Shaving the head for bigger bangs

[hessam69]

Quote from stealths page:

I have long believed that to remove material from the deck surface in amounts greater than the absolute minimum needed to restore flatness was not wise; whether the head be iron or aluminum. As a result of this forced, but not unwelcomed or regretted, excercise and investigation; my bias against such material removal has only intensified: to "shave a head" to raise compression ratio, especially on an aluminum head, is very ill-advised; and to do that on an aluminum head used in a boosted motor is, as I have come to see things, a very stupid and counterproductive idea....if you are concerned with longevity and durability.

This goes against John Vanlandinghams idea that you should shave 1.5mm off the head.

So who's right?

[culberro]

All of us who have shaved more than 2mm from a head without any issues.

[VB242]

You can get a Cometic gasket as thick as you need the counter the effects of cutting too much off the head. The last one I ordered was 2.6mm thick.

[hessam69]

That's a thick gasket!

[hessam69]

So what happens when I shave my head that much and I use the pinto cam belt but my engine is a B230FB with a round tooth cam belt?

[culberro]

Originally Posted by hessam69

So what happens when I shave my head that much and I use the pinto cam belt but my engine is a B230FB with a round tooth cam belt?

There’s a round tooth belt that will work. I think it’s a Hyundai or something??? Klr142 knows the exact belt, as he’s running it.
Or switch over to square tooth gears.

[towerymt]

Originally Posted by hessam69

Quote from stealths page:

I have long believed that to remove material from the deck surface in amounts greater than the absolute minimum needed to restore flatness was not wise; whether the head be iron or aluminum. As a result of this forced, but not unwelcomed or regretted, excercise and investigation; my bias against such material removal has only intensified: to "shave a head" to raise compression ratio, especially on an aluminum head, is very ill-advised; and to do that on an aluminum head used in a boosted motor is, as I have come to see things, a very stupid and counterproductive idea....if you are concerned with longevity and durability.

That last part, in bold, is very important.

[NotSoFresh]

Originally Posted by towerymt

That last part, in bold, is very important.

If you are going to go as far as shaving the head, with the costs and risks involved, might as well just leave the head alone and put in higher comp pistons, and do it the right way.

Or just turn up the boost.

[mikep]

Machining the deck of the block gives you more bang per thousandth.

[culberro]

Originally Posted by mikep

Machining the deck of the block gives you more bang per thousandth.

But less bang per $$$...

[Dirty Rick]

Originally Posted by mikep

Machining the deck of the block gives you more bang per thousandth.

Exactly! plus you get more squish as the piston gets nearer to the head.

More squish makes more turbulence.

More turbulence makes a more homogenized fuel mixture and helps getting all the fuel lit sooner.

Bumpy pistons get in the way of flame propagation.

So over the course of time it's not so expensive to deck the block.

There is also the piston to valve clearance to be concerned about, you gotta have room for the .900" lift cam!

[shoestring]

Well the Greenbook says you can go 0.020" on a head recondition, so you can do at least that. Run that with a thinner head gasket and you can pick up a half point static or so. I run N/A and am over 2.5mm milled off, no problem.

[klr142]

Shorter timing belt thread:
http://forums.turbobricks.com/showthread.php?t=235689

I've run .040" off a 530 for many years(N/A!) and we just installed a BCP 405 head with 3mm/0.123" off it on our endurance race car that was previously run with 2mm off without issue. Hopefully it continues to have no issue... Still non-turbo.

[klr142]

Originally Posted by hessam69

So who's right?

They both are. It depends on your goals and usage, just like anything else. The more material you have in the head, the stronger it is and better able to deal with heat. The less you have, the weaker it is and less able to absorb/dissipate heat. In a non-turbo application, I don't think the full strength, original head matters. People who aren't in the US who have been modifying these things for years have been shaving 2mm off of them for years and years and years with success. I haven't heard of a car with an issue due to being shaved before, but I don't sit online all day and read about this on forums all over the world.

Originally Posted by VB242

You can get a Cometic gasket as thick as you need the counter the effects of cutting too much off the head. The last one I ordered was 2.6mm thick.

If your pistons aren't sticking out of the block a ton, that is one way to lower compression but a horrible way to promote good combustion as you want the pistons to be, at most, 1mm/0.040" away from the head surface in a proper build. I would open up the combustion chamber on the cylinder head if compression was too high, well before putting such a thick gasket on it. But, both work and have been done.

Originally Posted by hessam69

So what happens when I shave my head that much and I use the pinto cam belt but my engine is a B230FB with a round tooth cam belt?

TB089/MD140228 belt.

Originally Posted by NotSoFresh

If you are going to go as far as shaving the head, with the costs and risks involved, might as well just leave the head alone and put in higher comp pistons, and do it the right way.

Or just turn up the boost.

Well, pistons are much more complicated than just yanking the head off for a skim and blend the edge of the chamber so it's not sharp(with at least a 0.5mm bevel preferred). But yes, turning up the boost is the easiest way as long as you're able to deal with the heat and fuel requirements. A thinner headgasket is the best/easiet option, but you will want to have the head resurfaced anyway so you might as well take some off.

Originally Posted by mikep

Machining the deck of the block gives you more bang per thousandth.

Or thin headgasket. On B21 and B23 motors a thinner headgasket still might not be enough to get your pistons within 1mm of the head, though, so those engines commonly need the block's deck surface machined. On B230 engines, the pistons are usually already flush or out of the bore, so you can get the proper piston-head clearance by going to a thinner headgasket.

Originally Posted by Dirty Rick

Exactly! plus you get more squish as the piston gets nearer to the head.

More squish makes more turbulence.

More turbulence makes a more homogenized fuel mixture and helps getting all the fuel lit sooner.

