compressors & turbines

This might get a little long winded....

I'll give it a shot.
There are many factors that I have found over the years with these cars which can affect spool up time. I won't go into wheel designs, but will tell you what I've found that works and doesn't work on our V6s. I've broken them down into categories.

Turbine housing A/R ratios and design.
On our 3.8L V6 motors, we typically run the factory T3 style 3-bolt turbine housing and over the years there have been some improvements to the original Garrett design. Namely the Precision turbine housing. .63 A/R was stock on the Garrett housing, and typically you don't need to go higher than an .85 on a 235 CI V6. The .85 A/R Precision housing has proven itself to support up to 875 flywheel hp on the PT76 GTQ turbo. The 3-bolt housing has a wastegate hole built into the housing for use with a downpipe that has an internal wastegate flapper and puck assembly. Aka Terry Houston style downpipe.

If your combo calls for more hp capability, or you are building a Stage II setup, then you can step up to the T4 and larger style housings.
There are two types of T4 style housings.

T4 On Center which is not recommended due to the extreme angle that the exhaust energy has to travel to make it's way to the turbine wheel. This housing was designed for use on engine bays that have very limited room and or space to mount the turbo. It's called On Center because the inlet of the turbine housing is on center with the discharge of the housing. It has a very small inlet area where the exhaust makes it first turn. This can result in very high back pressure ratios when running the boost up high. Typically available in .69 A/R and .85 A/R, and having a round 4-bolt flange for the downpipe. Designed for use with an external wastegate only.

T4 Tangential with a V-band flange for the downpipe is the most efficient T4 design. These style of turbine housings help reduce back pressure and are typically available in different A/R ratios. These are .58, .68, .81 and .96 A/R ratios. This housing has the inlet of the turbine housing off set from the center line of the discharge. Also, it has a wider inlet area where the exhaust makes it's first turn, than the On center housing has. On a V6 application, the .58 A/R will work on a stock 231 CI motor, so will the .68 A/R on larger turbine wheel equipped turbos, but it will require more stall speed to get it up on boost. The .58 A/R T4 Tan housing flows very similarly to what the .63 A/R 3-bolt Buick housing does. The .68 A/R T4 Tan housing flows very similarly to what the .85 A/R 3-bolt Buick housing does. A .81 A/R housing should only be used on larger CI motors than 235 and the .96 is reserved for 270+ CI V6 motors that have enough converter for the turbo. Designed for use with an external wastegate only. Almost all of the T4 On Center and T4 Tangential housings produced by the aftermarket are of a single throat design. Where as almost all of the Garrett GT series turbine housings are of the divided housing design.

Divided turbine housings or split housings where typically only used on diesel applications where exhaust energy was low and transient response was critical to making hp and torque on big rigs. This technology was developed further and incorporated into smaller frame turbine housings for use on small CI motors, such as your sport compacts. This quote taken directly from the article referring to divided exhaust manifolds as used on Inline 4 cylinders and divided turbine housings or twin scroll turbine housings. "The concept is to DIVIDE or separate the cylinders whose cycles interfere with one another to best utilize the engine's exhaust pulse energy. For example, on a four-cylinder engine with firing order 1-3-4-2, cylinder #1 is ending its expansion stroke and opening its exhaust valve while cylinder #2 still has its exhaust valve open (cylinder #2 is in its overlap period). In an undivided exhaust manifold, this pressure pulse from cylinder #1's exhaust blowdown event is much more likely to contaminate cylinder #2 with high pressure exhaust gas. Not only does this hurt cylinder #2's ability to breathe properly, but this pulse energy would have been better utilized in the turbine. The proper grouping for this engine is to keep complementary cylinders grouped together-- #1 and #4 are complementary; as are cylinders #2 and #3. Because of the better utilization of the exhaust pulse energy, the turbine's performance is improved and boost increases more quickly."
There is a point where the divided housing design becomes a restriction, but this typically is not until you are in the 1500 flywheel hp range on large single T5(T6) turbochargers and larger CI V8s.

T5 (also called T6) housings.

Typically only spec'd on 90mm and 91mm compressor wheel equipped turbos with the F-trim turbine wheel and a 1.0 A/R ratio. It has a huge 5 1/4" v-band discharge flange for the downpipe and a larger inlet flange. Typically you will only see these turbos and turbine housings used on full blown single turbo Stage II race cars. And in some extreme street/strip applications. Custom headers and downpipe are required as well as inner fender modifications. In other words, crazy applications.

Here is a link at Garrett's site that talks about wheel trims, A/R ratios and how they affect the transient response of the rotating assembly, as well as divided turbine housings.

TurboByGarrett.com - Turbo Tech102

Turbine wheels in relation to our V6 setup.

