Garrett GT25/40R on RB25DET

[Lithium]

Has anyone tried this combination? I have been thinking of getting one of these with optional T3 flange with .86 turbine a/r for my R33 GTS25t as they are currently available for a very reasonable price from ATPTurbo.com.

[bigcarl]

are you talking about a/r .86 exhaust housing with t3 flange from garrett/ atp?? how much are they asking?

[Lithium]

are you talking about a/r .86 exhaust housing with t3 flange from garrett/ atp?? how much are they asking?

Yep, that is the one They are asking US$1075

ATP/Garrett GT25/40R

[Lithium]

Awesome man - thanks for the input

What came with the turbo? Did you have much hassle with space, getting oil to it or anything weird like that?

[Lithium]

Wow - $1500, thats more than I had anticipated... I had set aside around $900 - not including intake piping as I've budgeted separated for the intercooler etc.

When you say custom made, you did the work yourself and it still cost $1500?

You have been an awesome help - very very appreciated

[discopotato03]

Yes an important point , fitting a non native turbo can add up quite a bit . The cost of the GCG Hi Flow is hard to beat considering it slots straight in and costs zip if you do the spannering yourself . I would insist on the VG30 housing though .

If you must fit one of the Garrett GT BB's there are better ones than that "2540R" dinosaur that ATP sell . Have a look at the turbine and compressor maps for the GT3071R and GT30R , much better . You could even ask Brett (GCG Turbos) if the Hitachi housings (std RB25DET or VG30DET) can be profile machined to fit the GT3071R cartridge (now re named GT6071R by Garrett for its 60mm turbine and 71mm compressor) . Doing it this way gets you more modern wheels than the Hi Flow which may be cheaper and needs the same amount of machine work , it would also bolt straight back in . Custom water and oil feeds/drains would be needed and cost a bit more .

Cheers A .

[Lithium]

Cheers DiscoPotato03 - I had initially rationalised that the GT25/40R would be a good turbo to go for in terms of a value for money upgrade, so the fact that the GT25/40R is a dinosaur wasn't going to bother me too much - especially when it looks quite cool too But if it is going to cost that much more to fit, it starts looking like the "expensive" alternatives from HKS etc are not that bad afterall.

I want to set up a nice and kinda cool "mild" street combination, 400flywheel hp would be plenty to keep me happy and I want to keep away from running over 1bar. I could be mistaken because I am still new to compressor maps etc - but the GT3071R compressor map didn't look a fantastic amount better to me than the GT25/40R, it looked more suited to higher boost (.. and power...) levels whereas just under and up to around 1bar of boost the GT25/40R looked in a higher efficiency area. While in theory the GT3071R is "better" for a RB25DET if you are going to push it harder, I don't really need the 400+hp the turbine could happily flow with the larger turbine so maybe it would be wasted on me - especially for the ~$200-300US higher price tag? Please correct me if I am wrong, I'm still learning

I didn't like the idea of the highflow, the turbine housing from the R33 turbo seems horribly small - though if people think they work fine... I could rethink that?! One issue with dealing with GCG is that I am NZ based, and getting stuff sent from Oz is one thing - but sending bits back and forth starts getting to be a bit more of a headache.

One thing I have to factor in which would be worth knowing, is I have stock dump+front pipes on the car and they have to be upgraded if I am going for any reasonable amount of power.... so fabricating one to fit a Garrett turbo isn't going to be an extra cost, as I'd have to do it even with an OEM Nissan turbine.

[discopotato03]

Hi Lithium , I was comparing the maps as to where the surge line is to the left and the flow limit is to the right along the 1 Bar (14.7 psi) line indicated by the 2 pressure ratio scale up the left hand side of the map . Sure the 3071R's compressor wheel is a higher pressure ratio wheel compared to the T04S wheel in the 2540R , but its also far lighter , has less and thinner while being mechanically stronger blades . Where the later smaller diametre GT compressors win is that they can be spun faster to generate the same airflow wth even less heat in the inlet charge than the older T04B/E/S compressors . Also while the 50ARR T04E compressor housing (cover) std on the 3071R is not the biggest dickest of the Garrett world it does the job and is easier to fit in todays compact engine bays . The great galoot of a T04S compressor housing is more difficult to plumb and hard to justify in this air flow range - unless of course its owner and followers gather around it can in hand for the ooh ahh hymn . Ill have a look at the map for the 2871R which uses the same family of compressor (71.1mm GT35) but in a smaller family housing and see if its any better .

As for cost it only hurts once , but if the result of the cheap job steams you for ever after the difference will seem trivial .

Cheers A .

[Lithium]

Ahh excellent, cheers for clearing that up The GT2871R was actually what I liked the look of as an alternative to the GT25/40R... it seems on paper to be very similar, if not identical to the HKS GT-RS.

