More random thoughts from George... Does anyone have any good suggestions for cleaning out and repainting this hard to reach area? As far as I can tell I don't have any cancerous rust there, but since water has collected over the years, some areas are starting to rust on the surface. How would one go about stripping the paint underneath the headlights on the floor of the car here, since there is only that one coke-can sized hole? Then, how would you go about neutralizing it and repainting?

Also, I have a rusted, but still useable front valence which I'd like to try to repair. The problem is the metal is so thin, I'm trying to think about how I'm going to do it. Not looking for concours stuff, but more or less wondering if anyone has even done it before? Just keep the welding heat low and try not to burn through?

Another random thought for exhaust builders: is there any advantage to having a cross-over between the two banks? On American cars its usually called an x-pipe or h-pipe, and I've heard it helps with scavenging. Always wondered why we don't see more exhaust systems, other than those like Chris' from Tangerine that connect both banks together before it exits.

Thanks for your thoughts and for putting up with my randomness.

I was walking down the street awhile ago and saw this shop had a 356 shell on stands they were painting and I dropped in to bug them. They showed me how certain areas they had "blackened". - I think they had used like 3M's rust inhibitor in there, like in the front trunk/ areas that were sort of unseen/ hard to reach. I've wanted to ask about.

Anyone know for sure about this "blackening"? or other thing you could pray in there? -I've been thinking about this, too.

Here's the easy way to get in there:
http://www.914world.com/bbs2/index.php?s=&...st&p=883872

The "blackening" may be phosphoric acid. POR-15 metal prep, ospho, or old fashioned naval jelly. Supposedly reacts with iron oxide and encapsulates it.

The main reason most exhausts don't do a cross-over is because the room to do so is quite tight. Also, the 914 fires cylinders left-left-right-right; a V8 is much more even if I recall correctly. In general, anyone who is interested in changing their exhaust out to make better power will use an actual tuned header like the Tangerine Racing one.

--DD

Dave Darling to the rescue again.

Any paint system that doesn't use "etch primer" (like shampoo and conditioner in one), you have to do the etching yourself using phosphoric acid, all those products are essentially the same. The challenge there would be to get access to apply and rinse it out. I'm thinking the stuff was the 3m rust inhibitor, shot right over surface rust.

About the uneven side to side firing in the type 4, it seems that would justify the use of balance pipes even more.- I was reading an article on V8's, crossplane vs/ flat plane, and the crossplane have a similar issue to our type 4's, firing consecutively from the same bank.

"This firing order anomaly is what creates the typical American V8 burble (so it's a sign of inefficiency!) - when two cylinders fire sequentially on the same bank, the two exhaust pulses combine to form a higher pressure and associated note from the tailpipe, which alternates from side to side.

Exhaust manifold design is not easy with the cross plane crank - cross over piping from side to side is required to improve scavenging - making this configuration unsuitable for racing/single seater applications. For road applications, balance pipes are often used to equalise side to side exhaust pressure, which helps scavenging somewhat at low RPM."

After completing my passenger side long repair I understand the purpose of the metal etching process and I've got some Ospho ready to go. I was more concerned with how to remove the old paint and loose rust from this area. Perhaps after using the paint stripper, a long wire brush? Then etch, then paint? I like SirAndy's thread, but I think that it wouldn't be warranted on my car (I'm tired of drilling spot welds).

Regarding the exhaust, thats a great article. Perhaps Chris will chime in here soon to shed some more light on the topic. I'm asking in particular because I've got a set of late flanges welded to cherry bombs for the track. I know this isn't an ideal setup already, but wondering what the benefit would be to have a crossover between the two. I'm sure it wouldn't make much of a difference in terms of power, but would it sound any different?

-George

Being a former V8 guy, the X-over was installed when you have true dual exhaust. Like stated earlier you would get a power increase due to better scavenging. I see no need for it if you go with a common collector to a single muffler. If you have a 6 and your thinking about it, I'm not sure the runs would be long enough to see any rewards.

No six here, unfortunately. Just a lowly 1.7. And thats what i thought, the run is so short, it probably wouldn't make a difference anyway. However, what I was saying is this would be a "true dual", straight out the back. I.e. two late-style manifolds running straight back.

That's where you are wrong.

Straight pipes without crossover on a /4 may look good, but you will end up with *less* power ...

Haha, shows how much I know! Okay, I'll see what I come up with when the time comes. Question then - what about the /6 exhausts that run straight out the back? Why didn't they have some kind of crossover? If you were to put in an "H-pipe" or "X-pipe," how close to the exaust ports would it need to be to be effective?

Different engine. Two more cylinders. Different firing order.

It's all about resonance in the exhaust pipes.

You da man Andy. So this system isn't ideal? Mine looks almost identical at the moment, but I still need to fab mounting tabs and lengthen it. Where would you put the crossover?

