Repower (MarinePower LS3 (420HP)

WetProcess · Post by **WetProcess** » Mon Apr 04, 2016 7:50 am

Hi I'm new to the forum Have had my '88 33SF for 2 years and are replacing the original 454 (340HP) with the 420 HP 6.2L Injected V8 (Gas). Torque is rated at 4600RPM and HP is rated at 5600RPM. Any suggestions for WOT target RPM for propping. Currently have 23 x 25 and 23 x 26 props available. Al WetProcess

lobsta1 · Post by **lobsta1** » Mon Apr 04, 2016 12:03 pm

Al WELCOME I can't answer your ? but am incredibly curious as to how these small blocks handle the weight of our boats. Especially how they handle climbing the back of a wave. Al

Post by **dougl33** » Mon Apr 04, 2016 1:20 pm

Welcome aboard Al. You're definitely blazing a new trail with these engines. The manufacturer's specs should tell you a min and max range for WOT. I'd try and hit the high end of whatever that number is for longevity.

WetProcess · Post by **WetProcess** » Fri Apr 22, 2016 7:53 am

The mfg specs for WOT (max) are 5600 rpm, but that is derived from the GM specs (which is max rpm of 6600!) for the LS3. Since they are not avail in reverse rotation, we needed to change from Velvet Drive to ZF trannys, which will run one fwd and one rev. I think 5600 is too high. Based on additional discussions with MarinePower we are going to target 5200 at WOT. Thankfully, there is enough space to swing big wheels, which are currently 23"dia. Will start with 25" or 26" pitch and see how it goes. Re handling the weight: The HP is rated at 425-430 and the torque is pretty flat from 3200 on at about ~400 lb-ft (peak at 4600 @ 435 lb-ft). Bear in mind the the old MIE 340HP's are 85 HP less, don't have orig torque specs handy and they are 200 lbs heavier (each!). Will keep all posted Al

WetProcess · Post by **WetProcess** » Mon Aug 29, 2016 10:01 am

FINALLY!!!! After 7 months and ~75K it's back in the water. Propping has been brutal(ly expensive). Been thru 3 sets so far and even Mich Wheel's recommendation (20 x 20 Nibral) was way off. The results are as follows" Fully loaded (23,600#) 23 x 25p Bronze 4500 rpm/33 mph 20 x 20 Bronze 5400 rpm/27 mph!!!! 21 x 23p Bronze 4650 rpm/37 mph 20 x 25p Bronze 4750 rpm/38 mph 21 x 23 Nibral 4850 rpm/39 mph Note idle speed 700 rpm/5.8 mph!!!(makes docking a lot more challenging) Not 100% sure on rpm as these original tachs are not matching and at least one is off by >150 rpm. Having the J1939 NEMA 2000's to my Garmin display and will have a better feel. Trying to get the fully loaded RPM 5100 or above, so if I can verify the last round I'll try taking an inch of the Nibral props. Cruising at 30 mph ~3600 seems effortless in a 2-3ft chop and the hole shot is UNBELIEVABLE. Pulling back necessary before I can even react! I believe that part of the prop issue is related to the shaft speed. Since these engines are not available in counter rotation we had to go with ZF trannies. To get them in time (if I only knew the yard was going to take that long) we had to get 2.31:1 rations which means that the props are spinning at almost 2300 rpm at WOT. That makes the 70% radius speed >90 kts and the recommendation is not more than 60 kts. There is also a relationship here with boat speed, and many of the prop programs don't compute when a 40 mph top speed is entered into the equation. I'd be really interested if anyone with solid prop knowledge has any ideas before I invest in another set of props or prop rework.

greysole · Post by **greysole** » Mon Aug 29, 2016 1:03 pm

There's a fellow on the bertram31.com forum who is extremely knowledgeable in this area. His name is Bob Lico. If you post a thread over there you will get some recommendations.

WetProcess · Post by **WetProcess** » Tue Aug 30, 2016 7:46 am

Thanks for the suggestion. I do need however to correct a typo...the current prop is the Nibral but it is a 21 x 25p speed and RPM are correct. Not sure how to move the post over so I will try contacting by email if possible.

greysole · Post by **greysole** » Wed Aug 31, 2016 5:15 am

Al, I took the liberty of copying & pasting the thread over on B31.

