DIY Throttle Body Spacer

[Christ]

Originally Posted by basslover911

LET ME KNOW!!!

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

Which just means less work for you. There are 3-4 bolts/nuts/studs/whatever holding the TB on, put a spacer behind it, and you're good to go. You'll need two TB gaskets though.

Subscribed for results - wanna see if "bigger is better" in this case.. If adding more than 1 spacer really does anything more for it.

This would be an easy/great first mod for wifey to try on her car, since she's into engine work anyway and wants to learn to fabricate stuff.

[SlowMo]

But there must be an optimum length, probably related to engine displacement and desired rpm. This sounds more complex than 'slap a 1/2" spacer in it and go!'... come to think of it, probably related to cam timing too b/c the valve opening and closing would set up the pressure pulses. Kind of like expansion pipes on 2-stroke motorcycles, no? (just on the intake side, and with valves...)

I'm also confused by the claims of lower RPM gains because this article Best Carb Spacer Cheap Horse Power - Popular Hot Rodding Magazine emphasizes the gains in the upper rev range (although there are some mid-range gains too) like Christ states, but I'm not an engine builder and I'm more than a bit rusty at all of this.

This leads me back to the use of a TB spacer as a thermal break rather than as a method of tuning the resonant frequency in the intake tract.

[Christ]

Thermal break is partially true too, although most commercial spacers, AFAIK are aluminum...thermally conductive.

I'm not sure about the low-mid TQ, although adding length to runners does move the resonance effect (n/a turbocharging) down lower in the RPM range, which would create a peak effect of TQ being lower than the actual peak... and still move the actual peak lower in the range.

PS - Runner resonance length is calculated as "distance from valve to valve" the plenum counts as an equal distance for all the runners, since it provides an interference of sorts.

What this means: effectively, adding a TB spacer, you're increasing runner resonance length.

I also didn't specifically note that with TBI - the "plenum" isn't like the MPFI plenum at all.. TBI is more like carbs, in that the plenum is an area that can actually be equally divided between runners without giving more or less volume for each runner's resonance length.

This would definitely attribute better fuel mileage to the TBI/Carb crowd, due to the same idea behind using it for anything else.. longer runner - lower TQ.

Obviously, if you're making more power on the same fuel, you're running more efficiently.

[mikemoss]

Well if it would actually increase the runner length then it should increase the torque. From what I have learned about runner length here, TPiS, says that a longer runner should result in more torque but slightly less hp. But for an ecomodder who never sees high rpm's this could be helpful. I am also into making things fast and I would not install a tb spacer for hp gains on my Camaro. No one has found gains, but they dont look at fe.

[mobilerik]

Am I correct to assume that this mod should benefit y'all's little racecars a lot more than a truck that's made for towing?

[mikemoss]

Originally Posted by akashic

Am I correct to assume that this mod should benefit y'all's little racecars a lot more than a truck that's made for towing?

No, longer intake runners mean more torque. Early gm efi truck motors had some awkwardly long intake runner length, like 12 inches or something maybe more, so they would make more torque but the length of the runners made it so the air could not go through the intake fast enough to allow the engine to spin much higher then 5000 rpm.

So a truck made for towing should benefit more bc of the added torque. If adding at the throttle body has the same effect.

Im not sure if anyone really knows if adding a throttle body spacer really does anything, a carb spacer is different and there are definitely gains there. Some people claim gains from a tb spacer and others dont I think it just kind of depends on the motor.

Good idea on using the cutting board I think that once it warms up a bit i will try this and do some testing to see if it makes a difference on my car. I have used cutting boards on my car for a different purpose but it wasnt for fuel economy. I used them to make strut spacers, I havent gotten them yet bc it got cold but I think they should work.

[Christ]

The only HP claim from throttle body spacers is due to velocity increase... it's pretty much BS. The idea is that the TB spacer will create a "turbo like" velocity increase that means more air gets "rammed" into the cylinder, so that it's pre-pressurized, and gives an increase in HP.

