[Editor’s Note: We initially ran this story in the November 2017 issue of Grassroots Motorsports.]
An engine gained’t final lengthy with out some kind of air provide. And for a cross-pollinated engine swap mission like our Miata-powered MGB, the answer isn’t going to come back from the catalog.
Till this level within the construct, we’ve stayed fairly true to at least one self-imposed restriction: All the elements used for this swap have come from both the Mazda or MGB elements bins. However now it’s time to wander off target a bit as we put together to put in a supercharger.
Our blower comes from Quick Ahead Superchargers and is predicated on an Eaton MP62 unit. We’ll element its set up and tuning after the MGB GT is painted and assembled, however first now we have an enormous mission to face: configuring an air consumption and filter setup.
Quick Ahead clearly doesn’t provide a supercharger bundle particularly for a Miata engine fitted in an MGB–though the parents there have been very useful in providing us a mock-up setup to test-fit earlier than we bought–so we have been on our personal for some elements of the equipment and set up. We picked a equipment for a 1994 Miata (our donor automobile) and made modifications as crucial.
Not constructing a Miata-powered MGB? You possibly can nonetheless comply with our growth course of for different swaps. It’s the identical science.
Go With the Movement
On the subject of air intakes, everyone appears to be an knowledgeable, particularly on the web. Individuals generally bounce to the conclusion that chilly air trumps all the pieces. Nevertheless, 1000’s of dyno pulls have confirmed us that cold-air intakes solely assist once they movement air nicely. In different phrases, movement usually trumps temperature.
On the subject of small engines, like these in MGBs and Miatas, a 20-to-30-degree enhance in consumption air temperature normally corresponds with a mere 1-horsepower lower on the wheels. In the meantime, movement points can price 10 horsepower fairly shortly. To translate this knowledge into technique: Design your air consumption for movement first, then look to decrease the consumption temperatures.
We’ve additionally discovered {that a} well-placed warmth protect could make nearly as a lot of a distinction as a full cold-air consumption. In our expertise, underhood temps close to an unshielded air consumption typically attain 150 to 250 levels. A warmth protect can drop them by as a lot as 60 to 80 levels.
A full cold-air consumption could decrease temps by one other 60 levels, however that’s not as simple because it sounds–particularly when the consumption is positioned in the back of the engine, like it’s with our equipment. With a setup like ours, the throttle physique can take in one other 30 to 40 levels of warmth from the engine bay.
DIY Movement Bench
You’ll be aware we’re utilizing precise, measured temperatures in our evaluation. That’s the beauty of working with consumption temperatures: They’re simple to measure.
Measuring movement, nonetheless, is tougher–except you may have entry to a movement bench. And we do.
We constructed our personal movement bench utilizing Movement Efficiency’s Fundamental 2.0 Movement Bench Package. The $997 bundle consists of the required movement charge processor, movement component and Home windows-compatible software program. We simply wanted so as to add a store vacuum and a cupboard, each of which we sourced from our native big-box retailer. For about $1200 plus a laptop computer, this setup provides a simple solution to get correct, repeatable movement knowledge.
Tubes and Turns
Time to construct and take a look at our consumption. We assembled a number of items of two.5-inch tubing, bends and connectors that will mate to our 2.5-inch mass airflow sensor. After test-fitting every setup to the automobile itself, we ran them on the movement bench. We additionally baselined the air filter and the MAF with its coupler to indicate how our varied tubes and bends influenced airflow.
Earlier than heading to the movement bench, we mocked up a number of choices to check. We had the best hopes for the long-runner configuration, which might clearly duct in chilly, ambient-temperature air. Along with these setups, we additionally examined totally different runner lengths.
To fulfill our curiosity–and supply much more worthwhile info to you, our devoted readers–we additionally examined some intakes utilizing versatile hose. We have been making an attempt to copy the home-brewed intakes we’ve seen. The outcomes, as you’ll be able to see on the chart under, weren’t fairly.
The outcomes didn’t shock us a lot, as we’ve realized two fundamental guidelines about air over time. Rule 1: Air doesn’t like altering route very a lot, so a straight shot is best than a curve. Rule 2: Air doesn’t like altering form drastically, so it’s essential to maintain tubing the identical dimension or use very gradual transitions.
A couple of details stood out, although. First, the air filter alone flowed higher than simply the coupler and MAF, but it didn’t movement as nicely when connected to the MAF. The tip of our filter was capped, in order that was probably limiting some movement. With out the cap, that 512 CFM determine would in all probability be larger.
The information additionally confirmed that Rule 1 may be very true: Air doesn’t like altering route, as every 90-degree bend had a measurable unfavourable impact.
As soon as we began including the assorted runners to our 180-degree bend, we noticed some stunning outcomes. Contemplating that the longer runners tended to carry out a little bit worse, it’s attention-grabbing that the 12-inch runner really outshined a setup that didn’t function any runners. We are able to solely surmise that the 12-inch runner provides some type of ram tuning, no less than on the movement bench.
Drawing Conclusions
Whereas the movement bench knowledge helped us predict some issues, the dyno will present actual numbers. As soon as the automobile is operating and tuned, we’ll probably retry a few of our setups to see how tightly the movement bench knowledge correlates to energy on the bottom. Getting the air cooler, whether or not by means of a warmth protect or one of many much less environment friendly intakes, will probably be a part of our retesting. We may check out some tapered runners–following Rule 2–to see if we will regain any of our losses. Within the meantime, we all know that our straight-shot setup will probably be an ideal place to begin.
The massive take-home lesson from this mission installment? It doesn’t matter what your scenario, some DIY movement bench testing will help you construct an environment friendly air consumption setup.
The straight-shot consumption was our clear winner. Nevertheless, we noticed yet another potential subject that was price one other journey to the bench. This setup put the filter up in opposition to the firewall and a couple of inches above an underhood shelf.
We wished to guarantee that these close by obstructions wouldn’t have an effect on our numbers, so we simulated them with some cardboard and retested. Consequence? No distinction. The truth is, we really picked up about 2 CFM.
That small quantity of airflow in all probability wouldn’t make an influence distinction on the rear wheels, but it surely’s a very good reminder that air doesn’t at all times do what you anticipate–so measure the place you’ll be able to.
