building a motor *HELP*

[Hondabeefast]

Ok,I have a 03' 400ex am i am going to do a 440 big bore kit in it.I want some advice on what compression i should get(i dont want to run any special
gas alcohol,ect.)?Should i run stage 2 or 3 hotcam?Should I buy different intake/exhaust valves?Is there anything else i should buy?

I am having a local shop do the work,i am just furinishing the parts,I dont really know much about this so any advice will help Thanks!!!!

[exrider23]

Ok, run 11:1 and you can run pump gas with no problem. In my opinion i would go with a stage 2 HOTCAM. I had it in my 440 and i loved it. And for the valves, I would go with a good set of Kibblewhite Diamonbacks. Hope this helped

[lil p]

go with the12:1 for power. stage two. any over sized valves will work. port the head and get a full sparks pipe.

[Wheelie]

If you don't want to run race fuel stay at 11:1 or less. I'm running a stg3 Hotcam in my stroker and couldn't be happier.

Have the head ported as well, also install a HD cam chain.

[Hondabeefast]

ok,thnx guys

i ordered 11:1 comp. kit and stage 2 hotcam so far...

[GPracer2500]

Don't forget heavy duty head studs.

[lil p]

and steel inserts in the head to keep those studs from pulling out

[exrider008]

Originally posted by GPracer2500
Don't forget heavy duty head studs.

yup dont forget the HD studs. i just got mine put in today. i have the same mods as you 11:1 and stg 2 cam. you can get the HD studs at gtthunder.com for 60 bucks but it cost me 90 to get them put in:eek2:

[smitht316]

i have an 11:1 426 and have to run a mix of race and pump. if you really want to not run race id go lower then 11:1. i read the same things from everyone else that 11:1 is ok on pump gas but mine still pings, just for you info

[GPracer2500]

Originally posted by exrider008
....it cost me 90 to get them put in:eek2:
It cost me $95. :ermm:






My old 416 needed a race/pump mix with a JE 10.8:1. It pumped ~175psi cold at 1300ft. The 406 10.5:1 I was running before that was OK on my local 91 pump, but even it would pick up a tiny little "ting" at the top of a large sand hill. With the 406 it was really easy to just ride around it--just had to back off a smidge when deto started.

A lot of it just depends on how it's ran, how it is jetted, what the weather is like, elevation, the particulars of your local pump fuel, cam choice, and other factors. Sometimes I get the feeling that alot of the "11:1 is fine on pump gas" folks probably DO get some deto here and there and just don't realize it. That's probably OK though. A little sporatic deto can be withstood by most engines. Its not good for them, but they'll put up with it for a reasonable amount of time.

[Kaleigh]

sorry stupid question but... what is deto..

[Wheelie]

Detonation. When the fuel starts to ingnite before the spark plug fires--pre-ignition?

[GPracer2500]

Originally posted by Kaleigh
sorry stupid question but... what is deto..
Ok, you asked for it....;)



"Deto" is just my shorthand for detonation. Detonation is commonly known as "knocking", "pinging", or "spark-knock".

There are two kinds of combustion that can happen inside an engine's combustion chamber. One is deflagration. This is the good kind of combustion--the kind that happens when everything is behaving as it should. Deflagration begins when the spark plug fires. Air/fuel mixture right next to plug ignites and begins to burn. It does not explode, it burns (the latin root word for deflagration means "to burn"). This burn happens at a subsonic speed. Deflagration works through thermal conductivity. In other words, burning a/f mixture heats up the a/f mixture right next to it until that a/f mixture reaches it's ignition point, which then heats up the a/f mixture that's next to it, and so on. This is how the "flame front" that starts at the spark plug spreads out until all the a/f mixture in the combustion chamber is consumed.

The other kind of combustion is called detonation. Detonation is abnormal--gasoline engines aren't designed to support this kind of combustion. Deto is a much more powerful type of combustion that propogates at supersonic speed. Deto occurs in a gasoline engine when a/f mixture is compressed and heated so much that the fuel actually breaks down into new chemicals that can be auto-ignited (no ignition point is needed). Deto ALWAYS occurs after the spark plug fires.

