I’ve experimented with DCOE and mechanical fuel injection on 2.0 and 2.4 liter straight six and 7.0 liter crossplane V-8 engines, but the results have been quite underwhelming. In some cases I have been able to achieve high levels of horsepower and/or torque using four barrel carburetors. I’m wondering if anyone might know what is causing this. The engines are set to a cam rating of at least 65.
It isnt always about raw power, you also have engine response, fuel economy, size, reliability, reliability with turbocharging, etc to worry about. I just built a 3.0 OHV I6 in 1980, nothing fancy, 4bbl, 116hp@4900 (cam at 40), compression 8:1, AKI of 86.2, I then swapped over to a DCOE and only gained 3hp BUT AKI dropped by 0.9, responsiveness went up to 29.7 from 16.
3.0L Square OHV all iron, cam 40, timing 35, 4bbl:
HP 116@4900
TQ 146@3000
Responsiveness 16
Reliability 52
Emissions 1553
Economy 14.12% (0.896 lb/hph)
Octane 86.2 AKI
Same engine but only changing to DCOE:
HP 119@4900
TQ 147@3000
Responsiveness 28.4
Reliability 49.7
Emissions 1871
Economy 13.90% (.910 lb/hph)
Octane 85.3 AKI
Same engine but only changing to M-FI
HP 117@4900
TQ 148@3000
Responsiveness 26.8
Reliability 59.1
Emissions 1283
Economy 14.75% (.857 lb/hph)
Octane 85.4 AKI
As you can see each successive option is not just a path to more power, each one is suited for different needs, the mechanical fuel injection would excel in fuel economy and emissions so if you were builing this in an area that had high restrictions (California perhaps?) you would use this, or maybe you wanted “immediate” throttle response then you would choose the DCOE and if you wanted just dirt cheap reliability and service costs you would choose the 4bbl. Each “upgrade” over the 4bbl gives you a bit more room to fine tune the engine due to the added buffer from the max AKI rating, this helps even further with whatever goal you may have in mind for your engine/car.
Now for fun lets toss on a turbo and see what the max boost each setup can take before the warning pops up. Compression changed to 6.0, fuel unchanged from last (13.5:1), economy button pushed and only bumping up boost:
4bbl:
Hits the limit at 10.44 before boost issues.
DCOE:
Same limit.
M-FI:
Unlimited due to the nature of the fuel injection, immune to reliability problems due to boost.
I know there’s a large jump in responsiveness, and I’ve used the technologies to help boost the responsiveness of some of my engines. I was just expecting a boost in horsepower as well, as there were usually large horsepower increases when engines were equipped with DCOE or mechanical injection systems in the 1960s instead of four barrel carburetors.
To be honest, as best as we can tell from our research, Mechanical Injection was never really quite as good for power as a really nicely set up set of DCOEs or 4 barrel carbs. Sure the carbs would be impossible to tune for emissions, but they’d go well!
It also seems that if you run enough big 4 barrel carbs you’ll make just as much power as a good DCOE setup, but people seemed to pick the DCOE setups for things that required excellent throttle response (and for engines where packaging a DCOE/IDE style carb was easier)
[quote=“Daffyflyer”]To be honest, as best as we can tell from our research, Mechanical Injection was never really quite as good for power as a really nicely set up set of DCOEs or 4 barrel carbs. Sure the carbs would be impossible to tune for emissions, but they’d go well!
It also seems that if you run enough big 4 barrel carbs you’ll make just as much power as a good DCOE setup, but people seemed to pick the DCOE setups for things that required excellent throttle response (and for engines where packaging a DCOE/IDE style carb was easier)[/quote]
Don’t forget that DCOE carburettors are also VERY sexually attractive!!! My opinion but I feel that DCOE’s sound better, look the bomb and scream classic racer to me! 
I take it the historical performance engines from the 1960s that featured DCOE and mechanical fuel injection had other modifications that led to an increase in horsepower?
Yeah they did… I dimly recall that to increase power they increased the rev range and the cars needed to be air started rather than an electric starter motor. The old rev range was about 9K (like Automation) but the new range STARTED at 6K and revved to (I think) 15k…
Look up the history of the Cosworth DFV V8 as this was the doco I was watching at the time.
[quote=“HighOctaneLove”]
Yeah they did… I dimly recall that to increase power they increased the rev range and the cars needed to be air started rather than an electric starter motor. The old rev range was about 9K (like Automation) but the new range STARTED at 6K and revved to (I think) 15k…
Look up the history of the Cosworth DFV V8 as this was the doco I was watching at the time.[/quote]
I was thinking more about options on production vehicles. Are you sure the air starting wasn’t for racing engines?
[quote=“DeltaForce”]
Yeah they did… I dimly recall that to increase power they increased the rev range and the cars needed to be air started rather than an electric starter motor. The old rev range was about 9K (like Automation) but the new range STARTED at 6K and revved to (I think) 15k…
Look up the history of the Cosworth DFV V8 as this was the doco I was watching at the time.
I was thinking more about options on production vehicles. Are you sure the air starting wasn’t for racing engines?[/quote]
Yeah, the air starters were for the race engines; I read your post and I interpreted the word “performance” as “race” 
Road cars tended to use race car engine designs and had DOHC and 2 or 4 valves… The Jag six and the Ferrari V12’s were de-tuned race engines and other engines like the Alfa 4’s were built from race designs. America used pushrod V8’s for racing so the race tuned engines also found their way into their road cars. This whole process became formally known as homologation and the greatest road car classics tend to be these cars… 
Aggressive cam profiles and hand built, precision made engines with custom carb settings is what makes the power… The fuel delivery system is part of the system and needs to be balanced with the other parts of the engine for the optimum result. Looking at historical engines, the DCOE was used on the inline engines mainly due to throttle response and optimum airflow; the V8’s better suited the 4 barrel and multiple 2 barrel setups.
As for me, unless I need to make a specific type/price range of engine I’ll use DCOE as they’re too cool for school! 