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Modified Spacer For Improved TBI Idle

2K views 11 replies 7 participants last post by  Rowdy 
#1 ·
In trying to improve my idle on my FiTech TBI I recently removed my 1" composite spacer and reinstalled an old 1/2" spacer with the middle chopped out to see if it would improve the idle. It seemed to help but jacked up the throttle response a bit. So I had the CNC guy at work take out a 2" diameter by 3/8" chunk out of the divider of my 1" spacer to hopefully regain the throttle response. Now I'm wondering if I should install it with the opening toward the TBI or manifold? The manifold is a dual plane Performer 289 that is way too small for the motor but is working for me at this time as I learn auto crossing. I think I spin out less with the corked intake and exhaust limiting the power!

No wrong answers.
 

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#2 ·
Easy enough to try it both ways - but I would install it with the new open area down. You don't want the air/fuel mixture coming out of the bottom of the TBI unit, crossing over the open area and smacking into the spacer (giving fuel a place to puddle), disrupting flow.
 
#3 ·
Originally I was thinking opening up, but when I got the spacer back from the CNC guy and saw that big flat spot I starting thinking opening down.

Thanks for the reply!
 
#4 ·
Opening down, it will create a low pressure area that should make it easier to draw from the other bank. It will be a high pressure area mounted facing up making transfer more disorderly through the milled section than drawn if it happens at all. I could be wrong though; try it both ways.

Good luck and let us know what you find!
 
#5 ·
Nailbender, I'm also running a fitech unit and while I'm certainly no expert, I've learned a couple of things. When you changed the spacer plate, did you reset the fitech's learning? If not then its still trying to run the settings its learned with the other plate. If you did and still have problems with throttle response, there are settings that can be changed in the handheld to improve throttle response. There are a plethora of videos on YouTube that go through what you can adjust in the handheld.
Finally, when your engine is warm check the handheld and be sure that your IAC steps are between 3 and 10. If they aren't, you may have to turn the IAC adjustment screw on the throttle body. If you do need to turn it, tiny adjustments are usually all that's needed.
 
#6 ·
Interesting! Are you doing this for idle quality? or something else? Looking forward to hearing what you think of it.

I've tried the open spacers 1/2 and 1/4in on my sniper with the dual plane (performer RPM) and saw little change. someone else said to try a 4 hole, I just swapped to a single plane and didn't try it. Probably should have. I've also seen a few cut down a little bit like yours. I know cutting down the plenum divider in some cases has also shown improvements, but I'm not there yet.

I've got a Torker II on the car and its crap. Huge loss of grunt down low. Although idle is decent. I'm now looking for an air gap, f4b or maybe if I can, one of the buddy bar or shelby intakes to keep that 'period' look the engine has. I've ditched the stock air cleaner (giant gold one) for the hipo style so I have a bit of room to play with...
 
#7 ·
I'm trying to improve the idle on the cheap for now. I'm actually waiting for you to find a manifold that works for you since our cars are so similar. Thanks Rowdy!

I installed the spacer hole down yesterday and went for a long drive without resetting the FiTech and it seemed to help on idle, but I have a stumble off idle when I stab the gas like I'm starting an autocross run. I'm going to reset the TBI and go for a drive today as suggested by New2me if it stops raining and drys out.

I saw this spacer on Summits home page today while logging in. Sometimes I just don't realize how smart I am!:grin2:
https://www.summitracing.com/parts/hvh-st4150-4al/overview/
 

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#9 ·
Slightly unrelated, but I have a 2" 4 hole phenolic and F4B under a 1406 and have wanted to try an under cut spacer like you've done , not so much for idle which is fine but for a better mix at higher rpm. I see many suggest to cut the diveder on the F4B for the same reason
 
#11 ·
So after putting some miles and a autocross on my modified spacer I found that while it improved the idle it had a significant bog or hesitation that the FiTechs self learning was never able to overcome. So off it came this week replaced with a aluminum 4 hole Mr Gasket 1" spacer. Reset the FiTech and the bog is gone and it seems to be idling pretty good.

It was an experiment that didn't work out for me. When I swap the Performer 289 for a Performer RPM I don't think I'll be cutting down the plenum divider.
 
#12 ·
I shoved an OPEN 1/2in phenolic for known top of the Torker II. I noticed a slight idle quality change and it puts the throttle linkage at at better angle. I now have 85% instead of 76 or so.

Still hunting for a dual plane and I'll do as you and run the 4 hole 1in.
 
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