Octane, A/F, and overboosting

[AGlobalThreat]

How do I determine what octane is safe for what boost pressure and a/f ratio?

My 57trim CT26 is overboosting and I want to run race gas until it's fixed just to be safe, and I'm wondering if I'll be ok using 100 octane till I get the boost down or if I'll need to be using 110. My fuel system is stock, stock 370 injectors, no FPR, stock rail, stock pump, stock ecu. I'm picking the car up tonight but was told the boost goes up around 17-20+ psi, which is much more than I intended and is obviously too much for stock injectors on 91. The setup originally was using a Zoonwen ddp, which had to be modified to fit, and then we assumed something with the ddp was causing the wastegate to stay shut or to not open completely, but after swapping to a BIC DDP the problem persists. The wastegate seems to be opening at 10psi but the turbo continues to spool and increase in boost pressure. I have an AEM wideband and an accurate mechanical boost guage (We already tried a diff. guage and got the same readings), the wastegate was changed along with the vac line but the problem continued. I plan to port the wastegate to help but if anyone has any suggestions as to why it's boosting so much please chime in. Also if anyone can explain to me the math for finding out what octane is needed that would be greatly appreciated.

:1zhelp:

 

[spoolint78]

what stock 370cc injectors do you have?

 

[sneakypete]

kind of unrelated to your question... but to clarify things:
1) our stock injectors are 440cc
2) i would never drive without a fpr
3) just because the car CAN boost that high, doesnt mean you have to drive it to that point. meaning drive carefully and dont floor it all the way home.
4) if this is as serious as you describe it, get it towed home until you fix the problem
5) if you have any type of fuel adjustment computer, enrich your mixture if you have to drive the car (lower A/F ratio)

i would check to see if you have some sort of boost controller. on a stock ct, its likely there is a mbc somewhere on that vacuum line.... check it out

 

[suprahero]

I know a few guys on upgraded ct's and they run twenty psi with 93 octane. I run seventeen psi through my gt35 on 93 octane as well. I would think 100 octane would be more than safe for your car.

 

[sneakypete]

he hasnt upgraded his fuel system at all, i wouldnt boost that high if i were him

 

[IJ.]

^ 3540r @ 17 is probably moving 2x the mass of a ct @ 20

Tune is king in this situation too much advance and it'll flush the engine in seconds.

Each combination is unique, there is no "one tune fits all".

 

[suprahero]

^ 3540r @ 17 is probably moving 2x the mass of a ct @ 20

Tune is king in this situation too much advance and it'll flush the engine in seconds.

Each combination is unique, there is no "one tune fits all".

That's what I meant IJ. I run seventeen on 93octane so I thought he should be able too. I know Noah runs 20psi on his 57trim ct and he's been running it for three years or so with no problems.
It's like the other guy posted, just because it will boost that high doesn't mean you have too. I'd get the fuel system upgraded if that's what you're planning on doing. Some 550's, fpr, and a walbro should do the trick. Good luck.

 

[IJ.]

Way too many variables to make a blanket statement on this subject J...

 

[AGlobalThreat]

Thanks for all the input guys, I know it's kind of hard to guess where I should be but I appreciate all the input. I'm going to put 100 octane in and then see how high the boost actually goes and then I will go from there.

 

[IJ.]

You need to creep up on something like this slowly and carefully as you don't get a second shot with a 7M if it's wrong.

Do you have any way to change the timing curve under boost?

 

[AGlobalThreat]

1.You need to creep up on something like this slowly and carefully

2.Do you have any way to change the timing curve under boost?

1. Trust me I am, no boost whatsoever until I get 100 octane in there

2. Not rly

 

[IJ.]

Ok I'd do most/least till ya get the Creep sorted.
(most octane/least boost as it has the potential to flush the motor)

 

[AGlobalThreat]

What do you mean flush the motor?

 

[IJ.]

Internals become externals

 

[AGlobalThreat]

I know a few guys on upgraded ct's and they run twenty psi with 93 octane.

What size injectors do they have?

Internals become externals

Thats why Ill be running 100 octane, to be safe

Currently, I dont know exactly how much its overboosting or the A/F. I will more than likely put it on the dyno Saturday to see exactly what its doing so I'll be able to see where I'm at and what I need to do.

 

[7MGTEsup]

You need to creep up on something like this slowly and carefully as you don't get a second shot with a 7M if it's wrong.

I thought he was running a 1J with a ct26??

 

[IJ.]

Still applies

 

[7MGTEsup]

Still applies

I know that, just thought I had missed something and he had thrown a 7M back in the hole.

Why did the the 1J come with 370cc injectors being as it makes more power stock for stock? Or did Toyota just way over spec the injectors for the 7M GTE??

 

[IJ.]

Dunno maybe a difference in base fuel pressures?

I think the 7M was overspecced though.

 

[foreverpsycotic]

I can already tell you that you will need a minimum of 440cc injectors, but your better bet is to get some 550s from a MKIV over on SF. With the 550s. you will need a walbro (@ minimum) and an AFPR, but with the 440s, you will be on the edge of pump gas with them. Happy tuning.