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Discussion Starter · #1 ·
Hey, I've done some searching here and a good bit of research and I've come across a Turbo dilemma.

I was going to go the Big T28 conversion from Gpop shop, but found it would fall short of my 350whp goal (+/- %10). I don't want to go the MHI route-PITA, hard to source, hot side a/r, spool.
So, I need a turbo that will give me at least .7-1.0bar (10-15psi) in the 2.5k rpm range( ZERO COMPROMISE), flows comfortably to 350+whp, is easy-ish to install, and is reliable.
I happened upon the GT BB series, but while these seem like the only option in my price range ($1,000), the BB aspect is giving me qualms (reputed to have horrible reliability)
That said:
Big T28?
Gt28?
GT28rs? Differences between these two?

Gt2871=smaller package, same cold side as bigger 3071? Negatives= high EGT's from tiny hot side and wicked surging. Positives=smaller than 30 series.

Gt3071 .63-heard references to this, what is the difference between the more often mentioned .64? Negatives=chokes out at higher rpm, potential surge problems as engine can't eat amount of air at lower thresh hold of boost.
Positives=nice spool, very responsive, mentioned as most streetable turbo (very important to me)
Gt3071 .84-400+rpm later spool, but when it does spool engine is ready to eat:shock:, which means nearly similar performance to .64, but better up top, especially with t5 cams, whereas the .64 works damn well with cams up top+responsiveness.
I wont go cams, at least not yet.

Gt3076-too much for me, in every way.

I am shamelessly looking for a BAMF mobile, but one that I don't need to rev to the damn sky over. Holsets are out for that very reason. I drove a 9k with a holset (bigger cc than my 2oh) and it lagged at an unacceptable level for me.
So, decent get up and go in the 2k range, with serious boost in the 3k range
Can someone explain to me the different trims? I got a/r and cm^2.
Thanks for any help.
-Cm
 

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holset hx27 have t2/t25 flange - maybe will small internal wastegate portin will be fine like expensive gt30 ?

i dont know for sure yet but if you will get hx27 with t25 flange and laggy hot side example 14cm2 You can reduce lag sending all exhaust gasses trought one scroll like on attached picture ..... then exhaust side will be 7 cm2 ( orig 14cm2)
faster spoool i will test it soon on hx4018cm2

good luck anyway
 

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I have a gt3071r .64 in my 9k. No choking at high rpms and Im at around 400whp and 410 ft/lbs. I havent heard a bad thing about reliablity or personally had any issues other than going real fast. I need bigger breaks. oh, the turbo starts really shoveling boost at 2900 or 3000rpms
 

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the only gt worth it in my opinion is the 3076 (given the cost to power ratio)

the 2871 and 3071 on a 2.0 are probably barely going to get to 340-360whp.

thing is they cost a lot to set up, and dont forget the oil restrictors.

i still vote 18t, since even on my evo im a believer in stock frame turbos. and keep in mind a 19t has been taken to the 330-350whp range on a 2.0.
 

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You cannot really have both low end spool and big power with one turbo, unless you use a variable vane type turbo and that has not really been figured out very well yet.

You ask .64 and .63, there are two flanges, t3 flange is the larger gt3071 with larger turbine wheel at .60mm and it needs a tubular manifold, will not bolt up to our cars, flows a little more, offered with .63ar and .82ar turbine.

The .64ar is the t25 flange turbo, will bolt up with a spacer to our stock manifold, gt 3071wg .64ar has a smaller 56.5mm turbine wheel, flows a little less than the t3 flange turbo.

These turbos have all been tested on our cars and some main points.

Gt3071wg .64ar is a t25 flange, will bolt up to the stock manifold, spools by 3500 or so on a 2.0, will make 28psi and 350whp with stock cams and 400whp with enem cams.

Gt2871wg is a t25 flange, it actually spools up slower than the gt3071 in real life and makes less hp, does have some compressor surge down low in my experience on a 2.0 car, would never use this turbo, bad wheel combo.

Gt3076wg .86ar is more laggy, spooled a good 800-1000rpm later than the gt3071wg .64 ar, it made around 75whp more, but was not on until 5k.

19T can spool by 2700-3200rpm at full boost of 27psi and make 310whp in my experience on a 2.0.

Most of these turbos and the dyno slips can be found on my website and then you can see the difference in spool and power,

John
 

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+1 on what John just said.

You can't have spool at 2.5K AND 350whp with anything larger than a GT28RS. Which, BTW will only flow about 5% more air than the Big T28 from gpop.

