race legal 2.5 efi typical HP?

verytricky · 24-11-2005, 01:06 PM

As in ..... Does anyone know what the typical HP would be for a race legal 2.5 EFI ?

roofer · 24-11-2005, 01:14 PM

Which engine? 260, 280 or 300 drag.

verytricky · 24-11-2005, 02:24 PM

Quote:

Originally posted by roofer
Which engine? 260, 280 or 300 drag.

I dont know. What about the ones they use for the 6 liter class boats - like the ones fitted to the racing Bladerunner.?

roofer · 24-11-2005, 02:44 PM

Probably fitted with twin 280's.

verytricky · 24-11-2005, 02:57 PM

So if they are 280's why call them 2.5 efi?

Q1) What is the HP output of such an animal race legal?
Q2) What benefit does a lightened flywheel give? Both generally and specifically.

Tony Davis · 24-11-2005, 03:06 PM

Quote:

Originally posted by verytricky
So if they are 280's why call them 2.5 efi?

two and a half litre, electronic fuel injection!

TheMutzNuts · 24-11-2005, 03:13 PM

Quote:

Originally posted by verytricky
So if they are 280's why call them 2.5 efi?

Q1) What is the HP output of such an animal race legal?
Q2) What benefit does a lightened flywheel give? Both generally and specifically.

The 280 is a 2.5l engine, as is the 260 and 300 drag.
The 280 makes 280hp, 260 makes 260hp and the 300 drag makes over 300hp
These are all 2.5 ltr engines, the 260+drag have the same/similar block but the 280 block is completely different .

Burty · 24-11-2005, 03:13 PM

dont think you can change anything if racing in 6ltr, you have to run genuine everything

Lighter flywheel means less rotating mass which means less wear on bearings etc and also equals more power. however too lighter flywheel can be dangerous if used in rough conditions.

TheMutzNuts · 24-11-2005, 03:27 PM

Quote:

Originally posted by Burty
However too lighter flywheel can be dangerous if used in rough conditions.

Whys that?

Burty · 24-11-2005, 03:40 PM

Quote:

Originally posted by TheMutzNuts
Whys that?

cus when you are in and out of water all the time with a light flywheel the engine will spin up quicker when you leave the water and slow down quicker when you re enter thus causing higher stress on the engine. a heavier will dampen this effect more

Matt · 24-11-2005, 03:46 PM

Are you sure about that?

roofer · 24-11-2005, 03:47 PM

I thought the only thing a lightened flywheel did was reduce the strain on the rotating mass.

Matt · 24-11-2005, 03:50 PM

It does improve pick up (less rotational mass to spin up). It does nothing for top end.
And less rotaional mass means less mass to slow down again when the motah goes back in the water, ergo, les likely to break cranks & propshafts. The pistons don't mind speeding up and slowing down a lot.
Just IMVHO of course.

Burty · 24-11-2005, 05:07 PM

not sure now but jay smith said it was dangerous so i believed him

verytricky · 24-11-2005, 05:44 PM

Interesting:

Anyone else have thoughts on this?
I know in the 2004 race season someone had a V24 with a lightened flywheel, and I could see no benefit, as I beat them in every race they finished, except 1 ( they did not race 2005 )

So I was thinking that it was possibly a 'neat trick' with no actual benefit.

So - a special lightweight aluminum flywheel at £800 an engine is possibly not worth the effort of doing the work?

There is possibly no better top end, and no real value ( for the outlay ) in doing so?

scottyboy · 24-11-2005, 07:56 PM

Quote:

Originally posted by Burty
cus when you are in and out of water all the time with a light flywheel the engine will spin up quicker when you leave the water and slow down quicker when you re enter thus causing higher stress on the engine. a heavier will dampen this effect more

Surely thats when "driving" the boat and "working" the throttle comes into play?

JamesM · 24-11-2005, 10:17 PM

The way I see it is as the prop goes in and out of the water the load the engine see's from the driveshaft output varys sharply, high load, no load, high load, no load etc. However a percentage of the engine load is from the flywheel, this load is fairly constant by comparison. So if you reduce the weight of the flywheel you reduce this constant load thus making the variation in total load more pronounced. So in short the heavier flywheel helps to dampen the high load, no load effect.

Quote:

Originally posted by Matt

And less rotaional mass means less mass to slow down again when the motah goes back in the water, ergo, les likely to break cranks & propshafts.

Put a 50 ton flywheel on there and see how much the engine speed slows down when the motah goes back in the water.

Matt · 24-11-2005, 10:27 PM

Yes, and also watch your crankshaft & driveshaft snap due to the increased rotational inertia, which is my whole point. An engine doesn't really give a shit about rate of change of rpm, it gives a shit about the rate of change of speed of masses. Or, using the linear formula for it cos I can't remember the rotational one, F=MA.
So you halve the mass, you can afford to accelerate or decelerate the components at twice the speed without putting any additional load on it.

I also accept the point about lightened flywheel being a risk - and at a guess I reckon it's down to reduced strength of the flywheel. I am looking for proof that this is the case though - I could be barking up the wrong tree.

Quote:

Originally posted by Johnny Boat Dude
Put a 50 ton flywheel on there and see how much the engine speed slows down when the motah goes back in the water.

Matt · 24-11-2005, 10:49 PM

Interesting. Certainly wouldn't have expected more top speed, but on a drag boat would have expected to see a slight increase in acceleration.
http://forums.screamandfly.com/forum...d.php?p=667769

JamesM · 24-11-2005, 11:04 PM

Quote:

Originally posted by Matt
Yes, and also watch your crankshaft & driveshaft snap due to the increased rotational inertia, which is my whole point. An engine doesn't really give a shit about rate of change of rpm, it gives a shit about the rate of change of speed of masses. Or, using the linear formula for it cos I can't remember the rotational one, F=MA.
So you halve the mass, you can afford to accelerate or decelerate the components at twice the speed without putting any additional load on it.

With rotating masses the distance of the mass from the center of rotation must also be a factor. The further the mass from the center point of rotation the greater its velocity and so the greater the energy stored, or required in order change its state. Thus weight taken from the outer most edge of the flywheel would have a greater effect on the rate of change of speed of masses than an equal amount of weight taken from the inner most edge of the flywheel. Therefore if you halve the mass, depending on where you take it from, the rotating components may see more than a doubling in the rate of change of acceleration/deceleration and thus an increase in load. Yes, no?

Where are all the mechanincal engineers when you need em