Do you think the GT3071R would could be used without the need to space the turbo out from the block like the GT25/40R does? Or if the GT28/3071R would have the actuator mounted in such a way to cause the kind of issue Mikka33 described, where he had to remount it to fit?

[Lithium]

Aweeesoommee thats a lot better Mikka33 - thats almost identical to what I laid out for the equivalent + a little more (hence $900) as most of the stuff done with mine will be done at home as well A mixture between me, legendary friends and various hookups I can get is something I am hoping will take the edge off it. Cheers!

I'll get info from you if I do buy one though, if thats cool? It'll make it a whole lot easier.. :Pimp2:

[RS500]

dude,

the GT25/40R which you are looking at on ATP's website is way too small for an RB25DET.

reason being is that the turbine wheel (53mm - 62trim) is too small to flow anything more than 320hp.

comparing the turbine wheel, it is actually the same wheel as found in the HKS GT2510 which was rated at ~310hp.

and now for the compressor wheel, the 60mm - 60 trim (as stated on the ATP Turbo website) is actually a smaller version of the comp wheel in the same HKS GT2510 (60mm - 63 trim).

this is the correct compressor map for the GT25/40R;

http://www.atpturbo.com/root/maps/gt28r.htm

so given this, this turbo would struggle to even make 350bhp let alone 400+ bhp.

i believe the ideal turbo for the RB25DET is the GT3071R, which has teh large GT30 exhaust wheel for plenty of flow and the larger 56 trim GT35 compressor wheel which can flow up to 450bhp. this would be a far more efficient turbo for the RB25DET.

otherwise you could go for the internally gated garrett GT3071R (with 90 trim turbine wheel and GT25 flanged A/R .86 exhaust housing). This should be able to flow around 420bhp.

[Lithium]

Thats interesting, ATP rate the compressor wheel as a 60trim 60mm, that isn't consistant with all else I know about the turbo. Its interesting that Garrett rate that turbo at 450hp, and Horsepowerinabox (and most other places) refer to it as having a 76mm 48trim wheel...

Why have you listed the GT28Rs compressor map as the GT25/40Rs "correct" compressor map? It doesn't really make sense.... especially when ATP have the GT25/40Rs compressor map on there. They definately don't run the same cold side as a GT2510 or GT28R, and most certainly don't flow less than the GT28RS either. I already know people using the GT25/40R on 4cyl 2l engines to make between 250 and 300kw @ wheels (albeit 300kw on C16 and lots of boost...), in NZ there is a 10s street EVO running one....

I agree, the turbine side is on the small side - but I don't think too small, considering its around the same size as various other turbos used in the RB25 dyno results thread which have made up to 270kw @ wheels.... keeping in mind I am only after 400hp @ flywheel, I think it looks to be more than sufficient. Given that, it seems to me a positive thing that the turbine is a bit small as it will get the compressor up to speed a bit quicker, so long as there isn't some dark reason beyond sheer flow potential that I shouldn't go for a smallish one on a bigger motor?

[discopotato03]

Sorry doesn't work like that . Small diametre turbines have short blades (hub to tip) so don't want to know about generating enough shaft torque to drive large diametre compressors untill the exhaust gas speed is very high , high enough to create pumping losses and thermal melt down . Just as you wouldn't use a short crow bar to lever a large rock why use short turbine blades to lever a large compressor . This is why its absolutely critical not to overdo the compressors flow capacity . Big compressors want to move lots of air and its the resistance of moving the airs mass , not the compressor wheels mass , that creates resistance to it turning . Remember its the TURBINE thats fighting this resistance to turning and if its wearing short blades all its doing is promoting turbo (turbine ) lag . Theres two ways to fix this 1) drop in a smaller compressor that works well within the shaft power limits of the turbine or 2) use a larger diametre turbine better equipt (greater mechanical advantage from its longer levers or in this case blades) to muscle the large compressor and its high mass flow .

Now getting back to that GT2540R and its dinosaur T04S compressor wheel . There is a rule stating that the more in number and thicker the blades are the less the pumping efficiency will be . These wheels are not a high pressure ratio item and this can be seen in their maps . The island of highest efficiency is cut off at the 1 bar line rather than being a complete island above it . They are designed to move a large volume of air at lowish shaft speed (living within the reliable limit of bush bearings) up to about 1 bar of positive pressure (15lbs boost) . When current (1976) they were teamed up with T04 turbines that were large heavy thick bladed relatively low speed turbines and bolted to diesel engines . Now jump forward 20 years to the point when some cork head decides to fit it on the end of a light weight high speed small medium sized turbine supported by ball bearings . The old bull T04S neither knows or cares that its not a T04 turbine driving it and basically says wake me up when ya get the lead out .

the best results will always come from the most modern wheels and a similar diametre on the turbine and compressor . An old rule of thumb was keep them within 15% of each other in the bush bearing days , 15-20% is not unreasonable with modern turbos . The 2540R is gettting up towards 30% which is a bit much AND has a totally inappropriate wheel design . You can do much better than this .

