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Hitachi SU's on a 100

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Hitachi SU's on a 100
#1
  This topic is about my 1955 Austin-Healey 100
cpcooper Craig Cooper
Chico, CA, USA   USA
I'm putting together an upgraded 100 motor for street shenanigans and, among the many lovely parts I've compiled over the years is a pair of 1-3/4" Hitachi SU carbs I believe came off a Datsun 2000 or maybe a Z. I also have some nice H6's, but the build quality of the Hitachis makes the British SU's look kind of primitive. I'm wondering if anyone here has tried the Hitachis on a Healey and what their experience was.

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Craig Clifton Avatar
Martinez, CA, USA   USA
Craig, there are two major differences between either of the Datsun/Nissan Hitachi carbs and the 100M style H6 SUs. I'm assuming you are planning to use a 100M manifold.

First, the Hitachi carbs are designed to be mounted at 0 degrees, aka horizontal. The SU H6 carbs are designed to be mounted at an angle of 20 degrees.

Second, the Hitachis are "short body" carbs compared to the H6 SU. The distance from the piston chamber to the mounting flange is about 1" greater on the H6. That additional distance is between the throttle shaft and piston chamber. That could be important if you want to stay with stock throttle linkage.

If the Hitachi is like the HS6, where it is possible to mount the float bowl at a variety of angles, including 20 degrees, then you would just need a spacer between carb and manifold to get the float bowls clear of the exhaust manifold. Add a cable throttle conversion and all that's left is determining the correct needle and jet.

One additional item I am uncertain of is whether the mounting bolt pattern of the Hitachi is the same as the SU. Might result in the need for the carb spacer to also be an adapter between two different bolt patterns.

By the way, at a previous job, I spent 13 years at a shop that was initially a Datsun specialty shop. Lot's of Z-cars and a number of 2000 Roadsters passed through my work stall. If you do go with the Hitachi carbs, make sure they are the "round top"(early) not "square top"(later).



Edited 1 time(s). Last edit at 2019-02-03 01:11 PM by Craig Clifton.

cpcooper Craig Cooper
Chico, CA, USA   USA
Thanks Craig, that pretty much takes care of it. My Hitachis are square top (I assume you are referring to float bowl) and mount as you say. I do have aftermarket M manifolds from DW and the Hitachis fit right on the mounting flange, but the other issues make it pretty impractical to pursue. Back they go on eBay. Maybe somebody with a Triumph, or, better yet, a Datsun...

Appreciate the help. Look me up if you're ever in Chico.

Craig

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Craig Clifton Avatar
Martinez, CA, USA   USA
In reply to # 208916 by cpcooper My Hitachis are square top (I assume you are referring to float bowl) and mount as you say.

I was referring to the piston chambers. Early ones had the same radiused corner as an SU. The later cars had chambers with a sharp right angle between the horizontal and vertical edges. Those were emission carbs and a fair pain in the ass to deal with.

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