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Tuning The Rb25det

InterCooL
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InterCooL Rising Star

InterCooL

Posted
Posted

hey guys

this question is aimed at those who have done a bit of rb25det tuning;

for a stock turbo setup, does MBT (Minimum [spark advance for] Best Timing / Maximum Best Torque) occur before knock?

or will an rb25det stock turbo knock before it reaches MBT?

cheers

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https://www.sau.com.au/forums/topic/218145-tuning-the-rb25det/
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daineisdabomb Collaborator

daineisdabomb

Posted
Posted

getting MBT (maximum brake torque) is achieved by igniting the fuel mix wen the cylinder reaches peak cyclinder pressure (top dead centre). as the air/fuel mix takes time to burn the spark must b initiated prior to the crank reaching (tdc). the tuner must no exaclty wen to start the burn to achieve (mbt). there are many variables that affect wen the spark must occur such as air/fuel ratio, charge temperature, load, boost ect. generally mbt is found by advancing the timing (with the correct a/f ratio for the condition already set) untill the knock threshhold is found and then backing off a few degree's to allow for any unforseen conditions that may see the engine knock. generally the more spark advance present the more efficient an engine will b.

InterCooL Rising Star

InterCooL

Posted
  • Author
Posted

i'm not after someone to tell me how much timing my engine will take.

some people have very definate opinions on MBT and knock, EG, some say that on an NA engine you will 100% hit MBT 2-5degrees before knock. others say that on any turbo engine you will never reach MBT before knock. others says that on engines such as CA18DET's you have something like 10degrees of headroom after MBT before the onset of knock

i thought there may be a general rule regarding rb25det's

GeeTR Grand Master

GeeTR

Posted
Posted

I think i see what your getting at.

I hear many a pro and home tuner say RB's are especially sensitive to knock. I take this to mean the IGN numbers needed for peak tourqe are quiet lose to det levels. Often why a car comes back from an inexperienced tuner who used the dyno only, and didn't compensate for real street load = det on the next 40 degree day with 2 passengers.

sall i got ha :thumbsup:

The Mafia Grand Master

The Mafia

Posted
Posted

Took me 2 good years before I considered myself a capable tuner, and I know\knew quite a bit of stuff already, and my background is IT orientated. High level too.

You can't just go out and buy some tuning gear and tune a car..

Guilt-Toy Grand Master

Guilt-Toy

Posted
Posted

Agreed. I been at it for nearly 5 years now... and I still have many questions that i ask my friends who tune cars all day.

Id rather dyno a car then road tune these days though.. starting to get lazy

Took me 2 good years before I considered myself a capable tuner, and I know\knew quite a bit of stuff already, and my background is IT orientated. High level too.

You can't just go out and buy some tuning gear and tune a car..

SevenAngryPenguins Proficient

SevenAngryPenguins

Posted
Posted

this is true, but you have to start somewhere don't you I'll just be very conservative with my boost, ignition and afr's till i feel more confident at tuning then I will get it checked over by a professional

SevenAngryPenguins Proficient

SevenAngryPenguins

Posted
Posted

well that would be a big problem wouldn't it, but that could happen to anyone really, I guess ill know there is something wrong if it starts knocking like crazy, but im sure there are other side affects that your talking about egt's emissions?. Why all the negativity about someone trying to learn how to tune themselves, considering you did it or did you just upload a program into your head like the matrix?

The Mafia Grand Master

The Mafia

Posted
Posted

lol, well, you're opening statement was pretty poor.

Sounded like you just wanted to do a few maths sums, and just put everything in, and off you go, tune done.

Also, there are so many factors involved to your question..

Guilt-Toy Grand Master

Guilt-Toy

Posted
Posted

I guess i was lucky when learning how to tune. My mate owns a workshop and i can use the dyno when i need it. I was allowed to hang around and help out with tunes he was doing... and even drive the cars for him while he was road tuning.

I have a few mates who have been tuning cars for years before i started as back in the day (late 90's) there was not many tuners around that could tune our turbo datto's (microtech lol) so we learnt for ourself

I put in many many many hours have been invested into this. Its not something that you can work out in 6 months.

Good luck with it anyway.. if there is anything i can help with let me know..

Guilt-Toy Grand Master

Guilt-Toy

Posted
Posted

Id swap places with them. any day of the week.... what does knowing how to tune get you ??? it dont get you laid... believe me.

I wish I was as lucky as you Guilt toy and have mates who tune cars for a living and own workshops.

I would give anything to be a capable tuner and engine builder.

My mates are too concerned about getting paid and getting laid.

SevenAngryPenguins Proficient

SevenAngryPenguins

Posted
Posted
I guess i was lucky when learning how to tune. My mate owns a workshop and i can use the dyno when i need it. I was allowed to hang around and help out with tunes he was doing... and even drive the cars for him while he was road tuning.

I have a few mates who have been tuning cars for years before i started as back in the day (late 90's) there was not many tuners around that could tune our turbo datto's (microtech lol) so we learnt for ourself

I put in many many many hours have been invested into this. Its not something that you can work out in 6 months.

Good luck with it anyway.. if there is anything i can help with let me know..

ah cool im sure I will have plenty of q's when I get started. I know I'm throwing myself in the deep end but this is something I want to learn how to do, just for the satisfaction of saying i did it myself. So fingers crossed I dont blow my engine up :P

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