Shaving B18c head. inputs please

[tekung89]

wat is the max mm u are able to take off the b18c head? been doing some reading and most take .20 off their heads which reduces the combustion chamber volume. in doing so u gain more compression, allowing ur engine to yield more power out of ur aftermarket goodies.

what are the average compression gain figures from this?

[Limbo]

i don't think there is a real limit, just depends on what compression you want to end up with and if the rest of your gear & tuning will handle the high compression.

I think this one would be best to speak with a proper engine builder and not net mechs.
Its one of those things that alot of factors need to be taken into consideration

[JasonGilholme]

there would be a limit.

I guess when valves start hitting pistons, you've gone too far lol

Seek profesional advice. :thumbsup:

[spardikis]

Before you shave your head - why not think about running hi comp head gasket.

And as a general rule of thumb -

If you can take .5mm out of the head gasket you will gain .25:1 static compression. If you can take 1mm out you will gain .6:1 static compression.


There most certainly is a limit!

From memory the service limit is a abosolute minimum of 0.75mm piston to head clearance - standard is I think 1.5mm - I will confirm later on.....

[Limbo]

yeah, you know what i mean ;)


there would be a limit.

I guess when valves start hitting pistons, you've gone too far lol

Seek profesional advice. :thumbsup:

[tekung89]

Before you shave your head - why not think about running hi comp head gasket.

And as a general rule of thumb -

If you can take .5mm out of the head gasket you will gain .25:1 static compression. If you can take 1mm out you will gain .6:1 static compression.


There most certainly is a limit!

From memory the service limit is a abosolute minimum of 0.75mm piston to valve clearance - standard is I think 1.5mm - I will confirm later on.....

so really speaking u can only shave off .5mm leaving urself 1mm to be above minimum clearance? for a gain of only .25:1 :( its practically not worth doin then

[spardikis]

Hope u like to read.. .lol..
its late -

here is the downlow on shaving blocks heads etc

ok the problem comes when decking the block is piston to head clearence - absolute minimum is 0.75mm piston to head clearance - thats a stupidly modified race engine - it will most probably need to be pulled down regulary (as often as 10 hours racing) to check this because even the slightest piston slap through wear, or slight miscalculation and bang piston into head. - one guy was making very good power in his race engine to 9.5k with .75mm piston to head clearence - he pushed it to 10k and the extra stretch etc from the extra revs and piston his the head....BANG and everythings over... I like to call it CATASTROFIC ENGINE FAILURE!

I would say .25mm off the block would be ok... and in theory (I know because I have done it)
you can take up to 1mm off the block but will need to run a bigger head gasket to give correct piston to head clearence so really it is pointless - ony do it unless you absolutly have to.

GOOD NEWS

there is alot more tolerence between piston and valve - so deck your head rather then your block. You can take off up to .75mm safely (any more and the shape starts to get really oval) and with ITR cams you will still have 2-3 mm piston to valve clearance in VTEC - PLENTY! and big increase in static comp - about 1.0 comp rise

Some other interesting things -

Now the values I gave you before were a general rule of thumb from a different engine build -.. - hondas are clearly different, I have done some more digging and compared to my own builds and hondas respond better to smaller head gaskets by alot....

.75mm is standard head gasket - 2 layer one is .5mm this should give u approx .3 comp ratio = good upgrade.

Best ways to gain compression to worst mods =
1, smaller head gasket - 0.25mm gain approx .3

2, shave up to .75mm off head - gain over 1.0

3, shave up to 0.25 off block - best not to do this


You have to be careful when doing more then one of the above as the chance of hitting greatly increases - checking and re checking clearences is necessary - but from my calculations and experience doing 1 and 2 should not give u to many problems if your engine has not been messed with. There are little divits in the block and head that have 1mm and 2mm dishes carved out of them to gauge what your head or block has been shaved already - good idea to check this!


on my engine when i have 0.90mm piston to head clearance i have 2.0mm piston to valve clearance with 6 degrees advanced = plenty.

you could also upgrade pistons = bigger dome on them, this is good and bad, it increased piston mass which is bad at Hi RPM but increases compression which is good. ctr pistons are not that safe with big cams... IMO..

hope this helps!

[VT18EC]

Why shave when can get a thinner gasket,my B18c2 is pushing 12:1 compression,but then again the chambers are bored and honed out to 20 thou.

[lil_foy]

Sorry top highjack but just a quick question before I go start talking to engine builders.

If I want to get my compression between 11:1 and 11:5

How much should I shave my head in combination with a toda headgasket?

