# Shaving 8V heads for increased compression ratio



## KenRally (Mar 3, 2002)

What is the maximum amount that can be shaved off 8V heads (assume GTI 10:1)
Trying to achieve 13.0CR for Rally race car.
Engine will initially be a 1.8L.
Race gas will be used.
KenRally


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## ATS (Jan 19, 2002)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

the quick and dirty way to figure (or estimate) is every 0.10" shaved = .1 compression change, so from a 8.5:1 JH engine if you shaved 0.30 for example you would be at 8.8:1 (approx) compression.
in your case you need to change the block to a 3A or ABA to get 10:1 and then work the shaving and overboruing of pistons into the equation.
13:1 from 8,5:1 would require 0.45" shaved (almost 1/2" here) and you would not possibly perform such a shave without mechanical serious problems (valves space to piston head for example is not 1/2" away from each other on a Stock JH engine.
you need to rethink you need/wantings here.


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## A1Rocco (Oct 6, 2001)

*Re: Shaving 8V heads for increased compression ratio (ATS)*

There is a very recent and long discussion about compression ratio's and headgaskets in a thread called "Group A questions..." on this page. See the whole thread for the complete discussion(ignore the banter) so you understand the arguement and what the results were. You will find that 1mm shave = .675-.7 of a compression pt., that's .39"= 1mm= .675-.7. Therefore an 8.5:1 JH motor would go to 9.85 with a 2mm shave.
Starting with a 10.0:1 GTI 1.8L from any 86 up GTI/GLI and then shaving 2mm would result in 11.35:1. By using a Group A headgasket you could get it to just over 11.7:1 I think.
The best way by far would be to build the short block with custom pistons as it would allow you to keep all the material in the head for good strength and better heat dissapation characteristics. Afterall we are talking about a Rally engine that will be raced and will generate a lot more heat then a street motor with much less compression. Build it with 12.5 pistons and a Group A headgasket.




[Modified by A1Rocco, 7:00 PM 3-3-2002]


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

Thank you for your responses,
I am sorry if this question seems stupid,
I am just trying to learn about VW modifications and their limits.
I understand I can not shave 0.500" off the heads, there would
be no more head left, and the water jackets would be exposed.
I understand that custom pistons are the way to go, but also the
most expensive route. I am trying to figure out how far I can take 
a 1.8L 8V engine before I need all the custom stuff. 
I am new to the VW's.
I am just seeking the experience of people who have shaved
heads, shaved blocks, and overbored cylinders as to resonable
limits and maximum limits for VW 8V engines.
You may now start flaming me,
KenRally


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## ABA Scirocco (May 30, 2001)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

You can shave off at least 2mm off of the head, due to the shape of the combustion chambers there is however diminishing returns i.e. you get more of a CR increase with the 1st mm than you do with the 2nd mm. I don't think there's enough material on the head to get anywhere close to 13:1, you're going to need different pistons. The easiest ones to find would be the flat top 16v pistons or you could put a 8v head on a 16v block. For a 1.8L engine 16v pistons with about .025" shaved off the head should put you in the right ball park, you'll need to cc a head and block to know for sure.


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## ABA Scirocco (May 30, 2001)

*Re: Shaving 8V heads for increased compression ratio (ABA Scirocco)*

I just crunched a few numbers, it may be possible to get to 13.0:1 just by shaving the head, I've seen a head shaved to the point where it had 17cc chambers if you did that to an engine with stock 10:1 CR you'd be close.


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## raylomas26 (Dec 14, 2001)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

Keep in mind that by shaving the head, you move the camshaft closer to the crankshaft. You need to compensate for the change in cam timing.


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

Thanks again for the responses,
I understand I will move the cam timing (retarded).
I will purchase an adjustable cam timing gear, and/or
jump the belt one tooth (one tooth = 8.18 degrees??).
Where are you geting the numbers to crunch. I understand
the math, just don't have the numbers to crunch.
According to my rough calculations with a 4 inch/102 mm(guess)
44 tooth(guess) diameter cam sprocket there willl be
around 1 degree retard per 0.035" milled off the head.
Shall we say 1 degree retard per 1mm (0.0394") milled
off the head. 2 degrees retard would probably help my
goal in 4000-8000 RPM torque. 
I have seen 2 mm shave as maybe ok, and 2.5 mm shave as
scary, anybody wish to comment on real life experience.
Thank you all,
KenRally


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## A1Rocco (Oct 6, 2001)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

Ken, I was commenting from real life expirience, I guess it just wasn't obvious. I did an 83 GTI head for a friends car several years ago with a 2mm shave. It was originally modified to be used on my 1.6L 1980 Scirocco but was re-modified to go on my freinds GTI. We did it with a full port job, 5 angle grind, unshrouded chambers and a G-grind and it was great. 
I'm currently preparing an 84 GTI air shroud injector head with huge ports for an Audi 5000 Turbo intake to go on a 3A 2.0L but it will not require as much of a shave. At 10.5:1 stock I may only take off 1mm. This will be a street motor on pump gas. 
I would think that a 2mm shave with the accompanied retard in the cam timing would work out good for you, however it really depends on the cam lift and duration you choose to run as well as how much advance or retard is ground into the the cam to begin with.


