Which ECU to use for motor swap

Hellica

New member
I Have a 88 st165 I am about to put a st185 motor and trans in it. I understand that the JDM motors harness is opposite our harness and has to be modified. I am going to be running supra tt injectors fuel pump a ct26 with a to4b and a DP. should I run the st165 ecu with a piggy back or the st185 ecu with a piggy back or should I get the st165 reprogrammed. Any help and or oppinions will be appreciated.
 

ChrisD

New member
You should use the ST185 ECU. Be careful that you understand the affects that piggybacks have on your timing maps. You must have a way to compensate timing maps if you are planning on using the piggyback to remove fuel. On that turbo with your mods I probably wouldn't advise changing the stock injectors. You are better off using the stock injectors.
 

Hellica

New member
chris_dittrick":1cwm0ung said:
You should use the ST185 ECU. Be careful that you understand the affects that piggybacks have on your timing maps. You must have a way to compensate timing maps if you are planning on using the piggyback to remove fuel. On that turbo with your mods I probably wouldn't advise changing the stock injectors. You are better off using the stock injectors.

I'm confused why would I want to remove fuel, I understand that running lean can give you more horsepower if done right (lean is mean but fat is happy) but with the to4b I would probably be running 14psi or so,in that case wouldn't I need to increase the fuel? I forgot to mention the car also has a supra tt fuel pumb already in it. There will also be a down pipe and boost controller. bla bla bla all the basic easy mod crap.
 

ChrisD

New member
In normal cases, yep you'd need more fuel, just not for the 3SGTE.

The 3SGTE uses the AFM to meter the amount of air entering the engine, and then injects the appropriate amount of fuel. The thing is, once you start adding more air to the engine (more boost, better turbo, etc), the ECU is set up to protect itself by injecting a LOT of fuel. You will find that you will run incredibly rich on a wideband o2 sensor. (richer than 10:1)

So you would end up trying to remove fuel with your piggyback. The ECU sees this as less load, and advances the timing automatically. Then the engine goes boom. :(

So the best bet is to do all the tuning with a wide band, and something that will adjust the timing maps backwards. OR you could just run more boost and live with the fact that you will run rich. If you are still using the CT26 you shouldn't exceed the stock fuel system, without quite a bit more work.
 

Hellica

New member
chris_dittrick":1vli66np said:
In normal cases, yep you'd need more fuel, just not for the 3SGTE.

The 3SGTE uses the AFM to meter the amount of air entering the engine, and then injects the appropriate amount of fuel. The thing is, once you start adding more air to the engine (more boost, better turbo, etc), the ECU is set up to protect itself by injecting a LOT of fuel. You will find that you will run incredibly rich on a wideband o2 sensor. (richer than 10:1)

So you would end up trying to remove fuel with your piggyback. The ECU sees this as less load, and advances the timing automatically. Then the engine goes boom. :(

So the best bet is to do all the tuning with a wide band, and something that will adjust the timing maps backwards. OR you could just run more boost and live with the fact that you will run rich. If you are still using the CT26 you shouldn't exceed the stock fuel system, without quite a bit more work.

Thanks for the information, I should have known that, but for some reason I thought the OBD computer in these cars was more trickable. But I was wrong. Sounds like a stand alone would be my best bet. How good is this megasquirt system and if I did get it what should I get to controll the ignition.
 

alltracman78

Active member
Hellica":2veo7u4k said:
I Have a 88 st165 I am about to put a st185 motor and trans in it..... I am going to be running supra tt injectors fuel pump a ct26 with a to4b and a DP.

You sound a bit confused. You say your going to run a CT26 with a to4b???

Also, keep in mind the supra injectors/pump send a whole lot more fuel than the 3s ones do. The computer is set up to open 440cc injectors, with the stock fuel flow. Adding the supra ones will make you run so rich you probably won't be able to even start.
 

Hellica

New member
alltracman78":2rnwna3d said:
Hellica":2rnwna3d said:
I Have a 88 st165 I am about to put a st185 motor and trans in it..... I am going to be running supra tt injectors fuel pump a ct26 with a to4b and a DP.

You sound a bit confused. You say your going to run a CT26 with a to4b???

Also, keep in mind the supra injectors/pump send a whole lot more fuel than the 3s ones do. The computer is set up to open 440cc injectors, with the stock fuel flow. Adding the supra ones will make you run so rich you probably won't be able to even start.

