I was wondering if I went from a 70/65 turbo up to a 7875 turbo which ways this swap may effect the tune I currently have on my 92lx?

Car is dyno tuned and has a sct chip running it.

In what ways could this go bad or would the effect possibly be minimal?

I’m asking because I have a buddy lending a hand with other projects in a few weeks and he suggested to ask what we might run into with the turbo upgrade.

Thanks guys.

 

I'm guessing It might run leaner with the larger turbo since it would move more air.

 

Assuming you don't run it up to more than it's tuned for, it should be OK.... BUT... If you turn it up past where the MAF is tuned for, you run the risk of hurting something.

 

From my experience, the tune will change. Air density, and boost threshold should change, and would most likely trend lean. Bolt it on, and monitor your a/f, and plugs.

 

Lol, if it's making more power then it's using more fuel

 

Lol, what’s so funny man? Other than your mundane post.

 

The bigger turbo is going to supply more air, and that will require more fuel. If the tune or hardware doesn't allow that, it'll go lean. Install and drive to get it tuned? Sure. I know nothing about tuning the stock EFI and it's allowable correction limits,have only tuned aftermarket systems. I switched from a 66mm to a 72mm and the Holley was adding fuel,don't rem the %, over the 66mm at the same boost level.

 

Assuming a eec4 maf based ecu like a a9l, a9s, ect, if the maf transfer function is carried out either because it was scaled, interpolated, or represented as a tested value from a flow bench (I.E. the tuner guy had a clue) its very possible it will be fine (by fine i mean good enough for a street/driver/hobby/project/fun car). Still recommend either some street pulls with a wide band or a dyno but the way MOST ford ecu's work is load/airflow based (at least the mass airflow systems). Not map/speed density based. Speed density uses map and rpm to extrapolate an airflow model that outputs a calculated volumetric efficiency the ecu uses to determine an injector open time. This poses a problem if the actual engine ve at a given rpm and map value changes, like when you change turbo, cam, cylinder heads ect. Maf systems actually measure it, modify it for air density correction, and compare it to the displacement to figure a VE value. (ford calls this load) More turbo, more air, more load= still fine if the tables are carried out passed where the last turbo was run. Think of it the same way as when you hear guys saying pull x amount of timing per pound. The ford load based tables do this. Its also why alot of ford factory forced induction apps carry the timing tables well passed the load values you will ever see with a factory pulley. If you ever looked at a ford GT supercar, or 03-04 cobra calibration you will see what I'm talking about. Ford Lightnings did it too but they usually only carried out their load tables to around 1.6 load. (sometimes less in the early 99-00 trucks) Re-scaling the tables out further is usually needed anytime you are adding more then about 4 pounds of boost. These particular stock calibrations will handle a pulley change very well with very little change to the timing or fueling tables. Usually the only thing 100% required changes involve open loop fueling delays, and a few airflow/load calcs so the afr's get rich enough.

In fact the NA calibrations do it as well when you routinely see 4.6 mustang 2v and 3v cars with tables normalized out to 1.1 load when they will never get there in NA trim. This is done to make sure the engine is still tuned for air density extremes. Like 20 below mine shaft air.

Ford ecu's only compare maf voltage to 5 volts but the mafs themselves will output to battery voltage. So if the new turbo moves enough air to make the maf output 5 volts (or 1023 counts in ecu talk) then the maf is "pegged" and no longer a viable reference for accurate airflow data. There are work arounds that include failed maf values and load with failed maf tables, but depending on the ecu the juice is not worth the squeeze and might not be an option at all so most just upgrade the maf to something that has the range required.

The exception to the load table rule I mentioned above is some older ecu's had a wide open throttle timing table that just set "x" timing for "y" rpm passed a "z" throttle angle threshold. Which as you might guess is a bit arbitrary. Also ford ecu's only calculate to 2.0 load or 200% VE. Which is USUALLY around 15-16 PSI. Its not likely to happen at 2 bar due to efficiency variations in the base engine and the turbo system. I.E. the NA engine was not at 100% ve or 1.0 load NA so it not be at 200% at 2 bar. So if the old turbo pegged the maf at 5 volts or pegged the load value at 2.0 load then your way more likely to need to modify the calibration for the new turbo.

Good luck!!

 

Yes sir, have an a9l with pmas slot maf. Dyno tuned on a burned sct chip.
I knew my a/f would change with a bigger turbo, I was trying to see past people that have done the same and the car was still safely driven on the street. My eyes are watching my wideband more than any other gauge in the car sadly.

I’m not smart like many on here, but I thought possibly the a/f changes from the bigger turbo would be minimal at best with me not getting on the car hard on the street.

Would be going from a 70/65 to a 78/75 if I go with it.

 

The point of my post is the afr might not change. In fact, it was tuned by someone who gets it, it most likely wont if the airflow stays close-ish. There are a million factory applications that people have upgraded turbo parts with little to no changes in actual calibration and enjoyed miles and miles of improved performance.

The fact you are asking before you scatter this thing makes you smarter then alot on here

 

A/F shouldn't change at all until you're running it in boost. And even then, it should be minimal until you reach the end of where it was tuned previously. That's where the trouble could start.

 

That chip has free tunes for life according to the website, why is this even a discussion?

 

Sct chip and dyno tune is a one time deal

 

Here's the deal. I'll assume you're using a 351w. The T70 on a 351 gives you very nice boost response but it chokes out quickly because the turbine side is just too small. Therefore your dyno numbers probably have you making noticeably more torque than horsepower because the power comes on strong and then just runs out of steam. The 78/75 on the other hand is nearly an ideal fit for a 351 and the HP and torque numbers will be almost exactly the same, provided you don't have an obscene stall on your torque converter. The power numbers will move to the right of the RPM range and just keep on climbing. Get a tune and save yourself from leaning out and toasting a piston.

 

Thanks, I just have a 3k stall converter 10”

 

This is all true.


My OPINION would be to use the turbo money to buy real management and tune what you have. By the conversation so far this is a street cart. A 351 t70 will be a ball on the street. Low boost threshold, fast response. And you'll likely not notice it choke because the tires will be hooped if they are not on a prepped track.

 

Standalone is currently being saved for. Most likely will be bought within a few weeks and the car will get its insurance taken off for the winter seasons.

I would love to begin wiring the ecu in my free time but I truly have to research if I have the skill for this. I have a local guy that has built many turbo fox setups but his price for an install is too steep for me.

You are correct about the spinning even on drag radials on the street here. The guy helping me with some smaller repairs even suggested the larger turbo when he heard the price it would cost. I may just buy it and let it sit along with other things I need.

Thanks

 

Plug and play=no install.
street car=micropsquirt from efi source, plug it in and run a vacuum line
street strip car with 2 step, boost control ect.=diy pnp. That does require a bit of wiring for whatever accessories your running but probably less then 10 circuits.

 

Tuner never said where I was at for capacity but I have too much injector at 80lbs and aeromotive a1000 fuel setup.