200 Too Slow, what to do

[GreaseMonkey]

Last year I purchased a 1995 Cobalt 200, with. 5.0LX rated at 205hp.
(My first boat)

Decent shape, but a little rough, but priced accordingly. I don't mind projects and am familiar with both fiberglass work (kayaks), and engines (cars, tractors, etc.). So I wasn't too worried and figure it was a good way to learn boats.

Previous owner said it would do 50mph (true GPS speed).
Before buying did a water test and everything felt fine but it was too rough to try out that top speed.

When I went to take it out on a calmer day after purchase I could only hit close to 40mph. (Verified on GPS)
It was the end of the boating season here in Michigan and time to winterize though so I went through it as I winterized and didn't see anything wrong, but figured I could just figure it out this year.

Well this year I have done everything but figure out why it will only do 40mph. I have tried almost everything that I can think of, Ignition system is new from the coil to the plugs, and the fuel pump is new and carb rebuilt. However at the end of all of that my max is only 42mph.

General driving around feels fine, and can cruise all day at 35 with no issue.


So my first question is am I correct to think that this boat with this Engine should be able to hit close to 50mph?


At this point my options are.
1. Live with it the way it is, and move on to fixing other things.
2. Tear down the top end of the engine and install new heads, intake and cam over this winter (only ideas I have left are a bad valve or cam)
3. Tear out the whole engine and build a 350 for it.
4. Start looking for a 226 or other Cobalt to replace this slow boat.

[Titaniumboy]

Welcome!!

What are the rpm’s at your 42 mph top speed? What pitch are your propellers?

[GreaseMonkey]

At 42mph RPM at 4100
Outdrive is 1.5 ratio, and 19P AL prop.

Have a 17P AL prop as well with that prop RPM moves up to around 4200, but top speed down to 38mph.

That seemed odd to me that I didn't pick up more RPM, and maybe a little bit more top speed with the lower pitch prop.

[bruceb58]

Sounds about right to me. Had a 21' boat with a 5.0L carb'd boat and it only did around 40 MPH.

How many hours and have you done a compression test?

In 1995, they didn't have the Vortec heads on it yet so you could gain more HP by adding that but you would be better off going to a 350 with Vortec heads. Bottom line, be happy with what you have. If not...buy a different boat and sell this one.

[GreaseMonkey]

Hours on the boat is just 568.
Compression test came out to 150-160psi on all cylinders (cold engine)

The only other symptom that I can find is a low manifold vacuum at idle.

If 40mph is normal then I just spent a lot of time chasing my tail for nothing. However a newer 200 with significantly more weight will do 48 with the V6, (of course that newer v6 has a little bit more power than my V8 was rated at)

I actually already have a set of vortec heads for it that I was waiting to figure out what the problem was before I started modifications.

[bruceb58]

I actually already have a set of vortec heads for it that I was waiting to figure out what the problem was before I started modifications.

You would need a new intake manifold as well.

[groberts4]

Hey guys - I have the same question for my 8.1L Volvo Penta. It's almost new, replaced following the 2021 "Valentine's Day Massacre" ice storm destroyed the original engine. Is there a simple or relatively inexpensive way to get some extra speed? I can hit 55 mph (speedo, haven't checked GPS) but my previous engine would do 59. Should I be happy with that or could I change props, better plugs, something to get another ~5 mph?

[kevincs23]

One thing you didn't mention was how you had the drive trimmed.
My last boat was a 20' Reinell with 5.0gi. 1.51 gearing. Had an aluminum 19 pitch prop (edges were a little rough). I could get 40-42 with the trim down all the way down and 48-49 with the trim up some. Ended up changing to a stainless steel prop, same pitch, and with a light load I could get 53-55. The boat is lighter than your Cobalt, but I would think upper 40's should be achievable.

Also, what altitude are you running at? That can make a large difference.

Like you said though, you could also go to a 226 (I recommend a big block)... that will get you some extra speed. I absolutely love mine.