Hello All,
More questions and what if's for spacing carbs. When searching on this topic I didn't find as much as I expected, there was more toward ported and adapting.
So my understanding of this type of spacer for both 2bbl and 4bbl of any type is this.
Hight - Effects Atomization of the fuel (the higher the better, to a point)
Type - Being a full open strait bore, individual bores per port, individual bores per port with horn or spiral machining
Material - Aluminum (best), polymer style (mid range), or wood (basic original)
Gains - Increase in top end H.P., better fuel economy
Am I correct in my understanding of these type of spacers?
Does anyone use these spacers or does anyone have a particular recommendation?
Chad
Well ? I guess nobody wanted to give info
Anyway, I still need some info on best materials and types, as well as recommendations.
But I did find this bit of info from an online site (had to remove a couple of Chev mentioning's)
A Carb Spacer Can Be The Cheapest Horsepower You'll Ever Buy. Here Are Six Tips To Help You Choose The Best One.
Carb spacers have been around almost forever and still, their modus operandi is largely shrouded in mystery. Part of this lack of understanding stems from the fact that they are so easy to test for function that it is often easier and quicker to run a test than to figure out how they might (or might not) work on any given application.There are six factors governing carb spacer function. We will take these one at a time and see how each influences the output of an engine.
Tip One-Spacers - Enhance Access To Carb CFM
In many instances, a given intake manifold and carb combination is more suited to low and midrange power than it is top-end output. Part of the problem here is usually that such setups are two-plane manifolds with inadequate carburetor cfm for the size of engine involved. Any time a two-plane manifold is used, any particular cylinder sees only two barrels of that carburetor through which to draw air. Adding an open spacer between the intake manifold and a carb allows any particular cylinder to see all four barrels of carburetion. This move, in essence, turns a two-plane manifold into a very crude single-plane manifold. In so doing, it invalidates the strong point of a two-plane manifold, namely its good vacuum characteristics and strong midrange output. These assets come about because there is no robbing by one cylinder from another since, in a 180-degree two-plane manifold, no induction events overlap.
Many stock 4bbl carbs back in the day (and there are still millions of these around) can benefit greatly from the use of an open spacer. But simply adding a spacer can create its own flow problem. Air exiting the carburetor enters the plenum created by the spacer. So far so good, but when it has to exit the mini-plenum created by the spacer, it must negotiate the sharp manifold face from the throttle-bore edges to go down into the manifold. Having such sharp edges can negate the potential airflow advantage of using the spacer in the first place. The key here is to provide a radiused entry into the manifold in order to make the most of the increased access to the carb CFM. This could be ground onto the manifold, but in the example shown, it was put on the spacer to conform to race regs. The nearby sidebar on pg. 62 shows how a composite 1-inch spacer made of four .25-inch-thick gaskets was made to pay off during the testing of a dirt car motor built to highly restrictive rules
Tip One-Spacers - Increase Air Density
What the tests in Sidebar 1 don’t reflect is the change in air density due to the fact that a spacer made of insulating material can reduce carb temperature. The reason is that the tests were carried out on an intake manifold, which, due to some serious insulation, ran at virtually ambient temperature. In most instances this would not be the case because an as-manufactured intake manifold would run much hotter. By using a spacer with good insulating properties, carburetor body temperature can be considerably reduced. This in turn means that the fuel is cooler, and as such, less turns to a volume consuming vapor. With more fuel in fine droplet form instead of vapor, there is more room in the intake manifold for the induced air. Because an insulating spacer reduces carb temperature, it leads to an increase in volumetric efficiency. Whether this pays off on the dragstrip or not, is questionable. It all depends on the time the carburetor has had to heat-soak. In practice we find that it takes about a minute for cool fuel from the tank to overcome the carb body heat it has soaked up from previous runs. On the other hand, if you’re running a road course, there’s enough time for the carb to cool down and deliver extra power. How much extra power? That’s somewhat of a variable, but certainly on a typical 350hp to 400hp engine, 2 to 4 lb-ft of extra torque throughout the rpm range is common, and numbers as high as eight are not unheard of.