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (A1Rocco)*

Thanks A1Rocco,
current cam under consideration is Schrick solid 288 dur 0.460" lift.
36/72 72/36 timing events.
That lift seems a little high for a 40mm inlet valve.
Did you manage larger than 40mm inlet valve.
Any other ideas for solid lifter 280+ cams and places to
buy in USA. The schrick's are a little pricey, but I have heard
they are the best.
KenRally


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## CABBY2L16V (Oct 19, 1999)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

Ken, I've known people to shave their heads 100 thousandths with no reliability problems. Just need a knock sensor or euro distributor.
BTW. I have the excact cam you want, It's the Schrick Assymetrical 288 degree solid lifter cam. I only put about 5k on it. You can have it for $225 shipped. http://****************.com/smile/emthup.gif


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## A1Rocco (Oct 6, 2001)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

Ken, I'm planning on using 42mm intakes and 35mm exhausts. They can also be done in 7mm stems. The Schrick 280 Assymmetric is a great cam for all out top end and still streetable. Do a search for the Cam Review Thread that I started several weks ago, all this stuff plus the links for other cams and there specs is listed in that thread. That was the purpose of the thread.
Cabby2l16v, the 288 is not an assymmetric grind. 
See joserotger.hypermart.net/camshaft for cam specs on many popular cams. Un fortunately the 280 assym. is not listed.


[Modified by A1Rocco, 8:16 PM 3-5-2002]


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## vwvapors.com (Jul 3, 2001)

*Re: Shaving 8V heads for increased compression ratio (A1Rocco)*

I know this is a dumd question after all this but I have a JH block and I'm confused because of the metric to standard equations. How much is 1mm in standard US sizes? What would the comp be with a 1mm mill?


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## A1Rocco (Oct 6, 2001)

*Re: Shaving 8V heads for increased compression ratio (vwvapors.com)*

I already said exactly that in the 3rd post up top.


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (A1Rocco)*

Ahhhh, A1Rocco,
now we are talking.
I was thinking along those lines,
what about 43.5mm intakes with 7mm stems.
Are 6mm stems available or are they too weak?
Why do the bronze valve guides stick so far down in the
flow path. I have seen them tapered for performance,
but why not taper them harder and cut them off shorter.
I'm not building a 100,000 mile engine here, it will see
it's race time at 4500-8000 RPM, and transits at 3000-4000 RPM.
My simulations indicate strangulation at the intake valve,
even with absurd lift, at the higher RPM. I have yet to
get my hands on a loose head and do port diameter measuments
up through the throat to see if there are tighter restictions,
but that overly protuding intake valve guide sure looks like one of them.
KenRally

[Modified by KenRally, 4:49 AM 3-6-2002]


[Modified by KenRally, 4:59 AM 3-6-2002]


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

I edited the above to
Whoops, I meant 43.5 mm intake valves(was 34.5),
DUH
KenRally
DoubleVdub DUH
there's an edit


[Modified by KenRally, 4:50 AM 3-6-2002]


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## ABA Scirocco (May 30, 2001)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

quote:[HR][/HR]Whoops, I meant 43.5 mm intake valves,
DUH
KenRally[HR][/HR]​Wow, that's a BIG valve, the biggest I've seen in a VW head is 42mm. I'd be worried that a valve that big would be severely shrouded by the side the the combustion chamber and cylinder wall. I wouldn't be surprised if a smaller valve flowed better because of it.


