DIY_EFI Digest V4 #579

[nhoj at cd.chalmers.se]

You Espen Hilde wrote:
> [About Yamaha HPDI]
> To reduce the fuel to a fine mist the system uses high pressure,
> 700psi , ficht uses (OMC) 300-400psi , DFI (Merc) 80 psi.

Note that you cannot directly compare Mercury's 80 psi with Yamaha's 700,  
since Mercury uses direct air/fuel injection, and compressed gas contains  
much more energy than a pressurized liquid. Pressure is just a marketing  
figure. It atomization that is interesting.

Has anyone seen atomization figures for HPDI?

> The pressure is developed through a very small high speed pump.

A large low pressure fuel pump pushes fuel into a liquid/gas separator to  
get rid of any bubbles, and then into the high pressure pump.

> Yamaha uses the common sensors , crank position sensor.TPS,KNOK,
> rpm sensor, water temp, air temp,MAP,O2.....o2.............?(patented 02
> sensors )

The fact that Yamaha can operate in a real closed loop mode was what struck  
me when I first read the specs. Yamaha already does this in the OX66 EFI  
system which is used on their 76 degree 3.1 litre engines, by the way.

The reason for going with a 76 degree engine is that it allows them to stay  
within the form factor of the 90 degree engines despite the new hardware.

> All manufacturers of theese dfi outboard engines has had some bugs
> that develop.....

To say it nicely. :)

> Mercury delivers a high perf 200 dfi that took 2 place at paris ruoen 24
> hour (river) race.The ability to run lean  burn  conditions is great for
> reliability as  I see it.

Do they really deliver it? Given that it has a lower unit that can't  
reverse, it wouldn't make much sense for anything but racing. And as a racer  
you get more power per cubic inch from an XR2, 2.5EFI or even a 300 ProMax.

> I have 2  2.5efi high performance engines that I am reparing, line boring

Are they any fun? I have very modified Yamaha 200 that will get an EFI  
system if it is still running when I can aford one (eg MADEFI) or find time  
to build something... Performance below 4000 RPM is not exactly stunning when  
using carbs.

> new crank, one piston 70grams to heavy +++

70 grams??? That's a lot of extra weight...

> They have analog efi with old d-jetronic peek and hold injectors.(As
> standard)

Is this the 260hp version?

> The new 2.5 efis has digital boxes ,Motorolabased.

The 280hp machines?

Regards,
John Hornkvist