VF Throttle body

[vr304]

little hard to explain but pretty much dont touch the 0-25% area that is critical for idle and idle corrections, basically the cnc smooth sections are to be left and the rest can be ground down to smoothly meet up with the rest (dont polish just smooth), the humps can be taken back and i took most out top and bottom so what i done was sit it in zero point pushed back fully closed (use outside of blade points) and mark with pen then using throttle control percentage set it to 25% and marked it with pen (again outside point front side) and took out and smoothed back all areas outside the marked points, do not touch any less then that dont even smooth it off it is super sensitive if u take too much out TB is screwed and i know cos it cost me a TB and the LS2 ones arnt cheap, ill see if i can do some pics and mark out what i done so u can see

Thanks mate would be appreciated wouldn’t mind having a play with my L98 throttle body

 

[07GTS]

pretty much push blade back to zero and mark then same at about the 25% area on the front side it will be just where the cnc machined area has a slight change of angle

this is the good TB once finished i have used a red line to show where the factory machined smooth section is dont go into that area especially around the fully closed point

and i found some pics of the original before and after but not smoothed yet (before i went further and stuffed it)

 

[43lr155]

 

[Wayne001]

What difference does it make , do you have to muck around with the tune ?

 

[panhead]

i ended up porting my own LS2 throttle body, takes some time to do properly and u can stuff them pretty easily if u take any off in the wrong spots, but the gains are worth it for a stock TB

Ain't this the truth.

I did one on an L98 I had and what I thought was a fantastic job ended up having the car placed on a truck and taken to the shop to find I'd stuffed it.

I'd rather tear down and rebuilt a carbie then touch a throttle body, who'd have thought just a minor polish could cause such a problem.

By the way a good write up and warning tips.




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[abuch47]

Why does it cause such a problem? Surely 99% of the air still flows through.

 

[panhead]

Why does it cause such a problem? Surely 99% of the air still flows through.

I guess it’s a bit like tuning a carbie when you adjust the primary and secondary butterflies to allow for idle and smooth acceleration.

It only takes the butterflies to be moved the width of a bee’s dick to make a difference between running right and having idling and flat spot issues.

After polishing the throttle body the car wouldn’t idle and the computer went a bit mental trying to make up for it.

I was initially only cleaning the air filter for my OTRCAI and without thinking about what the impact may be I had the bright idea to remove the throttle body and give it a polish.

I used metal polish and took too much, I also moved the position of the blade which made things worse.

Live and learn.



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[07GTS]

yep that early 0-20% is machined for a reason for idle especially the ecu needs to know that if u idle at 10% and it has an error it then opens to 13% to correct it but if u change the airflow at 13% its now adding more airflow then predicted so it then over corrects and then it has to correct for the over correction also, cams surging up and down is a good example of incorrect correction and sometimes it dosnt have the ability to correct itself without precise changes to the idle tables, then think about the people that clean the TB and it idles at 1000rpm that is from even the small amount of dirt on the area which is almost not noticeable but its enough to affect the airflow which is also why the have the TB relearn procedure

 

[Wayne001]

What is a throttle body relearn procedure ?

 

[Skylarking]

yep that early 0-20% is machined for a reason for idle especially the ecu needs to know that if u idle at 10% and it has an error it then opens to 13% to correct it but if u change the airflow at 13% its now adding more airflow then predicted so it then over corrects and then it has to correct for the over correction also, cams surging up and down is a good example of incorrect correction and sometimes it dosnt have the ability to correct itself without precise changes to the idle tables, then think about the people that clean the TB and it idles at 1000rpm that is from even the small amount of dirt on the area which is almost not noticeable but its enough to affect the airflow which is also why the have the TB relearn procedure

All rather informative and I’m also interested in how TB relearn procedure works.
However doesn’t this also imply the system is rather sensitive to gumming up the idle and low throttle position settings due to oil in the inlet stream which in essence means GM should really have included a catch can as standard fit to avoid such issues rather than rely on a s/w relearn (or have I misunderstood the catch can plumbing)?