Two things wrong with that one:

- No crossover pipe
- Headers are not equal length

For a /4, the best design is a 4 in 1 setup. 4 headers of equal length go into one muffler.



(I hope Chris doesn't mind me posting these pics here)

Truly a thing of beauty. I actually used his as a reference in my previous posts as well. However, I don't have that kind of budget. I was more curious would a crossover be of any benefit on the system that I talked about, with two late-style manifolds? Like a simple H-pipe between them.

A "H" won't work since that does not force the air through the crossover.

You could always modify a banana muffler to fit your system ...

If you take a look at the stock 914 (70-74) exhaust, you'll see that it has pipes that go from the exhaust port all the way back to the muffler. The pipes are completely independent, at least until they dump into the muffler. We would hope that the muffler has some reasonably intelligent way to combine the exhaust flows, but it may very well not.

A collector like a Bursch muffler does, in fact, join the pipes together in pairs and then all four. In theory, it can be better than the stock system. In practice, it seems like it's about the same.

So, if you want to add a single cross-over pipe, which two cylinders are you going to join together? Whichever it is, it leaves the other two without. So then you need two cross-over pipes. Oh, and you probably need a way to join them together. So where do all of these go, anyway?

By the point you have gotten that far, you have probably put as much money and effort into cobbling up an exhaust as it takes to make something like the Tangerine Racing setup. Which has been refined over the years, and is very effective as well as being beautiful to look at.


The six-cylinder motors fire rather like a pair of three-cylinder motors, with one pulse every third of a two-revolution cycle. (I think that's every 240 crank degrees?) So once the three pipes on a side are combined, the exhaust pulses are very even. You might be able to get a little by adding a cross-over joining the two sides after each of the primary tubes has been joined together, but maybe not--because the exhaust pulses are very very even.


The 75-76 914 exhaust is another kettle of fish all together. You'll notice the F-shaped pipes come off the head and join together right away. No thought is given to exhaust pulse timing, and the primary tubes are very short and not at all even in length. Not so good. And in the 914, the outlet of that F-shaped thing goes forward and makes a very tight 180-degree bend. Not good for flow either. Then it goes to the back, where the left side only goes all the way across the car to the right, and dumps into the muffler. Again, not so great for flow--and that's ignoring the ancient catalytic converter that may be present in the system!!

Those are the major reasons that the 2.0 motor loses almost 10% of its power rating from model year 74 to model year 75. Because the later exhaust is pretty lousy.

--DD

There are two distinct ways to go about building an effective exhaust system.
They are named Independence and Interference.
The flat 4 engine with left-left-right-right firing order makes it real difficult to design a system which fits the car, helps the engine make power, and isn't too costly.
The firing order of a -6 makes two separate 3 cylinder Interference headers work perfectly.

The early -4 setup relies on Independence, ie. all 4 pipes dump individually into a large chamber which has the sound absorbing material.
The sound waves in one pipe are only reflected back in that pipe and therefore don't influence the scavenging of another cylinder.
Where the stock system loses effectiveness is the very long pipes, and the convoluted exit path through the muffler.

The Tangerine IV Silencer deals with those shortcomings to improve output while retaining the early heat exchangers.
The individual pipes are kept as short as can be, and enter the muffler independently.
The muffler has the flow characteristics of a straight thru muffler but has good sound reduction due to my unique design which separate sound waves from the gas flow.

All the other aftermarket "header/mufflers" which go on early HEs change the system from Independence to Interference, but don't apply the principles that make Interference work well.
The primary pipes are usually much longer than the original. One (Triad) has shorter primaries but doesn't pair the collection sequence properly.
Even if these designs create equal length pipes they won't produce much gain except for what comes from having a more free-flowing muffler.

A good Interference system relies on reflected sound (pressure) waves travelling from one primary into another.
The goal is to have pressure in the pipes go below atmospheric at a particular time in the combustion cycle to improve scavenging.
The pipes need to be joined in a particular sequence with a specific length, determined by the engine's firing order, rpm powerband, and to a limited extent, cam timing.
The ideal length is much shorter than stock HE's so anything added onto them will not be an improvement.
HE pipes are in the range of 50 inches.
European Racing Header primaries are 40" long - good for low end torque but not great for peak power.
A Kerry Hunter Header has 34" primaries IIRC.
Tangerine EVO Street primaries are only 30", Race primaries are 26".
The Tri-Y (4-2-1) layout of the Tangerine header takes the Interference design to the limit and creates midrange gains not available from a 4-1 header, while still making great peak power by having a tuned short overall length paired with the most free-flowing quiet muffler.

Not at all.
The first exhaust pictured went in a dune buggy.
Click to view attachment
The second pic is the previous generation 914 system.
The muffler was improved a couple years ago - making them lighter and quieter, and improving the fit in the vehicle.
Having our own CNC Plasma table has been a big help.
Click to view attachment