PTB (Part Throttle Boost)

[gudeman00]

Starting this thread for everyone who searches for PTB not knowing what it is and seeking answers.

Part throttle boost is when you're at say 1/4 or 1/2 throttle yet you are at full boost. This happens with an aftermarket WGA (wastegate actuator) or for those of you with a spring mod (like myself).

Eventually you will learn to drive around it, either staying under 5 psi at all times or full out wide open throttle. I personally HATE PTB.

So, I'll let you mechanically gifted ones answer the questions even better for those out there who have no idea on the subject, and need to learn.

Explain in more detail PTB.
How lean will the afr be while in PTB?
Can PTB damage anything?
Is it bad to spike extremely high if only for a moment?
How much will this shorten the life of the turbo/engine, if at all?

If you have something else to add, feel free to do so.

Hope this helps you guys who didn't know about PTB.

[jhempstead]

What the heck is part throttle boost? Oh wait, thats what you get with the itsy bitsy stock turbo! I remember that stuff! :jester: Yeah its bad for the engine and turbo. Try to keep it below 5 psi. You will eventually get used to driving around it. The reason ptb is bad is because the ecu is programmed to adjust the fuel and timing maps up to (but not exceeding!!!) 15%. So if you get full boost at 50% the ecu can't adjust as much as much as it needs to and runs lean. Extreme ptb also causes compressor surge, which is very hard on the turbo. Your boost gauge will "flutter" when it does this. Keeping the turbo on the stock lines can help get rid of ptb but your boost will not be consistent because the ecu will fight the wastegate. Will ptb blow up your car instantly? No. An extreme boost spike or ptb wont blow up your car the first time. Just don't do it all the time! Hope that helps! :thumb:

[gudeman00]

Bump for you guys who are online to completely answer this.

Just saw a thread on fluttering, made me think we need more answers in this thread about the problems with this little turbo.

[jhempstead]

Bump for you guys who are online to completely answer this.

Just saw a thread on fluttering, made me think we need more answers in this thread about the problems with this little turbo.


What else do you want to know?

[blackbird]

Combine a small turbo that builds boost extremely fast (which was done to reduce lag) and manually taking boost control away from the PCM. The NGC engine controller in the SRT-4 doesn't use tables/maps alone, but it still isn't expecting to see high boost at low rpm's, with low TPS voltages, etc. On the older turbo Dodge's you'd actually run leaner (and slightly quicker because of it) if you backed off the throttle and went closed loop at WOT.

If your boost spikes up really high it will probably go lean for a small fraction of time. Combined with the higher pressures you'll probably also get mild to moderate knock and the PCM, since it isn't and can't control boost, will retard timing to correct for that knock. Most of the time the computer can run the engine on the verge of knock but what we're talking about causes something of a bigger hiccup. Although relatively minor it does put more stress on engine components (especially bearings) when you get any knock/deto.

The fluttering is actually surge and isn't directly caused by having the throttle partially open. If you look at a compressor map that shows the characteristics of the compressor wheel and how it flows air, on the left side is the surge line. What you're doing is building a lot of boost and getting a high pressure ratio but aren't moving a lot of air. That causes the compressor wheel to stall out. Imagine the turbo spinning at north of 100k rpm's and instantaneously wanting to start and stop.

To summarize, going over the surge line is bad and lean spikes are bad. The extent you do either of these things and for how long will probably be what effects long-term reliability.

[boostin03]

i only get fluttering at WOT. its at about 17-18 psi and it flutters until it drops to about 15-16.

[warman]

PTB + fluttering sucks hardcore.. stay away from it.

[gudeman00]

What else do you want to know?

Me, nothing. I just wanted to get all of this out there for people who search for answers.

[Broken5hift]

the simple facts are, if you PTB your hurting your engine. its not safe. dont do it.

if you have a wga or spring mod, dont boost over 10 psi unless your WOT

[blackbird]

I just wanted to get all of this out there for people who search for answers.

People who use the search functionality?

:lol: Right…

:bs:

:rofl: :rofl: :rofl:

[gudeman00]

Alright, I put my MBC back in and have to adjust my driving to get used to it. I've hit the overboost code twice, once was in 4th gear at low rpm's just from not being used to it.
I just hit the CEL again on my way back from class, I was in 2nd gear staying right at 0 psi up until about 3k RPM and the code went off. Im not sure why it went off at 0 psi.....

Anyway, I have it set so it's at 16 psi when at WOT. I got into a little race with one of those newer :gay: eclipse's today and downshifted to second at probably 3k RPM and went WOT, it spiked to about 20 and then dropped back down to 16. So, obviously it won't overboost if I don't spike too high?

[gspeedaddict]

mine set at spike=16,hold=14 i threw a ob code,when i wasnt even boostin high

[boostin03]

i usually throw codes when i am not boostin really high (7-8) but i have never thrown a code when i run the hell outta it.

[gudeman00]

i usually throw codes when i am not boostin really high (7-8) but i have never thrown a code when i run the hell outta it.

Yeah, I try to stay at 0 or else I go WOT.

mine set at spike=16,hold=14 i threw a ob code,when i wasnt even boostin high

Yep, CEL comes on when boosting low. I just didn't understand how mine came on when I was at 0 psi at 3000 RPM

[newhaircut]

pffft, I love ptb! Nothing like WOT in 5th gear at 30mph!

[gudeman00]

Well I haven't had any problems but today I noticed my gauge is fluttering from 16-15. Only in that range. Why would it just start to happen today?