Tech question about throttle plates
Thread Starter
Racer
Joined: Oct 2011
Posts: 417
Likes: 2
From: Blacksburg Virginia
Tech question about throttle plates
I bored out my throttle bodies on my 84 to 2". And I bought a set of 2" throttle plates.
The problem is that I think the fit is an interference fit. When the plates are fully closed they are not perpendicular to the tb. They stop just before that and feel like they want to bind.
How much gap should be around the throttle body plates, if any?
I cannot get my idle set correctly because the plates don't seem to be fully closed.
Can I just order a 49 mm throttle plate instead of the 50.8mm one I have?
The problem is that I think the fit is an interference fit. When the plates are fully closed they are not perpendicular to the tb. They stop just before that and feel like they want to bind.
How much gap should be around the throttle body plates, if any?
I cannot get my idle set correctly because the plates don't seem to be fully closed.
Can I just order a 49 mm throttle plate instead of the 50.8mm one I have?
Le Mans Master
Joined: Nov 2009
Posts: 6,882
Likes: 234
From: Bangkok, Thailand
A 49mm plate would leave too much of a gap and you'd have a very hi idle.
Did you measure the gap (difference between the stock bore and stock throttle blade before getting it bored?
Did you measure the gap (difference between the stock bore and stock throttle blade before getting it bored?
Thread Starter
Racer
Joined: Oct 2011
Posts: 417
Likes: 2
From: Blacksburg Virginia
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
I bored out my throttle bodies on my 84 to 2". And I bought a set of 2" throttle plates.
The problem is that I think the fit is an interference fit. When the plates are fully closed they are not perpendicular to the tb. They stop just before that and feel like they want to bind.
How much gap should be around the throttle body plates, if any?
I cannot get my idle set correctly because the plates don't seem to be fully closed.
The problem is that I think the fit is an interference fit. When the plates are fully closed they are not perpendicular to the tb. They stop just before that and feel like they want to bind.
How much gap should be around the throttle body plates, if any?
I cannot get my idle set correctly because the plates don't seem to be fully closed.
As for "gap spec"...there is a spec for inches of water in each TB's ported vacuum port, but I set mine like this;
I adjusted my linkage so that both TB's were fully closed (binding) at the same time, and as I open the throttle, they "unbind" at the sime time. Now I know my throttles are in damn near perfect SYNCH. Then I block off the IAC ports, start the car, and adjust the "minimum air" adjustment (AKA "throttle stop") to 400 RPM. Unplug IAC ports, adjust your TPS and your throttles should be synched and set.
Thread Starter
Racer
Joined: Oct 2011
Posts: 417
Likes: 2
From: Blacksburg Virginia
I can't get the idle adjusted low enough. That's why I was thinking the plate is too big.
I was following the service manual to balance the two tbs but I can't get my idle very low.
I was following the service manual to balance the two tbs but I can't get my idle very low.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Following the FSM on a bored TB isn't likely going to work; the FSM is looking for a specific vacuum reading at the edge of the throttle blade/bore wall. You can get achieve that reading, but your bore is bigger than stock now, and consequently, so is the AREA revealed by the partially opened throttles. IOW's at the same throttle angle, they are flowing more air.* The FSM procedure won't work now.
Feed it what it wants. Get the throttles synched w/one another, then adjust the main throttle stop to get the idle right.
*This is the reason most people think bigger TB's give "more power"; b/c less throttle angle (pedal movement) flows more air. So, the effect is better throttle response -but not necessarily more total power.
Feed it what it wants. Get the throttles synched w/one another, then adjust the main throttle stop to get the idle right.
*This is the reason most people think bigger TB's give "more power"; b/c less throttle angle (pedal movement) flows more air. So, the effect is better throttle response -but not necessarily more total power.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Maybe. But he admitted that he's using the FSM method...which as I stated, won't work right, now.
I'ts certainly possible that the throttle plates aren't aligned with the bores...we don't know how the installer installed them. IF the throttle plate is binding in one place and not touching in another place, the way that I "fixed" that was to simply loosen the throttle plate screws a tad, let the throttle places "self align" when closed, then tighten the screws with the throttles closed.
I'ts certainly possible that the throttle plates aren't aligned with the bores...we don't know how the installer installed them. IF the throttle plate is binding in one place and not touching in another place, the way that I "fixed" that was to simply loosen the throttle plate screws a tad, let the throttle places "self align" when closed, then tighten the screws with the throttles closed.
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Thread Starter
Racer
Joined: Oct 2011
Posts: 417
Likes: 2
From: Blacksburg Virginia
I do think they are binding early. Which is why I can't adjust the idle down. I'll try reseating then tonight.
If that doesn't work should I make the plates smaller or the bores bigger.
If that doesn't work should I make the plates smaller or the bores bigger.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
I don't know. If the bores are ROUND...then the plates should work if aligned properly. I guess if trying to align them doesn't work, you could shine a light through them, where the light doesn't come through, hand-file those areas until they seat uniformly.
Thread Starter
Racer
Joined: Oct 2011
Posts: 417
Likes: 2
From: Blacksburg Virginia
when the plates are fully closed....should they be 90° perpendicular to the bore of the TB?
Or do they "seal" a little earlier than that? I have seen where the plates themselves have the edges beveled by 5-15° so they seal up before they get to the full perpendicular position.
Or do they "seal" a little earlier than that? I have seen where the plates themselves have the edges beveled by 5-15° so they seal up before they get to the full perpendicular position.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
They should not be 90* to the bore...they should seal at a slight angle...maybe 5* of so? Therefore, the throttle plate SHOULD be oval in shape.
I too, have seen beveled edges on throttle plates.
I too, have seen beveled edges on throttle plates.
Burning Brakes
Joined: Feb 2013
Posts: 1,173
Likes: 152
From: norway
take a bit of sanding paper , and use this to fit the plates in the hole !!http://forums.corvetteforum.com/memb...ire-31877.html this is mine , on the car and runs perfekt !
Burning Brakes
Joined: Feb 2013
Posts: 1,173
Likes: 152
From: norway
put small pices of sanding paper between plates and the bodies (push down with a finger on the plate) . and pull the paper upp ( or down ) this will take some time to do but the plates will fit ! use light to se the fit !
Thread Starter
Racer
Joined: Oct 2011
Posts: 417
Likes: 2
From: Blacksburg Virginia
take a bit of sanding paper , and use this to fit the plates in the hole !!http://forums.corvetteforum.com/memb...ire-31877.html this is mine , on the car and runs perfekt !
Nice pictures...
you wouldn't have a picture of the plate in the "closed" position with the vacuum hole showing? That way I could see the relative position of the top of the plate to the hole.
Burning Brakes
Joined: Feb 2013
Posts: 1,173
Likes: 152
From: norway
Burning Brakes
Joined: Feb 2013
Posts: 1,173
Likes: 152
From: norway
orginal plates are 46.97 mm long and 45.91 mm wide = 1.023 % !!!!!! i bored mine to ca 50,28 mm and used 2" plates ( 50.80 mm ) = 1.023% off ! then you will get the right angle !!! race on !!!!!!!!!!!!!
Thread Starter
Racer
Joined: Oct 2011
Posts: 417
Likes: 2
From: Blacksburg Virginia
I think my front plate was in a bind too early. I loosened both and reseated them....also backed off the back tb stop so that the plates would fully close. Then I adjusted the front balance set screw to get them in the same place.
Tomorrow ill fire it up and check again with engine running and use the rear stop screw to set idle.
Tomorrow ill fire it up and check again with engine running and use the rear stop screw to set idle.