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a friend of mine was talking to me about things to do in order to increase horsepower and he mentioned that you can take the head to a machine shop and have it cut down to increase the compression. Now i have no doubt that this works, but how much power could i expect and how much could i take off before there would be valve interference?
 

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Milling the head for increased compression will change the cam timing; something that's not good. The best way to increase compression is with higher compression pistons.
 

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If I'm not totally incorrect I'd say that DOHC or SOHC heads won't have any affect on head timing or valve lif because cams are placed on head and are pressing shim-plates which presses valves. And when you mill your head to be lower only thing you have to worry is to have chain (on GA16DE) tight. There are not any cross sections that changes when you mill your head betveen head and valves. Though other thing to worry is not to mill too much from head so your valves wouldn't hit on pistons.

Also remember that it isn't always clear that more you mill away is better.

- No-Pain -
 

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Milling the head will certainly retard the cam timing, as well as physically bringing the valves close to the pistons. If there was a way to correct the cam timing (via aftermarket cam gears) then I'd say you could get away with it, but as no company offers these gears it's best to stay away from this method of increasing compression.

Best bet is to have custom pistons made with a higher static compression ratio.

Bob
 

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I have custom flat top with 250 psi with stock cams (stock head) but my friend have std. bore with D16 ZC 0.40 pistons, (1mm shave dome) maybe 12.0:1 CR, have 295 psi with stock cams.
 

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Pauter machine was able to do rods and pistons for high or low compression turbo pistons for the GA16DE. they need your samples. My uncle (nissan master for 35 years, told me that you can mill the head, but never did this, so he did not know how much you could do this safely. I assume if you had JWT cams, more lift, you need that point of reference or even more lift cams custom. to see how much of the head you can mill off. you would loose combustion chamber quench area though. would milling the head be that good then? I wonder typically how much you can remove off the GA16DE head. we need someone to experiment!!! a machine shop that can run the interference specs.

Chris 92 GA sentra
 

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you would loose combustion chamber quench area though. would milling the head be that good then? I wonder typically how much you can remove off the GA16DE head.
Actually with a GA16DE you would *slightly* increase quench area if you milled the head. The chamber outer permimeter would dimensionally shrink, exposing more 'flat' area of the head and increasing the quench. Good for N/A, not as much for turbo (nor needed). I actually reduced the quench area on my GA16DE head for turbo use by unshrouding the chambers. It dropped the compression with the stock pistons as well.

Bob
 

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Importperformanceparts.com offers a rebuild kit for the GA16DE with 77mm Wiseco or Ross pistons (your choice), which makes the engine a 10:1 compression ratio. You don't have to deck the head, or adjust your timing. Just bore your cylinders to accommodate the 1mm larger diametre pistons.

To be honest, with the GA16DE having a relatively low rev-limit, why would you want a high-comp engine? You can get E-series (either E16s or E16i) connecting rods, and attached to your stock pistons, drops the compression ratio to in the 8s. Perfect for a turbo engine. The GA16DE loves boost, as well.
 

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I think the best thing to say is that milling the head really wouldnt increase compression all that much. It's usually only done to correct for a mildly warped head, and they only take a few thousands off of it. My uncle has been building drag racing engines for about 50 years, he's done the machine work on a few of my engines, and he never even takes into account the change in compression milling the head will do, it's that negligable. Unless off course you mill it a WHOLE LOT, which just isnt a reality in most cases as most heads cant be milled hardly at all safely.

I dont see how milling the head would change overhead timing, but i'm a pushrod guy when it comes to performance. I'd think it would put a tiny bit of slack in the chain, which a tensioner would adjust, but thats just a quick guess, no experience with it. But the main point is that milling the head is a very minor thing to do performance wise (especially in a 4 cyl), not really worth the effort to just do that. better pistons would be the way to go.
 

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yes but the length of chain changes from the crank sprocket to the head sprocket, since this only adjustable in whole links the cam timing will change. So you have to live with it, if its small, then ok, or adjust the timing with an adjustable cam gear if you remove a lot of material or you want to get it exactly to spec.
the amount of change can be calculated.
 
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