Cams - Intake vs. Exhaust

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Cams - Intake vs. Exhaust

Postby h-bot » Thu Feb 06, 2003 11:37 am

From: cossie_REMOVE_428223_THIS_@yahoo.com


I'm thinking of cars too much today, when I should be working.
Does anyone know if the intake & exhaust cams are different profiles?
Just thinking that, with such good exhaust ports, it might not be necessary
to have slightly more duration on the exhaust lobes, as is popular with
many other engines.
Thanks,
Mike Chardon, OH




[This is message #10513 by user cossie on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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Cams - Intake vs. Exhaust

Postby h-bot » Fri Feb 07, 2003 2:59 am

From: shark93726_REMOVE_225567_THIS_@yahoo.com

You are right. 20 years ago, when I was building my engine for
autocrossing, the builder talked me into using the stock exhaust cam
with a 3/4 track intake cam, (higher lift and longer duration) and
that engine made LOTS of Horsepower at the top end, without losing
too much torque at low RPM. The same principal could be used to make
a very good combination for street, by regrinding the exhaust cam to
have shorter duration.

The new re-indexed cams with less overlap that Duke designed and Mark
is making, make a real improvement though, so I don't know whether
most people would want to spend more money and work for the little
gain available from a re-ground cam.

Gerald Storvik


--- In <a href="/group/cosworthvegas/post?protectID=219233066105193209050199029077192253163098100009128121188190230091025019053061151110147">cosworthvegas@yahoogroups.com</a>, Mike Vee <<a href="/group/cosworthvegas/post?protectID=219233066112082198015038190036129">cossie@e...</a>> wrote:
>
> I'm thinking of cars too much today, when I should be working.
> Does anyone know if the intake & exhaust cams are different
profiles?
> Just thinking that, with such good exhaust ports, it might not be
necessary
> to have slightly more duration on the exhaust lobes, as is popular
with
> many other engines.
> Thanks,
> Mike Chardon, OH




[This is message #10517 by user shark93726 on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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Cams - Intake vs. Exhaust

Postby h-bot » Fri Feb 07, 2003 3:44 am

From: doctorduke_REMOVE_488193_THIS_@yahoo.com

The inlet and exhaust lobes on the production cams appear to be
identical. Because the CV exhaust port flows about 90 percent of the
inlet port, it can use a shorter exhaust cam - just the opposite of a
SBC that needs more exhaust duration because the exhaust port only
flows about 65 percent of the inlet.

As a rule, exhaust port flow of about 75 percent of the inlet is
"ideal" and would call for equal duration.

The CV with reindexed cams would benefit from a delayed exhaust
opening. Simulations suggest that delaying the opening 16 degrees
adds about two to three percent more torque at 2000 with a zero to one
percent loss of top end power, so the improvement is marginal for the
cost.

With the exception of a little too early opening of the exhaust valve,
the reindexed production cams provide optimum torque bandwidth for a
street high performance engine - more low end torque and more top end
power with much improved low end driveabililty and a butter smooth 900
RPM idle. You can also expect in the range of 5 to 10 percent less
fuel consumption for a range of normal driving conditions. The best
increase in fuel economy is in city driving because of the higher
operating efficiency in low speed driving without all the exhaust gas
residual from the excessive overlap.

Duke




[This is message #10519 by user doctorduke on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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Cams - Intake vs. Exhaust

Postby h-bot » Fri Feb 07, 2003 5:22 am

From: doctorduke_REMOVE_795945_THIS_@yahoo.com

I ran some more simulations on both DD2000 and Engine Analyser with
the reindexed cams and delaying the exhaust valve opening 16 degrees
improves low end torque by 3 to 5 percent with no more than about a
one percent loss of peak power. This is a good tradeoff as the
biggest problem with the CV engine is lack of low end torque. A peak
power increase of 20-30 HP is available via improving the exhaust
system and 5-7 at the top end is available by replacing the engine
driven fan with an electric fan. The improvement in low end torque
with the delayed exhaust valve opening increased as exhaust back
pressure is reduced.

