From: markrock_REMOVE_368878_THIS_@yahoo.com
Duke:
<You end up with ... 110 degree inlet centerline and 118 degree
exhaust centerline for 114 degrees overlap.>
Actually you don't. The Intake and Exhaust centerlines do change,
but the 114 that results is the Lobe Separation Angle. It went up
(i.e. got wider--i.e. moved the lobes apart) from the stock 106, and
thus decreased the overlap.
The overlap numbers depend on whether you are measuring at .005" lift
or at the standardized .050" lift.
The Chevy Power Manual specifications do not indicate whether they
are measured at .005" or .050" lift.
Jim Reardon and I have calculated that, assuming the Power Manual
specs are .050" measurement numbers, the overlap decreases from 64
degrees to 48 degrees.
If anybody has or can get a cam specification card for the production
camshafts, we would be most appreciative!! Paul?
Mark
[This is message #10384 by user markrock on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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Vega, Monza, Sunbird, Astre, Starfire, Skyhawk
Valve Overlap
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Valve Overlap
by h-bot » Thu Jan 23, 2003 2:29 am
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Valve Overlap
by h-bot » Thu Jan 23, 2003 4:05 am
From: cosworth0078_REMOVE_480538_THIS_@yahoo.com
Duke, you have finally shed some light, as to "why" in a certain
aspect, the Cosworth Vega engine is different from every other
performance car I have ever driven. The Cosworth always feels like
it has an excessively heavy flywheel, keeping the revs up when you
shift and seeming not as quick to rev when the throttle is "blipped"
under no load conditions. Your statement that this is caused by the
unusual amount of valve overlap makes perfectly good sense to me. I
was always aware that the engine had a lot of valve overlap for
emissions, I guess, but I never connected the two until now. I
always thought it was a "too heavy" flywheel, as was told to me once
by Hutton. Let's all get on the ball and get a cam indexing program
going. This would be the development work that GM should have done
on this engine. I am all for 6 degrees advanced intake cam and 6
degrees retarded exhaust cam, or do I have it wrong?
-Clark
[This is message #10375 by user cosworth0078 on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
Duke, you have finally shed some light, as to "why" in a certain
aspect, the Cosworth Vega engine is different from every other
performance car I have ever driven. The Cosworth always feels like
it has an excessively heavy flywheel, keeping the revs up when you
shift and seeming not as quick to rev when the throttle is "blipped"
under no load conditions. Your statement that this is caused by the
unusual amount of valve overlap makes perfectly good sense to me. I
was always aware that the engine had a lot of valve overlap for
emissions, I guess, but I never connected the two until now. I
always thought it was a "too heavy" flywheel, as was told to me once
by Hutton. Let's all get on the ball and get a cam indexing program
going. This would be the development work that GM should have done
on this engine. I am all for 6 degrees advanced intake cam and 6
degrees retarded exhaust cam, or do I have it wrong?
-Clark
[This is message #10375 by user cosworth0078 on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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Valve Overlap
by h-bot » Thu Jan 23, 2003 4:19 am
From: markrock_REMOVE_301673_THIS_@yahoo.com
Clark:
The cam re-indexing program is already a reality! Roy Linenberger
and I are offering them for sale, either outright or on an exchange
basis. Sprockets are precision machined per Duke's recommendations,
with the Exhaust advanced 8 crank degrees and the intake retarded 8
crank degrees.
Check out our information sheet at www.cosworthparts.com.
If you would like additional photos, or have any questions, send me
an e-mail at <a href="/group/cosworthvegas/post?protectID=029166091163127190025067203043176223041146031189251049173150166091061">markrock@c...</a>
Mark
[This is message #10376 by user markrock on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
Clark:
The cam re-indexing program is already a reality! Roy Linenberger
and I are offering them for sale, either outright or on an exchange
basis. Sprockets are precision machined per Duke's recommendations,
with the Exhaust advanced 8 crank degrees and the intake retarded 8
crank degrees.
Check out our information sheet at www.cosworthparts.com.
