Cam change.

Im changing up my combo just a little and am thinking about changing the cam as well.

Currently its a 500 with out of the box -1's and i have a comp 23-000-9 cam. .681 lift 282 @.050 on intake and exhaust. installed at 104. It has 13.06 compression now the heads are cut to 67cc


Ive gotta have new pistons so im changing the bore to 4.500 and adding a small dome to get the compression to 15.05 ish range.
Having the heads ported and adding the 2.250 intake valves. I run injected alky (toilet) and i will possibly try a 1050 and 1150 alky carb as well.

Can i improve much with a new cam? if so which one? It will be in a dragster. will be used on some throttle stop stuff too.

Thanks, Chris

I currently run 4.50" bore, 14.8-1, ported -1 w/2.250. 285/292@112 LCA .470 lobe in at 108.1.7 rocker, .785" after lash. Has pushed my 3350lb car to 9.02@151. Comp RX 1718 int lobe, XCX 1812 exh lobe.
Doug

What rocker arms do you have? 280 is in the ballpark for duration but you need a ton more lift. 681 lift is choking that engine down, you're probably leaving 50 to 100 hp on the table.

I run a 282 duration cam in my 514 dyno motor but I have .890 lift. Compression is 15:1 and I have EZ heads. That engine makes a little over 900 hp with a 1250 Dominator on a cast intake.

Get a copy of PipeMax and run your numbers thru it. I bet it tells you that you need .900 lift to avoid choke.

I have jesel 1.55 rockers. I would like to move up to the 1.7 rockers but thats out of the budget right now.

Look into changing just the intake rockers for now

I highly recommend buying a copy of PipeMax so you can run some dyno simulations. Or look around and pick a different SW package but find something that you trust. $100 for a dyno package can save you a lot of money down the road. Or call around and talk to some cam guys and engine builders. I'm pretty sure they'll all tell you the same thing.

Based on my own experience I'll say that you need at least a 1.70 intake rocker arm and probably more like a 1.80 rocker arm on that engine to wake it up. I learned this lesson a few years back after working with Jones Cams on a project. I switched my EZ heads over to 1.85/1.70 rocker arms and added a ton of power. The 1.50 rocker arms just can't get the valves open fast enough for a big race engine with smallish cylinder heads.

One issue with the big rocker arm ratio is that you'll run into valve to piston clearance problems so you have to watch that. The aggressive valve train will also be more demanding on valve springs.

Spend your money on rocker arms and camshaft rather than bigger valves. I think you'll get a better payback.

The cam you have might work with 1.70 or 1.80 rocker arms. I think you have the 23-704-9 camshaft but I can't tell for sure. Call Comp and see if they can tell you what lobes are on your cam and if they'll work with higher ratio rocker arms. If you have 0.440 lobes then a 1.80 intake will give you .790 lift which is starting to get you in the ballpark of where you need to be. You shouldn't have any problem finding a good valve spring that can handle 0.800 lift that will fit the -1 heads.

So curious if I would gain anything on my .680-.660 276-281 @ .050 solid roller going from my 1.5(actually 1.54)HS rockers to a 1.6 in the same brand. IIRC I have good p/v clearance now..........

Comp makes a .750 lift that's about a tenth faster in the 1/8 then the .680 lift

I have a very similar motor, 4.5 bore 4.15 stroke, 440-1 ported heads, Terminator injection, alky. I run a Comp cam with 283/296/112 duration, .501 intake lobes, less on the exhaust. I am going to 1.7 intake rockers this spring to get .850 lift on the intake side.