427 TBI ECU from 350 on a 250 Inline

[Rat Chevelle]

Hello,
I am planning on using a 427 ECU from a '95 350/4L60E on my 250 Inline.
I normally do mainly LS swaps at my shop, but because of the Siamese intakes on the 9 port head i'd rather not mess with MPFI, although that would be much easier programming wise.
Anyway, my thinking is that I see a lot of people trying to match the CID of the complete engine to the one they're trying to swap into -eg. Using a 4.3 ECU or memcal for a 250 since the size is closer to the 4.1L of the 250.
I see that the TBI is not sequential as it does not have a cam sensor, therefore it does not know or care when one cycle ends or where it begins.
Unless I am wrong this is a 1 pulse per fire system then it is irrelevant either the engine is an I6, V6, V8... or 16 cyl for that matter.
So I guess it would be better to match up cylinder displacement rather than total displacement when retrofitting a TBI or any non sequential ECU. Am I on the right track of has dementia finally caught up with me?
That would mean 350/8=43.75 is close enough to 250/6=41.66 to make it work. BTW the 4.3 had the same swept cylinder volume as the 350, but everybody knows that.
I will be using a nice tall PES RAM Intake from Tom Lowe and a single megaphone lakes style header and plan to upgrade to a three wire O2 sensor.
What are your thoughts on the 350 427ECU working for my Stock for now 6 Inline?
Thanks

[1project2many]

Hello and welcome.

You're asking good questions about using an older TBI ECM on an engine it was never inteded to operate. The ECM doesn't really car about how your engine is configured. Plenty of people have lied to the ecm and made the engine run well enough to enjoy driving the vehicle.

The ecm records the time between reference pulses. It uses that and the number of cylinders to calculate an RPM value. The RPM value then references a number of variables including TCC lock/unlock, shift speed, Volumetric Efficiency, Spark timing, Power Enrichment values, and more. For ease of tuning there are a few variables that are important for your swap. Setting the number of cylinders to match the engine will allow you to build VE and spark timing maps that accurately reflect the actual engine speed.

The displacement per cylinder affects the volumetric efficiency calculation. Setting the displacement to a higher value than what's actual will cause the ecm to deliver too much fuel. The 4.3 and 5.7 engines generally use the same per-cylinder displacement values in factory calibrations although the injector sizes are not always the same.

I agree that matching an engine's displacement to a factory calibration is not always the best route. OEM 4.3 calibrations are often very different from OEM V8 calibrations. My experience is that people used to a carbureted V8 or I6 are not happy with a 4.3 based calibration. I have actually used 454 calibrations on six cylinder engines. After tuning I find the old I6 is much closer to the early 7.4 with heated carburetor spacer than the later 4.3 or 5.7 with coolant heated intakes and thermac systems.

I believe the stock 350 cal might be a decent start for your project. I would change the number of cylinders to six and I would change the cylinder displacement to match the current engine. I would also look at the shape of the VE table and check it against the torque curve or the new engine if possible.

Good luck.

[Fast355]

Too bad nobody swapping the 250 to TBI can get their hands on the factory GM 250 I6 TBI chip for a read and get their hands on the factory intake and TBI.

[Fast355]

This is a factory one in a GMT400 in Mexico with the NV3500 behind it.

[Fast355]

This is a factory MPI in a Mexican Tahoe usually with a 4L60E behind it. Although this one has a NV3500 too.

[Rat Chevelle]

Thanks for the reply, there are a few things I hadn't considered. I was thinking about just getting the engine running and not much about trans routines and so on. I ensured to use the 350 TBI ECUs because I have a couple complete systems laying around that are leftovers of LS swaps.
My intention is to get the engine just running stock while I finish the Hot 250 and I have a Holley TBI and stuff, I'm only waiting to upgrade the Holley HP ECU for a Dominator and then will use the HP on the Rat. But the 2K price is a bit ouchy so I'm waiting for that.

[Rat Chevelle]

Too bad nobody swapping the 250 to TBI can get their hands on the factory GM 250 I6 TBI chip for a read and get their hands on the factory intake and TBI.

Fast355, I could have access to one of those TBIs, a neighbor no more than 100 meters from my house has one of those trucks. Too bad I don't have the Chip reader as I can not leave his truck inoperative to remove the Chip to have it sent to be read.
Also, I believe the 4.1 MPFI is not a Mexican truck but rather a Brazilian or Argentinian as we never had those in Mexico. I'd love to get my hands on one of these ECUs.

[Fast355]

Fast355, I could have access to one of those TBIs, a neighbor no more than 100 meters from my house has one of those trucks. Too bad I don't have the Chip reader as I can not leave his truck inoperative to remove the Chip to have it sent to be read.
Also, I believe the 4.1 MPFI is not a Mexican truck but rather a Brazilian or Argentinian as we never had those in Mexico. I'd love to get my hands on one of these ECUs.

Are you sure of that. Seen a couple here in Texas wrecking yards with Mexico license plates.

[Rat Chevelle]

Are you sure of that. Seen a couple here in Texas wrecking yards with Mexico license plates.

As far as I know we only had the TBIs, I've seen them and owned one of such engines (without the ECU unfortunately) but a MPFI I have not seen them or heard about them being available. Only in the very South part of the American Continent.

[In-Tech]

Those are cool. If either of you can get me a vin number for each I might be able to track down some parts.

[dave w]

I helped with an I6 250 16197427 TBI conversion, using donor parts from a 1994 full size pickup / 4.3 liter /4L60E. The I6 250 distributor was converted to an ACDELCO 88864755 ( https://www.carid.com/acdelco/profes...-88864755.html ) to simplify computer controlled timing. The conversion incorporated a new custom 16197427 harness unitizing the donors VSSB. The chip was custom programmed, without Knock Sensor or Emissions. Tuning incorporated using a WBO2 http://www.gearhead-efi.com/Fuel-Inj...g)-Spreadsheet The 4L60E shifting was tuned using Bluecat https://forum.hptuners.com/showthrea...Table-Software

dave w