924Board.org

[Euro924S2]

Hi Guys.

Whilst searching the web to gain info about exhaust gas temperatures and using them to tune ignition timing I found this really good link from which I learned a LOT!!

Worth sticky maybe?

http://www.clubwrx.net/forums/tuning-electronic-engine-management/14426-engine-basics-detonation-pre-ignition.html


Cheers, John.
_________________
UK spec '83 N/A with 931 motor with Eaton MP62 'charger @ 15psi. EFI - 565cc inj. Standalone Adaptronic ECU. 951 FMIC. Ally rad. Twin throttle. Recirc valve. Custom manifolds and CAI. 232bhp

[gegge]

A very good article! Well writen by an expert.
_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs

[morghen]

thanks ! quite an educational read.
_________________
Supercharger and EFI kits
https://www.the924.com

[gegge]

I would like to emphasise the importance of the CR. In a tuned engine you must raise the static compression in order to maintain the dynamic compression running a cam with high duration. But just increasing the CR does NOT give the powergain you are looking for. Especially if you have to delay the ignition. The reason for high CR in modern turboengines are efficiency and emission, not power (a highflowing 16V head helps). A low CR turboengine recovers the thermal loss in the turbo (which improves the response). In a NA engine it is a costeffective way to increase the hp slightly though.

Raising the CR from 8:1 to 9:1 will give you 3,5%, and from 9:1 to 10:1 2,9% more power in THEORY. Unfortunatlly is 16:1 not applicable on the 924 engine.

http://www.popularhotrodding.com/tech/0311_phr_compression_ratio_tech/index.html

Keep the CR low and the ignition high! Not the other way around.

Read the part "Running High Ratios and Living", it´s about detonation. A word about coating. If you decide to coat your combustionchamber and piston it will increase thermalefficency and raise the temperature of the endgas (leading to detonation). Good on a NA, but might be on the limit on a turbo.

Other articles (program and calculations) about dynamic CR and detonation:
http://members.uia.net/pkelley2/DynamicCR.html
http://www.rbracing-rsr.com/comprAdvHD.htm

Longer rods change the dynamic CR, but more important dwelltime at TDC and stands higher at 14° raising the maximum cylinderpressure slightly. Good on a NA, but could be problem on a turbo.
_________________
Carl Fredrik Torkildsen

924 turbo -81 Carrera GT RESTOMOD
924 turbo -80 Dolomite De Luxe
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black turbo with Fuchs