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]

Tim, if you would be so kind as to take a tape measure and the external dimensions of the Porsche plenum. I roughed an estimate at 18x12x3, that should be about 10 litres. Close to my 2.5 rule.

QUOTE

However, it seems to me that just because engine parameters change slightly doesn't mean you have to start from scratch. I just don't see how you need a plenum that is 3-5 times bigger, and a TB that is 1.3 times bigger with an engine that is only about 13% bigger, even with the other changes you are talking about.

You are assuming the factory dimensions are correctly sized for a stock motor? My stock 1.6 litre Honda motor made 108HP from the factory at something like 6500rpms. It uses a 56mm TB. Although I believe the plenum volumn to be less that 3 litres though.

A smaller plenum will yeild good throttle response and drivability. The plenum should not have a flat bottom with defined corners. Airflow doesn't like corners. I would not bring the runners in at a 90 deg. angle like the manifold pictured in a previous post. Airflow does not like radical changes in direction. Notice how Porsche brought their runners out the bottom. You could do the same or you could bring them out of a rounded plenum at the angle where the corners should be.