I am thinking about replacing a S5 Turbo and exhaust manifold with my S4 turbo and exhaust manifold. Now I am having some questions about the difference between S4 and S5 turbo system. What's the difference for a S4 and a S5 factory turbo (the A/R raito and the size)?? Is the exhausd manifold designed dirrerently?? If 10 psi of boosts in a S4 turbo and 10 psi of boosts in a S5 turbo, which one will give me more torques and horse powers (my car is a 88 TII). Is it safe to run 10 psi of boosts in a 88 TII engine (I had hks fcd, f-cons, racing beat full exhaust, FD fuel pump already)Is it a good choice of basic turbo upgrade??
Thanxs

 

i believe its the same turbo (same a/r ratio and size) but the wastegate on the s5 is better and a little larger than than of the S4. concluding this, i have always thought that the turbo is the same. the only difference is the internal wastegates. (s5 one is better)

 

I'm a bit confused on your wording...

S5 turbo into your '88?

The turbos all are basically the same, so power levels won't change.&nbsp the Kouki turbo DOES make power a lot sooner than a Zenki turbo does - that's basically your advantage.


-Ted

 

The compressor size between the S4 and S5 turbos is the same. The exhaust is where the differences are. The S4 manifold is junk pure and simple. Basically the 2 exhaust ports dump into a poorly designed open manifold that has tons of power robbing turbulence. The turbo inlets from this manifold don't even line up well even after grinding on it for a while. The S4 exhaust housing is also smaller. It has a smaller a/r ratio and a smaller wastegate. The S5 exhaust manifold is much more refined. Each exhaust port from the engine stays seperated through the manifold and right into the turbo. No flow problems here. It is because of this that the turbo response is so much faster. The S5 exhaust a/r is bigger than the S4 and consequently flows more air. More flow equals more power.

Why would you want to go to the S4 instead of S5? No gains to be had here. You will lose performance.

If you had 2 engines with the same setup but one had the S4 turbo at 10 psi and the other had the S5 turbo at 10 psi, the S5 equipped engine will make a little more power. This is because of less exhaust back pressure. Less backpressure results in less manifold pressure to overcome the restriction. If you don't believe me run your car with and without a cat but leave the boost pressure the same. Which one has more power?