millenniumtree
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posted on 16/7/06 at 04:04 PM |
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Restrictor Butterfly in '89 Civic
I have a 1.5L, 1989 Honda Civic, Fuel injection.
In the throttle body, there are two butterflies, mounted inline - The one on top is usually closed, leaving about a 1/2 inch wide notched hole for the
air to flow through. It only opens when the revs get above a certain point, but even then it doesn't open much! The main throttle butterfly is
underneath that, and will open all the way (inline with air flow)
For a bit of free power, I decided to remove or make my own butterfly plate out of an old cookie pan.
I did try revving the engine WITHOUT the plate, and it was a bit scary. The revs increased a bit quicker, and it sounded nice and angry, but I was
afraid of sacrificing reliability (blowing the engine up). I don't think these engines have rev limiters.
I layed the old plate on the pan, scribed around it, then cut it out with a snips, drilled the screw holes, and it fits!
I then modified the new plate by making the notch a bit bigger (maybe twice the airflow) I took it out for a drive and did notice a bit of a
performance increase at the top end.
My concerns are twofold:
1) Will this modification effect the max RPMs - if I stomp on the gas accidentally in neutral, will I blow up the motor?
2) Will this lead to an overly lean fuel mixture, as the stock injectors can't keep up?
I previously, occasionaly got a check engine light from the ECU (two or three times a year, always when on the highway) It's the code for
air/oxygen problem, so it may be a lean fuel mixture or a dying oxygen sensor.
Thoughts? Comments? Want pictures?
[Edited on 18/7/06 by millenniumtree]
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andyharding
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posted on 16/7/06 at 04:13 PM |
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Are you a Mac user or a retard?
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ruudbeckers
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posted on 16/7/06 at 08:26 PM |
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I have had a '93 Civic with a 1.5 DXI engine, which is similar to your engine, and it had a rev limiter at 6300 rpm.
Some pictures of before and after are always nice.
Cheers, Ruud
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millenniumtree
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posted on 17/7/06 at 01:18 AM |
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Maybe "Thought the engine was going to blow up" was an exxageration. I had certainly never heard it rev that quickly, but it didn't
seem like it was over-revving at all.
Here are the pictures. The silver one is the new plate, cut slightly smaller on the 'notch' end for a bit more airflow.
My basic question is just this: Is this small modification anything to worry about, in terms of reliability, performance, or otherwise?
Size Comparison
![](/galpreviews/civic-throttle-1.jpg) ![Butterfly Comparison](/gallery/civic-throttle-1.jpg) Butterfly Comparison
Butterfly fully open
![](/galpreviews/civic-throttle-3.jpg) ![With screen on](/gallery/civic-throttle-3.jpg) With screen on
Large particle screen back on
![](/galpreviews/civic-throttle-2.jpg) ![Fully Open (high revs)](/gallery/civic-throttle-2.jpg) Fully Open (high revs)
[Edited on 17/7/06 by millenniumtree]
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millenniumtree
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posted on 18/7/06 at 12:19 AM |
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Ok, I took the butterfly completely out to see how it drove...
Normal temperature, a little low on torque, but quite good top end. It revs a bit quicker, but not scary fast like I initially thought it would.
I think my modified butterfly has a better top end than stock while also not sacrificing torque like removing it completely does.
This piece obviously doesn't make a huge difference to the overall performance picture - I think it's most likely there just for fuel
atomization, as it is about a quarter inch from the primary injector nozzle.
I just wanted to see what I could do performance-wise for absolutely zero money. ![](/images//smilies/tongue.gif)
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