Compressor-turbine Matching

[180bfj20det]

The topic of turbine and compressor matching has been bothering me for a while (more than a year) and with all these turbo combinations on the market available now, which seem to work quite well in certain applications but not others, Id like to have more theoretical and practical input from people on this forum.

American racers a while back set themselves a rule of thumb through years of race proven research: "compressor and turbine external diameter must not surpass 15 percent".

Looking through garrett's range of turbos:

GT28R - 53.35mm turbine and 60mm compressor = 11.4%

GT28RS - 53.35mm turbine and 60mm compressor = 11.4%

GT2871R - 53.85mm tubrine and 71mm compressor = 31.8%

GT2876R (aka GT2540) - 53mm turbine and 76mm compressor = 43.4%

GT3071R wastegated - 56.5mm turbine and 71mm compressor = 25.7%

GT3071R externally gated - 60mm turbine and 71mm compressor = 18.3%

GT3076R externally gated - 60mm turbine and 76mm compressor = 26.7%

GT3082R (aka GT3040) - 60mm turbine and 82mm compressor = 37%

GT3540 externally gated - 68mm turbine and 82mm compressor = 20.6%

the only turbos that meet this rule are the:

(1) GT2860R (the same turbo as the s15 200sx)

(2) GT28RS (aka disco potatoe or GT2860RS)

(3) Externally gated GT3071R

Now the performance of the GT28R and GT28RS are proven and no one can argue about their performance. I have not seen anything on the GT3071R externally gate version yet so if you have info, please do tell.

If anyone can post the specs of other turbos like above then comment with respects to ths 15 percent rule and their performance, it would be great.

Who agrees with this rule?

If its to go by, then the GT2876R is a definate mismatch and this is known (favouring the rule) but then also the GT3040 and GT2871R are bad combos....

Cheers

Edited January 30, 2006 by 180bfj20det

[MattSR]

Either Garrett got more than 60% of their turbo product line wrong, or the american racers rule of thumb is bullshit...

Theres a lot more to the aerodynamics of a turbo than the OD of its wheels...

[RACESPEC]

each turbo application needs to be looked at differently. This is where you need to know engine flow rates to match it to the turbo, such that its too small or too big and most importantly

- PREVENTING SURGE

- MAXIMISING COMPRESSOR EFFICIENCY

This can be done by plotting engine flow rates in cfm, against pressure and rpm range. Depending on the RPM and boost pressure you are running you can maximise your comp efficiency by using thos point on the comp map of the turbo

Cheers

Tarek

RACESPEC

[discopotato03]

Actually there are a lots more of them though many are in the large or dinosaur categories . 2530R , TO4Z , I believe the GCG Hi Flow is ~ 65x69 so about 6.1% .

The TO4B's had 74.2mm turbines with 70 mm comp wheels so turbine diametre was larger , large enough to drive 76mm compressors like TO4E's and the small shaft TO4S's eg 60-1 .

The Americans (some) learnt that this 15% ratio works well with bush bearing turbos - lots of good and bad combinations can be bolted together so they had lots to experiment with cheaply .

There is a bit of a leg up with the compressor/turbine diametre ratio thats not the best way but a workable solution . In some cases you may not be able to get a compressor to flow as much as you'd like for its basic size (major or OD) ie its not a family of wheels that is available in big trim numbers . You can go to the next size up ie 60.1mm to 71.1mm family and start with the lower trim sizes . A good example is the GT28RS at 60.1mm 62 trim . Had there been a 65 trim version of the wheel with good efficiency it could be a better thing spool wise that a small ie 48 trim 71.1 mm wheel . However no such 65T 60.1mm compressor is available so 48T 71.1mm is the next step ie GT2871 48T .

So this is the grey area where the 15% rule may be bent a little . On paper the 2871's don't look famous but the small trim ones spool far better than the large trim one . As I keep saying HKS are not stupid - their 2871 (GT-RS) uses a 52T compressor so has fair response . My choise would have been the 48T comp which would have come on a little sooner (and have a bit less turbine inlet pressure) , but then HKS may have been chasing a certain power figure and have been prepared to wear the compromises .

