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

According to the literature (through 1985):

B28E and B28F pistons are identical except for height (65.3mm overall
vs 62.8mm). Diameters do vary however (irrespective of engine series):
 "A" marked pistons go in "1" marked liners (90.975mm), "B" marked
pistons go in "2" marked liners (90.985mm), and "C" marked pistons go
in "3" marked liners (90.995mm).

Connecting rods are identical.

1980 B28F camshafts have 6.004mm max lift (stamped 7401269138 left and
7401269139 right).
1981 onwards B28F and all B28E camshafts have 5.96mm max lift (stamped
7401269615 left and 7401269616 right).

Valves and springs are identical.

Ignition distributors are indentical. Timing spec is 10 degrees BTDC
for both E and F series (at 900 rpm). Volvo distributors have a much
sharper advance curve than DeLorean by virtue of having both
centrifugal counterweights active. Ported vacuum is run to them
directly rather than full vacuum via a cutoff solenoid. 

All B27 and B28 throttle plates are the same size. B27 throttle plates
do lack deceleration valves. As you've surely noticed, B27 fuel/air
mixture units are single piece assemblies (integral throttle plates)
and B28 are two pieces (separate throttle plate assembly). There's no
place to attach a CIS microswitch on a B27 unit, nor an extra screw on
the throttle plate arm to trip one. Air sensor plates and fuel
distributor activation levers are identical.

Intake manifolds are identical. U pipes vary only in routing of PCV.
Note that one of my B28F U pipes (1989) does have a cruise control
cable bracket cast into its underside.

Series 004 CPR's start at ~12 PSI and warm up to ~51 PSI at 155
degrees F. Series 038 CPR's start at 0 PSI and warm up to ~51 PSI at
160 degrees F. Series 066 CPR's start at ~15 PSI and warm up to ~51
PSI at 110 degrees F. Series 004 has no full throttle enrichment.
Series 038 full throttle enrichment is active at all times, operated
directly by manifold vacuum drop. Series 066 full throttle enrichment
is only active below 125 degrees F (via a thermal vacuum cutoff) and
even then is only active for ~10 seconds (via an equalizing delay
valve). DeLorean lowers thermal cutoff to 104 degrees F.

All B28 fuel injectors are identical (Bosch #0437502013, Volvo
#12692745). B27 injectors open at slightly lower PSI (Bosch
#0437502005, Volvo #2691848). They are interchangeable (CO adjustment
screw compensates), but in complete sets only! (Can not mix B27 with B28).

The only part numbers I don't have are fuel distributors (ask John
Hervey). E series differ from F series by lacking Lambda influenced
lower chambers (lower chambers are there, but operate at line pressure
at all times. Are fed internally). You can accomplish the same thing
by simply unplugging the frequency valve.

As to your best course of action: Are you planning to rebuild the
engine, or simply change bolted on components? The only way to
increase compression is a rebuild with taller pistons. You can do a
lot even with 8.5:1 however. I'd recommend unplugging your frequency
valve, swapping the 004 CPR for 038 (don't forget full throttle
advance -- that's a vacuum port on the 038, not a "vent"), and
ensuring ignition vacuum advance is routed directly to the ported
vacuum barb under the throttle plates (if you've got the funny advance
diaphragm with two barbs simply use the outer one). CO can be
increased closer to 2% (European spec, albeit high compression). You
may need to remove the catalytic converter. If you've got a smog pump
(air injection pump), that can be removed too (check valve may have
rusted -- I'd recommend removing attendant plumbing and capping off
the manifold ports). If you've got EGR, it can be removed too (simply
cap the U Pipe port with a plate and gasket as DeLorean did).

Bill Robertson

>--- In dmcnews@xxxxxxxxxxxxxxx, "Rick" <rdevaux@xxxx> wrote:
> I've got a stock '80 B28F in my Volvo 262(K-Jet, Lambda/cat/freq 
> valve, de-accelerating valves on throttle plates, ignition 
> distributor with vacuum delay solenoid, stock F cams, stock F 
> pistons, 004 warm up regulator, no micro switches, same full 
> distributor as a stock Delorean).
> I also have my original B27F that has the smooth throttle plates.  
> I've also got new B28E cams and pistons, and a B28E dizzy from a UK 
> spec Volvo.
> Question:  What is the best configuration I should go with to improve 
> performance?
> My consideration:  Use B27 throttle plates, de-Lambda the engine (O2 
> sensor, cat and freq valve), use the B28E dizzy and remove the vacuum 
> delay solenoid components, B28E cams and pistons, advance timing from 
> 10 to 13 and adjust CO from 1% to 1.5-2.0%.
> I'm also trying to hook up with a B28E fuel distributor and CPR.
> When I'm looking to locate the B28E fuel distributor do I need just 
> the distributor or do I need the distributor and the air intake?  
> Which CPR should I look for, 038 or 066? Remember, no micro switches.
> After replacing all the components, what is the best way to tune for 
> best results without the Lambda system?
> I'm also considering doing some head porting.  Does anyone have any 
> pointers/tips on doing PRV heads?  I know the exhaust really needs at 
> least gasket matching and a good cleaning and polish.  What about 
> doing the intake?  Any tips on how to match the intake manifold to 
> the heads?
> I have a source to have headers made but I'm trying to get 
> information on what the best specs for the headers will be: runner 
> length, tube ID/OD and collector size.  Thanks for any and all help!  
> Rick

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