HOT Cam / General Cam question
#1
Racer
Thread Starter
HOT Cam / General Cam question
OK, here's the story:
I'll be using Sportsman II heads with some porting and bowl blending. When all is said and done they'll be flowing about 255cfm and will have an I/E efficiency of 70-72%
Is a cam like the HOT cam with 218/228 too much of a spread for these heads?
The machinist warned me that with a pretty good exhaust port it can lead to scavenging too many gases out of the cylinder and it'll fool with the O2 sensor and throw my tuning off...
anyone ever deal with this?
I'll be using Sportsman II heads with some porting and bowl blending. When all is said and done they'll be flowing about 255cfm and will have an I/E efficiency of 70-72%
Is a cam like the HOT cam with 218/228 too much of a spread for these heads?
The machinist warned me that with a pretty good exhaust port it can lead to scavenging too many gases out of the cylinder and it'll fool with the O2 sensor and throw my tuning off...
anyone ever deal with this?
#2
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Originally Posted by DrEvil11417
OK, here's the story:
I'll be using Sportsman II heads with some porting and bowl blending. When all is said and done they'll be flowing about 255cfm and will have an I/E efficiency of 70-72%
Is a cam like the HOT cam with 218/228 too much of a spread for these heads?
The machinist warned me that with a pretty good exhaust port it can lead to scavenging too many gases out of the cylinder and it'll fool with the O2 sensor and throw my tuning off...
anyone ever deal with this?
I'll be using Sportsman II heads with some porting and bowl blending. When all is said and done they'll be flowing about 255cfm and will have an I/E efficiency of 70-72%
Is a cam like the HOT cam with 218/228 too much of a spread for these heads?
The machinist warned me that with a pretty good exhaust port it can lead to scavenging too many gases out of the cylinder and it'll fool with the O2 sensor and throw my tuning off...
anyone ever deal with this?
Too much scavenging and fooling with the O2 sensor??? I have never heard of that one. The only thing that would mess with the sensor is if you have an exhaust leak before the sensor, that will cause an irratic output from the sensor. That hot cam wouldn't be a bad cam for your application depending on what intake that you are running.
#3
Racer
Thread Starter
Originally Posted by tjwong
Too much scavenging and fooling with the O2 sensor??? I have never heard of that one. The only thing that would mess with the sensor is if you have an exhaust leak before the sensor, that will cause an irratic output from the sensor. That hot cam wouldn't be a bad cam for your application depending on what intake that you are running.
#6
Originally Posted by Dan Parker '96
Hotcam specs?
Just from memory:
@.050 218 intake, 228 exhaust
Lift... .525 (w/1.6 rockers) both sides.
Lobe sep. 112 deg.
Correct me if I'm wrong...
Just from memory:
@.050 218 intake, 228 exhaust
Lift... .525 (w/1.6 rockers) both sides.
Lobe sep. 112 deg.
Correct me if I'm wrong...
There are others out there that will make more power but they will likely cost some low end torque and economy. I think the Hot Cam is a very good "street" cam. If I wanted an all out race car I would run something else. It just all depends on your application.
#7
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Originally Posted by DrEvil11417
OK, here's the story:
I'll be using Sportsman II heads with some porting and bowl blending. When all is said and done they'll be flowing about 255cfm and will have an I/E efficiency of 70-72%
Is a cam like the HOT cam with 218/228 too much of a spread for these heads?
The machinist warned me that with a pretty good exhaust port it can lead to scavenging too many gases out of the cylinder and it'll fool with the O2 sensor and throw my tuning off...
anyone ever deal with this?
I'll be using Sportsman II heads with some porting and bowl blending. When all is said and done they'll be flowing about 255cfm and will have an I/E efficiency of 70-72%
Is a cam like the HOT cam with 218/228 too much of a spread for these heads?
The machinist warned me that with a pretty good exhaust port it can lead to scavenging too many gases out of the cylinder and it'll fool with the O2 sensor and throw my tuning off...
anyone ever deal with this?
Also what is the intake closing timeing in degrees ABDC of the HOTcam?
thanks,
#8
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Originally Posted by DrEvil11417
LT-1 intake conversion
Then perhaps the person was refering to intake reversion. This is the phenomenah that occurs during the overlap period of the cam where both intake and exhaust valves are open. However in the case of the LT4 hot cam, there will not be enough reversion in the intake tract to affect it. In a lot of instances where a large cam is installed, there can be an excessive amount of reversion in the intake.