GT3040R - another classic example , 60mm turbine driving an 82mm compressor so nearly 36.5% difference . They both use 82mm GT 40 compressors , 50 Trim for HKS and 56Trim for the Garrett marketed versions . HKS knows the 50T wheel is a far better match for the GT30 turbine than the 56T so that is what they get made up . Sadly the sweetheart deal between HKS and Garrett means Garrett won't sell it to you at their prices . For the number crunchers the 50T cartridge no is 700177-0009 and the 56T one is 700177-0014 .

I could not recommend anyone buy the 56T GT3040R or 56T GT2871R . They will be laggy and have more turbine inlet pressure (backpressure) than is necessary . Note the HKS uses a .60 a/r comp cover and the Garrett a .70 one .

That GT2876R or GT2540R is an evil device and note what Garrett say on their site about this thing . The HKS version was equally hideous but had a later TO4E compressor with a smaller trim I think 46 vs Garretts 48T TO4S water pump wheel .

I've dug up some compressor maps of the 71.1mm GT35 wheels mainly because I have the 48 and 56T maps . They run out of flow at ~ 18.5 psi (1.25Bar) and ~ 39 and 45 lbs/min so about 6 lbs flow the difference . That extra 6lbs at 18.5psi is more load on the turbine and if you didn't need the extra 6 lbs flow you've thrown away that energy for no gain , energy paid for at the bowser , energy to spool the 48T sooner and have less exhaust restriction .

If you look around the mid frame size Garrett GT BB's you'd see the turbines are generally 84T and the compressors 56T , it starts to change with the GT40R's and TO4R/Z's , the turbine trims fall a bit and the compressor trims climb ie 76 and 63 for the TO4R/Z same approx trim and ratio as the 2530 . I think the future trend will be along these lines maybe with slightly larger a/r turbine housings .

So yes I believe the 15% rule is valid but the compressor wheel type and trim is equally important .

Don't fall into the trap of thinking small a/r turbine housings are the answer to laggy big trim big diametre compressors - its the compressor thats the problem not the turbine or housing , fitting a more appropriate compressor even if it means another cartridge or turbo is the real fix .

Cheers A .

[180bfj20det]

Thanks for the reply.

Disco, you seem to overall agree with the fact there must not be too much differenc in size bt compressor size and turbine. I agree with you. But lets refer to the 3040, the one from Garrett and the other from HKS. Now I dont know about the specs of these turbos exactly, but since this thread is about matching turbine and compressor size I will leave it at this with respects now to trim in addition.

I get the feeling you agree that the Garrett GT3040 is a mismatch, and infact Im sure you have said this time and before in an another forum (apologies if I am wrong). Now it runs the 56T rather than the 50T and 0.7ar and 0.6ar respectively for Garrett and HKS variants. You say the HKS is superior, but can these small differences in AR and trim make all the difference?

Lets compare 3 Garrett GT30s - all with 60mm and externally gated:

1) T04S compressor (7-bladed) with 0.7 AR cover

2) 6-bladed GT wheel with 0.6 AR cover (proper GT3076R)

3) 82mm GT40 compressor (GT3040 talked about above, supposed mismatch)

Clearly "2" is the winnner. Less of a mismatch and plus less blades and smaller AR to achieve the same flow (compressor maps avail at atp turbo).

Now I dont care about peak power, so take this into consideration for the next question: which turbo would make your car fastest on the same engine eg FJ20 as you love it or lets say an RB25? If the GT3040 is mismatched, it will lag then eventually produce power = slow. If the 6-bladed is better, it will make power far earlier taking into consideration the smaller AR, wheel and trim (i think for the latter) which will make it a faster car.

If you can describe other characteristic differences bt these 3 turbos, please go ahead. It may just allow me to understand more of what is going on.

