ITG air filter

I bought a ITG maxogen air filter for my Mk2 111S land fitted it last week. When fitting it I noticed that there was a primary air filter above the wheel arch which then fed air into the secondary filter with the element. I removed both units and fitted the ITG filter as instructions found on a web site. I am very pleased with the noise but seem to have lost around 4 mph off the top end. Can anyone advise me why this might be? Also I am planning to fit the Janspeed Motorsport Cat combined with a Larini back box. Has anyone changed there cat and backbox with good improvments? Is there much point to change the manifold as I can’t see how this would restrict the exhaust gas from exiting the engine, nad at around �400 its quite expensive!

Anyones engineering experience would be greatly appreciated.

I have no idea on the S2 111S, but didn’t the first air filter pick up cold air (like from the outside?) and the ITG one picks up air from the engine bay?

If so, it could be the effect of the hot air (I have seen some of these conversions picking hot air from the engine bay). In that case, I would say the original setup was better.

Just my 2p without having seen your setup.


like Uldis says… is it breathing hot air? if not already routed… you need to route cool air from the LH duct to an airbox to stop hot engine-bay air getting drawn in.

If you already have this it may be that the ITG is more efficient and so its running a little lean at full throttle??.. if its a standard ECU then maybe it will relearn ?? DOes anyone know if the VVC ECU does any learning?? if its a mappable ECU then you need to tweek the maps (i doubt this is the case tho ?? and you probably have the standard VVC ECu ??)

Cheers for the replies guys.

The ITG air filter has its ducting that takes its cold air from the scoops behind the door on the passenger side. The previous filters didn’t have ducting like this and this is why I can’t understand why performance is a little off at the top end. On PTP’s website the ITG that they fitted and had tested independently showed a drop off of a few bhp at the top end at 6000 rpm, maybe this is the problem?

Anyone changed their catalyst for the motorsport one and backbox for the Janspeed or Larini?

…and backbox for the Janspeed or Larini?

Larini is not yet available. There’s a queue forming!


Like Rox says, it may be lean. If it’s pulling colder air (denser) the ECU could not be compensating.
If I was you and didn’t have a programmable ECU I would modify slightly the fuel pressure regulator to give some extra fuel, with the risk of having it rich elsewhere (but normally they’re lean everywhere so this could compensate)

Hint on how to do that here

Thanks again for the advice from all and the for the link Uldis.

Not quite sure how exactly to modify the fuel pressure regulator, seems a bit tricky might let a professional have a dabble.

Shame about the Larini backbox will put my name down and join the queue.


Spoke to Larini last night. They are doing back box’s now and I should have mine in 4 weeks. They are also going to do CAT’s and they may be ready in 5 weeks if you want one. They said around �290 for the CAT. Get yours when you can!