How much boost in reverse ?

[SRT-What?]

Good morning guys,


Something I've been wondering for a while now : how much boost is there in reverse ? and is the traction control activated when being in reverse ?

serious question

thanks,

[bbowers825]

I can't imagine why you might be asking this, but I would assume they limit the amount of boost in reverse so you don't break anything. The last thing you want to do while backing up is boost 10 psi lol.

[jsmonet]

I'm having flashbacks to "VTEC in reverse?" days. Wow.

[b1aze]

Just a speculation, but im wondering if he wants to do burnouts in reverse... like at a drag strip.

[cheshirecat79]

Pretty sure the engine throws out about 20psi the instant it senses you've thrown the car into "R".

i think I read that in the manual

[Colt]

With JB4 who knows, it could be 17psi

[Dackelone]

This reminds me of a story my Porsche tech friend told me about many moons ago... He was working at a Porsche dealer and they had one of their very first Porsche 930's (911 turbos circa early 1980's) was towed into the dealer with a blown manual trans. Those early turbos had an unique 4 speed manual. The customer "said" they were just backing out of their driveway when the trans make a loud BANG! The trans had to be rebuilt... took my buddy a month or two in waiting for parts and special tools. He was glad to see that car be fixed.

Then... the next week at the dealer... ANOTHER 930 was towed into the shop with the SAME problem! My buddy thought he would be only overhauling transmissions for this new uber Porsche model. Their dealer had only sold a few and this was the second car with a blown gearbox. So... he went about repairing the trans. But halfway into the repair... he noticed something "funny" These two 930's were next door neighbors. He fixed the trans... and when it was ready for the customer to be picked up... he stayed until the customer came to pick up his new 930 with a rebuilt trans.

He wanted to talk to the owner... he told him... "Look I know you and your neighbor both own 930's and BOTH of you had this blown trans problem"... "...but I want to know the REAL STORY as to how the trans blew. Just between me(the tech, my buddy) and you the customer."


And the customer said: "Ok... He is what happened... My neighbor and I had a bet who's car was faster in reverse... we both have a long driveway... SO... we started to race each other IN REVERSE... and as soon as our cars got on boost... we heard a loud BANG and the trans blew a hole in the side of it!! We knew we couldn't take both of our cars into the dealership at once... so first my buddy had his car repaired and them I brought my 930 in."

So... while you could probably pull a decent amount of boost in reverse... You really do not want to do that... bc the ever smart under engineers did not think someone would be so dumb to put that kind of load on the poor reverse bearings inside the trans!

[miro2296]

Originally Posted by cheshirecat79

Pretty sure the engine throws out about 20psi the instance it senses you've thrown the car into "R".

i think I read that in the manual

+1

[Freon]

Not sure if you'll get an answer, but they may not have bothered to sense the difference between 1st and reverse. There is almost a limitless list of questions you could ask about engine operation in reverse besides "boost limit."

Given a raw flash image of the ECU, someone could disassemble it and look at the code, but that is not available. Even if there was an image available, you're talking possibly dozens or hundreds of hours of work to get started.

As above, I wouldn't try your luck. The reverse gear in the transmission may not be able to handle high levels of load. If you want to do a burnout, use 1st. It wouldn't be safe to do it in reverse at a drag strip where someone's car or a human is behind you.

[SRT-What?]

Thank you all for the answers.

Don't worry, my goal is not to do burnouts or whatever in reverse (would have to be really dumb..)

My question had two aspects : really know how much boost the PCM would allow in reverse (if anybody had tried !), and see the reaction to the question.

Pretty satisfied of both results !

[ShocknAwe]

930 story was epic, thank you.

[Sequence]

Originally Posted by Dackelone

This reminds me of a story my Porsche tech friend told me about many moons ago... He was working at a Porsche dealer and they had one of their very first Porsche 930's (911 turbos circa early 1980's) was towed into the dealer with a blown manual trans. Those early turbos had an unique 4 speed manual. The customer "said" they were just backing out of their driveway when the trans make a loud BANG! The trans had to be rebuilt... took my buddy a month or two in waiting for parts and special tools. He was glad to see that car be fixed.

Then... the next week at the dealer... ANOTHER 930 was towed into the shop with the SAME problem! My buddy thought he would be only overhauling transmissions for this new uber Porsche model. Their dealer had only sold a few and this was the second car with a blown gearbox. So... he went about repairing the trans. But halfway into the repair... he noticed something "funny" These two 930's were next door neighbors. He fixed the trans... and when it was ready for the customer to be picked up... he stayed until the customer came to pick up his new 930 with a rebuilt trans.

He wanted to talk to the owner... he told him... "Look I know you and your neighbor both own 930's and BOTH of you had this blown trans problem"... "...but I want to know the REAL STORY as to how the trans blew. Just between me(the tech, my buddy) and you the customer."


