custom individual throttle bodies? fab your own

[bcal]

Found it
http://www.abdgraphics.com/iansite/ianthrottlebody2.htm
Same TBs as mine but different way of skinnin the cat

[jpnovak]

Brett, Thank you so much for your tips on setting these up. I was thinking of doing the same thing as your Bakelite adaptors in Al. I was going to get them water jet cut. The nice thing about the 911 heads is that you can bolt directly to them and they are round just like the bottome of the TBs.

How did you extend the linkage between the TBs to retain the adjuster screws on the butterflys? Did you just add a section of flat stock to the L bracket that extends over to fill the gap where the TBs have been spaced apart? That is what I plan to do but have not started yet.

[bcal]

Jamie, I think Aluminium would work fine. I see you're using the later TBs so you have the advantage of them being centric. You should then be able to bore straight thru the block instead of just reccessing like I did. I had to do this to provide enough gasket face for sealing on the alfa manifold. You may not need as thick a material either, maybe 12mm or so would do the job.

I simply bent the metal taps on the linkages. This is what I've seen done on most of these setups. Standard weber spacing is 92mm but afla add an extra 2mm between carbs just to make things difficult.
If you have the inclination it would be better to weld on longer tabs instead.
One thing to watch is binding between TBs. I've read about this on other boards and experienced it myself. You have to be careful to size your top spacers correctly and play around with the bottom strap bolts to get the butterflies to move freely in unison and not fight against each of the linkage springs.

I set the opening of each of the butterflies using a piece of .6mm mig wire and after I got the engine running I used a carby balancer to check the air flow rates and they were spot on.

Did you notice the soleniod I used to flip open the butterflies a little for Idle air control. It's an anti diesel soleniod off an old ford carby and works a treat. Much easier than trying to adapt a proper IAC valve.


Go for the largest diameter fuel rail you can get. I had proplems with fuel pressure pulsations and I ended up making a custom rail from 3/4 inch ss tube. Also you're gunna suffer from a pulsating vacuum signal and will need to dampen it using a restrictor. This then presents problems with signal speed response during quick acceleration. I used a megasquirt ECU and they have little tricks you can employ to get around this but you need to remember that with ITBs you will be operating over a very small MAP range and therefore good speed density control will be difficult, especially with long duration cams.
A lot of guys end up running apha N mode which is ok for the track but not the best for the street
Good luck.

[kstylianos]

Jamie,

How is this coming along? Was thinking about this recently and I had some extra time today to poke around a bit and came across this bit of information. Pretty much deals with calculating the optimal intake runner length (top of velocity stack to back of intake valve) to take advantage of the harmonic ram effect. Anyway, maybe this will come in handy. I noticed they assumed D to be a constant throughout the bore. Could be used for a good guesstimate at least.

from: http://rogueperformance.com/UpperIntakeManifold.html

Build your own intake:

Warning: Math! (Thanks to Alex for pointing out my mistake!)
L = ((ECD × 0.25 × V × 2) ÷ (rpm × RV)) - ½D

To compute the intake runner length (L), we need to know a few things:

-Effective Cam Duration (ECD) = 720° (4 cycle engine) - Advertised Cam Duration (Factory ~248° ) - 20° (lifter slop)
-Runner Diameter (D) = 1.5 (or so)
-Speed of Sound (V) = 1250 to 1300 fps,depending on temperature (use 1300)
-Reflective Value (RV) = How many times is the air going to bounce before the intake valve opens? Use 2 for LONG runners with high RPM's or 4 for short runners with moderate RPM's.
-Revolutions Per Minute (rpm) = 2500 for a good street intake, low RPM, daily driver or tow.

ECD = 720° - (248° - 20°)
The ECD of the factory cam would be: 492
The formula for "optimum" intake runner length (L), with are numbers would be:
L = ((492° × 0.25 × 1300 × 2)÷(2500 × 4)) - 0.75
...or L = ((319800)÷(10000)) - 0.75 ...or 31.98 - 0.75.
Meaning L = 31.23" from the Plenum to the valve face.
Now, the lower intake is 5" long and the head is 3" to the valve face.
So, L = 31.23 - (5" + 3") or L = 23.23"

(Stump-pulling Torque Intakes)
Upper runner length = 23.23" for 1.5" intake tubes tuned at 2,500 RPM, 4th bounce.
Upper runner length = 55.21" for 1.5" intake tubes tuned at 2,500 RPM, 2nd bounce.
Upper runner length = 17.9" for 1.5" intake tubes tuned at 3,000 RPM, 4th bounce.
Upper runner length = 44.55" for 1.5" intake tubes tuned at 3,000 RPM, 2nd bounce.
(Screaming Banshee Autobahn Intakes)
Upper runner length = 9.02" for 1.5" intake tubes tuned at 4,500 RPM, 4th bounce.
Upper runner length = 26.78" for 1.5" intake tubes tuned at 4,500 RPM, 2nd bounce.
Upper runner length = 7.24" for 1.5" intake tubes tuned at 5,000 RPM, 4th bounce.
Upper runner length = 23.23" for 1.5" intake tubes tuned at 5,000 RPM, 2nd bounce.

Notice something strange about the first and last line? Just a coincidence? No, a harmonic! This is why long tubes are better, you have two peaks one at 2,500 RPM's (4th bounce RAM) and one at 5,000 (2nd Bounce RAM).

Using 1.5" aluminum tube, and the flanges cut off an existing manifold (too easy!), weld up an intake similar in looks to the Mustang GT-40. The plenum should be 3" tube and displace 90in3 (or 1/2 you engines displacement), the runners are determined with the formula (above) based on your desired RPM.