If you want to wait a few more weeks, I'm going to put my Big 28 on a dyno and see exactly what it's making.

BTW, exactly how did you "find out" that the gpop T28 won't produce 315whp on a 2.0l SAAB? The hot AND cold sides of that turbo are larger than the Mitsu 18T 6CM. I believe there is a youtube vid of the gpop T28 putting down 310whp and Christian's car put down 285whp with an automatic trans at only 17PSI on a big T28 from another builder. Wherever the info came from, I believe it to be inaccurate. I would agree that 350whp is probably out of the question but 315-330whp is possible from everything I can see.

D-
 

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I agree, the power is possible if you are shooting for those PEAK numbers from a T28. But in my opinion, if linear power is the goal of the day, a Big T28 will not get you there since 315-330whp will be pushing the limits of the compressor efficiency and will lend to a lot of mid range power but falling significantly in the upper revs.

I have to say though, the T28 is the best turbo out there in terms of having great spool up with a nice kick in the top end if you don't push it too hard. I found the automatic/T28 pair was great but I could never push it much past 18-19 psi for the sake of the transmission.
 

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Discussion Starter · #9 ·
All of these points are helpful and valid. However, I understand and stated so in the first post, that higher boost figures in the lower rpm band are not happening with a big(er) turbo. I need SOME boost in this range, a little over .5 bar would be plenty of scoot for around town driving.
Dave, I actually asked Christian in the Dyno thread about the T28-he said, and I can quote, that the T28 can do around 300whp. I took this to mean ~290-310whp. If I am going to spend a grand on a turbo, I want the most I can get without sacrificing DD characteristics.
If it helps you help me, then here are my criteria:

1) Need .5 bar in the 2-3k rpm range

2) No tubular headers (extra grand)

3) No cams (extra grand+)

4) Minimal PITA to install/setup

5) At the least, 100+ bhp over stg 3+,

6) Total cost from cradle to grave cannot exceed $1,800, the less the better.

I was set on a GPop T28, but when all is said and done it will be almost the cost of a gt3071 .64.

Thanks for bearing with me,
-Cm
 

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ill tell you right now that you cannot set up a gtbb for $1800.

the turbo itself will be 12-1500.

with your criteria and budget you are stuck with a t28 if you want low end or a 18/19t if you want top end and low end.
 

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I agree, the power is possible if you are shooting for those PEAK numbers from a T28. But in my opinion, if linear power is the goal of the day, a Big T28 will not get you there since 315-330whp will be pushing the limits of the compressor efficiency and will lend to a lot of mid range power but falling significantly in the upper revs.

I have to say though, the T28 is the best turbo out there in terms of having great spool up with a nice kick in the top end if you don't push it too hard. I found the automatic/T28 pair was great but I could never push it much past 18-19 psi for the sake of the transmission.
I hear what you are saying Christian but the Big 28 has a cold side that is larger than an 18T and just shy of a 19T with a hot side close to a Mitsu 7cm. The bottom line is that there isn't any better balance between spool and top end for the OP goals. The truth is that mathematically, my T28 is making it's peak HP just below my 6500 RPM redline. There is obviously a fall off in torque between say 3500 and 6500 but the HP keeps climbing, pretty much right to redline. Now I am running 23PSI at 6500 and that's a good bit more boost than you ran so that may account for the difference.

Here's some interesting discussion from the archives of the DSM boards. The gpop T28 is the same design and spec as the old Forced Performance (FP) Big T28.

Big T28 dyno sheets - DSM Forums

Some interesting reading in there, including a link to the Far North Racing Eclipse site where that car made 348fwhp on a big 28 on the dyno.

With the T28, the actuator becomes a very significant part of the equation as well. That is discussed in the DSM thread too. My car runs a FORGE actuator with 18PSI BB.

D-
 

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Dave, I actually asked Christian in the Dyno thread about the T28-he said, and I can quote, that the T28 can do around 300whp. I took this to mean ~290-310whp. If I am going to spend a grand on a turbo, I want the most I can get without sacrificing DD characteristics.
If it helps you help me, then here are my criteria:
-Cm
I should have been clearer, I probably could have hit 300whp on my automatic transmission but I just did not want to push my luck. With the smaller drivetrain loss associated with the manual transmission, I believe you will see between 310-330whp on a pretty aggressive tune. David has his setup dialed in very very well, much better than my tune by mail system so provided you have someone who is able to tune in car, you can easily coax more top end than I had.

This turbo should slot right into your cost bracket, you will also need injectors though.

