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Boost pressure question
Posted: Wed Aug 02, 2023 7:46 am
by rh15
Hi, I’m looking at a 944 as my first Porsche and had the opportunity to test drive a 944T recently—which was my first time in any 944. My question is regarding how a 944T should normally “feel” when the boost comes on. I’ve owned and driven other late 80’s (non-Porsche) turbos and it was quite noticeable when the turbo kicked in on those cars. This particular car seems very well cared for, but the boost gauge was unfortunately inoperative. Around 3200 rpm I noticed a definite acceleration improvement, but didn’t feel that kick that I had experienced in other 80’s turbos. Is the 944 Turbo’s boost ramp up more gradual and refined than those other 80’s turbos, or could there be a potential problem with the turbo? I wasn’t 100% sure if the acceleration improvement starting around 3200 was due to the turbo, or from just being in the powerband of the 2.5L. Thanks in advance for any insight!
Re: Boost pressure question
Posted: Wed Aug 02, 2023 4:08 pm
by blueline
rh15 wrote: Wed Aug 02, 2023 7:46 am
Hi, I’m looking at a 944 as my first Porsche and had the opportunity to test drive a 944T recently—which was my first time in any 944. My question is regarding how a 944T should normally “feel” when the boost comes on. I’ve owned and driven other late 80’s (non-Porsche) turbos and it was quite noticeable when the turbo kicked in on those cars. This particular car seems very well cared for, but the boost gauge was unfortunately inoperative. Around 3200 rpm I noticed a definite acceleration improvement, but didn’t feel that kick that I had experienced in other 80’s turbos. Is the 944 Turbo’s boost ramp up more gradual and refined than those other 80’s turbos, or could there be a potential problem with the turbo? I wasn’t 100% sure if the acceleration improvement starting around 3200 was due to the turbo, or from just being in the powerband of the 2.5L. Thanks in advance for any insight!
Welcome to Carpokes! Sorry that I cannot answer your question but someone here will have some thoughts on it. Hopefully you'll hear something soon.
Re: Boost pressure question
Posted: Wed Aug 02, 2023 5:28 pm
by Dave W.
It's normal for a stock 944 Turbo to have gradual spoolup. There's no real torque spike like a tuned car will have.
Re: Boost pressure question
Posted: Wed Aug 02, 2023 8:06 pm
by Tom
When I test drove my car in the late 90's, it was bone stock and I thought there might be something wrong with it because there was no big burst of boost. It was weirdly gentle actually. I bought it after driving other stock 951s and realizing they were all like that. First thing I did was install a set of APE chips and 'boost bolt' and was stunned how dramatically it transformed the car.
Re: Boost pressure question
Posted: Fri Aug 04, 2023 2:33 pm
by Doyle623
Those Autothority chips were a gateway drug for the 951 community!
Re: Boost pressure question
Posted: Sun Dec 31, 2023 7:52 am
by 944m3
Late to the thread.
Trying to learn more about tuning our engines (or engines in general).
I first bought my car with a powehaus 27/6 hybrid turbo and Autothority chip installed. The car was quick, pinned me to my seat to give me that turbo rush. I could spin the wheels in 3rd gear, it was great. I’ve even considered going back to that chip.
Question, in general, what was that chip doing? Dumping more fuel and advancing timing?
Re: Boost pressure question
Posted: Sun Dec 31, 2023 9:29 am
by cda951
Welcome!
See the attached image from Porsche's original Service Information Technik manual for the 951----Porsche purposely regulated the boost curve to provide a smooth increase in torque rather than a sudden spike.
If you install one of the Lindsey Racing "boost enhancers" or upgrade to a dual-port wastegate with proper electronic control, the boost will build as quickly as possible and provide that 1980s turbo rush that you are accustomed to.
@944m3 , I would not go back to that ancient chip. Contact @Fast951 if you want a proper and safe tune, and you can get that turbo rush back if you want.
Re: Boost pressure question
Posted: Sun Dec 31, 2023 9:42 am
by Tom
944m3 wrote: Sun Dec 31, 2023 7:52 am
Late to the thread.
Trying to learn more about tuning our engines (or engines in general).
I first bought my car with a powehaus 27/6 hybrid turbo and Autothority chip installed. The car was quick, pinned me to my seat to give me that turbo rush. I could spin the wheels in 3rd gear, it was great. I’ve even considered going back to that chip.
Question, in general, what was that chip doing? Dumping more fuel and advancing timing?
It is adding more fuel to keep up with the turbo. With the k27, a lot more air is getting forced into the motor, so additional fuel is needed to maintain a safe air-fuel ratio (AFR) somewhere around 12 to 1 on boost. People sometimes make the mistake of thinking that just adding more fuel with bigger injectors or higher fuel pressure will make more power, but all that does is make the motor run overly rich, wasting fuel and making less power. The chip is programmed to deliver the 'right' amount of fuel given all the other parameter -- injector size, fuel pressure, air flow, temps, etc. Most chips try to add a little ignition timing too, to pick up a small bump in power, but the 951 blows head gaskets too easily to go too crazy on that front.
Re: Boost pressure question
Posted: Sun Dec 31, 2023 12:30 pm
by 944m3
Makes sense. Thanks for the replies.
Re: Boost pressure question
Posted: Mon Jan 01, 2024 7:52 am
by Jay Wellwood
cda951 wrote: Sun Dec 31, 2023 9:29 am
Welcome!
See the attached image from Porsche's original Service Information Technik manual for the 951----Porsche purposely regulated the boost curve to provide a smooth increase in torque rather than a sudden spike.
If you install one of the Lindsey Racing "boost enhancers" or upgrade to a dual-port wastegate with proper electronic control, the boost will build as quickly as possible and provide that 1980s turbo rush that you are accustomed to.
@944m3 , I would not go back to that ancient chip. Contact @Fast951 if you want a proper and safe tune, and you can get that turbo rush back if you want.
Thanks for sharing.
Q: What is the curve labeled 'C' depicting?