Stupi9d Compression Question...

I was wondering if any one had any answers to the following:

1. Would having the cylinder head milled while rebuilding raise compression??

2. If Yes then would I recieve any minor/major HP changes?

3. I know that it would lower my displacement but what I'm really interested in is the HP change..

Thanks to anyone who can help...Mike

Mine got milled and has raised compression... it requires premium gas but the power is lower than before. This may be a cam timing error (though we could not measure one), or maybe it's a problem with the stock computer program.

In theory this should raise power, but they say if you want to raise compression you should do it with the pistons, not the head... but then, some of the fancy heads they sell, like Esslinger's, are shaved this way.

It does not change your displacement -- that number refers only to the volume swept by the motion of the pistons, not to the combustion chamber volume.

I would think you have to be careful to not take off too much when milling the head. You dont want the valves hitting the piston

More compression always means more power, Im not sure why your engine doesnt run stronger.

Originally posted by CRZYDRVR:
I would think you have to be careful to not take off too much when milling the head. You dont want the valves hitting the piston
More compression always means more power, Im not sure why your engine doesnt run stronger.

I was thinking of the same thing.

So that's why it's losing power... the friction of the valves bumping into the pistons all the time.

Seriously, I'd like to figure it out, because they're starting a group buy of superchips, and it would be nice not to stick one on a mis-tuned engine.

Originally posted by Paul Kienitz:
the friction of the valves bumping into the pistons all the time.

Physically hitting the valves ??? Are u sure ???

Originally posted by Paul Kienitz:
So that's why it's losing power... the friction of the valves bumping into the pistons all the time.

That is scary.

In reply to:

So that's why it's losing power... the friction of the valves bumping into the pistons all the time.

LOL sounds pretty bad

Is it possible that the cam gear(s)-to-crankshaft gear dimension is affected by head milling enough to affect cam timing (assuming that the timing belt teeth are sitting in the same pulley grooves)?

Hopefully, this makes sense.

Dunno...just my $.02

It doesn't affect the gear ratios, but it does effect the length of belt between the drive gear and the driven gears, so it could throw it off. But when we put the belt on, we measured the cam timing as accurately as we could and found no error. I sure wouldn't be surprised if it was actually off by a degrees or two, though. I think the error would be in the retarding direction.

How is performance affected if your cams are two degrees behind -- does anyone know?

In reply to:

How is performance affected if your cams are two degrees behind -- does anyone know?

I have read from several people, mostly on the Focus forum, that retarding the exhaust cam is good for a few horsepower.

Originally posted by CRZYDRVR:

In reply to:

How is performance affected if your cams are two degrees behind -- does anyone know?

I have read from several people, mostly on the Focus forum, that retarding the exhaust cam is good for a few horsepower.

I think you should get a set of adjustable cam gears and get them tuned. It will be a little costly but it might fix your power loss problem, Paul.

Is it that difficult or painful to adjust cams using the stock gears?

Maybe I should just buy a whole new performance head.

Originally posted by CRZYDRVR:
I have read from several people, mostly on the Focus forum, that retarding the exhaust cam is good for a few horsepower.

I wonder if there are emissions issues with that.

In reply to:

I have read from several people, mostly on the Focus forum, that retarding the exhaust cam is good for a few horsepower.
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I wonder if there are emissions issues with that.

Not that I know of.

Originally posted by Paul Kienitz:
Is it that difficult or painful to adjust cams using the stock gears?

Maybe I should just buy a whole new performance head.

is it possible to adjust the stock gears?

In reply to:

is it possible to adjust the stock gears?

I dont think so.

Originally posted by Kremithefrog:
is it possible to adjust the stock gears?

Of course it is. How do you think a mechanic sets the cam timing after changing the belt?

i thought they could only be used to a certain degree to get it to stock timing,,, why do companies sell aftermarket gears?

Originally posted by Kremithefrog:
Originally posted by Paul Kienitz:
Is it that difficult or painful to adjust cams using the stock gears?
is it possible to adjust the stock gears?

I would expect them to be keyed to the shafts, so that no adjustment would be possible. For them not to be keyed would, I think, introduce an unacceptable risk of slipping out of adjustment during normal use.

Originally posted by Paul Kienitz:

Originally posted by Kremithefrog:
is it possible to adjust the stock gears?

Of course it is. How do you think a mechanic sets the cam timing after changing the belt?

Stock gears aren't adjustable...
when a mechanic sets cam timing; all that is being done is getting the belt on the correct teeth on the cam since 1 tooth is equal to about 9 degrees. Being 1 tooth off on the gear would cause the car to run like total crap.

I accidently installed my cam 1 tooth retarded once and there was NO power at all...felt like a geo metro or something. One cam tooth made the difference between having uncontrolable wheel spin through third gear when it was right and hardly enough power to accelerate when it was wrong.

that's what i was thinking, and the engine has to be at TDC or something like that. a set of adjustable timing gears may be your fix paul.

Exactly, CYL 1 is set to TDC on the compression stroke; then the cams are set to TDC with a camshaft alignment tool (ford part# T94P-6256-CH). Put the belt on; set belt tension.

There is no adjustment able to happen in the stock system (except in 9 degree increments). So maybe one of your cams is off by a whole tooth Paul. You might want to look into that. It would cause a serious loss in power.

ummm ever hear of moving the gear a tooth forward or back.... hence advance or retard timing....

and I would say doing that is not a good thing... that is WHY ther are cam gears out there... where to take and loosen it up and rotate it forward or back to adjust and they are marked telling exactly how much you are advancing or retarding the timing... and NEVER do this without dynoing your car to see if you make a gain or lose... each car even with the SAME MOTOR AND MODS can still respond differently...

Umm...are you implying it's common practice to advance or retard a whole tooth at a time?

Originally posted by Blackie:
Umm...are you implying it's common practice to advance or retard a whole tooth at a time?

ALL I am saying is that is how you could do it... BUT that is not they way you should do it...
but being that I did say it I bet some people would be dumb enough to try it.

Originally posted by ZetecRacing:

Originally posted by Blackie:
Umm...are you implying it's common practice to advance or retard a whole tooth at a time?

ALL I am saying is that is how you could do it... BUT that is not they way you should do it...
but being that I did say it I bet some people would be dumb enough to try it.

Yeah, that's not the way you should do it. Advancing 10degrees would shift the powerband so high that you'd have no power below 3500rpms. And retarding it 10 degrees, it would run out of steam around 3000rpms.

The unorthodoxracing.com install page for the zetec says "We have also found 2-3 retard on the exhaust cam and 1-2 degrees advance on the intake cam give the best overall results"

I guarantee if anybody tried to adjust cam timing a whole tooth at a time, I'm sure they changed it back REAL quick.

Originally posted by Bob Blaylock:
I would expect them to be keyed to the shafts, so that no adjustment would be possible. For them not to be keyed would, I think, introduce an unacceptable risk of slipping out of adjustment during normal use.

They are not keyed, they are bolted on flat. The process of adjusting them is awkward but routine for e.g. the dealership mechanics. (Loosening the bolt can be an awkward business... perhaps best done with an impact wrench.) The risk of slippage is not great because the forces exerted on it when the engine runs are very moderate.

Originally posted by Blackie:
Stock gears aren't adjustable...
when a mechanic sets cam timing; all that is being done is getting the belt on the correct teeth on the cam since 1 tooth is equal to about 9 degrees.

This is not true. Check your Haynes.