Came out of the 5.3 that's installed into a 78 Glastron jet boat with EFI, ported heads, LS2 cam specs. It ran really good all summer long. Last time on the water in December it let go. Heard that the LS rods can handle all kinds of blah blah blah horsepower and that's a totally incorrect way to rate the rods. The real test of a rods strength is RPM, the ability to grab the piston hauling the mail going up and yanking back down without coming apart. In a jet boat the motor has two speeds. Idle and WOT. In my boat with a C cut impeller, WOT is about 5,100 constant RPM. Most runs will go for about 15 minutes or so at this RPM. Depending on air quality, it has run as high as 5,300 rpm sustained.

I see lots of threads on these motor making ridiculous power but that's usually on dyno pulls or 11 second drag strip passes. Haven't see much on dropping the hammer and holding it for 15 minutes.

Plan is to now go with some SCAT forged H-beam rods and maybe bore it to 5.7 specs as long as my nicely worked heads are OK. IF the head on the cylinder that came apart is junk, then I'll go with a 6.0 and L92 heads. Another thing we do in the jet boat world is open up clearances by .002 for the extreme duty of sustained RPM, which was NOT done on this motor.

Anyway, anyone have any experience with this kind of duty on a Gen III motor? What little info I have found the rods are the weak link for sustained high RPM use.

 

People ask a lot from stock bottom ends. They think just because so n so revs their motor to 7000+ a few times that itll be ok, and it will last.
Wrong.

Stock rods really arent designed for more than about 6600rpm and the rod bolts especially. If you want sustained high rpm use you need strong lightweight parts with arp bolts and good bearings to keep everything lubed up.

 

And balancing in a marine application is a must. I had my small block (5.7 with vortex heads, yada yada) fully balanced and ran the snot out of it with no issues. I ran up to about 5400 at WOT. Needed more prop ��. I would go with the 6.0 regardless. No replacement for displacement in boats. I run a Mercury Racing 500EFI now, nothing like 600 lb-ft of torque.

 

Somewhere in this forum (gen3 internal engine) there is a thread a year or so ago about this person using an ls1 in an airplane application ,,,,,,,,not sure what rpm but I know it would be sustained ,,,,,,,,,You might do a search and maybe You can find it ,,,,,,,,I remember the guy was asking for suggestions to make the engine more reliable for His application .

 

I remember that thread as well but it may be in the hybrid section. Theres also been a few others with lsx in boats you may want to check out.

 

on marine engines we just set the fuel, spark and throttle limiter 150 rpm above the 5300. that way tue engine does not overrev when you fly off the water.. I think it could work for you

That was killing our rods... just use katech or ARP bolts

 

Some forged rods will do you good in the next motor you build. The stock cast ones are talked up to hold a lot more than they actually can.

 

amen to that

 

Thanks for the replies everyone. While a 6.0 would be sweet this boat is no race machine. All my EFI and tune and everything are spot on now. Shoot, it runs 2-3 mph faster than it did with a Ford 460 big block. It's a day cruiser that gets a lot of use. It's pushed to it's limits a couple of times a week in the summer. I see a lot of guys that build these hot rods boats, then they only put them on the water like three times in an entire season. I'll get more use in a week.

Anyway, thanks for the advice. Next question, I beam or H beam for this application? BTW, the stock rod bolt are still torqued onto the broken pieces. They didn't fail, the rod itself did.

 

I put powdered metal rods in the same category as hypereutectic (cast)pistons. Neither one has any business being in a true high-performance engine.

Give a cheap part a cool name and realize more profit while reducing production costs. It's just good marketing.

 

The I beam would be lighter id imagine, but also more expensive. either choice I dont think you will go wrong, its a significant upgrade over stock rods either way.

 

Are you just running an automotive harness and computer. How do you tune it? Wideband in the exhaust manifolds? I assume it has dry exhaust?

 

Yes, automotive harness and computer modified by S&S Performance in Arkansas. It has fully jacketed exhaust manifolds, then I made a spacer to go between the manifold and riser for the O2. Water flows thru the channels on the ends. The water enters the exhaust at the end of the riser. Had to relocate the coils under the exhaust. This baby even runs drive by wire!

Pic attached...

 

That's awesome. I'd love to have 408 in my little Donzi.

 

OK, been a couple of weeks, but last night I scored a set of flat top pistons and rods out a 2008 5.3 all aluminum motor with under 20,000 miles. These will drop right into my block assuming all is well with the crank and block, right? Where the 2002 have 143 cast into them, these have GKN as a casting number. These look WAY beefier than the 2002 rods too.

 

That's a huge assumption given the damage to that rod in your 1st post. You haven't pulled it apart yet?

 

there is a company that sells ls out board motors ,600+hp .

 

i can safely say ive never seen a rod in that many pieces. Good luck on the new engine sir!

 

Forged rods and pistons. my 6L lost a piston I think. #7 and #8 rods were in 8 paces it had 235 hours on it took out block and pan both pistons were in paces crank was ok. I am going with all forged stoker.

 

Got it all the way apart today. There were TWO busted rods in there. Crank and block are junk. One of those pieces in the first pic belongs to the other rod. The big end was still on the crank, the piston end was still in the hole.