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (ABA Scirocco)*

For vwvapors.com
1 inch = 2.54 cm (centimeters)
1 inch = 25.4 mm (millimeters)
Just memorize 25.4
to convert to inches take the inverse.
1/25.4
so 1mm = 1/25.4 of an inch or 0.0394" (actually 0.03937")
or for a rough estimate (pretty close just use 0.040" per mm).
so they say I can take 100 thous (0.100") off my head,
so 0.100/0.040 = 2.5 mm ( actually 0.100 * 25.4 = 2.54 mm)
Use 0.040" for guessing math and 25.4 or 1/25.4 for spreadsheets,
and serious compression or interferance calculations.
Sorry if off topic,
KenRally


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (ABA Scirocco)*

Yes, it is a big valve.
I know it will be shrouded,
but LOOK at the pattern on the valves in an 8V,
and the intake ports for a 8V.
The intake will flow in a spiral into the cylinder,
unlike a 16V which will tumble into the cylinder.
The exposed edge of a spiraled flow would "PROBABLY"
benefit from more exposed trailing edge area for increased
edge area as the spiral grows below it. I know I will strangle
some side bleed into the spiral. At high RPM the air will be
flowing fast and will be resistant to changing directions, so
a big valve will feed the spiral more effeciently. A smaller
valve would help low RPM torque, something I am not
after.
KenRally


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## ABA Scirocco (May 30, 2001)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

Sounds like you've done your home work. You've got an interesting project underway, I hope you're post to let us know how everything turns out, I'm sure I'm not the only one who's interested,


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (ABA Scirocco)*

Thanks ABA Scirocco,
I not new to engines,
Just new to VW's
KenRally


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## vwpat (Oct 25, 2000)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

Just use 16V flat top pistons. In a 1.8 they yield ~13:1.


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## A1Rocco (Oct 6, 2001)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

When going oversize with the valves the largest you can fit is a 42mm intake with a 35mm exhaust. Even with this size the valveseats which have to be changed will touch each other in the center and the valves will be very close to each other. The only way to get a bigger set in there is to make your own head with a wider valve spacing but them you would have to increase the bore size to 83+mm to fit it in the chamber.


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## G60Jetta2dr (Feb 11, 2000)

*Re: Shaving 8V heads for increased compression ratio (vwpat)*

quote:[HR][/HR]Just use 16V flat top pistons. In a 1.8 they yield ~13:1.







[HR][/HR]​Dang you beat me to it. He's right ya know. I happen to have a set. $38 shipped.


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (G60Jetta2dr)*

To G60Jetta2dr,
Is $38 for the four,
email me at
[email protected]
KenRally
13.0CR is a PayPal away


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (A1Rocco)*

Thanks A1Rocco,
Where can I get the 42 mm intakes and 35 mm exhaust valves
and seats. Is there actually an intake valve seat (That's unusual).
Preferably small stemmed on intake. What about shorter valve
guides or heavy taper and truncation on valve guides.
KenRally
ps. Beryllium (it's a metal) would be a SUPER good exhaust valve
guide seat, the only problem is that Beryllium metal is a DEADLY
poison.


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## rough_8v (Mar 30, 2001)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

Beryllium isn't used for valves/seats because it's too brittle. It is poisonous the same sort of way that asbestos is, i.e it is fine when in a lump, but harmful as a dust - in fact I use tools made from beryllium copper at work, because it is a non-sparking metal! Pretty pricey stuff too








PRZ


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## A1Rocco (Oct 6, 2001)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

I'm checking into the bigger valves with 7mm stems from a local source, several poeple have expressed interest. There are shorter guides available and they are commonly used, also tapering the stock ones is common. 
Why is an intake valve seat unusual? How else would you cuts the angles you want?


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## ABA Scirocco (May 30, 2001)

*Re: Shaving 8V heads for increased compression ratio (A1Rocco)*

For an intake valve 42mm with a 7mm stem try a 84-88 Nissan 300ZX 3.0L sohc vg30d turbo vg30t. This valve is 125.8mm long so you'd have to cut it and machine in a new retainer groove.
I think Ken's probably used to working with cast iron heads, that would explain the comment about intake valve seats.


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## A1Rocco (Oct 6, 2001)

*Re: Shaving 8V heads for increased compression ratio (ABA Scirocco)*

Cast Iron! What's that!


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## ABA Scirocco (May 30, 2001)

*Re: Shaving 8V heads for increased compression ratio (A1Rocco)*

quote:[HR][/HR]Cast Iron! What's that!







[HR][/HR]​That what they use inNorth American engines you know Ford and what not.


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## A1Rocco (Oct 6, 2001)

*Re: Shaving 8V heads for increased compression ratio (ABA Scirocco)*

Oh, you mean Ford/Chev/Dodge stuff. My Dad had one of those back in the 70's. It weighed 4000lbs and started to rust into the ground, he sold it for a song.








It had a police pursuit 429/4 barrel that I think is powering a lobster trawler in Nova Scotia now.










[Modified by A1Rocco, 9:35 PM 3-7-2002]


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## ABA Scirocco (May 30, 2001)

*Re: Shaving 8V heads for increased compression ratio (A1Rocco)*

Actually, I was talking about those 4 cylinder grocery getters like escorts and cavaliers, eeew I feel the sudden need to wash my mouth out with soap and hose down my keyboard.


