# How much did you shave the head to increase compression and was it worth it?



## 89VWdieselGolf (Feb 22, 2004)

I can get my engine head shaved a bit for free at work, just wondering if this creates any advantage. But i still want to keep it street driveable meaning lower octane gas (87-89)
thanks,
Jeff


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## Cyrus #1 (Sep 29, 2005)

*Re: How much did you shave the head to increase compression and was it worth it? (89VWdieselGolf)*

What engine code do you have? If you have a low compression engine you will notice bigger gains than if you have a high compression engine. This is due to pumping losses.


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## 89VWdieselGolf (Feb 22, 2004)

*Re: How much did you shave the head to increase compression and was it worth it? (Cyrus #1)*

RV engine with ME head.....10.0:1 compression if im not mistaken
Just did a compression test last week: 155/160/155/155 (from 1-4 respectivly)


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## 89VWdieselGolf (Feb 22, 2004)

*Re: How much did you shave the head to increase compression and was it worth it? (chickenfriend)*

well i do the odd auto-x, but 1HP.....i'll leave it alone. thanks


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## C LePoudre (Jan 19, 2005)

*Re: How much did you shave the head to increase compression and was it worth it? (89VWdieselGolf)*

link to online calculator for hp gains from increase cr. 
http://www.bgsoflex.com/crchange.html
don't hesitate to take a bit off of your head. If you put a straight edge on it, you'll usually find it isn't flat anyways. I took off 0.040 (~1mm) to see a gain from 10:1 to just over 11:1. Take note that most guys who do this work will look at you pretty funny when you ask them to take that much off. 
According to the calculator above..this gives me a 3hp increase from stock (but it's got some other goodies too). 



_Modified by C LePoudre at 3:55 PM 7-19-2006_


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## 89VWdieselGolf (Feb 22, 2004)

*Re: How much did you shave the head to increase compression and was it worth it? (C LePoudre)*

ya i just calculated it, 1hp.... meh... not worth it.... I'll just get my co-worker to make it straight..... although, is the block guarenteed to be straight or would it warp with the head? (i know its not alot, just normal warp, but i dont want it not to line up ya know)


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## Cyrus #1 (Sep 29, 2005)

*Re: How much did you shave the head to increase compression and was it worth it? (89VWdieselGolf)*

It's highly unlikely the deck of the block is warped. The aluminium head is far more likely to warp from the effects of heat.


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## zero666cool (Apr 17, 2004)

*Re: How much did you shave the head to increase compression and was it worth it? (Cyrus #1)*

i shaved it roughly about 1.2 mm, the maximum you could shave. and i'd say DO NOT do it this much, just slight shave....
the HP gains are unlikely to be noticable, however due to higher CR you'd have more torque and it will help your engine to rev up faster (common problem on the 8vs, takes forever to rev up) http://****************.com/smile/emthup.gif


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## ABA Scirocco (May 30, 2001)

*Re: How much did you shave the head to increase compression and was it worth it? (zero666cool)*


_Quote, originally posted by *zero666cool* »_i shaved it roughly about 1.2 mm, the maximum you could shave. and i'd say DO NOT do it this much, just slight shave....


You can shave off a LOT more than that without compromising the structural integrity of the head, I've seen twice that much removed from an 8v VW head, I'm not recommending you do that, I'm just saying it's possible. 
Probably the best thing to do is to determine what your current compression ratio is, determine what compression ratio you want then have your machine shop calculate how much to shave off the hit your target. As for deciding what compression ratio you want, a good place to start is with your cam manufacturer if you consult with them, they'll often tell you in what range of compression ratios your cam is most effective.


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## zero666cool (Apr 17, 2004)

*Re: How much did you shave the head to increase compression and was it worth it? (ABA Scirocco)*

oh machine shops could do that ? the machine shop that i took the head too didn't even know sizes in inch, he's like give me metric sizes... so i told him about 1mm... and he still didn't get it, so his buddy comes and draws a line with a pen, he's like shave untill you hit this mark.... (and the pen marking was more than 1mm. 1.2 i assumed.)








but as far as i know, after putting the buttom end and head in correct timing, the valves would bearly clear. so i don't think you could shave anything more than that safely (unless if you stack headgaskets, then what's the point of shaving that much)...


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## ABA Scirocco (May 30, 2001)

*Re: How much did you shave the head to increase compression and was it worth it? (zero666cool)*


_Quote, originally posted by *zero666cool* »_oh machine shops could do that ? ... 

Yes, good ones can. Typically you seldom see people shave more than 1.5-2.0mm but it is possible to shave an 8v VW head until you're almost cutting into the spark plug hole, that's TONS, close to 3.0mm. At that, it's absolutely critical to set the valve timing properly if the timing's out too much, the valves will hit but when it's properly timed everything clears, without any extra gaskets or spacers. 


