Going for mapping soon and I think my injectors will be first to max out, Hoping be get 320-340bhp from my V3 type R. Was looking a set of 550cc injectors but would something bigger like 740cc be better or would they be too big.

Car will have (once fitted)... Full De-cat, RCM un-equal headers, fuel pump, air filter.

Turbo etc all as subaru intended.

Thanks

Walton

 

you should have yellow subaru 440cc injectors which should be ok for that sort of BHP but it does depend on what turbo your runing with it to weather you get that BHP figure or near it and 740cc are def not needed for that sort of power

 

550s are perfect. They wont be stretched at all at that level and they'll give you the option to push up to 400 if you want to in future.

 

Yellow 440s will max out somewhere between 320 and 340 bhp as a rule.
550s will see you all the way to around 400 bhp and a bit more if you have an FPR.
Don't fit 740s unless you have plans to exceed the 380-400 bracket.
Can I quote you for tubular headers?

 

will it effect performance or run rough then - with larger injectors than it needs ? , only ask as I have fitted some nismo 740cc injectors to my 95 wrx they were sold to me as 550's but have since found out they are 740cc's , have yet to get a remap when cars on the road again, cheers

 

I've got direct experience of this very issue.

I went from 440's to 740's. Both were used on a VF28 as I had planned to go for a bigger turbo at a later date.

Long and short of it is that I got better off boost economy with the 740's and to be honest I also think I got better fuel economy all round.

One thing I would say is that it's all in the mapping. Mine idled exactly where it should and ran as sweet as a nut.

So if you have a good mapper I see no reason for you to not go to 740's. Done right, you'll never look back and you'll have plenty of head room for the future but you WILL need to get the car mapped for them.

 

the thing is its all about how far you want to go if you not going to run more then 340 bhp then 440cc will work and you can pick them cheap on here 60- 80 quid but 550cc and above tend to go for 150-250 quid so think off it like that i had 340 bhp out of 440cc injectors and the were at 92 percent duty or along there not quite maxed out

 

at 92 percent they are very nearly permenantly open. This will use loads of fuel.

The 740's have a really nice spray pattern and you will use substantially less fuel for the off boost stuff. When I first had mine done I was all set for my fuel bills to go through the roof. Infact the opposite hapened.

If you have no plans to go for more power at a later date then the 550's make sense. But the OP already has the 740's. My point is there is absolutely no reason for him to swap IF he gets the car mapped properly. There are NO downsides to using the 740's he already has.

 

im not saying your worng buy all means if he already has them then fair play job done i didnt see he already had them oh and im running 550cc injector son mine at 390bhp ish and im still getting 300 miles to a full tank on long motorway journeys like you say a good bit of mapping

 

I have a v4 sti still running 440s and a vf23. it has simtek fitted and mapped by andy f. I had it on the rr today and it ran 333 and 320 lbft. But i think the ijectors are maxed at that. Turbo is also nearly at limit. When i replace mine andy f advised me to go for 740s and a td05 20g. Hope this helps..

 

If this was a brain surgery forum would you feel qualified to post on it?

The AFR is set, the duty cycle has no effect on taotla fuel injectedm, for the same AFR ist the same amount, so the 500's or 440's wouyl inject the same amount of fuel as the 740's wouldn't they - DOH!

Spray pattern has 2 parts of no effect on FE, maybe 1/2% at most.

74-0's are too big on a 2.5, at idle and light load cruise you are running below the minimum pulsewidth (so fueling becomes inconsistent) and has in the apst lead to engine failure due to bore wash.

Simon

 

Utter tripe!

I'm speaking from my own experience here.

I can state that when I swapped from 440's to 740's I had better fuel off boost economy with the 740's.

The car also drove smoother thoughout the rev range on the 740's.

As for 740's being too big on a 2.5 that's gash. Mine were first used on a 2.0L VF28 car.
They were perfect. No idle issues at all. Did 30K miles in this guise and when I sold the short motor on to go 2.5 it was in fantastic condition.

I then went up to a 2.5 with a rotated GT30R and used the same 740's again they were perfect for the job.

As I said before it's all in the mapping, fortunately the guy who mapped mine knew exactly what he was doing. OP will have no problems using his 740's providing he uses a decent mapper.

Here endeth the lesson

 

I also have experience in this field.

Went from 440s to 550s when the car was on the std JECS ECU. Mapper = Bob Rawle, so no issues there; car was at the 340bhp level, so right on the limit of 440s, but arguably 550s a bit overkill.

David at APi too my car out for an MOT and came back complaining that the car felt awful on small constant throttle openings and explained that the standard JECS ecu had minimal facility for mappers to adjust for larger than required injectors. The explanation he gave was more technical, but that was the jist. His other comment was that Bob was a wizard with Jecs, and if he'd mapped it that was as good as it was going to get given the spec. No surprises there. To be honest I had noticed a little bit of lumpiness at small constant throttle openings, but nothing to write home about. David, however, sees a LOT of optimally specified and tuned Imprezas.

Anyway, Simtek installed, mapping constraints on fueling adjustment vanished, problem went instantly.

So it's an ECU AND mapper permutation!

The OP has a V3, so presumably he'll be looking at an aftermarket ECU?

 

 

PMSL!

 

As you can no doubt imagine, today was a slow day at the coal face.

 

What have I missed?
Coalface? I only see crops.

 

im in exactly this situation also,

have 440's, want 550s but cant seem to find any at less than £400!!

would fit bigger if i knew it wouldnt be an issue

will run a simtek shortly

 

lol