Brand new 8.2L H.O. Not performing as expected

This is true but should proform better than the old engine, I would think
 
Scott215 said:
496 vs 502. Not a huge difference depending on how the motors are built the 502 by nature should have more torque than the 496 when the 502 came out it was 502 cubic inches 502 horsepower I know Marine applications are different. I think something in the tune of the engine cuz I don't think the 496 the computer can run the 502 or did you get a new ECM with it
Click to expand...
It did come drop in ready with its own ECM
 
Does it ldle really smooth and have really good response to the throttle. I wonder if they could have cracked a plug. That all it would take
 
Well since no one bothered to answer my question.....I did some checking.

Your new 8.2 is rated at 430 Horsepower and 505 lbs of torque at 4,000 rpm. Mercruiser for some odd reason doesn't show torque in their specs anymore.

Your old 8.1 (496 Mag) on dynos ran 400 Horsepower and 526 lbs of torque at 4,000 rpm. https://www.marineindustrieswest.com/installation/496_Dyno.pdf

So....without a lot of commentary....that would explain why you are not seeing much of a difference. I have seen this movie before and logic no longer applies when buying an engine ......dyno results are the only way to actually know what is going to happen when you put it in the boat.

I like Mercruiser products but in this case some of the folks who advised you did not do their homework.

A 30 Horsepower difference won't change anything. Torque on the other hand does. Maybe that is the reason Mercruiser doesn't show it anymore.

As to the previous movie.....we see this everyday with go boats. The engines that show up from Mercruiser are monster 1,000 HP engines but if you don't dyno them you won't know that a properly race built big block engine will drive the boat faster with less horsepower.
 
PlayDate said:
Well since no one bothered to answer my question.....I did some checking.

Your new 8.2 is rated at 430 Horsepower and 505 lbs of torque at 4,000 rpm. Mercruiser for some odd reason doesn't show torque in their specs anymore.

Your old 8.1 (496 Mag) on dynos ran 400 Horsepower and 526 lbs of torque at 4,000 rpm. https://www.marineindustrieswest.com/installation/496_Dyno.pdf

So....without a lot of commentary....that would explain why you are not seeing much of a difference. I have seen this movie before and logic no longer applies when buying an engine ......dyno results are the only way to actually know what is going to happen when you put it in the boat.

I like Mercruiser products but in this case some of the folks who advised you did not do their homework.

A 30 Horsepower difference won't change anything. Torque on the other hand does. Maybe that is the reason Mercruiser doesn't show it anymore.

As to the previous movie.....we see this everyday with go boats. The engines that show up from Mercruiser are monster 1,000 HP engines but if you don't dyno them you won't know that a properly race built big block engine will drive the boat faster with less horsepower.
Click to expand...

Yup, and if you look at the BSFC at the cruise rpm the old motor shows maybe 5% better FE, and it actually be a bit more as the dyno sweeps are at WOT, not a full BSFC 3d map (cruise is probably 95kpa, maybe 90... it's been a while since I looked at data).

Here is some more info I found on the new engine at various HP versions:

Visit the Javits Convention Center on 11th avenue in New York City during the boat show to see Mercruiser’s 8.2 engines that come in 380 Hp, 430 Hp H O, 525 Hp EFI, and 700 Hp SCi variations, among the other engines on display, although not all engines are guaranteed to be at the boat show, in their booth (C-18) and installed in boats on the boat show N Y convention center exhibit floor.

These engines are based on at least two chevy engine blocks with various heads to develop their reliable marine horse power at these levels. The 380 Hp is the one that is popular in a cabin cruiser and bigger family bow riders. Its full throttle rpm range is 4,400 – 4,800 rpm and has a cam and valve train that works best for those kind of rpms. The peak power has been dyno’d at 4,200 rpm before it starts to fall off and the 430 Hp H O version exchanges some low end power compared to the 380 Hp for more clearly power over 4,000 rpm that then peaks at 4,700 – 4,800 rpm. The full throttle rpm range for the 430 Hp H O is put at 4,600 – 5,200 rpm.

A 380 Hp engine will best a 430 Hp power boat up to about 4,000 rpm, where the 430 Hp then really pulls ahead.
XXXXXX has done a sea trial with each of these engines, and in a 7,000 lb type boat it proved hard to tell the difference between them in a pleasure boat application.
 
PlayDate said:
Well since no one bothered to answer my question.....I did some checking.

Your new 8.2 is rated at 430 Horsepower and 505 lbs of torque at 4,000 rpm. Mercruiser for some odd reason doesn't show torque in their specs anymore.

