dogashes

Anyone ever have a head shaved or milled down to increase the compression ratio? Doesn't it alter the timing to the crank?

I know that the best way to increase CR is with pistons, but I am looking for ways to modify a vk45 and there aren't any aftermarket parts for that engine.

VQ35Kompressor

Try going with a thinner head gasket. How many layers is the stock one? If it's like 3, just run 1 layer! You might increase it a little. Next thing up is porting the head, but don't think you want to go there eh? And 3rd option, custom higher cr pistons. But man, that's a lot of money. Maybe call up some of the big dogs and inquire about them making maybe a supercharger. Good luck!

FairladyZ

1. Not worth it you might pick up 5-10 rwhp. If you had cams it would definately help. Not sure how much/if these heads can be milled safely.
2. no

g356gear

iTrader: (12)

Why would it not change the timing?? This is a common problem on Honda's with milled heads

FairladyZ

How does adding compression add timing? It didnt on my Trans Am. Timing has to do with camshafts.

350Zteve

iTrader: (6)

When you mill a cylinder head on an overhead cam engine, you shorten the distance between the crank pulley and the cam gears. This effective changes the CAM timing, not the ignition timing.

FairladyZ

OIC now thanks! I was thinking in terms of an "american" car.
I quoted this

"Head thickness is critical on most overhead cam heads for a couple of reasons. One reason is that some engines have very tight valve-to-piston clearances and valve damage can occur. Also, camshaft timing is affected by lowering the camshaft toward the block because it will retard cam timing causing poor running, unexplained overheating and poor fuel mileage."

Lateapex

iTrader: (9)

However, some engines respond positively to slightly retarded cam timing.

Z1 Performance

iTrader: (564)

you NEVER go toa thinner headgasket...thats a sure fire way to introduce all sorts of problems.

Milling the head can work - its a bit old school, but only a machinest could tell you:

1. if it can be done on these heads
2. how much CR you could gain.
3. you do not retard cam timing on an NA car typically from my experience, you advance it. This is stuff best left to all but the most experienced engine builders and tuners though IMHO.....not something to be ventured into lightly.

Adam

VQ35Kompressor

Sure head milling can and will work if done correctly. But one thing; once you mill the head, you can't go back. Unless you run a thicker head gasket. So I suggested a thinner head gasket. It's safe. Why won't it? If it's a good gasket, and done right, no leaks. Goes both ways, milling too much or running too thin of a head gasket can increase chances of valve tap. But, compression is so darn low, chances are highly unlikely. Unless other things go wrong or red line the $hiet out of the motor and keeping it there... And one other thing, you retard the timing if compression is too high and/or running on lower octane, etc., etc. Most people advance it for race and on race gas...do I here detonation? Lolz...

*Will the engine builders and tuners please stand-up!?!

Z1 Performance

iTrader: (564)

have you ever seen a thinner headgasket offered? I have not, and I think its for good reason..the gasket needs to be of a minimal thickness to beging with. At most I would estimate stock one is 1mm thick

g356gear

iTrader: (12)

Stock gasket is .025" thick

Ben Davis

Yeah milling the heads for CR is not the way to go, the cost/risk ratio is poor and the benifit if it works well is minimal. They cannot take off much to begin with, and this may also limit the cams tou could put in as well.... not worth it unless they are warped!

Z1 Performance

iTrader: (564)

Pretty good guess then by me

VQ35Kompressor

In many race motors, for the low budget minded, milling is an "option" and also thinner head gaskets (for N/A). For fellas with fat wallets, high CR pistons would definitely be the way to go.