Over the years, I myself and my close friends have run many of the different turbine wheels that are out there. In chronological order, these are,

T31 "Stage 3" wheel
GT3255E turbo
T350 "Stage 5" wheel
T4 69 wheel
T4 76 P-trim wheel
T4 Q-trim wheel
GT series GT-Q wheel
GT42 series turbine wheel
PT88 series turbine wheel
GT4788 series turbine wheel
F-trim turbine wheel

With that said, here are some observations and results that I have stored away in my memory banks.
T31 wheel will work on a stock 231CI V6 with a stock 2200 stall at zero psi D5 converter. This wheel is used on a TA-49, TE-44, TA-60, TE-60, PT6131E and the PT6131RE. When you step up the compressor wheel size, the stall requirements and lag time increase. This is mainly in part due to the extra rotating mass of the rotating assembly that comes with the larger compressor wheel. Compressor cover sizing can affect spool up as well. Compressor covers have A/R numbers just like turbine housings do. The larger the A/R number that the cover has, typically the larger the compressor cover will be. Aka, larger scroll size, larger inlet diameter and larger discharge diameter. Naturally, it takes longer for the compressor wheel to digest the larger volumes of air being drawn in, than on smaller compressor covers. Example would be comparing a stock Garrett TA series compressor cover to a TO4S Garrett compressor cover. This lag time is not that big a deal tho when you have the correct stall converter matched to the turbo.

IMHO, you really need a converter on a TE-44, to really realize that tire frying from a punch feeling, but a lot of people have lived with the lag associated with their stock converter and TA-49/TE-44 for years. The GT3255E turbo was also designed from the get go to work with the stock D5 converter, and to basically displace the TE-44 as the HP capabilities are very similar with a slight edge in spool up going to the GT3255E because of it's GT series wheels.

The T350 or Stage 5 wheel needs a converter period. This wheel was first introduced in the PT51 and PT52 turbos. It gained a somewhat trouble some reputation in the beginning, but eventually, all of the issues were ironed out and there are tons of them still going strong today on not only our Buicks, but also on small V8 applications. It was when this wheel was married to the GT series 61mm compressor wheel that comes in the GT35R, that we really found a winner in the PT6152. This turbo likes a converter that will stall to 3200 at zero psi. Anything less and you will see some lag. This T350 wheel, was originally called the GT350 wheel before Garrett started their GT program. When they came out with the GT program, they changed the designation to T350. But it incorporated early GT series technology with regards to the pitch and design of the blades.

T4 69 trim wheel is an old school T series wheel. It's not a bad wheel, but it needs a stall converter as well. 3200-3300 stall works good with it. You very rarely see this wheel spec'd with todays more modern technology, but they are out there.

T4 76 or P-trim turbine wheel. One of my favorites, it is typically spec'd on applications that are trying to make 650-785 flywheel hp. It is available in small shaft and large shaft versions, the large shaft requiring a slight bump in stall requirements due to the extra rotating mass. This wheel has been successfully used with these compressor wheels, 63mm, 64mm, 66mm, 67mm, 68mm and the 70mm. It did not work very efficiently with the 72mm wheel, even though some companies will still make it. The differences in spool up times between the 63-67mm wheels when married to the P-trim wheel are very small. All of them will work well with a converter that can stall to 3500 at zero psi. It wasn't until the advent of the dual ball bearing cartridge that this rule was changed. With the DBB cartridge, you really only need a converter that will stall to 3000 at zero psi to spool it up well. But a 3400 will make it scream. Also note that when used on a motor that is larger than 235 CI, the stall requirements lower slightly. So if we need 3500 on a 235 CI, you might get away with a 3200 on a 248CI motor. On your 252 - 274 CI motors, this wheel could start to become a restriction. Even though people have run P-trim equipped turbos for years on Stage motors, they are not typically spec'd for applications that would require high boost numbers to make the target hp goal. In other words, if you have a 274 Stage II and you want to make 780 flywheel hp, on a 6776 turbo, you would have to run the boost very high and you would also need to run a .85 A/R ratio to keep the back pressure somewhat under control. Now, if you stepped up the compressor and turbine wheel size to say a 70 GT-Q, you could make the same hp with less boost and have tolerable back pressure numbers.

T4 series Q-trim turbine wheel. Worked well for years with the 68, 70, 72 and 76mm compressor wheels. It needed a 4000 stall converter on 235-252 CI motors tho, and back pressure issues would typically limit the overall hp potential. It was trumped by the invention of the GT series GT-Q turbine wheel and PTE discontinued using it back in 2002.

GT series GT-Q turbine wheel. The flood gates really opened up when this wheel hit the streets. In some extreme cases, we were told up to 100 hp was gained by changing from a Q-trim to the GT-Q turbine wheel. Spool up times were slightly decreased, but not by much. The small CI motors still liked the 4000 stall, but the Stage motors really only need a 3600-3800 stall to get it up to speed. It took awhile for the competition to catch on, but this wheel has proven itself to be a killer and there are many TSM combinations that are running the 70 GT-Q into the 9's on a regular basis today. Speaking of the 70 GT-Q, that to me is the largest turbo that I would safely run on a stock or 235 CI motor without a girdle. If you built a stroker motor with girdle, then you could step up to even a 76 GT-Q.