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## A1Rocco (Oct 6, 2001)

*Re: Shaving 8V heads for increased compression ratio (ABA Scirocco)*

emmm Chevette, cooool.


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## ABA Scirocco (May 30, 2001)

*Re: Shaving 8V heads for increased compression ratio (A1Rocco)*

Now we're on the same page.


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (ABA Scirocco)*

OK guys,
That was dam*** ****** funny.
Ok, so am I banned, because I play with Chevy's.
Or, can I still play as long as it is only a VW???
Whoops,
I forgot to mention the Mitsubishi Eclipse GSX turbo
sitting out in my driveway, that I just ordered the
16G turbo cartridge for, with plans to take it to a 20G
if my water/methanol injection system works properly
with the 16G.
Ok,
am I now SUPER BANNED?????
KenRally


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## ABA Scirocco (May 30, 2001)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

You're not banned just on probation


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## A1Rocco (Oct 6, 2001)

*Re: Shaving 8V heads for increased compression ratio (ABA Scirocco)*

He has too many cars, I say we ban him.


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (parz8v)*

To Parz8V,
Beryllium has been used for valve seats.
Not in streat motors,
but in VERY VERY VERY special race motors.
If you alloy Beryllium with other metals,
then the poisoness disappears,
and you also ruin the EXCELLENT heat transfer
properties of pure Beryllium
KenRally


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## vwpat (Oct 25, 2000)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

quote:[HR][/HR]
Where can I get the 42 mm intakes and 35 mm exhaust valves
and seats[HR][/HR]​www.eurospecsport.com


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## rough_8v (Mar 30, 2001)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

Seems you need to use copper beryllium valve seats when you are running titanium valves! No danger of me needing a set in the near future then.......








PRZ


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (vwpat)*

I also want to know where to get the valves, seats, short guides, etc.
Ok guys,
I'm Rally Racing this Saturday March 16th.
This is a big time race called Cherokee Trails right here
in Chattanooga, Tennessee.
the website is: http://www.cherokeetrailsrally.com 
I will be running in the Nationals (ProRally). Cherokee Trails is part
of the SCCA ProRally series, and is also part of CNAR
FIA championship of North America (Canada, USA, Mexico).
I will be codriving (it takes two people for rally). My Driver is
Roland McIvor. Our car number is #514. It is a turbocharged
all wheel drive Mitsubishi Eclipse (sorry guys, my VW's are not ready yet).
You might also be able to check our progress on http://www.specialstage.com 
in the Forums section under USA.
Please be nice if you post anything.
The race starts on Saturday at 6:00AM and lasts till around midnight.








If anybodywants to see what the hell Rally racing is, Speedvision
(The Speed Channel now) is showing the WRC FIA rally racing
tonight (Friday, March 8th) and Saturday from 11:00PM till midnight EST.
They don't have any Chevy's, but there are a few Ford's that will make you
drool.
My posts will be limited (probably none) until after the race. As the codriver 
I have to do all the paper work and scheduling and other things. Although I
might check this thread for some encouragment and inspiration.
How about a round of thumbs up and wishes of good luck from the
group. http://****************.com/smile/emthup.gif 
I will post the results in a new thread if there is interest assuming I don't
die or end up in the hospital. We will be racing at high speed on gravel
next to 500 foot cliffs. There are no guardrails








KenRally
Ken Blain (on the car and the results)
car #514 http://****************.com/smile/emthup.gif


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## wvonkessler (Mar 5, 2002)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

Good luck on the rally http://****************.com/smile/emthup.gif You won't be beating DJ and me.
Wilson - Navigator for the #816 Mazda 323 GTX (boy, I wish VW had made a 4 wheel drive rally monster . . . Oh yeah, they did, the RallyeGolf, and I want one, but VWAG in their infinite wisdom did not sell it in the NA market . . . I know of two over here, much to rare to rally, and $$$). So, I guess I have to settle for a look-alike. 
Come to think of it, this years National ClubRally champions in Group 2 are in an Isuzu Impulse - which we all know was a Scirocco that VW rejected.


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (wvonkessler)*

Hey Wilson,
if we are doing the VW thing Saturday morning,
I am supposed to go over to Rivergate at around noon
on Saturday to help with signage for the rally, etc.
KenRally


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## A1Rocco (Oct 6, 2001)

*Re: Shaving 8V heads for increased compression ratio (KenRally)*

Valves and guides etc. available from Eurospec thru a dealer, check their site for the dealer list.


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## KenRally (Mar 3, 2002)

*Re: Shaving 8V heads for increased compression ratio (A1Rocco)*

Thanks A1Rocco,
KenRally


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