Changing boost spring
05-17-2004, 02:36 PM
#18
RL Technical Advisor
Hi Sameer:
John is correct.
FWIW, John's motor is still leaner than it ought to be at 1 bar. I prefer seeing 12-12.3:1 on boost to help prevent ring failures from detonation.
Please remember, you never hear the kind of detonation that shatters rings as the ambient noise levels on these cars is too high for that.
The human ear is a notoriously poor "knock sensor" and one's pocketbook will get significantly slimmer if one relies on those,...
John is correct.
FWIW, John's motor is still leaner than it ought to be at 1 bar. I prefer seeing 12-12.3:1 on boost to help prevent ring failures from detonation.
Please remember, you never hear the kind of detonation that shatters rings as the ambient noise levels on these cars is too high for that.
The human ear is a notoriously poor "knock sensor" and one's pocketbook will get significantly slimmer if one relies on those,...
05-17-2004, 10:39 PM
#19
Nordschleife Master
Join Date: Oct 2001
Location: Mount Pleasant, South Carolina
Posts: 7,568
Likes: 0
Received 5 Likes
on
3 Posts
Steve and all,
It's been a while since I did my last dyno run with a sniffer, but here it is. What do you think of this at 1 bar? Gets very fat fast and then leans out to 12.7 at higher rpms.
Jim
It's been a while since I did my last dyno run with a sniffer, but here it is. What do you think of this at 1 bar? Gets very fat fast and then leans out to 12.7 at higher rpms.
Jim
05-18-2004, 12:39 AM
#21
RL Technical Advisor
Hi Jim:
LOL,...You are witnessing the main fault with the CIS used on 930's. They are too lean at higher RPM and on boost.
If one tries to band-aid the problem by adjusting the CO screw, it gets too rich to run in the low & mid-range. This is why we modify the airflow meter and FD to flow more fuel where and when the engine needs it.
Still,....CIS is very limiting in this regard and will not provide quite enough fuel to be safe above 450-460 HP. We use richer mixtures to help contain cylinder head temps on air-cooled turbocharged engines and anything leaner than 12.7:1 is not good for one's wallet,....
LOL,...You are witnessing the main fault with the CIS used on 930's. They are too lean at higher RPM and on boost.
If one tries to band-aid the problem by adjusting the CO screw, it gets too rich to run in the low & mid-range. This is why we modify the airflow meter and FD to flow more fuel where and when the engine needs it.
Still,....CIS is very limiting in this regard and will not provide quite enough fuel to be safe above 450-460 HP. We use richer mixtures to help contain cylinder head temps on air-cooled turbocharged engines and anything leaner than 12.7:1 is not good for one's wallet,....
Last edited by Steve Weiner-Rennsport Systems; 05-18-2004 at 08:21 PM.
05-18-2004, 09:48 AM
#22
Racer
Join Date: Jun 2003
Location: CO
Posts: 497
Likes: 0
Received 0 Likes
on
0 Posts
Here is my latest dyno chart where I skinned the cat in a different way to get a good A/F curve with CIS. Still my wideband was reading a little richer than the one at the dyno was saying on boost.
05-18-2004, 02:06 PM
#23
Nordschleife Master
Join Date: Oct 2001
Location: Mount Pleasant, South Carolina
Posts: 7,568
Likes: 0
Received 5 Likes
on
3 Posts
Originally posted by Brent 930
Jim,
That is a typical CIS curve, what enrichment are you running if any? I agree with Steve, you should shoot for 12:1 A/F especially in the summer.
Brent
Jim,
That is a typical CIS curve, what enrichment are you running if any? I agree with Steve, you should shoot for 12:1 A/F especially in the summer.
Brent
I'm also thinking of going back to the .8 spring for insurance.
