Rons Fuel Injection has provided us with air flow data for their throttle body setups. We analyzed the power potential of these simple and very popular fuel injection systems. Racing engine size capabilities were determined at the flow CFM numbers provided by Rons Fuel Injection. For 100% air density, horsepower capabilities were also determined.
Rons mechanical fuel injection throttle body model: Toilets
3-3/4″ = 1240 cfm*: can feed 595 cubic inch engine @ 8,000 RPM with 1,071 HP at 1.8 HP / ci
4″ = 1435 cfm: can feed 689 cubic engine @ 8,000 RPM with 1,240 HP at 1.8 HP / ci
4.1″ = 1800 cfm: can feed 864 cubic inch engine @ 8,000 RPM with 1,555 HP at 1.8 HP / ci
Rons mechanical fuel injection throttle body model: Terminators
1-7/8″ = 1150 cfm: can feed 552 cubic inch engine @ 8,000 RPM with 993 HP at 1.8 HP / ci
2-1/8″ = 1475 cfm: can feed 708 cubic inch engine @ 8,000 RPM with 1,274 HP at 1.8 HP / ci
2-1/2″ = 2100 cfm: can feed 1,008 cubic inch engine @ 8,000 RPM with 1,814 HP at 1.8 HP / ci
Rons mechanical fuel injection throttle body model: T2’s
2-1/8″ = 1880 cfm: can feed 902 cubic inch engine @ 8,000 with 1,624 HP at 1.8 HP / ci
2.400″ = 2300 cfm: can feed 1,104 cubic inch engine @ 8,000 with 1,987 HP at 1.8 HP / ci.
The engine sizes that can be supported by these various throttle body assemblies are quite high. Reasonable horsepower per cubic inch potentials are shown that are also quite high from these very simple fuel systems. Achieving these high horsepower numbers would depend on high compression and top-of-the-line cylinder heads, intake manifold, & exhaust manifolds.
Flexibility in Application
The beauty of mechanical fuel injection is that smaller engines can also be fed by these throttle bodies without bogging. Mechanical fuel injection pumps fuel into each intake port at high pressure when the throttle is slammed open. Fuel pressures often higher than those in EFI can produce more horsepower from better vaporization. Furthermore, air is not interrupted by venturies or boosters necessary in the carburetor alternative, providing even more horsepower. Stand back!
Response from Rons Fuel Injection*
‘Good morning Bob, yes these numbers are very similar to the calculations I’ve figured for engines cfm usage. We do typically try to “oversize” the throttle body for motors though so that there is no restriction and since mechanical fuel injection does not rely on a vacuum signal to pull fuel, it isn’t an issue just as long as the motor can get as much air as it wants. For example, our normal standard we use for new customers is as follows:
- 1240 cfm toilets for up to about 383 ci
- 1435 cfm toilets up to 502 ci
- 1800 cfm toilets for up to 572 ci.
The Terminators are typically paired at:
- 1150 cfm Terminators up to 383 ci
- 1475 cfm Terminators up to 496 ci
- 2100 cfm Terminators up to 632 ci.
Also this depends on the heads on the motor, how well they flow, and their combustion chambers. As you have shown, the engine is not pulling air into all cylinders at once. So the cfm calculations you came up with show how large of an engine that the throttle bodies can actually support, but it does complicate tuning a bit (regarding the larger sizes). Looks great and thanks for adding us to the news letter.’
*Thanks to Alan Greszler, Rons Fuel Injection.
Math for These Ratings
The engine size and HP additions were determined using the following math:
- step (1) CFM x 12 x 12 x 12 = cubic inches per minute
- step (2) cubic inches per minute / 8,000 RPM = cubic inches per revolution
- step (3) cubic inches per revolution x 2 = cubic inches of 4 cycle engine (normally aspirated)
- step (4) cubic inches of 4 cycle engine / 0.9 = adjusted ci @ 90% VE typical at horsepower peak
- step (5) adjusted cubic inches at 90% VE x 1.8 = horsepower assuming 1.8 HP / cubic inch.
Further Rons Fuel Injection Information
- Fuel Injection Racing Secrets, pp. cover, 3, 22, 129, 139, 177, 185
- 5000 Horsepower on Methanol, pp. 7, 32, 37-38, 40-43, 57-59, 244, 257, 286
- Jetting for Racing Mechanical Fuel Injection for Normally Aspirated Small Block V-8 Racing Engines, pp. 9, 32, 35, 44-46, 63-63
- Jetting for Racing Mechanical Fuel Injection for Normally Aspirated Big Block V-8 Racing Engines, pp. 9-10, 13, 14, 17, 49, 54-55, 74-75, 77-78
- Blown Nitro Racing on a Budget, pp. 36, 158
- High Horsepower Tuning for Mechanical Fuel Injection, pp. 3, 16, 24, 25, 38, 43, 51, 52, 53, 64, 90, 101, 105, 147, 149.