The physics behind it assume that you're making the same space of air move a further distance than it normally would, as in an airplane wing. (The air over the wing is moving faster, which creates a low-pressure zone, allowing lift. It's the same volume, at a higher speed, when the plane's speed increases.) not that the air is constantly being consumed. (The airplane effect doesn't work unless it's in open-air, with a splitter. Air will only travel faster to meet the same airspace that it was separated from. If no separation occurs, no increase in velocity occurs.)

The physics also assume that the engine isn't under vacuum. A net velocity increase while under vacuum would require a longer AND thinner runner, and there is a point of diminishing returns.

The point is, you can get better power gains elsewhere. Such as extrude honing (sandy water). If you're looking for a quick torque gain, then use a TB spacer.

The effect is greater on direct runner setups (Refer to D16Y7 and D15B2 honda engine, which has a "up and down" throttle body, which resembles a carb.) than on large plenum or offset plenum setups. (Offset plenum - most MPFI cars, runners go into a "bottle" with a TB at one end. Large Plenum - Plenum contains more volume than the runner length does, from intake valve to end of runner.)

[mikemoss]

^^Id agree with everything you posted.

But the question is can it help with fe?

I think that it might bc if you could increase the torque a small amount then the car could push down the highway better and not need to down shift up hills with cruise on.

[Christ]

I believe, generally, that anything you can do to maximize the power output of your engine without increasing the fuel it consumes to do so will give you better FE.

I call this "wasted potential". Since you're going to be building it on your own, with almost no money invested, and we all know that it can't hurt, but it seems that noone can provide scientific evidence that it will help, maybe you could just try it for yourself?

What's the worst that could happen? It doesn't do anything, and you have a nice talk piece under the hood that netted you a few hours mechanical experience and a few hours of cutting, grinding, shaping experience.

See what I'm getting at? At the very worst, your gains equal experience and knowledge, rather than FE and torque. You've nothing to lose by just "giving it the old college try" as it were.

[mobilerik]

The internals of cars are a new thing to me, so please excuse me while I try to apply my limited experience with engine-talk...

I'm getting that the idea of this mod wrt FE is to lower the resonance of the intake and shift the peak torque -- and simultaneously the island of minimum BSFC -- to lower RPMs. Is that right?

I guess maybe what I was asking was if a car already tuned for more low-end torque would benefit less from the same spacer than one tuned for more high-end torque. At least with given thickness of spacer, the car with the shorter intake would increase it's intake-length percentage-wise more than one that's built with a longer intake. If that's actually how it works (and I didn't completely munge that explanation), then it seems sort of mathematically obvious that a lower-tuned engine would benefit less from the same thickness of spacer.

And to go with that thought, a car tuned for high-end performance has the most interest in a retuning mod like this, to get the BSFC curve into an accessible range for a hypermiler's driving style. Yes? No? (wtf?)

Christ: "I believe, generally, that anything you can do to maximize the power output of your engine without increasing the fuel it consumes to do so will give you better FE."

This intuitively-appealing statement keeps reappearing in different forms and on different forums. Doesn't it need to be qualified as to HOW you're maximizing your power? If you're maximizing your power linearly across-the-board, then I think this statement might be true. But it generally doesn't work that way, right? You might amplify your power in a certain rpm range much more than in others. And you may even retune the system in such a way as to create resonance peaks in one range that reduce power in other ranges.

So any power increase isn't necessarily helpful. Hypermilers need efficiency increases in a very particular RPM range particular to the vehicle. If we can retune the system so that that particular range gets more power, then that should be helpful.

btw, I understand a little about "tuning" from the acoustical world. It occurs to me that little hacks like this can accidentally work to your advantage if you happen to disrupt the response curve in such a way as to make a little bump in the "right" part of the curve. You might end up with a bizarre profile with several low peaks, but if you only care about 1900 rpm or whatever, then it might just work for you. So I suppose as you said, this is something that you just hack at until something works, maybe even without a predictable pattern.