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-   -   3800 rpm wall (https://www.offshoreonly.com/forums/drives-lower-units/304342-3800-rpm-wall.html)

Toolman62 10-22-2013 10:30 AM


Originally Posted by lil red (Post 4015314)
If that motor doesn't run like a complete piece of $hit at all rpm then those results are wrong.

Engine runs smooth as silk, thats why I want to do my own test and verify. My shop is next door to an engine shop and he was out when I was running it and said he couldn't hear any miss. Throttle response is as crisp as a whip, starts and idles at 600 rpm's, no backfiring, plugs look excelent, and no raw gas smell with captains call ON.

Toolman62 10-22-2013 10:34 AM

I found the fuel pump finally!!! I think if they tried a little harder they could have found a better place to put it. I may have to pull the engine if it ever needs replacing.

Toolman62 10-22-2013 10:39 AM

If I end up pulling this engine then is getting gone through from the top to the bottom so it will be ready for next season. What do you guys think about the Imco or the Dana Marine exhaust manifolds? The reason for asking is my port side is rusting thru

Griff 10-22-2013 12:49 PM


Originally Posted by Toolman62 (Post 4015305)
Griff I agree about the rebuild!! I'm going to do my own leak down test to confirm results from service. If this is the case then I think that I'm just running out of HP because of loosing power from the week cylinders. 57 mph at 3800 with the equivalent of a 5.5L in a 4200 lb boat running a 23P prop isn't to bad. She should come up and be happy with all cylinders working again

Its impossible to run 57mph at 3800rpms with a 23"prop and 1.5 ratio drive. Get a GPS speed and be ready to be severely disappointed.

Toolman62 10-22-2013 12:56 PM

I had a gps app on my phone and it matched the speed-o within 1 mph. The drive has no serial # on it and I haven't taken it apart to verify ratio, so I really don't know what ratio is in it. Plus I was running with my buddy beside me the whole weekend.

Griff 10-22-2013 01:33 PM

Then you need to verify your tach readings.

hullofjustis 10-22-2013 03:15 PM

if it is not running horrible at all other rpm ranges those leak down results are incorrect. you said the fuel pressure is low what is it reading??? i believe you have a bad high pressure fuel pump. also the imco or eddie are all good exhaust and much lighter.

Toolman62 10-22-2013 03:50 PM


Originally Posted by hullofjustis (Post 4015489)
if it is not running horrible at all other rpm ranges those leak down results are incorrect. you said the fuel pressure is low what is it reading??? i believe you have a bad high pressure fuel pump. also the imco or eddie are all good exhaust and much lighter.

I believe the techs computer was showing 35 psi but was holding at all rpm ranges. I feel it needs to be up in the 40's. That's why I was going to run it again with a pressure gauge on it to get a second reading. I'm also going to do my own leak down test before pulling the engine. Tach was also checked using the computer while running on the water and it was dead on (I was actually surprised how close it was).
The tech said it had a mechanical and an electric pump. I looked where a mechanical pump "should" be but I can't find one, just the electric.

nailit 10-22-2013 10:39 PM

Agree with Griff, your tachs off by 6-800 rpms on the low side. 3800 at 57 would be -3.3% slip. Using 11% would be running 4400ish. Note: 1.5 and 23p used in calc.

kidturbo 10-23-2013 02:06 AM


Originally Posted by Griff (Post 4015446)
Its impossible to run 57mph at 3800rpms with a 23"prop and 1.5 ratio drive. Get a GPS speed and be ready to be severely disappointed.

I'll "somewhat" agree, the drive is probably a 1.26 ratio.

Here is a screenshot of my radar verified GPS speed on a 1.26 XR , 37 pitch 5 blade, slipping 21%

http://www.altfuelsgroup.org/picture.../Top-Speed.JPG

Yours would be slipping 13% if that tach and my 1.26 calculations are correct.


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