Supplement to Port Matching thread.

[xxtrizz]

Ok I was reading that post and decided I would write down some info I was reading from a book of mine that might help with some builders concept on what works for a NA and Turbo set up.

This post goes over a lot of N/A but covers Turbo port setups as well with emphasis on low-end torque. Or as I read or understood basically that is what we are dealing with.

OK this is going to be a barrage of erratic information so sit back and hopefully we can piece this beast together.

First off Forged pistons may be stable at high temperature but are not suitable for a street use. The more thermally stable the alloy, the less the piston will expand when hot. We all seem to know this tid bit of information as true. But we also know that a forged piston is also stable. This excerpt was taken merely to the fact that a lot of people don’t use Forged pistons for rebuilds that are simple; they use them for higher horsepower build-ups.

In engines designed to produce average or moderately high power output, cast pistons use thermal expansion limiters.

Cast pistons are usually less conducive to heat energy transfer and keep the heat for the combustion in the chamber. Secondly they are designed to have minimum bore clearance providing amore stable platform for piston rings. Third they are lighter than forged pistons. Ok I’m not sure about the validity of some of the things they were impressing here but I’m sure they are referring to cast aluminum. Not cast iron as we usually refer to cast pistons in that metallic sense.

Hyper -eutectic (pistons) are made from a material that is manufactured at a higher temperature. The result is a light piston having nearly the same strength of a forged piston combined with the desired hardness and low expansion rates of a typical cast piston. Furthermore they go on and reference how these pistons are practically unbeatable in 4 cylinder engines. Also how these pistons are excellent in N/A engines. But from my understanding I don’t think that we get high enough Rpm’s to ever necessitate the need for forged pistons. Although they are widely manufactured compared to the latter examples maybe your buying the wrong piston? Some of us are trying to pull a large amount of horsepower out of a engine but end up using a piston that absorbs heat and expands rapidly compared to something that is less conducive off heat. Rather than putting in forged pistons for a 260 hp engine maybe your looking more at hypereutectic pistons. By putting the forged pistons in to make your 260 your actually loosing the horsepower gain that you wished for initially because of the bore clearance, ring ride on the cylinder walls and the reflection of heat energy by the hyper eutectic piston.

Its also from my understanding that detonation on a forged piston occurs when there is extreme amounts of heat pockets in the combustion chamber that build up and affect the piston. It is also from my understanding that if you have these high amounts of thermal energy in a "pocket" on one side of the piston then in turn your forged piston would not be able to handle the heat in one specific spot all at once and thus create wear or a detonation on that side of the piston eating away its compound. So for a 260-hp detonation to occur I'm sure you need to rethink your fuel management but also maybe you’re looking at the wrong pistons?

You could always take your pistons and get them ceramic coated or hard coated. This would help greatly with any absorbed heat into the forged pistons. Ceramic coatings act interestingly and I’m sure this next bit of information will have you on your seat. But Ceramics absorb in the top layer of the ceramic coating the heat energy from the combustion and every other layer of ceramic coat reflects the energy. Wow interesting eh? Well that would definitely help with any heat energy faults or even producing more energy. If you have a lot of energy absorbed into the piston as forged pistons do then your loosing a lot of potential energy from the system. But if you have a ceramic coating then you would reflect this potential energy rather than absorb it and in turn the energy will be used more to "push" or add downforce to the pistons rather than loose that capability in the system after combustion.

A Company that handles ceramic coatings would be:

Swain Technology (7168892786)Polydyne Performance (7136943296)

You could also go the hard coating way. Hard coating is applied or bonded at the molecular level by process similar to plating. These coatings produce a hard surface that reflects heat energy mechanically off the surface.

A Company that deals with Hard Coatings is

"Lovatt Technology" (2139466679) specialize in such coatings and works on several of the parts for the space shuttle. Also this process is reasonably inexpensive dependant on what you consider expensive.

As you all know and probably are going to contend to the fact that having a piston that completely reflects the heat energy is unsafe and not a good method. The reasoning behind this is you would much rather have the piston heat up and then heat the air upon entering the combustion chamber itself rather than have a cold piston that would fire cold air and cause a whirlwind of hot/cold gases in the combustion chamber allowing for a hot pocket of detonation in the engine combustion chamber.

So that is why I would have to promote ceramic coating it absorbs that heat in the top layer allowing for the heat to expand the air for better combustion. You might as well even get a hard coating with a ceramic top but that is completely up to you and your budget.

Now well take a break from pistons and move onto ports and combustion chambers for now. I will cover valves and valve lift and port and polishing or not polishing which was touched on in the other post as well.

As any of us tuners should know a stock intake port should have a small cross- sectional area, a rough surface texture, and a shape conducive to flow. But who says that any car company gets this just perfect hmm? So lets hit some points about ports and valves, flow, and various other erroneous materials. These are going to be sparse so try to take the info and gather it so it makes sense to you.

