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Old 08-25-2009, 05:18 PM   #1
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Duratec Turbo Cams Selection

Well I've been doing A LOT of reading about selecting cams since I obviously want to get the most power out of my engine possible and I just wanted to throw some things out there.

Taken from Crane Cams Website..
What is Camshaft Duration and why is it important?

Duration is the period of time, measured in degrees of crankshaft rotation, that a valve is open. Duration (at .050" lifter rise) is the deciding factor to what the engine's basic RPM range will be. Lower duration cams produce the power in the lower RPM range. Larger duration cams operate at higher RPM, but you will lose bottom end power to gain top end power as the duration is increased. (For each ten degree change in the duration at .050", the power band moves up or down in RPM range by approximately 500 RPM.)

What is the difference in Advertised Duration and Duration at .050" Lifter Rise (Tappet Lift)?

In order for duration to have any merit as a measurement for comparing camshaft size, the method for determining the duration must be the same. There are two key components for measuring duration-- the degrees of crankshaft rotation and at what point of lifter rise the measurements were taken. Advertised durations are not taken at any consistent point of lifter rise, so these numbers can vary greatly. For this reason, advertised duration figures are not good for comparing cams. Duration values expressed at .050" lifter rise state the exact point the measurement was taken. These are the only duration figures that are consistent and can accurately be used to compare camshafts.

-With turbo cams, you want as little overlap as possible. Also, you would usually want a little more intake duration than exhaust. This is to help with exhaust gas reversion due to higher exhaust pressure due to the turbo. Since we are looking at duration at .050", you want the overlap to be definitely in the negatives because below .050" it will have more overlap. Like I said, you want as little overlap as possible.
-You also want as high a lift as possible. Basically with f/i motors you want the valve to lift 20-25% past its peak flow point (something you calculate based on the cylinder head). You don't want it to open only to its peak flow point because that would only happen one time per cycle. If it opens past, then there is time where it is open to its peak flow point while the valve is still going up and then starting back down. Basically it allows you to have the valve open at its peak flow point longer. Since I doubt anyone knows the peak flow point on our heads, I would think that the higher, the better. Keep in mind with some profiles, you may need valve relieft in your pistons.

Now to compute OVERLAP you:
-Add the intake and exhaust durations
-Divide the results by 4
-Subtract the lobe separation
-Multiply the results by 2

STOCK DURATEC CAMS
Lobe separation: 112
Intake duration at .050": 202
Exhaust duration at .050": 189
Intake lift: .358"
Exhaust lift: .317"

{[(202+189)/4]-112}x 2 = -28.5 degrees of overlap at .050"

Well everyone says that the stock cams work great for F/I, and you can see they are right. -28.5 degrees is great. That means that below .050” is still going to have little if any overlap.

CRANE STAGE 1 CAMS – no longer produced, but can be found
Lobe separation: 110
Intake duration at .050": 212
Exhaust duration at .050": 204
Intake lift: .374"
Exhaust lift: .354"

{[(212+204)/4]-110}x 2 = -12 degrees of overlap at .050"

Not too bad. Its solidly in the negatives, which means below .050” will still have very little overlap. It is however 16.5 degrees more than the stock cams. These cams do have .016” more intake lift and .037” more exhaust lift than stock, giving you much more airflow, especially on the exhaust side. Obviously, more air = more power.

CROWER STAGE 1 CAMS
Lobe separation: 114
Intake duration at .050": 211
Exhaust duration at .050": 205
Intake lift: .397"
Exhaust lift: .347"

{[(211+205)/4]-114}x 2 = -20 degrees of overlap at .050"

As you can see these are a little better than the Crane Stage 1 Cams as far as overlap, having only 8.5 degrees more than stock and 8 degrees less than the Crane Stage 1 cams. They also have .039” more intake lift and .030” more exhaust lift than stock. More air = more power.

