The Stovebolt Site Forums The Shop Area Engine Shop split exhaust manifold

I am thinking about makeing a split exhaust manifold for my 54 235 engine. Currently it has tube headers istalled[ previous owner install] The reason why I am thinking this way is for carb heat. Or would it be a better idea to just go back to single exhaust. Searching for reasons to go either way. What do you fellow bolters think is the best way? I am not looking for the noisy exhaust. Thanks in advance for your suggestions!
Dave

What do you mean by "carb heat"?

Are you trying to get your carb warmed up properly or do you thing it's too hot?

I drive a stock 216 and have no problems with the carburetor getting too hot or not hot enough. The General knew best when it was designed.

The standard exhaust manifold with a working heat riser valve is all it takes to get proper performance.

Find an old school welder who knows how to work with cast iron. The stuff is brittle, and very unforgiving of mistakes. I've been more successful using bronze fill rod and flux to work with cast iron instead of nickel alloy arc welding rod. Preheat, weld a short section, peen, and post heat the weld, plus you'll need to bury the part in sand and let it cool down for several hours after each welding session. "Rinse and repeat"! It's a good idea to keep the manifold bolted to a junk cylinder head while you're welding, to minimize warping and heat stress. The head acts as a heat sink, as well as reinforcement. Do not try to do the entire job in one session. In addition to adding a second outlet flange, it's also necessary to have a baffle in the center of the exhaust manifold that almost (but not quite) blocks off the back of the manifold from the front two ports, just behind the heat riser area.
Jerry

I believe he means a heat riser to heat the intake manifold for better vaporization.

If you’re looking for performance, you’re not going to get much from a split exhaust manifold. The issue is the head is too restrictive so a split exhaust is not going to help much.

If you’re going for the wow factor, split exhaust mimicking a corvette style manifold is the way to go. The sound of a split exhaust on a 6 cylinder is pretty sweet too. I too would like to go that route in the future.

So let me ask if I may, besides the tube headers, is there a dual intake or stock intake?

What else has been done to the motor and how do you use the truck?

Hi Wilbur,
If you have a stock intake manifold your carburetor will be happier if you use the stock exhaust manifold (single output). Particularly if you live where summers are generally mild and winters are colder. But even if you live in Dallas (where summers are not mild) you will do better with a stock exhaust manifold and (very important) a working heat flap with a good spring.

The cylinder head and intake/exhaust port contour on any stovebolt engine is the choke point. There's simply no way to get an effective improvement in gas flow by improving carburetion or exhaust with that head in the middle. It's like joining two pieces of heavy tow chain with a paper clip. Fancy carburetor(s) and/or exhaust systems are like making a silk purse out of a sow's ear- - - - -it makes the pig look funny, and it doesn't hear very well afterwards!
Jerry

Jon;
Yes I have the stock 235 intake with tube headers. Here in the Laurel Highlands of SW Pa. we get cold warm hot rainy weather. Thanks to all for the info

Dave

You will be much better served with a stock exhaust manifold with a correctly working butterfly. If you really want dual exhaust, make one out of the stock manifold, but truth be told, there is no real benefit to a dual outlet exhaust manifold with a stock motor with a stock intake.

My own experience is that I got a noticeable performance increase by changing from a 2-1/2" Flow Master muffler to a school bus muffler. I don't like the low RPM twitter but it doesn't "drum" at 2800 RPM. So in my case it seems the choke point has been the muffler. Otherwise, I have a Offy 2x1bbl manifold and a Fenton exhaust Manifold with the exhaust-heater tubes going to the intake. Works well except for carburetor icing at idle in damp weather till the thermostat opens but it did that anyway with the original manifold and working flapper.

I've made so many small modifications over the years that I can't really remember what had the most benefit. The two biggest bennies were changing from a 216 to a 235 and then to a 261, with compression going from something like 6.7:1 to about 9:1. Gas mileage improved a lot with a cam change and then with the compression boost.

I'm hoping to be able to get an engine built up with a 3/8" longer stroke and considerably more compression pretty soon. It will have much lighter weight reciprocating parts than a stock stovebolt, which should allow RPM somewhere in the 5K+ range. A 261 with a 60 overbore and a 4 5/16" stroke comes out to 299 cubic inches. That should be an interesting combination, especially if I'm successful at building one of those engines with a roller cam and roller bearing rocker arms.
Jerry

Dragsix/Hotrod/anyone else

Would you guys expand on the conversation with some recommendations for making an otherwise stock engine (235) run better? Such as, replacement for the Rochester carb, exhaust tube diameter, muffler recommendation, anything else...