I have read everything I can but I cant clear things up. So these questions are not here to annoy, but simply get a "deeper than normal" understanding of what is really going on. So please dont hammer me for not knowing and asking

Cheers

Edited January 21, 2006 by 180bfj20det

[The Mafia]

I'm about to try a RB25 Exhaust housing machined to a GT30 core, with the TO4S 7 blade wheel, and a .7 comp cover.

Hopefully it will eliminate the massive lag I have..

This VG30 edx housing I purchased "pre ground" I think was ground too much. Perfect for a 3l bottom end, though.

[T04GTR]

it all doesnt matter(sort-of)

so long as the presure in the turbine housing doesnt get over %50 more than the inlet manifold.

ie: 1 bar boost/1.5bar in the turbine ect. needed to make good power.

generaly speaking the major diameter if the turbine/comp wheel of ang given turbo frame will not change.

its just the miner dia of the comp/exducer of the turbine. ie trim

nothing wrong with "vintage" turbo wheels. THEY WORK.

gimmi a p trim and any to4 front. soooooo versitile and they dont "choke" like the current gt range

well, only some like the chokemaster gt35/66. on a 13b lost 46kw at the wheels due to turbine choke.

(a trusted turbo workshop that is "precise")

my main point is the "early" design turbos are quite versatile in there design. meaning you can "hi-flow" them easily and not worrie about the turbine choking.

one thing ive noticed is that with the "gt" range your pretty well stuck with what you get in the box. albeit a nicly matched turbo. but limiting for the engine etc. in that there are very limited choice of turbine housins/configurations.

any way my 2 cents

Edited January 21, 2006 by T04GTR

[discopotato03]

it all doesnt matter(sort-of)

so long as the presure in the turbine housing doesnt get over %50 more than the inlet manifold.

ie: 1 bar boost/1.5bar in the turbine ect. needed to make good power.

generaly speaking the major diameter if the turbine/comp wheel of ang given turbo frame will not change.

its just the miner dia of the comp/exducer of the turbine. ie trim

nothing wrong with "vintage" turbo wheels. THEY WORK.

gimmi a p trim and any to4 front. soooooo versitile and they dont "choke" like the current gt range

well, only some like the chokemaster gt35/66. on a 13b lost 46kw at the wheels due to turbine choke.

(a trusted turbo workshop that is "precise")

my main point is the "early" design turbos are quite versatile in there design. meaning you can "hi-flow" them easily and not worrie about the turbine choking.

one thing ive noticed is that with the "gt" range your pretty well stuck with what you get in the box. albeit a nicly matched turbo. but limiting for the engine etc. in that there are very limited choice of turbine housins/configurations.

any way my 2 cents

<{POST_SNAPBACK}>

Hmm , roticeries (sp?) are a different thing to piston motors . I get the feeling that to make them scavenge properly they must have little or no backpressure hence the huge turbine housings .

Everyone in the US that works with GT turbines will tell you that they have enormous flow potential for their size . In the past Garrett have not tended to use large family GT turbines with medium sized compressors probably because most of what they make is aimed at four stroke Diesel engines .

I agree that the old TO4's are versatile but thats only because big turbines can easily have smaller family compressors fitted to form a hybrid that's very much exhaust side biased .

I can't agree about the 1.5 times boost pressure in the turbine housing (turbine inlet pressure) being the roads to good power . Any measurable TIP is working against the engine so not a desirable thing , a case of least is best . In fact the ultimate is higher inlet manifold pressure than exhaust manifold pressure , I think the Americans call this "in crossover" .

By the name GT3566 I assume you mean GT 35 turbine with Turbonetics T66 compressor . If so I'm not surprised - 68mm 84T (GT35 turbine) driving 92mm 52T (T66 comp) , not a real smart match . Guess only but GT40 turbine (72mm 76T) driving a TO4R (84mm 63T) should have worked better . Can get this one from the US in BB form ie GT4067R . If you search turbobygarrett site and some others in the US ie Full Race/Precision/ITS you will see that all the GT turbines offered in BB turbos and a few more are available in bush bearing shaft form .

