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gt 42

4K views 34 replies 14 participants last post by  urbanwheeler 
#1 ·
Ok guys ive read page after page but I dont think I fully understand yet. The differences in the 4202 and 4294R and 4294. Or the exact inducer sizes that would fit best for my truck. I think the 4294R is bb. Also the T4 footprint or T6. I know moore2001 ran a 4594 off a volvo. What did these other turbos come off of or are like the 38r and just a upgrade? Also where is the best place to get the ic pipes and collector, up pipes to run one of these turbos. What im looking for is 500-550ish running hybrids and tuning. Still be streetable.
 
#2 ·
The R means it's a ball bearing turbo versus a journal bearing. The 4202 has a bit larger compressor side wheel than the 4294.
I believe most are a T4 foot print, you don't want the T6 one.
The 94 may spool up a bit quicker and maybe be a bit better on the bottom end for daily driving, the 02 will give you more top end at the track.
The mounting kits and hardware are a custom fab job for the most part unless you do it yourself.
 
#3 ·
Do either one of those turbos come in anything production like the 4594 moore2001 runs in his off a volvo.thanks
 
#7 ·
I have never measured mine as I have a TN BB right now. It does fine but looking to upgrade for down the road just trying to put stuff together. I assume the drive pressure would be less w/ a Gt42. Thus safer for stock HGS?
 
#9 ·
Thats what I think also. And I was wondering if they were both T4s. I thought they were. But the Gt 45 is a T-6??
 
#13 ·
moore isnt running the normal gt45 you see on garretts website. gt42's come with both T6 and T4 housings. the difference in the two is mainly the wheel sizes, but they are built on completely different frames. if you would like to know what it takes check my webshots and shoot me a pm.

if i remember right, from the data logging we did my drive pressures stayed pretty close to 1:1 all the way up to around 40psi of boost. im seeing 53psi at WOT.
 
#14 ·
Mine matches the GT4294 closely with a 1.19 A/R T6 turbine housing.

I am working on a GT4294r now that is T4. It is very close to mine just has a T4 instead of a T6.

I love the T6 now that it is all mounted up and installed. The larger inlet allows much more room to work with as far as getting the inlet piping to flow smooth into the turbine. Look at the difference in the flanges before you knock the T6 footprint, there is WAY more potential for flow through the T6.
 
#15 ·
I was under the impression that all of the 42 series of turbos are meant to be on a T6 but that the turbo builders are machining out a T4 to except the 42 center section??

BTW, do you 94mm guys get considerable barking when you let off from a full throttle run? Is this unavoidable when you are cramming a lot of air in? Is this an indication of being too far off to one side of the compressor map?

So many things go into how your turbo reponds (head porting, intercooler piping size, compression, ceramic coatings, stall speed of the TC, programming, etc...) and in my case I struggled to get my T6 4202R to respond to my liking but it has now became 'somewhat' responsive. The smallest turbine housing RCT could install was a .79 I believe and that is what I now have.

Thanks.
 
#18 ·
With my 4294r and the 1.01 exhaust housing my back presure was 65psi with 53 psi boost pressure which is max. Back pressure didn't exceed boost till after 40 psi boost. BP was measured off the exhaust manifold and boost was measured at the intake Y.
Suns, the only time I can get mine to bark is if I mash it and let off right away before it has time to build boost. It never barks after a wide open run.
 
#20 ·
My pressure ratios seem to in line with Cota too. I also have the same exhaust housing (1.01).

Mine will bark if I am above about 30 psi and let off, otherwise I haven't noticed it too much.

I also really like the 4294 with a T4 configuration. Its great for a daily driver and its very responsive and has great top end. The only issue is when its in OD at about 55 and you accelerate, it can black out the freeway in a hurry.

I think most everyone will agree, you have to drive a truck with a large single charger differently.
 
#21 ·
the gt42's found on OTR trucks pretty much all come with T6 housings, if you were to call garrett and order one it would come with a T4 unless you asked for the "large diesel" housing which is the T6. i am thinking that i may drop down to the 4294 or put a tighter housing on the 4202 until i get the 300cc injectors in it. seems to smoke too much for my liking.
 
#26 ·
You do have to pay attention on the go pedal w/ a big single but my smoke is at an all time low. You can really drive it around, pop out in traffic, etc, w/o worrying about even in my all out program. As all the guys w/ big singles know, it's all about the progression on the pedal. You definitely can't just stand on it w/o lots of smoking unless you already have some pretty good boost going.

So the T4 versions have smaller turbine wheels than the T6 versions? Well that would clearly explain why I kept needing smaller turbine housings. Chris at RCT sounded incredilous when I kept wanting smaller housings as if he wasn't aware of the larger turbine wheel. He kept saying "that is already equivalent to a 1.15 on a T4 and you want smaller!"

My drive pressures are very good down low, hit about 1:1 at 42 psi, and then the DP starts to climb pretty quickly. Highest I ever saw was 80 psi drive to 57# boost (w/ bigger squirts than I have now). Since I measure boost post CAC I guess I'm really 1:1 up to around 45 psi or so.
 
#28 ·
You do have to pay attention on the go pedal w/ a big single but my smoke is at an all time low. You can really drive it around, pop out in traffic, etc, w/o worrying about even in my all out program. As all the guys w/ big singles know, it's all about the progression on the pedal. You definitely can't just stand on it w/o lots of smoking unless you already have some pretty good boost going.

So the T4 versions have smaller turbine wheels than the T6 versions? Well that would clearly explain why I kept needing smaller turbine housings. Chris at RCT sounded incredilous when I kept wanting smaller housings as if he wasn't aware of the larger turbine wheel. He kept saying "that is already equivalent to a 1.15 on a T4 and you want smaller!"

My drive pressures are very good down low, hit about 1:1 at 42 psi, and then the DP starts to climb pretty quickly. Highest I ever saw was 80 psi drive to 57# boost (w/ bigger squirts than I have now). Since I measure boost post CAC I guess I'm really 1:1 up to around 45 psi or so.
No the turbine wheels are the same regardless of whether its T4 or T6.
 
#27 ·
Off Garrett's website:

GT4294 - compressor 70.3mm inducer/94mm exducer - turbine wheel 82mm
GT4202 - compressor 74.3mm inducer/102mm exducer - turbine wheel 82mm
GT4202R - compressor 74.7mm inducer/102mm exducer - turbine wheel 82mm

Both GT42's have the same turbine side, no matter what a/r housing or footprint
 
#30 ·
Interesting turbo talk, I likey.

I will agree though, driving on the street with a big single is a pain in the azz if you're trying to accelerate hard or "hot rod" around.

Ahhhhh.... the beauty of twins
 
#31 ·
I dont consider the 4294 a big single and it works great for hot rodding around town, although I have old school 238 hybrids which are probably smaller than what most of you guy's are running but are perfect for the 4294r.
 
#35 ·
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