Quick question on fuel cut

TGPilot · 03-31-2005

Sorry for the slew of "newbie" questions I am spewing lately...but I am learning as I go.

Please realize I am at high altitude (6000') when answering these questions. Up here higher boost levels are normally acceptable due to the thinner air (less oxygen).

If I run 20psi on my 1G 94 Talon with a Big 16G bolted to EVOIII ex-manifold, Supra TT SMIC, and Stock injectors & fueling system....when I get to 6k RPM it hits what I am guessing is fuel cut. Abrupt chop in engine.

On my Auto-Meter A/F gauge I am still up in the high green lights until fuel cut hits and it bounces around in the "Stoich" area of yellow. I have been running the car at 12-14 PSI since I got it. When I put the Supra SMIC on this thing pulls like no car I have ever driven...yes that actually is saying ALOT!

I bumped the PSI up a bit as a "let's see" type of experiment. It is an experiment I want to keep playing with...but I am afraid that the A/F guage is giving me a false sense of security being up in the green.

Any advice on using the A/F as an "it's ok to run this much boost" security blanket?

Thanks and sorry for the newbie questions!

-Kenny

Alpine TSi · 03-31-2005

That blinky light gauge is only accurate to a small range of AF ratios. I wouldn't rely on it in the least. I had one and encountered the same thing you are talking about. Either add more fuel, or turn down the boost.

Also, are you staying right on at 20psi, or are you starting to creep around 6K rpm range?

Alpine TSi · 03-31-2005

Wait, I just looked at your mods again, and even for being at 6000 above, you are really expecting a lot out of those stock injectors and pump.

I would get some 550's and rewire your stock pump. If you can't get an AFC or some other piggyback device, try and get your hands on a 2G MAS so you can counter the 550's and be almost right on for fuel.

TGPilot · 03-31-2005

It stays dead on at 20 PSI...zero creep.

It is nice how fast it gets to 20 and just locks on to it.

A//// Guy · 03-31-2005

20PSI is really ALOT for the stock fueling system, even at a higher altitude and no way of really seeing what your AF is (blinky gauges do not count) its too much air coming in and not enough fuel.

You definetly need bigger injectors and a bigger fuel pump and a way to deal with mixture (afc).

Is it really fuel cut? I mean are you almost eating the steering wheel when it hits?

TGPilot · 03-31-2005

Quote:

Originally Posted by EclipseTurbo

Is it really fuel cut? I mean are you almost eating the steering wheel when it hits?

YES...

I had posted in another thread that I connected my MBC to the Red Dashed line on the Throttle body...not a good place as it seems. I just got back from playing and turned the MBC down three full revolutions and no change...stuck at 20 PSI. I am going to put the BOV and MBC lines back to the way they were.

What do you guys think a "safe" (I hold no one liable for my idiocity

) max boost would be for my wanna-be mods and altitude?

**JET** · 03-31-2005

20 psi is a lot for a 16g and SMIC. You might want to back it down to 18 psi and see what happens. That air is getting pretty hot coming out of there.

awd-drifter · 04-05-2005

That supra SMIC...is it that good, because I was thinking about that. But 20 psi is pretty crazy. My friend with a 02 Subaru WRX pushed his WRX up to 20 psi once, and that was without mods, crazy but true. I still cant believe that engine is still alive. You should get a bigger downpipe and other things so that hot air will get out of the car faster.

**scheides** · 04-05-2005

550's and a fuel pump and you'll be dandy. Get a datalogger & see what p/w you're running on your injectors, I think you will be kicking yourself. Best to get a datalogger & make sure everything is ok when you're running above 15-17 psi on a smic. that supra smic is thick as a tree, but I still wouldn't even go past 15psi on a stock fuel pump.

fuel pump. injectors. datalogger. tune.

ooh, actually, you have a 1g, you're probably over-running your stock MAS, best get a 2g one or a maf-t setup...ahh, the fun, the fun. (by fun, I mean money)

TGPilot · 04-05-2005

I am in the process of getting a datalogger setup. Would rather know what the present setup is doing rather than throwing $$ at it without needing or knowing what direction I should be going.

I know it sounds like alot running 20 psi, but at high altitude (6000' and up to 10,000') you lose alot of compression in the motor from the start. Running 20 up here would be like running 17-18 down at sea-level. Plus up here there is less burnable oxygen so you actually run richer up here if the ECM does not correct properly. It still sees the same amount of airflow...just more nitrogen & less oxygen...but as we all know nitrogen does not burn.

Tuning at high altitude is very different from sea-level. I have learned that the hard way more than once!!

I truly appreciate everyone's input. Datalogger software and connector is on it's way.

**scheides** · 04-05-2005

Quote:

Originally Posted by TGPilot

I truly appreciate everyone's input. Datalogger software and connector is on it's way.

Sweet. Yea, we're all basically just making conclusions based on experience rather than looking at the raw data. A datalogger will answer all your questions, and really should be mod #1 for everyone, rather than a boost gauge & mbc.