496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specifications"

[RichardS]

Just curious guys......especially those of you with a 270 SLX, but of course any model that may be of similar weight and size ....

What is your 496 MAG engine spinning at it's top speed? RPM and WOT numbers are what I am looking for.

Lately my boat seems to be slower, and it was just out of water for service so the bottom is clean and the props polished and in good shape. (Stock 26P set)

If hours matter, I've got about 120 hours on mine, with very recent complete cooling service to the tune of $3500. My temp at WOT is running around 165. Curious about how your temps are too, although I suspect my warm bay waters where I am running have something to do what my running temps, and it would be lower if I were in deep blue waters.

Anyway, I really look forward to hearing from you guys running this engine, no matter what boat it's in!

 

[paulswagelock]

Re: 496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specificati

165 degrees regardless of water temp - that is the thermostat set point.
4500 -4600 rpm with a 4x4 26p prop set.
47 - 48mph with painted bottom.

 

[RichardS]

Re: 496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specificati

Paul, I'm running 4140 RPM WOT at 42.1 MPH, painted bottom, 1/2 tank fuel, 2 people. I have the stock 3 blade 26P blades, not the 4 blades like you. Don't know what that means to the equation though.

But it seems like earlier in the season (May), the boat was hitting a 300-400 hundred RPMS higher and several MPH faster. Thus my concern.

Thoughts?

 

[tdgard]

Re: 496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specificati

Stock blades no paint. 4600ish and 53 on gps.

 

[paulswagelock]

Re: 496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specificati

But it seems like earlier in the season (May), the boat was hitting a 300-400 hundred RPMS higher and several MPH faster. Thus my concern.

Thoughts?

When I hear that, my first thought is always the fouling on the bottom. It does not take much to drop the boat a few hundred rpm.
Other than that, I would go to spark plugs second as the 496 is tough on them.

in my area, if you don't bottom paint, by mid season the boat will be down 10mph from growth.

 

[scoflaw]

Re: 496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specificati

Replace your plug wires as well. Do a compression test while the plugs are out to see where your at.
T stats set minimum temps and have no control on anything higher once it's fully open.

 

[RichardS]

Re: 496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specificati

I think the plug wires and plugs will be my next endeavor to improve performance, but at this point I might as well wait until next season. Don't want to lose any more boating time.

I only mentioned the running temp because I noticed when I get out in deeper waters (thus cooler than the very warm and shallow bay) the temp drops down to the 150's, which I thought interesting.

Any other guys with the same running gear, I'm very interested in hearing your experience. I'd love to be getting tdgard's numbers! I've never seen my boat break the 5-0 mark. Is that common with this boat or the 27 foot SD version?

 

[Leardriver]

Re: 496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specificati

2004 270 Sundeck 496 Mag. Pretty close to your weight and hull shape.

At sea level, 26 pitch props, 2.0 drive ratio, clean bottom hull, never painted, fresh water only. 49.6 GPS 4800 RPM

At 5900 feet, 22 pitch props to adjust for altitude (26 pitch turns 4100 RPM here) at 4780 RPM, 42.4 mph GPS.

 

[tdgard]

Re: 496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specificati

I'll have to page through the smartcraft & double check the rpm next time. Could be in the 4800 range. Problem with doing that is I will see the gph screen & slow down.:smt101

 

[skibum]

Re: 496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specificati

Problem with doing that is I will see the gph screen & slow down.:smt101

:smt043That's what keeps me off the throttle...

 

[BleednBlue]

Re: 496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specificati

Sorry, but I can not answer your WOT questions because never really paid attention. However, I can say when cruising @ 3000 rpm I am moving at ~30 mph (gps). Likewise 3500 rpm I am moving at ~35 mph. I say ~ because I can never find calm seas at LOTO. That said, surprised no one has asked you about where your out drive trim is at? Also, are your trim tabs in the completely raised position? I ask about out drive trim because my trim sending unit is out and needs to be replace. Anyway, wondering if your trim sending unit is not giving an accurate reading and your trimmed too low?? Lastly, the highest temp I've seen is 170 (coming off of ~WOT to idle). At cruising speed consistently between 165-167 degrees.

 

[highslice]

Re: 496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specificati

After replacing the spark plugs, WOT is back to 4,800 with a gps speed of 54ish. Always run between 160 and 170. Actually higher at idle than cruising or WOT.

 

[tdgard]

Re: 496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specificati

Did double check today. 4660 and 52. Little less than ideal out today as well. Temp is always low 160s and like highslice, does creep up at idle a few degrees.

 

[LawyerMan]

Re: 496 Mag 8.1 DTS Top Speeds and RPMS, Actual Experience vs. "Technical Specificati

I had my boat out over the weekend. It is a 2006 270 SLX with 496 Mag. We had it loaded down with 10 people (three of them were pretty big - 250lbs plus) and I was able to get it up to 48 MPH (on the GPS) trimming the motor only, no trim tabs.

 

[2006 270SLX]

Yday I opened her up with 3 people and full gas and only got up to 42mph @4500 rpms.

 

[sbw1]

Interesting about those 8.1s. Great engines. We had a totally different boat at 18,000 pounds and wider and longer. Still at 4500 RPMs we did 41MPH on the gps.