GT42 series. These turbos were first tried on 252 and larger CI motors and showed great results. When the GT4276 was adopted as the official TSL turbo, it was further fine tuned with trying different A/R housings and matching the converter. The hot ticket wound up being the GT4276 with a 1.28 Garrett divided T4 inlet flange 4" V-band flange housing. Capable of making 1200 flywheel hp it really screams. However, it will not fit in a stock location without major fabrication work and a custom downpipe. Awesome turbo to hp ratio on a serious street driven, big CI V6 turbo motor.

PT88 series turbine wheel. This turbine wheel was originally designed and raced in TSE class at the GS Nats. Back when the rules stated any 3-bolt turbine housing turbo allowed. PTE developed this monster. It dwarfed everything that was out there and made at least 200 more hp over the 76 Q-trim at the time. It was banned from competing after that one year at the Nats, but it eventually was developed for use with a new T4 inlet flange Tangential style turbine housing that had a 4-bolt downpipe flange. It worked great on Stage II setups running low 9's to high 8's. That housing would eventually evolve to have a V-band flange for the downpipe and had a .96 A/R. There have been some who have tried to run this turbo on a 235CI motor, only to have poor results with spool up even with a super high stall converter. It's just too large a rotating assembly to be used with such a small CI motor. You will see this turbo still being used today with good results in TSO class cars.

GT4788 turbine wheel. This turbo has only been around for about 2 years now and has found a good home on TSO series cars. Typically used only on a 274+ CI size motor. Very tricky in determining the right converter as a lot of guys are still fighting with this combo even today.

F-trim turbine wheel. For those crazy folks out there trying to run 7's on stock suspension stage II cars, this wheel has been used with 90mm and 91.5mm compressor wheel turbos. It definitely makes power, but needs a lot of stall to spool it up, even on a 278CI motor. 1.0 A/R is common for this turbo on our V6s. Not for the faint at heart.

New Top Secret Technology.

And then you get into the latest technology. Which would be your Borg Warner extended tip and fin turbine wheels and compressor wheels, as well as the T-netics F1 series wheels. I personally have no experience with either of them yet, but from what I have read and have heard, they are working very well on Buick applications. Jose at Forced Inductions is on top of the BW technology and Buick applications, and Jack Cotton of Cottons Performance Center is on top of the T-netics technology. It won't be long before we start hearing about these two surpassing the other competitors performance records and horsepower levels for a given compressor wheel size.
Here's a couple of links.

Turbocharging: Design and Function | BorgWarner Turbo & Emissions Systems

Turbocharger: Technology | BorgWarner Turbo & Emissions Systems

Turbonetics Inc. | Home | Technology | Turbine Wheels

Sorry this was so long and hope some of it helps.

Patrick

Thanks for that Update.
BTW, for those of you who don't know, that is Jose of Forced Induction in AL. Great guy to work with when I was at PTE.

Patrick we need to talk to Shane about putting you on the payroll
with at the time you spend helping folks!
Thanks for the awesome post!

patrick good lord. thanks for the info i learn alot from you.

I think you are referring to the GT4202 which has a 74mm compressor wheel. It should work fine, but only if it were equipped with the dual ball bearing center cartridge. It will need the right converter, as well as a custom set of headers, intercooler pipe connector (The GT42 series turbos use a V-band discharge flange to the intercooler pipes) and inlet plumbing to fit. It's an 1150 flywheel hp turbo. The standard journal bearing GT4202 might have some issues spooling up on a 235CI motor, even with the smallest 1.01 A/R turbine housing. This turbo is similar to a PT74 GTS, but the bearings, bearing housing, physical size of the turbine wheel shaft, compressor cover, backing plate and turbine housing are larger than the standard T4 series components used on the PT74 GTS.
Glad some of this helps.

Patrick

Patrick I am not sure it will make that kind of power on gas at the pressure ratios we run in these cars. We made 1850FWHP @ 27PSI/25* with 2 of them and I don't think there was 450HP left.

You may be right on that with regards to our cars, but I do know that other applications with more efficient head designs have made 1000 to the wheels with this turbo. At very high boost levels. 42-44psi. There are some crazy people out there, and those Supra and Mitsubishi guys are some of the craziest.


Patrick

Ok guys. Here's a good question for you. I'm still carbed but With the stock turbo. What are the options on changing the wheels and/or housings to get better boost other than just puting an adjustable wastegate on it. The 301 turbo is the same design but has a larger housing. Give me some ideas.