If you would like additional photos, or have any questions, send me
an e-mail at <a href="/group/cosworthvegas/post?protectID=029166091163127190025067203043176223041146031189251049173150166091061">markrock@c...</a>
Mark
[This is message #10376 by user markrock on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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Valve Overlap
by h-bot » Thu Jan 23, 2003 4:45 am
From: doctorduke_REMOVE_937432_THIS_@yahoo.com
No, it's retard the inlet cam 8 crankshaft degrees and advance the
exhaust the same amount. You end up with the same cam phasing as the
L-79 327/350 HP Corvette small block - 110 degree inlet centerline and
118 degree exhaust centerline for 114 degrees overlap. The exhaust
cam actually has too much duration and after reindexing the point it
opens should be cut back about 16 degrees with the same closing point,
but let's save that for next year. This will yield centerlines and
overlap of 110. The CV doesn't need as much exhaust duration as inlet
because of it has a lot of exhaust port capacity relative to the inlet
port. The SB is just the opposite. The exhaust port is restictive
relative to the inlet port, so you need more exhaust duration and an
earlier opening exhaust valve.
The flywheel is not too heavy. It only weighs 18 pounds. It's all
the exhaust gas dilution, particularly at low revs that causes the
sluggish response and poor low speed torque. Because of the emissions
test failures in '74 GM really overkilled the '75 emissions, and
that's why they indexed the cams as they did - to lower NOX. I figure
they started out with the L-79 phasing, then reindexed them for more
overlap.
I known that the OEM cam indexing had too much overlap for a long
time, but I couldn't quantify it. Once I started working with engine
simulation programs the amount of reindexing and the expected results
became apparent, and the actual improvement in engine performance
exceeded my expectations by a lot!!!
Duke
[This is message #10377 by user doctorduke on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
No, it's retard the inlet cam 8 crankshaft degrees and advance the
exhaust the same amount. You end up with the same cam phasing as the
L-79 327/350 HP Corvette small block - 110 degree inlet centerline and
118 degree exhaust centerline for 114 degrees overlap. The exhaust
cam actually has too much duration and after reindexing the point it
opens should be cut back about 16 degrees with the same closing point,
but let's save that for next year. This will yield centerlines and
overlap of 110. The CV doesn't need as much exhaust duration as inlet
because of it has a lot of exhaust port capacity relative to the inlet
port. The SB is just the opposite. The exhaust port is restictive
relative to the inlet port, so you need more exhaust duration and an
earlier opening exhaust valve.
The flywheel is not too heavy. It only weighs 18 pounds. It's all
the exhaust gas dilution, particularly at low revs that causes the
sluggish response and poor low speed torque. Because of the emissions
test failures in '74 GM really overkilled the '75 emissions, and
that's why they indexed the cams as they did - to lower NOX. I figure
they started out with the L-79 phasing, then reindexed them for more
overlap.
I known that the OEM cam indexing had too much overlap for a long
time, but I couldn't quantify it. Once I started working with engine
simulation programs the amount of reindexing and the expected results
became apparent, and the actual improvement in engine performance
exceeded my expectations by a lot!!!
Duke
[This is message #10377 by user doctorduke on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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Valve Overlap
by h-bot » Thu Jan 23, 2003 6:30 am
From: doctorduke_REMOVE_869269_THIS_@yahoo.com
Yes, I meant to say LCA.
The Power manual specs are "seat to seat" duration at .014" checking
clearance. From my measurements, the ramps are .016" high off the
base circle, so the Power Manual duration number include a little
ramp. If you set the cold clearance at .014" the running clearance
with the engine hot will be .016", and the actual seat to seat
duration is 268 degrees. At .050" total lift off the base circle,
which includes the ramps I measured the duration at 204 degrees. The
ramp velocity is approximately .0005" per degree of crank rotation,
and as I recall, from my measurements the total duration including the
ramps is 348 degrees.
You didn't answer my question. Have you tested a set of your modified
sprockets on a car???
Duke
[This is message #10388 by user doctorduke on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
Yes, I meant to say LCA.
The Power manual specs are "seat to seat" duration at .014" checking
clearance. From my measurements, the ramps are .016" high off the
base circle, so the Power Manual duration number include a little
ramp. If you set the cold clearance at .014" the running clearance
with the engine hot will be .016", and the actual seat to seat
duration is 268 degrees. At .050" total lift off the base circle,
which includes the ramps I measured the duration at 204 degrees. The
ramp velocity is approximately .0005" per degree of crank rotation,
and as I recall, from my measurements the total duration including the
ramps is 348 degrees.
You didn't answer my question. Have you tested a set of your modified
sprockets on a car???
Duke
[This is message #10388 by user doctorduke on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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Valve Overlap
by h-bot » Thu Jan 23, 2003 10:44 am
From: markrock_REMOVE_187203_THIS_@yahoo.com
> You didn't answer my question. Have you tested a set of your
modified sprockets on a car???<
Duke: I might yank your chain on occasion, but I never ignore you.
