Thread: Camshaft advice (again...)

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And I am gonna need torque to get my tank movin...

Your on the right track now!!!
Just make sure the cam has a intake valve closing point that puts your dynamic compression close to 8.5 .This is where my exspertise ends.........I have no idea about lifts and lobe seperation and which what does when where.......but I know only certain lifts and lobe seperations are going to fall into the selection of cams that will give you the proper dynamic compression.

Originally Posted by shawnlee28

Your on the right track now!!!
Just make sure the cam has a intake valve closing point that puts your dynamic compression close to 8.5 .This is where my exspertise ends.........I have no idea about lifts and lobe seperation and which what does when where.......but I know only certain lifts and lobe seperations are going to fall into the selection of cams that will give you the proper dynamic compression.

Shawnlee, I've watched you come along in your education and I'm very proud of you for making sense out of all the gobble-de-goop that I and others have posted on this forum. In my opinion, you have a better leg-up on cam selection than 90 percent of the rodders out there and I'm pretty sure that when you begin preaching the gospel of cam selection to newbies, they look at you like you have two heads.

As far as lift, the more the better within the confines of mechanical clearance. The things you have to check closely when getting into extreme lifts are:
1. piston to valve clearance. Ideally, 0.250". An absolute minimum would be 0.080" on the intake and 0.100" on the exhaust. Some builders say the absolute minimum is 0.100" on the intake and 0.120" on the exhaust. More is better. Less could be disastrous.
2. pushrod to head slot clearance. A miss is as good as a mile. Turn the motor through 720 degrees of rotation and observe closely.
3. rocker slot to rocker stud clearance. Use a piece of small diameter solder held between the slot and stud while turning the motor through 720 degrees of rotation. If the solder gets pinched, grind the rocker slot for clearance.
4. valve spring coil bind. At full lift, you must be able to slide a 0.010" feeler gauge between each and every coil. If insufficient clearance is observed, you may be able to remove some shims to correct the condition. If not, change to a different spring or different retainer.
5. retainer to valve guide boss interference. 0.0625" to 0.125" clearance at full lift. If insufficient, change to a different retainer or machine the top of the valve guide down slightly. This could be done at the same time as machining the guides for PC seals.

LSA, LDA. Lobe separation angle is the more commonly used term, but I grew up knowing it as lobe displacement angle. Either is correct. The short explanation is that a narrow angle (100 to 110) will give the motor more low end, building torque quickly and then laying down on the top. Manifold vacuum will be low. Idle will be choppy. A wide angle (111 to 118) will not make quite as much torque on the bottom, but more in the higher range. Manifold vacuum will be high. Idle will be smooth. Look at Compcams. They grind nearly all their cams on a 110 LDA, right in the middle of the range.

Using the calculator, I ain't ever gonna get it up to 8.5??? Even at 0 degrees it only calulates to 7.83... its depressing. I geuss I will deal with what I got now to get the car on the road and find another motor to build s-l-o-w-l-y

my specs used for the calculator:
heads 120cc
bore 4.25
stroke 4
rod length 6.135
stat comp ratio 7.83 (calculated)
dynamic comp 154.60psi (calculated)

I am now looking at a Comp Cam 268H, found a new one with lifters cheap on ebay.
268 advertised duration, 218 duration @.050, .485 lift, 110 lobe sep , no specs for intake valve closing point
Seems kind of close to what Nitro recommended (I think)

It will still get your heart pumping!!!!!Those figures are just to get the maximum.you will still have plenty of power!!!

Originally Posted by Gusaroo

Using the calculator, I ain't ever gonna get it up to 8.5??? Even at 0 degrees it only calulates to 7.83... its depressing. I geuss I will deal with what I got now to get the car on the road and find another motor to build s-l-o-w-l-y

my specs used for the calculator:
heads 120cc
bore 4.25
stroke 4
rod length 6.135
stat comp ratio 7.83 (calculated)
dynamic comp 154.60psi (calculated)

I am now looking at a Comp Cam 268H, found a new one with lifters cheap on ebay.
268 advertised duration, 218 duration @.050, .485 lift, 110 lobe sep , no specs for intake valve closing point
Seems kind of close to what Nitro recommended (I think)

I like those cam specs for your engine. For the $50 or so to get the compression up I would use a metal shim style head gasket. This will be typically 1/2 the thickness of a typical Felpro style gasket...then with heads off maybe get them resurfaced a little too...this little bit will help.

