Shawn

Ok, a little question here. What does it mean to deck a piston head. If I has to guess I would say it means adding another layer of steel (or whatever is used) to the top of the pistons. That way they would take more volume in the cylander and thus cause the air to be compressed more. Am I even close on this one?

Here's another one. What is a "port and polish". I don't even know what part of the engine this takes place in so I won't guess.

Sir Nuke

Shawn, you DECK the HEAD...not the piston...and its NOT adding material to it....its removing material from it.....and its done for various reasons.....if you over head an aluminum head and it warps...you can deck it to flatten it back out.....you can also deck it just to decrease the size of the combustion champer size and thus as you guessed increase the actual compression ratio.

Porting and Polishing.....this is also done to the cylinder head....and it refers to the internal passages of the intake and exhaust. PORTing consists of opening these passages up to allow more flow INTO and OUT OF the cylinder....its not something you just dive in there and do....as they need to be BALANCED...all of them.....what you do there is use a flow bench and "flow" the individual passages to match them. you can also do something called "match porting" which is where you ensure that the flanges of the intake manifold and the head...and the head and the exhaust manifold match perfectly....as in the openings match perfectly so that there isn't a bump our mismatch of the openings from one part to the other.

and Polishing....well you do exactly that....you polish those same passages to make them as smooth as you possibly can....

it all has to do with FLOW of the gasses going in....and the gasses going out.........we are driving cars with a PUMP that makes us go.....MORE in...means more power.....and if you put MORE IN...you have to let MORE out.

does that explain it?

Shawn

Sort of. I did some searching and understand decking the head. So if you are an idiot and you over deck the head is there a risk of the valves smashing into the pistons?

As for porting. I wish I had a cool picture of all the basic parts of an engine but I don't. So it porting like making the diameter of the intake and exhaust ports larger?

Is there a difference from an engine head and a cylander head? I really need some pictures. I'll do more researching, that should help.

mkdxxx

Yes it is possible to smash the valves into the piston if too much is removed. But remember head grinding is done in thousandths of an inch. Remove .005 and you should be okay. I have no idea though how much clearance there is in protege engine. the machinist should be able to find out. The drawback to this can be excessive wear on the starter and battery if too much compression is gained. I plained the heads of diesel and it would barely spin. Tore up the starter and had to get a bigger one. I have seen this plaining many times with no ill effects.

Sir Nuke

Yes, if for some reason you did take too much material off you could theroidically have the valves hitting the pistons...but they would only do it for a short time! lol

the Cylinder head and the "engine" head are the same thing....its the HEAD....its what is on TOP of the cylinders...and houses the valve train....and the intake and exhaust manifolds attach to it.

does porting enlarge the ports? well yes....if that is what you want to do....the idea is to make the head "BREATHE" better...be able to allow more air/fuel to flow through the head....stream line things.

Shawn

You know what, I think I get it Those pics did it for me. So if you are "match porting" you may need to shave a little off the inside of the lip of the intake manifold to widen the opening a little? Also, if you use an aftermarket header do you do a similar thing and enlarge the openings that attach to the exhaust ports on the head?
I wouldn't consider doing this until my warranty is gone but it is interesting. I suppose you would want to make sure you have your final intake manifold, cams and header before doing this.

Is a high compression piston simply a larger volume piston that takes up more room in the cylander? Swapping pistons seems like a safer mod to make than this head decking work. Is a piston swap more labour intensive or less?

I know I asked a lot of questions(about 4) but this hasn't really been covered before. Considering that in October I could only point out the intake piping and battery under the hood of a car, I think I'm making progress.

mkdxxx

Shawn,
Understand that this must be done with a flow meter. If not, one cylinder could be getting more air and be leaned out to the point of frying and/or seizing the piston. I do think that it would be safer to port and/or polish the exhaust manually but this is still dangerous. Polishing as stated above will only smooth the ports which, in whole, is easier and safer...although will not improve performance that much. When I was about 13 I did this porting and polishing to a 2 stroke motorcycle and oh **** did it perform better. Much faster and a lot stronger. I removed a whole hellava lot of cast and it didn't matter because it was 125cc one cyclinder. This jug was very restricted and it paid off to remove the metal. Just my two cents.

Shawn

I definately would get a reputable company with a guarantee to do this kind of work. I'm always willing to pay more money for a guarantee that the work will be done properly and fixed if done wrong.

njaremka

a little more information:

when i had my triump spitfire, i had the engine BLOCK decked to make it flat and to provide a higher compression ratio. before doing the work, the pistons at TDC were speced to be below the block surface about .015-.020", and after the work the pistons had a pop-up of about .010". this takes quite a lot of work because the pistons have to be shaved to be the same hight, and to clear the head gasket i had the machine shop cut a lip around the top edge of the piston. (i also had them deck or shave the head to bring it down as well) decking the block is a more effective way of increasing the compression ratio because the piston sweeps out a greater volume than the removal of material from the head will give.

depending on how much "pop-up" you want you piston to have and how much clearance you have with a compressed head gasket, you have to have the head machined to provide a recess for the pistons to rise in to.

chdesign

Hey Nik I had a Triumph Spitfire too!! I built mine for just a pure sleeper car though...I had custom forged rods made and 10:1 JE pistons made also. I put a whipple charge on it with a custom sheet Carb adapter with a Dual Webber setup. Plus we through a direct port NOS kit on there just for laughs....let me tell you all that in a car that weighed maybe 1400 lbs....it woudl get off...it was very very hard to control though.

njaremka

yeah, i just wanted to give it a little more push than the stock ~60hp that the motor pushed. (stock for the 1300 '72 engine) based on the SOP dyno, i'd say i was pushing 90 or so after the work i did. i was running the stock single carb, a fast road cam, decked head and block to about 10.5:1 compression. the car had the stock 4.11 gears and no overdrive. i retro fitted a '69 exhaust to it and it would top out at 90-95 mph. like you said, damn fast for a car that wieghs roughly 1600lbs.

i think if i had kept that car, i would have converted it to fuel injection, custom header and exhaust, crank-fired ignition, tr4 tranny (for strength), and all the lighter/stronger bits for the engine. of course, i found a website that sells high performance goodies for those cars AFTER i sold it.

totaly off subject now. if you want to continue this, send me a private email.

zeus

Actually, you dont want it perfectly smooth....what you really want to do is port on a flow bench and then have the intake and head extrude honed together. It's like forceing a thick grinning toothpaste through the runners; takes out the rest of the inperfections. It leaves just enough surface ruffness to set up a good boundry layer.

Before decking anything or changing cam profiles, you really need to either have a blue print or measure everything yourself. Which is what I plan to do. That's why I'm looking for someone who's swapped out the OEM cams for the M-speed and J-spec ones. I'd buy them, use those for regrinds and give my OEMs back as cores. Sweet deal huh.

I'm going to do the head at the same time, like you all talked. I know what I'm doing, I'm going to do it right and I've done good before.

I'm probably going to go as far as measuring things like the valve spring rates, and pass all this fine info along. So, doesn't anyone have spare OEM cams?

I'm not in a rush, just slowly getting it together, so knowledgable input is appreciated. I spent over a year getting the last car ready and less than 2 weeks doing the actual work; that one worked out very well for 265,000 miles.

Oh, I still need a good header for the Protege5, stainless steel too.

zeus

What's this 'newbie' crap?
Zeus ain't no 'newbie'.
I got references damn it!