Fadi,
Don't forget, you've got the new GTX29 turbine wheel midway between the 28 and the 30 for even more choice...

 

Yes you are right, a few months ago was looking for specs regarding the gtx29 series, not too much out there.. just saw the 2967 @garrett site. I guess the 2971 might be ok, the gt29 turbine comes with two wheel options, imo this turbo will be much better than any alpha30

 

FWIW I still think that the sweet spot for a stock 3.6L motor is a gt28 (or equivalent, K16, EFR6258, TD05H, etc) sized turbine wheel with a suitably-matched billet comp wheel if response is an overriding concern..

 

I looked into the gt29 and word is that it's a cut down gt30 wheel that was used on the small trim gt3071-wg that's be rebranded as a gt29

 

In freezing cold the car does over 600 whp on E70 gas but recently with temps at 65-70F power is way down which is weird because last year in 85F it was doing implied 600 whp but I am at absolute max for the K24s.

I was thinking 3076 at even 1.3 bars would give an easy 600 whp on something like E30 gas

 

After having 3 turbo setups on my car and looking for the 4th, I would say if you dont plan for 800whp than dont go with 3076, pick the smallest turbo that accomplishes your targets. My guess is a hybrid K24 will be the best way to go if you look price/performance and gt28 or efr62/6758 if not taking into consideration price for upgrade.

Expect 3076 to spool like 400+ rpms later than K24

 

I hear you but I am doing mods slowly as I get used to power levels and so my missus doesn't keep busting my *****.

My plan and you can help me with the thinking is this is that I can run larger turbos with great fueling at lower boost. My poor old K24s now on E85 hit 1.5 bars which is a wee bit much

so

1. A3076s
2. Run an E85 tune at about 1.3 bars

I am MAFLESS with excellent ETS Intercoolers rated up to about 1000 bhp

That will give me a car in the region 770-800 bhp ???? and 5.8s 60-103 mph

Mafless and E85 will help me spool much quicker than otherwise by about 500-550 rpms or so but as this is on a stock block I do not want A28 type spool as the few A28 cars I have been in have scared the bejesus outta me

The plan is to do rods and minor engine stuff next year and run higher power to do the Tx Mile

 

@1.35bar 93octane timing I was able to get 6.0s 100-200hmh or like 6.5ish 60-130mph, I expect E85 to lower that by .2-.3s or so, I would guess you need at least 1.5bar to get 5.x 60-130.

I dont have a dyno of my A3076 setup, but now I run a bit bigger turbos gt30s based though, 1.3bar did 660whp, 1.65-1.7bar did 800whp or a bit more, this done with meth and racegas timing

I have never run E85, but spooling 500-550rpms earlier seems too much to be true..
If you plan for rods take A28 into consideration, otherwise A3076 are the best step to do

You have to run 1.5bar+ to wake up A3076, otherwise isnt worth it... on stock rods you can run 1.5bar for a while, maybe limit torque a bit or use 93octane timing on a E85 tune and I guess you can run for a long time

 

My MAFLESS and E85 runs 550 rpm quicker than the stock K24s, that is across about 100 measured runs but I am measuring from insta boost not peak boost so you may be correct but even MAFLESS made them spool quicker.

If I run E85 at lower boost will that give the added oomph on 3076s... I see that Spoolbus pushed 690 awhp on alpha 3076 with meth inj and 93 octane on 1.5 bars.. so I guess 1.3 bars on E85 will give mid 6xx whp

 

I guess so... 650hp is what they should be good for at 1.3bar, also the above times of my car 100-200 and 60-130 were stock weight, 4wd,0% decline, no break boost, no flat shift, etc... So if you use all the tricks in the book maybe you will see a 5.x 60-130

 

This is good to hear! My 5431's are a tad smaller on the inducer side than the 3076r's and I'll also be on E85. I'm Hoping to be in the 6xx whp on 1.3-1.5 bar. What RPM were you seeing the K24s come on? I do not remember any discernible 'lag' with the smaller k16s at all.

 

TY that is what I was looking at

 

With the current E70 and 4th gear at WOT the boost at 4400 rpm is over 1bar... I will take a video and datalog when I get back to my house this week and check old E85 logs

 

So final choices are the following
gtx2867
gtx2871
gtx2971

Let's take them one by one

1. gtx2867 - 48lbs capable compressor wheel, so should be good for 800whp on a 996tt, I would do the small A/R to have better spool as the compressor wheel shouldnt maximize the turbine
Anyway housing choices are:
Turbine Housing Options
PN A/R Type Divided Housing Inlet Outlet
430609-230 0.64 Wastegated N T25 5-Bolt
430609-231 0.86 Wastegated Y T25 5-Bolt
827690-1 0.57 Free Float N V-Band V Band
827690-2 0.72 Free Float N V-Band V Band

I guess the 0.72 V-Band is the way to go, giving both good spool and decent high end. I would say this should be the best turbo for a daily/street 996tt on stock displacement

2. gtx2871 - 56lbs wheel, for sure a bigger A/R is needed as the turbine wheel is huge, I would do it with smaller A/R first and if will still miss more power, might switch only turbine housing to a bigger one. Also TIAL housing is available ! Would do it with either 3.8L or 3.6+heads work to increase red line so they should provide enough power band.


3. gtx2971 - same 56lbs, bigger turbine wheel (old gt3071 turbine). Only for high boost lovers and guys looking for every HP. Guess will spool really fine with a 3.8+ liter and higher red line

I would exclude the gtx2971 as will have another car to be build with gtx3076, also I will eliminate the bigger A/R options, so will stick to 0.64 or 0.72 A/R with either wheel 67 or 71. I would match the bigger wheel to the bigger housing so the options would be

Gtx2867 A/R 0.64 or 0.72, externally gated - 480 hp rated
Gtx2871 A/R 0.64 or 0.72, externally gates - 560 hp rated

I guess the 2871 will loose 4-500rpms (combined form bigger comp wheel and bigger A/R) in spool and hit but should deliver 100hp more up on top and still being very enjoyable on the street and raceway at lower boost.

By the other hand I would have no problem to stay bellow 800hp on the 2867... problem is I can not estimate what the difference would be between the two options.

Any inputs you gt28 guys?

 

Here is what I did with my Alpha 28's (GT2871) on both stock motor and built 3.8L. Car leaned out cause I was running out of fuel. 29+PSI Stock dyno is at 26 PSI, and a more aggressive dyno (Dyno Dynamics)