Datsun Roadster Forum-311s.org

Hey fellas,

I got a crazy idea for a quad SU setup or larger dual SU for my U20.

I am not familiar with Z cars, so I will ask. Did all Z cars have triple SUs? I ask becuase I am wondering if there were any dual SU's setups...

For a quad SU setup, what do you guess would be the car/motorocycle with a proper enough SU carb candidate.

Did Datsun have a 1000-1200cc displacement engine with SUs?

I am really starting to like the SU carbs over the dual dual-throat Solex/Mikuni/Weber/Dellorto/SK.

Minh,

All stock Z cars came with two SU carbs. They are about the same size as the 2 liter carbs. The linkage is totally different from the roadster carbs. The 2 SUs on a stock L24 provide plenty of performance. For racing the triple setup was popular. You would drown the engine with quads on a 2 liter. Even triples would be a bit of overkill but that is just my opinion. What happened to the tubo charger?

Steve

The turbo charger scheme is all laid out on pile paper on my desk. I will need a custom 3mm copper gasket, intake and exhaust. It'll have a belt driven charger from a modified generic turbo positioned where the stock alternator is located. This has all the benefits of a standard turbo with drawbacks remedied - no lag, no excess heat. The only drawback is the 1-3 HP draw from the main crank, but it's worth the 30-40% HP increase. I just can't decide on either a dual 40mm Dellorto/Webers or a single dual-floated SU. I'm having a fix on where to start looking for the that proper dual-floated SU. However since I would prefer an intercooler the Dellorto/Webers are the way to go. I have already repositioned the overflow tank to the other side radiator - real easy to do. Will get the GM one-wire after I driven the car a month or two. But, I digress; back to the main point.

I'm just thinking of a plan "B." Something unconventional yet would be less complicated involving only a custom intake and linkage. I can dial down the fuel or changeout the needles to tune the amount of fuel delivered. With four SUs, air flow restrictoon would be better than using two SU. The same principle applied from the dual-throats.

I might be misleading myself.

The enhancement would be utilize the one thing the SU do better than the dual-throats and that is that the SU mix the air and fuel dependant upon the amount of air drawn thru no matter what elevation. Unlike the dual-throats they are depending on the throttle and must be re-tuned at different elevations like from low-land/sea-level California to say Mt. Shasta/Reno.

So, with four seperate smaller or dialed-down SUs I think there might be a considerable performance gain equal too if not better than the dual 44mm.

I am also thinking the motorcycle SU are bit better since the are designed to handle the float bowls fuel levels better on heavy cornering and acceleration because the motorcycle sway/lean when cornering. This would limit fuel starvation burps when doing heavy corning and acceleration - if any.

One thing to keep in mind about bikes. The lean angle is just enough to counteract the centrifugal force. The more speed in a corner, the more centrifugal force is generated, with the corresponding increase in lean.

I don't think bikes generate a lot of side forces except at the tire contact patch. Acceleration and braking are something else...like totally, dude!

DatsunBucky wrote:One thing to keep in mind about bikes. The lean angle is just enough to counteract the centrifugal force. The more speed in a corner, the more centrifugal force is generated, with the corresponding increase in lean.

I don't think bikes generate a lot of side forces except at the tire contact patch. Acceleration and braking are something else...like totally, dude!

Bucky your right! I did not think of that.

I did think of something else - fuel pressure per carb. The fuel pressure for the Roadster is 3.9ish PSI. That's stock 1.95ish PSI/carb. With 4 carbs that drops back to .9875ish PSI/carb.

There are lots of import cars that run motorcycle carbs. I have seen several sites for Toyotas that discussed how to do it. The easiest way is to modify a Solex intake for it or to build a custom. If you want SU carbs, then the smaller bores that are used on MG Midgets and Triumph Spitfires are an option.

The fuel pressure does not drop in a linear manner like that. The pumps are such that they only build a certain pressure. That pressure is the same (with some fluctuation from increased demand) among all the carbs. The fluctuation occurs when the volume demand exceeds the supply capacity.

The belt driven turbo is a supercharger. If you really want to pursue the turbo route, I have a water cooled turbo from a Volvo out in the garage. I don't need it and would be happy to sell or barter with it.

Cool,.. Sid. Hey, thanks for the leads. I will check them out.

The British carbs probably have available full rebuild kits too. I thought about the solex manifold, but it will require 4 adaptors.

To build a custom manifold for this setup actually might appear the same. 2 plates; 1 for the header, 1 for the carbs. 4 large pipes to connect the 2 plates. 2 smaller pipes from header plate and 1 plenum that jackets the 4 pipes to run the coolant thru for the pre-heat. Fashion a custom linkage atop the 1 plenum. Sounds like a lot of work, huh? Haven't decided what material to use. PVC would be easy but can't stand the heat. I am not comfortable using aluminum. Steel could work but it would rust up eventually. Copper is starting to appeal to me. Carbon fiber is out of the question. Fiberglass... I don't know since the tinsel strength to support 4 carbs might exceed it's ability. Anyone got suggestions or preferences?

Sid, please send me a photo of that Volvo supercharger (aka, belt driven centrifugal blower).

But, does my crazy idea has enough merit that would could perform better than the Solexes?

I once knew a guy, probably as crazy as you...He ran 4 SU's (38's) on a 2L L-series in a 510. He made a custom intake (two aluminum plates with pipes between, no balance piping, no preheat), I don't remember the linkage...

The car would not idle below 2K and was difficult to start, but when it cleared its throat and got above 3500, it was a lot of fun.

He had a custom cam and barely an exhaust and a lot of porting, etc. to match the carbs. A lot of real simple shade-tree mechanic type of modifications. He made the intake and ported the heads with hand held tools, even...No mill available...

Anyways, you would probably want to downsize the carbs a bit to make it more streetable, then tuning would be the last headache...TR

One Option I used once upon a time for an intake design was to design the intake in a solid modeling program (I used SolidWorks) then send the model to a friend who had a 3D printer. Viola instant plastic intake. I can't remember what type of printer he had and what type of plastic it was made out of, but heat wasn't as much of an issue. The neat part was I could use the exact model I built for the CFD analysis to create teh exact part I wanted. The 3D printer might or might not be an option. Even if you can oly find one of the old glue and powder type printers you could build a plug to pull a composite part off.

Sorry I just felt like rambling today.

Ian

No man... that was helpful.

I got a color wax printer here at work. No worries. I just need to get that program.

You could try wood for the material, it's easy to carve and less heat soak. This guy seems to have had good results with his wooden autoparts.


http://sambarcroft.com/pages/Livio/livio.htm

Mark

LOL! your killin' me.

With my Dremel maybe I can do the draft template in wood.