Datsun Roadster Forum-311s.org

That is some very interesting reading on the V-Performance website. I'm wondering how they would perform on my R20 Stroker that uses the Isky DR66 cam. If there is a known, straight forward solution to throttle and choke cable installation and operation, I'd be keenly interested in these HSR's.
I'll have to compare cam lift and duration specs of my DR66 cam, with the U20 A & B cams to determine which of the HSR 42's or 45's would be suitable. Comments and advice are welcome.
Mike

One comment would be to not go too big. 45mm will kill torque and gain little to nothing top end... that's been proven by another U20 EFI pioneer who tried to switch from 44mm Mikuni to 45mm TBs and could never get the same useful power. I've run 40mm chokes in 45mm Dellortos and gained a little top end but with some low end loss vs 37mm chokes (mainly due to how air velocity influences how well the carb's jets get a "signal", making the slow speed system harder to jet and the car less streetable). Granted, these carbs are not the same and may be able to address this issue. I currently run 40mm TBs and have gained everywhere, and have since improved low end torque with 80mm velocity stacks. I personally would not go over 40mm, and figure out some kind of decent velocity stack that's as long as you can fit.

Can I assume that a U20 / SU uses the "A" cam, and the U20 / Solex uses the "B" cam ? As you can tell, I'm not widely U20 knowledgeable.
Thanks, Mike

Correct!

So, regarding the Mikuni HSR carbs.... does anyone know, or want to comment on, or suggest how the throttle and choke cables could be installed, and operated on a stock 1600 intake manifold ? ...Pjackb ? ...JT ? ...D. Premo ? ...anyone ?
Mike

Gregs672000 wrote: Mon Apr 28, 2025 1:38 pm One comment would be to not go too big. I currently run 40mm TBs and have gained everywhere, and have since improved low end torque with 80mm velocity stacks. I personally would not go over 40mm, and figure out some kind of decent velocity stack that's as long as you can fit.

I always wondered about adding a choke to 45 mm TBs

fj20spl311 wrote: Tue Apr 29, 2025 10:18 am

Gregs672000 wrote: Mon Apr 28, 2025 1:38 pm One comment would be to not go too big. I currently run 40mm TBs and have gained everywhere, and have since improved low end torque with 80mm velocity stacks. I personally would not go over 40mm, and figure out some kind of decent velocity stack that's as long as you can fit.

I always wondered about adding a choke to 45 mm TBs

One of the things I wondered about was what the effect is on flow etc when a 40mm TB is matched to a 45 mm intake... there's a step off, and I wonder what that does, if anything. When I was looking to purchase a set up, I asked around but nobody could give me an answer.