When this happens and if it is a MAF strategy car, the pulses that occur during the overlap period can cause the MAF sensor to give an erroneous air flow reading. This happens because the MAF sensor can read air flow in both directions, so it sees the pulses and the incoming air flow as more than actual flow. Thus the PCM sees this additional flow and fuel for it, then of course the O2 sensors sees a rich condition and then the PCM trims back the fuel. When all is said and done, the fuel trims in the PCM will be low in these cases, and in the very worse conditions the trims willl peg at the low end of their control range.
#9
Originally Posted by mean8t
Making sure that you don't exceed the lift where your flow #'s tappers off at will make sure that you are getting the most out of your cam.
#10
Racer
Thread Starter
Ok basically what i'm saying is that the heads have a very good exhaust port and with the extra 10 degrees at .050 the cam will hold those valves open, my machinist is worried that it'll suck unburned fuel and spit it out the exhaust port and give the O2 sensor an incorrect reading and make the car run lean - he's suggessng a cam where the exhaust duration @.050 is no more than like 6 degrees bigger than the intake
#12
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Originally Posted by Nathan Plemons
Not always, you can slightly exceed the peak airflow and still make more power. So long as the total area under the curve is greater you'll still make more power. The problem is that it's a bastard to actually calculate it. It's a matter of how much time you spend at any given lift point.
I forgot to mention that.
Thanks Nathan
#13
Originally Posted by mean8t
I forgot to mention that.
Thanks Nathan
#14
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Originally Posted by Nathan Plemons
What I'm saying is that even though the airflow of your heads starts to stall above .600 lift you should still make more power. This is because with the higher rocker ratio you will reach any given lift point faster sooner. The total area under your flow curve should still be higher with 1.7 rockers than it would be with 1.6's.
My method of determining that is somewhat flawed because even if the flow stalled completely it would still result in a higher number. I need to figure out a way to include time into the equation, which is going to make it a very nasty little integration. Maybe someday when I'm really bored I'll think about it enough to do it.
My method of determining that is somewhat flawed because even if the flow stalled completely it would still result in a higher number. I need to figure out a way to include time into the equation, which is going to make it a very nasty little integration. Maybe someday when I'm really bored I'll think about it enough to do it.
Josh
#15
See the problem you run into though is that unless you find a way to take time into consideration you will always see an increase which simply isn't the case.
Example, you've got an equation and this is a graph. Unless the graph actually goes negative your area under the cruve ALWAYS goes up as you move further across, even though the graph may be headed back on a downward slope. This looks all well and good on paper, but in reality it might not work that way. Say just for the sake of argument that airflow stalled at .400 lift and fell dramatically. Getting above 400 quickly and staying there might cost you more airflow than if you just went to .399 and held there.
The only way to know that for sure is to introduce the time variable. Now "time" doesn't have to mean actual seconds, it could be represented as crankshaft degrees or something that isn't RPM dependent.
Example, you've got an equation and this is a graph. Unless the graph actually goes negative your area under the cruve ALWAYS goes up as you move further across, even though the graph may be headed back on a downward slope. This looks all well and good on paper, but in reality it might not work that way. Say just for the sake of argument that airflow stalled at .400 lift and fell dramatically. Getting above 400 quickly and staying there might cost you more airflow than if you just went to .399 and held there.
The only way to know that for sure is to introduce the time variable. Now "time" doesn't have to mean actual seconds, it could be represented as crankshaft degrees or something that isn't RPM dependent.
#17
Racer
Thread Starter
He tells me that it should work fine on stock heads but when you have a more efficient exhaust port coming into play it starts to get a little wacky
EDIT: The lt-4 head also seems to have a favorable exhaust port
http://chevyhiperformance.com/techar...mage_large.jpg
EDIT: The lt-4 head also seems to have a favorable exhaust port
http://chevyhiperformance.com/techar...mage_large.jpg
Last edited by DrEvil11417; 02-19-2005 at 07:28 PM.
#19
Racer
Thread Starter
Wow, what kind of heads did you get that kind of efficiency with?
The other cam i was looking at was the edelbrock rpm single pattern cam, 218 @.050 w/ .525
The other cam i was looking at was the edelbrock rpm single pattern cam, 218 @.050 w/ .525
#20
They're ported LT1 heads from Total Engine Airflow. The LT4 would show similar results but a slightly lower I/E efficiency. The LT4 if I understand it was redesigned more on the intake side than it was on the exhaust. When you go and port them the intake gets even more efficient while the exhaust doesn't do just a whole lot more.
I calculated efficiency by matter of integration and only over the lift values for which my cam actually operates. This might skew the numbers slightly but it's meaningless to look at .600 lift numbers when you're dealing with a cam that only goes to .525.
I calculated efficiency by matter of integration and only over the lift values for which my cam actually operates. This might skew the numbers slightly but it's meaningless to look at .600 lift numbers when you're dealing with a cam that only goes to .525.