See message #10383. That's where I answered your question, with the
very first word!
OBTW, got my radiator back today, along with the old core. The old
core was too bad to fix. The recore cost me $128 plus tax, and I
received a two year warranty. It looks to be an exact duplicate of
the original core. The shop I went to had no problem getting a new
core.
I asked for and received back the original core, and I'll take a
couple of pictures this weekend. That original core was boiled out,
but the deposits mostly remained, and even if it had not been
leaking, it would have needed rodded out in order to be serviceable.
Mark
[This is message #10390 by user markrock on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
> You didn't answer my question. Have you tested a set of your
modified sprockets on a car???<
Duke: I might yank your chain on occasion, but I never ignore you.
See message #10383. That's where I answered your question, with the
very first word!
OBTW, got my radiator back today, along with the old core. The old
core was too bad to fix. The recore cost me $128 plus tax, and I
received a two year warranty. It looks to be an exact duplicate of
the original core. The shop I went to had no problem getting a new
core.
I asked for and received back the original core, and I'll take a
couple of pictures this weekend. That original core was boiled out,
but the deposits mostly remained, and even if it had not been
leaking, it would have needed rodded out in order to be serviceable.
Mark
[This is message #10390 by user markrock on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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Valve Overlap
by h-bot » Fri Jan 24, 2003 1:53 pm
From: doctorduke_REMOVE_602487_THIS_@yahoo.com
I must have missed that message.
Mine idles at 900/18" dead smooth. My initial timing is set at 15 and
I also have 10 degrees of vacuum advance for a total of 25 degrees
idle advance. Without the vacuum advance it probably won't pull as
much vacuum and the EGT will be higher. As I mentioned befor, with my
setup the top of the header pipes read about 500F with an IR gun.
It would probably idle lower, but I think I'm at about the limit of
how much I can close down the two big throttle bodies with the idle
speed adjustment, plus if I go much lower the alternator might not
charge as the CV has a lower numerical alternator drive ratio
than a 140 because of the high OEM idle speed and redline.
Right now I'm configured for emission testing and hope to have it
completed next week. All the original emission equipment is in place
except the internal PAIR tubes. I've never installed them for
emission testing in the past. My only deviation from OEM spec is
timing, which I am going to retard to 8 degrees from the 12 specified.
The lower timing will decrease peak flame temperature in the
cylinder, which should lower the NOx production. The actual test at
15 and 25 MPH will only be about 2000-2200 revs, so with the OEM
centrifugal advance starting at 2000 there won't be much more than
just the basic timing.
As I've said before, my concern with the reindexed cams is that the
NOx will go up because of less exhaust gas residual with the lower
overlap, but I've got a lot of margin. In my last test two years ago
NOx was only about 20 percent of the limit. If it fails NOx I'll
richen the mixture by biasing the MAP sensor as richer mixtures reduce
NOx and I've got lots of margin on HC and CO.
Duke
[This is message #10391 by user doctorduke on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
I must have missed that message.
Mine idles at 900/18" dead smooth. My initial timing is set at 15 and
I also have 10 degrees of vacuum advance for a total of 25 degrees
idle advance. Without the vacuum advance it probably won't pull as
much vacuum and the EGT will be higher. As I mentioned befor, with my
setup the top of the header pipes read about 500F with an IR gun.
It would probably idle lower, but I think I'm at about the limit of
how much I can close down the two big throttle bodies with the idle
speed adjustment, plus if I go much lower the alternator might not
charge as the CV has a lower numerical alternator drive ratio
than a 140 because of the high OEM idle speed and redline.
Right now I'm configured for emission testing and hope to have it
completed next week. All the original emission equipment is in place
except the internal PAIR tubes. I've never installed them for
emission testing in the past. My only deviation from OEM spec is
timing, which I am going to retard to 8 degrees from the 12 specified.
The lower timing will decrease peak flame temperature in the
cylinder, which should lower the NOx production. The actual test at
15 and 25 MPH will only be about 2000-2200 revs, so with the OEM
centrifugal advance starting at 2000 there won't be much more than
just the basic timing.
As I've said before, my concern with the reindexed cams is that the
NOx will go up because of less exhaust gas residual with the lower
overlap, but I've got a lot of margin. In my last test two years ago
NOx was only about 20 percent of the limit. If it fails NOx I'll
richen the mixture by biasing the MAP sensor as richer mixtures reduce
NOx and I've got lots of margin on HC and CO.
Duke
[This is message #10391 by user doctorduke on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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