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www.KA-T.orgThese are the Prerequisites to building a DOHC Turbo. Together we will go through typical setups from mild to extreme to reach the power goals you desire. These are lists of typically used items that are easily attainable by the average person. All setups should have the Air to Fuel Ratio verified on a dyno with wideband or at very least on a track using an in-car wideband setup (NO watching the standard O2 signal and calling it good). If your using pump gas and seeing air to fuel ratios more lean than 11.8:1-12:1, some rethinking on the tuning/fuel setup will be needed. A narrowband guage(typical A/F guage from Autometer for instance) is not complex enough to be a real indication of the ratios inside your combustion chamber.
Very Mild Build: around 180 rwhp
Turbo Manifold
Blow Off Valve
Turbo (T25)
Downpipe 2.5" is perfectly fine
Pipe to connect turbo to throttle body
Fuel Control:
FMU (not recommended, but doable) Raises fuel pressure per boost to make injectors flow more than normal.
SR 370cc Injectors. These can be found at places found at the bottom)
Apexi SAFC2
Greddy Emanage
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Mild power adder, say you want around 200 rwhp.
Turbo Manifold
Blow Off Valve
Small Intercooler (potentially get away with a side mount)
Turbo T25/T28/14B, etc. Smaller T2 setups. Usually will be internally wastegated.
Downpipe 2.5" is perfectly fine
Replacing the Exhaust is starting to be very necessary at this stage, so I would start to shop for that as well.
Fuel Control
SR 370cc Injectors
Apexi SAFC2
Greddy Emanage
Back off base timing at distributor or MSD BTM
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Average: 300 rwhp to 350 rwhp, you have to start to expect a little more lag. This is about the perfect "street car" limit. No race gas, just good honest street car fun that is fully capable of bring home a 12 second timeslip on a good run.
Turbo Manifold
T3/T04E .50 Trim compressor, .60 trim compressor housing / Stg 3 (aka TA31) turbine wheel, .48 to .63 A/R exhaust housing. Internal wastegate optional but not recommended.
Downpipe can still be 2.5", but this is as far as I would want to push that.
Front Mount Intercooler (FMIC) It's time to upgrade to a larger front mount as the larger will push more air than the smaller sidemount can cool.
Fuel Control
550cc Injectors
SAFC2 to control your fuel injectors, along with the stock ecu.
MSD BTM At this stage I would be running the BTM to control timing retard.
Reflashed ECU-This can be a DIY thing with Megasquirt Tuning or a JWT.
Z32 Maf is required, as the stock Maf stops being able to read at around 260 rwhp.
Wideband O2 Sensor should be installed for tuning.
Block Internals
This is where I would start to consider it necessary to replace you pistons.
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Above Average: 350 rwhp to 425 rwhp
Turbo Manifold
Blow Off Valve
T3/T04E 50 Trim .48/.63 or slightly larger turbo, this is where I would start to make the switch up to an external wastegate. You have the option to reroute it back into the exhaust, or merely "dump" it out into the open. "Dump" is usually a mini exhaust in the form of 1.5" piping routed out to the open.
FMIC Larger is starting to be necessary. Typical for setups from here on, are 12"x24"x3" for the core.
Downpipe 3", at this point I would switch to the larger downpipe. You can probably get away with it at 2.5", but it will be causing a little bit of backpressure. Moving to 3" piping as quickly as possible is what you want though. Usually it is necessary to have the first bend 2.5" to clear the steering shaft though.
Exhaust 3"
Block Internals
At this stage you'll want to "build" or fortify your block to better handle boost. Previous to this you can walk the line, but here and forward I find it necessary to do so.
Forged Rods
Forged Pistons
Stock Crank
Plus your typical rebuild items.
Fuel Control
Standalone fuel management is recommended at this stage in the game and is absolutely necessary at the next. These allow you control not only very large injectors, but the tuner to have complete control over both timing and fuel.
720cc Injectors.
Wideband O2 Sensor is necessary for tuning.
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Wild Build: 425 rwhp to 600 rwhp. Lag is obviously going to be much more apparent, full boost isn't going to happen until around 4000-5000 rpms or so. Once spooled it will pull very hard.
Turbo Manifold
Turbo T3/T61/SC61 or GT35R seem to be the typical turbo's in the area. External Wastegate is your only option that should be considered.
Blow Off Valve You'll want a good performing more expensive blow off valve to alleviate reverted air when the throttle body closes from pushing against the compressor wheel.
FMIC the 24"x12"x3" Core's are still effective in this range.
Downpipe 3" is still capable of handling these power levels
Exhaust 3" or larger
Fuel Control
720cc-1600cc Injectors
Standalone Fuel Management
Recommeded to switch to Map instead of Maf for reading airflow.
Wideband 02 Sensor installed and wired into standalone for adjustments and monitoring.
Dyno tuning is very valuable.
Block Internals
Along with the previously mentioned internals I would add these to the list
Cams (per your discretion)
Build your head as well
Valve Springs
Valve Retainers
ARP Head/Main Studs
Cometic Headgasket or similar
Absolute turbo necessities...amongst the aforementioned goodies above.
Oil Lines
Fuel Pump:
The stock pump is decent but not intended for such use. For Walbro 255's being as cheap as they are, anyone turboing their vehicle should upgrade previous to turboing.
Boost gauge
