossx: I was wondering what type of replacement crate motor I could put into it. It has a 12J Berkely jet. Does the new motor need a special cam? Any help would be nice. Thx

[FASTRAT]

I was just given a 1978 kona jet with a rebuilt 454 motor. It has original cam , holley carg, panther exhaust manifolds. Its starting to tick, knock, backfire etc. :crossx: I was wondering what type of replacement crate motor I could put into it. It has a 12J Berkely jet. Does the new motor need a special cam? Any help would be nice. Thx
Welcome to HB...1st off i would ck to see where all the funny sounds are coming from ie: lifters not adjusted rite, timing not set rite, rod knock etc...ck all that & see what happens?, then, if money is no object...i personally would opt for the HP502/502...a very good & reliable motor, on the other hand, if ur mech inclined, i would pull the 454 apart & see what all the funny sounds are?...u can build several good motors from the 454 ie: 460, 468, 480, 496...i would weigh the cost to build one of those against a new crate motor!...add a good cam & manif & ign & ur good to go...just my.02 cents
fastrat

[SmokinLowriderSS]

I'm with fastrat here, but I'm a wrench-twister. The 454 can be rebuilt and built up generally by a person for a lot less than a crate engine, and when you fire it up, you know all the tolerances are what they need to be. No chance of something being on the snug side and biting you. Crate motors are not marine motors and though they may work just fine, probably most of the time, boat engines demand a bit different tollerancing care in the rings & bearings, and deserve heavier duty parts as they are never under light load conditions like a car cruising the highway. That 454 can, if assembled right, be built to make nearly 600HP on premium, NA, single carbed, arround 5,500RPM, AND be reliable (user friendly). Now, that's 10:1 comp and heads much better than stockers (either ported or aftermarket), and a very careful thought process to make it all work together and give you power you want WHERE YOU NEED IT.
Either you wind up saving some coin over the crate, or you wind up with more motor, with better parts, for similar outlay. My $0.02.
Best of luch wherever you decide to go. :)

[DrGoodfella]

Thanks guys. If when they get into the motor the suggest a new motor, is there a particular cam etc. that needs to be put in the crate 502 for example. What things do I need to know when they ask me how the motor should be built. Thx

[SmokinLowriderSS]

Thanks guys. If when they get into the motor the suggest a new motor, is there a particular cam etc. that needs to be put in the crate 502 for example. What things do I need to know when they ask me how the motor should be built. Thx
Boat engines, and especially Jet boat engines tend to run colder than "normal". Mine used to run 140* WFO, 180 at idle. She is now colder (118/155) due to plumbing changes from new headers so I am working on readjusting. They work harder so you get a situation of hot pistons & rings, colder cylinder sleeves, and high RPM's.
IMO, follow the factory clearances range, but stay to the middle and wider of the range (the "upper half") for piston to cyl gap, ring end gap, and bearing clearance on mains & rods. I don't have number specs at my fingertips, sorry. Trying to get those clearances near the minimums works OK on an engine running a stable 190*, but will bite you with the temp swings on a jet-boat motor combined with the high loads durring a hard run.
The cam all depends on what you want to do, as well as what heads you have or intend to have, comp ratio you intend, tons of variables. Running my solid and strong lake boat, ease of use was a key, as well as wanting good power and I think I am heading the right way.
My454 gave up the factory .461/.480 268/274 deg cam as well as the cast iron dual plane manifold for an Edelbrock Performer RPM Air Gap and an Isky 280H (.565" lift, 280* dur) but in a custom grind from DuaneHTP. Went from about 280 HP stock to right at 350 according to programs I have and the actual running data last year. Headers went under her hood this winter, and we should get close to 400HP, that's on an 8.3 to 8.5:1 engine. She drives nicely, pulls skiiers, tubes, and is very mild mannered, till you slam the loud pedal to the floor. Next winter is either heads or porting work and should get us worked close to 500HP, still 8.5:1, 87 octane, 5,000 RPM and a very wide, flat torque & HP curves. My budget forces me to do a step at a time.