Having owned my Blob STi for five and a half years I recently had a few jobs done including a VF48 upgrade with somewhat disappointing results, which has left me wondering whether going back to the VF35 is the way to go.

In fairness the last mapping was done by Andy Forrest about 4 years ago with the following specs/mods:

• VF35 turbo
• STi pink injectors
• 3 port boost solenoid
• K&N Panel Filter
• KYB Iridium IX 7's
• equal length headers and decat up-pipe
• 3" full decat downpipe and 3" resonated centre
• 2.5" Scoobyworld Racebox
• HKS ssqv dump valve
• Nitrous Race Formula Octane Booster 2.5-3ml/ltr with v-power/momentum

The result of the mapping are shown in the graph below - 360bhp / 362lbft




Since then there have been a couple of changes.

• now has fully wrapped 3" bellmouth downpipe with 100 cell sports cat
• custom 3" non resonated centre
• VF48 turbo
• 666cc top feed injectors
• alloy pitch stop mount
• Perrin anti lift kit

Other mods include uprated brake discs/pads, BC BR's, Exedy pink box clutch, etc.

I opted for the VF48 after some research on SN and reading how it should have little lag, quick spool up and potential for power around 380+.
However, the reality has been far more disappointing.

So back to AndyF but only managed these results 350bhp / 372lbft




The VF35 would hit boost around 2800rpm and pull right through to the red line, while the VF48 isn't kicking in until around 3800rpm but is then dropping off quickly and not holding boost much beyond 5300rpm.

As I'm sure you can imagine, I'm not finding this much narrower band of available boost which arrives late and goes home early very rewarding and certainly not in keeping with the various threads/reviews/opinions etc I'd seen suggesting this was the way to go.

Anyhoo, it seems the problem may be back pressure from the exhaust restrictions i.e. sports cat and 3" step down to 2.5" back box. Since mapping I've also noticed an occasional noise which I initially thought were wastegate chatter but having done a bit more research now think is more likely to be compressor surge.

Here's an image of my custom centre which is 3" and only steps down to 2.5" over the last 4" or so before the flange.



So, the questions really are...

• do I perceiver with the VF48 or go back to the VF35?
• will a 3" back box make any real difference with back pressure reduction?
• if not what will?
• what could be done to get the VF48 to spool up earlier?
• what could be done to get the VF48 to hold boost longer?

Any constructive thoughts would be appreciated.

 

Don't forget the vf48 was meant for the 2.5 engine

 

What he said^^

It sounds to me like the only thing you'll be happy with is going billet, so your looking at something like an SC40 or 42 to get a noticeable gain as well as keeping the early spool.

Bite the bullet time, got to get your wallet out again.

What did Andy suggest?

 

Did you use octane booster like with vf35?

 

Would have been better just swapping the 35 for a 34 for spool and with the meth/NF you'd get iro 370.

 

Perrin/Samco inlet hose and Harvey Smith Up-pipe both claim to give an increase in spool. 200rpm each I believe.

 

what a pointless expense, if your going to do a turbo change at least buy an upgrade

 

Agreed, the VF48 is only a later version of the VF35 turbo. I wouldn't expect to see any benfit as this really isn't an upgrade!

 

What did Andy F say to these questions?
If you didn't ask him, maybe that should be your first port of call.

 

I've heard good things and seen massive improvements from porting the turbo. If your old VF35 is ok and off the car maybe you could send that off to get ported and fit a decent actuator. This may allow you to hold more boost and ultimately allow you to achieve a higher BHP on the dyno.

That said though, how does the car drive? It's not all about the dyno figures.

 

tbh been said above, 48 is ment to work on a 2.5, not on a 2.0. given the position you are in i'd be tempted to sell on the 48 and go down the route of a sc42/sc38 that are ment to work on 2.0's.

 

What was the reason for going sports cat?

