OK, so i milled my head 60 thou to keep the compression up on my B20VTEC.

i compression tested last night and got straight 200's so the compression of my "stock" B20VTEC is about 10.3:1ish.

now, it is running pretty hot, way hotter than before (it heats up much faster), so i set the spark timing back to 16' (stockish) but it still gets hot pretty quick.

my question is this:

how retarded is my cam timing?

i have heard that every 0.012" removed from the head retards the cams by 1 degree.

is this true?

if so, this means my cam timing is 5' retarded.

what effect is this having on the engine?

will fixing this cam timing have a great impact on performacne?

(cam gears will be next on the shopping list if so!)

thanks for any advice/tips/experiences,

t..

 

60 thou is way to much to have milled off the head........i would consider that head almost garbage........

good luck trying to fix your problems...........


[Modified by non-VTEC, 10:07 PM 10/15/2002]

 

why garbage? please explain..?

t..

 

you removed so much materal from the head. it not only changed the cam timing alot it also affects many other thing. timing belt tension, piston to valve clearence ignition timing and some other stuff as well.......

if you wanted more compression you should have just gotten a thinner headgasket or higher compression pistons............60 thou is about 55 thou to much............

i would assume you overheating problems is from the combustion chamber being so small now since so much material was removed. the chamber is generating more heat with less cooling from the cooling system.........your best be might be to get a thicker headgasket and upgrade your cooling system and hope for the best......

ask any professional engine builder and they will tell you milling the head to get more compression is a bad idea........heads and blocks should only be milled for making a true flush surface.......

good luck

 

OK, i do NOT have an overheating problem, the engine heats up quicker than before, that is all. it does not go past 1/3 of the gauge.

timing belt tension is OK.

piston to valve clearance was clayed and is fine (at currnet settings).

(a thinner head gasket would give same results as milled head - just not as much)

i could not afford high compression pistons ATM...

anyways, this thread was not to discuss the pros/cons of milling a head.

i know all of these, but thanks for clarifying

these were my questions:

t..

 

from what i've read online is that for every .010 milled off the head will affect the cam timing -1 degree. so your at or around -6 degrese.

if it's -1 degree for every .012 then your probably a little less.........maybe -4 or -5

when you retard the cam gears you shift the peak power higher in the RPM band with the sacrafice of low end power.

you will need a set of adjustible cam gears anyway to dyno tune then engine properly so get it on a dyno and have fun!

 

.012 = 1 degree of retardation. you shouldnt have milled 60 thousandths but no need in getting into that. you should get cam gears asap because there is no way you are making the amount of possible power running that retarded. what cams do you have? pity i just sold my cam gears for 100 shipped. anyway, get some cam gears and if you arent overheating why are you worried why your car warms up quickly, nothing wrong with that

 

thank you

so i need adj. cam gears, which will help alot from what you guys are saying.

i was expecting slightly more from the B20VTEC, I just like to know that the cam timing is proably the most important problem first up.

bigger exhaust system will help too, as will better cams (using stock B16A now)

thanks again,

t..

 

oh, and another thing that comes to mind -

the cams are both retarded so they open later.

as i clayed it for clearance in this state (and it was good), will returning the cams to stock or a little advanced create better piston to valve clearance or worse?

(i am having trouble visualising the relationship of the internals)

thanks,

t..

 

should be better, but overall its for more power. again what cams are you running

 

t..

 

I think he may be right about your timing belt tensioner possibly not being able to take up the slack properly. I'd watch it very closely.

 

it was pretty hard to put the belt on with the tensioner fully loose, but i will check it tonight for looseness

(i am using a GSR belt with the 22 tooth pump)

thanks,

t..

 

Not to pick on you, or beat it to death, but what made you want to shave so much off your head?

 

perfectly valid explaination:

to increase the static compression ratio using the stock 8.8:1 pistons of the B20B block,

without milling the head it would have only been 9.1:1 CR

with 60 thou removed, it is about 10.3:1 (confirmed by the 200psi compression numbers)

mainly so i didnt have to use with forged pistons and rods right now... (which would have almost doubled the build cost - which incidently came in at US$1500)

the only problem the milled head is causing is the retarded cams, (and possibly loose belt - will check)

i had my valve reliefs resized for the 33mm valves, so this sould not be a major concern either...

have i got it about right?

t..

