Mapping

[Ytmsn]

My boat is supposed to run 50 mph but all i get is 38 at about 4200 RPMs. I'm beginning to think the prior owner may have had a prop strike and had the props trimmed down instead of fixed or replaced, but that doesn't explain my RPMs only hitting 4200.

Has anyone ever heard of a Volvo Penta being remapped? I found this Gizmo and thought about giving it a try but thought I would run it by you guys first.

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[Bfun220]

I would find out why your only getting 38 mph first. But I dont care for most aftermarket performance add-ons. It takes a lot of ponies to push a boat faster. For example: Even the addition of 100hp would only get me about 7mph.

[Big Block Power]

Yt you don't want that thing on your boat. Ok. I think you said it had f6 props right? that is right prop. Your engine isn't waking up for some reason. Is the timing set right? Something isn't letting you get rpms. I would say it's over propped but I don't think so. I take out the new fuel pump didn't help our didn't you run it yet with it?

[AsLan7]

I would find out why your only getting 38 mph first. But I dont care for most aftermarket performance add-ons. It takes a lot of ponies to push a boat faster. For example: Even the addition of 100hp would only get me about 7mph.

+1

[Ytmsn]

BB the new pump didn't do it. Every now and then it'll go a little faster at a higher RPM, usually in the morning when it's cooler.. which makes me wonder if the fuel pump is running too hot.

Even when it revs higher, it won't break 40 on the GPS. After looking at that boat yesterday we talked about, I'm thinking my props have been trimmed at some time in the past. I swear it seemed like those props were a little larger circumference.

It runs excellent. Smooth, no hiccups or issues, shifts like butter, and I love it. But if the sumbiscut is supposed to run 50, I wanna run 50!

If I get it I'll be switching the props for Sure! (Still haven't heard back from him)

[Big Block Power]

I would ship you mine but that gets pricey. Ok if your props are smaller than they should be they would be slipping and your rpm would go up. I sent mine out I should get them back soon we can measure them. Look at your drive see what ratio is for me when you get back to it.

[Alaskabound]

If you suspect that the former owner may have hit something, is it possible that the prop is slipping.? I think that props have a protective feature, kind of like a shear pin, that helps protect the outdrive gearing if something is hit. Has it always performed this way or just started? Maybe having the props looked at or trying out new props would tell you. After reading BB's post again, he is probably right that it would be over reving. Is it possible that the engine or outdrive could limit the RPM's if it detected prop slippage?

Good luck.

Dub

[Ytmsn]

No, the props aren't slipping Alaska. At least I have no indication of that from my experience with past boats. No, it's more like the rev limiter is maxing out at 4000 to 4200 RPMs at 38/39 mph. I've trimmed up way up, way down and everything in between. If it's not the props, I keep thinking it must be in the electronics. I don't know how to test a rev limiter though. Anyone have any ideas?

A 5.7 GXI is just a standard 350 GM motor with big heads. The mechanic told me the cam in boat motors are specific to the hp output and marine use (whatever that means, lift and duration are lift and duration, marine or not?).

This is right off off the web: "The Chevy 350 engine is a 350 cubic inch (5.7-liter) small block V8 with a 4.00 and 3.48 inch bore and stroke. Depending on the year, make and model of a car, horsepower ranges from approximately 145 to more than 370"

145 hp to 370 hp in the same motor is HUGE.

The hp difference comes from the size of the pistons, the heads, cam, exhaust configuation and mapping the EFI as I understand it? A GXI motor has big heads with roller rockers. And it should rev to 5000, 5200 RPMs.

We bored my motor 30 over and went back with all the same components along with new bearings, bushings, seals, ect. A new oil pump was installed. I started out with a Chinese knockoff fuel pump, and thought that might be the problem, so I ordered an OEM pump and replaced it. Same results.

The only other thing I can think of is the power steering pump? The shaft seal leaked a little, and every now and then the bearing would make a noise. The steering would be just a touch "notchy", so I'm wondering if there was a bit of drag on the motor? The pump is being rebuilt right now and should be ready today but I can't go out until next weekend.

I'll post the results and keep trying to figure this thing out..
.

[Big Block Power]

Not that I would ever try it but your rev limiter is prob close to 5200 rpms until you get up there you won't hit fuel cut off. You could run the prop with the right hand rotation and see how quick the rpm gets up there prob in a hurry. Never know. Like I said I wouldn't do it but you never know. Just one of my stupid ideas. Our you find some one with f5 or f3 props.