Effect of displacement on Camshaft selection

[JamesonRacing]

Assembling an engine for my 66 F250 that will be used for towing and some cruising, no racing.  Block is a std bore 427 with a 4.25 crank setup, for about 480 cubes.  Compression ratio is right at 10:1.  Block isn't drilled for hydraulic lifters, so I'm trying to spec a solid cam.

All the cam recommendations seem to be for 390-428 size engines, with durations starting at 224, 230, 236, 240...., with LSAs at 110 for the smaller cams and 108 for 240 on up. 

How much more duration should the cam have to account for the additional size?  I'd be looking at the 224 duration if it was a 390, but the extra ninety cubes should make a difference.

Thanks for your input and discussion.

[jayb]

Big cubes will eat up camshaft duration.  If you are running 20% more displacement, you probably need 20% more "area under the curve" of the cam lobe, so to speak, to get 20% more power.  One thing I've done in the past is map the intake valve operation with a given cam lobe, for lift and duration.  Here's a comparison I did between two cams a while back, where I just stuck each cam into a set of V blocks and checked the lobe lift every 10 crank degrees.  You will get a curve like the ones shown below:



If you have a preferred cam that would work on a 400" engine, what you would be looking for in the stroker would be a cam where the area under that curve is about 20% bigger.  From a practical standpoint, I'd guess that would be in the range of an additional 12-15 degrees of duration, and maybe .050" - .075" lift at the valve.  But if you had a couple of cams you were considering, you could run them in the V-blocks and get a better idea...

[JamesonRacing]

Thanks for the info Jay.  Makes a lot of sense.  Eager to see how much torque this one will make.  Think I'll be filling the tank with premium with the 10:1 CR and towing a trailer.  Will be good to be able to tow the race trailer with some style and power this Summer.

[hotrodfeguy]

Wonder whre I heard this before? 12-15 degrees more duration  I know this much that truck is you lol and that engine builder needs to get back to work he is fired.

Wasn't that Van Halen that said "COME ON Dave" @ 2:30  one change coming up, good music man I miss that.
http://www.youtube.com/watch?v=maQjttazW6Q

[JamesonRacing]

Yeah, heard that somewhere before recently!

Hope the blocks arrived in Green Bay okay.  Engine's on the stand, looking for a little warmer weather to get wrenching.

[hotrodfeguy]

I can wait to see it go down the digs a few times 

[My427stang]

For peak hp numbers, I agree that you need to feed the beast, and the 12-15 degrees seems pretty close

However, remember that you are also changing overlap, advertised valve timing, and the engine has a different piston dwell time and cylinder fill capability, etc.  To go from a 224 degree 390 to a 236 degree 445 with the added overlap, I think you'd have a little rowdier engine than you expected, not radical, but a little more choppy idle.

If you use the 12-15 degree increase, I think I'd spread the centers to maintain the same overlap and keep the intake lobe timing early.  That way you wouldn't lose part throttle low rpm behavior, but you'd get the cylinder fill.

What I think is more important as you go up in displacement is intake and cylinder head selection.  You'll go far by making a deep breather using heads and intake, then camming for where you plan to use it the most

BTW, I used a 270H in my 445, rolled it back to 110 ICL and wonder sometimes if I should have went 112, but mostly because I had a tough time getting to the DCR I wanted.

With that being said, I did it because I was being cheap and I had a good cam and lifters matched to the block I used, already broken in.  We'll see how it does, the heads flow 280 and the RPM intake was worked and balanced.  Hopefully the heads and intake will hold on at the upper end of the curve

No doubt it would make more power with more cam, but in a 4x4 with 3.50 gears and 33 inch tall rubber, we'll see how it does when I get the body back together.  It sounds REAL strong, but the story will be told when the tach hits 5K LOL

[rockhouse66]

You made this statement;

"If you use the 12-15 degree increase, I think I'd spread the centers to maintain the same overlap and keep the intake lobe timing early.  That way you wouldn't lose part throttle low rpm behavior, but you'd get the cylinder fill."

then later you mention rolling the ICL back.  These are not the same thing and I just want to confirm that what you meant was you would have a cam ground on more LSA (like 112 instead of 110 or 108) if you were trying to take advantage of the extra cubes without ending up with a rough idle.  Yes?

[My427stang]

Two different situations, sorry I wasn't clear

For his motor, assuming he is buying a cam anyway, I would add duration and lobe seperation,  spread the centers to reduce overlap, but keep an early intake lobe.   

In my 445, I DIDNT do that, I ran the small cam, made some up with the head and intake, and then retarded the cam a bit because I couldn't control DCR otherwise, plus I wanted it to hang in a little longer.

Thats why I made the point that I was being cheap, and that I was hoping the heads and intake would make up the difference.

If I didn't have the 270H, I probably would have added duration, kept overlap low with LSA, and then kept an intake valve closing point similar to where I am now.

[fe66comet]

Well this is what I got for my 445 any advice on which timing gear key to use?

[afret]

How much spring do you have to run with that cam?  Wondering what was the reason for choosing an LS1 intake lobe and a lift rule  aggressive race only exhaust lobe? 

[fe66comet]

Well I failed to mansion it is a hydraulic roller so the profiles look a little odd. I wanted a big breather up to 6500 that would still be somewhat streetable. I am running a stick so idle is not a big deal either. The lift I did not go too crazy as it will rarely see 7000 rpm but will do it on the lifters, I just want to stay in the safe zone. Seat pressure is 350 psi into/ exh to hold the heavy rollers down. I would have liked a stabilizer kit for more rpm but could not find a compatible one and I would have to get a main girdle too. I may do that anyhow for extra cap support, it is your basic 390 block so nothing special.

[afret]

Boy that's a lot of seat pressure!   What's your open pressure?  Didn't know they make hydraulic roller lifters that can handle that much.

[JamesonRacing]

Going with a Comp Cams 282S, 236/236, 0.571/0.571, so about 12 degrees more duration than what I would have picked for a 390.  Using an iron CJ intake manifold, and a set of nicely ported D2 heads with CJ valves.  For the RPM range I'm planning on using the engine, I think the combo should good low and mid-range torque, idle okay, and still rip when I need it to.  If it doesn't, I still have my two Fairlanes to go play with!
 

[fe66comet]

I have had many 390 powered pickups they all would leave wrinkles in the asphalt so I think you will be surprised LOL