Throttle Body Spacer Design - Need advice

[TJTJ]

I am getting conflicting opinions from my engineers as to what (light truck) engines would benefit from an aftermarket throttle body spacer. (We'd sell them...)

Some opinions are that a throttle body spacer improves performance, others are that it will not do anything for modern engines.

Half of us are slide rule era, the other half are computer geeks. (help?)

As a starting point...what engine types might benefit, and what types can not? (Like fuel injected vs carb, or DOHC vs SOHC, or already throttle body injected vs not, etc)

Both camps here SAY they know how they work...but disagree IF they would help...is that possible?

 

[MikeHalloran]

HRM just wrote up a Ford 400M buildup where one spacer helped, and a second spacer helped more.

Carbureted.

No theory offered.



Mike Halloran
Pembroke Pines, FL, USA

 

[jbthiel]

First - valve actuation (SOHC, DOHC, cam-in-block, etc) has no bearing on the matter directly.

Second - I doubt that you will find any measurable difference with port fuel injection UNLESS you change the throttle area or are correcting for some really bad plenum inlet geometries. (i.e. a 90deg turn right before the throttle, size mismatch, etc.)

Third - spacers can help with carbs & thottle bodies (glorified carbs) - but they can also hurt or make little difference. The three main influences are fuel distribution, plenum volume tuning, and intake pulse smoothing.
--Fuel distribution: The fuel has more time to make the turn to the end cylinders. It also has longer to atomize (which can be more of a problem with throttle body injection since a vacuum signal is not present to help shear the fuel)
--volume tuning: depends on engine displacement, cam, manifold, RPM of interest, etc.
--intake pulse smoothing: In a worst case scenario a single cylinder demands XXliters only once every two revolutions. Can also be demonstrated by a 350 chevy only needing a 650cfm 4-barrel carb with a standard manifold, but needing at least double that when going with individual velocity stacks. Smooting the intake pulses helps to decrease the instantaneous demand on the carb and can up the HP if CFM limited and/or by improving fuel metering.
**Another benefit can be thermal isolation, depending on the fuel and manifold material.

Different tests over the years by Hot Rod, HRM, etc. show that there is no clear cut usage of spacers. 4-hole, 1-hole, 4-hole taper, 1/2", 2", etc. They usually just recommend that you try a couple and see what happens. An then you can also get into plenum floor modifications.....

Your best bet will be to work with standard factory configurations, since you can test various options beforehand. I think the big problem is that you have to do all the work, and once the end user knows what the solution is many of them will just make one themselves. And you have to keep hp/dollar in mind. It's been a while since I looked at these for one of our vehicles, but I don't remember being blown away by the HP improvements.

IceStationZebra

 

[Fabrico]

The OEM's used carburetor heat spacers for decades. Some, no doubt, had to do with vapor-lock concerns.

There have been OEM throttle body-to-manifold heat isolators, but some of those have been eliminated and replaced with manifold-to-head isolators.