Z300, z250

[pstephens46]

What was the problem with these big motors that made them so unreliable?

[cpostis]

I think Rodbolt has some input on this!

your compaering apples to rotten kumquats.

the Z250 and some of the Z300 recalls were useless. they would blow up any way.
dunno about the latest bulliten but we do have 2 2.8L engines in stock that have to be modified.

[boscoe99]

Cylinders are IMO detonating. Usually the number 2 taking a number 2.

The problem can be mitigated somewhat by making sure that

- the motor is propped to get to its red line RPM when the boat is loaded and the motor is at WOT,
- letting the motor warm up in gear,
- using Pennzoil 100% synthetic oil,
- using 91/93 octane and
- don't be hammering down on the throttle to get onto plane with a 27"/29" pitch propeller like those bass boaters with a hot foot do

Now keep in mind that many, many big block HPDI users never have nary a problem. The few have the same problem over and over again. I think the motor is just not very tolerable of being mishandled by the few.

Here is a damaged piston from a big block HPDI. It is very typical of the damage seen when the motor fails.

[pstephens46]

Nasty looking piston. 27-29 pitch props....that's crazy.

[boscoe99]

Nasty looking piston. 27-29 pitch props....that's crazy.

Hammering down on a motor with a 29" pitch propeller might be like trying to drag race a car with the transmission if fourth gear. Not too good for the health of the motor. Now do it over and over again and then bitch when the motor does not survive. It is always Yamaha's problem isn't it?

[cpostis]

Cylinders are IMO detonating. Usually the number 2 taking a number 2.

The problem can be mitigated somewhat by making sure that

- the motor is propped to get to its red line RPM when the boat is loaded and the motor is at WOT,
- letting the motor warm up in gear,
- using Pennzoil 100% synthetic oil,
- using 91/93 octane and
- don't be hammering down on the throttle to get onto plane with a 27"/29" pitch propeller like those bass boaters with a hot foot do

Now keep in mind that many, many big block HPDI users never have nary a problem. The few have the same problem over and over again. I think the motor is just not very tolerable of being mishandled by the few.

Here is a damaged piston from a big block HPDI. It is very typical of the damage seen when the motor fails.

Agreed!
Here's a great link on "DETONATION/PRE-IGNITION AND THE OUTBOARD MOTOR"

http://members.iinet.net.au/~pauldaw...TON-PWD-94.pdf

[99yam40]

Hammering down on a motor with a 29" pitch propeller might be like trying to drag race a car with the transmission if fourth gear. Not too good for the health of the motor. Now do it over and over again and then bitch when the motor does not survive. It is always Yamaha's problem isn't it?

I read something the other day about how many revolutions a dragster motor does running down the drag strip and how much fuel it runs thru duing that time frame to get all of that HP out of the motor.

Never thought about it before, but if a motor turns 10,000 RPMs during a race, and runs the race in 5 seconds.

it only turns 833 revolutions during that 5 second time.
It burns many gallons of fuel during those 833 revolutions of the crankshaft

[boscoe99]

Agreed!
Here's a great link on "DETONATION/PRE-IGNITION AND THE OUTBOARD MOTOR"

http://members.iinet.net.au/~pauldaw...TON-PWD-94.pdf

Good read.

Notice in figure 8 how the combustion chamber type affects the octane rating? Notice that the hemispherical combustion chamber has a need for the highest octane rating? Ever wonder what type of combustion chamber the HPDI has?

Ever wonder why models before the HPDI and after the HDPI have knock sensors but the HDPI does not use one? What was Yamaha not thinking?

The HPDI uses a lot less fuel than does its predecessor the OX66 model. A leaner mix is more detonation prone than is a richer mix. The OX66 is considered all but bullet proof. The big block HPDI is considered by many to be a POS.

[boscoe99]

I read something the other day about how many revolutions a dragster motor does running down the drag strip and how much fuel it runs thru duing that time frame to get all of that HP out of the motor.

Never thought about it before, but if a motor turns 10,000 RPMs during a race, and runs the race in 5 seconds.

it only turns 833 revolutions during that 5 second time.
It burns many gallons of fuel during those 833 revolutions of the crankshaft

I oft times see raw fuel being blown out of the exhaust stack. How does it not hydrolock a cylinder?

[cpostis]

I read something the other day about how many revolutions a dragster motor does running down the drag strip and how much fuel it runs thru duing that time frame to get all of that HP out of the motor.

Never thought about it before, but if a motor turns 10,000 RPMs during a race, and runs the race in 5 seconds.

it only turns 833 revolutions during that 5 second time.
It burns many gallons of fuel during those 833 revolutions of the crankshaft

So, for every revolution that dragster in your example, it will travel an average of .792 feet on a 1/8 mile (660 foot) strip.

[99yam40]

I understand there is a fine line between making it past that TDC without breaking something.
seems the fuel does not all vaporize in the motor unless it is lit and burning properly

[99yam40]

So, for every revolution that dragster in your example, it will travel an average of .792 feet on a 1/8 mile (660 foot) strip.

I guess it depends on what trac they run on.
not sure on how long the tracs are that all of these things run on, but think they shortened them to keep the top speeds down and maybe saving motors and lives too

The 10K I posted was just a number I came up with for easy math, I belive they do more RPM than that

[boscoe99]

Tracks used to be 1/4th mile. Speeds got too fast for the tracks such that they could not get them stopped past the finish line. So, they reduced the track length to 1000 feet I recall. Still, with some top speed at or over 330 mph they have a hard time getting stopped. Particularly if one both of the parachutes do not open.

https://en.wikipedia.org/wiki/Top_Fuel

http://wediditforlove.com/techtalk21.html

[cpostis]

Tracks used to be 1/4th mile. Speeds got too fast for the tracks such that they could not get them stopped past the finish line. So, they reduced the track length to 1000 feet I recall. Still, with some top speed at or over 330 mph they have a hard time getting stopped. Particularly if one both of the parachutes do not open.

https://en.wikipedia.org/wiki/Top_Fuel

Don Long Builds The Old Master

I stand corrected. Then for every revolution the dragster will travel an average of 1.2 feet.

So if in my car I travel a stable 60MPH for 1 mile @ 1800RPM, for each revolution I'll travel 2.93 feet. Ha, I'm better than a top fuel dragster!!!

[pstephens46]

Interesting that these modern ecu computers cannot compensate for the load and autocorrect for the drag that "blows" these motors. Some sort of vacuum sensor?