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4A-GE 20v supercharged questions - Long technical post, stay with me!!

bi22le - 30/4/24 at 10:11 PM

After reading pretty much every single article and forum post the internet and FaceAche can give me I still have questions. . . . This does however make me an "expert" so watch out!!!!

The back story:
I bought a supercharged 4A-GE Striker (Rotrex C30-84, 8.5:1 pistons) as a blind and a bit of an unknown. I took it to Northampton Motorsport where Troy did his best but struggled with it.

- It was not making much boost at around 0.5BAR. Boost was mapped during runs and showed no signs of leaks (linear plateaus on the graph)
- Cylinders compression tested (not leak down) and were even across all 4.
- VVT was stuck but he managed to free it up (these are obsolete and now impossible to buy new)
- I took with me some 380cc injectors (as proven good for ~270bhp) to replace the 295cc but didn't need them as it only produced 185bhp.
- Main comment to fix is "fuelling seemed erratic".

The reason I Think it was under power was because it had low boost and low compression pistons. The majority of RAW supercharger builds used stock 10.5:1 ST pistons and 1Bar boost to ~270bhp. I cant solve the low comp pistons (too expensive of a rebuild) so going to keep them to stay "safe". I am getting the Rotrex upgraded to a C30-94 gen2 T2, that should solve the boost issue but I dont know how much it will give me. I am hopin for more than 1Bar as I need to compensate for the low CR. Questions

1) Any ideas what boost I should be getting? Anyone with a SC 4A-GE 20V with a new Gen2 C30-94? Even better if you also have low CR pistons!!
2) If I use an online injector flow calculator is states I should use ~470cc injectors to achieve 270bhp with 90%DC (seems about right) and 37.5PSI fuel rail pressure (seems about right). How the hell are people commonly using "yellow" 380cc injectors to hit that power, its not theoretically possible even with 100%DC.
3) I want to maximise boost, so I am now looking at hard boost pipes and an improved intercooler (currently a stock MR2 turbo one). Is this worth the effort?
4) I dont know what fuel pump is in there but am thinking to just change it anyway to a known brand and litre/hour so I can ensure I maintain fuel rail pressure.
5) Last time I was at NM they removed my lambda sensor and said its not needed for my OMEX600. This bugged me slightly as I want it to be MOT and run as best as possible, surely I need it!!
6) To help the day go as smoothly as possible help diagnose issues I was thinking of installing a fuel pressure gauge for the rail and a 2nd boost gauge for straight after the SC to confirm losses. Do we think this is worth it and what else should I fit?
7) If you have a boosted 4A-GE on throttle bodies, do you still have the IAC plumbed in or did you remove it and adjust the butterfly stoppers?

I am booked in for 2nd June so I have time to check and upgrade if need be.

Thanks all. All comments welcome, especially those who have walked the walk.

scotishstriker - 1/5/24 at 09:45 AM

Hi,
What size pully are you using?

My rotex supercharger zetec started off with a 95mm pully and only made 0.5 bar and 170bhp. Changed the pully to 70mm it then made 1.1bar and 245bhp.

If it was a fueling issue it would lean.

bi22le - 1/5/24 at 11:10 AM

quote:
Originally posted by scotishstriker
Hi,
What size pully are you using?

My rotex supercharger zetec started off with a 95mm pully and only made 0.5 bar and 170bhp. Changed the pully to 70mm it then made 1.1bar and 245bhp.

If it was a fueling issue it would lean.

Unsure of the exact pulley size but it was a little large and that is going to be changed on the new charger to match SC RPM and engine RPM.

sebastiaan - 2/5/24 at 06:15 AM

Start from the basics. Post pulley sizes (charger and crank, of course) and we can work from there.

I get a sneaky suspicion that someone might be selling you a supercharger upgrade you do not need. The C30-84 should be more than large enough to get you to your power target so if it is functioning as intended, why upgrade? Larger ain't better...

sebastiaan - 2/5/24 at 06:25 AM

oh, and:

quote:
Originally posted by bi22le
1) Any ideas what boost I should be getting? Anyone with a SC 4A-GE 20V with a new Gen2 C30-94? Even better if you also have low CR pistons!!
2) If I use an online injector flow calculator is states I should use ~470cc injectors to achieve 270bhp with 90%DC (seems about right) and 37.5PSI fuel rail pressure (seems about right). How the hell are people commonly using "yellow" 380cc injectors to hit that power, its not theoretically possible even with 100%DC.
3) I want to maximise boost, so I am now looking at hard boost pipes and an improved intercooler (currently a stock MR2 turbo one). Is this worth the effort?
4) I dont know what fuel pump is in there but am thinking to just change it anyway to a known brand and litre/hour so I can ensure I maintain fuel rail pressure.
5) Last time I was at NM they removed my lambda sensor and said its not needed for my OMEX600. This bugged me slightly as I want it to be MOT and run as best as possible, surely I need it!!
6) To help the day go as smoothly as possible help diagnose issues I was thinking of installing a fuel pressure gauge for the rail and a 2nd boost gauge for straight after the SC to confirm losses. Do we think this is worth it and what else should I fit?
7) If you have a boosted 4A-GE on throttle bodies, do you still have the IAC plumbed in or did you remove it and adjust the butterfly stoppers?

1) depends on pulley sizes
2) 380cc/min on a four pot = 68.4 kg/hour of fuel to the engine (petrol's density is around 0.75 g/cc). With guestimate specific consumption of 300k/kWh that gets you to 228kW at 100% duty cycle, or around 200kW at 90% DC. Tight but doable.
3) No. See 1), first make sure you get the right pulleys on there, then start chasing boost loss / pressure drop over piping and I/C
4) better to spend the money on a fuel rail pressure sensor (does your ECU have a spare input for this? surely a nice-to-have when logging and chasing the inevitable fuel sloshing at half a tank issues)
5) if there's a wideband in there, use it! If a narrowband, meh...
6) yes on the 1st one (but sensor, not gauge). You can also move the boost gauge connection around to get an idea on pressure drop in consecutive runs.
7) no 4A-GE here, but my Alfa is on ITB's with a mechanical idle screw and it's hateful. If you can get closed loop idle control, go for it. But get the basics right first or drown in complexity.

Good luck. But pulley sizes first!