Over Boost?

[Dom]

Evening, All.

I recently fitted a PNM exhaust. Since then, I seem to be suffering from overboost as it’s like I hit a brick wall at full throttle and high revs. The CEL shows, then goes out. It didn’t happen before the new exhaust.

The car is well maintained and had a service very recently, including new plugs. I have done the waste gate waggle, too.

So, how do I overcome this problem?

Many thanks,

Dom

[par]

Definitely sounds like overboost which is apparently common when more free flowing exhaust is fitted. This is usually overcome by porting the wastegate, there is a link in WikiLEC which covers the details:-

wikilec.com/view/Porting_the_wastegate

The guide suggests porting to 20mm but I had mine increased to 21mm which solved the problem for me.

[rip]

This is not a design fault.
The wastegate would have been designed to control boost by opening/closing fully with the standard exhaust. Now you have increased the exhaust flow, the wastegate needs to be open more than 100%, which is impossible. The only way around it is to make it bigger by porting it.

I have read a lot of comments about "like brakes came on" / "like hitting a brick wall".
Even without looking at the boost gauge, you know when you are getting close to overboost. The car hesitates before the fuel cut kicks in, giving you plenty of time to lift off.

[Rambo]

Porting the wastegate should sort the problem of overboost as par and rip have stated

[Steve A]

If you search the forum this subject is well documented, even I've had it at one time due to messing with the exhaust,
porting was the answer, not a 5 minute job but if you want to go faster you have to pay the penalty

[V8vroom]

It’s trying to find someone somewhere who understands AND is willing to port it for you! 2 lotus experts near me deny the problem exists !

[Dom]

Thank you for your suggestions. Yes, I’ll have to get the wastegate ported, by all accounts. I don’t have the facilities to do it myself, so it’s a job for a garage. I’ve got Lakeside Engineering and Steve Williams near me, so I’m lucky in that respect. I’ve never used Steve Williams, but have heard good things.

[Steve A]

It's best done on a milling machine which any toolroom will have, just find a good one.