side draft carbs

[austinsailor]

somewhere I've seen a setup where the flathead had three sidedraft carbs mounted over the head on curved intake pipes.

I don't know yet what sort of intake I'm going to put on mine, but that seems like an interesting option. it seems fairly simple, but I don't know anything about these and wouldn't know how to select things. I suppose figure cfm of both and find a close match. but I'd probably start looking for something rare when another similar one would be common.

anyone know about this type setup? is it practical for a street car?

[moose]

Maybe this one?

This is on my '54. It was real nice to drive, good idle and midrange but didn't pull through the top end. These are Mikuni 32mm, and they are too small. They were a set of four from a 750 Kawasaki, and the motor has three intake ports. Removed one and it works. Even has the choke set up. Started like a fuel injected motor, didn't need to touch the throttle at all.

Edited May 4, 2011 by moose___
add video

[austinsailor]

yes, that is one I've seen.

I wonder if there are bigger one that would work better?

normal manifolds with no heat have problems. there is no heat on these when used on motorcycles, or on small sports cars, as far as I know. I wonder why one type needs it and another doesn't?

[greg g]

I still think a pair or set of 3 SU carbs would look good on a flathead. And since main jets are externally adjustable they make for easy set up and adjustment of t F / A mixture.

http://www.zparts.com/zptech/articles/mal_land/ml_sucarb2/SUcarb_111601b.htm

The solex clones from an early Datsun Z car would be a good source as well as Jaguars, and Triumph tr 6.

[austinsailor]

like these?

eBay Item #: 130516040090

[moose]

They do make bigger ones, 34mm, 38mm, probably bigger too.

For heat issues, I don't know about this one. I drove it mostly in the summer time in Missouri. I wouldn't be too worried about icing the carbs, as they are not too far from a good heat source(the head). Also the metering on these carbs is done slightly differently, with the constant velocity throat. It's got a throttle plate and a slide valve that goes down near to closed at idle, and pulls quickly open with more airflow from the opening of the throttle plate. It has a better metering effect throughout the throttle range.

At least that's my understanding. Please feel free to educate me/all of us, if any of this is incorrect.

yes, that is one I've seen.

I wonder if there are bigger one that would work better?

normal manifolds with no heat have problems. there is no heat on these when used on motorcycles, or on small sports cars, as far as I know. I wonder why one type needs it and another doesn't?

[greg g]

Those could work. Usually go by choke diameter, so you would be looking for 2 X 2 or 3 x 1 3/4.

Chec your area for places that work on british cars, they probably have several shelves of them in various forms.

our engines are in the the 3.5 to 3.9 Liter displacement.

Edited May 4, 2011 by greg g

[austinsailor]

looks like 3 from a 71 or 72 240z would be ideal.

would there be an advantage between mounting them over the motor on long tubes like above, or short tubes straight into the ports?

[greg g]

What ever you like and makes the linkage and plumbing the least hassle.

[moose]

I believe in long individual runners. Long run equal length intake tubes produce a harmonic effect on the intake charges. Something to do with the speed of sound coupled with the volume of the cylinder and the volume of the tube. Blah, blah, blah...

All I know is the intake that I ran on my 55, made it pull hard and go fast!

looks like 3 from a 71 or 72 240z would be ideal.

would there be an advantage between mounting them over the motor on long tubes like above, or short tubes straight into the ports?

[austinsailor]

It looks like 71-72 is pre-emmissions stuff, and also has provisions for water heat. it's hard to say for sure from what I can see from my Internet research, but it sounds like the hot water hookup is on the carbs, not the manifold. this is sounding possible.

It appears that they are 1 3/4" dia, so from the charts, 3 of them should be in the ballpark.

I need to find one I can hold in my hand and think it through.

I like it!

[james49ply]

I have motorcycles and have contemplated installing three Harley carbs one for each intake. they are side draft and one will provide power for 74 to 80 ci, so three on flat six equates quite well. haven't had time to experiment with it tho. If I do I will post the results.

[rustyzman]

Info on Datsun SU's. I was a real Z guy in my past, had a '72 240 (hence the username). The SU's from 70 to 72 are desirable. The 73-74 units are boat anchors.(seriously, I won the carburetor toss contest at one of our Z club car shows with a 73 unit)

The manifold is water heated. The carbs are mounted on phenolic isolators and the coolant communicates to the carb through those. There are no other direct water connections on the carbs. These also have no traditional chokes as they are choked by lowering the jet tubes to increase the surface area at the needle base. They are tremendously reliable as long as you adjust and balance them and keep the air chambers for the needles clean. For performance on those vehicles I had triple 44mm Mikunis. Lots more adjustment but tremendous power potential. Even the bigger stroked Z engines would likely not be able to outflow that setup, and they generally redlined at around 8300 RPM.

If you go SU, the Hitachi units on the Datsuns are the way to go IMO. Anything english will probably not have the same reliability from my experience. Others may disagree.

As for the power brake chamber, I still have mine from the dismantling of my Z. They are very compact units and very reliable as well. They are MasterVac units.

If you have any questions about the Datsun stuff, ask me and I will help if I can.