Getting my 1st 300R V8 this week.

**bassmasterffej** · 07-20-2018, 01:17 PM

The bass boat guys are having to go down at least 1 prop pitch when switching from the 250 Pro XS 2 stroke to the new 250 Pro XS 4 stroke...TM lower unit on both motors but 200 more RPM with the new V8...Seems odd to me since the new V8 has more torque...? From what I can gather top end appears to be about the same with both motors.

**WILDMAN** · 07-20-2018, 01:21 PM

We were talking, and I think the reason that all the standard over the hub 14 - 14.5" props would not hook up (even at 90 mph) is the extra exhaust over the blades. While the 2.6 litre 400R works with standard props and the 300R doesn't may be because the bigger 4.6 puts out almost twice the volume of exhaust over the 2.6. All this extra exhause over the blade won't let the props hook up. The through hun Max 5 had no problem. We even ran a 36" four blade and it hit the 6400 limiter at 90. Like I said, we are just gonna need to figuer it out.

**RSWORDS** · 07-20-2018, 01:26 PM

Originally Posted by WILDMAN

We were talking, and I think the reason that all the standard over the hub 14 - 14.5" props would not hook up (even at 90 mph) is the extra exhaust over the blades. While the 2.6 litre 400R works with standard props and the 300R doesn't may be because the bigger 4.6 puts out almost twice the volume of exhaust over the 2.6. All this extra exhause over the blade won't let the props hook up. The through hun Max 5 had no problem. We even ran a 36" four blade and it hit the 6400 limiter at 90. Like I said, we are just gonna need to figuer it out.

Doesn't the R have a selectable exhaust to dump it up high?

**Z06man** · 07-20-2018, 01:48 PM

No selectable on R that I saw , I think that's on the verado type mid only.

Originally Posted by RSWORDS

Doesn't the R have a selectable exhaust to dump it up high?

**Radiant** · 07-20-2018, 01:51 PM

Maybe someone has to come out with a mod to make more of the exhaust come out of the mid. Time will tell

**Z06man** · 07-20-2018, 01:57 PM

I tried to talk Wildman into short Zoomie headers even brought hole saw, He would not let me get close to cowling.

**WavetoWave** · 07-20-2018, 03:02 PM

Thanks Randy, great info here. Really like this engine. Probably not long before they have an optional gear ratio.

**mjw930** · 07-20-2018, 03:06 PM

Originally Posted by engineermike

I think the dbr dyno of the 300xs was showing more like 310. My math says the 300r is 322-329.

Originally Posted by WILDMAN

We were talking, and I think the reason that all the standard over the hub 14 - 14.5" props would not hook up (even at 90 mph) is the extra exhaust over the blades. While the 2.6 litre 400R works with standard props and the 300R doesn't may be because the bigger 4.6 puts out almost twice the volume of exhaust over the 2.6. All this extra exhause over the blade won't let the props hook up. The through hun Max 5 had no problem. We even ran a 36" four blade and it hit the 6400 limiter at 90. Like I said, we are just gonna need to figuer it out.

I know it's way too low to hit top speed but I've got a 32 ProMax that could at least help test the theory. It should pull up to redline HARD if it stays hooked up. Should be around 103 if you can get to 7% slip, 100 @ 10%.

**Hot Shot Merc** · 07-20-2018, 03:31 PM

Out of curiosity,what does one of the 5 blade wheels cost this thing seems to like. Yeah yeah I know "if ya have to ask you cant afford it"

**skydog** · 07-20-2018, 03:35 PM

I would not think the amount of exhaust coming out would be more if any. That boosted motor i guarantee is shoving that exhaust out at a much higher velocity. Can't wait for some time with the new R set up sweeeet stuff!!!

**xb03fs** · 07-20-2018, 03:39 PM

Originally Posted by mjw930

I know it's way too low to hit top speed but I've got a 32 ProMax that could at least help test the theory. It should pull up to redline HARD if it stays hooked up. Should be around 103 if you can get to 7% slip, 100 @ 10%.

There are blowout rings available for promax props that would force the exhaust through the hub.... well depending on in inside of Id of case is similar to Id of 3 liter case... we know the OD is .75” larger

**engineermike** · 07-20-2018, 04:15 PM

Originally Posted by Hot Shot Merc

Out of curiosity,what does one of the 5 blade wheels cost this thing seems to like. Yeah yeah I know "if ya have to ask you cant afford it"

The cnc 5 blade cleaver is like $5k. The max5 is the best I've run and it's about $1800. The Maximus, p5x, and 5-speed are cheaper but still over a grand. In all fairness, all max5's are labbed.

As a side note, the promax was the best performing 4-blade on my boat.

**Davidlake** · 07-20-2018, 04:39 PM

Originally Posted by WILDMAN

We were talking, and I think the reason that all the standard over the hub 14 - 14.5" props would not hook up (even at 90 mph) is the extra exhaust over the blades. While the 2.6 litre 400R works with standard props and the 300R doesn't may be because the bigger 4.6 puts out almost twice the volume of exhaust over the 2.6. All this extra exhause over the blade won't let the props hook up. The through hun Max 5 had no problem. We even ran a 36" four blade and it hit the 6400 limiter at 90. Like I said, we are just gonna need to figuer it out.

Horsepower in a function of calories burned. A boosted engine making 400 HP will consume more air and fuel than a NA 300 HP one regardless of displacement. They all run around 13:1 to 14:1 air/fuel ratio.

**mjw930** · 07-20-2018, 05:58 PM

Or another way to look at it, a NA 4 stroke motor moves 1/2 it’s displacement per revolution. A 2 stroke motor moves its displacement per revolution. A forced induction 4 stroke motor moves 1/2 it’s displacement per revolution x 2*(boost pressure / 14.7).

NA 4-stroke 4.6L = 2.3L per revolution
NA 2-stroke 3.2L = 3.2L per revolution
Supercharged 2.6L with 14.7lbs boost = 2.6L per revolution

At 7000 rpm the 400R is moving more air than the 300R at 6400 rpm but still less than the 300XS at 6200.

The power the motor creates is more than a function of air flow though better air flow does increase power since it makes the motor more efficient. Compression ratio or effective compression ratio in a boosted motor has the biggest effect on power. The higher the compression ratio the more energy is released in each power stroke. That’s highly simplified but it’s a basic rule of thumb.

So, the idea there’s more aeration on the prop is more a function of the hydrodynamics of the lower unit than airflow from the exhaust. What’s surprising is the difference in performance between the 300R and the 400R, aren’t they essentially the same lower? Could be the lighter motor is being carried higher than the 400.