[DML] Re: PRV Performance - Set me straight please

["endotex23" <endotex23@xxxxxxxxx>]

--- In dmcnews@xxxxxxxxxxxxxxx, "content22207" <brobertson@xxxx>
wrote:
 
> Biggest flaw I see in the North American version is heat.
Irrespective of any other advantages or disadvantages, a richer fuel
mixture simply burns cooler. Domestic PRV's are hot as a firecracker.<

Not true. While a richer mixture does result is cooler exhaust stream
temps the fact is running at a best power mixture (and why would you
run at anything else if you're seeking power) results in the highest
cylinder head temps across the mixture regime. I also remind you an
engine running leaner than about 50 degrees on the lean side of peak
EGT (which occurs at stoich) runs cooler and cleaner than at any other
point where combustion is useful. 

The bottom line is running at stoich is harder on exhaust components
but results in cooler cylinder temps. This is basic combustion theory.
Anyone familar with air cooled engines also knows this.

>I once got 2nd degree burns on my fingertips touching a stock
DeLorean engine!<

Good metrology there Bill. You'd burn yourself touching any engine,
running rich or not. I suggest you get a gas anaylzer or wide band O2S
and stop using your fingers for tuning.

>My Renault block (Z7, European spec) never ran as hot as a B28F, and
my current carbureted Peugeot version was running so cool this winter
that I bumped the thermostat up to 195 degrees (versus 188 degrees F
spec).<

No doubt because you're running richer than best power. What can you
expect from something as crappy at fuel delivery as carburation? You
should've re-jeted and not fooled with the cooling system. As I said,
you're wasting fuel, making less power than you should, and polluting
more than you should. A giant step backwards. 

> All that heat can't be healthy for gaskets and seals, or even the
aluminum itself.<

Better brush on your metallurgy. For example piston aircraft engines
are air cooled and aluminum alloyed. They run at much higher power and
temps than your PRV and suffer no ill effects. I'd be willing to bet
many motorcycle mechanics would also take you to task on that comment.

>Don't forget that PRV's, especially in K Jetronic trim, are very
dependent on tight gasketing.<

Dependent in what way? If by mixture than somewhat true but what FI
engine isn't?  And what engine doesn't depend on tight gasketing in
many other ways?

>I also wonder if infamous PRV "oil problems" are exacerbated by
barbequing the stuff. Americans seem to be the only people
complaining.<

Infamous oil problems? What would those be in the B28F? And how many
Deloreans suffer from them? I'll grant you oil temps are very
important for many reasons but I've notice there is so much
misconceptions about oil in general I'll skip the subject.

> Heat is also Enemy #1 for alternators (what's the single most common
> engine accessory failure experienced by DeLorean owners...)<

Alternator failure on the D is unrelated to heat. In fact, it's
mounted in a better position than on most cars and runs relatively
cool. Measure it and see, just be sure you're not asking too much of
it electrically at the time. Btw, a blast tube does wonders for
reducing it's temp even more.

>Europeans did several things on their PRV's much better than US
> regulations allowed: Kept compression high. Gives you the same
benefits of forced induction without any of the complications. Does
require a richer mixture, though.<

Huh? what "complications" of forced induction are you referring
too? I have a turbo car (not a D) that has 80K miles on it and can
make nearly 500 HP all day long. It's never had any complications.
And it runs at stoich, it doesn't "need" a richer mixture at all. What
is *does* need is decent intercooling. Where do you come up with this
stuff?

>Didn't monkey with fuel/air ratios (engine warmed up -- key word
> "warm", not "hot").<

A particualr A/F ratio is selected for a reason. It's true richer (to
a point) produces somewhat "cooler" combustion but since it produces
more power it also produces the highest BMEP, cylinder temps and
stresses. How is that "better" other than for driver enjoyment? Any
engine that is built to provide power over any other aspect will
suffer from quicker wear, shorter life, lower fuel economy, will
require more maintenance, and in general be less reliable. But if by
"better" you meant performance than yes, I'll give you that.

>Didn't force the engine to breathe its own exhaust (EGR).<

EGR reduces power somewhat but it does so by reducing combustion
temps. Therefore it does not increase engine temps. It's sole purose
is NOX reduction. An added benefit is a widening of the detonation
margin. 

>Didn't try to burn anything where nothing was never intended to burn
(exhaust system via catalytic converter and smog pump).<

Converter operation has no bearing on engine temps. Neither does air
injection other than stealing a bit of HP to drive it. The Delorean
doesn't use either EGR or air injection. Cats? A modern honeycombed
bed cat has little to no effect on back pressure. An older pellet bed
type cat is worse but the Delo doesn't employ one. And I remind you
too much of a free flowing exhaust is a bad thing.

Everything else you state is true and if more power is to be gained on
the B28F it's simple enough to do up to a point. Tight mixture control
 and proper timing is still important however, whether at stoich or
best power. Emissions equipment is not the kiss of death for making
power. I point out again I own a car that can eat 90% of others on the
road alive and still pass the most stringent emissions standards in
the country, all while running with factory emission gear at a lambda
of 1. How does it do that? Not by using poor fuel metering, that's for
sure. 

Finally, while I'm no great fan of emission standards I accept the
very real benefits they provide to the environment. It seems you do
not. Until you and a few others accept that gobs of power can be made
and still keep the air clean you're doomed to drive clunkers. Put
another way there *is* a substitute for cubic inches...it's called
technology.


For Martin: A D with emissions equipment is speced at 1% (measured
pre-cat with the lambda loop open) because the cat needs it there. 
With no cat 2% CO is still leaner than best power, a bit higher on the
CO will get you more. If you're looking for max power than 2% is too
low but it'll still be less than your max when you get there. Do some
dyno pulls (if you can) to get it dead on but generally speaking it
should end up around 4%.








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