Inliners International Forums General Discussion Vortec 4200 Increasing compression

Is there a good way to increase compression on the 4200? I know it's common to shave heads on cam in block engines, but I know that it's possible the cams will be out of time if the head is shaved down on an OHC engine. Would it take the cams out of time by shaving the head? Or would it be better to fill in the combustion chamber with weld material?

You can cut the head .020 - the stock compression is 10.1 or 10.2:1 year dependent...

What are you planning on running for fuel?

How much higher would that bring compression?

I plan on e85 at the least, race gas if I need to. I really want to run close to 12:1 compression NA, 11.5 at least.

So .020 should bring me to around 11.2, I would be comfortable with that. What is preventing from shaving it down further? Valve clearance?

Timing chain slop could also become an issue. I used to build some BMW road race engines and I had to also modify the chain tensioner to compensate for excessive head milling. You'll also need to have a way to degree the cams if you don't already.

I too have built a few BMW engines. In the 4200, is there something like the BMW M5Xs have in the back of the cam where there are two flat spots and you can use a special tool to hold them in time? While you are installing the timing sprockets.

I'm not worried too much about tension, I am comfortable with modifying the tensioner itself.

I think there is a tool to sync the cams. I know the Jags I've built did, so I'm sure most other DOHC engines do also.

yes cams have flats at the back of the cam

you need to have the pan/timing cover off to set cam timing

TDC #1 - crank timing gear gets a black chain link at the timing dot

cams flat

both intake and exhaust get a black timing chain link.


Engine is interference - watch what your doing once the cams are installed in the head...

Are there pistons available which are non interference? What about the chain tension, have you ever done that/know people who have experience doing that?

EDIT: I guess that would lower compression more, and I'm aiming to raise compression. I'm trying to make 500hp NA with high compression (Maybe NOS? if I don't)

no mod to the stock tensioner needed.

As for cams, at what point does the amount of lift introduce clearance issues (valves hitting cylinder walls, etc.)

valves hitting cylinder walls
How would that happen?

More static CR + more valve clearance = new pistons.

Since the valves are at an angle relative to the cylinder, then by definition, because they are not parallel to the cylinder wall, they will eventually hit the cylinder wall. I don't think that will be an issue for any amount of lift you could realistically have.

3.000" lift (not .300") might do it.

Just got around to picking up an 06/07 block, what are the cam situations like these days? Still all custom grinds? Anything off the shelf yet?

no change yet

what have you all been doing for cam specs?

look at comp cams - ecotec

the 4200 shares the same cam geometry as the ecotec - pick 1 of the biggest 3 lobes for the intake/exhaust.