[Diy_efi] RE: Diy_efi digest, Vol 1 #408 - 13 msgs

Sun Dec 15 22:23:09 GMT 2002

Message: 11
Date: Sun, 15 Dec 2002 08:38:51 -0800 (PST)
From: bob limo <fatbillybob at yahoo.com>
To: diy_efi at diy-efi.org
Subject: [Diy_efi] re: Newbie? refined now a Nitrous ?
Reply-To: diy_efi at diy-efi.org

Thanks all who responed.  In general I'm trying to be
lazy with the Nitrous.  There is a huge differnece
between running an engine and all the parameters that
have to be correct VS. dumping extra nitrous and fuel
for 10 second blasts.  With Nitrous the key is to add
enough fuel so you don't have a lean burn.  I
understand how EFI dry manifolds can flow air evenly.
The real question is can a dry maifold flow a wet
mixture well enough like old car car manifolds?  It is
way easier to inject extra fuel and nitrous in a dry
manifold than it is to do the extra fuel injector
stacking on OEM injectors.  Besides, I question
whether the stacked injector method will harm the
delievery of the OEM injector for the other 99.9% of
daily driving.  I don't think that adding 8 things to
upset the flow stream is unobtrusive as one injector
further upstream.  There are methods as one poster
presented that increase fuel pressure that in thory
keeps the duty cycles the same.  This may be true or
is it?  Don't these modern systems sence with o2
sensors etc... some feedback and the ECU's will lower
the duty cycle because it knows there is more fuel
going in?  I think there is a way that OEM full engine
management systems like Motronics will sence the
relationship between injector time and fuel pressure
to keep the volume the same right?  I just don't know
enough about that.  So if dry manifolds can flow a wet
mixture well enough then the problem is easy to solve.

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Message: 12
Date: Sun, 15 Dec 2002 09:26:18 -0800
From: Brian Dessent <brian at dessent.net>
Organization: My own little world...
To: diy_efi at diy-efi.org
Subject: Re: [Diy_efi] re: Newbie? refined now a Nitrous ?
Reply-To: diy_efi at diy-efi.org

bob limo wrote:

> sensors etc... some feedback and the ECU's will lower
> the duty cycle because it knows there is more fuel
> going in?  I think there is a way that OEM full engine
> management systems like Motronics will sence the
> relationship between injector time and fuel pressure
> to keep the volume the same right?  I just don't know

Closed loop feedback is only used for idle, cruise, and part-throttle
acceleration.  In other words, you will be in open loop for those times
when you enable the nitrous, and the ECU will have no idea what the
actual mixture is.  Think about it, hard acceleration requires an AFR
that's more rich than stoich -- probably in the 12 - 13.5 range -- and
the stock narrowband O2 sensors can only really tell you if you're close
to 14.7 or not.

Brian

Not quite true, Brian. While some systems act this way, most proper high end
systems monitor A/F ratio via a Lambda sensor right through the RPM range.
Bosch are especially fond of this idea as are most Motorsport systems as it
gives a rapid and accurate picture of mixture formation that the ECU can act
on.
Narrow band or two step lambda's are actually limited by how lean they can
read. Again, the Bosch production narrow bands have a range from 0.68 to
1.35 Lambda (about 10:1 to 20:1) whereas the wideband operate from 0.7 to
infinity. (ref; Bosch Motorsport catalogue)
Some engine management companies have an argument against closed loop
control as an ignition misfire can cause a lean out as the lambda sends an
over rich signal to the ECU which then counters by leaning out the mixture.
My answer to these people is they do not have a very sophisticated control
loop as the ones that work with closed loop use the lambda signal in a
filtered manner which prevents rogue data like this presenting a problem.
(e.g. Bosch Motronic EFI Technologies, MoTeC all have a filter algorithm for
the lambda signal).
Engine management systems use injector time as THE way of metering fuel flow
in relation to airflow. The fuel pressure is and should remain as constant
as possible. This relates more to the injector itself. Bosch injectors work
best at 55-60psi for instance. Not many injectors can work accurately above
70-75psi. About the only ones I have ever seen were TAG injectors which
could run at up to 120psi but the price tag was the size of the national
debt so we'll just ignore that idea and move on.
The use of fuel pressure regulators to up the fuel delivery is likewise not
quite right. Especially when the pressure starts to spike over 70psi. A word
of warning here, not all adjustable fuel pressure regs work! Especially when
you start trying to attain higher pressures. While some may seem to hold a
nice steady pressure in the workshop, the cheap ones while spike out in
cases where the throttle is shut off at moderate to high RPM, causing the
injectors to leak and an overrich condition on deceleration which effects
throttle response next time you get on the gas. The really cheap ones will
spike the pressure  at idle!! I have seen this condition before where the
pressure could fluctuate between 45 and 90psi while stationary in the
workshop. The problem is caused by the regulators inability to handle the
volume of fuel. If your engine is getting close to the flow rating of the
regulator then it won't be able to regulate properly as the flow overcomes
the size of the control valve in the regulator. Another note of caution,
just because it is a name brand doesn't mean it's right. For anyone
considering the purchase of an adjustable reg. There is, for instance, a
Bosch one which is sold by numerous "experts" which only flows 10L/HR!
As with most things, the real ones are rarely cheap although Aeromotive make
a great range of custom regs that aren't too pricey as does EFI Technology.
Bosch do have some great ones but the price will scare you. These conversion
kits you find that bolt on top of your existing one are not worth the cr**
they are made from.
N.B. Most of what I have written here either comes form the Bosch Automotive
handbook Ed.4, the Bosch Yellow Jacket on Petrol Fuel Injection or years of
hard won experience in tuning race and street engines with some of the most
complex engine management/data logging systems in the world. I thought I'd
put that in after reading errors that could have a perfectly natural
explanation posts. :)

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