More Cam Questions - Looking for a lot of input

[dodge_em]

I posted a little on the "509" thread that was going last week, but want to know some other information.
It seems a lot of good things are said about the Hughes HE3844 cam. I was looking at some of the other ones that Hughes offers as well. I think I have decided to go ahead and go with a Hughes cam, but for a guy is is pretty much a novice at this I want some more information to be able to select the right one for my application. About my car. It is a '68 GTX with a 440 and 4 speed. It has an 8¾ with 3.91 SureGrip in it. I am adding a brand new 6 pack setup. I am not sure of what size tire and rim I am going to go with yet, so any input on that would be appreciated as well. Right now it has the factory "Magnum" 14x6 wheels on it with some cheap Firestone tires on it.

Anyway, it seems a lot of guys are running an automatic with stalls. I want to be able to drive my 4 speed on the street most of the time, with only the occassional run down the strip. I see the Hughes 3844 requires a minimum of 175 PSI of cylinder pressure. How do I measure cylinder pressure? I think my engine is pretty much stock at this point. I am going to do some headwork, but maybe just a valve job for right now. Porting may come in the future, so I want to be able to build the engine to run well now, as well as accomodate future modifications. It will never be a strip only car, so must always be streetable. The other cam I am considering is the 3038. Duration at .050" on that cam is 230 intake/ 238 exhaust with .515"/.536" of lift for each respectively. A little less on each spec., than on the 3844. But this cam only requires 160 PSI and will run in the 2000-5700RPM range rather than the 2400-6000 for the HE3844. Any thoughts on this?
Next question has to do with lobe separation. In laymans terms, what is it, and how does it affect the performance? The 3038 cam has separation of 110° whereas the 3844 has 108°
Next is something I don't have a clue on. It has to do with the opening at .050" of lift. The 3844 has 14° BTC for intake and 53° BBC for exhaust whereas the 3038 is 8° BTC and 52° for intake and exhaust. I assume that BTC is Before Top Center and BBC is Before Bottom Center which I know are timing issues, but what is better and once again how do these affect performance.

I appreciate all that has already been discussed, as I have learned a lot for someone who is farily new to the art of engine building and performance tweaking. Thanks in advance for help given.

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[PRO]

Geez dodge em do you want us to write a book? really though youve asked some good questions,better yet just call Dave at Hughes eng. and talk with him afterall he is the expert on his cams,by the way I ran the 3038 in a 440 which previously had a 509 in it,to compare the too the 509 sounded way cooler at idle because of its lumpy idle,the 3038 had more bottom end although being a 4 spd car it didnt make any difference down the 1/4 but made city traffic easier,the 3038 redlined at 5400,the 509 at 5800,the car went faster with the 509 by 2 tenths but got better mileage with the 3038,you know they guarantee that their cams will out perform all others,I rated them pretty equal but I think Id lean towards the 3844 with your set up,call Dave........PRO...

[rumblefish360]

Go to huges and check them out, then call them for a recomendation. You'll get input and thoughts and all sorts of writings here.
Truly the best way of doing things is to know what you want. What do you want out of the car? Tell it to the cam maker. (Knowing tire size will help, they also may recomend running tire size "X" with this cam and rear ratio)
The best recomendation is from the makers of the cam. Also, if you call several cam companys, you'll get several differant ans.'s as well.
The tighter the lobe centers are, the peaker the power is. If there wider apart, it will give a wider torque curve.
The next ? is the @.050. It is telling you when & where the valve is opening in relation to the crank in degrees. Or where the pistons are, because there connected to the crank. The timing of the valves are important to idle quality and power. The @.050 is used for larger cams. Its how far the valves are off the seat. At .050 inchs of lift is when the reading starts.
The differance in cam specs are small. Only a few hundred rpm's. Thats not alot to worry about. But I can see your looking to maxa-mise<SP> the package. That intake is good to 6500rpm. So with that, both cams will work well.
For the street, I would use a 110 or 112. This gives a wide torque curve. It dosn't make for a fire breathing monster. But it is better than a tighter lobe like 108 or 106 and so on. When there this tight, there like...a cranky kid.
You can measure cyl. pressure with a gauge that screws into the spark plug hole. With the throttle wide open crank but not start the eng. Read the gauge.

[rumblefish360]

PS to the last message.
Get a book on it. A comp cams catolog has a write up in the begining that explains it all.

[fox]

Dodge-em they have given you good advice.
If you are running stock compression, 10 to 1 or so use the bigger of the two. It will lower the cranking compression and hopefully keep it out of detonation. The most important spec of a cam is the intake closing point. It starts the compression stroke.
By all means, buy Hughes are Ultradyn.
I would also suggest 1.6 rockers if it is in you budget. Smokey Yunick's book is a good read and so is chuck Senatore'
foxs.

[MOPARMANJAMES]

I'll try to answer your questions in order, youv'e got pretty good advice so far.
Question 1: measuring cylinder pressure?
The gauge that rumblfish is talking about is called a "compression tester" and you can buy this at most parts stores. Your cylinder pressure will vary depending on what cam you have installed so the pressure that you read now with your present cam will not be the same with the new cam.
Question 2: which cam?
I would go with the 3038 for now with your combo even though you could use either cam. The smaller will be more liveable on the street.
Question 3:lobe separation.
This is the separation between the intake and exhaust lobe peaks in degrees. A 108 separation angle just means the lobes are 108 degrees away from each other. Generally, a wide lobe separation angle, say 115 degrees produces good idle characteristics and vacuum and like rumblefish said, a wide but lower torque band. A tighter separation, say 108 will make the torque band narrower but much higher torque will be produced. This along with total duration and duration @.050" helps cam manufactures taylor the the rpm range that they want a cam to perform in.
Question 3: duration @ .050
You rotate the cam until it lifts the valve off the seat and bring it up to .050". Then you measure how many degrees in cam rotation it takes to bring the valve up the lobe and down the other side of the lobe back to where it is .050" from closing, in your case the intake is 230 degrees @ .050". This gives you a general idea of how radical the cam is and when you compare this to the total duration by subtracting the duration at .050 you can see how "agressive" the lift is or the intensity of the cam. For example, the Mopar 284/484 cam is 241 @ .050, 284 -241 = 43 intensity rating, very good for a hydraulic grind. The more intense, the better the performance, but the greater the wear also. For example, if you have two cams, both with a duration of 284 but one has a duration @ .050 of 230 and the other is 241 @.050, the latter is more intense and will perform better, but will wear faster.

Now that you have this info I can tell you that different cam manufacturers measure their total or seat duration at different lifts, it is not measured at the seat and is not standardized!! ,so intensity ratings can be misleading. For instance, Elgin rates their total duration for solid cams starting .006", while Utradyne measures at .020". So given two cams with the same advertised specs, the Elgin would be more aggressive.

Whew! got all that. Sorry about being so long winded but there's alot of homework to do when you get into camshaft selection!