"All About Compression" by Toda - Boost + NA

[poid]

if you are getting pre-ignition, it doesnt matter what plug you run...the fuel is igniting because of cylinder pressure and not spark.

[saxman]

if you are getting pre-ignition, it doesnt matter what plug you run...the fuel is igniting because of cylinder pressure and not spark.

detonation is a result of heat and cylinder pressure... using a colder plug, which will remove some heat from the cylinder, could help prevent some detonation, if you were detonating from heat problems. If you're at the point where you've reached the knock threshold of the fuel from cylinder pressure, than, yes, you're correct, changing plugs won't really make a difference.

[nd55]

shebangs, try this link.

No formulae, but very useful.

There's a field to input atmospheric pressure.

http://www.not2fast.com/turbo/glossary/turbo_calc.shtml

Nick.

[nd55]

> thought colder lower gapped plugs with an improved coil could improve the situation....

David Vizard says the primary benefit of improved (eg CDI) ignitions is enable the spark under fouling conditions which colder plugs create.

That was before EFI systems though.

Further, I suppose a slightly colder plug in a boosted situation doesn't have the fouling issues.

Nick.

[IZY-10]

interesting read. so basically you figure out how many bar you are running plus surrounding air pressure (1bar at sea level) then multiply by compression ratio.

[votek]

very good read thanks but theres a limit til when 'knocking' starts

find a good tuner guys!

[EfiOz]

You shouldn't ever get near the bit where the knocking starts if you know what you're doing.

[lil_foy]

But with the lower compression engines running super boost, because they have higher air fuel mixtures they have more potential energy in the cylinder correct?
Meaning high hp in the end yes?

[votek]

wouldnt more boost mean more torque

[Benson]

e85 with boost goes very well together

[Limbo]

yeah when you reach that knock barrier its when fueling is important and a higher octane fuel is needed.

That is why sometimes it is recommended to drop compression to stop pre-igntion of fuel that goes into the head, cos you its hard to get fuel that is consitently the right octane for you car. If you don't have a buffer then if you get a bad batch of fuel you'll pre-ignite and there goes all the hard work & money.

I'm not an expert but that's my understanding

[SeverAMV]

with most cars though, there is a certain amount of overlap between the exhaust and intake valve opening times, and on some cams, valves may be open slightly during compression stroke, which means that the actual dynamic compression can be lower than the static compression initially calculated.