If one were to regrind the exhaust cam to 252 degrees top of ramp to
top of ramp from the OEM 268 degrees and install it with the OEM
sprocket you end up with the same exhaust closing point as with the
reindexed cams and the opening is delayed 16 degrees, so rather than
install both modified sprockets, you just modify the inlet sprocket
and install the OEM exhaust sprocket with the cut down exhaust cam.

If anyone wants to experiement with regrinding the exhaust cam, this
is where you should start.

Duke




[This is message #10522 by user doctorduke on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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Cams - Intake vs. Exhaust

Postby h-bot » Sat Mar 08, 2003 2:12 am

From: img width=12 height=12 border=0 src="http://opi.yahoo.com/online?u=gentec2000&m=g&t=0" alt=""_REMOVE_850300_THIS_@yahoo.com

Gerald (or Duke),

Did you run the cams "straight up" or did you reindex either of the
cams? If you did reindex the cams what did they get reindexed to? I'm
thinking of doing the same thing (short track intake with the stock
exhaust cam) with my car (the supercharged Cosworth) but before I go
through all that work, I wanted to be fairly sure the cams would work
with each other OK. I'm making up a set of adjustable cam gears so
reindexing the cams won't be a problem. Do you happen to know what
kind of power you were making this setup?

Todd
2384


--- In <a href="/group/cosworthvegas/post?protectID=219233066105193209050199029077192253163098100009128121188190230091025019053061151110147">cosworthvegas@yahoogroups.com</a>, shark93726 <<a href="/group/cosworthvegas/post?protectID=091233212180056219138097203245129208071">no_reply@y...</a>> wrote:
> You are right. 20 years ago, when I was building my engine for
> autocrossing, the builder talked me into using the stock exhaust cam
> with a 3/4 track intake cam, (higher lift and longer duration) and
> that engine made LOTS of Horsepower at the top end, without losing
> too much torque at low RPM. The same principal could be used to make
> a very good combination for street, by regrinding the exhaust cam to
> have shorter duration.
>
> The new re-indexed cams with less overlap that Duke designed and Mark
> is making, make a real improvement though, so I don't know whether
> most people would want to spend more money and work for the little
> gain available from a re-ground cam.
>
> Gerald Storvik
>
>
> --- In <a href="/group/cosworthvegas/post?protectID=219233066105193209050199029077192253163098100009128121188190230091025019053061151110147">cosworthvegas@yahoogroups.com</a>, Mike Vee <<a href="/group/cosworthvegas/post?protectID=219233066112082198015038190036129">cossie@e...</a>> wrote:
> >
> > I'm thinking of cars too much today, when I should be working.
> > Does anyone know if the intake & exhaust cams are different
> profiles?
> > Just thinking that, with such good exhaust ports, it might not be
> necessary
> > to have slightly more duration on the exhaust lobes, as is popular
> with
> > many other engines.
> > Thanks,
> > Mike Chardon, OH




[This is message #10638 by user img width=12 height=12 border=0 src="http://opi.yahoo.com/online?u=gentec2000&m=g&t=0" alt="" on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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Cams - Intake vs. Exhaust

Postby h-bot » Sat Mar 08, 2003 3:33 am

From: img width=12 height=12 border=0 src="http://opi.yahoo.com/online?u=doctorduke&m=g&t=0" alt=""_REMOVE_800054_THIS_@yahoo.com

The process I went through to determine the ideal indexing of the
production cams is extensively documented in the Twin Cam Times
Portfolio, which is available from CVOA.

If you want to start with different cams on either a normally
aspirated or boosted engine, the best approach would be to do your own
system engineering. Anything less is just guessing.

With the methodology outlined in the TCT Portfolio and a PC
simulation program you should be able to arrive at an accurate answer
for your specific case.