greysole · Post by **greysole** » Wed Aug 31, 2016 5:49 am

Al, Some great input from our friends on B31 site. XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX Bob is the best to answer, but they need to add cup, not pitch. I would have stuck with the 23 inch prop if there is room, reduced pitch to get the RPM's up as much as possible, may need to over rev then added cup to offset the reduced pitch and would have reduced RPM's to the RPM's you need to have them running at but picked up speed. A good prop shop should have been able to help with this. This one is blazing new territory. I think the engines will work too hard pushing that boat, but Bruce or Bob can answer that one since they have the most knowledge in this area. Bob is the best to answer, but they need to add cup, not pitch. Tony XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX The gentleman is all over the map. First thing I'd do is get working tachs. Then I'd need to know a firm WOT... I believe we have GM@ 6600, mfg@ 5600. Marine Power came in at 5200rpm, "after discussions", what does that even mean? Even with that owner is striving for 5100....?? My experience...owner is hearing what he wants to hear, wants fast over longevity...till motor dies. I have found Talks tend to go like this... Marine Power(MP)- "yes you need to hit 5600rpm at WOT". Owner(O)- "Does it have to be exactly 5600 or is there some wiggly room." MP- "If your 100-150 below, you should be okay" O- "So 5450 is OK?" MP- "Yes, it should be okay." O- "What if really loaded and can only achieve 5300?" MP- "Ummm...guess you'd be okay for a bit till you burnt some fuel, but really 5600." Owner takes away -- Okay 5300 it is....and if I'm 150-200 below I'll be fine, yup they said 5100 is good. I could be 100% off base here...but in his words 5200 WOT from marine power and he's striving for 5100...and tachs are out. Concern "seems" to be over speed. For me What I want to know is "IF" the engine blows...who stands behind their WOT number. Stand behind as in will replace blown engine and not say, motor was overloaded, over propped not covered. I then use those WOT numbers. Without working tachs and a definite WOT its a crap shoot. Next... 20 x 20 is way off? Maybe I am wrong...but that is the only set I see as being correct...yes speed is down, but 5400rpm. Which according to owner with tach 150rpm off could be as high as 5550 or low as 5250. If I was at this point...20x20 @ 5400...I'd stop and get tachs calibrated...change for new...verify the WOT. Anything else is just guessing and hoping. Worth saying again: Without working tachs and a definite WOT its a crap shoot. Then check numbers again. If in WOT ballpark, its time to start tweaking prop diameter, style, blades, material, cup, rake to achieve WOT and bring that speed up...if possible. In my book the WOT takes precedence then we turn to performance. I stopped playing with customers props for just this reason. Carl XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX step one Calm down! step two believe none of what you hear and half of what you read on prop wanna beee. ok lets get a positive starting mark by simple timing light on engines (with vacuum disconnected and pluged) to verify BOTH tachs. prop tech is very expensive if your buying props to experiment.i had a couple hundred at my disposal and two fork lifts capable of lifting a 38' boat out of water on concrete pad and change props in 10 minutes and drop back in.i am retired and will try to point you in the right direction. the ultimate answer is a two speed ZF transmission to lower idle speed with high speed cruise ,trolling valves are out of the question they are not made to dock a boat (repeaded forward,reverse) so lets get to propping a LS small block.to get to proper rpm to load we do not just up and up pitch------wrong 25/26" pitch is way out of line! off course you have 6mph idle speed.the answer is cup, cup and more cup, better yet a varable pitch and cupped.loaded SHOULD be 5700 loaded not 1 rpm less.just for test afterward don`t exceed 4000 rpm. 21" to 23" varable pitch with full cup i would tell you to rake 4 degree but prop shop will not listen or will not comprehend for inboard use.i am not in favor of LS small blocks in a 33' boat this is diesel only. torque not horsepower is the key to a boat of that weight.BTW. is this a 6.0 or 6.2 LS motor? capt.bob lico

retman · Post by **retman** » Wed Aug 31, 2016 5:57 am

Those are impressive numbers. Took the liberty after work last week on a calm evening and put the old girl to the stops. 26.5 knots at 3850 rpm and slowly climbing. I have 23D x 26P 3 blade with 2.57:1 gears. Bottom and gear are probably not pristine, motors are original. Looked down at the fuel gauge end it read E. It was coincidence as the sender crapped out. BTW, any idea of fuel burn at those numbers?

Post by **dougl33** » Wed Aug 31, 2016 12:15 pm

A shit load.