Just thought id ask if anyone knows.

[VTec1987]

would the clearance be ok if i got thinner head gasket but having buddyclub cams with 12mm lift?

[beeza]

Is it really worth the .1 to .3 bump in compression by using an aftermarket Head Gasket?

[Slaz]

There are plenty of online compression calculators available to work out your compression with different combo's, might be worth trying there, or learn how to do it properly yourself.

[fatboyz39]

wat is the max mm u are able to take off the b18c head? been doing some reading and most take .20 off their heads which reduces the combustion chamber volume. in doing so u gain more compression, allowing ur engine to yield more power out of ur aftermarket goodies.

what are the average compression gain figures from this?

Compression is not always the key to make power;). I wouldnt even bother removing head to shave and gain comp.

[grumpy rooster]

I have to disagree with that. I know of many many examples on numerous different engine types where compression has really woken up an engine. And retuning in a lot of cases was not necessary.

I am a big fan of decking the head to achieve more compression.

[beeza]

How about using a thinner aftermarket HG,is it worth it Grumpy?

[grumpy rooster]

I much prefer to deck the head and use a OEM headgasket than use thinner gaskets. That may not seem to make sense but I'd prefer to still have my HG act as the fuse and not something else be the weakest link.

Of course, there are limits to everything. If you decide to take a lot off the head if you go to big cams then you'll need suitably notched/flycut pistons or your valves and pistons will be lovers in an instant.

Real world example. The Hi-Comp Civic. It has a heavily shaved and ported head but still retains the standard cams and standard bottom end. 145kwatw. Its just bolt ons and the head that has made the big gains. But, to go to bigger cams it would need different pistons or start with a different head and not take as much off it. The main advantage is the increase in torque. It is quite large for the mods done. It really does make a sizable difference. And its not particularly expensive compared to other mods. A couple of hundred dollars should see it done if you take the head off yourself and give it to a suitable machine shop.

The same principle has been applied to many of their customers NA SR's and even my own Mirage. It still retains the 4G15 1500cc engine but makes a heap more power and particularly torque. Its a totally different car.

Its just a different approach to making power than most Honda guys take. As I've mentioned a few times coupled with a lightened flywheel it is one of the first mods I would do.

[beeza]

Yeah,using a thinner HG just seams a cheap and sketchy way of gaining compression...I know a lot of guys do it but I always thought I would rather the piece of mind knowing a OEM HG is in there.

Thanks Grumpy!

The High comp civic you described above sounds awesome.Would it be a suitable daily driven car though i.e. Smooth...or is it quite aggressive/noisy?

[grumpy rooster]

Most of the cars with these mods are daily drivers with compression, I/H/E. My Mirage is. I still run the standard exhasut which chokes it a lot but I didn't want the noise. And it still is a huge gain over standard.

It doesn't hinder the drivability at all. It makes it better to drive. :) The raised compression does make the exhaust louder but thats why you have mufflers. And its not massively louder, just a bit louder.

[beeza]

Hmmmmm a Hi-comp engine.

A 4.7 Final drive is a Torque multiplier and high comp engine is high torque engine,if you put a 4.7 final drive in your mirage would it still be a friendly daily? I can't see why not but...

[grumpy rooster]

The Hi-Comp Performance Civic has a 4.7FD as well so I know it works well.

[beeza]

Wicked.Thanks for that mate.

[fatboyz39]

I have to disagree with that. I know of many many examples on numerous different engine types where compression has really woken up an engine. And retuning in a lot of cases was not necessary.

I am a big fan of decking the head to achieve more compression.

Each to their own. Just shows how experience you are with honda motors.

[Slaz]

Opposed to replacing pistons with positive material, decking the block, or running a thinner gasket which wont gain you much comp, i agree with Darren, as long as your P2V is ok, shaving is the way to go and extra comp with correct tuning, is never a bad thing.

Big call just quietly having a go at Darren's knowledge of engines opposed to your's Jimmy.

[H.B.]

Compression is king!

Think about what an engine does, it allows an air/fuel mix to enter the cylinder, squashes it up, then ignites the compressed mix to give a controlled burn to push the piston down the bore, the decompressed burnt air/fuel mix is then allowed to leave via the exhaust. Improving the efficiency of any of these processes improves the power output either directly or indirectly. You want to get as much air/fuel in the cylinder as possible, compress it as much as possible and allow the burn to use as much of the fuel as possible. So ignoring getting more air/fuel in and out and concentrating on what happens inside the cylinder, you want lots of compression . Of course there are practical limits to this, if you compress too much with a poor quality fuel or bad mix, it will self ignite before the spark plugs gets to do it's job, pinging is a good way to kill a lot of engine components in a short period of time. Also, if you end up with a poorly designed combustion chamber, you will burn less of the air/fuel mix at the correct time and lower the power output.

