Help with turbo choice

[a s b]

Hi , I am about to buy this week a new turbo and have it down to either a vf35 or a vf34 but would like some feedback on which would be the best with current mods car is a classic v4 wrx
Spec is
Full decat 2.5 inch with custom up pipe
Walbro 255 pump
3 port boost solenoid
440 cc injectors
Newage wrx intercooler with matching undertray
Samco intercooler y pipe
Ngk pfr7b plugs
K&N panel filter
Turbo will have a turbo blanket fitted
any advice would be great thanks

Edited by a s b on Monday 4th January 19:08

[Kedlestone]

I've had both turbos, all be it on newages. I found the VF34 came on boost a lot earlier and pulled right through the Rev range. The 35 is also a great turbo but I have found it to be a bit laggyer but on the plus side it doesn't tail off boost at the top end like the 34.

If it was my money I'd go with the 34.

[a s b]

Hi thanks for reply , for a classic I have read the spool is the other way round , the vf35 spooling quicker than the vf34 but the vf35 running out of puff higher up the Rev range , I have seen a vf34 for sale which has only done 1000 miles , or looking at buying a reconditioned vf35 from central turbos possibly with a billet wheel , I think I'm going to go for quicker spool so I don't lose the drive ability the car currently has with a td04 mapped to 290 bhp

[TEKNOPUG]

Depends what your ultimate power goals are. You could fit a hybrid Td04, such as a SC320 and have practically zero lag and still comfortably push 300+ bhp/lbs.

[a s b]

Hi thanks , yes I was initially looking at a td04 hybrid as the quick spool up sounds good , but I'm after a bit more of a power increase I was hoping for around 330 bhp with my current mods at the moment I'm leaning towards the vf35 . I waited ages to get esl fitted now I'm bored of the td04 so looking forward to a bit more power

[fatjon]

You won't get there on 440cc injectors. You need circa 600cc or a major increase in fuel pressure over standard. You are currently fueled for a about 240BHP.

[a s b]

Thanks fatjon , I was thinking of upgrading the injectors to 550cc before I got the 440cc but after doing a search on scoobynet I have seen plenty of people running 320 plus bhp with them so thought they would be ok

[Vixpy1]

440's are fine for 320 to 330.

Both the VF34 and 35 work well. i can never really tell much difference between them

[a s b]

Thank you vixpy1 , I have just sent my 440s off to be cleaned and flow tested to make sure they are running at there best

[AntiLagGC8]

I'm running a VF37 (@353bhp) which I think is great but I'd like 420-450 so I'm considering a bigger turbo.

I think as ever the answer for best spool is either smallest turbo you can fit to achieve the goal or do something like I did and convert to twin scroll (significantly more expensive due to all of the other parts that need to be changed). It's worth pointing out though some of the benefits of twin scroll are lost without AVCS heads.

Let us know how you get on!

[fatjon]

a s b said:

Thanks fatjon , I was thinking of upgrading the injectors to 550cc before I got the 440cc but after doing a search on scoobynet I have seen plenty of people running 320 plus bhp with them so thought they would be ok

I have checked a whole variety of injector size calculators which apply the standard formula and they all say too small unless you run them at 60PSI and exceed the generally accepted max duty cycle of 80%.

http://www.rceng.com/technical.aspx

take that one for example. Assuming an at the CRANK figure of 360BHP to give 320 at the wheels and assuming BSFC of 0.6 and a duty cycle of 80% at standard 43PSI fuel pressure you need 714cc/min

Running them to 90% you can get down to 630cc

This is the one I have used regularly and found it very accurate when actually tested on the engine dyno as opposed to Joe Bloggs tell you what you want to hear rolling road.

Others like

http://fuelinjectorclinic.com/flow-calculator

Suggests 708cc/min

Even dropping power output to 240BHP suggests 472cc/min

There are dozens more from well respected tuners and injector manufacturers that indicate that either the power outputs claimed are BS or the the injectors are being driven to 100% duty cycle at 60PSI. At 100% duty cycle (IE it never shuts!) and 60PSI 440CC/min can just do it. They will also have no headroom to handle any lean conditions and might get a tad warm. You could fool yourself that the brake specific fuel consumption of the Subaru boxer engine is unusually low but it's not, it's actually unusually high, they are not noted for fuel efficiency. Of course you will also need the map fixing for these big injectors. For what you have already spent and are going to spend do the job right and don't follow the herd.

[a s b]

Antilagc8 thanks and I will let you know once I have it all sorted . Fatjon wow that is some very interesting reading thank you , looks like you are right and it would be best for me to go larger than 440s , I will be selling my phase 1.5 and buying some phase 2 injectors , then sending them to lateral performance to be flow tested and modified , I will need the adaptor kit to fit them ,the car will road mapped when everything is bolted on , I have narrowed the turbo down to a vf34 or a td05 big 16g with a Evo 3 billet wheel , the vf34 has covered 1000 miles and the td05 will be a reconditioned one any thoughts

[Vixpy1]

fatjon said:

a s b said:

Thanks fatjon , I was thinking of upgrading the injectors to 550cc before I got the 440cc but after doing a search on scoobynet I have seen plenty of people running 320 plus bhp with them so thought they would be ok

I have checked a whole variety of injector size calculators which apply the standard formula and they all say too small unless you run them at 60PSI and exceed the generally accepted max duty cycle of 80%.

http://www.rceng.com/technical.aspx

take that one for example. Assuming an at the CRANK figure of 360BHP to give 320 at the wheels and assuming BSFC of 0.6 and a duty cycle of 80% at standard 43PSI fuel pressure you need 714cc/min

Running them to 90% you can get down to 630cc

This is the one I have used regularly and found it very accurate when actually tested on the engine dyno as opposed to Joe Bloggs tell you what you want to hear rolling road.

Others like

http://fuelinjectorclinic.com/flow-calculator

Suggests 708cc/min

Even dropping power output to 240BHP suggests 472cc/min

There are dozens more from well respected tuners and injector manufacturers that indicate that either the power outputs claimed are BS or the the injectors are being driven to 100% duty cycle at 60PSI. At 100% duty cycle (IE it never shuts!) and 60PSI 440CC/min can just do it. They will also have no headroom to handle any lean conditions and might get a tad warm. You could fool yourself that the brake specific fuel consumption of the Subaru boxer engine is unusually low but it's not, it's actually unusually high, they are not noted for fuel efficiency. Of course you will also need the map fixing for these big injectors. For what you have already spent and are going to spend do the job right and don't follow the herd.

Yes but we are talking about 320bho at the fly , not the wheels , also the 440cc injectors actually flow 480cx

That's with base pressure of 45psi and around 23 psi of boost

[fatjon]

On those figures you still need 614cc at 80% or 550cc at 90%.

[a s b]

Little update , I've gone with fatjon's advice , I now have a set of phase 2 440 s that will be getting flow tested and modified to a higher cc , once I gather all the parts I will speak to my mapper to see what size injectors he recommends