NA-T setup choice

Hi all,

I'm currently rebuilding my spare engine and looking for some advice on how to continue the build. First some specs and bits I already have collected.

Base engine specs:

2JZ-GE with TT pistons, new bearings and ARP bolts

GE cylinderhead with new stem seals, ARP studs and Brian Crower valve springs with Ti retainers

Toyota GE Engine Gasket Overhaul set

HKS adjustable camshaft pulleys and HKS timing belt

Whifbitz cambelt bracket, pulley set and idler pulley

New oil pump, water pump, cambelt tensioner and tensioner pulley

550cc RX7 injectors

Custom T4 tubular manifold

GReddy Emanage Ultimate

Major parts still to find/decide on:

Turbo, Intercooler, FFIM, AFR controller

My goal is to build a NA-T engine with a good engine response and as little as possible turbo lag. I'm going to use my W58 which is already fitted with a stage 3 DCA clutch kit. It should hold 486 Nm (359ft lbs) of torque so I will definitely not go near that number to minimise the risk breaking both the clutch and the gearbox.

Now I have the following options to choose from:

NA or TT headgasket, my question being simple, is the lower compression from the TT pistons going to be enough to achieve 400BHP without the risk of detonation? Knowing that the Whifbitz NA-T kit manages about 360 bhp on stock compression lets me to believe that only the pistons will be enough. I would rather not lower the compression any more than necessary because it would only make the engine less efficient.

The turbo, I've read so many contradicting stories everywhere that I would rather ask you guys what to choose. I can basically choose anything I want from all available Holset or Garrett parts/turbos. There is a turbo importer that lives about 5 minutes from my house and he still owes me a favor for helping him with a sale so he offered me a (custom) turbo at a good price .

I could either pick a smaller turbo with higher boost levels or bigger turbo with lower boost levels. The bigger turbo is obviously less stressed and said to be more efficient but may lack the low RPM torque and have more of an "on/off feeling" than a smaller turbo has. The airflow should be the same so the engine couldn't care less. With my current valvetrain my rev limit should be about 1000 RPM higher than stock so there is also the extra heat to be considered at the peaks during spirited driving.

The exhaust manifold, I currently have a custom undivided tubular style manifold which is extremely sturdy and should easily handle the power. However, a log style manifold helps clear the distributor cap and should help the turbo spool up better than a tubular one. Would the difference be noticable?

My personal choice would be the NA headgasket with a tubular manifold and a GT30 ball bearing turbo. But let me know what you think, all options are considered . And a picture with the car the engine once sat in:

NA or TT headgasket, my question being simple, is the lower compression from the TT pistons going to be enough to achieve 400BHP without the risk of detonation? Knowing that the Whifbitz NA-T kit manages about 360 bhp on stock compression lets me to believe that only the pistons will be enough. I would rather not lower the compression any more than necessary because it would only make the engine less efficient.

Yes easily, the Whifbitz kit with bigger than stock injectors should get to 400BHP on stock 10:1 compression without detonation (assuming that you have capable engine management) so you should have no problem with the 9.0:1 compresion that the stock headgasket with TT pistons gives.

I could either pick a smaller turbo with higher boost levels or bigger turbo with lower boost levels. The bigger turbo is obviously less stressed and said to be more efficient but may lack the low RPM torque and have more of an "on/off feeling" than a smaller turbo has. The airflow should be the same so the engine couldn't care less. With my current valvetrain my rev limit should be about 1000 RPM higher than stock so there is also the extra heat to be considered at the peaks during spirited driving.

There's a fundamental misconception here. Whilst it's basically true that the volume airflow will be more or less the same regardless of boost pressure, that's because the engine is an air pump and the volume airflow is a function of displacement, engine speed and efficiency, nothing to do with boost pressure. However it's the mass airflow that counts. Mass airflow is a function of volume airflow and density. Air density is a function of pressure and temperature. The higher the pressure the higher the density, conversely the higher the temperature the lower the density.

What you should choose is a turbo which is working as close to it's best efficiency as possible at the power target you are looking for. That way the turbo will transfer less heat to the intake air during the compression and you will end up with cooler (more dense) air going into the engine. It doesn't follow that a bigger turbo turning more slowly will be more efficient and you can see this by looking at any turbo map which will show that the peak efficiency is in the middle of the map.

The exhaust manifold, I currently have a custom undivided tubular style manifold which is extremely sturdy and should easily handle the power. However, a log style manifold helps clear the distributor cap and should help the turbo spool up better than a tubular one. Would the difference be noticable?

Yes the difference in spool time / lag would be noticable.

Yes easily, the Whifbitz kit with bigger than stock injectors should get to 400BHP on stock 10:1 compression without detonation (assuming that you have capable engine management) so you should have no problem with the 9.0:1 compresion that the stock headgasket with TT pistons gives.

 

 

 

There's a fundamental misconception here. Whilst it's basically true that the volume airflow will be more or less the same regardless of boost pressure, that's because the engine is an air pump and the volume airflow is a function of displacement, engine speed and efficiency, nothing to do with boost pressure. However it's the mass airflow that counts. Mass airflow is a function of volume airflow and density. Air density is a function of pressure and temperature. The higher the pressure the higher the density, conversely the higher the temperature the lower the density.

 

What you should choose is a turbo which is working as close to it's best efficiency as possible at the power target you are looking for. That way the turbo will transfer less heat to the intake air during the compression and you will end up with cooler (more dense) air going into the engine. It doesn't follow that a bigger turbo turning more slowly will be more efficient and you can see this by looking at any turbo map which will show that the peak efficiency is in the middle of the map.

 

 

 

Yes the difference in spool time / lag would be noticable.

Thanks, great info and very helpful. I couldn't really figure out the turbo maps before but it makes sense now.