The castings look rough because the pictures are pixelated. The manifolds are a good design and they fit where they are supposed to. He's just down the road from me. They also make a conversion manifold which bolts to a sidedraught weber manifold, to which you can then bolt any of the 20V Toyota 4AGE throttlebodies. The conversion manifold has injector bosses for top feed injectors, so you only use the throttles themselves. We have done this with an A14, went quite well, but was a little on/off around town because the throttles are so big.

Video of it running http://www.youtube.com/watch?v=eI3OYuhoLO4

Both the sidedraught manifold and conversion one in these pictures come from him.

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Weber do produce a kit to convert DGV type carb to synchronous operation. Commonly done to DGV's fitted to Kent engined formula fords.

Got it. So larger runners is the main feature. Use a Weber 38/38 or 28/28 instead of a Weber DGV (28/36 progressive)

for medium built street motors, the larger individual runners will better suit engines with upgraded cam, exhaust and compression. You should pick up a fair bit of mid-range with that design on a moderately worked street engine. Pretty well proven principles on 6cyl motors.

It does look as though it was designed with synchronous carbs in mind though.

definitely a performance part that would be healthier on the bigger A series than the smaller ones in stock form. I found the oval port engines breathe quite well but restricted in this area with a stock manifold and carb compared to the A12 or smaller than A14 engines. About 20 years ago I witnessed a simple piece of square tube plenum bolted up to a set of Su oval port manifolds and a 28/36 weber on a stock A15 sunny engine and it definitely seemed way more responsive than the same carbie on the stock oval port mani with adaptor plate. There are many factors but that hillbilly larger volume setup didnt lose any torque at low speeds either.

Ive always been after a set of twin SU manifolds alone to recreate the hillbilly square tube plenum for a turbo setup but SU manifolds are very pricey these days unless I can possible source them from the states or some generous ratsun member.

The stock factory manifold is a single-plane downdraught manifol. Rowland's version looks like a 1-into-4 type with plenum vs the stock (1-into-2-into-4 with plenum). What are the advantages and disadvantages? Are the runners larger diameter? That might increase high RPM full-throttle power, but would result in decreased flexibility at cruising rpms?

We have lots of choices thats for sure for an old donk.

That single plane downdraught manifold is a nice looking design, and the first time I've seen anything like that made for an A series. Should definitely be a good upgrade for a street car.

Both good options, of course the Bpro setup is worth considering too as it comes with linkages and soft mounts. Just trumpets and carbs and Bobs your auntie

I usually guide myself by recarbs and other fatter prices for these but some good points there to consider by Harry. The single plane downdraft manifold beats oval port stock factory manis as mentioned and depending on numbers he can do group discounts.
http://www.ebay.com.au/itm/INLET-MANI ... ories&hash=item2332bc6b4a