supercharging F7P?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

nah its just the same questions asked by the same people who get the same answer then ask the same questions again.

Standard CR is 10:1

Skimming pistons is the muppets way of lowering CR, it opens up the squish which reduces throttle response, economy and mid range power. Thicker or twin headgaskets do exactly the same.

The only way to lower CR properly is different pistons or to machine a bowl in the existing piston which again is not right, new pistons are the wise choice.

You cannot tell and engine how it will run, how much fuel it will take etc etc, 2 identical engines will require very different fueling and ignition characteristics.

Thats why off the shelf/out the drawer chips can on 1 car give a power hike of 10bhp and on another may lose 15bhp to a stock chip.

Compresion ratio, the compresion ratio thats there at the moment is worked out very simply, it assumes a closed chamber being full and the air being compressed but not heated, thats how you end up with the 10:1.

Throw in variables like heat, humidty, air density, valve over lap, reversion, throttle opening etc etc and it means nothing

These variables also affect boost. Ask yourself what is boost? A reduction to flow, thats what it is.

What makes an engine give power? Flow of air through it.

This is being very simplified here so the more knowledgeable be quiet.

Boost is also made by temperature, get a can fill it with air then heat it up by 100 degrees and the can will now have 5 PSI of boost in it. 100 degrees isn't that much heat to instill in the intake charge on a turbo btw.

Lets say we had a boost reading of 10PSI with standard cam timing, lets increase the overlap on the cams, the boost may now drop to 3PSI, the engine may still have the same or more power. Lets now advance the inlet and retard the exhaust, boost may now climb to 15PSI but we will probably have less power.

Lets now talk about lag, a charger will get up to boost a lot more rapidly than a turbo, lets say we have one engine everything is identical down to boost characteristics, heat imparted etc etc, only difference is one has a superchager whilst the other is turboed. The engine is at 4krpm on a closed throttle. When you floor the turbo engine it will take longer than the supercharger to get back up to max boost, by the time the turbo gets to max boost it may well be 2 krpm behind the supercharged engine. So this means they require totally different fueling and ignition characteristics.

Also an engine will run with very crap setting up. They can go as rich as 10:1 and as weak as 20:1, this will not give anything like peak performance or efficiency but the engine will run. It will not give out anything like its potential.

A relatively crappy engine design (very undersquare, small valve, push rod 4 cyl) which has had time spent on mapping the fueling and injection, may outperform in every area a 16V twin cam 4 of greater capacity with medicocre mapping.

Some stock engines leave the factory and are demon lumps, great power, wide power band and great economy, then an engine 10 blocks behind on the production line may be well down on power etc etc. All due to manufacturing tolernces and givign enough missmatch to not run right at all on the manufacturers pre pregrammed fuel and ignition maps.

Thjis has got a bit long winded and off topic soi shall stop.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

no....u r right! thats why re-programmable managment is the way forward, not "chips"

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

I know I am right Stan. i always am.

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

except 4 when i am Wink

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

which is never! hehehehe

Gay Rights Activist Joined: 07 Apr 2004 Posts: 1268

u fuckin had me!