Also, it sounds like you believe dual exhaust may hurt performance?? If so, how much? Gotta admit I like the looks of those Fentons.

Since the basic design of a stovebolt engine dates back to the late 1920s or early 30s, there's a very limited number of options for improving the performance. These old boat anchors are more or less glorified tractor engines, mostly designed to pull heavy loads at moderate speeds with long stroke crankshafts at low RPMs. The only viable performance improvements are going to happen in the low end of the RPM range, with moderate increases in compression, and/or more cubic inches. I've been working on various methods to increase the stroke on 235 crankshafts, up to about 3/8" or slightly more, and adapting connecting rods and pistons from other engines to make up for the difference in dimensions that changing the stroke involves. That requires some pretty sophisticated machining modifications, involving using non-original parts from other brands and years of engines- - - -flathead Ford V8 connecting rods, rod bearings for a Jeep 4 cylinder engine, and pistons from Japanese Diesel engines, etc.

External modifications such as multiple carburetors, dual exhausts, etc. look good, but they can only offer a very limited improvement in performance unless some pretty extensive internal engine mods are also done at the same time.
Jerry

Here is the thing. The 235 responds to engine modifications just like any other motor. More compression, more carb, more cam, more ignition, all adds up to more power but its relative. Little motor little gains. That, and the design of the motor essentially limits how much improvement you can make. Early hot rodders learned this early on and that fact begot the famed 12 port heads.

I have seen inquiries, "how do I make a 235 or a 261 run like a raped ape." Well the simple fact is you cant. But if you like to tinker, and I do, you can do all kinds of things to modify a 235. You just have to be prepared for the old adage for every action there is an equal reaction.

My motors are all modified. Dual and triple intakes, of my current Clifford intake with a pair of Holley 350 2 bbls. Vertex magnetos, solid lifter cams with big lifts and duration, forged pistons, GMC rods, all kinds of stuff. You could build a V8 chevy cheaper then my motor and it would go way way faster. But I like to tinker. If you don't like to tinker, then modifying a 235 or 261 or any inline is not for you. If you like dead reliability, stick with stock. The engineers designed a very reliable stock motor. No reason to mess with perfection if you want no hassles.

So, if you like the looks of a dual exhaust, and want to keep the stock heat riser system, you have to make a dual exhaust manifold out of a stock manifold (unless you are lucky enough to come by the rare 53-55 vette exhaust manifold). There are a couple of ways to do this. One, simply cut a hole in an appropriate spot and braze in an additional outlet. The old catalogs, like JC Whitney use to sell add on outlets for just that purpose. This would be the quietest version.

The second way is to actually split the manifold, and braze in a sheet metal baffle with a say 1 inch hole in the baffle, add an additional outlet on the other side of the baffle, and then weld the halves together. The bigger the hole, the bigger the rap effect, so a little bit rappier. The third way is to isolate the manifolds. Cut in two, braze the ends closed, add an outlet in the second half and away you go. This would be the rappiest version. But all would allow you to keep the stock heat system to the carb.

The Fentons save you the fabrication issues (yep, rusty carbon soaked cast iron has its welding issues) but you loose the heat to the intake. You can use the plate and copper tube arrangement for heat, or run hot water to the bottom of the intake. I don't want to opine on which is better. I use hot water. The one exception, Fenton at one time made a dual exhaust with the heat riser. The are very rare. I have never seen one in person, only a photo.

There is also the cheap but crappy sort of tube headers. Those are not worth messing with but if you do, same issues as the Fentons.

The best tube headers on the market are the Clifford Headers. But they only sell the shorty version now as the jigs for the long tube versions were either destroyed or otherwise disposed of during a dust up between some person who was working for Jack and his family after his death. But the Clifford headers, long or short, suffer the same issues as the fentons and crappy tube style. So you need hot water or hot air.

Somewhere a very long way down the project list is an idea I have to get my water brake dynamometer mounted on a trailer, with enough support equipment to make it possible to pull into a swap meet or a car show and offer stovebolt owners a definite way to document their modifications. That one bolts to a bellhousing, so the engine would have to be out of the vehicle to run a dyno test. It's entirely possible that some of the hotrodders really don't want to know if their "improvements" are all that effective. I think they would be surprised to find that most of the extra power that most modifications make happens at RPM levels the average street-driven engine seldom, if ever sees, and that a well-tuned "stock" engine will almost always make more low end and midrange power than a modified one.
Jerry

Thanks for all the replies and info about split manifols how to's. I am going to split the stock exhaust manifold so that I have a working heat riser,more so for the heat to the carb.With a little fab work on the existing dual pipipes I will wind up with the problem solved.
Dave