Datsun Roadster Forum-311s.org

I am going to get a PE wideband O2 sensor. But what else should i bring to maximize my time there. I know that the PO did EI ignition, rebuilt carbs. i feel that a tune will help quite abit.

Fresh fuel never hurts.

Unless you're running solex type carbs, not SUs, then there not much you can do unless you have different fuel needles, and even then that's not likely to make a lot of change in HP. The EI dizzy is great too, but it has a fixed ignition curve that can only be changed regarding initial timing and the eventual total advance (i.e. setting initial timing a few degrees advanced or retarded, which will of course change how much total timing the engine sees at high rpm, though the rpm where the curve operates will change too). What I would watch for on the dyno would be a safe and useful air to fuel ratio with no dangerously lean spikes (under load you want to be around 12.5 to 13.5, with a cruise of 14.5 or so on premium fuel. If you start seeing consistent 15.5's or above then you're too lean and risk detonation depending on where you are in the rpm range and what the timing is doing). The operator will probably do some testing at different rpm to watch for too much or not enough advance at each point by holding the engine at a certain rpm and loading it while watching what the torque number is doing, but with a distributor and a set curve every change you make by rotating the distributor will effect the timing everywhere... you are stuck with the curve you have. Fortunately the stock curve is pretty appropriate for most engines. The goal will be to identify max SAFE advance that creates the most torque at a given rpm with a good air/fuel ratio. Power is in the ignition timing much more so than A/F ratios.

I've done a few runs over the years as my engine is high compression, and has evolved from points to the EI dizzy to a Ford EDIS crank-fired system run by Megajolt (where I can make my own curve and adjust it anywhere in the rpm range) to the same EDIS system being paired with EFI being run by Microsquirt that handles both ignition and fuel injection. This spring I will finalize the timing curve on the dyno as described above. One thing you may want to consider if you're into this thing and are motivated would be to consider the 123 distributor option and sell your EI dizzy to help pay for it. The 123 gives you the ability to adjust the timing at any rpm, so the dyno operator will be able to add/subtract a couple degrees at say 2500rpm, then move to the next rpm point and do the same, depending upon what the torque number is saying and what the engine wants. It may result in more and safer power output, but is fine tuning and takes time and therefore money while running on the dyno. I think you will find the wideband a very good tool for understanding what the carbs are doing, and should result in (hopefully) some peace of mind, or at least identify a problem that could put an engine at risk if really lean.

Also, make sure your engine is in tip top tune... carbs balanced, linkage in good shape, valves adjusted, plugs newer and properly gapped, etc. Dyno time is money time.

Good luck and let us know how it comes out! You can pm me if desired or have additional questions.

Ever watch those YT dino fail videos ?
mostly turbos though .
Is there any steep entrance ramp out in LA where many are from ? You can guage yours against another as mph when you level out at the top from a stop
I used to do it on Eclipse turbos and 3000vr4 s @ the mitsu dealer there's no speed limit on entrance ramps
when customers complained of lower power ( had 86 octane and dirty intakes & valves usually)

Ya, it's always a mix of excitement and shear terror listening to your engine be challenged to 7000rpm+, especially when you're the one that built and tuned it and it's being asked to produce more power!

Sounds like I need to invest in getting the engine tip top and more adjustment before I get into dyno time! Appreciate the post. The info posted was great to read.

Happy to try and help. The wideband is an extremely useful tool for tuning carbs, including SUs. SUs are not as easily adjusted at different rpms as say a solex/weber/dellorto style carb with changeable air and fuel jets. An SU uses a graduated needle, with the thickness of the needle determining the amount of fuel being pulled past the needle seat or "nozzle" as the attached piston's position changes based on engine vacuum. It is important to understand how an SU carb works and how to make adjustments to them via the dial on the bottom, how to adjust linkage if needed, function of the oil in the tops/dampeners etc. If you are unfamiliar, do some reading and/or ask questions here... we're happy to help.

Start first with good plugs, wires, etc,. valves adjusted and carbs balanced using a unisyn or similar (I like the "snail", much easier to use). Any imbalance in carb flow will throw off your air/fuel readings on the wideband. Set your idle mix equally in both carbs and watch your wideband meter for the ratio. My car does not like to idle as smooth as I like at 14.7, and is much happier nearer to 13.5.. your experience may vary. Slowly rev the engine up higher and higher, watching to see what the meter says. If you're seeing ratios between 12.5 and 15ish you should be fine, but that needs to be seen while driving the car and while under load, say going up a hill. If you find concerning ratios (15.5 or leaner), especially while under load then it may be necessary to adjust your idle setting on the dial, as that's your only easily "adjustable" part of the carbs fuel ratio other than changing out the needle. Also, do some quick hits on the gas pedal while driving at different rpms and see what the ratio does. It may spike lean, and this is where some changes to the oil in the dampeners, either making sure there is oil in them and/or changing the weight of the oil can make a difference. This all takes some time and understanding with a bit of a learning curve, but we can help you, and having the wideband makes it much easier to see what's going on and what effect your changes are having. All of this is worth doing IMHO, and will improve your connection to the car. You're welcome to get set up, do some testing and then post back for guidance. There are several SU experts on this site who can help guide you and offer suggestions.