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Old 03-29-2012, 04:47 PM   #1
fixityourselfer
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Default sending head out for machining

I want to send out my dohc head out and get it machined down a little and raise compression.

when i took it off I see there are small indentations in the piston for 2 of the valves.

can this head be machined a little to raise compression, or will ir cause the piston to hit the valves?
if there is some clearance, how much?

the shop can do 1/1000th, or 50/1000ths, or anywere in between, etc etc.

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Old 03-29-2012, 04:55 PM   #2
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Default Re: sending head out for machining

.020"-.040" I believe is what people usually do. The more you shave the head, the more shaving the timing cover the same amount becomes a good idea.

Verify the head and block haven't already been cut down. You don't want to find out the hard way the block's been cut down and cut down the head...pretty sure someone recently had that happen

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Old 03-29-2012, 05:39 PM   #3
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Default Re: sending head out for machining

Quote:
Originally Posted by fetchitfido View Post
.020"-.040" I believe is what people usually do.
does this apply to our dohc saturns? or are you saying a general rule?

I'm just nervous about this specific motor after having seen those 2 indentations in each piston. that seems to indicate that the valves go into those indentations when the piston is at the top.

do I still have enough clearance between the piston top and the valves to grind off .020"-.040" on this specific engine?

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Old 03-29-2012, 06:00 PM   #4
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Default Re: sending head out for machining

Back when SDA sold performance DOHC head's they gave the option of .020", .030" and .040" decking/shaving. Much more then .040 and your getting close to the service limit of ~.060".

I believe the indentations are more of a "just in case" rather then every revolution thing.

If you can think of it to ask(about modifying), somebody already has...a couple of times, on here: www.sixthsphere.com

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Old 03-30-2012, 06:50 AM   #5
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Default Re: sending head out for machining

Quote:
Originally Posted by fetchitfido View Post
Back when SDA sold performance DOHC head's they gave the option of .020", .030" and .040" decking/shaving. Much more then .040 and your getting close to the service limit of ~.060".

I believe the indentations are more of a "just in case" rather then every revolution thing.

If you can think of it to ask(about modifying), somebody already has...a couple of times, on here: www.sixthsphere.com
I disagree with your sig about the bag of scorpions.
that would apply to european vehicles like my fwd volvos and saab. they're a man made pain in the neck

the saturns are so simple and straightforward in comparison never mind the parts are so much cheaper

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Old 03-31-2012, 09:11 PM   #6
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Default Re: sending head out for machining

I wonder if I could get away with machining the head like .015 or so and still use regular gas?

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Old 03-31-2012, 09:35 PM   #7
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Default Re: sending head out for machining

Quote:
Originally Posted by fixityourselfer View Post
I wonder if I could get away with machining the head like .015 or so and still use regular gas?
depends on what you call regular gass, some stations use 87 octain as regular and others use 89(most do around here anyway i think) though i could be wrong.

i guess it depends on how hot this mod makes the engine doesent it?

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Old 03-31-2012, 10:01 PM   #8
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Default Re: sending head out for machining

Quote:
Originally Posted by fixityourselfer View Post
I wonder if I could get away with machining the head like .015 or so and still use regular gas?
You can take off a lot more than that and still use regular gas, but it's not a good idea. The PCM will automatically retard the timing to prevent pinging, which will result in loosing power and mileage. With any significant shave, the decrease in mileage would make the regular gas more expensive than premium (because you'd use more of it).

With a mild shave like .015" you might be able to save money with regular fuel, but it would depend on a lot of factors (climate, driving style, fuel quality, etc, etc). With anything more significant than that, it's often more economical to use premium.

If you want to maximize power, you need premium. Even with the stock compression ratio, premium fuel will sometimes get you a bit more power by allowing more aggressive timing (technically it doesn't increase power, just prevents you from loosing it due to knock retard).

...
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Old 03-31-2012, 10:19 PM   #9
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Default Re: sending head out for machining

With a fresh rebuild and the dual intake cam mod premium costs less per mile than 87 and there is no contest with 89 even with the 5 cent Iowa discount, the 89 is a looser.

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Old 04-01-2012, 03:22 AM   #10
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Default Re: sending head out for machining

How about blending in some e85 to up the octane?

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Old 04-01-2012, 07:42 AM   #11
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Default Re: sending head out for machining

The 89 fuel is E-10 and the BTU difference is sufficient to drop fuel mileage sufficiently to make it not cost effective to use.

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