Cams Verses Compression

[I am Technoman]

If you’re only at 9.5.01 compression you should not go to high. A lot of people think if they get radical cams on stock compression that it will make loads of power. 262-degree cams is not as efficient with 9.5 compression but if you have say 11.1.0 compression and use the 262 degree cams that will be a very good combo!Here is my cam chart

9.5.01 248-degree max10.0 1 252-degree max10.5.1 258-degree max11.0.1 262- degree max11.6. 1 268- degree max

input please!

Note this is for street use not all out drag!

[S14Zilvia]

So are you saying that if you were to use too radical a cam on stock compression you would actually be losing power compared to say a 248 on stock compression, or be making just a bit more peak power but lose gas mileage, low end, idle and things like that?

[I am Technoman]

So are you saying that if you were to use too radical a cam on stock compression you would actually be losing power compared to say a 248 on stock compression, or be making just a bit more peak power but lose gas mileage, low end, idle and things like that?

On stock compression 248 would perform much better than say a 262 degree cam... Torque wise..

[JNM240]

Where'd you get these numbers?

I ask because i have a 270 degree cam (SOHC) and am awaiting my block to get back from the shop with 10.5:1 compression pistons, and according to your chart i should have 11.6:1 compression ratio. Thats fine and all, but Daunttless told me that the highest compression ratio you could effectively run on a STREET car using 91 octane pump gas is 11.1:1, so i decided to make mine a little more streetable and lower the CR down to 10.5:1. Ive just never seen a chart like that before so im curious.

[TrunkMonkey]

If you’re only at 9.5.01 compression you should not go to high. A lot of people think if they get radical cams on stock compression that it will make loads of power.

i'm not sure what you mean by loads, but there will be a definite increase in hp

262-degree cams is not as efficient with 9.5 compression but if you have say 11.1.0 compression and use the 262 degree cams that will be a very good combo!

what do you mean by efficient? in this example it's the compression ratio that is making the extra power, not the cam.

Here is my cam chart

9.5.01 248-degree max10.0 1 252-degree max10.5.1 258-degree max11.0.1 262- degree max11.6. 1 268- degree max

this is pretty much useless. it means nothing.

input please!

i'd like to know exactly what you're trying to say.

-demetrius

[MarkEmark]

JNM240, and anyone else who knows...how much would a shop charge to take out my existing pistons and rings and replace them with higher compression pistons and new rings? (just labor, not parts cost...) Do you have to pull the whole engine to replace them?Thanks

[JNM240]

You dont HAVE to pull the engine, its just soooo much easier with the engine out.

My shop is charging me $370 to clean up the block and head, check both of them, change my heads valve stem seals, clean the valves, check the block for cracks, replace the freeze plugs, then bore and hone each individual cylinder to the new pistons. This price included taking block measurements so i could have custom pistons forged, pressing off the old pistons from my rods, pressing back on the new pistons, and he is installing the rings and rod and crank bearings. Not a bad price at all.

The pistons cost me $520 and the engine rebuild kit (all the gaskets, bearings, seals, freeze plugs, and a new oil pump) cost me $300. But i still need to get a new timing chain kit and new water pump (old one isnt bad, its just everything else is going to be brand new, why not that too?).

[C-Kwik]

Cams are a whole lot more complicated than just duration. Cam Timing, Duration, lift, and overlap all play major roles in how it affects the output of a motor. Even the angle of the lobes can affect performance significantly. And more than CR, I'd say header tuning in conjunction with a cam would net you the best power increases. Especially in high overlap cams that are used in conjunction with long tube equal length headers that are tuned to the cam. The scavenging effects created by the exhaust pulses can actually be strong enough to pull air from the intake into the cylinders at certain RPM's.

[S14Zilvia]

jnm240, if I wanted to have something like this done, who would I go to?

There are hardly any performance shops around here... and no import motor builders that I know of.

[JNM240]

Just locate a machine shop. They will do the machining for you. As far as removing your engine, i did it myself. You can usually rent an engine hoist for $40 or so. I did buy the engine stand for $40 since it was that much to rent it.

[SSS]

I plan on running a 268 deg cam on 8.6:1 compression....EDIT: i know of someone here in australia running a reground 268 deg duration inlet/exh SOHC cam and it runs just as well as it did with the std cam, on 8.6 comp ratio.

[S14Zilvia]

That's cool, I'm sure there are places I can go to do the machining, but what about actually replacing the pistons, rings and such? I'm not sure I'd trust myself to get everything in there right, and to have everything machined to the right tolerances.

Does anyone know of any good write-ups for an NA buildup, or just a rebuild on a KA?

[JNM240]

Again, thats what the machine shop is doing for me. He is boring and honing the block for each cylinder, ie: he is installing the pistons on the rods and in the cylinders with the bearings and the crank as well. I will be picking up the complete block in about 5 days. Check with your local machine shop though to make sure what all they do.

[I am Technoman]

My cam to compression chart was not facts it was an example to make a point about cam sizes to compression ratios. Sure it’s ok to run a 270 cam with 10.5 compression but would you make more power with 11.1 of course you would, but at the same time you would need c16 or some crap to keep from pinging. The point I was trying to get across was the way motors react with cretin combos to make the best power.

[TrunkMonkey]

The point I was trying to get across was the way motors react with cretin combos to make the best power.

but there is no majic combo because compression ratios and cams have nothing to do with one another. no matter what cam you use you will always make more power with the higher compression.

the only way you would limit yourself to certain cams with certain compression ratios is if you used custom dome pistons. you may not be able to use a high lift long duration cam if the piston isn't designed for it.

-demetrius