Cheers A .

[Lithium]

Theres two ways to fix this 1) drop in a smaller compressor that works well within the shaft power limits of the turbine  or 2) use a larger diametre turbine better equipt (greater mechanical advantage from its longer levers or in this case blades) to muscle the large compressor and its high mass flow .

That was really really good information (the whole post, not quoting it all for ease of reading for other people...), thanks for that!!!

If you were to guess what would get the best average power between 4000 and 7000rpm out of these turbos when used on a stock RB25 running 13psi with supporting mods and tuning for each - which order would you put these:

a/ GT25/40R

b/ GT2871R

c/ GT3071R

Mikka33 - if you are still watching, when do you get full boost with your turbo?

Cheers both of you, I feel my picture getting both broadened and filled in quite nicely Fortunately I'm not going to be buying until late next month - so there will be no hasty purchase.

[discopotato03]

The 2540R will always be last - bar none except some lousy backyard hybrids .

The 2871R would be next - good response but a 53.8mm turbine is getting a little small for 2.5L once it starts to rev . For a lowish boost application it could work ok - note Garrett unfortunately don't make a T3 flanged .86ARR integrally wastegated exhaust housing which is the minimum needed for 2.5L and that turbine .

The GT3071R would have to be the pick of the three and with its GT30 turbine has lots of turbine housing options in T28 and T3 mounting flange patterns .

If its the 4-7000 rpm band your interested in GT30R is worth considering as well . Its larger higher flowing (and modern/efficient) compressor will do it better up high than the GT3071R . Its the choise you need to make based on what the car is used for most of the time . If you dont want to upgrade computer and fuel systems its pointless having more airflow than the std components can support . If however you intend to make serious power and live within the 4-7 rev range the higher airflow is needed .

My choise in your situation would be a GT30R (700382-12) with one of the HKS T3 flanged integral gate turbine housings in .68 ARR for response or .87 ARR for a bit less restriction up high . I would do the fuel pump , PFC ECU , and injectors in that order first because I use my car for every day transport and it has to be useable and reliable after each mod .

Cheers A .

[32vspecII]

when i was talking to a local well known performance specialist and turbo guru he said the TO4s thats in the current garrett gt30 for example is not the same as the 1970s t04s as garret change the design and manufacturing over time .

i dont know enough about the subject either way so i cant make any comment .

[discopotato03]

I know the difference - the hole through it is 7mm to suit the GT BB turbine shaft . The original is 6.35mm (1/4") to suit the bush bearing shaft .

The fact that they have seven full and seven splitter blades is significant when you consider virtually all Garretts (post 1990 CAD designed) compressors use six of each . If you put them next to one another (a T04S and a BCI 18 compressor) and look closely they really are worlds apart . Start at the exducer tips , their angle is far closer to vertical than modern designs . The angle of attack of the blades is more toward the wheels axis than later types . What is really is obvious is the blades thickness on the old T04S wheels .

The effort has gone into making newer designs slice easily through the air at low rpm (less energy needed by the turbine to accelerate it to boost threshold revs) , make it mechanically stronger to withstand the centrifugal forces of high rpm , make it an efficient pump which equates to less heat or density change on the way through . Keeping the mass to a minimum helps reduce the innertia of the turbos rotating assembly .

In todays world I doubt any engine manufacturer could afford to ignore the benefits of modern turbocharging as response/power/fuel consumption/bulk/weight are all directly tied to it .

Cheers A .

Cheers A .

[Lithium]

Cheers guys, I have a much much clearer idea on things now

Discopotato, I didn't mean to look for a power band that starts in the 4000rpm area - which is what the GT30 sounds like it does. I mean something that is already making good power at 4000rpm, and is still making good useable power at 7000rpm. I'm sure the GT2540R or GT2871R can't drop off THAT badly at the top end if you're running under 1bar? Ie, no worse relative to peak power level than the stocker?

[discopotato03]

Lithium its going to come back to what you think feels good . If you want a punchy power curve where it all comes in with a rush at 3000 use a GT2871R/GTRS because thats what it can do . When it spools up and the engines torque can double in 500 revs thats what appeals to some .

I prefer to muck around with the engine management to enhance the low down (off boost) torque and throttle response to get all the engines capable of giving . Depending on engine capacity and the weight its expexted to pull , where in the rev range the turbo enhances torque is important . If your car had say an RB20DET it needs to be biased toward the lower end because its no torque demon at low revs and R33's are no feather weight . Having 2.5 litres means a bit more torque at low revs so the turbos useful range can move up the engines rev range . If it had an RB30DET/VG30DET it can go even higher because the off boost torque is heaps (particularly if the compression ratio is in the 8.5 - 9.0 range) .

If you want the most flexibility go for a larger engine in a slightly lesser state of tune , thats what I aim to do .