greysole · Post by **greysole** » Thu Sep 01, 2016 11:34 am

Al, More thoughts from our B31 friends. XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX Bob-- Agree with getting tachs right on. Agree with achieving 5700 WOT. Assuming if starting to complain about wheel cost a two speed tranny is out of the question. Confused past that point...making assumption the tach is right for now. Square 20's are only attaining 5400rpm Increase to Variable pitch 21-23", add cup, add rake...they all eat power and he is already 300rpm under WOT. Where does he get the additional rpm to offset those modifications? If 4 blade, go 3? Reduce diameter? Reduce pitch? or Go Nibral? Reduce pitch and add cup would be my starting point. But all guessing till tachs are right. Not arguing...just trying to understand and learn your thought process. Mine has been to keep simple and safe over chasing customers dreams of achieving huge improvements. Carl XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX carl-----------yes,yes,yes,and yes and yes bottom end torque sucks compare to cummins QSB-420hp diesels. and yes huge trim tabs to get that baby on plane loaded. yes i would play safe at 20". capt.bob lico XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX bob lico wrote: bottom end torque sucks compare to cummins QSB-420hp diesels. While true...no diesels in the picture, 6BT's even a nice choice, or 6BTA's. However, it looks like he pulled Big block 454's out for the small blocks...he's up 85hp but loses 85lbs of torque, even more if using his numbers. Big tabs to get over the hump, yes...but that's not gonna help climbing up the back of a wave, needs to be able to spin them props uphill first...torque. Smaller wheel or more gear reduction. Like to hear how it plays out. 2 Speed...nice idea...get over the hump, shift and go. Carl XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX carl in my old age i become relundant to judge to quickly. some years back this guy came into marina and ask my prop advise;" i have the fastest fishing boat and will use it to go to hudson canyon (72 miles out of fire island inlet) ok lets sea the boat before giving my opinion .low and behold a beautiful 32' catermarian built near bruce`s shop in FL. looks identical to Skater Cat. for power two 500 hp yammar diesels , as we went down river i look down at levers for gear shift between the front seats -----huh!!! three speed gears . he took it up to twenty with black smoke pouring out the transom shifted into second and the boat went up to 92 or 93 mph and settle back down to 68 mph cruise. yes quite fast for a fishing boat .built a set of props to break 100 and cruise at 72mph. so i am a believer on two speed ZF for fishing boat and thats exactly what Cabo did with 350hp cats in there 30footer. the main benefit was a 4 mile a hour idle speed and jump on plane.carl never say never but in this case and don`t be led astray i fully aware of the twin turbo 1500 hp 6.2 LS motors but thats pushing a 3000 lbs car not a 20,000 lbs boat lets put a ZO-6 corvette 650 hp in a 18 wheel tractor trailor going up hill and see what happens.i can only see running the balls out of those engines with high tuned 3 blade Ron Ellis props. but the engines will not last! capt.bob lico XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX Bob I agree, I don't see these engines lasting very long. Not set up right for that size boat. Tony XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX If I've said it once I've said it a hundred times... The more HP you squeeze out of the same physical size engine (let alone a smaller one) the less longevity you'll get out of it... There's a reason a 1,000 HP marine engine is more like triple if not quadruple the size of two 5 liter something GM LS (small block) engines pumping out 500 HP each!... And the reason isn't only the fact that Diesel engines are built heavier... The US Army wanted more HP for the Abrahams then was possible at the time with Diesel technology... They also wanted to shed some of the weight... So they went for gas turbine (essentially a jet engine) technology... An added advantage is that the gas turbine is a lot more flexible in terms of the fuel requirements... Navatech XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX To play devils advocate... I think the engines could last in a 33. But it would be a choice of running conservatively, meaning gear the thing down and not try to make it into a speed demon so you have the low end torque to get over the hump, climb waves with a bit of reserve. Yes, the drawback a slower cruise, slower top end...but the trade off is some longevity. It's been done for years...boats up to 40' with gas big blocks...they were not high hp, but had the torque. But that was also when boat owners cruised happily at 16-18knts. Now we have lighter high hp motors with less torque...spin em faster with more reduction gains the torque back...but speed is the killer...today everyone wants fast. Look at our 31's...they originally came with diesel options of GM 140hp and the big hp diesel was the 170hp Cummings or gas started with only 225hp motors and for the speed demons went up to 325hp Today, how many guys even consider the Cummings 210hp motors...discussion is between the 270's or 315's. Yanmar 210's great motors for the 31...but considered a slower cruise boat. Carl XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX Good Luck & keep us posted Post some pictures too!

h2ojst · Post by **h2ojst** » Fri Sep 02, 2016 9:11 am

Hi Gerard. Your buddies have some pretty good ideas and seem to have a handle on props, torque & HP. My solution to the 2 speed gearbox is cam timing. I think I've gone over this a few times before you joined us. I took a pair of new 8.1's and tore them down & rebuilt using a few racing techniques to get more HP and advanced the cam timing about 1.5 degrees. This makes the same engine that used to have it's maximum torque at 5400 now produce the same amount of torque at 4000. This enables you to climb out of the hole like there's no tomorrow and although I'm not attaining the top end speed that Al is, (He's also talking MPH & not Knots), I can reach about 33 knots at 4000 and cruise comfortably at 25 at around 3200 (fully loaded water, fuel & people) & I'll guarantee you that I'm burning 1/2 the fuel that Al is. I think I can also safely say that I believe my engines will last longer at 3200. The engines dyno'd at 400HP when they left the shop and I'm turning 21 X 21, 4 blade Nibral's.

greysole · Post by **greysole** » Mon Sep 05, 2016 3:53 am

Joe, What gears are you running with those engines?

greysole · Post by **greysole** » Mon Sep 05, 2016 4:49 am

Bill, Doug's correct ! my 454's 2:1 gears 23 x 26 3 Blade Federal Equipoise 4100 RPM 28.9KTS FLOWSCANS 28 GPH each side (x2) OUCH !