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425 Timing

Started by waterzap, April 03, 2015, 09:32:21 AM

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waterzap

So I was playing around with the timing on my 78 the other day.
The book specifies 18* @ 1400 rpm. I spoke to the guys at MTS once and they said there is too much timing on these 425s
So I decided to play around with the vacuum gauge a bit and see whats up. I have a timing light with advance so once it went off the indicator lines I could still follow it. I bumped it up to 20*, then 24*, now running at 28*. The car runs so, so much better. When I floor it, the engine just spins up.  I think will take it down to 26*, almost feel it was slightly more optimal there.

The vacuum advance works well, and I lubed and cleaned the weights. So all works well. Im running regular ethanol free gasoline.
I read somewhere that todays fuels burn slower than the old ones. Whatever the reason, it just runs much much better.
Those 425s really aren’t the boat anchors they are made out to be
Leesburg, AL

"Cadillac Kid" Greg Surfas 15364

With your specs I am ASSUMING we are talking about an FI car. If so, with the vacuum advance disconnected and the line plugged, 18 degrees at 1400 rpm is correct.  Just guessing, but that would put it somewhere around 12 degrees at idle.  You might try and see what it falls back to at say 00 rpm.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Scot Minesinger

BTW, first things first the 425 engine is wonderful, by no means a boat anchor.

I looked in the book too and it did read just as you wrote 18' @ 1,400 rpm, maybe I was looking in FI section, but thought I got that right.  It seemed so high had to quickly check.  Might have checked more thoroughly if actually was working on a 1978 (never have), newest Caddy I worked on in years is a 76.

Anyway a word about over timed engines in my experience is they do seem to start, idle and operate at low speed much better.  However, if really setting the timing ahead was such a huge improvement the factory would have done it.  I do not do it though.  Not in my experience but have read that you will ruin the engine running it over timed for an extended period.  Highway speeds will result in less efficient operation, which means the car will run hotter and get worse gas mileage, in addition to potentially destructive operation.

Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

waterzap

I was reading up on this. Seems the later 425 engines had distributors that looked like the others, but was very retarded?
So once again, who knows what distributor is in that car. I know the book has tables on what the advance should be at each stage of rpm’s Might have a look at that to see if its still stock
Leesburg, AL

"Cadillac Kid" Greg Surfas 15364

FWIW an HEI centrifugal advance at 1400 RPM will add about 8 degrees to the timing.  Subtract 8 from 14 leaves you with an actual initial of just about (+/- 2 degrees) 6 degrees.  Since you hook up the vacuum advance, that gets added.  They developed the timing curve to provide maximum performance within the given engines parameters.  In spite of many urban myths, advancing the timing does not necessarily improve performance across the engine speed range.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

bcroe

The first problem for the 425 is the factory exhaust (starting with a terribly restrictive cat)
holds the engine back.  The next thing is the HEI advance curve.  There are many different
curves possible.  In the case of Olds the 350 has a much better curve than the 403 which
is just a bigger bore version.  Put a 350 HEI in your 403 and you will notice the difference. 
This was done to help the bigger engine meet emissions.  I don't have the numbers, but
there are mechanical restrictions on advance built in. 

Advancing the 425 HEI may help in one range, hurt in another.  Maybe someone
should develop a universal curve for use with dual exhausts.  I did that with an
electronically programmed system.  Bruce Roe

"Cadillac Kid" Greg Surfas 15364

Bruce,
You should know, with the FI being triggered by the distributor shaft wouldn't changing the ignition curve from factory specs. possibly have detrimental effects on the fuel delivery/ignition sequence?
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

TJ Hopland

I don't think it would have any noticeable effect on fuel.   The fuel delivery on that system was called batch fire and in this case there were 2 batches of 4 cylinders each so its not like you were getting the pulses perfectly timed with the valve opening anyway.   4 injectors fired then the other 4.   They were spaced out so at least they were not 180 out of time.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

"Cadillac Kid" Greg Surfas 15364

Think about it TJ, the "first" cylinder to fire on the alternating "batches" or even the last "could" be sensitive.  That is why I posed the question to Bruce.  If there is ANYONE that knows Cadillac FI I would bet on it being him.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

bcroe

Quote from: "Cadillac Kid"  Greg Surfas 15364Think about it TJ, the "first" cylinder
to fire on the alternating "batches" or even the last "could" be sensitive.  That is why I
posed the question to Bruce.  If there is ANYONE that knows Cadillac FI I would bet on
it being him.      Greg Surfas     

I am entirely in agreement with the explanation by TJH on this.  I'm a lot better at fixing
engines than designing them.  But the Cad engineers spent a lot of effort on this. 

I have a 70s HEI injection chart on my PHOTOBUCKET, first album.  As I was able to deduce,
the injection pulse starts by firing at the intake valve when it is closed.  At low rpm and min
throttle (narrow injection pulse), the injector will finish before the valve opens on every
cylinder, the time will vary.  At high rpm and heavy throttle, injection timing becomes not
important.  Emissions requirements have pushed us back toward sequential injection with
much more precise injection for each cylinder.  In fact I have tried sequential injection on
the stock injectors in my 79 Eldo, and haven't so far noticed any difference. 

