GM 6.5 V8 diesel

[PCUK]

In the UK these engines have a terrible reputation thanks to a company buying ex-military engines, fitting marinising equipment and selling them on. There must be millions of them in trucks and military vehicles so they can't all be bad. I'm about to fit one which we've rebuilt into a sport fisher driving through a 280 Volvo DP-C. Anyone here using them either in their boat or their truck and have any advice on keeping them happy?

 

[Scott Danforth]

Re: GM 6.5 V8 diesel

If electronic fuel pump - move the PMD off the engine. There are many PMD relocation kits on the market.

Then again, not sure the electronic fuel pump would be marine approved.

 

[PCUK]

Re: GM 6.5 V8 diesel

Thanks Scott,
This engine has the manual fuel pump, but now I'm wondering whether it can be upgraded and if there would be any advantage to doing this?
Cheers,
Peter

 

[Scott Danforth]

Re: GM 6.5 V8 diesel

There is really not an advantage on the electronic pump, except for on-highway emissions. Since you are in a boat, I would not worry about it. if you have a manual fuel pump, just turn up the fuel. Do a bit of internet research. the big mod on 6.5 trucks and suburbans for towwing is to run the Marine injectors (higher flow capacity) and turn up the fuel pumps.

Banks turbo was working on a few Marine diesels on and off for a while when they were looking to get heavy into the marine diesel market. They may have some aftermarket goodies now. Banks Power | Diesel Performance and Gas Performance Products

 

[HT32BSX115]

Re: GM 6.5 V8 diesel

If electronic fuel pump - move the PMD off the engine. There are many PMD relocation kits on the market.

Then again, not sure the electronic fuel pump would be marine approved.

Yeah,

The stock injection pump cannot be turned up enough to make much additional power .......Peninsular has the modified pumps that can be turned up but you'll need to turbocharge it.

The DS4 pump is the electronic one ........... It wouldn't matter if it was "marine approved" anyway, That's really only a gasoline engine problem.

Most of those engines out of military trucks and HMMV's are NOT turbocharged. In a boat, without turbocharging, it WILL be a complete DOG.

If you decide to turbocharge it, you'll need to rebuild the engine using low compression pistons. (the stock engines are around 21:1) You need to use 18:1 pistons.

You'll want 18:1 compression or you'll end up with seriously high cylinder pressures and exhaust temps (and subsequent engine destruction)

Also, don't forget you'll need a charge air cooler (intercooler) too.

My suggestion would be to contact Peninsular Engines and ask them what they do to "marinise" them.

It won't be cheap.




I have had my 1994 6.5L GMC Suburban since I bought it new. I've never had a serious problem with it except having to replace the DS4 injection pump at 60,000 miles (did it myself) I am on the third PMD in 200,000 miles..........still "PM" (pump mounted)


Just my opinion, I wouldn't put a 6.5L GM diesel in a boat unless I did to the engine what Peninsular does to them.

After you do that you'll have so much money in them that you might as well get a Cummins, Volvo, Yanmar, or other engine that will probably be much more reliable in a marine application.


Regards,


Rick

 

[PCUK]

Re: GM 6.5 V8 diesel

We're not thinking of pulling extra power so the only work being done is the usual ends, mains, rings, water pump, etc. (The engine has very little wear).The idea is to use it lightly with more emphasis on reliability than performance. It will replace a 70hp UK Ford lump so even with its modest power we should see a difference. So far cost has been low so if it keeps going we'll be happy.
Thanks all.

 

[HT32BSX115]

Re: GM 6.5 V8 diesel

We're not thinking of pulling extra power so the only work being done is the usual ends, mains, rings, water pump, etc. (The engine has very little wear).The idea is to use it lightly with more emphasis on reliability than performance. It will replace a 70hp UK Ford lump so even with its modest power we should see a difference. So far cost has been low so if it keeps going we'll be happy.
Thanks all.

You'll of course need jacketed exhaust manifolds, closed cooling heat exchanger, raw water pump mounting etc. That engine will reliably produce about 160hp 'continuously' ..........you probably won't run it that way though..........

70hp lump? is that a 4 cylinder lump? If so, That 6.5l V-8 will probably be twice the weight in the back of that boat. Pay particular attention to the drive ratio in your DP-C and propset.

That engine is only going to turn 2000-3000 (cruise) the way you'll use it probably.................but you still want to be able to turn it 'up against' the governor at wide open throttle up (WOT)

If you are geared too "tall" (to high ratio/high pitch propset) .............It will be an over-fueled smoky mess when you throttle-up!!

Geared too low, and you'll be right up against the gov and barely moving!

If the drive is a petrol engine drive (fairly low ratio) then you might be able to make up for the gearing by going with a fairly high propset. I don't know how high the VP prop-sets go (F1,2,3,......7,8 etc) but you'll need to experiment.

If that's NOT a planing type hull and you don't expect to plane, it might not matter much but for best efficiency, you want the engine to still be capable of making max RPM at or near the governed max speed @WOT.

If you still have a LOT of throttle left, at governed RPM, then the gearing and/or propset is WAY TOO LOW.


The non-turbocharged 6.5L engine is a really smooth, reliable engine with the mechanical injection pump. It's just not a "power-house"


Regards,


Rick

 

[PCUK]

Re: GM 6.5 V8 diesel

Thanks Rick,
The engine came with all the cooling equipment and the drive ratio is OK. We'll need to experiment with props to get the right WOT. The boat is a semi-D by the way. Your last comments sum up exactly what we want. A smooth, reliable engine that will get us there and back without too much fuss and at a no great speed.
Cheers,
Peter