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85 Throttle body vacuum/Coolant port help

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Old 05-15-2018, 08:27 PM   #1  
Markever234
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Default 85 Throttle body vacuum/Coolant port help

So short story long... I wanted to upgrade my 85's throttle body.. just
because.. I bought a Summit racing model #SUM-228707. My stock TB has (on the passenger side) one upper port going to my passenger side valve cover and one lower port (IAC housing) going to heater core...
So I swap everything out.. and the new TB has 3 ports on the passenger side.. what the crap. what does the other port go to? So I began looking at other throttle bodies and they all seem to have 3 ports.. So maybe my 85 stocker is the odd ball out...Any help in clarifying what I need to do with this extra port would be greatly appreciated.

- Mark
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Old 05-15-2018, 10:03 PM   #2  
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Originally Posted by Markever234 View Post
So short story long... I wanted to upgrade my 85's throttle body.. just
because.. I bought a Summit racing model #SUM-228707. My stock TB has (on the passenger side) one upper port going to my passenger side valve cover and one lower port (IAC housing) going to heater core...
So I swap everything out.. and the new TB has 3 ports on the passenger side.. what the crap. what does the other port go to? So I began looking at other throttle bodies and they all seem to have 3 ports.. So maybe my 85 stocker is the odd ball out...Any help in clarifying what I need to do with this extra port would be greatly appreciated.

- Mark
What makes it an upgrade?

If they are vacuum ports, cap them off if you are not using.
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Old 05-15-2018, 11:19 PM   #3  
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What makes it an upgrade?

If they are vacuum ports, cap them off if you are not using.
An upgrade? hmm... its not 30 years old.. and thats probably about it. Its a twin 58mm, but there isnt really any mods done to the car yet to take advantage of the increased size. I'm planning long tubes and straight-piped 2.5inch exhaust. I might see a few horses then. Going back to the capping. I could be wrong but wouldnt capping(especially at the TB) increases turbulant air going into the runners thus reducing flow/HP?
You guys havent steered me wrong yet. Let me know!

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Old 05-15-2018, 11:40 PM   #4  
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An upgrade? hmm... its not 30 years old.. and thats probably about it. Its a twin 58mm, but there isnt really any mods done to the car yet to take advantage of the increased size. I'm planning long tubes and straight-piped 2.5inch exhaust. I might see a few horses then.

Going back to the capping. I could be wrong but wouldnt capping(especially at the TB) increases turbulant air going into the runners thus reducing flow/HP?
You guys havent steered me wrong yet. Let me know!
Seen an L98 go slower consistently with it at the track. Guy said it felt better but there it is. Put 58 on, slower. Stock, faster. I suspect the issue is isn't set up for the plenum so maybe it didn't work as well. Now if you are doing the intakes, I'd go for it. I have it on my Holley Stealth Ram and had it on my Superram but those were feeding 383 engines.

If you don't cap it, there will be a vacuum leak and that will cause problems. I doubt it will do anything bad if you cap it.
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Old 05-16-2018, 08:09 AM   #5  
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58 mm is too big for your stock 85.

52 mm is probably even too large.

Your best bet is too clean your stock TB (including the IAC housing) and reinstall.


Sell the 58 mm on ebay or CL; your preferred method or here in the For Sale section.
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Old 05-16-2018, 09:06 AM   #6  
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58 mm is too big for your stock 85.

52 mm is probably even too large.

Your best bet is too clean your stock TB (including the IAC housing) and reinstall.


Sell the 58 mm on ebay or CL; your preferred method or here in the For Sale section.
Kinda why I was wondering why it was an upgrade For my car, sure. His car? IDK depending on whether or not he is changing the intake and adding LT headers and maybe a cam?

Or if he just purchased it, return it
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Old 05-16-2018, 10:18 AM   #7  
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Kinda why I was wondering why it was an upgrade For my car, sure. His car? IDK depending on whether or not he is changing the intake and adding LT headers and maybe a cam?

Or if he just purchased it, return it
The stock TB is 700 - 750ish CFM, right? 6k rpm (higher than my or most other TPIs get) with a 383 can only suck down about 730, assuming everything is ported well. I had thought about getting a bigger TB, but the given the math and the cost, I decided against it. If you have a big cam, and 383+ cubes, then you might need it. But the stock TB will support plenty of power, I still run my stock one and I have no complaints about it.
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Old 05-16-2018, 03:53 PM   #8  
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The stock TB is 700 - 750ish CFM, right? 6k rpm (higher than my or most other TPIs get) with a 383 can only suck down about 730, assuming everything is ported well. I had thought about getting a bigger TB, but the given the math and the cost, I decided against it. If you have a big cam, and 383+ cubes, then you might need it. But the stock TB will support plenty of power, I still run my stock one and I have no complaints about it.
Absolutely. The 1000 cfm one CAN support more. Problem is it isn't going to help if the engine only uses 500 cfm. Also, IDK if that will cause turbulence as some have suggested.
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Old 05-17-2018, 01:20 PM   #9  
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Absolutely. The 1000 cfm one CAN support more. Problem is it isn't going to help if the engine only uses 500 cfm. Also, IDK if that will cause turbulence as some have suggested.
My brother understands fluid dynamics better than me, but we ran through the math, and having a larger than necessary throttle body will decrease air velocity, as well as introduce turbulence at WOT due to pockets of inconsistent air pressure. However, a bigger TB will feel faster, because your new 1/4 throttle is now much more air than before. You just top out at 3/4 throttle, and anything past that creates more turbulence.
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Old 05-17-2018, 02:17 PM   #10  
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My brother understands fluid dynamics better than me, but we ran through the math, and having a larger than necessary throttle body will decrease air velocity, as well as introduce turbulence at WOT due to pockets of inconsistent air pressure. However, a bigger TB will feel faster, because your new 1/4 throttle is now much more air than before. You just top out at 3/4 throttle, and anything past that creates more turbulence.
That makes sense. It ran slower at WOT.
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