Hey has anyone upgraded to one of these yet? How do they spool? How is their daily driving manners? I am starting to get my ducks in a row for a turbocharging upgrade and would like to keep it a single... I saw that the hot side uses a 72.5mm wheel and a .99 A?R housing... How would it compare to a turbo that uses a 77mm wheel and .8 housing in spool?

Anyway if anyone has any good info post up!

 

It sounds like you've been poking around the Garrett site, too!

The 77mm wheel you are referring to is no doubt the GT40 series (gt4088, 4094). The smallest housing they show for this turbo is a .85 A/R

We can calculate the "area" since we know the A/R and the radius (the turbine wheel diameter divided by 2).

The .99 AR housing on the 72.5mm wheel gives us an area of 35.88
The .85 AR housing on the 77.0mm wheel gives us an area of 32.725

In other words, the smaller housing would have a slightly smaller sectional area, even though fitted to a larger wheel.

Now the 3788 and the 4088 have the same compressor side, so the only difference is in the turbine. The 4088's housing is proportionally tighter, so the the only thing keeping it from spooling faster than the 3788 is the rotational inertia of the larger wheel (77 vs 72.5). My guess is that the rotational inertia difference is NOT that substantial, and I'd expect the 4088 to spool very close to the same as the 3788 "stg 3". If it turns out to be slower, the benefits of the 4088 make the additional lag worthwhile.

What benefits?

1) The 4088 has a much larger V-band outlet instead of a tiny 4-bolt 3788 outlet. Wheel flow means very little of the outlet itself is very restrictive.
2) The T4 inlet is larger in sectional area, and will flow more.
3) You have choices of turbine housing, starting at .85 and going up to 1.15

I *highly* suspect that the reason the GT37 was chosen for our trucks has as much to do with the drop-in T3 inlet flange as it does anything else. Garrett basically put a 4088 into a GT37 frame--- same compressor, smaller hotside. So you get a marginal increase in spoolup with the GT37 because of the smaller turbine wheel-- but you pay a bigger penalty in EGT.

I suspect that the 4088 would have MUCH lower peak EGTs for three reasons. First, the turbine is better matched to the flow rate of the compressor. Second, the outlet is larger diameter. Third, the 4088 does NOT use a restrictive adapter to mate the turbine outlet to the factory exhaust.

I can tell you that I'm strongly considering a Garrett, but I'm convincing myself that the hassle of going to a T4 manifold and going to a custom downpipe are more than worthwhile to fit a 4088 in place of the "drop in" GT37.

The other advantage of going to the T4-inlet GT4088 is that you can also upgrade to a 4094 and pick up some pretty substantial flow without having to swap turbine housings out. The 4094 though is a pretty big single, comparable to a Sledpuller 66 or Silver bullet 66, only the hot side of the 4094 will flow a LOT more than the SB or SP66 because the turbine wheel is larger, larger A/R housings are available, and the outlet might be larger (I'm not sure on the outlet-- I *think* it's larger than an HX40 outlet.)

So you could run the 4088 as a very good single charger (though it will be a little laggy, but not too bad given the flow and the BB cartridge). Then you could swap that 4088 for a 4094 when you decide to build some massive twins.

I suspect that the 4088 is probably probably has a pretty high boost threshhold-- like it won't even make any boost until 1800rpm or so. But once it start to make boost, you'll probably see it rocket up to peak boost due to the larger turbine wheel and BB cartridge.

I'd expect spoolup to be better than or the same as a typical 66-class charger--probably not a very tow-friendly turbo, but I don't tow and I have a 6-speed, so I have options!

Justin

 

Looking at the outlet flanges on the 3788 and 4088, the 4088 is all of 1.3mm bigger.

Looks like that's not really an improvement for the 4088-- but losing the restrictive "adapter" sure is. The adapter that comes with the Stg 3 3788 kit has a lip protrudes into the outlet-- so basically your 72.5mm outlet on the Stg3 hits a "wall" that necks it down to 68mm or so.

Ditch the adapter and improvements are available.

DTR member Hammer ditched the adapter and said he lost almost 200º EGT without it!

 

One of my buddies has one in his 12v which is pretty heavily fueled. It does have a little bit of lag there til it starts to spool. After 10 psi though it shoots up there quick! He did say that he towed with it and it got hot pretty easily, it was hard to spool when towing.

 

Also I do hafta add that a lot of the heat prob comes from his lazer cut delivery valves.

 

The turbo is nice for guys wanting a usable 400 RWHP. Spoolup is nice when properly tuned but boy does it get hot fast on trucks above 400 HP. As far as I can tell from maps and actual usage around 490 RWHP is all it will make regardless of how much fuel you can throw at it.

Doug

 

One of these days...I'll get my fueling figured out, and see what this 4088R will do! BTW, HOHN, I have a .68A/R undivided housing on mine...cheaper than a factory Garrett housing too Next time it runs though, it'll be with a Helix 2, ported head, and cool twist IC!