Tip Three-Spacers - Help Displacement-to-Plenum Volume Ratio
Whether you’re contemplating running a tunnel ram or a single four-barrel open-plenum race-style intake, there is a certain optimum plenum-volume-to-cylinder-displacement ratio for the rpm range involved. Most intake manifolds, especially single four-barrel ones, are manufactured with a plenum volume deliberately made too small for the typical engine they are going to be put on. This is done so that those manifolds will also suit the smaller displacement versions of whatever engine they are intended for. For instance, a Victor Jr. has a plenum volume better suited to about a 300-inch engine rather than to the 350-inch engines they are most commonly used on. This being the case, a spacer brings the plenum volume into line with what we may expect would be required for a 350-inch engine. From this you can see that for any given open-plenum manifold, the bigger the engine, the greater the spacer thickness needs to be to generate the plenum volume required.
Looking back on some old dyno tests done with small-blocks, all with Victor Jr. intakes, illustrates the trend. Some marginal gains were seen with a .5-inch open spacer, but a 1-inch spacer cut output, especially midrange torque. The best results were found with a 2-inch spacer. Its use produced up to 6 more horsepower at peak and as much as 14 more at 750 rpm over peak power. On the large small block engine, a stack of three 1-inch spacers produced the best results. Here the engine was so desperate for extra plenum volume that peak power went up by over 11 hp.
The optimum plenum volume is not only interconnected with engine displacement, but also the rpm the engine makes peak power at. If all the aforementioned engines had peak-power rpm at say, 1,000-rpm higher, they may have needed to have as much as 1 inch of extra spacer to access that power.
Tip Four-Spacers - Increase Carb CFM
If designed as one of its primary functions, a carb spacer can be used to increase the cfm delivered by the carb. It does this without necessarily affecting the carb’s ability to adequately atomize the fuel. An example might serve best to show how to use a carb and a flow-enhancing spacer. Let’s say the engine needed to have 780 cfm. Rather than use a 780-cfm carb and an open spacer, an engine builder may elect to use a 750 carb with the spacer shown above. This can augment the flow, thus giving a 750 carb the same or similar airflow capacity when on the engine. The usual result here is that the engine will make the same top-end output, but have a better low and midrange due to having a little more active carburetor. Another example of the use of this type of spacer is when race rules prohibit the use of a carb any more than a certain cfm. For instance, there are many race classes, both on the dragstrip and circle/road track events that call for a maximum of 750 cfm of carburetion. Adding a flow-enhancing spacer often allows such a carb to deliver another 15 or more cfm.
Tip Five-Spacers - Use A Spacer To Suppress Flow Reversion
Pressure pulses generated by the valve opening and closing events and tuned lengths of both intake and exhaust can often produce unwanted flow reversions in the intake. These offending flow reversions considerably upset the carb booster function. What happens is that as the flow reversal goes through the booster in the opposite direction, it draws fuel. When the flow about-faces and returns to the carb via the booster, it draws yet more fuel. This results in the mixture-during the reversion event-becoming very rich, thus killing a good deal of horsepower. There are a number of means to suppress reversion. One of these is to build something approaching a mechanical diode into the intake system. That is, the system will have good flow into the engine but bad flow out of it. Some spacers are designed to do just this. They are normally used on very highly tuned engines that have monster cams and turn equally monstrous rpm. A Pro Stock-style engine would fall into the category we’re dealing with here.
And a bit on nitrous
There is, of course, one type of reverse-flow that is not that uncommon that no amount of anti-reversion redesign is going to deal with. I’m referring to a nitrous backfire. Unless steps are taken to the contrary, a nitrous backfire can easily bend all the throttle plates in the carburetion system. You may think you’ve built a system that guards well against a backfire in the first place, but it only needs one mishap to cause a nitrous backfire. Keith Wilson of Wilson Manifold fame came up with a simple solution to this problem: spacer plates with burst panels.
Let Me know what you think,
my intension was to add a l1ttle over a half inch to a stock 318
Thanks
Chad
