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Discussion Starter · #1 ·
OK, so aiming to upgrade from the standard Aero turbo and after doing all the searches and thoroughly confusing myself and clouding my head even more:confused: , I have come to the vague conclusion that my personal options are between the GT2871R and the GT3071R?

I don't want to generate anymore lag as Maptun at stage 4 is noticeably slower spool up than Speedparts was at stage3, but I also don't want the car plateauing on the track before its had the chance to hit 160ishmph:cheesy:. Does such a device exist to give these characteristics;)? So the plan is, get the Maptun stage 5 software for top end ooomph and add a larger but faster spooling turbo to decrease lag, yet aid top end............sound good so far:confused: ?

Then I confused myself further by looking at the individual options on each turbo!
The GT3071R has compressor trims of 48, 52 and 56, with turbine A/R of 0.64 or 0.86.
The GT2871R only has a 56 compressor trim but has turbine options of 0.64 or 0.86.

So what is the meaning of compressor trim? Do the different sizes affect performance or will only one of these sizes fit the saab? As far as I understand it, the larger the turbine A/R the more lag but easier breathing at high revs?

So if I go for the smaller A/R will the top end be dramatically reduced/back pressure increased? Conversely if I go for the larger A/R will I have more lag, even tho these are ball bearing and so quicker spooling than the current turbo.

Now if my logic makes sense and thats debateable:confused: , I'm favouring the GT2871R with a 0.86A/R. Or maybe the GT3071R with the 0.64A/R. But which compressor option?

Decisions, decisions;)

Can anyone help? What's the perfect turbo?

Cheers,

Andy
 

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well andy i will just sit behind you on the confussed bench :eek:

i think marrk is the one to answer this as he is in the middle of building his carlsson into a super car :roll:
 

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Andyaero said:
I'm favouring the GT2871R with a 0.86A/R. Or maybe the GT3071R with the 0.64A/R. Cheers,Andy
I agree!
 

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Andyaero said:
hey, with my knowledge, looks like I could be a Super Moderator too!;)
The rank is based on the ability to pass the initiation ;)

Still brings tears to my eyes :eek:
 

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Andyaero said:
so, the turbo..........................................................................................
Ah yes, I would recommend that you get the best one out of those you mention.

HTH ;)
 

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Andy,

Maptun reckon a TD04-18T for stage 5 which isn't a bad choice at all, would minimise lag and give you reasonable air-flow capacity.

A ball bearing GT32 would give you more flow capacity (for post 400bhp) but you'd need to size it correctly to ensure lag was minimised, 71mm compressor wheel wouldn't be a bad choice and give you capacity for somewhere around 440bhp based on the compressor maps I have here

GT28 with 0.86A/R will give you decent response with a reasonable air-flow capacity.

Mail me what your target power is along with current mods over and above the Maptun stuff and I'll do some math for you when I'm back in the workshop on Monday.

Best Regards
Matt
 

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Hi Andy
What happened to the GT28RS? the GT281R will give you slightly more lag but more top end power, if you were still going for the RS...I would say go for the A/R .86 on the 2.3ltr power kicks in at 2500rpm.
I myself am considering the A/R .64 due to the slower spool up of the 2.0ltr which I have.

Not sure about Maptun but I spoke to one of the Nordic mechanics this week, they sell the GT28R and the software I asked if the software would be ok for the RS, his reply was "Yes" however I am waiting until his boss returns from holiday to get confirmation, if it's a goer I will be slapping on the potato within the next few weeks:cheesy:

Steve
 

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mattfaulks said:
Andy,

Maptun reckon a TD04-18T for stage 5 which isn't a bad choice at all, would minimise lag and give you reasonable air-flow capacity.
Have you driven a car with this turbo, especially the favored one with clipped turbine blades?
IHMO you cant write minimized lag and that turbo in the same sentace.
I raced my viggen when it still had stage III+ agaist a friend of mines stage V MY98 9-5 (B235R swap done) and my car was faster. Two runs, first 80-230km/h starting in third, second 100-220km/h starting in fourth. Both cars dynoed in the same dyno, mine 288hp and the 9-5 341hp. Lag with this turbo compared to a maxed out 15T is that big that the extra 50hp or so cant make up the ground even when the acceleration is that long.

