FI Plenum Design, MS'ing my 2270 Options

[Tom Perso]

Hey Guys,

I am designing a MS system for my 2270 (163.86b cam, 48x38 valves, future Triad header). I am looking at running stock intake runners and possibly making a new plenum to run my Ford TB (probably from a 4.0L Exploder/Ranger).

Are there any "design guidelines" that should be followed when making a new plenum, such as a certian volume required for engine displacement?

Looking at space requirements, I see running the TB on top of the plenum is the only way to go. That, of course - begs the question... Is the stock 914 2.0L plenum a good starting point to modify to allow for the Ford TB?

Here are some pics for reference... I had a Bus 2.0L intake system to borrow, so I am basing my measurements and ideas off of that.

http://www.qtm.net/~persot/MS/

Any ideas, suggestions, etc, are appreciated!

Thanks,
Tom

[Brett W]

QUOTE

I never claimed to be settling any argument by what I wrote. I was asking how you figured a 300%+ increase in plenum volume for a 13% increase in displacement, given the stock intake runners. I'm still not sure. But I can respect what you know. Just don't read more into what I wrote than I intended. Like most here, I am trying to learn.

I am not working on ratios from the stock parts. I feel they are to restrictive. Based on the calculations I have done on some Honda engines and Suzuki engines I feel that the plenum on the 914 is too small for good performance in the range where a good high performance engine will make its best power. Although a plenum system will always offer less throttle response than an IR type system, it can make more overall power. Most guys with a 914 will want throttle response over maximum power.

QUOTE

My suggestion was simply to look at something that works and start from there. You can look at Hondas, I am looking at Porsches (including type 4s.) Maybe Porsches don't work the same way your Hondas do, but I think I can assume Porsche's engineers know a thing or two about engine design. Did they build it "right?" I think you answered that yourself: "all engines are a compromise..." Not just factory stock engines. Yes, even Honda engines. So why dis the Porsche engineers for the compromises they chose? Don't agree with them? Fine. That hardly makes them wrong.

I look at Honda because I feel that, as far a production NA engines, they are some of the most highly developed. I am not "dissing" Porsche engineers, I am making a statement about what I feel is some drawbacks to how Porsche does things. Please stop thinking of the T4 as a Porsche motor. Porsche would hardly have anything to do with this engine if it weren't for the original success of the early 70s cars.


All this being said I am stating my opinions based on my experiences and research. When VW decided to make the T4 an oversquare engine they had to do something to create torque. That is the part reason behind the 54+ inch exhaust primaries and common plenum design with very long runners and a small throttle body. Increase torque. When you modify the factory engine beyond the stock characteristics you move the powerband up in the rpm range. Thus creating the need for more airflow.