Max Boost vs AFR Question on 7M

[Scot]

I currently have my manual boost controller set to max out 1.3 bar while pulling hard between 2nd thru 4th gears. When I accelerate at higher cruising speeds the boost jumps up to 1.45, the warning light on my boost gauge goes off and I back off immediately. Boost creep? While I am in the process of figuring out how to control the upper limits of the boosting, I want to avoid a piston melt down.

My question is, based on my mods below, if the AFR remains in the 10 or so range, how much boost can I run on pump gas before bad things happen? Or maybe the question should be posed with 550cc injectors, timing, etc, taken into consideration as well. I just don't want to assume anything.

The AEM WB, usually stays pegged at 10.0. and maybe hits 11 while at WOT. Keeping in mind I am watching the road and just glancing at the WB. Of course this all happens super fast. Also, FYI, I never hit fuel cut. (yet)

Like most of us, I've put a few coins in the build. The car is idling good and pulling hard at 1.3 and I am not really trying to squeeze more HP out of it at this time, I just want to avoid an ignorant mistake. Better to ask now than to come back here later asking, "why did I melt a piston", and have to listen to everyone pile on my dumb ass! lol

If you can improve my question to give a better explanation, by all means.... I'm all ears....

 

[suprahero]

I don't know how much boost you can run without knowing if you're getting knock or not. I personally wouldn't run that much. Isn't that like 20-21 psi when creeping? I run 22psi on mine with a larger turbo, but I have meth. I know people that run 23 psi daily on pump gas with turbo's equivalent to yours, but in my mind it's only a matter of time before you detonate. Hopefully you want, and I am by no means an expert on this topic. I'm only stating what I run and that I would be scared to run that much boost on pump gas. Good luck.

 

[Scot]

exactly... I feel safe at 18 or so. But the creep to 21+ gets me backing down pronto.... In the mean time I am either not going to run at high speeds in 4th and 5th or lower the MBC so it never goes above 18 at 4th and 5th gear pulls.

 

[suprahero]

I "personally" would back it down. I doubt in a highspeed race, you could keep your foot out of the throttle.
Again, I don't know that your boost levels are unsafe and I doubt anyone can tell you that they are because all cars are different. I ran 17.5 psi through my gt35r for over a year and a half with no problems at all on my 1jz on 93 octane. I might could have ran more, but I wasn't willing to risk it. Good luck., Jay

 

[IJ.]

It will break the ring lands long before it melts anything.

 

[mkIIIman089]

Ugh... seeing that reminds me of a motor that comes out of the box - pin pre-removed. LOL

 

[Scot]

It will break the ring lands long before it melts anything.

In your experience, at what boost threshold would you estimate that the rings lands begin to fail?

 

[IJ.]

About 2 psi over the first bad bout of detonation.

Personally I find what I consider to be a safe tune on the dyno listening for incipient detonation then back it down 2psi and 2 degrees of timing from there as a safety margin.

 

[Scot]

About 2 psi over the first bad bout of detonation.

Personally I find what I consider to be a safe tune on the dyno listening for incipient detonation then back it down 2psi and 2 degrees of timing from there as a safety margin.

Thanks for the info.... I need to take a trip to the local dyno for some tuning. Might be time to start a new thread....

 

[IJ.]

I tend to go for a very safe tune compared to a lot I see here, I also tend to spend long times at high rpm/boost during top end runs so don't like running my engines ragged.

 

[isnms]

Are you logging?
I would do that, if you're not, so you're not "assume anything".

 

[IJ.]

Are you logging?
I would do that, if you're not, so you're not "assume anything".

x2 squiggly lines rule!!
(MoTeC term from one of their engineers)

 

[Scot]

yes I should go aead and hook up the Data logger from the AEM WB. I was getting ready to order the Zeitronix for better analysis. But say I hook up the AEM and see low 10:1 AFR's boosting to 1.4 bar, verifying what the AEM guage is displaying. Would it be safe?

 

[isnms]

lol squiggly lines.
I could see my clutch slip in squiggly lines before I upgraded to the Spec

Scot - You're running a 18yr old fpr with large turbo, 1.4bar and bigger fuel pump.
You said it yourself, it happens super fast.
I would want to start slow and know what is happening from my logs as I gradually up the boost.
No one is going to say Yeah you'll be fine at 1.4 bar.

Here is a good read on AFR:
http://www.supramania.com/forums/showthread.php?p=159348&post159348

BTW: Zeitronix is good. I like mine.

 

[Scot]

Going to order the Zetronix tomorrow.... get the AFPR installed soon, taking the IC pipes to get ceramic coated tomorrow too. In the mean time I'm gonna back her off a bit.

Since no one is gonna tell me what want to hear! lol

 

[suprahero]

Nobody wants to be responsible for you rebuilding your engine and then blaming it on the 7m.........:biglaugh:

 

[TurboStreetCar]

First question i have is how are you running 18+psi on stock TCCS without fuel cut? What are you using to tune with? 20+psi on pump gas is a little more then i would trust, i wouldn't go much over ~16 without methanol or race gas. But thats me, and i share the same feeling as Ian about running a safe mild tune.

AFR, while important, doesn't change the detonation characteristics of a fuel thats not up to octane par in an environment it cant handle. I wouldn't be so much worried about the AFR being correct as much as id be worried about the boost pressure alone causing severe detonation.

 

[tekdeus]

My turbo and mods are similar to yours. On the dyno we noticed knock starting to happen at 24psi of boost WITH water/meth using the biggest AEM nozzle. I did what IJ does, and backed the stock base timing down 2 degrees and I limit my boost to 21psi on pump/methanol. On your turbo, I would limit the boost to 15 psi on pump gas, and suggest adding a meth kit to run up to 22psi, retuned on the dyno to 11.5 AFR.

Also, get an electronic boost controller installed that can adjust boost-per-gear. I had to adjust my Apex'i AVCR in each gear, because I got a little creep in the higher gears as well. Not only that, I can limit my boost to wastegate spring in 1st gear, 18psi in 2nd, and 22psi in 3rd, 4th, and 5th. Grip in all gears FTW!

First question i have is how are you running 18+psi on stock TCCS without fuel cut?

Running a rising rate fuel pressure regulator with 50psi base pressure raises the fuel cut very high. Water/meth can also add fuel. I got up to 28psi with no fuel cut and 515rwhp on my 550's and SAFC + water/meth/C16, pulling 19-25% fuel on the SAFC.

 

[Scot]

Thanks for everyone's helpful responses...

I have some tuning theory to learn.... Off to search land....