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

["content22207" <brobertson@xxxxxxxxxxxx>]

(Comments apply to DeLorean PRV as well...)

If you have an opportunity to increase compression, go for it.
Provides the same benefits as forced induction without all the
complications. PRV's can obviously handle 9.5:1 no problem (in the
B280 redesign, compression was even increased to 10:1). Just make sure
your pistons match the liners.

Also go for the highest cam lift possible. Will pull maximum mixture
into the cylinders.

Make sure your engine DOES have PCV connected. Not only ensures that
damaging internal pressures do not build up, but goes a long way
towards avoiding sludge under the valve covers. If you've got the
breather hose connected but not the calibrated nipple, you are
probably sucking oil backwards into the intake. 

I believe the dual barb spark advance is Volvo's attempt to avoid over
advancing ignition (what is base time on your EPA sticker?). Ford did
the same thing in the 1970's when base time was advanced all the way
to 16 degrees. Under certain conditions vacuum is shot to both barbs,
disabling it. That's the purpose of the solenoid your inner hose is
routed through. E series engines simply run one hose from the ported
barb under the throttle plates straight to spark advance. You can do
the same using the outer barb. Be sure to then time your ignition at
10 degrees BTDC (900 RPM). Vacuum advance is superceded by centrifugal
advance at higher RPM's anyway.

All fuel distributors have lower chambers. Non-Lambda models feed them
internally at full line pressure. Lambda models feed them externally
at moderated line pressure. By simply unplugging the frequency valve
you can accomplish the same thing. John Hervey sells barbed banjo
fittings and high pressure hose if you want to bypass it altogether
(flexible hoses do not affect performance between CI and the tank). My
previous Renault installation didn't even use banjo fittings in/out of
the fuel distributor, but had inline barbed fittings with whatever
that thread pitch is (x1 I believe).

Series 018 CPR is not far removed from Series 038: starts at ~6 PSI
and warms up to ~51 PSI at 155 degrees. Also has the same full
throttle enrichment mechanism (do NOT try to plumb it like a Series
066. Simply run a single hose straight to full manifold vacuum). Was
used on B27E through 1979, and thus would be a perfectly suitable
substitute for the later Series 038.

I've never had an engine with deceleration valves, and thus can not
comment on their merit. Ostensibly Douvrin introduced them for a
reason. Of course even the greatest innovations sometimes succumb to
age or mileage. I'm guessing their purpose is to smooth out some of
the undesirable characterics endemic to PRV's (that's Volvo's stated
purpose of the separate B28 throttle plate assembly). I seem to
remember the transition between idle and throttle on my Renault Z7
(B27) block being less than seamless (manual idle, not CIS).

Be aware that running your engine richer can negatively impact a
catalytic converter. Overall engine temp will be reduced (you may want
to bump the thermostat closer to 200 degrees). Exhaust will be much
cooler too, especially if you jetison the converter, which can
accelerate rust. Needless to say emissions testing will be out of the
question. 

And don't neglect your ignition. I'm a big fan of high voltage coils
and wider spark plug gaps. Perhaps that's the only way I'm able to
combust all this fuel...

Bill Robertson
#5939

>--- In dmcnews@xxxxxxxxxxxxxxx, "Rick DeVaux" <rdevaux@xxxx> wrote:
> 
> Bill, Thanks for the great reply.  Since I have new cams and pistons I'm
> planning on a rebuild, but that will wait for at least a year. 
Engine is
> fun to drive as is (no smog pump / EGR / PCV same as a Delorean) but
I'll
> likely remove the Lambda system once I find a 038 CPR.  A few
questions for
> you:
> My current distributor vacuum advance does have the two barbs.  Do I
just
> cap off the "inner" barb?  Is there any difference between the E and
F dizzy
> curves?
>  What is the "best" way to remove the Lambda system?  What needs to be
> capped off and what needs to be completely removed?  
> What's the best way to configure the fuel distributor sans freq valve?
> Do you recommend removing the deceleration valves and filling in
their holes
> or replacing the throttle plates with the ones from the B27 or
leaving as
> is?
> Once the Lambda is removed is tuning basically setting desired
timing and
> CO?
> 
> Since I've got the B27 to play with I was considering looking at head
> porting possibilities.  Any tips, pointers or warnings?  Thanks
again for
> the reply, Rick








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