I hear what you are saying Christian but the Big 28 has a cold side that is larger than an 18T and just shy of a 19T with a hot side close to a Mitsu 7cm. The bottom line is that there isn't any better balance between spool and top end for the OP goals. The truth is that mathematically, my T28 is making it's peak HP just below my 6500 RPM redline. There is obviously a fall off in torque between say 3500 and 6500 but the HP keeps climbing, pretty much right to redline. Now I am running 23PSI at 6500 and that's a good bit more boost than you ran so that may account for the difference.

With the T28, the actuator becomes a very significant part of the equation as well. That is discussed in the DSM thread too. My car runs a FORGE actuator with 18PSI BB.

D-
Without question, I completely agree with you on the balanced nature of the turbo! My original tune pushed around 21psi peak which I felt was just too much for the auto and I never dyno'ed the car until the 18psi tune. I apologize for failing to specify, I meant torque will fall off as you seek the highest peak numbers the turbo will support (my dyno HP curve looked pretty much flat until 5,500rpm, torque fell flat after 5krpm). But agree, this turbo spools sooner than a 19t while supporting nearly identical power levels.

I think part of the reason I experienced the huge mid range --> weak top end was due to the tune, your car is much better setup on the ECU side/tune.
 

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+1 on what John just said.

You can't have spool at 2.5K AND 350whp with anything larger than a GT28RS. Which, BTW will only flow about 5% more air than the Big T28 from gpop.

If you want to wait a few more weeks, I'm going to put my Big 28 on a dyno and see exactly what it's making.

BTW, exactly how did you "find out" that the gpop T28 won't produce 315whp on a 2.0l SAAB? The hot AND cold sides of that turbo are larger than the Mitsu 18T 6CM. I believe there is a youtube vid of the gpop T28 putting down 310whp and Christian's car put down 285whp with an automatic trans at only 17PSI on a big T28 from another builder. Wherever the info came from, I believe it to be inaccurate. I would agree that 350whp is probably out of the question but 315-330whp is possible from everything I can see.

D-
I would love to see how another T28 performs, all the ones I have seen have been from JSP and I have tuned quite a few of those and all of the made right around 280whp, manual or auto. I got 284whp out of a viggen with the jsp t28 and multiple ng900s right in the 281-283whp range, at least 5 dynos all with the jsp t28 and all 5 of them made 280-285whp. Jak's own car with the same turbo made 282whp.

I have made 310whp with the 19T, I feel this is the better turbo, you can get it with the larger 6cm2 housing and it seems to flow about 20whp more than the jsp T28, would be nice to see another turbo configuration on the T28.

PS, you can't really compare dsm to saab, they just do not run the same, they consistantly get more power with the same turbos from my experience and comparisons, just a little bit better flowing head, etc.

Here is the layout of the JSP T28 vs. 19T, both on the same dynos, the same day and both were 2.0 ng900's, even both were 1996 years. You can see the JSP T28 did not do very well when compared to the 19T. This is why I would love to see another T28 on the playing field. !

John
 

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I would love to see how another T28 performs, all the ones I have seen have been from JSP and I have tuned quite a few of those and all of the made right around 280whp, manual or auto. I got 284whp out of a viggen with the jsp t28 and multiple ng900s right in the 281-283whp range, at least 5 dynos all with the jsp t28 and all 5 of them made 280-285whp. Jak's own car with the same turbo made 282whp.

I have made 310whp with the 19T, I feel this is the better turbo, you can get it with the larger 6cm2 housing and it seems to flow about 20whp more than the jsp T28, would be nice to see another turbo configuration on the T28.

PS, you can't really compare dsm to saab, they just do not run the same, they consistantly get more power with the same turbos from my experience and comparisons, just a little bit better flowing head, etc.

Here is the layout of the JSP T28 vs. 19T, both on the same dynos, the same day and both were 2.0 ng900's, even both were 1996 years. You can see the JSP T28 did not do very well when compared to the 19T. This is why I would love to see another T28 on the playing field. !

John
I agree with you John. JAK's T28 never performed all that well. My theory is that JAK never actually sold a T28 configured like the old Forced Performance or Gpop ones. I believe his T28 was ALWAYS the T28 cold wheel with a stock T25 Hot side. (Perhaps with a turbine clip or some other "custom" touch) This would explain why the thing runs out of puff well before the 19t. The compressor wheel on the T28 is almost identical in rated flow to the 19T so the limitation pretty much has to be on the hot side.