CROWER STAGE 1 INTAKE CAM/CROWER STOCK REPLACEMENT EXHAUST CAM

Lobe separation: 114
Intake duration at .050": 211
Exhaust duration at .050": 210
Intake lift: .397"
Exhaust lift: .363"

{[(211+210)/4]-114}x 2 = -17.5 degrees of overlap at .050"

I would love to try this combo. This would give you .016" more exhaust lift than the stage 1 which is .046" more exhaust lift than stock and slightly longer duration at .050" than the stage 1, but still very low duration seeing there is still -17.5 degrees of overlap at .050". THIS IS PROBABLY WHAT I WILL BE CHOOSING.

CRANE STAGE 2 CAMS
Lobe separation: 110
Intake duration at .050": 226
Exhaust duration at .050": 216
Intake lift: .410"
Exhaust lift: .385”

{[(226+216)/4]-110}x 2 = 1 degree of overlap at .050"

You can see that there is positive overlap at .050” which you definitely don’t want. This means that there is a great deal of overlap below .050”. Lift is good though, with the intake having .052” more than stock and exhaust having .068” more than stock.


CROWER STAGE 2 “F/I” CAMS
Lobe separation: 112
Intake duration at .050": 220
Exhaust duration at .050": 220
Intake lift: .400"
Exhaust lift: .400"

{[(220+220)/4]-112}x 2 = -4 degrees of overlap at .050"

You can see the overlap with these is much greater than the stage 1 crower and crane cams but it is less than the stage 2 Crane Cams. It is fairly close to positive which means that below .050” will have significant overlap. Overlap = Bad. Also, the durations are the same for the intake and exhaust cams, which depending on the turbo setup (type of turbo, log vs. tubular manifold, etc), can cause exhaust gas reversion. The lift is pretty high, however, which is good. Intake lift is .042” more than stock and exhaust lift is .083” more than stock.

CROWER STAGE 2 CAMS
Lobe separation: 112
Intake duration at .050": 220
Exhaust duration at .050": 214
Intake lift: .374"
Exhaust lift: .363"

{[(220+214)/4]-112}x 2 = -7 degrees of overlap at .050"

This cam setup looks to work better than the “F/I” Crower Cams. The overlap is 3 degrees less than the f/i cams and only 5 degrees away from the Crane stage 1 cams. There will be some overlap below .050” but significantly less than the crane stage 2 and crower stage 2 f/I cams. The intake cam has a little more duration than the exhaust cam which helps with exhaust reversion. There also is a good amount more lift than stock, especially on the exhaust side. Intake lift is .016” more than stock and exhaust lift is .046” more than stock.

COSWORTH YD0222 AND YD0173
Lobe separation: 112/113
Intake duration at .050": 216
Exhaust duration at .050": 216
Intake lift: .374"
Exhaust lift: .374"

{[(216+216)/4]-112.5}x 2 = -9 degrees of overlap at .050"

Not bad. Close profile to the crower stage 2 cams. There is less overlap than with the Crower stage 2s but equal or more lift. Intake and exhaust duration are the exact same so there could be some exhaust reversion. Intake and exhaust lift are higher than stock with the intake being .016” more and the exhaust being .057” more.


COMPARING THE STAGE 3 VERSIONS OF THESE IS POINTLESS. LOOKING AT THE DURATIONS ITS OBVIOUS THERE WILL BE LOADS OF OVERLAP. I ALSO DIDN’T INCLUDE ANY CRESPO CAMS DUE TO ALL OF THEM HAVING A TON OF OVERLAP. ALSO, NONE OF THE OTHER COSWORTH CAMS ARE WORTH CHECKING AS THEY WOULD HAVE A TON OF OVERLAP AS WELL.



Last edited by streetracer; 09-01-2009 at 09:29 AM.
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Old 08-25-2009, 07:20 PM   #2
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Awesome Jeff. Very good info! You've got me looking into cams now.
Keep in mind that even with cams that overlap by a little below .050 but have a high lift profile that you desire, you can always get adjustable sprockets to adjust the cams so they don't overlap. However, that will further hurt bottom end power and increase the rpm range, which if you're going for a badass street/drag setup, would be perfect. Just my input.

