12v71 Detroit Diesel Govenro Shim Spec

Hi Everyone,

I finally got around to getting my both DD's rebuilt. They were originally 930Hp versions using the 9A31 injectors (From a 12v92) however I decided to return them to original spec of 870Hp using the 9215's.

I went on the first Sea Trial and everything looks good except that WOT is only 2000 rpm and only buring 38 GPH on the flowscans. The throttle at the helm reaches that RPM about 70% of the travel range. Down on the engine the Governor is top'd out at that setting does not have more travel.

Both Engines are at the same RPM and fuel consumption. Speed is 23.5 knots and the boat has a clean bottom but needs paint and is also very light at the moment.

My Mechanic says that I might have to cut the Props but I also think the this engine needs to see more fuel.

What is the Governor Shim spec for a 12v71TI with 9215 injectors, 870hp. The spec show 48gph at WOT and im no where near that.

Current props are 29 x 33 no cup.

Thanks in advance,
Ozzy

My theory is that the Governor was restricted a little to prevent the large old injectors from dumping too much fuel and perhaps now with the smaller injectors, it needs to be opened back up.

So can some one tell me what the Governor Shim Spec is for this motor setup?

2650 is the Max RPM no load.

Before rebuild and injector reduction the old setup was maxing out at 2250 on a good day before engines lost the rest of their power.

The 9215's where the largest injectors ever put into a stock 12v71TI. Thats what I have returned to. The company that marinized these engine back in 1986 decide to drop in the 9A31's from the 1080hp 12v92TA's. Those injectors bumped up HP to 930 from the stock 870. Hence I'm having 6.5% drop in HP if my engines before rebuild where at full power which is totally not the case. Props were are set at 29 x 33 which is what the calculator comes up with for 900hp engines. (Not sure if calculator does Crankshaft HP or Prop HP). Do I have to cut the pitch? Sure. but an inch maybe 2. Thats only 6 % at most, however I'm 300 rpms short at WOT which is 13% of the total max.

And just to add insult to injury boat is super light as it is going through a major refit. Missing are: 1 generator, all the salon furniture, all the gear and crap stored aboard. Back fuel tank is empty (600 Gal) , water tank is empty (250 Gal), So let just say she is not her usual self.

Plus, there is no black smoke at the current full throttle rpm of 2000. It almost seems and feel like a fast cruise speed.

Ship? I think you mean tranny. ZF BW 195's reduction is 1.54 or close to that.

Engines were rebuilt in place. I agree the curve on the chart are not linear. However at WOT engine is doing 38 GPH (870HP 12V71TI with 9215 Injectors) and only 2000 RPM on 3 bladed 29x33's . Yes I have to cut pitch by 1 at most 2 inches, but boat is extremely light!

Thanks Capt. J. Good feedback.

Boat is a 1986 54' Bertram with original 12v71TI's marinized by BK Power in Miami. 930hp using the 12v92TA 9A31 Injectors which we know we know produce 1080HP for that motor.

I have run Prop Calculation and yes I have to reduce my pitch a little. I have original 3 bladed props 29 x 33 and new calc says 29 x 31.5.

The prop calculation says I should be doing 28 knots at 2300. Currently doing 24 knots at 2000. Im thinking It should at least get to 26 knots at 2300.

I will call F&N on Monday to see if I can get a loaner Prop.

F&J does not lend out props.. I guess you have to be a Family member or something.

I agree to cutting props some, but down to 29 x 29 might be too much. Im only dropping HP by 6.5% so I expect to get 26-27knots at 2300(WOT) and 22-23 at 1900(cruise). 29 x 31 is what boatdiesel.com prop calc comes up with.

No old injectors where traded in to remove core charge.

Rebuild was caused by Startboard engine ingesting sea water on the right bank. Water leak was fixed immediately however Intercooler was clogged and ran quite a bit of time like this forcing the already tired Port engine to work even harder.

Upon disassembly Port engine has, broken Fuel/Air Modulator, a couple of broken piston heads, broken rings, bad injectors, etc. Starboard had blowers locked up, turbos locked up, slight crack on one head not machineable.

In the end boat would not plane. Hence full rebuild.

Another piece of information that I left off for this first sea-trial is that the Mechanics disconnected the Air/Fuel modulator on both Engines so that we were guaranteed max fuel out of the hole. This was done because boat would not plane on previous sea-trial attempt. It was noted that all four racor bowls were full of algae from the boat sitting for 1 years with out planning. They were removed and cleaned obviously.

So at 2000 RPM's we were seeing 10 PSI on both engines. Is that the normal? Seems a little low for me. Does the modulator being disconnected affect the PSI?