 

I just dislike head milling. It can't be undone. If you'd gone for a thinner gasket, which you should've changed anyway...n/m, it's done.

If you can advance the cams enough to compensate and the timing belt isn't slipping then you got a big C/R jump for few $$$. It won't take much slipping of the belt for the valves to meet your pistons though. Make sure you turn your engine over by hand a few times every time you change a cam gear setting. I do this myself and I'm not even close to introducing my valves to my pistons.

 

you see well my friend,

i have one spare head anyways - so it can be undone (and when i go with pistons/rods - i will used this un-milled head BTW)

the thiner HG would have only increased compression by about 0.4 points, where the milled head increaed by over 1.1 points (ie good $$$ return)

(all this from http://www.c-speedracing.com/howto/c.../compcalc.html )

so, what is done is done, i am getting JUN adj. cam gears tomorrow (approx US$150 ea) so it will ease my problems significantly!!!

then i will have to look at the fueling system (upgrade injectors to 290cc) and exhaust system (get rid of B16A ex manifold etc) then she will be getting potent !

t..

 

I know the head gasket is only a small bump in C/R. Glad you have another head though. I'm spending about $243 for a 1.3 point boost, so I think you got me beat in the price/performance dept. I needed new rings anyway though and the JDM ITR pistons come with them. Seems like a lot for gears. Good luck bro.

 

hello sir, 60 thous of an inch would cut the valve seats so its prolly .060 mm which is roughly 20 thous of an inch...

Also, cylinder pressure is different than compression ratio. One measures sealing in the cylinder with respect to dynamic compression, i.e. taking into account cam lift an dduration, the other is a ratio between your head and gasket chamber volume to the cylinder volume in the block.


Greg

 

To answer your question, if you advance the exhaust cam you will gain valve to piston clearance, advancing the intake you will lose clearance. You need to know what the clearance was before you move the intake,also the valve relief in the B-20 is smaller in diameter than the B-16 valve, so take that into consideration. .060 is not too much , increased compression and power will make your engine heat up faster.

 

greg, you are wrong - it did not touch the valve seats.

60 thousandth of an inch = 1mm

which = 5' retarded (from what i have heard - no one has confirmed this yet)

really? you think so? J/K

with a calculated compression ratio of about 10.3, this was confirmed by the good compression test numbers. sorry if i did not make this clear and confused you.

did you have any helpful input greg? i sorta needed some...

t..

 

thank you DonF,

that makes me feel better about the situation. i have enlarged the intake valve reliefs to account for the larger valves.

for clarification: are you saying the intake valve clearance will decrease if I:

1. advance it from retarded;
2. advance it from neutral; or
3. advance it at all?

thanks again

t..

 

If you advance the intake cam you're keeping it open closer to TDC and therefore increasing the risk of a collision. I'm not suggesting this will happen, but by increasing the intake timing you're increasing the risk of it occurring.

 

[QUOTE]If you advance the intake cam you're keeping it open closer to TDC and therefore increasing the risk of a collision.QUOTE]

yes, that makes sense...

damn, thanks for that

t..

 

Take it easy on Greg man, I don't think that he was aiming to **** you off. Besides, he knows his ****, so you might need his help someday.

.012" loss in distance from crank to cams = 1° retardation of the cams. Don't forget that changing the intake cam timing also changes the ignition timing.

DEFINITELY check the tension on your timing belt. It's not recommended to mill more than .040, and the main reason for this is the tensioner not being able to make up for much more of a loss in heighth. Clearance issues aren't a thought until at least .050, I believe, but being that you clayed things when you put it back together, this is not a problem. Another thing to remember when you get your gears - you'll want to clay things again @ 0/0, and with both cams advanced - I'd recommend going as far as you think possible to give yourself the largest tuning window that your setup will allow. Generally, you probably won't need more than 6° adjustment either way, at the VERY most for optimum tuning, but if you get to your farthest known-good cam setting & you're still gaining power, you'll be sorry that you didn't clay further!

Keep us posted on how it goes man. I LOVE to see people do things that other people say can't be done.


[Modified by 94gsr, 8:17 PM 10/16/2002]