SU Tuning
Turbo Mini Forums

I have played about tuning Sus before but not with a fancy wide band. So it has always been on feel or down at the rolling road.

So, I have been tuning my NA 998. It has a 940 head and an SW5 cam and goes well enough. While tuning I have manages to get the mixture more or less spot on at all critical points. WOT is between 13 and 12, cruise is around 15 and all in between is between 13 and 15. I can change the tickover to more or less what I want.

However, I am struggling with the transients. If I snap the throttle to WOT it is fine, but if I go from say 1/4 throttle to 3/4 throttle then it leans out massively for a few seconds before settling down. I have tried different damper oil with little effect. The only fix to this has been to increase the mixture in the middle part of the needle, but now my cruise is about 12, so not a real fix.

Any suggestions?

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

What spring are you running?

stiffer spring?

I'm sure you've read this Ben, but lots of useful info with similar issues iirc

Gays only

Eidted to make hyperlink work

Edited by wil_h on 12th May, 2010.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Mmmmm, that is an interesting read. No easy answers and I was doing the right thing. It seems I need a different spring for a start.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

I'm having very similar problems with Axel's Mini 30. It has a 12G295, MG Metro inlet, HIF38 and an LCB.

Leans out badly on a gear change.

I ordered a Yellow spring on Sunday.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

The spring determines how high the piston rises. at the highest load (note - thats not rpm) it should allow the piston to rise to the top. If its too strong you are throttling the engine, too weak and the piston tops out too early so there is no ability to richen the mixture any more.

So before you get into springs I would first look at how high it gets(A little easier with an NA as the dashpot can be removed-- you can use a stick.) then select one from there. Then look at the profile. Stations 1-5 cover most cruise situations yours sounds OK, WOT is around station 12 also sounds OK The area you are talking about is probably stations 6-10.

Beware of the oil thickness fooling you, it will retard the rise of the piston so giving lower positions than "real" you can drive without oil, but you need to feed the throttle in slowly so it does not lean out initially.

Terry

website:- http://www.terryhunt.co.uk

As it turns out there are only 2 choices of spring for the HIF, 4oz (standard) and an 8oz one. I have now got an 8oz and I will put that on. I am also starting from scratch with a new needle. Hopefully my experience with the last needle will help.

I think what happened was that in my haste I have let the file change the cruise when I wanted to change lower down.

I will have all the birs this weekend so will see how I get on. I am not looking for perfection, just an improvement.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.