Need RPM’s on 383MPI 1970 SeaRay 24’ project

[Scott Danforth]

Attached the Dyno graph here…

something wrong if you only get 244 hp out of a 383

 

[jrglombo]

What condition was the transom in when you rebuilt it? Was there rot?

Yes plenty of rot. The transom and engine stringers were removed and replaced. Transom built to merc spec.

 

[alldodge]

HP ratings for a installed motor and one one the shelf
Installed 320HP , measured at the prop
On the shelf 360HP , measured at the flywheel

Same motor

 

[jrglombo]

Is there such a thing as a break-in dyno?

 

[ROY WILLIAMS]

Roy - I’m sorry your sister was a 24’ Sea Ray ! I’m not too sure what you’re asking though,

SISTER the 1980's buy it 1979 then 1988 sold it .... SEA RAY 1970 24FEET .....
Did the very good boat ....I was buy it in Florida 1979 ... MY sister is MASSACHUSETTS ...

I did not paint any wooden surface. It’s all fiber glass over.

yes that resin polyester wooden then the fiber glass ....

 

[Scott06]

I don’t have it in the report but I was told it made 360hp (advertised as such too) maybe the dyno company can give me a better report.

Thank on the compliment, we really enjoy the boat and the new reliability aspect. Just working out the things like this. Believe it or not the injectors are the same part number for both engines…

On the bottom right of the graph it reports max hp as 244 which matches the graph. You have to download and blow up the pic to seeit. If you pd for 360 tell them to show u where on the dyno graph it is. The power falls way off at higher rpm likely due to the carb used it ran out of air. It said AFr ratio was calculated, which is bs cause an afr meter costs like $400 all in .

If you paid extra for dyno time id be pissed, if it was only to break in-then that is different. With a bigger cam yeah 360 makes sense as a little bump from stock 340 hp, but you need the fuel to do that.

 

[jrglombo]

SISTER the 1980's buy it 1979 then 1988 sold it .... SEA RAY 1970 24FEET .....
Did the very good boat ....I was buy it in Florida 1979 ... MY sister is MASSACHUSETTS ...

yes that resin polyester wooden then the fiber glass ....

Right on. They’re good ole boats!

 

[jrglombo]

On the bottom right of the graph it reports max hp as 244 which matches the graph. You have to download and blow up the pic to seeit. If you pd for 360 tell them to show u where on the dyno graph it is. The power falls way off at higher rpm likely due to the carb used it ran out of air. It said AFr ratio was calculated, which is bs cause an afr meter costs like $400 all in .

If you paid extra for dyno time id be pissed, if it was only to break in-then that is different. With a bigger cam yeah 360 makes sense as a little bump from stock 340 hp, but you need the fuel to do that.

I will call the dyno sometime and see what they say. When I ordered it I thought it was to test its capabilities but when picked up it was presented as a break-in dyno.

 

[jrglombo]

Here’s two plugs from each side. A little reddish. According to the charts I’m on the lean side but not dangerous. Does anyone think differently? Thanks!

 

[Scott Danforth]

youre running lean

 

[Scott06]

Here’s two plugs from each side. A little reddish. According to the charts I’m on the lean side but not dangerous. Does anyone think differently? Thanks!

When reading plugs they show what you last ran which was likely idle to read them you need to run at what ever rpm you want to look at afr then cut it off immediately and pull a plug

 

[alldodge]

Agree, running lean
My guess is you idled back, and later pulled plugs. Only reason there isn't more white is because of idle time.

Your ECM is nost likely saving your motor by retirding timing. Only way to verify is with scanner

 

[jrglombo]

Got it. Yes idled for maybe 3-4minutes after full throttle. How does the 555 know the AFR?

 

[alldodge]

Got it. Yes idled for maybe 3-4minutes after full throttle. How does the 555 know the AFR?

The 555 doesn't know the AFR, it just has fuel tables

Fuel tables are determined by Merc running the motor with AFR probes in the exhaust under various loads. The tables are built in conjunction with MAP, TPS and Air/Water Temps. Ones the tables have been designed, then based on what the drive/boat the motor is being installed the variations of the tables are changed. This is the reason there can be several different ECM's all based on what the motor is connected to.

So the ECM fuel tables will need to be changed going from 350 to 383.
One saving grace is Merc usually builds the tables fat (more fuel). Building tables fat means that when the motor is bored the ECM does not need to be reflashed

 

[alldodge]

Again we are just guessing because we have no data (scanner) to compare with

 

[jrglombo]

Okay. Would it be best to get someone on the boat with testing equipment or just send the ECM to Whipple to get flashed?

 

[alldodge]

If you had a scanner attached to the motor it would tell what is happening. It could be something else is happening along with lean but we just don't know right now

If O2 sensors are installed this to will provide good data, but without a means to change, it's not a good choice

Sending it to Whipple or anther site just changes it to closer to where it should be

If a 350 was bored out to max at .060 over, there is a increase of 10 cubic inches of volume to equal 360.423

As we can see a 383 is 23 cu in above that

350​
bore	stroke
4.001​	3.48​	12.573​	350.024​
4.03​	3.48​	12.756​	355.116​
4.04​	3.48​	12.819​	356.881​
4.06​	3.48​	12.946​	360.423​

 

[jrglombo]

Well I have free access to a scanner so I will do a run before my season is unfortunately over (Michigan)! Criteria to scan and watch would be spark advance and ???. How far should the computer advance the timing?

 

[alldodge]

Your looking for error codes not actual advance

 

[jrglombo]

Okay. Would error codes show on my Vesselview? There are none.