Mechanical issues can also occur, pistons hitting valves is never a nice thing and you need to take a few things in to consideration. Firstly, there is the turn over speed clearance test. Checking the partially assembled engine for clearance between the piston and valves is relatively easy, but it's not the closest things will get so extra clearance may be needed. The higher the revs, the more likely you are to suffer the impact of cranks flexing and conrods stretching. As a general rule of thumb, the higher the revs, the bigger the clearance needed. Good quality components can reduce the need for extra clearance, but it can be a very expensive exercise to work out the smallest clearance usable, generally you have to reduce the clearance until something fails and then back it off a bit to know what you can do.

The absolute best way to increase compression is with properly designed pistons, other methods such as shaving the head or block or using a thinner head gaskets work very well, but cannot cater for the combustion chamber shape. You need a proper squish zone for complete combustion and simply moving the head closer to the block/piston can adversely change this squish zone. With a properly designed high compression piston, this can be taken into account and used to give an even better squish zone then what the factory gave you. Of course the pistons must be designed with the rest of the engine taken in to account, in particular, valve clearance for your valve size and cam lift. Thats not to say that the other methods are bad, just not as good as a piston change, in fact, there may be no difference between a piston change and shaving the head in some cases. Relatively small changes would be in this area, for example, going from 9.5:1 to 10.5:1 ratio would not warrant a piston change in most modern engines.

As far as tuning changes are concerned, the only change possibly needed is reduced timing advance to eliminate pinging. As mention earlier, the combustion process is a controlled burn, not an explosion as most people imagine it to be. It starts small and builds up to a large burn, timing this large burn to occur at the correct time relative to the piston movement is critical to get maximum power, however, if it starts too early, you can get pinging. A general rule of thumb is that you should be able to advance the timing 4 degrees past the maximum power output without getting pinging, if not, use a higher octane fuel or reduce the timing. There may be some small advantages in adjusting the mixtures, but nothing absolutely necessary for the changes we are talking about.

You only need to look at the compression ratios of proper race engines to realise that high compression is a good thing. If the team has the budget and the rules allow it, they will run the absolute maximum compression possible and highest octane fuels to cope with the added combustion chamber pressures.

So if you have an engine that you want to get more power out of, shave the head and enjoy the across the power increase. It's one of the better mods to do as it give a power increase across the entire rev range without any drawbacks when done properly.

[beeza]

Thank U.

[TODA AU]

Compression is king!

You only need to look at the compression ratios of proper race engines to realise that high compression is a good thing. If the team has the budget and the rules allow it, they will run the absolute maximum compression possible and highest octane fuels to cope with the added combustion chamber pressures.

So if you have an engine that you want to get more power out of, shave the head and enjoy the across the power increase. It's one of the better mods to do as it give a power increase across the entire rev range without any drawbacks when done properly.

+1 Rep point :thumbsup:

[lil_foy]

Compression is king!

<snip>.

Fantastic stuff mate, rep'd.

So raising my comp to 11:1ish in my vtir would be safe with shaving a head?

Thanks to everyone who's been helpful!

[Benson]

Shaving the head is the shit.. lol

Do you research before you do anything especially with Honda motors, very expensive if something goes wrong

[grumpy rooster]

I don't understand why you think its such a bad idea? What makes the Honda engine so special? Is it because of the VTEC? If it is that, it still doesn't make sense.

[H.B.]

Shaving the head is the shit.. lol

Do you research before you do anything especially with Honda motors, very expensive if something goes wrong

What has Honda done which is so different to any other manufacture that the laws of the universe have changed? If you meet the criteria of mechanical clearance and sufficent octane rating with the fuel used for the compression ratio, there is no issue.

[Benson]

I just said make sure research is done before decking the head. No many ppl on this forum is mechanically knowledgable to know how much to take off the head.

[beeza]

Leave that one for the Pro's.

[Benson]

Then there is the matter of cam timing being off due to less distance between the crank and the cam or cams. And clearance between the valves and pistons which MUST be rechecked. Not just a do it and throw it on job.

Spot on :thumbsup: Rep for you

In saying this, you would require adjustable cam gears to move the cams back into its orginal place.

[VT33EC]

Can anyone please tell me if 12:1 compression is good for your engine,i mean performance wise yes,but im talking about in the long run,health of the engine wise ???