Try this l http://www.compcams.com/Community/Ar...?ID=1108284073
Its off of compcams website. I went with the xe268 in my 454. I love it. I have the 781 heads on it with about 10.25 compression. I have it in my mud drag pickup.

I kinda like the specs on the cam, especially with the standard tranny, assuming that the first gear is in the 3.00 range? My only concern was the "truck" heads. Are they the peanut ports?? I am not sure how the cam would work with the smaller peanut ports. As far as the low comp ratio, try to keep the cam over lap way down by staying with a LSA in the 114-115 range. The specs on the 2162 cam look very similar to the stock chevy L-78/LS-6 cam, just in a hydraulic version. I don't think you have any problem moving that heavy weight along. Good luck!!

Rich

Saw, I think you'r eheading him in the right direction. Gus please redo the calculations. I think you're higher in comp ratios than you think. When I first suggestion for cam selection was considering what you stated you had. I think you have more setup than you think. Run a bit higher cam than stock. Remember, your rear gears and stock components won't take much until you beef them up. But they will tale a little more to get it moving without breaking. Comp cams 280-292 will be okay if you tune, fuel, and worry more about streetability.

Good job Tech. More info is always a plus for those who spend the time to be well informed.

Thx guys, I think this stirng has been one of the best ones for me. I went with the comp cams 268H, got it new for $100 (includinig lifters) on fleabay.

You guys really helped take the mystery out of cam selection. I will be bookmarking this one. Ill let you guys know how it goes when I get the car running.

Gus, I'm going to make a suggestion to you. If this were my car/motor and I was installing a 268 cam, I'd advance the cam by 6 to 8 degrees. The hotter cam (over the stock one) will retard the intake closing point, closing the intake valve later than the stock cam. This is going the wrong way with your very low static compression ratio. By advancing the cam on installation, you will close the intake earlier and capture more of the fuel/air mixture, giving a more favorable dynamic compression ratio.

This is never going to be a race motor as it sits and advancing the cam will give you more driveability in the low and midrange, where you need it for the street. You'll give up some on the top, but how often will the motor see time above 4,000 rpm's? Any cam you install will be a compromise in one area or another. The best you can do is try to get a little better performance in the range where the motor will be run most of the time.

If you're unsure of how to position the cam for advance, either ask here or PM me for a tutorial. I'll give you the straight scoop.

Use a degree bushing kit such as this and drill the pin hole in the cam sprocket to 13/32"....
http://store.summitracing.com/partde...0&autoview=sku

Originally Posted by techinspector1

Gus, I'm going to make a suggestion to you. If this were my car/motor and I was installing a 268 cam, I'd advance the cam by 6 to 8 degrees. The hotter cam (over the stock one) will retard the intake closing point, closing the intake valve later than the stock cam. This is going the wrong way with your very low static compression ratio. By advancing the cam on installation, you will close the intake earlier and capture more of the fuel/air mixture, giving a more favorable dynamic compression ratio.

This is never going to be a race motor as it sits and advancing the cam will give you more driveability in the low and midrange, where you need it for the street. You'll give up some on the top, but how often will the motor see time above 4,000 rpm's? Any cam you install will be a compromise in one area or another. The best you can do is try to get a little better performance in the range where the motor will be run most of the time.

If you're unsure of how to position the cam for advance, either ask here or PM me for a tutorial. I'll give you the straight scoop.

Use a degree bushing kit such as this and drill the pin hole in the cam sprocket to 13/32"....
http://store.summitracing.com/partde...0&autoview=sku

I.M.O.,if you have to advance a cam more than 4 degree's the cam is to large.

Get some Rhodes lifters,they bleed off duration and lift under 3000 rpm for better torque and dynamic compression.

Originally Posted by erik erikson

I.M.O.,if you have to advance a cam more than 4 degree's the cam is to large.

Exactly.....

Look at this Crane at 266 degrees ground on 110. Check out the recommended static compression ratio in the upper right hand corner, 8.5 to 10. That's a long ways from 7.83:1.
http://www.cranecams.com/?show=brows...tType=camshaft

Several members have suggested increasing the static compression ratio by thinner gaskets/head shave and I think that is valid advice. Shawnlee has come up with a great suggestion also, with the Rhodes lifters. I've used them and they work.

Pat thinks the cam will be ok straight up and has a lot more experience with big block Chevies than I do. I just know what the numbers tell me.