180bFJ20det - the one you chose (2) is the pick of the three but arguably not the best depending on how much airflow you wanted , the 52T 6/12 blade GT compressor is said to spool ~ 500 rpm earlier than the 56T version so if it had enough flow potential its the better thing . For the record its called HKS GT3037 52T or cartridge no 700177-6 , fancy name for a GT30R with 76mm 52T BCI-18 compressor .

Gotta run , cheers A .

[MattSR]

So the GT3071 is a better match if you dont need the 76mm comp wheel?

[discopotato03]

So the GT3071 is a better match if you dont need the 76mm comp wheel?

<{POST_SNAPBACK}>

Depending what you put it on yes , its a cheaper alternative to the HKS/Garrett turbo and more a reduction in wheel diametre with larger trim size ie 71.1mm 56T . It seems to take a bit of fiddling to get it right and is fickle with turbine housings . That compressor wheel in 56T may work better in a TO4B cover than the TO4E like 3071R's usually have . Given a choice the 52T wheel would have worked better again . HKS turbine housings seem to do it a bit better than Garretts because of better nozzle section and volute passage shape .

I think a lot of the problems with GT30 based turbos is because of the style and trim of the GT30 turbine ie 60mm 84T . It was designed to be light and have high specific flow for Diesels which usually work over a narrower rpm range than petrol engines . Its a bit of a juggle to get it to work over the wider engine speed range and balance it against compressor speed and airflow to get a reasonable boost threshold and power range . I think the trim is a bit big which tends to make it too free flowing at lower gas flow rates . Personal theory but it dosen't work well over a wide range of exhaust gas flow . There is another 60mm Garrett turbine which I believe is used for Champ Car turbos that is the 60mm version of the 54mm NS111 that the higher performing GT28's use . I tried to get a production engineer from Garrett California interested in using this turbine in a GT BB cartridge but he said it would flow less than the GT30 , my point was it may have worked better over a wider variation in exhaust gas speed , but I'm not there doing his job .

That GT3037 52T is a known but expensive to buy and then have to fiddle expensive turbine housings . I'm a bit surprised HKS didn't offer it in Pro S form for RB25's . I suppose they though the cropped GT30 turbine and the 52T 71.1mm compressor in the 2835 was a better compromise - could well be a case of expensive but best result and virtually impossible to copy on the cheap .

Cheers A .

[discopotato03]

Hmm , roticeries (sp?) are a different thing to piston motors . I get the feeling that to make them scavenge properly they must have little or no backpressure hence the huge turbine housings .

Everyone in the US that works with GT turbines will tell you that they have enormous flow potential for their size . In the past Garrett have not tended to use large family GT turbines with medium sized compressors probably because most of what they make is aimed at four stroke Diesel engines .

I agree that the old TO4's are versatile but thats only because big turbines can easily have smaller family compressors fitted to form a hybrid that's very much exhaust side biased .

I can't agree about the 1.5 times boost pressure in the turbine housing (turbine inlet pressure) being the roads to good power . Any measurable TIP is working against the engine so not a desirable thing , a case of least is best . In fact the ultimate is higher inlet manifold pressure than exhaust manifold pressure , I think the Americans call this "in crossover" .

By the name GT3566 I assume you mean GT 35 turbine with Turbonetics T66 compressor . If so I'm not surprised - 68mm 84T (GT35 turbine) driving 92mm 52T (T66 comp) , not a real smart match . Guess only but GT40 turbine (72mm 76T) driving a TO4R (84mm 63T) should have worked better . Can get this one from the US in BB form ie GT4067R . If you search turbobygarrett site and some others in the US ie Full Race/Precision/ITS you will see that all the GT turbines offered in BB turbos and a few more are available in bush bearing shaft form .

