The T28 is one of Garrett’s older line of turbochargers while the GT25 (pictured above) is from the newer GT series of ball bearing turbos, both of these turbochargers have similar power ratings, and can both be had for around the same price, but how well do they deliver the power?

The GT25 turbo is a newer and more efficient design than the old T series, so they spool up quicker and being ball bearing the GT’s are more reliable and they are also the smallest dual ball bearing turbo in Garrett’s GT range where as the smaller units like the GT22 are only single ball bearing.

Both of these turbochargers are super responsive due to the small size and they spool quickly, you can feel the T28’s power coming on at 3800-4000 RPM but as the GT25 newer, more advanced and is a ball bearing you can really feel it coming on at 2500-3000 and pull strong all the way up to redline. Both of these being excellent street turbos for sport compacts.

The T28 is a journal bearing turbocharger rated at 250hp however some JDM manual S15’s and S14’s came in a ball bearing version which is rated at 260hp, they also came with different A/R’s on the turbine housing. Both turbo’s are oil and water cooled, even on the ball bearing version of the T28 the maximum safe boost you can run is limited to 15 psi, anything beyond this is outside of its efficiency range and all you would be doing is pumping hot air into the motor and you are more likely to blow a hole in the piston. Also be carefull on which T28 you buy as there are many versions, the SR20 has an 0.60 A/R housing and GTR version has a 0.42 A/R, if you plan on a single turbo setup then the GTR’s 0.42A/R will be useless as you will have no top end power and blow the turbo or your motor very quickly. You can’t really buy a T28 new but they can be picked up for around $500 second hand.

The GT2554r is dual ball bearing turbo that is rated at 270hp but has seen figures on mildly work SR20’s of 300hp and has a maximum boost pressure of 18-20 psi, which it a lot of boost for a small turbo, its super responsive and really spools early and not to mention its also highly reliable, brand new you can expect to pay around $1500 and it’s a bolt on upgrade so no messing aroud.

Again the turbo you choose should be depending on your mods and goals, if its only a street car with nothing but a pod filter and blow off valve then I would suggest the T28 as they are cheap and easy to find and make a great replacement if you have blown you T25, but if you plan on installing or already have supporting mods such as a larger intercooler, dump pipe and ecu/ tuning upgrades then the GT25r is certainly the turbocharger for you.

Tech Specs – GT2554r
RRP $1500
Max Psi: 18 – 20
Rated HP: 270-300

Tech Specs – T28
RRP $500 Second Hand
Max Psi: 15
Rated HP: 260

You hear a loud whistling noise followed by a BA XR6 turbo nailing past you, that’s Garrett’s ball bearing GT3540 working hard, the GT3540 has to be one of the best matched turbos to a production car since the CT26 on the MR2 and Celica, producing a nice 320hp with only 5psi of boost (on the BA – BF models, FG runs 9-10psi).

The housing and centre are standard GT35r Garrett gear, so anyone who thinks the GT3540 is unique then your dead wrong, Garrett doesn’t list the GT3540 as a turbocharger but the compressor housing and cartridge are identifiable to the GT35r, but the turbine housing is one of Ford’s best contributions to the turbo world, an internally gated 1.06 A/R 5 bolt housing, this is great if you want to upgrade a stock turbo on another car and keep it all internally gated for that stock appearance, a lot of people retrofit the GT3540 turbochargers to older cars such as the VL turbo or and RB25’s due the availability and reliability of the Garrett ball bearing turbochargers oh and did I mention the GT3540’s hp rating of 400hp – 600hp?

The stock wastegate isn’t much chop with only a 5psi spring and if you know the rule of wastegates you should only be running a maximum of double the spring pressure, so if you plan to use a boost controller to crank up the psi then you should only be using a maximum of 10psi, but fortunately Turbosmart has a nice solution for this, the bolt on WG75 wastegate for the GT3540 with interchangeable springs depending on your desired boost level, for the same price as an electronic boost controller you have have a wastegate and spring fitted for the stock appearance and less of a defect chance.

The standard Ford turbine housing is a 1.06 a/r so if you are planning to use the GT3540 on a smaller engine like an SR20 you might want to change to a .86 or .63 housing for better response and quicker power delivery.

RRP $1650

Tech Specs

Rated HP: 400-600

You typical cast iron turbo manifold or also known as a log manifold (as shown on the left) is usually found on most engines out there as they are an oem part that come standard on most production turbocharged cars, tubular turbo manifolds are after-market manifolds typically for adding a turbocharger to your engine or upgrading / replacing you old manifold.

Both manifold types do have pros and cons, for example cast manifolds are extremely strong and durable and tubular manifolds (especially the cheap eBay ones) crack very easily due to the thickness of steel, quality of the steel, fluctuation of heat and vibrations.

It has always been a general rule with any exhaust manifolds / turbo manifolds that tuned length pipes will give you the most amount of power available from your manifold, a lot of tubular turbo manifolds will do this easily where as this really can’t be achieved on cast due to the thick and bulky design.

Custom Designed Manifolds can be made with tubular steel, so when your pressed for room in the engine bay you can always get tubular manifold fabricated to suit your application, this can’t exactly be done with cast iron material unless you know someone who has cast production factors and thousands of dollars of tooling at there dispense.

Customising an existing manifold can prove to be a challenge with cast material, trying to add a external wastegate port or or change your factory ct26 flange to T3 is quite expensive with cast, but is quite easy with tubular steel.

Now with boost the biggest killer is heat soak, so keeping those temperatures down in you engine bay is very important, a hot engine bay = hot piping = warmer air = less power = more detonation, cast manifold are relatively good at keeping in the heat and work even better with nice thick heat shield covering them also, this can be a pain in the muffler when you try to remove that manifold and all the studs / nuts have seized but that is why got created WD40. Tubular manifold look great in the engine bay and even better when covered in heat wrap but they tend to throw our a lot more heat than cast manifolds.

In reality it depends on your application and what you prefer, for me I tend to stick to cast for durability and less heat soak but if I needed a custom manifold I would use tubular if not flange adapters would suit, not to mention cast also looks stock so it doesn’t stand out in the engine bay to the 5 – 0 to pick on.

External wastegate sizing is a critical decision and from what I have read on forums people seem to think bigger is better and the more power you plan on running the bigger wastegate you need, wrong.

You see the idea of an external wastegate is not only for better control of your boost levels or a really cool sounding screamer pipe you cousin Ahmed welded up in his garden shed that will get you defected faster than you can hit boost! No, a really import function is to bypass the excess exhaust gas before it enters the turbine housing, and in order for the wastegate to do this efficiently you need to choose the right size wastegate.

The more boost you are running then the smaller the wastegate, because you want to run more boost less needs to bypass the turbine, and if you plan on running low boost then a bigger wastegate is required, use this simple guide below:

Small Turbo/High Boost = Smaller Wastegate
Small Turbo/Low Boost = Bigger Wastegate
Big Turbo/Low Boost = Bigger Wastegate
Big Turbo/High Boost = Smaller Wastegate

Now that you know how to choose a wastegate you can understand that just buying any wastegate is not a very smart move, work out you engine specs, turbo and boost level and depending on you goals choose wisely.