So we are comparing a 3/4 crank revolution variation (batch fire for 4 cylinders) against
less than a dozen degrees variation to optimize the always critical spark timing.  I just
don't  see that it matters here. 

  http://s93.photobucket.com/albums/L71/bcroe/

  click on an Album
  click on a picture to enlarge + description

Bruce Roe

R Schroeder

These are the spec's from my Cadillac repair manual.
There are many different types of distributors in the 78. Mine is the second one down. Number 1103389.
It runs the greatest advance of any of them. My car is timed at 22degrees @ 1600 rpms. My car idles like a rock, and pulls 22 degrees of vacuum , steady , with vacuum advance connected.
Book says to plug vacuum advance , and the vacuum line to the EGR valve, to time the car.  Now, I don't run an EGR valve on my car. I have removed it, and made up a plate to cover the mounting area. I also don't run a CAT on the car.
Took pictures of what my book shows . Also one of my distributor, with the number on the side. I just replaced the gasket on the distributor the other day.
Don't know if this info matches what your book shows.
Roy

waterzap

#11
How did you know to do 22@1600?
I also didn't plug my egr. I'll do that next time I adjust the timing. The 77 book says 18*@1400.
The 78 book says to adjust the timing according to the emissions label. That's not on my engine anymore. I might not have been far off then thinking the car runs better @26 than @18. I was following the 77 book instructions. The 78 is just a supplement, not a whole book
Leesburg, AL

R Schroeder

That's what is on my label. 22@1600
Roy

waterzap

#13
Yeah. Mine doesn't have the label anymore.
Wish could buy one somewhere. All the ones I can find is not for the Eldorado.  But will set mine to 22@1600 too
Leesburg, AL

Jon S

If it is advanced too far (not knowing ig the harmonic damper has shifted), you will find it has tons more pep at low RPMs, but will probably stall if gunned as it will be running too lean.
Jon

1958 Cadillac Sedan De Ville
1973 Lincoln Continental Coupe
1981 Corvette
2004 Mustang GT

"Cadillac Kid" Greg Surfas 15364

Gentlemen,
Please note two things.
1. The charts above indicate distributo RPM which is of course 1/2 of engine speed.
2. The distributor above is not for FI
I do not see an appreciable advantage to varying from factory specs.  18 (crankshaft) degrees at 1400 (engine) rpm.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

R Schroeder

Greg is correct. My car is not FI.
But , the data plate on the front of the fan shroud, is RPM's for the motor, while setting the timing.
Is Waldo's a FI car ? I thought FI didn't come out until 79. In the DeVille's it was 79 anyway.
This is a factory setting ,and she runs beautiful in all ranges.
Roy

waterzap

Mine is carb too. Just put it at 22. Runs very very nice now.
Leesburg, AL

bcroe

Maybe MTS will tell us the best curve/parts to use.  I'll ramble some
here on the subject. 

The 70s analog ECU fuel injection was available on some 1975 500s. 
It was optional on the big blocks thru 79 and standard on the Olds 350
engines used in 76-79 Seville, 79 Eldo and a few 1980 E cars to meet
CA emissions (it did better than its replacement).  My feeling is the EFI
cars were somewhat more responsive, but the difference was small. 

My experience with spark tuning is limited, some described here.  It was
with Olds which had a lot more options to play with, but likely the lessons
would apply to the similar sized Cad engines of the same years.  And
yea, if you have a harmonic damper, don't be misled by an outer ring
that has slipped and moved the mark.  I eliminated this issue by using
FluiDampers on every engine. 

The 78 Toro 403 used electronic spark timing with temp input,  I swapped
one of these including the electronics for the diesel in a Delta 88 and
it did 0-60 in 7.5 sec.  Then I tried an Olds 350 HEI, 7.5 sec.  Why
carry all that complexity of super rare parts for no performance gain,
I dumped the computer? 

Later I got a Delta 88 with 403, 0-60 in high 8s.   Put in a 350 HEI
and noticeably improved, haven't got the duals on for the final
measurement yet.  So the answer to the above was, the usual 403
spark was detuned for emissions, but on the big Toro they used a
3D + temp spark map computer to both meet emissions and get
performance.  I only need to get performance. 

Examination of the 350 and 403 HEIs showed differences in the
advance mechanism, not sure the 403 could be upgraded without
changing the shaft assembly.  There isn't a 350 Cad mechanical
HEI to swap in, but the curves bear examination.  Its possible to
plot out the curves using the engine.  Remember there are at least
the rpm and manifold vacuum inputs, optimum is a 3d curved
surface.  The HEI tries to emulate that with a pair of 2D curves. 
My fear is just changing the HEI position may improve things one
place on the curve, and hurt them at another.  Hard to optimize
without electronics.  I have a car I'd to run a lot of advance on
most of the time on the crap unleaded.  When I wanted WOT,
I'd first use my JACOBS booster to retard the spark with a knob. 

Had a big 20 hp garden tractor with fixed spark timing, I didn't like the
way it ran at all.  I put on a crank triggered electronic ignition with
3D spark map.  With very little tuning effort, the engine performance
was absolutely transformed for torque, idle, and fuel economy. 

Bruce Roe