Under performing Kad32

[QBhoy]

Its been a long day . If the leg gearing was for a higher revving petrol engine would the diesel not rev freely but the boat make little speed?

It’s been a long day for me too…too long to quite think too much about it out loud…but I know that outwith the requirement for it to be geared and propped to suit the lower revving diesel..it’s also a fine balance that requires the gearing and propping to be able to load up the diesel hard enough to encourage suitable conditions allowing boost to be created, or something along those lines.
Good thinking though, to throw in ! Be interesting to hear what the rpms reached might be at the top end..and how quickly too…when she does perform.
Of course…there is also a chance that the ratios are very similar between the two…and what’s required is a change to the more eager to accelerate, A series set. From memory, one of the props are 4 bladed I’m sure.
But certainly, b5 props (on a boat like this) would usually be found on an outdrive matched to a GM v8, throwing out 4400-4800 rpm, with peak power somewhere close to the latter figure.
Perhaps a suitable comparison to the boat in question here..(if the ratio was similar) would be a sealine s25 with a kad32. These almost exclusively, tend to be propped with A4 props. And certainly seem to be just about as good as it gets, when they are.

 

[SC35]

Its been a long day . If the leg gearing was for a higher revving petrol engine would the diesel not rev freely but the boat make little speed?

I think it could go either way.

A small 4.3v6 might have had a 2.30:1 drive which would allow the engine to rev more freely.
A big 7.4v8 might have had a 1.78:1 drive which would prevent the engine from revving more freely.

KAD32 usually comes with a 1.95:1 drive.

 

[QBhoy]

I think it could go either way.

A small 4.3v6 might have had a 2.30:1 drive which would allow the engine to rev more freely.
A big 7.4v8 might have had a 1.78:1 drive which would prevent the engine from revving more freely.

KAD32 usually comes with a 1.95:1 drive.

Good info and fair point too ! I assumed around the 2-1 ratio five or take either way might be not too far off. If we are on the right track with the idea that it may have had a transplant at some point along the way..it’s likely props might be able to make the difference perhaps. Only a guessing and assumption at the minute, I suppose.
Another wee example from one of my own boats years ago.
Sealine 218 at about 23ft and maybe 1800kgs or slightly more…
4.3 VP AQ205 mated to a 290dp from new. She had b5 props that were near as damn it as perfectly propped as it comes. She would rev to 4700/4800 rpm at about mid 30’s from memory. No idea of the ratio she had back then.
Not terribly relevant to this, but also currently very familiar with a princess 286 that previously had twin 5.0 VP and 290’s. But was since repowered with potent twin vortec 5.7’s with big Holley’s. She’ll now have around 600hp or close, compared to her previous assumed combined of around 450/460hp perhaps. She still wore the e original b3’s, meaning a far too easily seen and quite substantial over revving set up, if allowed. Swapped out for a pair of b5’s then saw her much closer to the mark…but could still top the rpm upper range fully loaded. A rather expensive investment in a pair of C5’s now has her perfect and just within the range. At an astonishing pace too. Unbelievable almost. She can see a pace genuinely approaching 50 mph. Incredible thing.

 

[Derek.J.W]

Great point Gents thank you, makes sense too, she was re'engined with a brand new Kad32 back in 2001 according to my receipts, unfortunately it doesn't mention what came out, the fact she's a Rinker (American) would suggest a petrol engine would have been fitted, IVSS did a stern drive refurb on the leg back in 2017, might give them a call and see what can be done without having my eyes out
Thanks again

 

[Momac]

Reading the first post again.
The turbocharger could be worn?

 

[SC35]

Reading the first post again.
The turbocharger could be worn?

See Reply #8
If the OP responds to your post instead of mine, I will have been "LakeSailored"

 

[Derek.J.W]

Hi Gents, sorry, been up in Scotland on the boat, Thanks for the info, I'll take a look at the Turbo when i pull her out end of season, I changed all the belts on Saturday as the rev counter was doing strange things, turned out the drive belt was loose which wouldn't help matters, I attempted to remove the aftercooler which would give me an indication of the turbos condition but the middle nut at the the back between the water pipes is a corroded stump which is refusing to budge, Hopefully these small jobs will improve matters.

 

[volvopaul]

When you place the throttle lever max position there is a switch on the injection pump that brings the super charger in irrespective of engine speed , as you saying the sc doesn’t cut in until 1500 you might have an issue there , check the switch with a metal object when engine is at idle to see if the sc cuts in , place a flat blade screwdriver against it , you willl see a metal bracket that pushes up to the switch bolted to the throttle arm in the injection pump .
sounds like the turbo is worn excessive on the exhaust fan if it drops power after the sc has cut out .

 

[Derek.J.W]

Thanks Paul, I'll check this out at the weekend when I'm back in Scotland, Turbo doesn't always miss, i had a good run down to Gigha then across to Jura on Thursday, boat never missed a beat, i couldn't achieve 3000rpm and only managed 15knots but i did have 6 on board none of which are light weights, I'm beginning to think the B5 props are the main issue and possibly the stern drive gearing as mentioned in earlier posts, i'm trying to ensure everything i can is addressed, aftercoolers clear etc., i think lack of use isn't helping her.