1974 46 conv-injector size and props??

[altmed]

please help--I have a set of 8v71 TI's, The previous owner put 9215 injectors in them and detroit diesel believes they are causing my engines to run too hot. they want to put in n90's. Anyone know what the right prop size to adjust too would be?? Also will this slow me down alot??
alt med

[hattitude]

I have a 1980 46C with 8V71TI's. My engines came with N90 injectors, it is on the engine placard.

The props will need to be specific to your boat, load, etc... But I am currently running 4 blade 26" x 24" cupped. I cruise 18knots at 1950 rpms....

Good luck...

[altmed]

thanks for the input--I took the props to the shop today

[seacolt]

I have a 1976 46c and have n90 injectors and 28" 34 pitch props

[altmed]

we switched to n90 injectors and ran 28X32 props today and the speed is awful-- 13 knots at 1900 and 18knots at 2200 rpms,
what are you guys gear ratios and any advice --please help

[Brian Degulis]

Hi If you give me some more information I might be able to help you. Did you lose performance from the injector change or did you change prop size or pitch also? With your current set up can you turn the full rated RPM?

You can use other boats as a guide but only as a guide your prop pitch and diameter will vary acording to load trim and condition of the engines.

Brian

[krush]

this made me think of a good question. Is there anyway to see what the "other side" of the governor is doing on DD's? I ask this because if a boat is way under propped, the engine will turn up to full RPM but it won't be loaded and the governor could really be giving the engine 1/2 fuel.

I guess one could check EGT's, but I would think there is a more direct way to observe this (in a gasser u can just look at the throttle plate if there is a governor).

[Brian Degulis]

Yeah there is you can remove the buffer screw and with the boat at WOT use a small wooden stick to push on the fuel lever. If the RPM goes up more than around 50 then the governer is holding the engine not the load. If it doesn't go up at all then the load is holding it. You have to be carefull not to over speed the engine which makes it hard to tell how much you may be under proped.

Brian

[altmed]

Hey guys--I tested the govenor like you said and it is running full fuel. I switched injectors to n90's and that is when I lost about 250 RPM's. The engines are running cooler though, but with my same props I can only hit 2000 RPM's now. When I tried 2 inch smaller props I lost alot if performance.
Question for hattitude--what is your gear ratio--mine is 2:1
thanks
Daniel

[hattitude]

Question for hattitude--what is your gear ratio--mine is 2:1
thanks
Daniel

I've got allison gears at 1.5:1

I checked and misspoke on my props. After I had them tuned, they are now 26" x 23" four blade with a slight cup.....