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Old 10-29-2012, 04:54 AM   #1
DONx3
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Default Are upgrading injectors worth it for VF39?

I remember when I did my swap years ago, I knew stockers were good enough so I kept them. I called a couple tuners and my local tuner and I feel the consensus is to upgrade them because they would be pretty close to 90% or more IDC. I am fine with being 90%+ IDC but if I can get more whp I would upgrade them.

What would be the difference in whp at my current state of tbe, tomei uel headers w/ uppipe, vf39, sti tmic, cobb sri, walbro fp, V.S. current state plus injectors, tgv deletes, turbo inlet?

So my question is, are my injectors limiting the vf39 full potential? Also, I am talking about protune whp numbers. Thanks in advance.
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Old 10-29-2012, 09:41 AM   #2
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Originally Posted by DONx3 View Post
So my question is, are my injectors limiting the vf39 full potential?
On gas, no

On E85, yes

your year WRX (if your side info is correct) came with 565cc/min injectors which is the same size as the STi
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Old 10-29-2012, 10:46 AM   #3
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do a pull and find out. I would say yes. Got vf43, tmic, spt intake, tgv deletes, inlet hose and my injectors are 97-99% at wot the whole time.
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Old 10-29-2012, 12:21 PM   #4
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Originally Posted by rocketperson7 View Post
On gas, no

On E85, yes

your year WRX (if your side info is correct) came with 565cc/min injectors which is the same size as the STi
Correct-O!

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Originally Posted by talvai View Post
do a pull and find out. I would say yes. Got vf43, tmic, spt intake, tgv deletes, inlet hose and my injectors are 97-99% at wot the whole time.
On pump gas? That doesn't sound right. What is your max boost?

I have my stock 565cc injectors on a VF48 setup with a Walbro 255 fuel pump and at 19psi my max duty cycle for the injectors is only around 82%-84%, which is plenty of headroom.
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Old 10-29-2012, 05:01 PM   #5
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Correct-O!



On pump gas? That doesn't sound right. What is your max boost?

I have my stock 565cc injectors on a VF48 setup with a Walbro 255 fuel pump and at 19psi my max duty cycle for the injectors is only around 82%-84%, which is plenty of headroom.
yup 93 octane. Boost is 19psi at max. I also have tgv deletes, grimmspeed ebcs, spt intake, inlet hose, 1 step colder spark plugs. Again not if its just me, but from my experience their pretty much maxed out. Just looking at logs they stay above 88% no problems and peak a 94%.


I don't race car or get on it, so not over concerned about it, but definitely something I am looking to replace in future when I get more power mods.


EDIT: Just to be clear not saying that's how it is. I have no idea of anything ECU or tuning related. Just giving my experience on a protune I have with my mods.

Last edited by talvai; 10-29-2012 at 05:13 PM.
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Old 10-29-2012, 06:01 PM   #6
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you can max out the injectors with a VF, but they are good enough to extract probably 98% of the performance you could hope for. If spending the cash for injectors, installation (if you don't do it yourself) and extra tuning is worth it to you, then go for it. I would think of it as a piece of mind thing, you wont feel the difference, but you will know it will run safe if the temps drop and the air is dense.

If you think you will upgrade the turbo later, then it might be reasonable. If you do injectors, it is a good time to do TGV deletes. If you do TGV deletes, it is a good time to replace the inlet with a high quality piece. If you have the intake manifold off, it is a good time to get rid of the secondary air valves. If you go through all that work, it is a good time to drop in that bigger turbo. It is a slippery slope.
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Old 10-29-2012, 07:26 PM   #7
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Originally Posted by northman View Post
you can max out the injectors with a VF, but they are good enough to extract probably 98% of the performance you could hope for. If spending the cash for injectors, installation (if you don't do it yourself) and extra tuning is worth it to you, then go for it. I would think of it as a piece of mind thing, you wont feel the difference, but you will know it will run safe if the temps drop and the air is dense.

If you think you will upgrade the turbo later, then it might be reasonable. If you do injectors, it is a good time to do TGV deletes. If you do TGV deletes, it is a good time to replace the inlet with a high quality piece. If you have the intake manifold off, it is a good time to get rid of the secondary air valves. If you go through all that work, it is a good time to drop in that bigger turbo. It is a slippery slope.
Thanks this is what I was thinking. I am actually thinking of selling my headers (not installed) because I would probably see minimal gains for how much it cost itself and the ceramic coating which was $$$. Or will I spool much quicker with the headers? What mods help spool quicker?

Last edited by DONx3; 10-29-2012 at 07:33 PM.
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Old 10-29-2012, 07:46 PM   #8
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What mods help spool quicker?
I noticed a nice improvement in spool going to an AEM cold air intake vs the stock airbox. I noticed a nice benefit in driveability going to a TXS TMIC vs the STI version.