I'm putting this thread on favorites, thanks for the info.
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Old 08-26-2009, 08:31 AM   #3
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yeah. i dunno exactly what im gonna choose yet lol.
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Old 08-31-2009, 10:57 PM   #4
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this is a very good write up!! i was thinking about doing a cam w/ my 2.3 head setup! jeff what u might want to do is get u head ported an polished while u have it off! i was looking at spec of the 2.0 vs. the 2.3 and the heads r exactly the same! so if u open up ur intake and exhaust ports alittle... it will help out alot!! and there is a lot to be taken off the exhaust side compared to the manifold gasket!!
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Old 08-31-2009, 11:14 PM   #5
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Here's something you also want to keep in mind. The information above is great info for a stock boosted motor w/ a small, quick spooling turbo. Should you have a bigger turbo (GT35R or higher), a bit of overlap would actually work to your advantage. Since you'd be boosting straight out the exhaust for that short period of time, you'd be boosting straight through the exhaust flange of the turbo spooling it up quicker. This can be beneficial for creating better low end power out of a big, slow spooling turbo. The downside is it will put your peak power even higher in the RPM range.

I've done a little research into adjusting cam timing and how it effects power gains and valve overlap.

Let's say you have a set of cams with +1 degree of overlap at .050". Well in order to prevent this overlap, you would need to retard the intake durastically and advance the exhaust cam. On the duratec, it would be completely non beneficial as it would the put the powerband so high, you'd kill drivability and low end power. Not to mention that this would cause the cylinder not to receive it's max volumetric efficeincy due to the exhaust cam closing before the piston hits top dead center, creating a vacuum.

Let's say you have a set of cams that have -7 degrees of overlap at .050". Well, this would only require a minor adjustment of the cams. The intake cam could be slightly retarded and the exhaust cam slightly advanced if not stay at zero. This would prevent the overlap but would still put your power range higher and take away some bottom end torque.

Here's where a good question comes to mind. Does the stock duratec head have long or short intake runners? The length of the runners will have a huge say in where the cam timing should be to achieve max efficiency. If the stock duratec head and IM have a reletively short intake runner, then a 2-3 degree advancement of the intake cam would produce the most torque and would be stronger throughout the entire RPM range, especially on the bottom end. It could possibly hurt this effect if it has long runners. This is where my research is stuck so any input on this would be greatly appreciated.
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Old 09-01-2009, 12:38 AM   #6
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Old 09-01-2009, 09:18 AM   #7
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Quote:
Originally Posted by jrescina0035 View Post
this is a very good write up!! i was thinking about doing a cam w/ my 2.3 head setup! jeff what u might want to do is get u head ported an polished while u have it off! i was looking at spec of the 2.0 vs. the 2.3 and the heads r exactly the same! so if u open up ur intake and exhaust ports alittle... it will help out alot!! and there is a lot to be taken off the exhaust side compared to the manifold gasket!!
i got the FR head :) stock cams and valvesprings for now due to $$$. spending ~$700 on cams and valvesprings isnt really worth it right now, especially since if i spend ~$1500 i could have ~375whp on pump gas with the gt2871r and a new intercooler

and smithboy, the intake runners on the head are about 3 inches.
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Old 09-01-2009, 09:30 AM   #8
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**edit**

added this to the top..

CROWER STAGE 1 INTAKE CAM/CROWER STOCK REPLACEMENT EXHAUST CAM

Lobe separation: 114
Intake duration at .050": 211
Exhaust duration at .050": 210
Intake lift: .397"
Exhaust lift: .363"

{[(211+210)/4]-114}x 2 = -17.5 degrees of overlap at .050"

I would love to try this combo. This would give you .016" more exhaust lift than the stage 1 which is .046" more exhaust lift than stock and slightly longer duration at .050" than the stage 1, but still very low duration seeing there is still -17.5 degrees of overlap at .050". THIS IS PROBABLY WHAT I WILL BE CHOOSING.
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Old 09-02-2009, 04:21 PM   #9
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what's goin on w/ the engine build?? anything new yet?
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Old 09-02-2009, 05:47 PM   #10
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should be driving the car on friday

along with the engine build hes installing fogs,debadging the rear, and connecting the rpm signal for the eboost 2.
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