5 GT Turbo My C1J Forged build

[DaveL485]

It's a transistor and relay coil with the relay switching mech taken out

It's to convert the megasquirt tacho 0-12v output into a high voltage "spike" output

Can you do me a diagram to make one? i'd like to try it out on a car i have here Please and thanks.

 

[Fordy]

This diagram mate

I'll be testing it out tomorrow night as picking up a new starter motor on lunch.

If it works perfectly, I've got a 3-4 transistors left and what seems like millions of 1k resistors
Just need a few 5 pin relays as found it easier to solder up inside

 

[DaveL485]

Muchos Gracias!

Skimlinks
100 Pcs 2N5551 Through Hole NPN Transistors FP7
100pcs 1/4W 0.25W 5% 1 K OHM Carbon Film Resistor Wholesale S*

 

[DaveL485]

@la21t and @johnspin hopefully this ^ means we can drop the OE coil and drive the tacho direct from the Adaptronic IGN3 feed...

 

[danb]

WIN!

 

[Fordy]

I've got a spare Rev counter if it doesn't work, so I'll bastardise it and find how to modernise it if needs be

 

[Fordy]

It works boys [emoji106]

 

[The old man!]

This diagram mate ..........
When I first saw this diagram instantly I screamed NO! and my stomach churned!
I then read the thread!
What is being done here goes against all electronic practices! You are playing with luck and there is a chance this won't work.

The 2N5551 is a NPN type transistor with a max Collector to Emitter voltage rating of 160 volts.

The transistor (as it is often used) acts as a switch and when turned on will allow current to flow through the coil. The current will build up and then remain stable dependant on the impedance of the coil. All good so far!
The moment the transistor turns off all hell lets loose. With the coil (an inductor) cannot change the current through it instantaneously. In such a circuit the voltage at the top end of the coil i.e. connected to the collector will rise extremely high (potentially thousands of volts). With a collector to emitter working voltage of just 160 volts the transistor will fail (maybe)
So why the maybe? if the impedance (a combination of inductance and resistance) of the tacho is sufficiently low it will dampen this voltage spike to under 160volts. Potentially it may also be too high for the tacho input and could also damage that.

I like the idea of using a relay as a cheap inductor (coil) but often relays have a built in diode to stop this voltage spike referenced above. In fact the part of the circuit that screemed at me was the lack of a back emf suppressing diode!

All I will say now is just be careful as there are two components that could be at risk i.e. the 2N5551 transistor (cheap) or more expensively the tacho circuit (although in this configuration it would be designed for a high voltage spike)
When selecting a relay pick a smaller one rather than a big heavy duty which will have a much higher inductance (and a much increased back emf).

I'm sure there are a few other electronics kids out there who have cringed at this

 

[Fordy]

Resistor in line of ecu tacho output will protect the ecu

There is a newer transistor begins with m I think which is stronger but the information was just an alternative part

Either way it works and lots of others on megasquirt and adaptronic are using this method on older cars

 

[The old man!]

Resistor in line of ecu tacho output will protect the ecu"
A resistor would not protect the ecu! It’s voltage that is your enemy here. If the transistor was to fail then it shorts between collector and emitter effectively bringing the base (where the ecu is connected) to ground or zero volts. In other words it would fail-safe anyway.
I’m approaching this as an experienced electronics design engineer and can see the flaws. This does not mean it won’t work. By the very fact it has been published means it’s more likely to work than fail but you are relying on luck more than design.

I need to do this myself on a 21 so may well use this principle but in my case I will protect with another component added to the circuit i.e. a zener diode.
I will post my final design on here at a later date.

 

[DaveL485]

I will post my final design on here at a later date.

Watching with interest! Thanks both, great information.

 

[Fordy]

It made it to work for mot today
After 2 failed attempts before valve guide issue and starter motor died




30 miles in and my Rev counter hasn't caught fire and exploded [emoji23]

Sucked the oil out as soon as I got home and put some fresh in

Oil pressure gauge is being a knob, knew I shouldn't of cleaned the sensor in the parts bath [emoji58]

 

[DaveL485]

30 miles in and my Rev counter hasn't caught fire and exploded

Cool, waiting for the parts to arrive (and the car to be running, that would help too lol)

 

[Fordy]

Made an Airbox

You can work it out via those pictures which might not be in order [emoji85][emoji23]

 

[Brigsy]

Airbox looks sound, always meant to make one for the van but never got round to it.

You not running water to your turbo ?

 

[Fordy]

Nah no more water cooling anymore, just used some 13mm Id hose and end blanks from ASH

It's not strictly needed on journal bearing turbos since they run a lot of oil flow feed, many have used the gt2560 with out water feeds on s13/s14/s14a

Not so sure that the roller bearing version would be as tolerant tho

 

[Brigsy]

Ah i see i thought you had a rb unit. What turbo is yours ?? Gt series ??

 

[Fordy]

Gt2560 journal with a replacement billet wheel

 

[Fordy]

Experienced carb freeze tonight for the first time ever in my 5 [emoji23]

Carb top and intercooler pipe work was super cold, condensation on the carb base aswell

Might block the morette hole for winter or hook up coolant again to the carb but I don't want too as the bay is pretty tidy now

 

[Mark Davis]

Experienced carb freeze tonight for the first time ever in my 5 [emoji23]

Carb top and intercooler pipe work was super cold, condensation on the carb base aswell

Might block the morette hole for winter or hook up coolant again to the carb but I don't want too as the bay is pretty tidy now

Had to turn my boost down tonight from 25 - 22 as was getting horrible Miss fire at full boost due to cooler weather.

Going to clean and reduce plug gap tomorrow.