I have recently purchased an auto shop as a means of leaving the corporate world behind. At this point, it would be a solid investment for me to finally get my car on a dyno and see what we are looking at. Not that a dyno printout is in any way superior to road acceleration mathematics but it's what everyone seems to consider proof and I suppose I can understand that.

I have a graph that charts two 300whp 9-3s one a Viggen and the other a coupe 9-3 against my car in third gear. My car, despite it's weight disadvantage and an 11% gearing disadvantage out accelerates the both of them. Obviously it is making roughly 330whp. It would need that just to make up for the gearing. So far, I have not seen anything short of a 3071 or Holset outrun my car from acceleration numbers. As a matter of fact, My car runs pretty dang close to two different vids of 3071s. From 60-120 shifting right at the limiter into 4th (6500) I have seen 10.4s in balmy weather on flat ground. That's pretty solid for a T28 vert, not short shifting at 5500RPMs to keep it in the typical torque swell.

Anyway, I have started looking for a local dyno facility. Sadly, the one that was right around the corner from my shop closed about six months ago.

I'll find one though and we'll take a look-see together. I too would like to see the numbers I believe my acceleration times show be proven with a dyno plot! :0)

D-
 

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Discussion Starter · #16 ·
Because I am slow; if the hot side of a Gpop T28 is bigger than a td04 6cm^2, and the cold side nearly matches the flow of a 19t compressor wheel, shouldn't the T28 put down the same or greater power? Just for reference, these figures are for a6cm^2 tdo4 right?
-Cm
 

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PS, you can't really compare dsm to saab, they just do not run the same, they consistantly get more power with the same turbos from my experience and comparisons, just a little bit better flowing head, etc.

John
Actually, it has little to do with the head or the cams. It has to do with being able to rev to 7K in stock-ish form. However, if the turbo can move the air, it can move the air.

D-
 

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I agree with you John. JAK's T28 never performed all that well. My theory is that JAK never actually sold a T28 configured like the old Forced Performance or Gpop ones. I believe his T28 was ALWAYS the T28 cold wheel with a stock T25 Hot side. (Perhaps with a turbine clip or some other "custom" touch) This would explain why the thing runs out of puff well before the 19t. The compressor wheel on the T28 is almost identical in rated flow to the 19T so the limitation pretty much has to be on the hot side.

I have recently purchased an auto shop as a means of leaving the corporate world behind. At this point, it would be a solid investment for me to finally get my car on a dyno and see what we are looking at. Not that a dyno printout is in any way superior to road acceleration mathematics but it's what everyone seems to consider proof and I suppose I can understand that.

I have a graph that charts two 300whp 9-3s one a Viggen and the other a coupe 9-3 against my car in third gear. My car, despite it's weight disadvantage and an 11% gearing disadvantage out accelerates the both of them. Obviously it is making roughly 330whp. It would need that just to make up for the gearing. So far, I have not seen anything short of a 3071 or Holset outrun my car from acceleration numbers. As a matter of fact, My car runs pretty dang close to two different vids of 3071s. From 60-120 shifting right at the limiter into 4th (6500) I have seen 10.4s in balmy weather on flat ground. That's pretty solid for a T28 vert, not short shifting at 5500RPMs to keep it in the typical torque swell.

Anyway, I have started looking for a local dyno facility. Sadly, the one that was right around the corner from my shop closed about six months ago.

I'll find one though and we'll take a look-see together. I too would like to see the numbers I believe my acceleration times show be proven with a dyno plot! :0)

D-
I would like to see another one on a dyno and would love to see how your car is running, if its not regular pump gas, that should be noted as well. Look for a dynojet if you can, that is what most of my data is on,

John
 

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Actually, it has little to do with the head or the cams. It has to do with being able to rev to 7K in stock-ish form. However, if the turbo can move the air, it can move the air.

D-
I am not convinced of that, I would like to see some real world data, I have compared a few and it did not have anything to do with rpm as any stg 3 or 5 in the case of a t28 has a 7k rev limit in the Saab :)

There is what should work on paper and how it works in real world conditions, I find that more times than not, these two are not the same. Jak's big T28 was sold as bigger than 19T, bla bla bla, but in real life, it was still down when compared to the 19T and it spooled up later. Mine did have a clip on the turbine side, it was supposedely the only BIG T28 Jak ever sold, he was not happy with the spool of the larger Big t28 for the 14whp it gained over his common smaller T28.

Anyway, here is the dyno of my Big T28 with turbine clip vs 19T, little closer, but 19T is still the better turbo in my opinion and from the data that I have from testing.

John
 

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