more powerful head!

[Kevin mr2 1985]

okay i was reading about my 4agze from a levin gtz it says that it is the small port head and i had the idea of taking a big port head from a 4age and port and polishing then bolting it up would it run even though the compressions are different?

[te51levin]

The smallport head is more desirable for 99% of us. Stay with it. Don't try porting your own head until you've been around the block a few times, built a few engines, etc. Most people who try it really have no idea what to do, and end up spending a lot of time doing things that make no difference. Worse that that, they often also end up ruining the head in a matter of seconds.

The difference in compression ratio is caused by different pistons. The combustion chambers are the same in all 16V 4AGE/GZE heads.

[Jackstand Queen]

Up to a point of diminishing returns, a smaller port, or intake runner flows more air per minute than a larger version.

Google "Boundry Layer theory and porting" engines on Google. I'm smoothing up some of my intake runners, but not polishing them. And if you polished the combustion chamber for example . . . you're cylinder head just became junk.

[Kevin mr2 1985]

oh so i should stick with the small port head i got and then get a professional to port it?

[te51levin]

Originally Posted by Jackstand Queen

And if you polished the combustion chamber for example . . . you're cylinder head just became junk.

I think you are alone in that opinion. Polished combustion chambers is very common. Besides looking cool, it is thought to improve efficiency (and thus power) by reducing heat transfer to the cylinder head, leaving more heat to push on the piston.

Originally Posted by Kevin mr2 1985

oh so i should stick with the small port head i got and then get a professional to port it?

Yes. That is the best route for almost everyone, almost all the time.

[Kevin mr2 1985]

where could i get a spare small port head for cheap?

[Papo J]

Forget the porting and get larger valves, that's where you'll find the power. A smaller port will maintain better air velocity on an NA motor, for a forced air application a larger port should work better since the air is being forced into the cylinders and not sucked in.

[Kevin mr2 1985]

really so a big port will work better with my 4agze?

[te51levin]

We can't say for certain because, to the best of my knowledge, nobody has tested them back-to-back with the head and manifold as the only variable. However, at this point in time, it will not be worth your trouble to swap heads. There are many other things you can do that will be more productive and more beneficial, as well as less costly and less time-consuming.

In other words, stop worrying about the cylinder head for the time being.

[Kevin mr2 1985]

lol okay what mods should i do next for power?

[Papo J]

I would say a free flowing exhaust, larger pulley, mild cams.

[donnyavery]

go turbo it really not that expensive i did could have don mine for about 550$ if you buy every thing used (if i was not doing ten other tings to my mr2 at the same time) or go nitrous you can get a wet kit for 400$ and the car will run and drive like stock and then you flip the switch and it becomes a hole new animal (thats going to be your best bang for the buck

[1stgen]

Originally Posted by donnyavery

go turbo it really not that expensive i did could have don mine for about 550$ if you buy every thing used (if i was not doing ten other tings to my mr2 at the same time) or go nitrous you can get a wet kit for 400$ and the car will run and drive like stock and then you flip the switch and it becomes a hole new animal (thats going to be your best bang for the buck

bang is right. NOS on an old motor is a quick way to get a new motor and its the least cost effective method of power in long terms.

Polishing a cylinder heads CC is a bad idea if done by an untrained pro. It will cause hot spots and detonation even in a N/A car. Sometimes you get lucky many times you dont.

Most N/A mods come with headwork/intake work and compression raising(you can change your compression ratio with pistons or decking the head depending on clearence)).get some cams.

If your going to get bigger valves might as well pay for a mild porting job at the same time to open up the breathing for those bigger valves. If your adding more air (porting and bigger valves) make sure you have more fuel to support it. FPR or bigger injectors. Then you need something to control the fuel like a reflashed ECU or a standalone or piggyback unit. In a nutshell everything works together in a harmony of explosions. If you upgrade one thing another thing must also be upgraded. If you go turbo thats a whole different set of equations. Entirely different engine build.

Your first step for building power would be to use the search function in the forums.

[328FTW]

^ What he said, I never really got the whole NOS!!!!!!!!!!!!!!!11111!!! thing its expensive, hard on engines, burns valves, cracks ringlands and heaps of other nasty things even set up right it seems you could of put that effort elsewhere. My club won't even allow nos onto the track its dangerous if a line bursts in an accident, fuel + fire + oxidant = bad things.

