This page details the installation of the disco potatoe AKA gt28rs

The disco potatoe uses a 53.8 mm turbine wheel in a .63 a/R turbine housing. The turbo housing is extermely huge and comes with a T3 inlet and 4 bolt t3 dowpipe outlet.

It can therefore be mounted on to a standard T3 manifold.. The compressor side is a 60 A/R housing with a 62 trim wheel which is more than adequate for a 1300 cc engine.

The compressor side can be upgraded if necessary by using the compressor wheel and housing from the gt2871r.

You will need a number of fittings to adequately install the turbo.

An oil return gasket along with the tube  

To keep the turbo cool a some water fittings with 3/8 barbs are reuired.

An oil feed line is then required with a restriction to reduced oil flow to the turbo as ball bearing turbos require less fuel.

For peace of mind always use 1/2 inch stainless steel flanges which are tapped.

Use these flanges along with the T3 inlet gasket below and you won't have any worries for a long time.

The oil inlet must be a -4an oil inlet fitting.

I have included the compressor map for the gt28rs below.

Performance of the Disco Potatoe

This turbo is a very big turbo for a 1300cc engine.. Never the less it really frees up the exhaust to the point that the reduced back pressure results in lower EGT. The EGTs drop by as much as 100f.

The .63 housing flows so freely that a silencer is now required to muffle the noise from the engine. The engine sounds and behaves like a supercharged engine. Full boost comes in at abut 5300 rpm and it comes on with a noticeably bang. You will notice that the boost rises rapidly with RPM especially at high RPM. Although the boost comes in late the car pulls from very low RPM (due to the low back pressure)  and continues pulling stronger and stronger at high RPM. Sometimes wheel spin can be realized in second at high RPM.

The only comparison I have at the moment is the gt25r which I have seen with full boost of 10psi at 4000rpm..The performance of the turbo is extremely different in that first and second gear is extremely strong and third is a lacking. However, more boost should remedy this problem.

The other comparison is the gt28r which was rumored to have full boost at 4700 to 4800. This needs to be confrimed.

The disco is the best bet especially if further upgrades will be considered...

This is the performance of the turbo in the quarter mile with too much wheel spin if first.I am still struggling to get the gtech pro programmed correctly to match engine rpm...

Note the 0-60 time is greater due to wheel spin. A bit of practice should get this into the sixes or high fives...

N/A cars: As most of you know, the design of turbo exhaust systems runs counter to exhaust design for n/a vehicles. N/A cars utilize exhaust velocity (not backpressure) in the collector to aid in scavenging other cylinders during the blowdown process. It just so happens that to get the appropriate velocity, you have to squeeze down the diameter of the discharge of the collector (aka the exhaust), which also induces backpressure. The backpressure is an undesirable byproduct of the desire to have a certain degree of exhaust velocity. Go too big, and you lose velocity and its associated beneficial scavenging effect. Too small and the backpressure skyrockets, more than offsetting any gain made by scavenging. There is a happy medium here.

For turbo cars, you throw all that out the window. You want the exhaust velocity to be high upstream of the turbine (i.e. in the header). You'll notice that primaries of turbo headers are smaller diameter than those of an n/a car of two-thirds the horsepower. The idea is to get the exhaust velocity up quickly, to get the turbo spooling as early as possible. Here, getting the boost up early is a much more effective way to torque than playing with tuned primary lengths and scavenging. The scavenging effects are small compared to what you'd get if you just got boost sooner instead. You have a turbo; you want boost. Just don't go so small on the header's primary diameter that you choke off the high end. .

Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure..

Again, less pressure downstream of the turbine is goodness. This approach minimizes the time-to-boost (maximizes boost response) and will improve engine VE throughout the rev range..

As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side..

"As for the geometry of the exhaust at the turbine discharge, the most optimal configuration would be a gradual increase in diameter from the turbine's exducer to the desired exhaust diameter-- via a straight conical diffuser of 7-12° included angle (to minimize flow separation and skin friction losses) mounted right at the turbine discharge. Many turbochargers found in diesels have this diffuser section cast right into the turbine housing. A hyperbolic increase in diameter (like a trumpet snorkus) is theoretically ideal but I've never seen one in use (and doubt it would be measurably superior to a straight diffuser). The wastegate flow would be via a completely divorced (separated from the main turbine discharge flow) dumptube. Due the realities of packaging, cost, and emissions compliance this config is rarely possible on street cars. You will, however, see this type of layout on dedicated race vehicles..

A large "bellmouth" config which combines the turbine discharge and wastegate flow (without a divider between the two) is certainly better than the compromised stock routing, but not as effective as the above..

If an integrated exhaust (non-divorced wastegate flow) is required, keep the wastegate flow separate from the main turbine discharge flow for ~12-18" before reintroducing it. This will minimize the impact on turbine efficiency-- the introduction of the wastegate flow disrupts the flow field of the main turbine discharge flow. .

