Lets talk about head shaving
- Thread starter Tire Shredder
- Start date
AJ, that's the point of this thread to remove the "if's and maybes" from my post. The assumptions I made are just assumptions but I stated them as so and backed them up with some logic.
if somebody has done research and the actual measurements before, they can post it up here. Pistons for moderate increase in compression like one discussed may not be required, even if it is the proper way to do it.....that's what I'm trying to find out.
I'll get to the bottom of it in the end, but the forums can speed things up.
if somebody has done research and the actual measurements before, they can post it up here. Pistons for moderate increase in compression like one discussed may not be required, even if it is the proper way to do it.....that's what I'm trying to find out.
I'll get to the bottom of it in the end, but the forums can speed things up.
Steve: On a serious note the only real cons to doing it that way will be increased emmisions and maybe a slight drop in economy.
Just because it is relevant here, what is the stock piston protrusion on an unmilled block? I may go find it but I might not come back. I feel dirty in here.
EDIT: Found this is another thread...
Which would be 0.508 mm.
EDIT: Found this is another thread...
IJ.;338699 said:
Which would be 0.508 mm.
thanks Jamie. excellent to have that info here. I believe less squish height (gap) is good too, but weird stuff happens when it gets too tight.
Granted, if it can be worked out to be a safe and easy mod, I mean if shaving the head would get you 20 more ponies at the wheels, it would be a fairly easy mod if like most have to do a HG job why not. You should get the head surfaced anyway to do a HG, why not shave it a little. But if all you would be realizing would be 5 or so, you probably won't be able to use that head again if something goes wrong and would have to pull it for some reason, am I right?Tire Shredder;955712 said:
Nice to see all the "high rollers" posting in here
AJ'S 88NA;956057 said:But if all you would be realizing would be 5 or so, you probably won't be able to use that head again if something goes wrong and would have to pull it for some reason, am I right?
Nice to see all the "high rollers" posting in here
yup AJ, that seems to be the biggest drawback right now, providing the tolerances do work out as hoped. Thanks for pointing that out.
Zumtizzle;956069 said:
provided Homer's roller has a decent bearing in it, and wasn't too expensive, it's a great solution to avoid buying cam gears in my opinion. it would only be required to take up the slack generated though, or you'd end up advancing the cams more than you'd like.
10.5:1 CR is decent on pump gas. I've run 11.3:1 CR on 93 all day long (well, summer did get mild pinging, but aluminum radiator + 160 thermo took care of that) - Not a 7m, but the physics stays the same.
You can mill the head, keep an eye on squish area, and use adjustable cam gears to take up the difference. Has this not been done before?
You can mill the head, keep an eye on squish area, and use adjustable cam gears to take up the difference. Has this not been done before?
I'm no expert and can offer only my limited experience. Is there anything anyone would like me to look for beyond how the car runs? I did recently do a compression check, but that's not quite the same as compression while running. When I peered into the chambers through the spark plug holes it did seem like there was a bit too much carbon for under 10,000 miles after rebuild, but I have no reference. I was mainly looking for a cylinder that was too clean, which is indicative of coolant getting in there.
It's my winter car, so gets only short runs in the summer, which could explain the carbon. Up until last December, I worked less than 5 miles from home, which doesn't help either. I'm now 17 miles away, so it gets run harder for longer, about half on the highway.
I don't have time right now to take the front cover off. It would've been easier 2 weeks ago when I already had the coolant drained. I'm planning on retensioning the timing belt this weekend, as per Honda's method, but that takes 10 minutes and doesn't tell me anything.
My heater valve broke from a combination of age and the mechanic cranking the hose clamp too much on the engine side and half my coolant left. I caught it quickly thanks to the birdcage light, but I had to check it out to make sure it was ok. Hence, the compression check.
Asterix
It's my winter car, so gets only short runs in the summer, which could explain the carbon. Up until last December, I worked less than 5 miles from home, which doesn't help either. I'm now 17 miles away, so it gets run harder for longer, about half on the highway.
I don't have time right now to take the front cover off. It would've been easier 2 weeks ago when I already had the coolant drained. I'm planning on retensioning the timing belt this weekend, as per Honda's method, but that takes 10 minutes and doesn't tell me anything.
My heater valve broke from a combination of age and the mechanic cranking the hose clamp too much on the engine side and half my coolant left. I caught it quickly thanks to the birdcage light, but I had to check it out to make sure it was ok. Hence, the compression check.
Asterix
sounds good Doward, thanks.
it took a lot of looking, and I was able to find only two people that did. No specific details such as how much room was left, if the combustion chamber was changed drastically, if material was removed from the block, slack in the timing belt or any running issues were discussed.
I'm hoping some people will chime in that have done this.
carbon deposits should not be related to compression ratio.
There isn't much you can do unless you remove the head and take measurments. Comments on how the car runs are great, but you shouldn't notice any pinging with decent gas, especially because you drive it in the winter. It would be great if you could tell us how the tensioner is handling the extra belt slack. is it still taught?
Doward;956162 said:
it took a lot of looking, and I was able to find only two people that did. No specific details such as how much room was left, if the combustion chamber was changed drastically, if material was removed from the block, slack in the timing belt or any running issues were discussed.