180bFJ20det - the one you chose (2) is the pick of the three but arguably not the best depending on how much airflow you wanted , the 52T 6/12 blade GT compressor is said to spool ~ 500 rpm earlier than the 56T version so if it had enough flow potential its the better thing . For the record its called HKS GT3037 52T or cartridge no 700177-6 , fancy name for a GT30R with 76mm 52T BCI-18 compressor .

Gotta run , cheers  A .

<{POST_SNAPBACK}>

To round off ...

Option 1) TO4S compressors have more blades because they were designed to move lots of air with limited wheel speed . To do this properly you need big turbines such as TO4's (74.2mm large and heavy) with lots of "sail area" to convert gas velocity energy into shaft power which drives the compressor . T3/TB31/TA34/GT28 and GT30 turbines do not have enough vane diametre/area to drive TO4S compressors properly . When combined they form a laggy combination because the compressor has greater shaft power demands than the turbine can provide .

Option 2) Best mentioned but the 76mm 56T comp is still slightly overtaxing what the turbine can develop .

Option 3) 56T GT40 comp (82mm) is far too big for the GT30 turbine , will again be laggy because the power demanded by the compressor is too great . The GT3540R is a better match , maybe laggy on an FJ20ET but thats because its a bit too much compressor AND turbine for most applications . This alone tells us that the GT40 56T comp was too big and that fitting a smaller less capable 60mm GT30 turbine was pretty pointless . Sounds more like a sales team spec decision than an engineers . There are a lot of these things waiting in warehouses for new victims .

In a crude sort of way you could say a mis matched turbo is a bit like a mis matched overly tall diff ratio - a real sloth till the speed gets up a bit . Only with turbos the exhaust restriction comes on earlier and kills the fun or your engine .

Cheers A .

[180bfj20det]

Option 2) Best mentioned but the 76mm 56T comp is still slightly overtaxing what the turbine can develop .

<{POST_SNAPBACK}>

Ok, what about the GT3071R externally gated version with 0.5 cover? Is this a better match ie the GT30 60mm turbine can drive it better? They claim it spools 1000rpm ealier than the GT30R 6/12 bladed 0.6 AR turbo and it seems ideal to put out 330rwhp.....

Thanks

[discopotato03]

Ok, what about the GT3071R externally gated version with 0.5 cover? Is this a better match ie the GT30 60mm turbine can drive it better? They claim it spools 1000rpm ealier than the GT30R 6/12 bladed 0.6 AR turbo and it seems ideal to put out 330rwhp.....

Thanks

<{POST_SNAPBACK}>

The .50 a/r cover they mean is a .50 a/r TO4E cover .

Actually I would have thought a GT30 based turbo was a little big for 330 RWHP , if you could afford it the 2835 Pro S may be better . If it were me I'd think seriously about the GT2871R 48 trim but with the .86 a/r turbine housing . In fact the GT28RS on its knees could nearly get you there . I haven't looked for a while but I think ATP was doing a special exhaust housing in .63 a/r with T3 flange to suit an integral gate GT28RS cartridge/comp cover . Have another look there as I think they got about 326 front wheel Hp out of an Audi of some sort . That housing is a custom one and looks like Garrett/Ford style T3 but GT30 passage and nozzle . I remember one fellow in the US that was drag racing A street driven Civic with this type turbo set up who really liked it . I could contact him and ask him what he got at the treads if you wish .

Just for the record is the 330 RWHP number set for any reason ?

Cheers A .

Edited January 30, 2006 by discopotato03

[fantasy]

Hi guys,

Both 180bfj & Disco know I have tried most of the GT30 combinations at some stage.

My new favorite is a modified version of the GT3071R. The first time I used a GT3071R it was in its original Garrett form on a SR20. It preformed ok but was nothing flash. It lacked HP.

The second time was another SR20 I put a GT2871R with 52T comp wheel. it was a laggy pig.