Remember that the spark plug doesn't actually fire at Top Dead Center. It fires many degrees of crank rotation before TDC (about 25 degrees before TDC in a 400EX). So, the plug fires and deflagration begins. The piston is still on it's way up so the burning and as-yet unburned mixture continues to be compressed as the piston approches TDC. As deflagration continues (it takes time to spread out) the expanding gases released from deflagration cause huge increases in heat and pressure inside the combustion chamber. Again, two things are happening here, 1) as the flame front spreads out pressure and heat levels increase rapidly, and 2) the piston is still on it's way up creating even more pressure (and heat).

The a/f mixture that's at the very edges of the combustion chamber are called end-gasses (simply because they aren't consumed until the very end of the combustion sequence). These end-gases have to sit there and wait until the flame front arrives to consume them. While they're waiting they are being subjected to ever increasing amounts of heat and pressure. If there is enough heat and pressure, the end-gasses chemically degrade into new and highly unstable chemicals. At that point, it's not gasoline anymore. It's a mixture of chemicals that are so unstable that if heated and pressurized enough they will auto-ignite. This is detonation--when the end-gasses are degrated by heat and pressure to the point where they will deto (explode) all by themselves before the flame front (deflagrating a/f mixture) can get there to consume it normally. It's not until the spark plug fires and deflagration begins that the pressure and heat in the combustion chamber gets anywhere near high enough to cause fuel to detonate.

Lots of ignition advance (i.e. a plug that fires sooner during the compression stroke) creates conditions that favor deto. This is because the sooner deflagration begins the more time the end-gasses have to wait before being consumed normally. A high compression ratio just adds more pressure to the equation.

Detonation is bad because is sends out extremely fast (supersonic) pressure waves. These pressure waves are so sudden that the engine can't even begin to absorb it by forcing the piston downward. The result is a sudden spike in combustion chamber pressures. The audible "knock" or "ping" that characterizes when deto is taking place is caused by these pressure spikes slamming into the piston/head/cylinder walls. It's like hitting the top of your piston with a hammer--the whole engine resonates from the force. Equally damaging is piston and head errosion caused by deto's pressure waves blasting away the protective boundry layer of a/f mixture that prevents combustion chamber gasses from ever actually touching the metal surfaces.

Octane rating is a measure of a fuel's ability to withstand heat and pressure without degrading into chemicals that will succumb to detonation. Octane rating is ONLY A MEASURE OF DETO RESISTANCE--nothing else. Octane rating says nothing about how a fuel deflagrates. And deflagration characteristics are what determine a fuel's abiltiy to turn chemical energy into mechanical energy. This is why octane rating all by itself won't make an engine more/less powerful, run hotter/cooler, or anything else related to the normal deflagration of the fuel. Other fuel specifications determine those things. Octane rating only determines where the threshold is between deflagration and detonation.

All of the above explains why octane rating, compression, and ignition advance are central issues in determining if the abnormal combustion phenomenon known as detonation will take place. An engine's ability to remove heat from the combustion chamber is another important factor.



Pre-ignition is the other type of abnormal combustion phenomenon (note that pre-ignition is not the same thing as the auto-ignition mentioned above). It is a seperate (although often related) phenomenon vs. detonation. It always occurs BEFORE the spark plug fires. It is somewhat less complex--pre-ignition is simply when something in the combustion chamber begins deflagration of the a/f mixture before the spark plug does. Deto and pre-ign are related because one can lead to the other and vice versa.

I could go on....but I'll have mercy on the few that have made it this far....

[Kaleigh]

hey... it just stopped.. lol... thanks for the info.. it was extremely helpful.. i knew deto meant detonation.. but never understood the concept.. now I know what to listen for.. again.. thanks ^_^:macho

[Hondabeefast]

thnx for the advice guys