Mikuni HSR review

[Daryl Smith]

Irrelephant

[Gregs672000]

Thanks for the update! Hope all comes out well. Keep us posted!

[ppeters914]

How much of this info done on a 2.8L six is directly applicable to the roadster's smaller fours?

[Pjackb]

"...as for the slight dip in midrange I've played around with different setting on the 123 and i can still feel its there and i'm thinking its a function of my cam profile."

I would be more inclined to blame resonance in the intake tract rather than the cam....You could try longer or shorter velocity stacks (stub stacks?) to check the effect.

It could be, It's there with both SUs and the HSRs and I've seen the same dip to different degrees across a number of dyno sheets using SUs and the common thread is the intake .
On cars with Mikuni/Weber or EFI it is usually very flat

[Pjackb]

How much of this info done on a 2.8L six is directly applicable to the roadster's smaller fours?

Well I'm focusing on the carbs only as an alternative to Hitachi SUs so I would think all the information would be relevant to someone looking for alternatives, especially considering that going to Mikuni/Weber nowadays is an easy 3500-5000$ spend

some of the lessons learned
1. These carbs are extremely easy to install an tune and even with jetting all over the place they will get you car running in no time
2. 2x 45s are too big for a U20, (they're a perfect match for my 6cyl pushing close to 240bhp )
3. They will increase performance compared to SU and maintain torque
4. They respond well to short stacks on cars

Right now I don't need them on my U20 as i have perfectly matched PHH40s but I'am rebuilding a 2.2 L series stroker for a 510 it has Roadster SUs righ now so i will do a back to back with HSR 42s