Off the top of my head I would say that my recommended reindexing of
the production cams will work quite well for a boosted application.
Being as how the reindexing results in a torque peak of about
5000-5500 and a power peak around 7000-7500, longer cams are
definitely not advised for a street driven engine. The actual amount
of torque/power and their peaks as installed in the car will be highly
dependent on exhaust system backpressure, and given the limited
undercar space, one of the biggest challenges is developing a low
backpressure exhaust system that will fit under the car and provide
acceptable acoustic attenuation. The production exhaust system
comsumes about 50 HP in pumping losses at high revs and the fan
dissipates 7 HP at about 7000, and these losses increase with the CUBE
of engine speed.

Duke





[This is message #10639 by user img width=12 height=12 border=0 src="http://opi.yahoo.com/online?u=doctorduke&m=g&t=0" alt="" on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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Cams - Intake vs. Exhaust

Postby h-bot » Sat Mar 08, 2003 8:45 am

From: img width=12 height=12 border=0 src="http://opi.yahoo.com/online?u=shark93726&m=g&t=0" alt=""_REMOVE_491775_THIS_@yahoo.com

I ran the cams straight up, no re-indexing. That engine made about
200 H.P. (an estimate since the stock cams with high compression and
webers would make around 180 H.P. with 1.1 inch ported out intakes.)

Gerald Storvik (8shark.com)


--- In <a href="/group/cosworthvegas/post?protectID=219233066105193209050199029077192253163098100009128121188190230091025019053061151110147">cosworthvegas@yahoogroups.com</a>, gentec2000 <<a href="/group/cosworthvegas/post?protectID=091233212180056219138097203245129208071">no_reply@y...</a>>
wrote:
> Gerald (or Duke),
>
> Did you run the cams "straight up" or did you reindex either of the
> cams? If you did reindex the cams what did they get reindexed to?
I'm
> thinking of doing the same thing (short track intake with the stock
> exhaust cam) with my car (the supercharged Cosworth) but before I go
> through all that work, I wanted to be fairly sure the cams would
work
> with each other OK. I'm making up a set of adjustable cam gears so
> reindexing the cams won't be a problem. Do you happen to know what
> kind of power you were making this setup?
>
> Todd
> 2384
>
>
> --- In <a href="/group/cosworthvegas/post?protectID=219233066105193209050199029077192253163098100009128121188190230091025019053061151110147">cosworthvegas@yahoogroups.com</a>, shark93726 <<a href="/group/cosworthvegas/post?protectID=091233212180056219138097203245129208071">no_reply@y...</a>>
wrote:
> > You are right. 20 years ago, when I was building my engine for
> > autocrossing, the builder talked me into using the stock exhaust
cam
> > with a 3/4 track intake cam, (higher lift and longer duration)
and
> > that engine made LOTS of Horsepower at the top end, without
losing
> > too much torque at low RPM. The same principal could be used to
make
> > a very good combination for street, by regrinding the exhaust cam
to
> > have shorter duration.
> >
> > The new re-indexed cams with less overlap that Duke designed and
Mark
> > is making, make a real improvement though, so I don't know
whether
> > most people would want to spend more money and work for the
little
> > gain available from a re-ground cam.
> >
> > Gerald Storvik
> >
> >
> > --- In <a href="/group/cosworthvegas/post?protectID=219233066105193209050199029077192253163098100009128121188190230091025019053061151110147">cosworthvegas@yahoogroups.com</a>, Mike Vee <<a href="/group/cosworthvegas/post?protectID=219233066112082198015038190036129">cossie@e...</a>>
wrote:
> > >
> > > I'm thinking of cars too much today, when I should be working.
> > > Does anyone know if the intake & exhaust cams are different
> > profiles?
> > > Just thinking that, with such good exhaust ports, it might not
be
> > necessary
> > > to have slightly more duration on the exhaust lobes, as is
popular
> > with
> > > many other engines.
> > > Thanks,
> > > Mike Chardon, OH




[This is message #10641 by user img width=12 height=12 border=0 src="http://opi.yahoo.com/online?u=shark93726&m=g&t=0" alt="" on Yahoo! Group Cosworth Vegas: http://groups.yahoo.com/group/cosworthvegas ]
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