Necking the exhaust down to a suboptimal diameter is never a good idea, but if it is necessary, doing it further downstream is better than doing it close to the turbine discharge since it will minimize the exhaust's contribution to backpressure. Better yet: don't neck down the exhaust at all..

Also, the temperature of the exhaust coming out of a cat is higher than the inlet temperature, due to the exothermic oxidation of unburned hydrocarbons in the cat. So the total heat loss (and density increase) of the gases as it travels down the exhaust is not as prominent as it seems..

Another thing to keep in mind is that cylinder scavenging takes place where the flows from separate cylinders merge (i.e. in the collector). There is no such thing as cylinder scavenging downstream of the turbine, and hence, no reason to desire high exhaust velocity here. You will only introduce unwanted backpressure. .

Other things you can do (in addition to choosing an appropriate diameter) to minimize exhaust backpressure in a turboback exhaust are: avoid crush-bent tubes (use mandrel bends); avoid tight-radius turns (keep it as straight as possible); avoid step changes in diameter; avoid "cheated" radii (cuts that are non-perpendicular); use a high flow cat; use a straight-thru perforated core muffler... etc..

"Comparing the two bellmouth designs, I've never seen either one so I can only speculate. But based on your description, and assuming neither of them have a divider wall/tongue between the turbine discharge and wg dump, I'd venture that you'd be hard pressed to measure a difference between the two. The more gradual taper intuitively appears more desirable, but it's likely that it's beyond the point of diminishing returns. Either one sounds like it will improve the wastegate's discharge coefficient over the stock config, which will constitute the single biggest difference. This will allow more control over boost creep. Neither is as optimal as the divorced wastegate flow arrangement, however.

There's more to it, though-- if a larger bellmouth is excessively large right at the turbine discharge (a large step diameter increase), there will be an unrecoverable dump loss that will contribute to backpressure. This is why a gradual increase in diameter, like the conical diffuser mentioned earlier, is desirable at the turbine discharge..

As for primary lengths on turbo headers, it is advantageous to use equal-length primaries to time the arrival of the pulses at the turbine equally and to keep cylinder reversion balanced across all cylinders. This will improve boost response and the engine's VE. Equal-length is often difficult to achieve due to tight packaging, fabrication difficulty, and the desire to have runners of the shortest possible length.” "Here's a worked example (simplified) of how larger exhausts help turbo cars.

Say you have a turbo operating at a turbine pressure ratio (aka expansion ratio) of 1.8:1. You have a small turboback exhaust that contributes, say, 10 psig backpressure at the turbine discharge at redline. The total backpressure seen by the engine (upstream of the turbine) in this case is:.

(14.5 +10)*1.8 = 44.1 psia = 29.6 psig total backpressure.

So here, the turbine contributed 19.6 psig of backpressure to the total. Now you slap on a proper low-backpressure, big turboback exhaust. Same turbo, same boost, etc. You measure 3 psig backpressure at the turbine discharge. In this case the engine sees just 17 psig total backpressure! And the turbine's contribution to the total backpressure is reduced to 14 psig (note: this is 5.6 psig lower than its contribution in the "small turboback" case). .

So in the end, the engine saw a reduction in backpressure of 12.6 psig when you swapped turbobacks in this example. This reduction in backpressure is where all the engine's VE gains come from.

This is why larger exhausts make such big gains on nearly all stock turbo cars-- the turbine compounds the downstream backpressure via its expansion ratio. This is also why bigger turbos make more power at a given boost level-- they improve engine VE by operating at lower turbine expansion ratios for a given boost level.

As you can see, the backpressure penalty of running a too-small exhaust (like 2.5" for 350 hp) will vary depending on the match. At a given power level, a smaller turbo will generally be operating at a higher turbine pressure ratio and so will actually make the engine more sensitive to the backpressure downstream of the turbine than a larger turbine/turbo would. As for output temperatures, I'm not sure I understand the question. Are you referring to compressor outlet temperatures?".

The car feels like a normally aspirated car. it pulls strong off boost and as boost comes in it pulls stronger and stronger. The power is delivered exponentially .I have encountered wheel spin even though the car has already been moving at reasonable speed.The performance will now be estimated using a Gtech pro.

The turbo runs 3rd gear to 7000rpm on the test hill.This is with a lazy move off and easy 1st to second change and part throttling up the hill to keep boost under 15psi

The .63 A/R t3 housing option is actually equivalent to a .86 A/r t25 housing. This explains why it appears so large. ATP turbo has A .48 A/R t3 housing which would be ideal.This option would be equivalent to the .63 T25 housing. This would drop the boost response to full boost in third gear in the low 4000rpm.Note that top end horse power will be traded for boost response.

This is the boost response to 4000rpm in third. This is made possible by a extrenall wastegate with a strong spring. The same can be had by a Electronic boost controller.9 psi by 4000rpm. A smaller A?R would promote tronger boost in the lower gears.