After porting my headers today I have a small problem.

The car (MY98 WRX) used to produce 0.5 bar boost at 3500rpm and then full boost, 1.21bar, at 4000rpm.

It now seems to be more responsive at low rpm and a lot smoother. However, it seems to take longer to make full boost at WOT than it did before. If I floor it in 2nd from around 2000rpm it responds in the same way as it did before. But, if I hit WOT from cruising at 4000 in 4th it takes time to spool up again whereas before full boost would be almost instantaneous.

I have been wondering about the fact that my up-pipe is a 2.5” item and if this affects the spool up time. Would a smaller diameter up-pipe make for earlier/quicker spool up.

Any ideas?

There are no leaks and nothing else has changed.

This is my work

http://www.zen24039.zen.co.uk/Scooby...20WRX/Headers/

 

By fitting a larger diameter up-pipe the spool will be slower. The larger diameter up-pipe will cause the gas flow speed to reduce thus slowing the turbos spool but does help the mid-top end flow. The smaller diameter up-pipe will help the spool but does effect the mid-top end flow.

Cheers

 

Ok, further to my post above I have now found what the problem is/was.

Driving home tonight, air temp nice and cool, I get full boost at 3500rpm in 4th and 5th!!

I am thinking that during the day with a high air temp the boost comes on later. Not sure why though?

Any ideas?

 

Possibly down to ECU pulling timing to help combat det, and as a result the engine isn't producing as much power, so not as much gases to spin the turbo, etc...?