Starting to think about boost
09-29-2012, 10:34 PM
#1
Drifting
Thread Starter
Starting to think about boost
I have the 1r rods but am still considering putting a mild boost kit on at some point. Likely a 6lbs kit and would go to full boost not very often. After boosting the 928 I can see how much more drivable a car is with boost. Even at low rpm and minimum boost it really transform the car to something modern.
10-01-2012, 01:28 PM
#4
Rennlist Member
I have the 1r rods but am still considering putting a mild boost kit on at some point. Likely a 6lbs kit and would go to full boost not very often. After boosting the 928 I can see how much more drivable a car is with boost. Even at low rpm and minimum boost it really transform the car to something modern.
Boost is boost, supercharging or turbo-chanrging. If our cars can run on 6psi of boost super-charged, no reason why they can't do the same turbo-charged. A 300hp low boost application running on stock compression would make it a great car around town.
10-01-2012, 05:55 PM
#5
Addict
Rennlist Member
Rennlist Member
The issue with supercharging IMO is that the change in boost pressure can be so rapid you can get a storm of detonation before the timing is pulled back. The supercharger is already spooled and bypassing and provides boost right away if you go to full throttle from cruise. A turbo has to spool up.
The 968 piston skirts are also rather short and thus the engine is more sensitive to bore scuffing under detonation.
Overall I think the supercharged 968 is a great car to drive but fuel quality and environmental factors are of concern. These factors can be mitigated but perhaps never eliminated.
I feel a V8 conversion would evolve to be a better, more reliable, more confidence-worthy car but the cost is much higher and I would expect some issues early on as conversion related problems are addressed.
-Joel.
The 968 piston skirts are also rather short and thus the engine is more sensitive to bore scuffing under detonation.
Overall I think the supercharged 968 is a great car to drive but fuel quality and environmental factors are of concern. These factors can be mitigated but perhaps never eliminated.
I feel a V8 conversion would evolve to be a better, more reliable, more confidence-worthy car but the cost is much higher and I would expect some issues early on as conversion related problems are addressed.
-Joel.
10-02-2012, 10:32 PM
#6
Drifting
Thread Starter
The issue with supercharging IMO is that the change in boost pressure can be so rapid you can get a storm of detonation before the timing is pulled back. The supercharger is already spooled and bypassing and provides boost right away if you go to full throttle from cruise. A turbo has to spool up.
The 968 piston skirts are also rather short and thus the engine is more sensitive to bore scuffing under detonation.
Overall I think the supercharged 968 is a great car to drive but fuel quality and environmental factors are of concern. These factors can be mitigated but perhaps never eliminated.
I feel a V8 conversion would evolve to be a better, more reliable, more confidence-worthy car but the cost is much higher and I would expect some issues early on as conversion related problems are addressed.
-Joel.
The 968 piston skirts are also rather short and thus the engine is more sensitive to bore scuffing under detonation.
Overall I think the supercharged 968 is a great car to drive but fuel quality and environmental factors are of concern. These factors can be mitigated but perhaps never eliminated.
I feel a V8 conversion would evolve to be a better, more reliable, more confidence-worthy car but the cost is much higher and I would expect some issues early on as conversion related problems are addressed.
-Joel.
10-03-2012, 06:06 AM
#7
Three Wheelin'
It is all in the tuning. I have my supercharger install tuned with minimal detonation through setting an appropriate AFR and retarding the stock timing. The knock count is no worse than it was before it was supercharged. For added safety I run an octane booster for track work.
If you don't change the tuning and fuel correctly, you will probably run into some issues in the longer term.
If you don't change the tuning and fuel correctly, you will probably run into some issues in the longer term.
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10-03-2012, 10:00 AM
#8
Addict
Rennlist Member
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Fuel quality: You can buy quality fuel but you have no control over what they actually sell you. If your build requires premium and you buy premium, what happens if you are sold regular?
I think more modern boosted cars are better at adapting to dangerous conditions caused by bad fuel or particularly hot days, etc. To make a boosted 968 safe IMO it should have some feedback so the driver knows if knock counts are way up. Water injection helps too, but it gets a bit fiddly. I was playing around with ideas like running an electronic BOV to limit boost until the car was in WOT mode and the water injection was activated and had pressure (to prevent boosting suddenly while still in part throttle mode.) An intercooler would help too, it would increase the plenum volume as well as cooling the intake charge.
The issue IMO is that a 90 or 95% solution is nowhere near as difficult as the 98% solution. With a 95% solution you might break the car on a hot July day. Or you choose to drive something else, or you have the forethought to use race gas that day.
Tuning is key but you can't tune a 968 to make it spontaneously grow a KLR or a MAP sensor.
I think more modern boosted cars are better at adapting to dangerous conditions caused by bad fuel or particularly hot days, etc. To make a boosted 968 safe IMO it should have some feedback so the driver knows if knock counts are way up. Water injection helps too, but it gets a bit fiddly. I was playing around with ideas like running an electronic BOV to limit boost until the car was in WOT mode and the water injection was activated and had pressure (to prevent boosting suddenly while still in part throttle mode.) An intercooler would help too, it would increase the plenum volume as well as cooling the intake charge.
The issue IMO is that a 90 or 95% solution is nowhere near as difficult as the 98% solution. With a 95% solution you might break the car on a hot July day. Or you choose to drive something else, or you have the forethought to use race gas that day.
Tuning is key but you can't tune a 968 to make it spontaneously grow a KLR or a MAP sensor.
10-03-2012, 10:24 AM
#9
There are people who succesfully tune 944T retaining the DME/KLR but using a MAP sensor plugged in place of the stock AFM.
Since the DME from the 16V engines handles knock with no KLR box, I see no reason a turbo'd 968 could not be run with the stock 968 DME box associated to a MAP sensor instead of the MAF...? Provided there are enough outputs on a 968 DME to control a cycling valve.
Since the DME from the 16V engines handles knock with no KLR box, I see no reason a turbo'd 968 could not be run with the stock 968 DME box associated to a MAP sensor instead of the MAF...? Provided there are enough outputs on a 968 DME to control a cycling valve.
12-10-2012, 11:59 AM
#10
Drifting
Thread Starter
So if someone was going to supercharge a 968 with reliable safe boost to enhance street performance what type of charger would you go with? I really like the Rotrex in my 928. It givse me immediate and very noticable low end power which is very usuable on the street. What tuning tools are used. The 928 has the sharktuner. What is the best way to moniter knocks in a 944 or 968?
12-15-2012, 04:15 AM
#11
Three Wheelin'
Rotrex C30-94.
Tune using TunerPro RT and an Ostrich Emulator. Hook up a datalogger such as an Innovate LM-2 and install a knock counter.
See the link in my signature.
Tune using TunerPro RT and an Ostrich Emulator. Hook up a datalogger such as an Innovate LM-2 and install a knock counter.
See the link in my signature.
