2.0 150HP vs. 2.5 150HP

**4Speed** · 12-08-2003, 12:34 PM

Any idea what the speed difference would be between a 2.0L 150 HP & a 2.5L 150 HP on the same boat. I assume more cc's, more torque, bigger pitch prop at same RPMs = more speed. Any idea what to expcet on the speed end? Boat is a 18'6'' Baja that has a hull alone weight if 1,400 lbs...Gear & Driver est 1,800 lbs. Both weights are w/o motor.

**LPB** · 12-09-2003, 05:59 AM

Don't waste you time with the 2.0 no balls,I've got a SST-120 motor which is a race verion of the 2.0 with 26cc heads,a stock XR6-150 2.5 liter on the same boat will pull me 4 boat lenths to 60 mph,and the sst 120 is 180 hp,the sst will out run the xr6 on the top side but its 180 hp John LIGHTNING POWER BOATS

**Scream And Fly** · 12-09-2003, 12:23 PM

I believe Viper Ronnie started out with a 2.5 150 and with a little (okay, a lot) of grinding and porting, etc, it made a lot of power. A lot.

Greg

**Reese** · 12-09-2003, 03:19 PM

you and the Baja will be much better off with the 2.5.

To answer your question, technically there should be no real speed difference between two motors with the same HP...150 hp is a 150 hp regardless how you slice it. If you prop to peak HP, both motors might use a different props but the end result would be the same speed.

One thing that would be different is how quickly each motor hit it's top speed...the 2.5 would get there a lot sooner.

**stray cat** · 12-09-2003, 04:24 PM

Are we saying that boats are the same as street cars,there is no substatute for cubic inches?

**1BadAction** · 12-09-2003, 04:37 PM

Originally posted by Reese
you and the Baja will be much better off with the 2.5.

To answer your question, technically there should be no real speed difference between two motors with the same HP...150 hp is a 150 hp regardless how you slice it. If you prop to peak HP, both motors might use a different props but the end result would be the same speed.

One thing that would be different is how quickly each motor hit it's top speed...the 2.5 would get there a lot sooner.

nope, the 2.5 has more torque than a 2.0. so, if they both turned 6000 rpm, and the 2.0 could only turn a 25p prop, but the 2.5 could turn a 28, the 2.5 is faster.

**Reese** · 12-09-2003, 05:16 PM

Are we saying that boats are the same as street cars,there is no substatute for cubic inches?

Yes, Cu.In. are always better just as long as we don't pay too big a price in added weight.

1BadStream:
Peak HP...not peak torque is what determines top speed...if both engine produce the same HP (150) they will produce similar top end numbers regardless of its size.

Torque is a good indication of how quickly top speed will be reached and no one props a boat to peak torque.

A 150 hp 2.0, 2.4, 2.5 and 3.0 litre engine (assuming equal weight) will all produce equal top end numbers.

**1BadAction** · 12-09-2003, 10:12 PM

Peak HP...not peak torque is what determines top speed...if both engine produce the same HP (150) they will produce similar top end numbers regardless of its size.

NO, even 500 HP is nothing unless you have enough torque to do the job. it takes HP AND torque to make a boat go, and since the engines both have 150hp and the 2.5 has more balls, it will be faster. yeah 10,000 rpm looks good on a dyno but if it only turns a 10 pitch prop its not worth ****. since we are concerned with real boats and not dyno queens, the 2.5 is faster. torque lets you turn a bigger prop at the same r's. therefore more speed. if you dont believe me get a vector with a stock xr2 2.0, and i will run my vector with the 2.5 xri. whatever prop you want to run, whatever prop i want to run, and I WILL beat you everytime- and thats with the best 2.0 150 merc ever made. i just got done testing the xr2 that we just got redone, and the 2.5 was 5 mph faster. the 2.5 that i have actually has 5 lbs LESS compression too give of take a few on all cylinders.

**Reese** · 12-09-2003, 11:58 PM

What do you think weighs more 150 lbs. of feathers or 150 lbs. of bricks?

If you said they both weigh the same then we're getting somewhere...

Two engines producing the same HP will mathematically and by the laws of physics produce equal top end numbers...regardless of what kind of torque they produce.

Obviously a motor with more torque will get the job done faster...but both motors will end up giving you the same top end numbers...there is nothing else to argue about.

Your 2.5 litre engine was faster than the 2.0 because it produced more HP...and I don't even have to put it on a dyno to prove that point.

I don't want to confuse 4speed...let at least agree that a 2.5 is a better all around engine for his Baja...

**Glowone** · 12-10-2003, 04:02 PM

okay...if I may comment. The 2.5 is better and a 3.0 is even better. It really depends on your budget. The question really is how much do you want to spend?

A 150hp 2.0 XR2 in nice condition will run about $2000.00 and in my opinion is the best "bang for the buck" . The XR2 uses alot of the 200hp parts and is a more robust engine than a rugular 150hp. (XR2 is important!)

If you get to a 2.5 litre your going to be twice that.

I am interested in who is right...Reese or 1badstream. I see both points. I know in race cars, torque is key to winning races but it is not because of a top end differences but because you can accelerate out of the corners better.

I dont know enough to comment about the torque v. pitch question.

**rev.ronnie** · 12-10-2003, 04:05 PM

So I have found.

**GP-1** · 12-10-2003, 05:18 PM

Well.... Actually you'd have to lay the torque curves next to each other. Most likely the 2.5 is gonna make more torque, but if they make the same horsepower (do they?) they would have an equal top speed if they could both be propped appropriately....I have no idea where the power peak is for either engine, but since HP=Torque @ 5250 rpm, and these fishing motors probably make peak horsepower before 6000 rpm, they're probably close in peak torque too... Yea, the 2.5 probably has more at lower RPM -- hence the edge in accelleration -- but with the correct prop, they should be awful close in top end..

**transomstand** · 12-10-2003, 07:48 PM

The issue is, two different engines with a 150 Hp "rating". The manufacturers are allowed a substantial variance in true HP while still maintaining the HP rating. I have to think that on the dyno, the 2.5 makes more real horsepower.

**Reese** · 12-10-2003, 08:09 PM

did the manufacturers use a pretty wide variance, they also had years where the HP figures were Crankshaft vs. Prop Shaft.

Regardless of the HP rating there is no doubt that the 2.5 had much better torque as well. In either case the 2.5 is a substantially better engine for this application compared to the 2.0.

BTW...a used 2.5 is pretty damn cheap.