And the customer said: "Ok... He is what happened... My neighbor and I had a bet who's car was faster in reverse... we both have a long driveway... SO... we started to race each other IN REVERSE... and as soon as our cars got on boost... we heard a loud BANG and the trans blew a hole in the side of it!! We knew we couldn't take both of our cars into the dealership at once... so first my buddy had his car repaired and them I brought my 930 in."

So... while you could probably pull a decent amount of boost in reverse... You really do not want to do that... bc the ever smart under engineers did not think someone would be so dumb to put that kind of load on the poor reverse bearings inside the trans!

best story i've heard in a while

[splitsecond]

Originally Posted by Dackelone

This reminds me of a story my Porsche tech friend told me about many moons ago... He was working at a Porsche dealer and they had one of their very first Porsche 930's (911 turbos circa early 1980's) was towed into the dealer with a blown manual trans. Those early turbos had an unique 4 speed manual. The customer "said" they were just backing out of their driveway when the trans make a loud BANG! The trans had to be rebuilt... took my buddy a month or two in waiting for parts and special tools. He was glad to see that car be fixed.

Then... the next week at the dealer... ANOTHER 930 was towed into the shop with the SAME problem! My buddy thought he would be only overhauling transmissions for this new uber Porsche model. Their dealer had only sold a few and this was the second car with a blown gearbox. So... he went about repairing the trans. But halfway into the repair... he noticed something "funny" These two 930's were next door neighbors. He fixed the trans... and when it was ready for the customer to be picked up... he stayed until the customer came to pick up his new 930 with a rebuilt trans.

He wanted to talk to the owner... he told him... "Look I know you and your neighbor both own 930's and BOTH of you had this blown trans problem"... "...but I want to know the REAL STORY as to how the trans blew. Just between me(the tech, my buddy) and you the customer."


And the customer said: "Ok... He is what happened... My neighbor and I had a bet who's car was faster in reverse... we both have a long driveway... SO... we started to race each other IN REVERSE... and as soon as our cars got on boost... we heard a loud BANG and the trans blew a hole in the side of it!! We knew we couldn't take both of our cars into the dealership at once... so first my buddy had his car repaired and them I brought my 930 in."

So... while you could probably pull a decent amount of boost in reverse... You really do not want to do that... bc the ever smart under engineers did not think someone would be so dumb to put that kind of load on the poor reverse bearings inside the trans!

Dude, I love how you have the answer to every question.

[Curare86]

Originally Posted by SRT-What?

Thank you all for the answers.

Don't worry, my goal is not to do burnouts or whatever in reverse (would have to be really dumb..)

My question had two aspects : really know how much boost the PCM would allow in reverse (if anybody had tried !), and see the reaction to the question.

Pretty satisfied of both results !

why dont you get a tune e.g. jb4 and log a run for us all in reverse?

[Exite]

Originally Posted by Dackelone

This reminds me of a story my Porsche tech friend told me about many moons ago... He was working at a Porsche dealer and they had one of their very first Porsche 930's (911 turbos circa early 1980's) was towed into the dealer with a blown manual trans. Those early turbos had an unique 4 speed manual. The customer "said" they were just backing out of their driveway when the trans make a loud BANG! The trans had to be rebuilt... took my buddy a month or two in waiting for parts and special tools. He was glad to see that car be fixed.

Then... the next week at the dealer... ANOTHER 930 was towed into the shop with the SAME problem! My buddy thought he would be only overhauling transmissions for this new uber Porsche model. Their dealer had only sold a few and this was the second car with a blown gearbox. So... he went about repairing the trans. But halfway into the repair... he noticed something "funny" These two 930's were next door neighbors. He fixed the trans... and when it was ready for the customer to be picked up... he stayed until the customer came to pick up his new 930 with a rebuilt trans.

He wanted to talk to the owner... he told him... "Look I know you and your neighbor both own 930's and BOTH of you had this blown trans problem"... "...but I want to know the REAL STORY as to how the trans blew. Just between me(the tech, my buddy) and you the customer."


And the customer said: "Ok... He is what happened... My neighbor and I had a bet who's car was faster in reverse... we both have a long driveway... SO... we started to race each other IN REVERSE... and as soon as our cars got on boost... we heard a loud BANG and the trans blew a hole in the side of it!! We knew we couldn't take both of our cars into the dealership at once... so first my buddy had his car repaired and them I brought my 930 in."

So... while you could probably pull a decent amount of boost in reverse... You really do not want to do that... bc the ever smart under engineers did not think someone would be so dumb to put that kind of load on the poor reverse bearings inside the trans!

That is crazy lol. I've always wondered how fast my cars would be in reverse but never tried it because just some common sense said something bad will happen. What that "bad" would be I never knew until now. Still some how I knew not to do it.

My fear was losing control I didn't even think about the tranny. In reverse it's like you're driving a forklift, and fork lifts don't go 40mph or the turning wheels would be in the "front".

[racer_x]

Great story Dackelone