low CR = lag ?

[maRS2]

Does a lower CR give more lag?

I read that on the Mtm RSR they increase the CR to 9:3 and this car seams to have less lag than RS2 according to what the tester say.
I know it has a inverse IM but it can not only come from this.


How to increase CR on a RS2?

[volcano rs]

you can do it by skimming the head a little

[Greg_S]

the problem would be increased likely hood of detonation on boost because of higher CR

[maRS2]

yes I know about detonation but may be you get same power and torque figure with less boost.

I know in scooby world they sell Jun high CR block fully reinforced and get nice power figure with litle boost compare to us.

but what do you think about lag with higher CR

[Billman]

Not very improtant! They wrote that the RSR has higher compression ratio like they say in many articles that the RS2 has also 9,3:1 CR!

The RSR has a bigger turbo witch makes it worse but on the other hand appart from The short intake, had also the head flowed!

[~Delta]

Lower CR will make the engine feel flat off boost, and fuel consumption suffers.

[S2central.net]

There is a compromise here - like most engine things...

Higher CR improves low-mid range response off boost in a turbo car, but at high boost levels it may not be possible to achieve optimal ignition advance.

As I like lots of mid range performance, I'm not a big fan of extremely low CR values - just so as boost and advance can be maximised at WOT.

From memory the RR, 3B and early AAN & ABY 20V engines were built with a CR of 9.3:1 . These used a paper head gasket. At som point in time the AAN & ABY engines got a metal head gasket and I think all the ADU (RS2) got it as well. That stiffer gasket doesn't compress as much as the less reliable paper one and gives a lower of CR of approx 9.1:1. A little skim off the head (or a thicker metal gasket) would return CR to the 9.3 value.


Paul

[Greg_S]

you mean a thinner gasket

[volcano rs]

use higher compression but use water injection

[Audi_CQ]

CR isn't that significant. You probably won't feel any difference between a 8.5:1 and a 9.5:1 engine. What matters is airflow and dynamic CR, not static CR.

[S2central.net]

you mean a thinner gasket

D'oh - yes of course.

[S2central.net]

CR isn't that significant. You probably won't feel any difference between a 8.5:1 and a 9.5:1 engine. What matters is airflow and dynamic CR, not static CR.

Go on then - please explain this dynamic CR - I have heard that term once or twice before but never understood it !

[BRY]

Go on then - please explain this dynamic CR - I have heard that term once or twice before but never understood it !

Theoretical (static) is not actual.
If you consider the actual volume of "air" entering the cylinder, when turbo charged, the theorectical CR is out of the window.
You can get volumetric efficiency of over 100% on a NA car with clever inlet design.

Note; All the above is what I have read and I cannot prove any of it - It seems to make sense to me though

[Jamo]

Theoretical (static) is not actual.
If you consider the actual volume of "air" entering the cylinder, when turbo charged, the theorectical CR is out of the window.
You can get volumetric efficiency of over 100% on a NA car with clever inlet design.

Note; All the above is what I have read and I cannot prove any of it - It seems to make sense to me though

Those A-Team comics are a wealth of information

in seriousness i don't get this dynamic vs static CR, anybody got any links explaining it?

[S2central.net]

Forgetting ramair tricks for now - as they don't apply to turbo'd engines - I know thats how you get VE above 100% in certain conditions.

I don't see how the static CR measurement is 'out of the window' when the engine is running cos it still tells us how much the inhaled air is compressed by the action of the piston.

True enough the actual volume of air drawn in on our engines is determined by VE, rpm, boost and what the turbo is capable of flowing. Of course the more important factor of air MASS drawn in is determined by ambient conditions, turbo and intercooler efficiency.

As someone else indicated, water injection can also be used to reduce air temps (and therefore increase MASS of the same volume of air) to good effect.

Paul