Needle Mods

Air Flow Mods

Other Mods

I am currently running the 38mm flat-top Hitachi-SUs on an L20B with a 268degree/.480" lift cam and Z-intake valves, all wrapped in a W53 peanut-head.

Needles I have used:

• The original needles that came with my set of SUs had no markings and I never knew what they were. I now suspect they were M66'ers (or close) because when I later switched to the M66 needles (bought from Nissan) I didn't notice much change. I also made some air flow modifications to the SUs at the same time as the needle change, so I can't accurately assign any gains to the needle change itself.
• I changed to M66 needles...for no real reason I can remember. I felt with my engine I needed a bit more fuel because I had run the same set of SUs (with the above mystery needles) on my old L-16. I currently am running the M66 needles and find good top-end performance, even with the two-liter, cam, and larger intake valves! It will pull solidly to 6000 rpm. Sure, a set of dual Webers would ultimately be faster...but then so would EFI.
• I just bought M43 needles from Nissan because I thought I was having a "Rich-At-Idle" problem. However, ten minutes of driving around (after tuning) convinced me to change back. There was a noticeable drop-off in top-end performance with the M43's. Anything above 5000 rpm was a trial to achieve. And to top it all off, I couldn't really get the car to idle much better (that problem was mainly attributable to poor float level adjustments).
• What I REALLY want is a needle that is leaner through the mid-range than the M66 yet richer toward the tip. For my particular engine combination, that would be the ticket.
• I finally made my own needles. I used M66 needles to start with and proceeded to sand/thin the needles from station 7 on down to the tip. This allowed me to lean out the needle overall yet still provide the engine with enough fuel at the top end for good performance. Now the car idles better, doesn't smoke at stoplights, and gets much better mileage!! I'll have more detailed information at a later date, but all the info is in the newest issue of The Dime, Quarterly (The 510 technical newsletter).

Air flow modifications:

If you are interested in making air flow mods to your SUs, I highly recommend you beg for, borrow, or buy a copy of Tuning BL's A-Series Engine. It's a British title (Mini A-Series, not Datsun A-Series). Lots of pictures, charts, graphs, and actual explanations!

• Epoxy on the jet bridge--A mod suggested by the Tuning book. This basically removes the 1mm vertical lip from the air flow, smoothing out the flow of air past the needle. I performed this mod using JB Weld (make sure you sand or wire-brush the area first). When you have finished applying the epoxy, test fit the piston to make sure its travel hasn't been limited by extra epoxy. The piston should still "thunk" and move freely. Note: It has been suggested that this mod may reduce the atomization of fuel, as the 1mm lip supposedly creates turbulence around the needle. Epoxy can always be removed if you don't like the effects.
• Grinding the Throttle Shafts--Another mod from the Tuning book. You want to take a Dremel to the middle section of the throttle shaft, grinding away the extra material so it will present as small a cross section as possible at WOT. You can go much further if you have access to more precise equipment.
• Velocity Stacks--This, by far, made the most improvement of all the air flow modifications I performed. While velocity stacks won't do anything at idle and low rpm, when you start really moving air, properly made velocity stacks are worth every penny! It's been suggested that the velocity stacks compound the advantages of any air flow modifications you may have made (i.e. greater than the sum of its parts). I didn't notice a great deal of difference after performing the above mods until I installed the velocity stacks. Be careful what you buy, and ask around before you do. A few companies make good ones (check out TWM or APT), though the ones I bought were locally made by a British car guy. There is a lot of information on velocity stacks and SUs in the Tuning book. What, you haven't bought that yet?? See the References page.
  By the way, the CNC Billet velocity stacks pictured below are the style I use, and I run them inside my K&N filters. The TWM versions won't fit inside any individual filters I know of.
• Pictures:

• CNC Billet Velocity Stacks - Velocity Stacks in K&N filters
• Stub Stacks

Other modifications

• I got tired of dealing with those old (usually stripped) screws when performing maintenance on my SUs. Those screws hold the domes as well as the float bowl tops. I took one of the screws down to my local Bolts R Us and bought 16 stainless metric Allen-head bolts. Not only do they look kinda sano, they're so much more servicable. To make it easy on yourself, buy a 4mm T-handle hex key wrench. Get one of the long ones since you'll be spinning that wrench around and you want it to clear the tops of the SU domes. Makes life easier, no?

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