I'm hoping some people will chime in that have done this.
Asterix;956344 said:
carbon deposits should not be related to compression ratio.
There isn't much you can do unless you remove the head and take measurments. Comments on how the car runs are great, but you shouldn't notice any pinging with decent gas, especially because you drive it in the winter. It would be great if you could tell us how the tensioner is handling the extra belt slack. is it still taught?
Last edited:
Adjuster
Supramania Contributor
That extra belt tensioner Homer Simpson has added is trick. (What is it, and where can I get one..?)
OK, on the head, I've only delt with a Turbo piston'd engine, and coated ones at that.
I think a domed piston is the way to go if you are building a complete motor.
On a budget, and if your only going to pull the head, then shaving it is a way to raise the CR, but as noted by many, brings up other gremlins you might not like in your search for more power.
1) Have to run high octane fuel.
2) Potential for valve to piston contact if the amount of material removed is extreme. (Not likely with the amount your talking about however.)
3) Timing changes. (Resolved with gears, or Homer's idler..)
4) Squish area, and combustion chamber shape changes. (The great unknown.)
Here is my take on this, and what I did on my stroker motor head.
It was machined only after we determined that the cam saddles were flat. (IE: The head was not warped.)
I don't have the exact figure of how much was removed, but it was not a small amount IIRC. Like 40thousands? That sounds about right, but it's been a few years.... Also my pistons are 9:1 to start with, but I changed my combustion chamber CC amount, so I really have NO idea what the final static CR really is actually.
I used a stock head gasket from the rebuild kit to protect the head, and while it was placed over the head, unshrouded the valves, and removed all sharp edges in the chambers. I have 1mm OS valves, so the valve seats had been cut for them, and we opened up the seats slightly too. Part of this work was porting the intake and exhaust runners, and just under the seats where there was quite a bit of sharp excess material that would screw with flow.
I removed my exhaust valve guides that projected into the runners. I tapered the intake valve guides and ramps to enhance flow. (They look like airplane wings now, where the exhaust ones are completely gone to enhance volume.. My own theory, but it seems to have worked OK on this motor.)
Anyway, the final deal, and why I think this worked as well as it has...
Coatings.
I coated the combustion chambers with thermal barrier coating. The same stuff that is on the piston crowns. (Very reflective to heat, and it distributes any heat that it does absorb across a wider area, reducing the possiblity of a hot spot.)
I coated the exhaust ports with thermal barrier coating. (OK, so that might be overkill, but why lose the heat to the coolant/head when I can use it to run the turbo?) The exhaust manifold is coated inside with thermal barrier, but it's not the same as the barrier used on the pistons/exhaust ports. It is smoother. The exterior is coated with a ceramic based thermal barrier as well as wrapped now. (My old system was a stock ported manifold, with these same coatings, and the stock heat shields coated.)
The intake ports are coated with thermal dispersant. The intake manifold is coated inside and out with thermal dispersant too. (As is the engine block, head outside and all possible coolant passges)
Valves are stainless, and come polished, but I measured the part that is always in the runner, and coated them with thermal barrier below that point from the stem down over the face etc. This is to keep as much heat out of the valves as possible.
I used the stock head gasket as a "template" to thermal barrier coat the combustion chambers, and then brush applied thermal dispersant to the coolant areas of the head with the gasket/template removed.
The cam saddles are coated with molydisulfied to reduce friction there as well.
The pistons are coated with moly on the skirts, thermal barrier on the crowns, and thermal dispersant on the underside.
The downside to all of this is cost. It's not cheap, and it's time consuming, and detail work that takes patience and you need access to an oven with good heat control and that will fit your engine inside of it...
The upside is you promote all the thermal actions of the engine in a positive way. And it protects your expensive engine parts from detonation better than uncoated parts. (This might allow you to get away with higher CR on a hot day for example.)
Also the fuel economy was an un-expected benefit. My car, with the ported stock manifold, a bolt on T4, the 550's and Lexus mod, with a E-manage blue, but running the stock O2 in closed loop, so 14.7:1 AF's averaged right at 30mpg fuel economy at 80mph steady running down to Vegas an back a few years ago. (Should be better now, as I've improved flow out the exhaust side, and somewhat the intake side as well.)
What I'd try on your head build is shaving your head, that's cost effective for you at this point. But I'd also clean up the intake and exhaust ports, especially under the valve seats, and I'd do the coatings if you can.
Heck, while you have the head out, change the valve springs to the comp cams ones, replace the valve seals. (And while your valves are out, you can port the head... be careful and do not hit the seats!)
Any improvements to flow seem to be a good deal, and any improvements to thermal handling also benefit.
I believe the coatings saved my motor too. (Serious detonation, broke two spark plugs, but did not melt the ring lands, or anything that I was expecting to see when I replaced the plugs, and the engine ran fine, no loss of compression etc.)
OK, on the head, I've only delt with a Turbo piston'd engine, and coated ones at that.
I think a domed piston is the way to go if you are building a complete motor.