"This is the most common of upgrades that are offered by some of the companies below. The compressor is removed and replaced with a TO4 "B" compressor wheel. These are usually from Garrett or similar larger turbos. The B series is not the largest of the TO4 series, but significantly larger than the stock or supra turbo compressor. The compressor housing is bored out to match the size of the new compressor wheel. The exhaust side is left alone. This formula leads to a turbo that has very little lag if at all. Speaking in trim, that actual size of the compressor wheel, this would be a 46 or 50 trim. Generally these have a strong flow up to 20 psi and can be found as little as $350. An example picture is below." (This is out of the tuning section on this site.)

No not confused, I did mean TO4b with ct26 housing. at one point I was going to use a ct26 housing with a to4e 60-trim, but after doing some research I decided to go with the smaller t04b for a more drivable car. Now about the supra injectors I could have sworn I read somewhere that if you boost more that 15psi you need to get bigger injectors but I can't find where I read it now so i must have been misinformed, maybe it was you need to upgrade your ecu if you boost over 15psi. Either way I was confused about that.
 

Hellica

New member
alltracman78":203a1ynk said:
Adding the supra ones will make you run so rich you probably won't be able to even start.

The car may run quite rich but it would start, even if it did take pressing the petal down to remind the computer that you let lots of gas piss into it's engine.
 

ChrisD

New member
You would want to start upgrading things like injectors and fuel systems, computer, etc., at roughly 250whp...you can get away with a bit more but it gets dangerous. Even at 250, you need to be pretty careful.

The old school of thought was that the ECU mapped according to boost levels, however it is now known that the ECU simply uses the AFM to derive the primary fuel/ignition maps, and makes corrections from readings of other sensors. So the "above 15psi...." doesn't really hold...it all depends on how much air is going into the engine, and by derivation, how much power you make.

The CT27 and CT20b are other good options as well, instead of going with the to4b upgrade to the compressor wheel.

Megasquirt is okay, but I'd get the one that has ignition control as well if you are going that route.

You can trick the ECU with piggybacks, dont get me wrong, you just need to know how the changes are going to affect the timing maps as well, and adjust them accordingly. :)
 

alltracman78

Active member
Sorry, I thought you meant a turbo :oops:

Nothing wrong with running the Supra pump/injectors, just won't work good with the stock ecu [and no piggy back].
 

celica90gts

New member
if i was to keep it a stock 3sgte in a st 185 gts would the wiring harness bolt up and would i have to change the ecu for fuel reference....
 

Hellica

New member
chris_dittrick":23lsbfbt said:
You would want to start upgrading things like injectors and fuel systems, computer, etc., at roughly 250whp...you can get away with a bit more but it gets dangerous. Even at 250, you need to be pretty careful.

The old school of thought was that the ECU mapped according to boost levels, however it is now known that the ECU simply uses the AFM to derive the primary fuel/ignition maps, and makes corrections from readings of other sensors. So the "above 15psi...." doesn't really hold...it all depends on how much air is going into the engine, and by derivation, how much power you make.

The CT27 and CT20b are other good options as well, instead of going with the to4b upgrade to the compressor wheel.

Megasquirt is okay, but I'd get the one that has ignition control as well if you are going that route.

You can trick the ECU with piggybacks, dont get me wrong, you just need to know how the changes are going to affect the timing maps as well, and adjust them accordingly. :)

How much adjusting can you do with a piggy back in open loop. Could I get 350 bhp with a piggy back and a stock ecu, or should I just go ahead and get a stand alone, hopefullly I will oneday build my bottom end and end up with around 400-450 whp so eventually I'll have to do something anyway.
 

Hellica

New member
alltracman78":1wi8whny said:
Sorry, I thought you meant a turbo :oops:

Nothing wrong with running the Supra pump/injectors, just won't work good with the stock ecu [and no piggy back].

Yeah I didn't think about injector durration having to be changed to comensate for more fuel being able to pass through the injectors. I figure it would be easier to have someone program the fuel maps for 550cc injectors into your computer rather than trying to tune it on your piggy back. I'm still new at this game and I'm learning more everyday.
 

3sgte4me

New member
So Chris, having done the St185 swap, the smt6 and other mods what are your recommendations for us guys with aging st165 3s-gte's.

Im trying to get a handle on what is a smart setup with room to grow. :D
 
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