(1) Improving flow without making the port significantly bigger is vital. Since a larger crossectional area will reduce low-end power.

(2) Top quality 3-angle valve job will make a significant improvement in port flow at all engine speeds.

(3) Picking cams that open the valve far enough to allow the port to flow at its best. Standard valve lift is .500 but may be increased to as much as .550 for street use in some cases, this increases the flow of the valves. Good low-lift can produce crisp acceleration and deliver good street derivability. Larger intake valves are one way to obtain these benefits.

(4) Install bronze guides, and consider using valves with hard-chrome stems. (Or titanium) This will keep guide and stem wear to a minimum. Usually valve stem and guide wear is attributed to high lift cams. Refer back to rule 3 for more info. Bronze guides made by APT (7147830344) are pre machined for Teflon seals. Only needed on Intake side really, but you also may use them on the exhaust side to help against oil leaking in the chamber.

(5) This next point was touched upon by the other post in that very informative web-site that was posted. A rough surface finish will help to mix the air fuel, this doesn’t hurt flow, and it requires much less time than polishing.

(6) Have the best valve job performed. Add a 30-degree top cut to the seats and backcut on the valves.

(7) Have any sharp edges on the bottom side of the valves ground away.

(8) Experience has show that the optimum exhaust valve size should be about 75 percent of the intake. Or mathematically the open flow rate should be 75 percent of the intake because hot gas escapes 25 percent quicker than the intake side consumes.

(9) As timing for cams is increased, (by installing a cam with a longer duration) the power gains from an increasing compression ratio become even greater. Typical set up is 248/248.

This was all documentation supplied to me. So some of it may not be true for the 240sx ka24e or de. But its experimentation that makes this business so interesting. Have fun

[nismofan14]

Thanks for more info. What book are you reading if I may ask? I can never read/learn too much.

[xxtrizz]

Crap forgot the name it was at barnes and nobles I was jsut reading and taking notes from it lol.

[C-Kwik]

I'd like to know what this book is as well. A lot of the information in there contradicts many things I have heard and even experienced. For example, a forged piston(at least the one my friend used) actually expanded more than a cast one. The cold clearance was a little on the loose side. You could totally hear it when cold, but went away once the motor was warm.This was a JE piston for a Supra.

It sounds like you were interjecting some of your own thoughts and opinions as well. So I'm not sure what the book may be saying or if it's just what you are saying...

[xxtrizz]

No what you said was right. Its the same thing I posted a forged piston has more bore clearance so is loose before it becomes stable at high temperatures.

The cast one if you read up again I said that it has thermal expansion limiters. means they dont expand at higher temperatures. Forged do however. But that makes them "stable" for race use at higher temps.

Basically what I was implying with the upper portion of the post is that everyone hops on to the bandwagon and buys a forged piston right off the back for a rebuild. But if you not going to make 300 hp I dont see the need for it. Especially i fyour not going to race. You would rather much have a cast or hypereutectic piston that seats better in the cylinder walls.

Yeah I was interjecting some of my thoughts but they were and I assure you not contradictive of the post itself.

[xxtrizz]

Oh and by the way for anyone who gets the hypereutectic piston confused with a better alternative for a turbo or supercharged application dont use hypereutectics for those forced induction applications. But you know for a naturally aspirated set up and especially on a 4 banger engine.

I know some of you are going to be saying "What?" but you said 260 was a safe range to put hypereutectics in, I know I said that but I ment in a general ideal. NA v6's get around that horsepower so it would be safe to put those epistons in the engine itself. But not a forced induction one.

[WDRacing]

Like I just posted in another thread, the stock cast pistons are fine under boost. You simply need to kill your detonation. Forged pistons will take a slight bit more abuse, but if your engine is detonating, then you'll blow rings, piston ring lands and scratch cylinder walls no matter what material the pistons are made from. There are quite a few stock block KA's rolling around making well over 300whp on a daily basis.

The only thing holding a few of them back is the turbo and cams. Dennis for instance would benefit from a bigger trim turbo and a set of cams. I'd be willing to bet he'd brake 400whp.

WD

[xxtrizz]

Hey WD if you put in hypereutectic pistons would those hold up pretty well compared to the stock cast ones?

[C-Kwik]

Well, according to Corky Bell, there seems to be two types. Cast hypereutectic pistons and T6 heat treated hypereutectic pistons. He doesn't really have anything bad to say of either. While he does seem to imply perhaps there is not much to be found of cast hypereutectic pistons. He says that T6 hypereutectic pistons have similar strengths to forged pistons. Unfortunately, he doesn't go into much detail about this. Keeps things very general. But he doesn't say anything negative about any of the pistons. Perhaps even cast pistons saying there really isn't much need unless redline is bumped up.

[WDRacing]

I think they would, but If I was gonna go through the trouble of changing out Pistons, bearings and rings I'd use Forged pistons.

My theory is stay stock or go big.

WD

[xxtrizz]

Thanks C and WD