Doug...while I don't disagree, I'll add this...I put together a setup of Jammer 5's, Smarty, and the Garrett Stg II for my friend, and he has no EGT troubles outside of towing heavy at 70mph+ on hills. When we go to Mach 4's in the next week or so, I'll report back. But according to most people, with the Mach 4's we should be right at 400HP.

Once he gets a clutch in it, he'll get a wiretap box ad see what it'll do...but I think we'll have results in line with yours Doug! That's when I find a GT4202R to help it out

Chris

 

The setup I am contemplating to give a whirl is an ATS Manifold ported out with the T-4 "Big Foot" outlet to a GT4094r with a .68 turbine housing (if they have one) and have a 38-40mm external wastegate plumbed into the manifold itself. I was hoping that with a ported head (being ringed right now) and a good cam (looking into) that I could get that turbo to start to light around 1700rpms and have boost comming on completely around 1900-2000rpms.

Much like you Hohn and Sig600 I want to try something new and I hope to get good results! Lol I figure a ball bearing would be a good efficient turbo and hopefully that GT4094r would support 550-600rwhp with good driving manners, what does everyone think?

Or would going with the Stage III be a better idea? About what RPM does it start to spool?

 

.85 is the tightest AR housing that Garrett has for the GT40.

I dunno if Precision or someone else has a tighter housing.

Honestly, I don't think you'd want anything smaller than a .85 with the 4094. My estimations show you'd be risking a surging nightmare with anything much tighter than the .85-- Heck, the .85 will ride the edge of surge as it is. Definitely need to consider a cam or some portwork to increase flow and relieve some of the boost.

The other problem is PR. For 550hp at 2700rpm, you're looking at 4.4 PR and 73 lb/min mass flow-- with mondo intercooling. With lesser intercooling, PR can clear 5 or worse.

This is beyond the map of what the 4094 can do. By my estimations, the 4094 is a 500hp turbo, and that's on the ragged edge-- near the peak of its map.

To have a "comfortable" 500+hp Garrett, you have to step up to the 4202, which is going to be seriously laggy. This thing is more of a primary than a single, imo.

The real limitation is PR, and why twins are really the way to go on our trucks. You simply can't make a usefully efficiency single compressor for PRs in the 6-8 range. Far better to share the workload across two compressors.

 

Forced Inductions can make a .68 housing!

My 4088 surges BAD...it will bark going into OD, and again locking up. You can drive around it, but it's not easy! The 4094 will be worse.

Basically, these chargers are meant for good airflow engines...like a 24v or CR, not the old 12v. BUT, we'll see how my latest BOMB make her react...it can't be any worse!

Muddin...if I were you, and could stand it...give me another couple weeks to get back and running, and see how things work. So far, I'm not overly impressed with the driving manners of these chargers...but my truck was never quite right since the time I put the charger and pump on.

Chris

 

I already have ported out my head quite a bit in the last month and a half when it has been off of the truck, right now it is at the machine shop getting a 3-angle valve job, 60lb. Springs, and firerings.

I am looking into cams right now, I am trying to see if there is anything better than a Helix II that doesn't require valve reliefs cut into the pistons.

Even if I had to use the .85 turbine shouldn't the GT4094R be able support 550+ ? I figured that because of the large turbine wheel I could use the smaller housing (.68) and it would still flow plenty, although no one has ever explained compressor maps etc. to me...

Hohn, you say that the GT4202 would be a 500+ turbo but extremely laggy, I would think the GT4294R would be a better choice just because it ha a 71mm inducer as opposed to the 74mm on the GT4202. Does anyone make smaller turbine housings for these? Perhaps housings machined to fit from smaller chargers?

Sig600, I will wait on you to get your truck back together. I am in that same boat! Hopefully next weekend I will be getting everything buttoned up. I would be looking at doing a turbo upgrade around a month afterwards so I have a little bit of time to spare.

 

Chris.
I've been running my Mid-sized S400 for a couple weeks now. It is similar to the GT4202. It has a 1.10 exhaust housing with an 87mm turbine wheel(vrs 83 on the gt42). I have an 80mm wheel and compressor housing and a 75mm setup. It seems to be working well, and spools a bit faster than the 80mm Large S400 I had a while back. I'm going to look at the drive pressure over the next week. I swapped a set of larger injectors in to get the primary boost up to the point where drive pressure may be an issue. Nice turbo to do the build with. Smaller external size makes fitting easier. Alot nicer to swap out by yourself. The lighter weight makes it alot easier to hold in place when getting the bolts started.

Ron

 

I thought the same thing about the 77mm turbine...but I also blew a HG, so I'll definitely be monitoring drive pressure when it runs again. The head should be getting ported now, so hopefully, I'll have everything here and put together in 3 weeks...then some time on the retorques, and it'll be game on!

I'll definitely keep everyone informed on the Helix 2 and ported head performance...I can't wait!

Chris

BTW, after I recover financially from this round of BOMB's, the GT4508R will be going on

 

Sweet...glad to hear that Ron...I have a charger with about those same specs I was gonna put on my friends 2002 this winter That sounds promising!

Chris

 

I had the GT40 76trim on my SRT4. Spooled very loud. I loved it. Dont know how the difference would be with a larger truck.