Just bought a 521

[mainer311]

The kit comes with the high filter. I think it should be okay.

 

I got the spacer plate made up this morning.

 

 

[Charlie69]

Nice work.

[Charlie69]

The Offenhauser dual plain manifolds were run with 1/2" phenolic spacers/heat shield between the manifold and the and the carb base on the datsun L motors.

 

Curious as to where you purchased your Weber? 

[mainer311]

From a Weber dealer on eBay. Probably not the best place to buy a Weber, but everything looks legit.

 

I looked around for a phenolic spacer, but everything out there has one big port at the bottom. There’s nothing where the primary and secondary are split. Yesterday in the shop, I found a big piece of Ultem, but I don’t know how Ultem fares when exposed to gasoline. It’s great stuff in high heat applications. 

[Charlie69]

I know Pierce Manifolds sells on ebay.  I think their ebay account is a bunch of numbers.  I find it odd the the base gasket does not fit.

[mainer311]

3 hours ago, Charlie69 said:

I know Pierce Manifolds sells on ebay.  I think their ebay account is a bunch of numbers.  I find it odd the the base gasket does not fit.

The base gasket doesn’t fit because it’s meant for the adapter plate that is used to adapt the Weber to the stock Hitachi manifold, which has that huge “ramp” on the secondary side. The gasket has a giant oval-shaped cutout that doesn’t work on my Offy manifold.

[Charlie69]

The stock Weber base gasket should fit the offy as the Weber should slide down the studs of the manifold no adapter needed.

[mainer311]

2 hours ago, Charlie69 said:

The stock Weber base gasket should fit the offy as the Weber should slide down the studs of the manifold no adapter needed.

Right, but all of the gaskets out there have a big cutout in the middle, which defeats the whole point of having a dual plane manifold.

[Crashtd420]

8 hours ago, mainer311 said:

Right, but all of the gaskets out there have a big cutout in the middle, which defeats the whole point of having a dual plane manifold.

I am trying to understand the dual plane manifold,  So the primary and secondary  have their own runner ? 

I could only find bad pics on the internet and so vague info, but I didn't search that hard...

I think I now see why you want the separate bore.. 

 

[mainer311]

23 minutes ago, Crashtd420 said:

I am trying to understand the dual plane manifold,  So the primary and secondary  have their own runner ? 

I could only find bad pics on the internet and so vague info, but I didn't search that hard...

I think I now see why you want the separate bore.. 

 

Yes, the casting is split down the middle horizontally. If you look down into the manifold where the carb bolts on, the primary side goes all the way to the bottom, whereas the secondary side is a lot more shallow. The theory is that the smaller openings for the primary cause the air/fuel mixture to reach supersonic speeds into the head, which in turn causes better atomization and better fuel efficiency and torque at lower RPM’s. On the other hand, when the secondary opens, there is supposed to be a scavenging effect as the high velocity primary charge picks up the secondary charge and “carries” it into the head.

 

That’s the theory. Better numbers and efficiency down low, and not necessarily any gain up high.

 

If you look at the manifold openings, you can see the separation between the circuits, and it’s pretty obvious that the high RPM flow rate suffers from the giant rib that’s cast down the middle. 

Edited January 26, 2020 by mainer311

[Stoffregen Motorsports]

13 hours ago, mainer311 said:

Right, but all of the gaskets out there have a big cutout in the middle, which defeats the whole point of having a dual plane manifold.

Not all of them. You can get better gaskets from shops that specialize in race cars that use DGV carbs (Formula Ford, etc). Pegasus racing has a whole section of performance DGV parts.

 

Worst case scenario, you make your own gasket.

 

I think the biggest gains in HP with a DGV have more to do with plenum volume and the dual plane manifold has very little of that. I have had success modifying manifolds to have a much larger plenum.

[mainer311]

Yeah, I mean, it’s not a race car. I put the manifold on there because it’s a small piece of nostalgia that is NLA. Most of the time I’m below 3krpm anyway, so if it gets me some torque and efficiency down low, then that’s cool. If it doesn’t, I don’t really care either.

[mainer311]

Getting closer. Carb is on, linkages are hooked up. Rigged up the return spring as decent as I could get it, and was able to rig up the stock gas line as best I could. The tubing loop is unsightly, but not bad.

 

[mainer311]

Ready to do hood rat stuff with my friends.

 

 

Edited January 31, 2020 by mainer311

[mainer311]

Filled the truck with new coolant tonight. No leaks anywhere. I’ll need to burp the lines and make sure the air gets out of the heater core, then top it off again.

 

Been focusing on my roadster. Met the minimum thread engagement on the rear drums, but had to install longer studs in the front hubs. Fitment is damn near perfect. The clearance on the brake caliper is soooo close.
 

 

 

 

[mrbigtanker]

Niceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[datzenmike]

3 minutes ago, mainer311 said:

Filled the truck with new coolant tonight. No leaks anywhere. I’ll need to burp the lines and make sure the air gets out of the heater core, then top it off again.

 

 

 

The air will self purge. Open the heater core set to HOT with engine running and the pump will push any air out and down to the lower rad hose and into the block. It will percolate up through the head and because it's tilted up at the front, to the thermostat. As soon as it opens, any air will gush out and settle in the top rad tank. Just top it up and check a few times as you drive.

 

Use only distilled water but if you didn't, use it from now on.

[mainer311]

6 minutes ago, datzenmike said:

Use only distilled water but if you didn't, use it from now on.

Always do. I take an old windshield washer jug and immediately make 2 gallons from a bottle of concentrate.

[datzenmike]

My water is from a mountain lake only 7 miles away so no chance to dissolve minerals into it. Soap really lathers in soft water. I visit my grand kids in Calgary and the water is so hard it takes 2 or 3 tries to wash anything.

[greenthumb]

Got to agree- that fitment looks terrific. Nice work

[Charlie69]

That is a nice looking roadster!

[mainer311]

Out with the old and in with the new.

 

 

3x9” stainless fits perfect. I can’t believe they can make these things for $20. 
 

 

After that I fired her up since the rebuild, did a quick tune on the Weber and let it idle for a while. Looks like I have a coolant leak somewhere near the manifold, but a very slow one. I let it cook for a while, and then I’ll retighten everything once it cools down.

[greenthumb]

Second the comment on that overflow. I couldn’t believe the price myself when I bought one for my 521. 

And the bonus is that it’s a nice piece

[datzenmike]

Mine is from a 720 I think. You do need the special rad cap for it to work. Plastic you can see if low.

[mainer311]

I think I have the right rad cap. It definitely has a spring-loaded pressure valve.