Taking from my experiences with the two turbos already mentioned I created my own combo using the GT3071R 56T comp wheel and a larger T04E comp.

The bigger comp cover does wonders for the GT3071R 56T comp wheel.

This turbo combo I have come up with I get built by Billet Turbochargers.

It is in my opinion the best streetable turbo for 275rwhp to 400rwhp on a 2L engine.

I am not giving away all my specs for now but the biggest improvement was found in the larger comp cover. But I do use a different Turbine as well.

Earlier it was said the HKS GT3040R comes with a .60 cover. Here is a bit of trivia. I have a Genuine HKS GT3040R with the 50T comp wheel sitting here and it has a HKS .70 cover on it.

Cheers,

Fantasy

[180bfj20det]

Just for the record is the 330 RWHP number set for any reason ?

<{POST_SNAPBACK}>

If the GT2781r 48 trim can get me the 330rwhp...then let it be!!!!!

Why 330 rwhp...i dont think a std FJ head will flow more than that on street fuel. Ive seen more, but i rekon dynos tell fibs sometimes... Maybe with cams and some head work you can get more.....

I want something responsive and fast on the street, so if the 2871r will do it, so be it!!!! Itll have to be much more responsive than the t04s GT30 i have now yes with mammoth 0.7 cover (ouch).

Whats the diff bt the HKS 2835pro s and the 2871r 48 trim garrett?

Thanks for all the help.

[discopotato03]

If the GT2781r 48 trim can get me the 330rwhp...then let it be!!!!!

Why 330 rwhp...i dont think a std FJ head will flow more than that on street fuel. Ive seen more, but i rekon dynos tell fibs sometimes... Maybe with cams and some head work you can get more.....

I want something responsive and fast on the street, so if the 2871r will do it, so be it!!!! Itll have to be much more responsive than the t04s GT30 i have now yes with mammoth 0.7 cover (ouch).

Whats the diff bt the HKS 2835pro s and the 2871r 48 trim garrett?

Thanks for all the help.

<{POST_SNAPBACK}>

Hi Fantasy , my listings show three different complete unit numbers (HKS GT3040) so there's bound to be some variations . 700382-0014 , -0016 and -0023 . They all show the same 700177-0009 cartridge . If I had to guess I'd say the optional turbine housing a/r is at the large end of the scale and the .70 comp cover upsized to suit . If you can let me know the ID tag numbers and turbine housing a/r it would help make my list a little more complete .

Interesting about the larger comp cover on your spec turbos , it seems logical that the higher a/r would make for a little less resistance to airflow so faster rotating group acceleration rate . Its kind of a velocity pressure rather than a static pressure thing . I've no way of knowing if your machinist or parts supplier got the tip height of the compressor right with the diffuser section channel of the housing but a bit of mucking around here can move things round a bit - can also change efficiency islands on the map .

Turbines I'd like to see used in BB cartridges are the GT32 , some including Garrett , use the TA34 76T (stage 3 in Turbonetic waffle) . Both from memory are around 64-65mm .

180BFJ20DET , getting better response than the GT30/TS04 can give should not be too difficult . I once wanted 400 from an FJ20 without knowing what 400 feels like , it seemed like a nice big number . What I should have looked for and eventually did find was a torque curve that started reasonably early say 2600+ but had very good low boost power at low revs and pulled like a locomotive from 3000+ . This felt responsive , torquey and fast because it could accelerate from low medium revs on an FJ20 - mine was the late higher CR intercooled FJ with way overkill intercooling by the way . It was in my old Bluebird with 16" wheels (205/50 tyres 3.9 diff) and could be driven round roundabouts in 3rd gear and pull away from 15-1600 revs . The answer was a Garrett GT28RS , they are not huge externally but use open bladed turbines in the all important .86 turbine housing . Mine was hung off a fabricated manifold made from 1.25" steam pipe which everyone said wouldn't work , they also said the turbo was too small but boy did it deliver .

