6LYA-STE Underpower

[Jeff Pollard]

Hi all,

New to me boat is a 1998 Bounty 293, 17,000 pounds (weighed myself) with single Yanmar 6LYA-STE (350hp), 3k hours. Seems in reasonable condition with no perceivable blow-by at the fill cap.

I’m only getting 3000 RPM (strobe verified) and 20 knots at WOT and was on the verge of repitching the prop to achieve 3300+.

I bought a SBMAR Turbocator which worked great to collect boost and exhaust data (after turbo). I’ve since compared my exhaust data to some SLYA-STP data (attached). It looks to me like I have a fuel restriction at high RPM based on my exhaust temp curve. In addition, the power calculators I’ve found predict somewhere between 22.5 knots and 24 knots, with 350 hp (~330 prop), which I’m well short of at 20 knots.

What do you think? Does my exhaust temp curve (solid green in attached) indicating fuel restriction?

Thanks

Topic

[Tony Athens]

Can you send me your drawing?

Tony

[Jeff Pollard]

In case anyone is interested, the ZF 220VLD and ZF 85IV have the same vertical drop within 1 mm. Good news for me should I choose to pull the trigger on a 5.9

[Jeff Pollard]

Hey Rob,

Thanks. That’s a nice side by side compare.

In my situation I’d need to upgrade my gear as well, so I’d need to factor in any difference it the drop from crank centerline to gear output (Tony pointed out in an email). In my case it’s a compare between the current ZF 220VLD and the likely replacement, ZF 85IV. I haven’t done the math yet to know if it’s going to help or hurt me.

One other complication for me is I’ve realized the Cummins exhaust is on the opposite side of the Yanmar. Maybe doable, but I think I’d need a new lift muffler at the very least.

[Rob Schepis]

6LYA vs. QSB5.9 Heights

Here’s a side by side of the crank centerline to top heights of the 6LYA vs. the QSB 5.9.

1 user thanked author for this post.

matt1

[matt1]

Fair enough… I got to the boat today and measured. I have 4.5″ from the valve cover and 3.5″ from the top of the Yanmar fuel line. The Yanmar exhaust elbow is already tight up against the hatch, but I will lower and reconfigure the exhaust anyway.

[Tony Athens]

Just get a straight and set across the inside gutter edge and do an exact measurement at both end of the valve cover, and one at the high point of the exhaust elbow..

When things are close, “ABOUT” does not cut it..

[matt1]

pics

Thanks for the info Tony. Appreciate it as always. This is the only pic I have with me now. The only concern I have is height. I have about 4″ from the engine to the hatch. The current exhaust elbow sits higher, but the Cummins is different anyway, so that can be changed. Tons of space under as the engine sits really high. 280-1 gear 1.1 induction for the Konrad 660.

[Tony Athens]

Apples for Apples, all done right, the QSB 5.9 480 would add not less than 2 knots to your “cruise speed” and stay well within Cummins cruise power curve. It’s quieter and smoke free too….About 2 years ago we replaced a pair of good running 440’s in a Sea Sport 32/34 Catamaran that had remote v-drives and he picked up 4 knots cruise.. His 440 treated him well for 2000+ hours, but he wanted more–He got it! The owner is easy to check out–Terry Maas –high end “free diver”

As to whether “it would fit” it just takes a good look at your present installation… With the right pics, I may not even need a rule to determine it.. Also would need to know what exact gear you have

[matt1]

I’m in a similar situation

I also have a single 6ly 440. My boat is lighter and performs a little better, but the engine is getting up there and I’m looking at options. How much is there to gain by going with a 5.9 480? I have a couple of boats with Yanmars and they have been as good as they can be to me, but I’d sure like to have a Cummins if they fit and perform at least as well. Unfortunately, I don’t think I can squeeze a 6.7 in there.

[Jeff Pollard]

Ah yes, that is a different pan.

I’ll send you and email with more info and some questions.

Thank-you.

[Tony Athens]

Zero issue with the oil pan.. The depth is about 1/2″ deeper.

The top will be tight but you definitely have the the room the QSB 5.9 480. You just need to be clever with your deck design and “thin it down.. The QSB 6.7 SL 425 is 3/8” higher than the QSB5.9..

You are not looking at the right drawings or working with a Cummins guy that does not know his product. .

[Jeff Pollard]

I see no path for an engine box.

I have about 4.5″ on top (see pic) which may be enough to shoehorn in a 5.9, but the bottom (2nd pic) isn’t even close. This is a V-drive and image showing the bottom was taken with camera pointed towards the front of the boat. I think I need about another 9″ for the Cummins pan, and I have about 3″ to give. Are there any shallow pan options?

Only option I’ve found to date that would fit to get an extra 100ish HP is the Yanmar 6LY-440

[Tony Athens]

Yup–A builder that used this engine and dropped the deck as low as possible made it basically impossible to use any Cummins product..

Crank C/L to the top of the engine is 4-5″ less than a Cummins engine. Your boat needs another useable 50-100 CRUISE HP to keep it up on top, or it needs to shed 2000+ lbs.. No chance of an engine box?

[Jeff Pollard]

Tony,

Clearly that’s not the answer I was hoping for, but I don’t doubt you.

Attached is boost data. Also speed vs RPM.

I need to find my notebook with the gauge RPM vs strobe data. My buddy and I collected data up to around 2500 RPM if I recall and it matched very closely so we stopped.

I have this thing torn down at the moment, going thru the aftercooler, oil and water coolers, etc. Aftercooler was “serviced” by previous owner and tubes look pretty good. I’m currently trying to get the core out. Soaked each end with acetone and ATF, then used heat and a press. It’s partly out, but need to make a press plate to get it the rest of the way. I think it’s been in there since 1998. I’ll post some pics when it’s out (before / after).

I need to drive a couple of hours to a shop that can scan the prop. Probably a few weeks before I can get that done.

I completely agree the engine is light for this boat. I was hoping for more like 23-24 knots at WOT as calculators predict, but if 20 knots WOT is all I can get, cruising speed is barely going to hold it out of the water.

Seriously considering cutting my losses and repowering. Unfortunately when I look at the dimensions of the Cummins engines (5.9, 6.7) they appear too tall for my engine compartment. Maybe talk to you sometime about options.

Really appreciate the quick reply and the reality check.

Jeff

[Tony Athens]

6LYA STE 350/370

The answer to your question is 100% no.. Your PYRO does not have anything to do with fuel restriction and is not directed related to the HP being produced….

Your issue is classic–You are over propped planing plain and simple.. You either accept that or you are in denial.. I know this engine top to bottom and everything in-between.. I like it a lot, but you need to set it up right.. That is a lot of boat for one of these..

1) Strobe your tach for accuracy, at the dock, in neutral at 3000-3100 RPM.. Write it down. Write down WOT no-load too………………………………………………… Why no boost numbers?

2) Remove the aftercooler, put in on the bench, and service per my protocol…………. Post some good before and after cleaning

3) get your prop off and get it scanned.. Send me a copy

Start there if you want to get all this engine has to offer..

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