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Old 14-08-2008, 06:02 PM   #1
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G.M V8 Diesel's

Has any one done a diesel conversion using the GM diesel engine ?
I no these engines are a direct replacment for the mercruiser petrol.
How do they conpaire with preformance and what sort of power bhp and rev's will they run up to?
Any info would be great.
Who is best to speak to regarding power tunning / parts for these engines?
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Old 14-08-2008, 06:07 PM   #2
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JF its over to you
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Old 14-08-2008, 07:22 PM   #3
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Quote:
Originally Posted by scarab racing View Post
Has any one done a diesel conversion using the GM diesel engine ?
I no these engines are a direct replacment for the mercruiser petrol.
How do they conpaire with preformance and what sort of power bhp and rev's will they run up to?
Any info would be great.
Who is best to speak to regarding power tunning / parts for these engines?
Would you like to buy a pair?
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Old 14-08-2008, 07:29 PM   #4
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At the moment NO but just toying with another project, and wanted some help/advice before i write the cheque out and find my idea's didn't work.
But might be interested if all goes ahead as planed what power / liter /rpm and the dreaded price are they?
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Old 14-08-2008, 07:37 PM   #5
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They're 6.5 litre, 325hp at 3600rpm and on bravo bell housings / merc front mounts and rigged using standard merc rubber plug wiring looms. direct merc petrol V8 replacement.
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Old 14-08-2008, 07:43 PM   #6
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go on frigten me ££££££££££??????
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Old 14-08-2008, 07:51 PM   #7
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really don't know, until you posted, I hadn't really given any thought to selling them separate to the boat.

I guess they'd have to be 5k each, or close to it.

My 28 runs 72mph with them in.
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Old 14-08-2008, 07:59 PM   #8
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why are you changing them? what planes have you got for your 28?
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Old 14-08-2008, 08:07 PM   #9
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The 28 was put together when diesel was quite a bit cheaper. It would have been far cheaper to build small blocks with 100hp per side more, and a fair bit lighter, but the running costs were important to me. The weight was a particular compromise, but one I considered a reasonable trade at the time.

Now the fuel is dearer, and the feeling that the boat deserves more power & less weight is a reccuring theme, I would consider building a pair of hairy chested small blocks for it, leaving the 6.5's TD's redundent.
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Old 14-08-2008, 08:42 PM   #10
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is 3600 max for rev's or can they go a bit more,
What about tuning is that the max bhp.
Do you think they are a good way to go when converting to diesel or would it be best to start again and go for yanmar or similar?
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Old 14-08-2008, 09:00 PM   #11
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It's currently propped to pull a max of about 38-3900 when trimmed right out hanging on it's heel.

No more power to be had with the current setup., in fact, the max fuel could come down a 1/4 turn without losing any power, but would run slightly cleaner at WOT.

I've been running them for 8 years, they've done about 270 hours and just short of 4000 miles. I like them, but fancy more power and less weight (they weigh about the same as a petrol BBC)

Yanmars are very good.
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Old 14-08-2008, 09:44 PM   #12
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Are you keeping the 28 then fought you was having a 31 made?
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Old 14-08-2008, 10:12 PM   #13
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A new 32 is a little way off yet, as I need to produce a new deck.
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Old 14-08-2008, 11:23 PM   #14
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What drive ratio and props / pitch are you running with the diesels? what sort of fuel consumption do they average ? sorry for so many quetions but best to have all the facts before i make a desision on my next project.
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Old 14-08-2008, 11:28 PM   #15
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I run Bravo ones at 1.36:1 turning 4 blade Bravo1 props at 30" pitch / 3 blade Mirage at 29" pitch.

The motors, when max fuel was were it needs to go back to, burned 15 imperial gallons per hour at WOT. (each) cruising in the 28 at around 60 mph it burns IRO 20-22 imp galls per hour total.
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Old 18-08-2008, 03:02 PM   #16
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have you had any problems with the drive leg gears due to the extra torque from the diesels? Do you think that the older trs drives would cope o.k or the newer bravo 2 or 3 ? be o.k with this sort of conversion?
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Old 18-08-2008, 03:09 PM   #17
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I've had no problems at all with my Bravo 1's. the Yanmars have broken a good few Bravos, with less power, but my guess is that there's something the bravos can't take from them, maybe something to do with an unfriendly harmonic produced by the Toyota 4.2, not sure really. But the V8 seems to be fine on them. They still suffer with the horrid backlash 'chatter' when in neutral and at idle, but over the 8 years I've learned to live with that and it doesn't appear to do any harm..

The TRS drive & inboard gearbox I think would be fine. they're generally considered to be stronger than the standard Bravos. and of course the Velvet Drive hydraulic gearbox is as sweet as a nut compared to the cone clutch arangement in a Bravo when shifting 'in & out of gear'.

Also, if the boat you're considering for a diesel conversion has TRS's currently fitted, it's quite a work up converting to Bravo as the hole in the transom required for a bravo is smaller than that of a TRS, so a transom repair, or conversion plate/adaptor is needed.
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Old 18-08-2008, 05:33 PM   #18
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It could be the amount of cilinders that both engines have ,lets say both engines are producing 800 nm torque ,the GMC is pushing 100 nm per cilinder ,the Yanmar 133 per cilinder ,so basically the GMC has softer crankshaft pulses than the Yanmar

The peak pulses are more agressive ,that could be the cause the Yanmars are harder on the drives...
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Old 18-09-2008, 05:59 PM   #19
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Quote:
Originally Posted by Jon Fuller View Post
really don't know, until you posted, I hadn't really given any thought to selling them separate to the boat.

I guess they'd have to be 5k each, or close to it.

My 28 runs 72mph with them in.
Are you still considering ridding yourself of the V8 diesels?
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Old 13-10-2008, 10:46 PM   #20
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Smile G.M V8 diesel's

Hi Jon,
Are you for selling the two G.M diesels as i may be interested in them!!!!
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