Tial 38mm spring advice

[rcsalmons]

I know the right thing to do would be to buy an ebc but cant afford one yet.

Anyway I run my car at 18psi boost with an mbc but the boost tails off as you would expect after peaking at 18psi. Question - would the tail off be less pronounced if I was to fit a stiffer (17.4 psi ) rated spring in the wastegate?

Any thoughts

Rich

 

[Diver944]

In theory you should hold a flat 17.4psi (as long as your turbocharger is up to the task)

I know if I switch my EBC off it holds a steady 0.8bar, whch is the spring the TiAL is fitted with.

 

[edh]

As Paul says - more likely your turbo - is it 26/6 or 26/8?

what does it drop down to at 6k? - I know mine's running at about 11psi by then - 26/8 with std wastegate & LBE

 

[sawood12]

Well 18psi is about 12.4 bar which is a bit much to ask for a K26/8 to hold to the red line so I guess your limitation is probably your turbo capacity. However I would have thought that in DPW mode the controlling factor in boost control would be your MBC or EBC and not your wastegate spring (i.e. in single port mode the boost pressure control is via the spring, but in DPW mode the boost pressure conrol is via your MBC or EBC). so changing your spring would not change your max boost.

 

[pauly]

1.24 [].

 

[Diver944]

It's a shame that Ricks website is down as I am pretty sure there are a couple of K26/8 cars on there with EBC's and MBC's so we could compare the boost charts. I 'think' a K26/8 will hold 18psi to the redline but I know that a K26/6 will not.

Actually now that I have stated that, I wonder if a K26/6 car that has a large exhaust, free flow MAF and intercooler mods would just be able to do it because all the restrictions have been improved.

Rich, how easy is it to swap over the spring in the TiAL? Sounds a very simple and cheap way to up your boost level

 

[TTM]

Sorry for wandering off topic but ... Is there really a point holding max boost pressure that high in the rev range when the engine is already past its peak power & torque outputs, well, at least with an original K26 ?
This is necessary to maintain a high top speed in top gear, which I believe doesn't happen much except on the few stretches of derestricted Autobahn left, but else ?

 

[Diver944]

Holding the boost for longer won't specifically achieve higher power figures than what was achieved further down at 4-5000 rpm, but the more area under the curve later in the rev range will make the car faster and easier to keep on the boil (which is I presume what most people are after [8D] )

 

[edh]

I'm be interested to see where peak power is when I eventually fit an MBC & DPW - what's the most power anyone has got from a 26/8? m (rick's site is down at the moment). I think I get peak power at 5200 rpm with my setup.

 

[rcsalmons]

The reason I asked is that Jon Mitchel said it was an option. Looking at Ricks site before it was down most cars with MBC had similar boost curves and EBC's were significantly better.

Paul - they are fairly simple to install.

Rich

 

[Fen]

Is it a temporary measure as in you'd take it out again when you fit an EBC? If so I'd say save the cost of the spring (have you priced one up, delivered to your door in the UK?), as it will be money wasted when you take it out again.

If you intend to leave it in all the time I'd say save the cost of the spring as once you have an EBC you ideally want it to be able to control your boost pressure down to a level lower than you'd ever want to run so that it's actually working for you.

I guess my advice is don't buy a spring or don't buy a spring, then.

 

[sawood12]

ORIGINAL: edh

I'm be interested to see where peak power is when I eventually fit an MBC & DPW - what's the most power anyone has got from a 26/8? m (rick's site is down at the moment). I think I get peak power at 5200 rpm with my setup.

Well I never dyno'd my car before I installed my DPW when it was completely stock, but with the DPW, MBC with max boost set to about 0.6 bar (just a bit below stock max boost pressure) I got 240bhp on the original rollers of truth. Therefore even if you assume my car was making 220bhp before (though it wouldn't have been) and that the rollers of truth would have measured 220bhp then you can crudely assume that you'll get circa 20bhp simply from the DPW swap with everything else being equal.

There was a very long and protracted debate on Rennlist a while back discussing whether a K26/6 can hold 15psi to the red line. Some reckoned they had managed it, some reckoned the turbo was not capable of doing that. From the rolling road I know mine peaks at 1 bar at about 3krpm then tails off in pretty much a straight line to about 0.7bar at the red line. The straightness of the line suggests to me that it is the MBC that is loosing me boost and that the turbo should be able to hold max boost for at least 500 - 1000 rpm - which is what i'm hoping to achieve with my EBC.

 

[edh]

I don't see any reason why an MBC should bleed boost Scott - and it's been used in some pretty powerful 944's!

 

[rcsalmons]

I too have the straight line in boost reduction at 18 psi and 15 psi peaks - dont really (at all) understand why. I know they are by no means precision objects and wonder if there is hysterisis in them - if thats possible.
Also wondered about buying a precision regulator from SMC.

Rich

 

[sawood12]

Well unless i've got a boost leak somewhere - but I doubt very much a boost leak would give you an almost perfect straight line deterioration in boost. I think that is a characteristic of the MBC. I'm not disputing that MBC are not effective - i've been very pleased with mine.

I guess one test is that I could connect my boost gauge to the output of the MBC to see what is happening there. That would determine if it is MBC or turbo related pressure drop.

 

[Diver944]

When my K26/6 car had a DPW and MBC fitted just like Scotts it was measured by Weltmeister as hitting 1.1bar at 3000rpm then dropping in a straight line to 0.9 bar by the redline. The Guru chips had it running quite a bit rich at this stage and it measured a peak of 283bhp

I subsequently fitted the Greddy EBC and it was able to hold the boost a little bit longer (and hopefully a little bit leaner) but I can't give you the precise figures as the turbocharger imploded before I could have it measured at the Dyno. It definitely did still dip towards the redline though

 

[sawood12]

I don't think that the K26/6 is capable of flowing enough air to maintain 1 bar to the red line. If I get another 500 or 1000rpm at max boost then that'll be a good result - because don't forget the boost ramp down to the red line is delayed by 500 - 1000 rpm which means at the red line i'll be holding more boost pressure (assuming i'm currently limited by my MBC) so it's more area under the curve which equals more umph at higher RPM's.

I'm a little bit reluctant to install my EBC until i've upgraded my chips just in case the extra air causes the injectors to max out - though you can get an injector duty cycle read-out with the Apexi. Though with AFM chips would it make no difference to my injectors as it's mapped against an assumed boost pressure? I'll have to look into that - maybe i'll be OK.