Sidedrafts without softmounts?

[EricJB]

Has anyone ever tried running dcoe's or phh's mounted directly to the manifold? I am wondering if I need them more or less with solid motor mounts. The vibrations are supposed to effect fuel supply or something. Just wondering if I still need them, as I am tight on room.

[datzenmike]

Aren't the phenolic spacers just to insulate them from the heat?

[Boaty]

Are you referring to phenolic spacers?

 

The phenolic spacers are there mainly to assist in minimizing heat soak from the manifold to the carbs (since the manifold is going to get pretty hot from the head as well as the exhaust manifold, hence a heat shield).

 

I'm sure the spacers would lose efficiency based on thickness, but I am also confident you could have the spacers machined thinner for the sake of saving some space. All depends on what you're running, I guess. I personally wouldn't run without phenolics. My L20B would get hot enough in summer, that if I disconnected the fuel hoses from the fuel rail going to the SU's I have, you could see the fuel boiling out of the rail. It was mounted directly to the manifold mounting studs. You can feel the temperature difference by touching the carburettor and the manofold, and the manifold was *much* hotter than the carburettors were at temp. As in the intake could likely burn your finger, and the carbs were just uncomfortably hot to work on until it cooled down.

 

Simple test. Spray carb cleaner on the intake manifold and you'll see it boil off immediately. But it simply evaporates off of the carburettors. At least in my case.

 

I would keep them. They are there for a reason, and I have never once seen anybody run without them, even the stock carb uses one for this purpose.

[EricJB]

The softmounts are the plastic spacer with the O rings on both sides, and springs under the mounting hardware. Yes phenolic spacers ( and possibly softmounts) are for heat issues, but the softmounts have another purpose. Just wondering if I eliminated the need with the solid motor mounts.

[Boaty]

Well being fair, the engine is going to shake the same regardless. But with rubber isolators the engine is going to move more. With solid mounts it's going to just shake the piss out of whatever you're working on. I had poly mounts with my KA for awhile, I promptly swapped to rubber mounts. The only thing I was worried about was a window/door/bumper/headlight falling off, haha. And I gave up entirely on using mirrors - they were useless even at cruise speed.

 

I thought you were referring to phenolic spacers. I'm not familiar with what you're referring to, so I am not sure and can't offer my opinion. But I'm a firm believer that when things are there, they are there for a reason.

[datzenmike]

Has anyone ever tried running dcoe's or phh's mounted directly to the manifold? I am wondering if I need them more or less with solid motor mounts. The vibrations are supposed to effect fuel supply or something. Just wondering if I still need them, as I am tight on room.

 

Keep the phenolic spacers. Maybe try to make thinner ones or something else that heat insulates.

 

Nothing to be gained by running solid motor mounts, nothing. Won't run better or faster. What it will do is make driving it a chore. The vibrations will make you piss blood.

[wayno]

I have a feeling this is for his drag truck, so nothing is likely comfortable about it. :lol:

 

I would wonder about the fuel jumping around in the bowls though with solid mounts, and having it boil in the bowl, as when it gets hot my SUs boil when I stop at intersections, even though I have a heat sheild, it still starts missing till the air starts moviing around in the engine compartment after starting to move down the road again, it usually misses till I get into 3rd, and my fuel does recirculate back to the tank, so it might quit boiling when the cooler fuel reaches the bowl.

[hobbes_the_cat]

I run weber 40's mounted directly to a cannon mani. Haven't had any boiling issues yet. I don't drive it daily but I did cruise durring the summer without problems.

[67411sss]

softmounts are to help keep the carb in tune by dulling vibration from the engine, doesn't have anything to do with heat. The mercedes 190sl had solex sidedrafts hardmounted to the manifold. Just make sure everything is true.

[EricJB]

Wayno is correct. It is the drag truck. The solid mounts are to make it react quicker off the line, and because it was starting to move a bit and creating other issues. I'm not too worried about the heat. It doesn't run that long. Just want to make sure fuel doesn't start blowing past the needle and seats or something like that. Those softmounts cost some $, and I'm sure there is a reason for them, but i will try it without them and see. Thanks for the feedback.

[ggzilla]

I run my twin carbs without soft mounts, they are bolted directly to the intake manifold.

 

No problems when using stock rubber engine mounts.

[EricJB]

I run my twin carbs without soft mounts, they are bolted directly to the intake manifold.

 

No problems when using stock rubber engine mounts.

 

 

Seems to me I saw a pic of your motor somewhere on here. i dont remember seeing them. Time to make some paper gaskets.

[Stoffregen Motorsports]

Vibration is definitely a concern, especially on a 4 cylinder, in line engine. Many manufacturers have used rubber isolators between the carb and manifold, even Nissan/Datsun. The Roadster had them.

 

There are two different varieties of soft mounts, or carb isolators/insulators (different terms), at least there are two I will consider: offset and non-offset. The offset isolators have a bolt spread on the carb side to match the carbs and a larger spread on the manifold side, to match the manifold. The non-offset isolators have the same bolt spread on either side.

 

Why two bolt spreads? Well in the casting process, the carburator flange side of the intake manifold has a thick flange, and the offset isolators are easier to get nuts and washers on.

 

But, the non-offset isolators are softer than the offset, so many times I have machined the backside of intake manifolds to make clearance for the hardware. Then sometimes I would use a "jetnut", for the small hex head and even more clearance.

 

Do they work? Yes they actually make horsepower (or more accurately, they don't lose horsepower) on the dyno.

 

What about heat? Yes they do isolate from heat, but I have a template for a heat shield that mounts between the intake manifold and exhaust header. I have made them out of aluminum or steel, but I always sandwich a sheet of woven asbestos in between to soak up that heat. Real gains are to be made by shielding from heat.

 

Lastly, the part number for the stock Roadster offset isolators is 16174-25501. They cost about $35 each. As far as I know, Nismo no longer makes the non-offset isolators. If you want to use the roadster isolators you will have to slot the holes in the manifold.

 

 

Here's the other side of the isolator. Notice the smaller bolt spread.

 

Here's a pic of a jetnut

[EricJB]

This is what I have. They were for 45 dcoe's, and I bored them (with the manifold) out for the 48's. They are just a piece of plastic with Orings on both sides. And yes I have a lot of work left on the manifold.

 

 

[ggzilla]

Those are soft mounts. You can also mount them with a paper gasket (like I do) but it is not recommended depending on the engine shake, which can upset the fuel bowl and fuel metering.

[Stoffregen Motorsports]

The soft mounts you pictured work, but they rely on an o-ring for sealing. And they aren't as flexible as the Nismo type. Another thing to consider is an air cleaner like a ITG. Even if you don't run the filter, the backing plate ties the carbs together. This is important because when the throttle linkage pulls onthe throttle shafts it can throw the balance off.

 

Like this.

[EricJB]

The plan is, to build an airbox, with a base plate simalar to your pic, and a heat shield, and draw cool air from the left high beam hole. The problem is, the rear horn is 3/8" away from the master cyl. I was hoping I could run carb to manifold and gain another 3/8". But it looks like I'm going to have to find shorter horns, or put the master cyl in the airbox. I am also building an 1 3/4" header with a merged collecter that dumps right behind the left front tire, so it's going to be tight in there. Thanks for the help.

[Stoffregen Motorsports]

The problem is, the rear horn is 3/8" away from the master cyl.

 

Notice in the pic, the front reservoir on the master is relocated to the inner fender well. You can do this using a Tilton (now Wilwood) reservoir relocation kit. The master is still close, but the reservoir is out of the way.