_Modified by ABA Scirocco at 2:38 PM 8-1-2006_


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## zero666cool (Apr 17, 2004)

*Re: How much did you shave the head to increase compression and was it worth it? (ABA Scirocco)*


_Quote, originally posted by *ABA Scirocco* »_
Yes, good ones can. Typically you seldom see people shave more than 1.5-2.0mm but it is possible to shave an 8v VW head until you're almost cutting into the spark plug hole, that's TONS, close to 3.0mm. At that, it's absolutely critical to set the valve timing properly if the timing's out too much, the valves will hit but when it's properly timed everything clears, without any extra gaskets or spacers. 


damn, that's crazy. maybe i should do that just for the heck of it..
do u know how much can you shave off a 16v head ?


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## ABA Scirocco (May 30, 2001)

*Re: How much did you shave the head to increase compression and was it worth it? (zero666cool)*


_Quote, originally posted by *zero666cool* »_
damn, that's crazy. maybe i should do that just for the heck of it..
do u know how much can you shave off a 16v head ?


No but it's a LOT less because the one set of valve seats are fairly close to the surface, there's only so much you can take off before you start to cut into the seats.
BTW, I've seen an 8v head shaved until the chambers were 17cc, stock is 30cc, I'm not sure what that translates into in terms of how thick the cut was but it's had to be close to 3mm.


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## zero666cool (Apr 17, 2004)

*Re: How much did you shave the head to increase compression and was it worth it? (ABA Scirocco)*

^^ damn, 
yah i know 16v head is a lot less cuz the intake valves are already interfeering with pistons. i had heard 6 thousandths or something but again i want to make sure before i do anything to my freshly ported heat.


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## ABA Scirocco (May 30, 2001)

*Re: How much did you shave the head to increase compression and was it worth it? (zero666cool)*

I've got a couple 16v heads kicking around, maybe I'll get out a straight edge and feeler gauges and check one of them out. I'm just starting to get into the 16v's myself, I'm planning to do some crazy stuff but right now, I'm still in the research phase of that, I really haven't done much of anything yet.


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## CaptEditor (Feb 23, 2004)

I wouldn't bother shaving additional material off of your head for performance gains. I think it messes with the cam timing more than it benefits power. if you shave significant material off your head, you will need an adjustable cam gear to time it properly.
while rebuilding my 8v head I only took .010 inches off because that's all it took to reemove the scratches und unlevelness of the head. Just take off what you need to.

-Kevin


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## ABA Scirocco (May 30, 2001)

*Re: (CaptEditor)*


_Quote, originally posted by *CaptEditor* »_remove the scratches und unlevelness of the head. Just take off what you need to.
-Kevin

For most people. most of the time, that's pretty sound advice.


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## outrunner (Jan 11, 2002)

*Re: (ABA Scirocco)*

I'm looking to shave 0.020" off the bottom of my head, just curious about how much more that will boost the compression ratio?
Also if I do shave some off the bottom of my head, I have an adjustable cam gear, would i need to retard or advance the cam?


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## ABA Scirocco (May 30, 2001)

*Re: (outrunner)*

.020" isn't a lot, you wouldn't need to worry about the cam timing and it'll raise the C.R. by about 0.5 of a point. As a general rule, shaving a head retards the cam timing so you'd normally need to advance the timing to bring it back to zero. 
This doesn't apply to your particular case but if you're interested in knowing how to zero a cam, check my post in this thread 


_Modified by ABA Scirocco at 9:26 PM 8-9-2006_


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## outrunner (Jan 11, 2002)

*Re: (ABA Scirocco)*

ABA Scirocco - What would you recommend that I shave off the bottom of the head, I'm looking at possibly getting close to 12:1 compression. I believe right now I have about 10:1 on a 2.0 9a bottom end with the dished pistons (maybe less).
I used to have an 2.0 ABA that my machine shop decked for me, he ended up taking off quite abit, because in the end, after bolting up my stock head i was making 13:1, it was alot of fun to drive.


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## ABA Scirocco (May 30, 2001)

*Re: (outrunner)*

Off hand, I can't really say. I'd recommend that you cc your block and calculate what the volume of the head chambers need to be in order to get your target compression ratio. With that information in hand, go to your favourite machine shop, tell them what your requirement are and see if they are able or willing to comply, if not try another machine shop.
A word of caution, don't rely on on-line calculators like the one at http://not2fast.com/ to determine how much to remove, they're good for giving you a ballpark figure and will get you pretty close but for the precision you want, there no replacement for real measurements.


_Modified by ABA Scirocco at 10:08 PM 8-9-2006_


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