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-   -   DIY Throttle Body Spacer (

Coyote X 11-14-2008 09:54 PM

DIY Throttle Body Spacer
This is an easy mod for most cars. I have been trying to think of stuff I have not done to my car and one thing I came up with was a spacer to put under the TBI. Of course nobody makes anything for a Metro and even if they did it is not worth spending much money on something so easy to make. Spacers can show a couple of mpg improvement on an engine using a carb or TBI injection. On multiport it can be hit or miss whether it works.

So you need two things to make one. A plastic cutting board and a TBI base gasket. I got my cutting board from RiteAid locally, it was a nearby store and it was exactly 1/2 inch thick. It cost 10 bucks.

Start by laying the gasket on the cutting board and drawing out the pattern on the board. Drill holes in the mounting bolt holes and some starter holes in the other areas. Use a dremel or a grinder with a deburring bit so it doesn't clog up. I couldn't find my dremel so I used an air grinder with a deburring bit.

One thing to note. You don't have to cut all the holes out. Some of them are much larger than are actually needed. They are used for vacuum passages and as long as they are big enough to let the vacuum source through they don't need a huge hole. On the main bore I made sure it was nice and smooth and properly sized to the manifold. The other holes I just shaved the plastic down so the vacuum signal could get through but otherwise didn't bother cutting it totally out. You can cut them out but it makes it take way longer and you don't gain anything.

Typical reports are a much better bottom end response and slightly improved mileage. I will find out soon with mine and report back. If I feel like it, I will make a second one and stack them for a one inch spacer. I am not sure what would work best on this setup one inch or a half inch. I might try both ways if I get time and if my mpguino ever comes in.

basslover911 11-14-2008 11:09 PM


All the Mazda 6 guys claim improved mpg, but for $80 I dont see the return on gas... but If I can make one like you for less than $10 then I will for shure do it...

I have MPFI though

Coyote X 11-14-2008 11:24 PM

I say go ahead and grab a board from a store or take the one out of your kitchen if you can get away with it :) If other people have reported increased mileage then you really won't have much to lose by giving it a shot. If nothing else the leftover part can be saved and put to use in your kitchen like it is supposed to be or used for fabricating other parts. The plastic is pretty easy to work with and if you warm it up it seems like it could be formed easily.

It took me probably 30 minutes to make the first one shown in the pictures. I Could probably make one in 5 minutes with a drill press. If I had a hole saw assortment and some routing bits to go along with it.

I am probably going to make one to go in my Astro van sometime or another as well. It will probably give me a more accurate number to show how much of an increase there is from it. The Metro is getting some other stuff done at the same time so I am hoping I can tell what it gives me but it might take a few months to sort out how much it helps that car.

SlowMo 12-30-2008 02:23 PM

Are you doing this to change the effective length of the intake runner or to make a thermal break for the throttle body?

MetroMPG 12-30-2008 02:39 PM

This is the first I've heard of adding a throttle body spacer to improve efficiency - aside from your earlier PM. (Coyote asked if I wanted to do an A-B-A test on it, but unfortunately my cruise control situation hasn't been resolved, so I can't run reliable tests with the Flea.)

It might be worth posting a note about the theory of why this mod may help.

PaleMelanesian 12-30-2008 02:53 PM

I think the idea is to lengthen the intake, giving it a lower resonance frequency, and moving the peak power band to a lower rpm. Should be perfect for the way WE drive.

Memorytwo 12-30-2008 03:17 PM

tb spacer, what about uim spacer?

SVOboy 12-30-2008 03:25 PM


Originally Posted by PaleMelanesian (Post 80774)
I think the idea is to lengthen the intake, giving it a lower resonance frequency, and moving the peak power band to a lower rpm. Should be perfect for the way WE drive.

Indeed, this design is evident in the length of the runners on the honda crx hf, civic cx, and civic vx. However, because of the overall intake design I think for these cars a tb spacer wouldn't do much since the resonance is along the runners into the plenum and would not change with a tb spacer.

basslover911 12-30-2008 05:21 PM

^ Well in the performance world throttle body spacers DO work to improve hp and torque all accross the rpm band.

So with that in mind, it does change something. How that translates to better fuel efficiency? Well, the engine is making more power because its more efficient and this mod does not add air (turbo/supercharger) or increase air consumption, it simply changes the way the air travels. This should in theory improve mpg's.

Christ 12-30-2008 06:10 PM

It also creates a larger plenum area, which means slightly more air available for higher RPM operation.

I'm also pretty sure that lengthening a tube while keeping the same diameter increases air velocity, though I might be wrong on that.

Anyway, if it does increase air velocity, that would mean better atomization, as there would be more turbulence in the air, which might make better power/economy.

AFAIK though, the biggest gains are seen in the higher RPM bands (mid-range torque and higher HP) due to the extra volume of air in the plenum.

As an add-on to this - Using thermal plastic to make an intake manifold will net you better HP and TQ as well, due to the temp differential (thermal plastic allows the incoming air to cool the intake manifold, as opposed to the cylinder head heating it... air temp decreases and you get better throttle response and HP)

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