Quote:
Originally Posted by 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. |
I know i'm late, but i did want to say that the pressure waves and intake pulses do play an important factor in power production. I'm not sure that a TB spacer would make much of a difference to it's acoustic frequency. Whether it's for better or worse. The true power comes from tuning the individual runners.
A TB spacer adds more plenum length, which has some noticeable benefit with the correct fuel injection setup (i mean the process by which fuel is added with the air, not the typical "fuel injection").
A TBI engine or any carb engine will see a benefit due to the location in which fuel is added. These have what are called a wet manifold design. It's because the fuel is added prior to the intake manifold and then to the heads. Combine a short travel, with a near 45 degree angle it hits when into the manifold itself, makes it less than ideal for fuel atomization.
Adding extra height gives the fuel more space and time to atomize and mix better with the air. It means that you get an efficient mixture for combustion and less issues with fuel puddling on the bottom of the intake. Using materials that absorb less heat adds to the benefit as well, keeping the fuel just a tad cooler helps with the efficiency as well.
Those vehicles with MPFI or any other sort of port fuel injection (dry manifold designs) will see little to no benefit with a spacer. Effectively just adding a few extra cubic centimeters of volume for air to occupy. If you see any gain at all, it will be minimal. It's basically like adding adding a large diameter fancy tailpipe to your exhaust. Basically just makes it a little longer, it won't do anything at all to aid in exhaust flow
If there is any gain to be had with dry manifold engines, it's either due to lower temps, terrible manifold runner angles, original TB gaskets were showing their age or miniscule plenum volume.