mattfaulks said:
GT28 with 0.86A/R will give you decent response with a reasonable air-flow capacity.
Are you aware that the max bhp figure does not improve much with the bigger turbine A/R with the GT28RS? Yes you might see 10bhp or so but,
you can pretty much max out the compressor with the smaller turbine housing, plus you get a better spool-up and reach the max boost in lower rpm. IHMO the A/R 0.86 is enourmous compared to the compressor.
I have this turbo with the smaller turbine in my car, so if anybody is interested in more results i can post them for you.

A Audi RS2 I know did dyno with GT2871R and small turbine (A/R 0.64) max power ~400BHP. I can post the sheet if you like. Dont see much point in installing the bigger turbine to that either.

A frind of mine will have his GT3071 9K 2.3 running in a week or so and results will be posted if wanted? This turbo is also with the smaller turbine.

In the end it depens on how high you want to set the best pull range of the turbo and what other mods have been done to the car, like cams, head, rev limiter aso. Also keep in mind the gear ratios of saab and how the whole pacage coms to gether. For instance if you install a bigger turbo with large A/R you might not see much pull before 4000rpm. Now look into gearing and around 80-100km/h from where we (I atlest) start to accelerate. I dont think you will find one. Second gear is almost to the rev limiter, bad choice. Third is not it range yet...
If you only target is to drive fast on strip then this does not matter, but for daily driver and "street racing" its poison.
 

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Discussion Starter · #12 · (Edited)
So do you reckon a GT28RS or GT2871R with the smaller turbine will still be pulling at high revs but give quicker spool up than the spec turbo? My current set up is as per maptun stage 4, plus a larger intake pipe. Apologies for thinking out loud and making this up as I go along, I'm discounting the GT3071R as too large now as max power levels on this car are only ever likely to be 360ish bhp.
 

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Andyaero said:
So do you reckon a GT28RS or GT2871R with the smaller turbine will still be pulling at high revs but give quicker spool up than the spec turbo? My current set up is as per maptun stage 4, plus a larger intake pipe.
Here is a comparision with std TD04-15T and the GT28RS with small turbine housing. We are looking at airmass values which is the most interesting parameter.

Ps. for the record stage V kit for the B235R does not usually reach even 250g/s for airmassflow and they do dyno around 340Bhp.
http://viggen93.mine.nu/kuva/m_g_potato.gif
 

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Discussion Starter · #14 ·
so in laymans terms (aka idiots guide:roll: ), although the potato kicks in slightly later that the td04, when it does spool up it does so much more aggressively before levelling out on a par with the td04 thru the mid range before going crazy again at higher revs?:cheesy:


Is there a down side then?:cheesy:
 

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Andyaero said:
Is there a down side then?:cheesy:
The cost of the pistons probably :eek:
 

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Chris 9-5 said:
The cost of the pistons probably :eek:
for a 9-5 ..yes

the 234 r pistons aare made from unburstium....
 

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Andyaero said:
so in laymans terms (aka idiots guide:roll: ), although the potato kicks in slightly later that the td04, when it does spool up it does so much more aggressively before levelling out on a par with the td04 thru the mid range before going crazy again at higher revs?:cheesy:


Is there a down side then?:cheesy:
The assumpition that the potato kics in later cant be made based on that graph above, since the potato run did start from 2500 and with std turbo I started the run from 2000rpm. Spool up can really be seen from it either.
Here is a short video if you want to get an idea how the car pulls with it.
http://viggen93.mine.nu/viggen/potato/potato.wmv

How much power is in your quest? This is one of the most important factors that lead to turbo choice. You dont want to choose a boy to do a mans work nor do you and to overkill it.
 
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