Some people claim headers help spool, others claim it hurts. I added a Perrin ELH and ran it for a week or so before upgrading the turbo & other stuff. Without tuning I did not notice much change in spool or power.
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Old 10-30-2012, 04:32 AM   #9
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Also, I forgot to ask which is a more worthwhile mod, TGV deletes or headers w/ uppipe?
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Old 10-30-2012, 08:20 AM   #10
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you can max out the injectors with a VF, but they are good enough to extract probably 98% of the performance you could hope for. If spending the cash for injectors, installation (if you don't do it yourself) and extra tuning is worth it to you, then go for it. I would think of it as a piece of mind thing, you wont feel the difference, but you will know it will run safe if the temps drop and the air is dense.

If you think you will upgrade the turbo later, then it might be reasonable. If you do injectors, it is a good time to do TGV deletes. If you do TGV deletes, it is a good time to replace the inlet with a high quality piece. If you have the intake manifold off, it is a good time to get rid of the secondary air valves. If you go through all that work, it is a good time to drop in that bigger turbo. It is a slippery slope.
Would caution removing secondary air pump. All it does is save you weight. 0 performance gain. Fact from the cars I have removed it from and got tuned they don't idle as nicely and when you have AC on they sap power from motor where with air pump none of that happens.

Not saying its bad to remove. If I was building a track car that **** would be first thing to go, but for DD one might want to put some thought on if gain is worth it or not.

For me I do plan on getting bigger turbo in future but would rather have any and all components in my car not be running at max at all the time. Running things on max max or close to it is how people start have reliability issues in my opinion. Spending $600 and a day work in the garage is better than me paying $1000 for a new turbo or $5000 for new engine. Again to me I rather play things safe than sorry, each is his own.

For spool up, noticed lightweight crank pulley and flywheel helps rev things up quicker. Inlet hose doesn't add any power but shifts curve to left a good 200-400rpm. TGV deletes moved curve over, gain some power and holds better up top. EBCS shifted power over to left, not sure if it gained me any but did hold power longer on higher rpms.

Plan on doing my uppipe and headers to gain a little more power and shift it. Will tell you though, easier to uppipe and headers your first time than TGV deletes. TGV deletes need a lot of patience to get intake manifold off least for me my first time. Second time doing it did it in half the time

Last edited by talvai; 10-30-2012 at 08:26 AM.
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Old 10-30-2012, 09:23 AM   #11
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If your never planning to upgrade the turbo you can just install a Fuel Pressure regulator to get alittle more performance out of the injectors you have. If you bump the pressure to 50psi. You'd end up with the equivalent of 605cc injectors which would give you the ability to flow enough fuel for an extra 25-30hp.

But if you plan on making more power later you'll need to get injectors anyways. The FPR will be easier to install and cheaper, but completely unnessesary if you just upgrade the injectors. (You can get a basic FPR for $25 off ebay, or a name brand nicer one for $175, injectors will cost closer to $80-175 ea(320-700).

If you do care about the reliability of your injectors you should try to run them at 80% duty cycle. Max hp for the VF39 should be around 375-400 crank hp(300-350WHP??? depending on the dyno) so you should get 750-800cc injectors for pump gas if you were upgrading. You could flow enough for that HP level with the 605cc + FPR upgrade with like 98% IDC.

Last edited by tunertype; 10-30-2012 at 09:36 AM.
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Old 10-30-2012, 11:28 AM   #12
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Stock injectors will be your limiting factor.
Is it necessary to upgrade? nope
Will it give you a bit more headroom to make power? yes

If it's just a daily driver that you want a solid tune no the stockers will do just fine.

If E85 is available though I always suggest going with that, it's a far superior fuel in every way. In this case you would need injectors though.
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Old 10-30-2012, 12:54 PM   #13
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Originally Posted by NoGraffix View Post
Stock injectors will be your limiting factor.
Is it necessary to upgrade? nope
Will it give you a bit more headroom to make power? yes

If it's just a daily driver that you want a solid tune no the stockers will do just fine.

If E85 is available though I always suggest going with that, it's a far superior fuel in every way. In this case you would need injectors though.
You will need about 50% larger injectors for e85 than with gas. so if E85 is the goal you'll need 1000-1200cc injectors.

Last edited by tunertype; 10-30-2012 at 01:06 PM.
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Old 10-30-2012, 01:19 PM   #14
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Originally Posted by DONx3 View Post
Also, I forgot to ask which is a more worthwhile mod, TGV deletes or headers w/ uppipe?
Define "worthwhile."

TGV motors can go bad, causing a bad condition for the motor. So deleting them would be important to me.

Headers/up pipe will do a fair job helping power, but not near enough to be blown away.