Your old 8.1 (496 Mag) on dynos ran 400 Horsepower and 526 lbs of torque at 4,000 rpm. https://www.marineindustrieswest.com/installation/496_Dyno.pdf

So....without a lot of commentary....that would explain why you are not seeing much of a difference. I have seen this movie before and logic no longer applies when buying an engine ......dyno results are the only way to actually know what is going to happen when you put it in the boat.

I like Mercruiser products but in this case some of the folks who advised you did not do their homework.

A 30 Horsepower difference won't change anything. Torque on the other hand does. Maybe that is the reason Mercruiser doesn't show it anymore.

As to the previous movie.....we see this everyday with go boats. The engines that show up from Mercruiser are monster 1,000 HP engines but if you don't dyno them you won't know that a properly race built big block engine will drive the boat faster with less horsepower.
Click to expand...
His old engine hit 4,600rpm, 40mph WOT with 24p props and 2.0 drive ratio.
His new engine hits 4,000rpm, 32mph WOT with 24p props and 1.81 drive ratio.

I guess it's possible the new engine isn't running right but I question the unnecessary change in drive ratio, less torque at the propshaft at any rpm.
 
Woody said:
His old engine hit 4,600rpm, 40mph WOT with 24p props and 2.0 drive ratio.
His new engine hits 4,000rpm, 32mph WOT with 24p props and 1.81 drive ratio.

I guess it's possible the new engine isn't running right but I question the unnecessary change in drive ratio, less torque at the propshaft at any rpm.
Click to expand...

True....but he is now running 22p props which mitigates the 1.81 drive ratio across the entire power band. My money is on the engine while new does not produce the same torque at 4,000 rpm.

It is possible to improve the performance of the new engine. Go boat owners do it all the time. The only issue is that Mercruiser will void their one year warranty if you make any performance mods to the engine.

Still I would start with at least two full diagnostic runs of the engine from idle to WOT with the 22p props. From there......if there are any items that can be tuned....you have a starting baseline to measure the gains.

There are also a number of Mercruiser Service Bulletins out on the 8.2 which might also be helpful.

Is this engine catalyzed?
 
I know the props might mitigate the ratio but it's still not the same ratio it's like changing the size of the back tires on a car You can change the ratio that way but you're still not changing the final drive ratio it's always going to be a 373 or 411 or whatever it is
 
Who chose/recommended the 1.81 ratio outdrive?
 
I would consult whomever you bought the hardware from and see if a 2.0 ratio is available. That with the props you’ve tried might possibly give you the performance you were expecting. As is stands you might be lugging the engine and that’s bad for longevity.
 
Scott215 said:
I know the props might mitigate the ratio but it's still not the same ratio it's like changing the size of the back tires on a car You can change the ratio that way but you're still not changing the final drive ratio it's always going to be a 373 or 411 or whatever it is
Click to expand...
Yes, no matter what the size of the props themselves, they don't change the amount of torque at the propshaft that they're mounted on. The new XR drive is a 10% reduction of torque at the propshaft, 1.81 vs 2.0. Add that to the possibility the new engine may be making less torque and it simply can't turn the 24" props.
 
I don't know squat about drive ratios, but my boat came from the factory with 8.2's married to B3 1.81's
 

Attachments

  • upload_2023-7-19_12-10-52.png
    upload_2023-7-19_12-10-52.png
    125.2 KB · Views: 39
marz989 said:
I don't know squat about drive ratios, but my boat came from the factory with 8.2's married to B3 1.81's
Click to expand...

Different drive. OP has Bravo3 XR. You have the correct ratio for your 8.2/B3:

Bravo One, Bravo One X Ratios 1.36, 1.50, 1.65 (high altitude)
Bravo Two, Bravo Two X Ratios 1.81, 2.00, 2.20 (high altitude)
Bravo Three, Bravo Three X Ratios 1.81, 2.00, 2.20, 2.43 (high altitude, Bravo Three only)
Bravo One XR Ratios 1.26, 1.35, 1.50
Bravo Three XR Ratios 1.65, 2.00

From the link I posted above.
 
0think ratio is off
 
None of those prop sets he's tried are optimum rpm wise, he needs to hit 5200 rpm with a regular load.
 
scoflaw said:
None of those prop sets he's tried are optimum rpm wise, he needs to hit 5200 rpm with a regular load.
Click to expand...

Agreed, but I'm willing to bet when he gets it running right to recommended RPM showing max speed he's not going to like the cruise RPM with the noise and gph that will go with it. I hope I'm wrong though...
 
I think once the ratio sorted it will be fine just like a street car or race car You got to get it dialed in especially when it's been modified
 
I’m definitely just following along as my6.2 is getting tired and it’s within 500 operational hours (1.5 seasons?) of being time
 
You must log in or register to reply here.

Forum statistics

Threads
113,210
Messages
1,428,650
Members
61,108
Latest member
rvlewis
Back
Top