[Jackstand Queen]

Originally Posted by 1stgen

Polishing a cylinder heads CC is a bad idea if done by an untrained pro. It will cause hot spots and detonation even in a N/A car. Sometimes you get lucky many times you dont.

Quote by Te51Levin:

"I think you are alone in that opinion. Polished combustion chambers is very common. Besides looking cool, it is thought to improve efficiency (and thus power) by reducing heat transfer to the cylinder head, leaving more heat to push on the piston."

Earlier post by Jackstand:

Originally Posted by Jackstand Queen
"And if you polished the combustion chamber for example . . . you're cylinder head just became junk."

Compounded with factual error is the grammatical blunder of "Polished combustion chambers is very common", [SIC].

[te51levin]

Originally Posted by Jackstand Queen

Compounded with factual error is the grammatical blunder...

You're going to have to try harder than that to disprove my point. Polished chambers do not ruin an otherwise good cylinder head.

And for what it's worth, the possessive form of "your" does not use an apostrophe or an E. Let's not start casting stones just yet, shall we?

[mr2magic]

Damn, I'm wrong here I thought this was a porn thread what with the title and all! You've ruined my day!

END of OT

[Jackstand Queen]

Te51Levin:

I dare you to polish the combustion chamber of the next head you remove from one of your cars.

The reason for the dare is: polishing combustion chambers makes the chamber too hot. The polished surface reflects (infrared) heat back onto the piston,valves and back onto the polished chamber metal. The increased surface area of the normal cast metal surface allows more heat to be absorbed and transferred primarily to coolant passages.

As far as I know, I'm just spouting theory, I've never seen it done, nor heard of anyone who did it. I could be wrong. But you are definitely right in the thermodynamics department . . . it would enhance thermal efficiency.

[te51levin]

Originally Posted by Jackstand Queen

I dare you to polish the combustion chamber of the next head you remove from one of your cars.

Chellenge accepted - but I beat you to it several years ago. The chambers in my 7AGE are polished, as were the chambers in my old 2TG:

YouTube - Toyota 2TG idles and revs

I do understand your theory, but for it to be valid, there would have to be so much heat in the combustion chamber that the valves, pistons, etc were in constant jeopardy of self-destruction, unless as much of that heat as possible was continuously transferred to the coolant via the cylinder head. None of those parts are in danger (unless something else is very wrong), so the more heat we can turn into combustion pressure, the more power we will get out of each unit of fuel.


This is not new thinking, and I'm not the only one doing it:
polished combustion chamber - Google Search

From Tech Data -
When we are speaking of Reflectability, we are looking at the ability of a surface to reflect heat. Generally this characteristic has been achieved by polishing the combustion chamber surfaces. A polished "bright" surface will reflect heat into cooler areas. This can be illustrated by considering an irregularly shaped room, lighted by a single bulb. There will be areas of the room that do not receive as much light, either because of being shrouded or simply because of being further from the light source. If you were to line the walls with mirrors the light would be reflected into the darker areas providing near equal levels of light through out the room. A combustion chamber would react the same way if the light/heat generated by ignition could be more evenly dispersed within the combustion chamber. More even and complete oxidation of fuel would occur, thus increasing the efficiency of the engine, making more power and reducing emissions. This has been demonstrated by the resulting increase in engine horsepower with a corresponding reduction in carburetor jet sizing.

[donnyavery]

bang is right. NOS on an old motor is a quick way to get a new motor and its the least cost effective method of power in long terms.

you should not hate on nitrous because its just as safe if not safer then turbos if install and used properly but to many people think you can just put it in and hit the button. 90 present of the time engine fails its be cause of install or operator i install these kits daily i have a customer with a 90s ford prob has 167000 miles on it he been through 17 bottles in 4 months and still runs like a champ and if a ford can do it a Toyota 4ag can do it better

i spray my mr2 with a 100 shot and run 12psi of turbo boost only failers i have are the clutch here are some pic with nitrous on my sc setup and the turbo setup
http://www.mr2.com/forums/attachment...1&d=1247868762