Megane RS250 engine into R26 - using mk3 fuel pump

[Ewan]

I am swapping the engine in my R26 with a RS250 unit retaining the R26 ECU and loom. Should clarify at this point that 'I' means 'I am paying Rentec in Edinburgh'

Ok, so we are keeping the R26 ECU and loom and swapping in the RS250 engine with turbo and the mk3 inlet manifold, fuel rail and injectors.

I know that we should be able to run the RS250 engine with the existing mk2 fuel pump, although it won't offer the rising rate fuel pressure. The question is can we fit the mk3 fuel pump to my car and take advantage of the rising rate rail with the mk2 ECU and loom without a massive headache?

 

[Mart]

I guess the old hammer/vice trick of increasing the reg's pressure hasn't been tried by anyone yet? (assuming the 225/26 fuel pump could cope)

2 alternatives...

Increase the supply voltage to the fuel pump (MSD do such a box of tricks) which will naturally increase its output.

And/or...

Remove/block off the in-tank fpr, and fit an adjustable Malpassi (or the old adjustable d-jetronic reg', if you can source one) somewhere in the engine bay.

I've been giving this some thought lately, and started to question why I need to pay out for 630cc injectors when stock 225 injectors are good for northwards of 400hp...if you can maintain/raise the operating rail pressure @ wot/full boost.

 

[Ewan]

Wouldn't an aftermarket fpr fitted in the engine bay require a return line to the tank?

 

[Mart]

https://www.summitracing.com/int/parts/msd-2351

 

[Mart]

Old skool d-jetronic adjustable reg'...

 

[Mart]

New skool Malpassi adjustable reg'...



If you leave the boost reference port to air, the fuel pressure will be fixed at whatever you set it to. If you plumb said port pre-throttle, it'll act as a rising rate regulator, but base pressure will return (off boost) as to what you've set it at.

 

[SP33DY]

So there's a lovely black Clio 200 for sale near home. I'm having uncontrollable thoughts about putting the 250 engine in it and buying the clio 200 specific specialist components ecu to run it all......

Oh and there's a black Meg 250 set up for track abuse that is also tempting me....

 

[andybond]

stock 225 injectors are good for northwards of 400hp...if you can maintain their 3bar (or 3.5bar, whatever it is) operating pressure @ wot/full boost.

No chance at all they will flow enough for 400bhp. Not a prayer.

The flow rate even at 100% duty is no where near.

 

[Mart]

They will at a higher/maintained fuel pressure. The reason 630s (increased flow) are fitted is to compensate for the lack/reduction in fuel pressure...which, imho, is a bit of a bodge way of resolving the issue.

For arguements sake, if the o.e pump/reg' is sitting at 3.5bar @ idle, then you apply 1.5bar boost, the fuel pressure will now be 2bar. You can increase the injector cycle to compensate, but you can only go so far. When that's reached, your remaining options are to increase fuel pressure or fit larger injectors (eg, 630s).

480cc injectors (which the 225/26 injectors are, iirc) will do 400hp or there-abouts with an increased rail pressure.

 

[Mart]

Whether the o.e fuel pump will cope is another thing though...

 

[SP33DY]

They will at a higher/maintained fuel pressure. The reason 630s (increased flow) are fitted is to compensate for the lack/reduction in fuel pressure...which, imho, is a bit of a bodge way of resolving the issue.

For arguements sake, if the o.e pump/reg' is sitting at 3.5bar @ idle, then you apply 1.5bar boost, the fuel pressure will now be 2bar. You can increase the injector cycle to compensate, but you can only go so far. When that's reached, your remaining options are to increase fuel pressure or fit larger injectors (eg, 630s).

I've just had this exact discussion on facebook earlier.....

 

[Mart]

Ha! What was said?

I guess for ease, the majority of people will stick to fitting 630s, especially as RST or the such like will have to map them in, so to speak, anyway.

I'm defo gonna look into the fpr/rail pressure side of things first though.

 

[SP33DY]

Some guy claiming 600bhp, he had 630 cc injectors, a walbro 255lph pump and was still using an in tank FPR at 4bar. I told him there was no way his fuel set up could run that bhp and used the same example you did to show the effects of injecting into a pressurised plenum and that his boost pressure will be working against his FPR as well.

It was a waste of time he still claims 600bhp

 

[Mart]

He'd need much more than 4bar pressure to get anywhere near 600hp with 630s in situ. Returnless system @ 4bar + I'm guessing a high boost level = 600hp my arse. Maybe 400-450 ish at best?

What blower is he using? GT35?

 

[SP33DY]

There was no reasoning with him mate. Even Paul from RS tuning commented and he wouldn't believe him either.

On the plus side it was a good technical explanation for the megane lot on there

 

[SP33DY]

He'd need much more than 4bar pressure to get anywhere near 600hp with 630s in situ. Returnless system @ 4bar + I'm guessing a high boost level = 600hp my arse. Maybe 400-450 ish at best?

What blower is he using? GT35?

He was using a td05 20g

 

[andybond]

He was using a td05 20g

That's George. He appears to be like Jesus and makes the impossible possible. Like tuning 600bhp on a compressor maps that's well outside its range!

 

[andybond]

They will at a higher/maintained fuel pressure. The reason 630s (increased flow) are fitted is to compensate for the lack/reduction in fuel pressure...which, imho, is a bit of a bodge way of resolving the issue.

For arguements sake, if the o.e pump/reg' is sitting at 3.5bar @ idle, then you apply 1.5bar boost, the fuel pressure will now be 2bar. You can increase the injector cycle to compensate, but you can only go so far. When that's reached, your remaining options are to increase fuel pressure or fit larger injectors (eg, 630s).

480cc injectors (which the 225/26 injectors are, iirc) will do 400hp or there-abouts with 3-3.5bar rail pressure.

525ccs will do 400z , the 480s won't. At all. Ever.

 

[Mart]

Yeah but no but yeah but...

The point still remains that there's no need for 630s at the power level 225/26's will run with o.e blowers in situ (even including 'upgrading' to the 15t units) if the rail pressure can be maintained.

 

[andybond]

Yeah but no but yeah but...

The point still remains that there's no need for 630s at the power level 225/26's will run with o.e blowers in situ (even including 'upgrading' to the 15t units) if the rail pressure can be maintained.

I disagree ! I think the duty cycle will be too high to cope. You have also backed down by 100bhp now as well. Thats changing the rules slightly !

 

[Mart]

I'm not backing down, I still say they'll do 400 or there-abouts with a raised rail pressure. However, the 14/15t units won't flow anywhere near that power, so it matters ye not anyway.