90 SN top speed

[showskier]

I just purchased a 90 SN. I is absolutely beautiful. I love this boat! I have one question though. What should I expect for top speed? Here are the specs. 240 hp 351. 123:1 trans. Acme 422 prop. Running at approx altitude of 100 ft above sea level.

When I did the test drive with the previous owner I thought the speedos read slow. I asked him about top speed and he said it was 39 mph. Last sunday I took it out and used my gps to check speedos. sure enough, 39 mph.

I am not looking to go fast but I do barefoot. I would like to have a little extra room at the top end. I am considering changing to an acme 470 prop. will that give me much? Any feedback will be greatly appreciated.[/b]

[M3Fan]

RE: 90 SN top speed

I'm sure TRBenj will chime in here about the prop since he has the same boat but we need to know what RPM you are getting at 39MPH. Then we can start dialing in what the problem might be. That boat should be capable of about 44 MPH stock.

[showskier]

RE: 90 SN top speed

max rpm is just under 4000 (I think) . The tach was reading 39** and the perfect pass display was reading 37**. I discounted the perfect pass because it appears to not be calibrated properly. What rpm should this turn?

[M3Fan]

RE: 90 SN top speed

Should turn up to 4400 RPM. Could be several issues including timing, throttle cable adjustment, secondaries not opening all the way, etc. You might also try correctcraftfan.com for more input on this issue as well.

[Millar]

RE: 90 SN top speed

This is interesting, because I have a '98 SN with dual air pitot tube speedometers. I thought the boat should go 44 mph, so I calibrate the air gages by opening the boat up to full throttle, then adjusting the gages. Never occurred to me that it may not be going that fast! I'll check the top end with a gps this weekend. Also, the RPMs.

I assume that the brass prop is stock. Anyone know the RPMs I should see? The boat has the carburated PCM/Ford 351 HO engine.

[darrel409]

RE: 90 SN top speed

Should be 4800 w/ HO motor.

[jdkenyon]

I just got a 94 SN and it runs 44MPH at 4800RPM. This is at 4,000 FT elevation though so down lower you should be able to do better. It is running the 351 Pro Boss.

[showskier]

well I just got home from work and decided to check a couple things. It is getting full throttle but the the rod for the secondaries was disconnected on the carburator. that could very well take care of the problem. I am taking it out Sunday so I will see how it does.

[TRBenj]

well I just got home from work and decided to check a couple things. It is getting full throttle but the the rod for the secondaries was disconnected on the carburator. that could very well take care of the problem. I am taking it out Sunday so I will see how it does.

Sounds like you found the missing ponies.

M3Fan was pretty much right on with his numbers. With the 422, a stock 240hp '90 should do about 42-44 MPH @4400 RPM.

[Millar]

Re: RE: 90 SN top speed

Should be 4800 w/ HO motor.

Thanks, I appreciate the info. The weather was not very nice last weekend, so I didn't get the boat off the dock. I'll try again this weekend.