Drilling the throttle body for IAC/BLM?
Thread Starter
Launching!
Joined: Jan 2007
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From: Mooresville,NC
Drilling the throttle body for IAC/BLM? Alright guys I'm looking for some advice. I have an Edelbrock 52mm tb and have been chasing split BLM issues. Many are familiar with inserting the "tube" from the IAC area in the throttle body into the IAC opening in the front of the manifold to help direct the air. My edelbrock does not look like say a holley or other brands on the backside. It does not have the machined area between the two bores where you'd normally want to install the tube. It is flat with just the IAC hole that is about .400 diameter. I need to find out from anyone that has expierenced using a similar tb or someone that has been through this same issue to see what to do next. I've read some posts that say to drill a small hole straight through the tb. Does that mean I would drill a smaller hole through the IAC bores to "connect" the two IAC areas? I'm very unsure about taking a drill to something especially a thottle body before knowing exactly where to drill to and from. I know this might seem elementary but I need to know. Thanks for any help.
https://ls1tech.com/forums/lt1-lt4-modifications/1539122-s-drill-mod-pp-tb.html
Search for tb drill mod on this forum or even google and you can find more info. Before you drill you need to scan your car and find out what your IAC counts are. From what I've seen, everyones car is different when it comes to IAC counts. Most start with a 1/8" that I think is pretty close to stock. Scan after that. If it needs more, drill in small increments. Scan after each time you drill. Don't just blindly drill and expect results.
Search for tb drill mod on this forum or even google and you can find more info. Before you drill you need to scan your car and find out what your IAC counts are. From what I've seen, everyones car is different when it comes to IAC counts. Most start with a 1/8" that I think is pretty close to stock. Scan after that. If it needs more, drill in small increments. Scan after each time you drill. Don't just blindly drill and expect results.
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^^^^^^
stock hole is 1/8". if after scanning IAC counts and they are high (30-35 is good) drill the 1/8" hole and scan again. if still high drill 1/64" bigger and scan
1/64" makes a big difference so again scan before just drilling blindly
and before you do any drilling confirm TPS vdc are correct as they will be off if the "stop" screw on the TB blade has been messed with other than its stock setting
vdc wants to be approx. .67vdc closed and 4.5 vdc full open on TPS
stock TB's bored to 52 don't have the split BLM issues as aftermarket TB's do. On modified motors with H/C "sometimes" the stock hole needs to be enlarged 1/64" or more to get the IAC counts back down to 30-35 range....but again scan first for IAC counts before drilling anything
stock hole is 1/8". if after scanning IAC counts and they are high (30-35 is good) drill the 1/8" hole and scan again. if still high drill 1/64" bigger and scan
1/64" makes a big difference so again scan before just drilling blindly
and before you do any drilling confirm TPS vdc are correct as they will be off if the "stop" screw on the TB blade has been messed with other than its stock setting
vdc wants to be approx. .67vdc closed and 4.5 vdc full open on TPS
stock TB's bored to 52 don't have the split BLM issues as aftermarket TB's do. On modified motors with H/C "sometimes" the stock hole needs to be enlarged 1/64" or more to get the IAC counts back down to 30-35 range....but again scan first for IAC counts before drilling anything
Thread Starter
Launching!
Joined: Jan 2007
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From: Mooresville,NC
I did a scan and the IAC position ranges from 63-160. The 63 is warmed up in closed loop. The TPS volts are .57 throttle closed. My question is where do I drill the TB? I don't think drilling through the blades is the way to go. So am I drilling the existing IAC holes larger or adding a new hole somewhere else? If anyone had a picture that would help a ton. I will also get the stock tb and take a look at it.
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Launching!
Joined: Jan 2007
Posts: 233
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From: Mooresville,NC
Alright I have drilled a hole in the IAC passage area to the same size as the stocker. I logged to car with Datamaster and with the TPS volts at .53 the IAC counts were around 80-90 cold and 27-32 warmed up in park. Now for adressing the other issue of split BLMs I am still chasing that. I logged the car with the TPS at .53 and the throttle set screw set to nearly closed all the way. While slowing down to a stop the left side BLM is about 116 and right 124, but the minute I put it in park the left drops to 110ish and right rises to 124-127. I then tried to open the throttle set screw about a 1/2 turn putting the TPS voltage still in spec at .57 and the BLMs then changed to 113 left side and 129-131 right side in park. So that helped the left a little bit but is now leaning the right out more. Does anyone know how often the IAC passages being dirty or clogged in the intake manifold are the cause of this bad of a split? One thing I have not tried is inserting the brass tube in the back of the throttle body. I did not think it would help since my edelbrock is flat in that area and the IAC hole matches up to the manifold well. Any suggestions? Thanks guys.
Thread Starter
Launching!
Joined: Jan 2007
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From: Mooresville,NC
What tables/settings are used to adjust this? I am using TunerCat so I'm not sure which area to adjust. I am also not sure if going back to closing the blades as much as possible and maybe drilling the IAC through hole a bit larger would help?
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your split BLM's can be adjusted..by tuning....but they are never "EXACTLY" the same from side to side under all conditions.
someone qualified in tuning software may be able to elaborate on what you can do regarding adjusting BLM's
boring out a stock TB to 52 is more plug & play vs making adjustments physically to a aftermarket TB
Thread Starter
Launching!
Joined: Jan 2007
Posts: 233
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From: Mooresville,NC
I am actually working with someone on the tune. He is asking I make sure all the mechanical things are being taken care of first. That is why I'm trying to make sure the TB and IAC/TPS are all in functioning order. This person however is slow getting back to me with questions and reviews of my DataMaster logs. I am trying to be patient but I am putting in the work on my end so I would expect the same from him, especially since I have paid.