during my stay here I had many thoughts about what FI system should I go. TT, ST or SC!

anyway I was wondering about the AFR in the underboost area? will it be rich or lean?
I am asking that because I travel daily on a 75+ miles highway and I concluded that being in boost for the whole time will hurt the engine badly..

my knowladge is that with a NA engine, it's much better for the enigne to be driven on highways than intown but with boost t's another story, please correct it me if I am wrong..

I read that the APS ST and Turbonetics ST's boost kicks in around 3100+ RPM and in the 6th gear around 72MPH the RPM is below 3000 RPM so that I'd be in the area before full boost.. will that hurt the engine?
I ruled out the TT because I will be running full boost the whole time.

 

This not exactly true. When I'm traveling at 80 mph I'm not in boost. It depends on how far down you press the pedal. Of course at 100 mph it's another story. Let's face it you don't drive with the gas to the floor all the time your on the highway. If you do you can tune the car to have boost come in later. It all depends on how you drive and tune your car. Plus FI will shorten the life of a n/a motor. If you worry about driving in boost all the time on the highway get a s/c since it's boost is rpm based. How fast do you drive anyway? What's your constant speed?

 

72 MPH (120 Km/h)

 

You shouldn't be in boost at that speed. Your tach will be under 3k. Any FI will work.

 

Nevermind, I think you are unclear on the nature of a turbo system. A turbo system is not RPM driven, it is LOAD driven. So cruising...even at 5000rpm with light load on the motor will not create boost pressure.

When cruising on the freeay at 70mph, for instance, you will be running the engine under vaccum, rather than under boost. Boost is on acheived when you load up the motor, or acclerate rapidly.

 

thanks Sharif, I sure was having that misconception
I did read alot about chargers systems in many websites but never actually caught that..
and now I just remembered reading one of your posts (probably) that says that the EMS that comes with the charger kit kicks in during load and the ECU is there when not under load.. so that's means when driving with "under vaccum" it's like you are running stock? and one last thing, what is under vaccum?

 

Thats correct. The only thing the aftermarket ECU's are doing when cruising under vaccum, is scaling the larger injectors. But the stock ECU is controlling the engine during start, idle, and cruise.

 

under vacuum just means, not under boost, to simply put it, lol. you will only start to get into boost once you pass about 1/3 throttle position or so. meaning around town or freeway driving, if you just putt around, you will never be into boost at all. now for the supercharger, different story. the supercharger will always spin in relationship to rpm, no matter if you are at 4000rpm with your foot to the floor or going down the freeway leisurely. on a supercharger a bypass vent is needed to keep you out of boost till you give it more throttle. hopefully this makes sence.

 

thanks guys.. really helpful

so the only difference is that in a TT setup once you push the throttle you get boost earliar than a ST setup and this is what is called turbo lag, right?

 

Newer Turbo systems don't have lag like the old ones. And on a NA high compression engine, there is virtually no lag. Even tho, you will notice a slight hesitation when in top gear and under 2500rpms. This is what turbo lag can be descripbed as but its no where near what it used to be.

 

thanks

 

I understand that all turbo systems are load based, but have one quick question. On 2 of my bosses cars ( srt 4, and R33 Skyline ) as soon as you hit the gas while parked his BOV will release air like its creating boost but the motor isnt getting any load on it ??? Is this because there is no turbo lag ?

 

Many factory turbochargers are very small, so the load generated by flooring the accelerator at idle is sometimes enough to generate a little bit boost....and then you get the BOV noise, even at idle.

 

Bypass Vent? Whats that? Im getting a Vortech installed in about 2 months, and my car is my daily driver, so what should I be doing to keep it out of boost while driving down the highway? Where can you get this bypass vent, what is it and who has it?

-Chris

 

Hi Chris,

You wont have to do anything special. Your Vortech kit will not produce boost until you are under load. There is a bypass that prevents this. So under vaccum, you will run just like normal.

 

So the Bypass Vent isnt necessary? Id rather be safe then sorry, so where would I be able to get it if I decided to put it on for extra safety?

-Chris

 

It comes with the kit.

 

Thanks, i guess i could have found that out when it was installed.

-Chris

 

many actually install a normal bov and eliminate the bypass valve. because when you start upping the boost, the bypass valves can start leaking and give irratic boost readings. wait till you get the kit and make a descision after that though.

 

Big thank you to Sharif@Forged, OverZealous1, Barthelb ..... Forum Mod Gods Another extremely informative thread for us FI pending enthusiastics.