 

Both the 43 & 48 will run out of puff around the 5500 mark regardless , as you can see from your graph your torque figure is up ..
Turbo design for 2.5 pulling torque through the centre of the Rev band

 

Hi there

As above VF43/48 are better suited on 2.5L

What can brings spool up to lower RPM,only thing which can helps is Harvey Up pipe which has been proven on numerous cars

Porting the VF43/48 and using stronger actuator Forge seems are popular upgrades,but still think VF35 or VF34 as Stu said,will be better choice there

2.5" exhaust should be OK for 360-400bhp

Thanks,Jura

 

Nice to see the advice offered has been so well received by the OP

 

The OP only has 34 posts from joining date in 2006 so that works out to 1 post every 2.8 months. I wouldn't expect a reply until mid Jan 2015!

 

Ha ha lol

 

A VF43/48 should definitely be a good upgrade from the VF35.

It should hold boost longer too due to the larger exhaust housing and lose a bit of spool.

When I went VF35 to VF43 I saw an increase of 30bhp. Went very well.

 

The purpose of the OP was to try and find anyone who had made the same/similar changes, what their results were and what 'supporting mods' they had for comparison. To that end, thanks to those who provided constructive posts with meaningful advice and information.

I had been looking to move from mid to high 300's on stock internals and not going to FMIC and the VF48 seemed to be one amongst other turbos quoted that could do the job. I had been considering switching back but to the VF35 but based Andy's advice re- back pressure and your comments am now considering keeping the VF48, replacing the 2.5" BB with a 3" one going for the Harvey Trick up-pipe and ported headers and making the most of it. Still undecided about going back full decat or keeping the 100 cell sports cat. Why not full decat, easy - it won't pass MOT emissions and it's a PITA swapping downpipe but who knows, mibee aye mibees no.

Of course in true forum style your damned if you do and damned if you don't. Thinking of the ubiquitous 'have you searched previous threads' comments, I did just that. I had a VF48 available to me and found several threads suggesting it was a reasonable step up from a VF35, going from 350-ish to 380+ for little cost (with the plan to recover some of the costs by selling on the VF35 and pink injectors). Of course I was aware of the issue of putting a turbo from a 2.5 onto a 2.0 car, but the research suggested the VF48 was more doable than the VF43.

Although not too recent, this thread https://www.scoobynet.com/general-te...obeye-sti.html seems to have 'mapper' endorsement at posts 2 & 4.

And FFS, yeah it's taken me 3 days to reply, excuse me for working shifts and having a life offline.

As for the 'wuda, cuda, shuda' and 'in my pointless opinion' posts..., they just optimise why after 8 years of Scoob ownership I post here so infrequently.

 

Does the car drive better and feel nicer on the road than before?

To be honest your thread and results are a good comparison between the 2 different turbos. As already said though, I wouldn't have really expected much different. If you really want more power then the vf48 probably wasn't your best upgrade option from the vf35.

Seems like you're not going to be happy though.

 

I would have to disagree with the comment of if you want more power a VF48 wasn't the right way to go. Maybe not the right way to go for big power, but for a smallish outlay compared to a new big turbo, you should see some nice gains.

Most of the VF35 to VF43/48 upgrades I have seen have resulted in more torque, more power, slight reduction in response, but power held higher up easier mainly due to the exhaust housing.

Personally I would port the VF48 exhaust housing, fit a stronger actuator, decat the downpipe, ensure you have a full 3" system and maybe fit a silicone inlet pipe... maybe!

Did Andy F comment on how the turbo was performing boost wise etc?

 

Twin scroll conversion would have been better if you're replacing exhaust parts and turbos

 

I ran a heavily ported vf35 on my newage 2.0 Sti and that made 352 horse.
Then went to same spec ported vf43 and made 384 horse, with a meth map it made 412 horse.



Top 2 vf43 v power and meth.
Ignore bottom line, first ever map standard car

Running diy rotated gt30 now.
Cheers Chris