I have an 90 JDM engine turbo 5spd with a 3 inch downpipe from HKS but not the whole exhaust system. I thought a 7 would start with only a downpipe but nooooooooooo. I learned that it requires back pressure. So my question is this:

Since the car cant start, should I get a full 3 inch exhaust from HKS or a 3 inch exhaust from any company or go to a custom exhaust shop ?

Also what's the purpose of the check valve on the stock exhaust ?

And do I need to keep my original check valve and weld it to the new exhaust system ?

 

no thats not true the best thing for a turbo is no exhaust , you must have another issue wrong , i have a 90 jdm as well and all i have is a pipe going out the back of the front wheel of course its strictly racing

 

ohh also it being a jdm its not going to pass emmisions so you dont need that check valve, you might as well get rid of the air pump, air control valve,

 

you've got some other issues going on

whats the car do just crank?

 

Check your compression... Most Jspecs have been sitting in a junkyard for years at this point... A TII should have no problem at all starting and running without the downpipe, although I wouldn't recommend it unless you've covered your bases (fuel, timing, etc) as it will raise the boost by default...

 

I ran my car with just a bonez 2.5" downpipe and then put on the full 3" RB exhaust. The full RB exhaust had substantially higher performance.

 

Liv the car cranks but does not start. I found out that I need to change the ECU.

Even if the car is gonna run on a stock turbo there's no harm what so ever going to a full 3" exhaust ?

Also no one answered me what is the purpose for the check valve ?

 

Other than the boost creeping with the stock wastegate and potentially causing the engine to run lean there is no problem running a full 3" exhaust.

Why do you assume that you have to change the ECU? Have you exhausted every possibility first? eg. it's not just flooded?