vtown

THIS IS NOT A POST ABOUT WHICH ENGINE IS BETTER. THIS IS ABOUT THESE ENGINES IN A SPECIFIC APPLICATION.


I know of two west coast MFG that claim the merc 600 is 2mph faster than the ilmor 710.

28ft single engine deckboat. Cat style center pod mod-vp hull (derived from talon).

data:

Both 1.5 ratio bravo xr, stock bravo props, center of propshaft 3" below centerpod

Ilmor 710: 26p 85mph@6300 rpm 16% slip weighs about 4700lbs

merc 600: 30p 87mph@5400 rpm 13% slip weighs about 5000lbs

I can only think of two reasons: weight distribution and prop speed.

What can changed in the setup to get the proper speed from the 710's hp and weight advantage.

mrb30

Where you using different props for each test?

Uncle Dave

I dont believe a stock merc 600 can outrun an identically equipped 710 boat.

The merc 600 can be leaned on for ton of power more, but the merc weighs at least 150 pounds more.

I question these data points as being unoptimized from the standpoint that - the numbers on the 710 dont line up from my personal observations (on a different theoretically less efficient hull)

A 26P on a 28ft cat deck seems just a bit off

I run as fast if not faster with a 710 in a 28.6ft stepped V.

I spin a 28 6K just a bit over 6K on a 5300 pound boat.
I can pull a 30 to about 5900 with a light load.


Uncle Dave

vtown

I did not do the tests but both props are stock bravo 1. both drives are 1.5 ratio. the ilmor is 700hp at 6300 and is prop'ed with a 26p. the merc is 600hp at 5400 and is prop'ed with a 30p.

400lbs of balast in trunk, and a re-gear to 1.65 on the ilmor boat should make the ilmor boat faster. solves the CG difference, makes the prop size and prop rpm nearly the same.....but that would be silly to add weight and make the drive weaker.

vtown

Every boat is different.

It must be the set-up...ilmor should be faster.

Assume this to be true. Other than ballast and gear change what could be done to get the ilmor boat faster?

DMOORE

A guy I know runs the 710 in an Advantantage 27 deck. He says the boat runs right at 85.



Darrell.

Uncle Dave

Try
1. try a 5 blade prop - It will slip less.
1. a -1 then -2" shorty lower to raise the propshaft a bit
2. swap to an Imco lower unit


Where is the boat located?

Uncle Dave

Marginmn

iTrader: (1)

I have had 3 different engine packages in the same boat with the same drives.

Boat: 2000 38 Fountain Fever running XR's on Imco extension boxes with -2 Imco shorties.

1st set of engines: Merc 525's (a set picked off the production line personally by an accomplished racer and later when I was selling them they were dynoed by Joey Griffen as part of the sale and he said it was one of the best sets of 525's he'd ever seen on his dyno at 570+ hp).

Results: 85MPH is the best I saw running a set of stock 4 bladed Bravos at 5250' ish. on a cool Oct day.

2nd engine package: A set of first Gen Ilmor 625's.

Results: 89 MPH on a moderate July day running a set of labbed 27 P5X's at 5850.

3rd set of Engines. Ilmor Gen 3 710's.

Results have only ran the boat a few times. 94 MPH running stock 27 P5X's around 6200 on a moderate June day. Not sure but I may have been getting in the rev limiter. I have a set of 28 labbed P5X's that should push the boat to around 96 mph.

Merc 525: 85


Ilmor 625: 89


Ilmor 710: 94 (with more in it likely)

I have heard countless people here on OSO recommend the Merc 525's over the 600's because they say the 600's are only a couple to 3-4 MPH faster than the 525's.

I had one of the best sets of 525's that a racer handpicked off the production line and it was at least 9mph slower than the Ilmor 710's that I have only briefly tested with one set of props that are likely too small.

From my experiences Id say the test was flawed.

CB-BLR

I have played around with a lot of Nordic Heats...one of them with a 710 Ilmor...and mine with a Merc 600 in various stages of tune. The Heat is a big boat for a single engine.

The 710 Ilmor Heat would run 86-87 mph any day...with a best of 90.6 mph.

My stock 600sci Heat would run a consistent 79 mph any day...with a best of 81 mph.

Having said that...the 600sci boat would simply walk away from the 710 boat in 30-75 mph acceleration tests....and then the Ilmore boat would take the rest of the lake to reel in the 600sci boat....and pass it. the Ilmore motor just doesn't have the torque of the supercharged 600sci.

After putting a Whipple Stage II kit on the 600sci...it would do a consistant 91 mph with a best of 93.8 mph....and destroy the 710 in acceleration.

Just my observations.

Also...my 600sci Heat is an open bow...which tends to be about 2 mph slower than its closed bow bretheren. All my testing was done with the bow cover on.

Chris

vtown

The testing has been confirmed by two different mfgs (talon based bottom).

It is true. At least assume it is. a gear change and added weight in the stern would duplicate the 600 in weight and prop speed and prop size.....what else can be changed to make the higher hp lighter ilmor work better?