But you can EASILY do TGV deletes in your home for free with a few tools.
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Old 10-30-2012, 01:35 PM   #15
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Would caution removing secondary air pump. All it does is save you weight. 0 performance gain. Fact from the cars I have removed it from and got tuned they don't idle as nicely and when you have AC on they sap power from motor where with air pump none of that happens.
Removing the secondary air stuff is not a performance mod, it is a reliability mod. Mine had failed, and it made no sense to spend a bunch of money "fixing" them just to have them fail again some time down the road. They only are active for a few seconds during a cold start, so I don't know why that would affect your idle, mine is fine. Perhaps you didn't get a good seal on one of your block-off plates? And what are you talking about with the AC? Unless I'm mistaken they are completely unrelated.
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Old 10-30-2012, 02:08 PM   #16
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Originally Posted by tunertype View Post
You will need about 50% larger injectors for e85 than with gas. so if E85 is the goal you'll need 1000-1200cc injectors.
not for a vf39. 850-1000 is plenty. 1200 would be overkill
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Old 10-30-2012, 07:29 PM   #17
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Define "worthwhile."

TGV motors can go bad, causing a bad condition for the motor. So deleting them would be important to me.

Headers/up pipe will do a fair job helping power, but not near enough to be blown away.

But you can EASILY do TGV deletes in your home for free with a few tools.
Worthwhile like where I will actually feel or see gains on paper.

I know my limitations are my turbo and injectors but I just want to squeeze out the best of what I have. I like the low and midrange of the vf39 and that's why I don't want to get bigger and ofcourse $$$. After talking with my tuner, I don't plan to use E85.
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Old 10-30-2012, 09:40 PM   #18
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Removing the secondary air stuff is not a performance mod, it is a reliability mod. Mine had failed, and it made no sense to spend a bunch of money "fixing" them just to have them fail again some time down the road. They only are active for a few seconds during a cold start, so I don't know why that would affect your idle, mine is fine. Perhaps you didn't get a good seal on one of your block-off plates? And what are you talking about with the AC? Unless I'm mistaken they are completely unrelated.
O agree they fail all the time their cheap to fix. Get valves for like $25-35 shipped easy. Idle issue is on a auto subaru, maybe that has something to do with it. But yes many have said that removing it when you use your AC engine will sap a little power from motor while its on. Modded cars probably have a hard time to notice.

Again not saying it bad to remove it just be aware of what tradeoffs you get with it. Agree that it is useless overall though since all it does is help heat up cat a little quicker when cold.
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Old 10-30-2012, 10:36 PM   #19
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Worthwhile like where I will actually feel or see gains on paper.

I know my limitations are my turbo and injectors but I just want to squeeze out the best of what I have. I like the low and midrange of the vf39 and that's why I don't want to get bigger and ofcourse $$$. After talking with my tuner, I don't plan to use E85.
Eh, I didn't personally feel it because the car was being rebuilt for 3 weeks. Some can claim they have, others not as much.
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Old 10-31-2012, 01:33 AM   #20
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O agree they fail all the time their cheap to fix. Get valves for like $25-35 shipped easy. Idle issue is on a auto subaru, maybe that has something to do with it. But yes many have said that removing it when you use your AC engine will sap a little power from motor while its on. Modded cars probably have a hard time to notice.

Again not saying it bad to remove it just be aware of what tradeoffs you get with it. Agree that it is useless overall though since all it does is help heat up cat a little quicker when cold.
I will reiterate, these have zero effect on how the AC works. The AC has a compressor which is basic to its operation, and that does require engine power. The air pump has no relation to this at all. Zero. Zip. Nada.
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Old 10-31-2012, 09:13 PM   #21
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Agreed, my FXT is an auto and the whole system is removed - no idle issues nor a/c effects, zero.

I could see if you removed the big valve with the baro sensor in it, you may have strange behaviors....
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Old 11-01-2012, 02:43 AM   #22
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Agreed, my FXT is an auto and the whole system is removed - no idle issues nor a/c effects, zero.

I could see if you removed the big valve with the baro sensor in it, you may have strange behaviors....
Correct, you need to keep the pressure sensor, as documented in the big thread.
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Old 11-01-2012, 09:21 AM   #23
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Agreed, my FXT is an auto and the whole system is removed - no idle issues nor a/c effects, zero.

I could see if you removed the big valve with the baro sensor in it, you may have strange behaviors....
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Correct, you need to keep the pressure sensor, as documented in the big thread.
Yea we left the sensor, maybe sensor is bad, but trust me not making this stuff up. So if you believe it or not o well. Maybe these are issues that are expecting with a bad sensor or no sensor installed. Car works fine regardless though. Will have to look into come spring time. Now its too cold to do anything.
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Old 11-01-2012, 09:24 AM   #24
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Note that the sensor is only in the pump housing for 07's, not 06's. (at least for the WRX)
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Old 11-01-2012, 09:29 AM   #25
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not for a vf39. 850-1000 is plenty. 1200 would be overkill
Yeah I was thinking about this, and your right. Stoich for E85 is 9.7 and gasoline is 14.7. So that's where i got the 50% more fuel, but forgot to factor in that because of the higher octane rating you'll be able to run a leaner mix, by around 10-15%(Lambda of .85 instead of .75).

So 9.7*.85=8.245, 14.7*.75=11.025. % difference in fuel needs for the same amount of Air=((11.025/8.245)-1)*100=33.7%.

750cc*1.337=1000
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