On a budget, and if your only going to pull the head, then shaving it is a way to raise the CR, but as noted by many, brings up other gremlins you might not like in your search for more power.
1) Have to run high octane fuel.
2) Potential for valve to piston contact if the amount of material removed is extreme. (Not likely with the amount your talking about however.)
3) Timing changes. (Resolved with gears, or Homer's idler..)
4) Squish area, and combustion chamber shape changes. (The great unknown.)
Here is my take on this, and what I did on my stroker motor head.
It was machined only after we determined that the cam saddles were flat. (IE: The head was not warped.)
I don't have the exact figure of how much was removed, but it was not a small amount IIRC. Like 40thousands? That sounds about right, but it's been a few years.... Also my pistons are 9:1 to start with, but I changed my combustion chamber CC amount, so I really have NO idea what the final static CR really is actually.
I used a stock head gasket from the rebuild kit to protect the head, and while it was placed over the head, unshrouded the valves, and removed all sharp edges in the chambers. I have 1mm OS valves, so the valve seats had been cut for them, and we opened up the seats slightly too. Part of this work was porting the intake and exhaust runners, and just under the seats where there was quite a bit of sharp excess material that would screw with flow.
I removed my exhaust valve guides that projected into the runners. I tapered the intake valve guides and ramps to enhance flow. (They look like airplane wings now, where the exhaust ones are completely gone to enhance volume.. My own theory, but it seems to have worked OK on this motor.)
Anyway, the final deal, and why I think this worked as well as it has...
Coatings.
I coated the combustion chambers with thermal barrier coating. The same stuff that is on the piston crowns. (Very reflective to heat, and it distributes any heat that it does absorb across a wider area, reducing the possiblity of a hot spot.)
I coated the exhaust ports with thermal barrier coating. (OK, so that might be overkill, but why lose the heat to the coolant/head when I can use it to run the turbo?) The exhaust manifold is coated inside with thermal barrier, but it's not the same as the barrier used on the pistons/exhaust ports. It is smoother. The exterior is coated with a ceramic based thermal barrier as well as wrapped now. (My old system was a stock ported manifold, with these same coatings, and the stock heat shields coated.)
The intake ports are coated with thermal dispersant. The intake manifold is coated inside and out with thermal dispersant too. (As is the engine block, head outside and all possible coolant passges)
Valves are stainless, and come polished, but I measured the part that is always in the runner, and coated them with thermal barrier below that point from the stem down over the face etc. This is to keep as much heat out of the valves as possible.
I used the stock head gasket as a "template" to thermal barrier coat the combustion chambers, and then brush applied thermal dispersant to the coolant areas of the head with the gasket/template removed.
The cam saddles are coated with molydisulfied to reduce friction there as well.
The pistons are coated with moly on the skirts, thermal barrier on the crowns, and thermal dispersant on the underside.
The downside to all of this is cost. It's not cheap, and it's time consuming, and detail work that takes patience and you need access to an oven with good heat control and that will fit your engine inside of it...
The upside is you promote all the thermal actions of the engine in a positive way. And it protects your expensive engine parts from detonation better than uncoated parts. (This might allow you to get away with higher CR on a hot day for example.)
Also the fuel economy was an un-expected benefit. My car, with the ported stock manifold, a bolt on T4, the 550's and Lexus mod, with a E-manage blue, but running the stock O2 in closed loop, so 14.7:1 AF's averaged right at 30mpg fuel economy at 80mph steady running down to Vegas an back a few years ago. (Should be better now, as I've improved flow out the exhaust side, and somewhat the intake side as well.)
What I'd try on your head build is shaving your head, that's cost effective for you at this point. But I'd also clean up the intake and exhaust ports, especially under the valve seats, and I'd do the coatings if you can.
Heck, while you have the head out, change the valve springs to the comp cams ones, replace the valve seals. (And while your valves are out, you can port the head... be careful and do not hit the seats!)
Any improvements to flow seem to be a good deal, and any improvements to thermal handling also benefit.
I believe the coatings saved my motor too. (Serious detonation, broke two spark plugs, but did not melt the ring lands, or anything that I was expecting to see when I replaced the plugs, and the engine ran fine, no loss of compression etc.)
Hommer's Idler.......
Might work ok at stock redline (maybe) but being that small a diameter the bearing speed is going to be insane if revved hard.
A sleeve pressed over the stock tensioner pully would be a far better way to address this issue.
Might work ok at stock redline (maybe) but being that small a diameter the bearing speed is going to be insane if revved hard.
A sleeve pressed over the stock tensioner pully would be a far better way to address this issue.
Since cam timing has been brought up. Is there any rule of thumb concerning how many degrees or teeth a cam should be adjusted after X thousands have been shaved off the head and which direction should it be turned?
I had .020 taken off the head to correct warpage and I'm trying to tune the 7mge and squeeze out a few ponies while I'm at it.
I had .020 taken off the head to correct warpage and I'm trying to tune the 7mge and squeeze out a few ponies while I'm at it.
Don't do it by teeth, please. If you want to adjust the cam gears, get adjustable cam gears.
Rule of thumb is to put it on a dyno
Rule of thumb is to put it on a dyno