On a dedicated 2L street car I would choose it over anything out there at the moment and unless you're suicidal its plenty enough to give a 180B a very healty kick in the ribs in my book . Now its not for me to say what you can or can't have , will or won't do but my combination in a 1230Kg car put many smiles on my face . It embarassed many much more upmarket cars and a lot of people asked what the hell is in that .

For me the result was fantastic and far more important than any number , the fact that it could respond so quickly and not become breathless never ceased to amaze me . Some Americans used one of these on an SR20DET powered Sentra SE/R (yank pulsar sedan and original Discopotato) and they found that they could largely modulate boost with the right foot and I found much the same thing .

Fantasy what to your customers find with it - those that have all the right support systems and go to a bit of trouble to tune their engine properly ?

180B FJ what octane fuel do you use on a regular basis ? I think at that time I was using Shell Ultra 96 though Optimax 98 would have been coming onto the market and I try to get the highest pump fuel available . It would have been good if the 100 octane around now was available when I had that car , tis just an engine on a shopping trolley base and a heap of bits now .

Cheers A .

[T04GTR]

sorry disco, just voicing my opinion and "limited personal experiance" i spose the new gen turbos are good. just i prefer a good kik when they come on :lol:

[180bfj20det]

Disco,

Whats the diff bt the HKS 2835pro s and the 2871r 48 trim garrett?

Also, I really dont see the GT28rs pulling 330rwhp....can you? How much of a difference really exists bt the rs and 2871r 48 trim in drivability? Cause I think for what I want, the 2871r 48t is the go...remember 330rwhp as I already 307...and i want just a lil bit more!!

Also, I use 98 ron bp and I need valve springs cause my NA head valve bounces on boost (anything over 13 psi.....).

[fantasy]

Hi Disco,

here are the id numbers off the HKS turbo,

Exhaust housing: HKS 1.12

Tag: Di 011 7J

GT3040-50T

700382-23

Comp Cover: HKS A/R .70

40 40 /3

I am keen to run my eye's over your list if you are willing to share.

Please email me at [email protected]

Edited February 2, 2006 by fantasy

[discopotato03]

Hi Fantasy , when I get a little more time will bash it out here for all to see . What do your customers think of the GT28RS ?

180BFJ20DET , yep I believe close to 330 can be done with these . One thing I should have mentioned last time is that the ATP housing is .63 a/r as in GT30 turbine .63 a/r . The physical size and gas flow capacity of a turbine housing will vary with the family of wheel the housing was designed for . The ATP .63 can pass more gas than the Garrett GT28 .86 a/r so turbine inlet pressure will be less so less pumping losses and overlap reversion / inlet charge polution/pre heating etc etc .

I think you'll find that the power curve produced by your last turbo was lacking because the thing probably didnt get up to boost revs untill fairly late in the engines rpm range . When turbo's like that get going they often make the torque but it doesnt feel responsive/torquey/progressive because you have to rev it to make it go and then its next cog time and likely to lag then come on and be a bit baulky . When you size it to work over a broad range it feels much better , more like a much larger n/a engine . I didn't make a habit of it but it was real easy to spin the wheels so torque was not a problem , it was perfectly suited to production gearbox ratios - usually larger turbos (for 2L four) that come on around 4000 are a pain to drive if you want some zip without being obvious to the constabulary .

Difference between 2835 Pro S and GT2871 48T .

Same series of compressor (GT35) , Pros 52T , 2871 48T = 48T .

Comp cover on 2835 Pro S TO4E .50 a/r , 2871 = .60 a/r TO4B

Turbine 2835 ProS 56.6mm 84 T (cropped GT30) , 2871 = 53.8mm 76T NS111

Housing 2835 Pro S integral gate .68 a/r GT30 turbine based profiled for cropped

turbine in 56.6 84T .

Housing GT2871R all trims . GT28 NS111 profile in .64 or .86 a/r .

Cheers A .

Edited February 2, 2006 by discopotato03