EvoIII boost creep questions...

[Import2nr99]

Sorry to bring this up again. But I've searched through the forum and also looked at the write up on POSR and all it served to do was confuse the hell out of me. The examples on kevins site were all from his 14b problems. and... I believe it was soyee who just installed an evo and he had problems with boost creep. some people's explanation was the 3" exhaust was causing it, but never really gave a remedy to the problem. Joewagon said that porting out the O2 and maybe the mani would solve it. is this true? and would I be ok just porting the O2 or do I need to match port the manifold also? would it be easier to just buy a new higher flowing O2 or will porting out the stock one be fine? also where can I send it and how much will it cost? I don't know of anyone around here who is really good with machine tech stuff. I could probably take it up to school (penn state) and have someone in the automotive section do it for me. but I'm not sure if I'd feel safe doing that. does that sound like a good idea? it would only cost me 7 bucks. any suggestions and information (such as a descriptions for retards like me on what BC is exactly) are greatly appreciated. I don't want to run into any major problems or have to take things apart once they're finally together.

Also, (I believe my setup can definitely handle it) would running a higher daily boost settting such as 19 psi or so help with this problem? I believe that was mentioned also. plus, with stock internals and compression, am I going to have any trouble running 20+ psi? I was talking to my friend who owns the shop and he suggested running a lower compression ratio for such a high boost setup. Thanks for any input and sorry for the mass of questions.

[JoeWagon]

You realize the problem, right? In order to control boost, the wastegate must divert the exhaust gas AWAY from the turbine, so that it doesn't keep building boost. Boost creep is not being able to expel enough exhaust from the turbine.. so it keeps building boost. It ONLY happens when you try to run low boost on a bigger turbo. If you set your boost controller to 20psi, the wastegate wouldn't need to be very big (or ported). The only reason to have a big wastegate, is to set low boost on a big turbo, which I don't think is necessary. You could run a 50 trim on the smallest Tial wastegate, but not as low as 15psi.

If you decide that there is a reason to run low psi on your 16g (under 20), you can solve boost creep by getting the larger wastegate flapper, which lets more exhaust bypass the turbine. You can also get some porting done, but I'm not sure what exactly get's ported. I think it's around the wastegate exit, and o2 housing... but not the manifold.

You could try 19 or 20 psi to get rid of the creep, but I would tune up to 24-26. Is there any reason not to?

Is your friend very DSM conscious? On a honda you would lower the compression, but there is hardly a need to on a DSM.

[kjewer1]

In most cases the wastegate exit area is the real culprit, not the O2 housing. But a local member with an EVO16g said he installed a tubular O2 housing (internal dump) and got rid of his creep. I guess his creep went up to about 23 psi. So you would have to set boost to 23 psi in order to not "see" the creep in his case. Thats kinda high. Porting is cheaper than parts though. I would do the porting I describe in my boost creep writeup (there is a vfaq with pics btw) to the WG exit and O2 housing and see where you boost is. Try to avoid the larger internal flapper mod.

Turning up the boost doesnt get rid of the creep, it just puts you over the minumum boost you can run so it doest rise higher than your set point. IF you creep to 18 psi, but set boost at 19 psi, you'll never see the boost creep. Makes sense right

Even small wastegates can control boost very well if they are setup properly. My Deltagate (32mm, lol) mounted so it vents all 4 runners would hold my 56 trim GT3040 at 13 psi. I would go lower, but thats what the spring pressure is. The same gate mounted in an O2 housing type setup may not go that low. Its all about flow. And venting all 4 runners is the key. Chads setup vents all 4 as well and will hold his 9 psi spring pressure to redline on a 60-1. (my setup is still for sale btw, I'm parting the turbo "kit" out).

You will be fine your stock motor with whatever the EVO 16g will run. How much boost you cna get away with without knock on pump though will depend on intercooling. With a good FMIC, you should be able to run over 20 psi daily with no knock. Its all in the tuning as well...