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

[Reiche]

QUOTE (Brett W @ Feb 1 2005, 04:56 PM)

The numbers for the stock plenum and runners are for an engine that is operating at 70% VE in stock form.  It was meant to run  to 5500 making peak torque at a reasonable range and run all day long without overheating.  When you change the stroke,bore, rod length, valve size, and valve timing, you have just changed all of the variables that went into the design of the stock plenum.  (if VW put any effort into designing it to start with) Your 2270 has a higher piston speed thus drawing more mixture into the cylinder, higher compression burns more mixture thus making room for more fresh mixture, you have to get that mixture into the motor.  Designing a plenum will either be a cut and try affair or you need to spend sometime doing some pretty advanced math.

I admit I am way out of my depth when it comes to knowing exactly how to calculate plenum volume (if it can be calculated accurately at all.) So I may be bringing a proverbial knife to a gunfight. 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.

Look at the 944. Here's an engine (in its weakest form) of 2479cc, 9.5:1 CR, making 150HP and 137 lb-ft of torque, with a redline of 6500. Its engine was designed as an autobahn runner from the start--hardly the VW 411 and bus-pushing slug the type 4 started out as. I bet you a dollar its plenum/runners/TB come pretty close to SirAndy's numbers.