3.0 Competition Engine - MFI or PMO Carbs

[rattytat]

I am looking at the following spec engine for a competition car (not a circuit racer).

3.0 engine - targeting around 300bhp and 220+lbsft torque, lightened and balanced bottom end, twin plug with electronic ignition and 10.+:1 compression pistons etc etc. What to do for the fuel system?

Torque is more important than absolute power, so the simple question is MFI or PMO carbs?

Please be gentle, but thoughts?

[Hi_Fi_Guy]

I love carbs but a well sorted EFI system with individual throttle bodies would be my vote for a build like that.

[2.7RS]

Depends on your "competition" rules

I don't know where you are planning to compete but you should check rules and regulations for each class.

Avoid surprises

[winders]

If rules allow, I would look at the AT Power ITBs with an ECU. They are really fantastic.....

[Marc Bixen]

Take a look at Rothsports eye-candy. There flat slide TB's ar fantastic!

[winders]

Flat slides look nice but butterflies offer better overall performance. What is good about the AT Power ITBs is the shaftless butterfly design. Most of the benefits of flat sides with none of the downsides.

[r lane]

What is the advantage of butterflies over slide valve. I understand that air doesn't behave necessarly like one would think, but at WOT, the butterfly, which I would thing would cause unwanted turbulence, is not there in a slide valve set up. Is having a straight not an advantage.
What is the science here. Bob

[winders]

Butterflies are better everywhere except wide open. The butterfly mechanism reduces the amount of air that can flow. The shaft is the biggest reducer. Slides are just not that good at anything other than full throttle.

F1 teams use butterflies or barrel valves these days and not slide valves (guillotine valves).

Butterflies are better at partial throttle response and general drivability.

[rattytat]

Thanks for the replies guys. The car will be used on street circuits and European rallies but no circuits, so will need to be on and off the power through bends and on short straights etc hence the need for torque over absolute bhp (though bhp matters). Under historic regs any equipment fitted should be 'in period' of the early to mid 80's. I've looked at AT Power ITBs and they do look good but not compliant, so with the above use, period regs and the need for reliable torque/ power its back to either MFI or carbs.....

[jpnovak]

PMOs can possibly be easier to tune and setup depending on your cam choice. The space cam and adjustment screws in MFI will be limiting factor if you deviate from factory cam grinds.

Ultimately it will come down to you/your shop/your tuner's familiarity with carbs or MFI. They each require some finesse to make run right in the majority of the load/rpm operating space.

[r lane]

I have MFI on 3 engines, 2 are track. I love their appearance, the aggressive looking trumpets, the looping injector lines from the pump, the sound and they work wonderfully. They CAN be a pain to set up. By the time you have acquired the pieces, found and done all the massaging required, found a pump tuner, you have spent a considerable sum, but neither are carbs inexpensive. With carbs, I think the advantage is in tuning due to the development that PMO has done. MFI has wonderful throttle response with no bouncing floats to deal with. You will be successful with either.

[nathanbs]

I would say a very considerable hardware price difference with MFI being a lot more. I’m guessing the MFI overall would have slightly greater horsepower and a way greater cool factor for sure.