I'm retarded....basic turbo/engine question.

[Mahalaleel]

So, I have a nub question: Cars have compression ratios. When you install a turbo, you have to match the ratio with fuel, right? Is there a point where you have too much air/fuel, and it just...won't fit? Or explodes, or what happens? Also, what do forged internals do? Does the e30 325is have them? Sorry for nub questions, I probably have more in the future.

Oh, and I don't mean, when you have 20:1 ratio, so bad stuff happens, I mean, when you have perfect ratio, but too much to fit. Actually....what is engine knocking? As opposed to detonation?

[Mahalaleel]

Does nobody KNOW? or is it just too retarded a question to answer... :(

[92 mtechnic cabrio]

Here's my theory on the whole thing, since I don't knwo too much about it.

say you're running an 11:1 compression ratio, and you try to cram more in, probably by changing the timing through use of swapping cams.

you would have a "larger" a/f mixture, creating a larger explosion, but since there is only so much space in the combustion chamber, most of it would be taken up by the fuel, and the air would be left out.

Causing a rich fuel mixture.

[mspiegle]

chances are, your motor will detonate to pieces before you get to the point where you couldn't physically fit more "mixture" inside the cylinder. I would assume it would be like hydrolocking (getting uncompressable water into your cylinders) and you'd break alot of parts in the motor.

forging is a process where you take a metal and compress it into a die. You get an extremely strong (and probably very accurate) part, but it is significantly more expensive to perform. The alternative is casting which isn't as strong.

and no, i don't think the M20 has any forged internals, but i also don't claim to know anything about the M20 or the forging process.

[Mahalaleel]

And the m42 DOES have forged internals?

[riverdale21]

The M42 has a forged crank whereas the later style M44 found in the E36 had a cast crank. Aside from the crank in the M42 nothing else is forged.

Detonation can be caused by a number of things. Cylinder pressure being too high is one cause. Hot spots inside your combustion chamber are another. Over time knock can destroy rings or if more severe break connecting rods in half and give you a nice air conditioned block.

[Dominick]

knocking, detonation, pre-ignition = fuel igniting too early and not beeing mixed with the air in the cylinders. With Pre-ignition, you can actually have fuel igniting into the manifolds (Intake- timing off and air/fuel mix flow is out of wack and being sucked bak into intake manifold....Exhaust- If cylinder isnt firing and letting unburned gas out, when it touches the hot exhuast pipes it ignites (backfiring also))

I doubt non turbo'd cars have forged engines, at least not BMW

when they forge a piece of metal, they actually continually fold and stretch the soft super hot metal over and over. So it has layers upon layers upon layers making it very strong and very expensive.

[Screaming_bmwe30]

lot's of misinformation.

Concerning compression ratio....the higher the pressures inside the cylinder head on the compression stroke...the hotter the air will be (air heats up when compressed, thermodynamics) Add a turbo to the equation...and your raising the pressure even further because of an intake charge of positive pressure....along with a hotter charge (turbos heat up the air) assuming you don't have a 100% efficiency intercooler. All of this heat leads to detonation. So the lower the C/R...the less heat...so less chance of detonation. with the stock 8.8:1....you should be fine up to 15psi or so. i am running 10psi with no problems...although you have to factor in proper fueling (11.5-12:1 AFR under boost) because running lean...like you all know can raise cylinder temps...also causing detonation. i'm running Megasquirt..so i'm able to tune the entire fuel curve...and keep the map rich (12:1) under boost. Proper fueling is a whole other matter.

Now concerning what detonation is. Usually...the air fuel mixture is in the process of burning....and as its on it's last 1/3 or so of the mixture...the cylinder pressures become higher and higher...and hotter and hotter.. This last bit of the mixture is usually the one to spontaneously combust...and create a small explosion. You can hear a ping or tick noise when this happens. The key is to supply the motor with enough fuel...which keeps combustion temps down....as well as keep intake temps down by using proper intercooling/ water injection/NOS or whatever.

I've got an entire DIY turbo writeup on my website if you want to take a look at it

http://jdturbocharging.com

Oh....and the m20 has forged rods. there are different processes for forging. I think Dominick was explaining how to make an Excaliber sword

[Dominick]

Oh....and the m20 has forged rods. there are different processes for forging. I think Dominick was explaining how to make an Excaliber sword

:P

[Mahalaleel]

Thanks a bunch! Checked out your site, and that DIY is pretty awesome...although being a car 'tard, (and poor as hell0), I bet i'd still mess it up :) That answered a lot of my questions, thanks again!