Bumpy pistons get in the way of flame propagation.

So over the course of time it's not so expensive to deck the block.

On a B21/B23.

[NotSoFresh]

Originally Posted by klr142

Well, pistons are much more complicated than just yanking the head off for a skim and blend the edge of the chamber so it's not sharp(with at least a 0.5mm bevel preferred). But yes, turning up the boost is the easiest way as long as you're able to deal with the heat and fuel requirements. A thinner headgasket is the best/easiet option, but you will want to have the head resurfaced anyway so you might as well take some off.

In for a penny, in for a pound.
The reality is, skimming is minor compared to what the Swedes and Norwegians do.
Here is a Norwegian thread about porting the 530 with bigger valves.
I'm pretty sure somewhere in this one is a guy relocated the head 3 mm to the exhaust side to fit bigger valves.
http://forum.vccn.no/showthread.php?...60-topp!/page8
You can google translate it, or just scroll through the pictures.

[redblockpowered]

2.5mm works great in an N/A application. Most I've read about is something like 3-4mm, but I won't speak on anything I don't have personal experience with.

[klr142]

Shoestring, just to confirm, no combustion chamber mods aside from shaving the head? And on the ignition tuning, is it less aggressive than stock at any point or would you be able to run stock ignition timing if you wanted? I’m trying to help a friend get his car faster and he’s worried about detonation with 2mm off a 405 head on pump gas.

Originally Posted by redblockpowered

2.5mm works great in an N/A application. Most I've read about is something like 3-4mm, but I won't speak on anything I don't have personal experience with.

You’ve run it before? What was the rest of the setup and what gas did you run?

[shoestring]

Originally Posted by klr142

Shoestring, just to confirm, no combustion chamber mods aside from shaving the head? And on the ignition tuning, is it less aggressive than stock at any point or would you be able to run stock ignition timing if you wanted? I’m trying to help a friend get his car faster and he’s worried about detonation with 2mm off a 405 head on pump gas.
You’ve run it before? What was the rest of the setup and what gas did you run?

No mods, shave only. 530 head. There is less overall ignition timing than the stock map in the -169 EZ116K we use. If you're using EZ116K, you could use the -3 or even -6 pinout grounding to achieve a similar result. If not, you probably have a distributor you can crank back? The key to all this is matching cam timing to static compression ratio to target a specific dynamic compression ratio. Dynamic compression ratio of 8.0 or thereabouts seems to ring a bell. Checking the stats on our race engine, we have a K cam in a 10.9:1 B230F and that's about 7.8:1 dynamic. We run that on pump 93 octane Shell.

B230Fs were not anywhere near the advertised 9.8:1. The couple I've measured were more like 9.1:1. I had to cut the head in my daily 0.040" just to get to 9.8:1, on a stock head gasket. Ran it for years on 87 pump Shell with an A cam with no problem. Dynamic compression on this is about 7.5:1. Recently switched to a V cam, still no problem. This is an EGR car, so that might be helping me out a little.

http://www.wallaceracing.com/dynamic-cr.php

[Dirty Rick]

EGR only works in cruise, when the pedal goes to the metal EGR is off.

SO EGR will only help in part throttle conditions.

[shoestring]

Originally Posted by Dirty Rick

EGR only works in cruise, when the pedal goes to the metal EGR is off.

SO EGR will only help in part throttle conditions.

Right. In many instances, part throttle might be when you are most detonation sensitive. Lean mix and heavy advance.

[OttoB]

Gasoline EGR is for better fuel economy, less oxygen needs more volumetric efficiency, and that means lower pumping losses.

[Fred Gwynne]

I have a few real beginner questions for you folks. Is there a difference between shaving, skimming and decking? Is one for the head while the other is for the block?

Also, if you remove material from the head that means that the valves will now be closer to each piston. If you use a high lift cam such as a "k" cam then the valves may collide with the pistons if too much metal is taken off of the head. Is that correct?

What exactly does shimming mean? Are the valves or is the cam shimmed? Is the idea there to keep the valves from hitting the piston?


Thanks for your help.

[2turbotoys]

Fred Gwynne, ya gotta start your own thread for those questions, we don't do threadjacking here.

Hessam, what car/engine combo are you talking about? A lot of people have thrown opinions in here, maybe they know what you have, but you haven't stated if its a factory turbo motor, a +T or NA, that makes a huge difference in the answers you will get.

[740atl]

Originally Posted by 2turbotoys

Fred Gwynne, ya gotta start your own thread for those questions, we don't do threadjacking here.

or just answer his questions.

Originally Posted by Fred Gwynne

I have a few real beginner questions for you folks. Is there a difference between shaving, skimming and decking? Is one for the head while the other is for the block?

Also, if you remove material from the head that means that the valves will now be closer to each piston. If you use a high lift cam such as a "k" cam then the valves may collide with the pistons if too much metal is taken off of the head. Is that correct?

What exactly does shimming mean? Are the valves or is the cam shimmed? Is the idea there to keep the valves from hitting the piston?


Thanks for your help.

You can shave the head. Take a bit off. Yes to the valve q. It also raises cr or is just used to correct a warped head.

You can deck a block... similar concept. This brings the pistons closer to the head. Used to correct a block surface or decrease squish clearance. There are some performance benefits to this.

You can also get the pistons closer to the head by using a thinner headgasket.

In a Volvo application shimming refers to changing the distance between the camshaft and the lifters. Typically by adding or removing shims of a specific thickness.

To keep a valve away from the piston typically you cut a valve relief into the piston top.

[classicswede]

Skimming is the English word and shaving is the US word for removing material off the cylinder head.

Decking is removing material from the block