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Discussion Starter · #1 ·
Intake & Exhaust Manifold Mods

I've got a '73 GT with the low compression engine. I was think about tearing it down, and installing flat top pistons to bump the compression back up. I've backed off that route, I'm now trying to get the most out of what I've got. The engine has about 90K on it, but it's still running strong, burns no oil. The head was done recently with hardened valve seats by the PO. It's now got a Weber, K&N air filter using modified OEM snorkle, Pertronix ignition, FlameThrower coil. I picked up an intake manifold on Ebay for $5 that I intend to take a shot at doing some moderate porting as per Bob L's excelent article. I also just obtained a "75 Sprint" exhaust manifold that I'll eventually be installing with a custom 2" exhaust system with a turbo muffler. I've heard flow in and flow out of is the key to getting a few more HP from the 1.9L engine. Just wondering if anyone out there might "guesstimate" how many HP's I might happen upon with the modifications described? Thanks.
 

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Welcome aboard!
Your question may have been answered in a previous post.
Try doing a search of the forums using some of the key words in your post. "more horsepower", "engine modifications", "Porting", etc. The forums search feature is a great tool for finding info that is in our 4,000+ posts.

One thing you may want to look at is if the weber is jetted properly. Out of the box webers 32/36 do not come with the optimum settings for the 1.9.
 

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Although that later engine is rate at 75 hp, it's closer to 62 stock...I tell you this to let you know where you're starting from! Properly tuned, those bolt-ons will bump you up to around 80-85 hp. That's quite a lot percentage-wise (over 30%), but it deals with many of the engine's shortcomings. Don't expect the next 30% to come so easily!!

Bob
 

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Discussion Starter · #4 ·
Thanks for the info, the search feature of this board works great; I've had less than nice things to say about most search features of other boards I belong to.

Dang, those are pathetic HP numbers, but I still smile when I'm out driving the GT. I don't expect to double the HP, I just want to coax whatever is obtainable with "resonable" work. The exhaust systems is leaking so I figured as long as I'm there I'd go the Sprint exhaust manifold route. The porting of the intake manifold seems like a fun and cheap modification, with great potential.

Now regarding the proper jetting of the 32/36, I see a thread was started to capture "what works well" but there didn't seem to be any follow up posts. I'm certain mine is "out of the box", the PO didn't modify the snorkle for proper clearance, and just left all the OEM hoses going to the valve cover and carbon canister just hanging in the breeze. So if anyone has some recommendations for jetting a 32/36 for a 1.9L with the mods I've mentioned; I'm all ears.
 

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FWIW, most of those jetting kits are way off....you can't jet a carburetor from a desktop.

The only way to jet correctly is hands-on. A box of jets, a CO meter, and someone who knows how to read spark plugs is all it takes. That and about 4 hours.

Bob
 

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Discussion Starter · #6 ·
Bob,
Thanks for the info, but with those qualifiers I guess I'll be running out of the box jetting for now. Maybe in the spring after I get all the intake/exhaust work done I'll take a stab at it; but a CO meter? The cheapest I fould is one Fluke makes on that plugs into a DVM for about $200, but that's kinds of steep and I still wouldn't know what to do with it.

Hmm, Pleasant Valley,CT about a hour north of the Bridgeport ferry....you wouldn't happen to do this for a living would you?
 

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jimsky said:
Hmm, Pleasant Valley,CT about a hour north of the Bridgeport ferry....you wouldn't happen to do this for a living would you?
Uh...no. But if we ever have a New England Opel meeting again or you go to Carlisle (and I happen to make it), it's easy to check on my CO meter.

Bob
'Will work for turbo'
 

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Summit racing catalog has a in-car Air/Fuel gauge for around $30... hook it straight up to an O2 sensor in your exhuast, and you're all set. It reads out in a digital bar graph. I have one in my Buick, used a O2 sensor from a chevy cavialiar, around $20 new... make sure you get a one wire O2 sensor. Works great for tuning. Also and in-car vacuum gauge helps plenty, optimal jetting will give you the most vacuum.
 

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Discussion Starter · #9 ·
Sounds very cool. Would you happen to have a part number, manufacturer or actual item name that would help to search Summit's website? Thanks.
 

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Discussion Starter · #10 ·
I did find the air/fuel guage in Summit's catalog, JC Whitney also carries it. Question: Just where in the exhaust stream would the O2 sensor need to be mounted? Where are they mounted on modern cars that use O2 sensors? Exhaust manifold? Engine down pipe? Before or after muffler? Would where it's mounted effect the calibration/accuracy fo the guage reading? Has anyone actually done this installation before?
 

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O2 Sensor Placement

The oxygen sensor operates properly once its up to temperature, what specific temperature I don't know. Therefore, it needs to be fairly close to the source/head for quicker warm up. But, you want the one single sensor to work by averaging the exhaust from all 4 cylinders. Therefore (again), it should be mounted at the closest location to the engine at which all four cylinder's exhaust merge. Did I beat around the bush, or what!

HTH
Paul
 

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Keep in mind most air/fuel gauges are pretty much 'gimmicks', and are there for observation purposes. They don't respond fast enough to really be used as a tuning tool, but they will let you know which direction you have to go if you are having an issue with your air/fuel ratio. Not to mention, they don't actually have an accurate marking system. So you don't really know where the gauge is supposed to read on your Opel anyway! A CO meter will provide hard numbers however. Opels make best power at 4.5 to 5.5 % CO at full throttle.

Another factor is the location of the sensor, as mentioned above, and the voltage running in your particular car...they're VERY sensitive to this. Mine was inaccurate until I trashed the stock Bosch alternator/regulator and switched to a GM alternator. Leaded fuel is a 'no-no', it will damage the sensor and give an improper reading.

BUT, they have merit. I had a Haltech A/F meter in my Ascona back in '92, and without it I'd have melted an engine down at the racetrack when I found that the stock fuel lines were not enough to feed a modified engine with a single carb...it went dead lean and the A/F gauge dropped to zero. I lucked out and only melted one plug, but that took less than a second from the time I saw the meter drop and I lifted off the throttle. Thankfully I carried a spare set of plugs with me to the track, and I was able to drive the car home intact.
 

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I actually know the right answer to this one!

The O2 sensor should be mounted just downstream of the y that joins the manifold "extension" pipes.

O2 sensors work at >700 degrees, and the need for near-ness to the motor is really for quicker warm-up. The exhaust gasses aren't actually heating the sensor so much as the chemical reaction in the sensor itself. With the exception of some very new imports, almost all oxygen sensors work the same. The chemical reaction between the exhaust gasses and the chemical plating in the sensor generate a 1 volt potential when at the proper stoichiometric ratio. Lean mixture (lots of extra O2) will produce a low voltage and rich mixture (too little fuel for the ammount of air, little O2 in the exhaust) will produce a higher voltage.

There are a couple of variations on the basic O2 sensor:
-The most basic one, typically gound in GM cars, just has one wire, and the output for the sensor is the potential from that wire to the exhaust pipe, which is typically grounded. With very few exceptions this is a black wire.
-The next variation is the 2 wire (hard to find) which adds an additional ground wire from the sensor to the chassis or computer to ensure more acurate readings with possible engine ground issues.
-Chrysler likes to use a three wire sensor where the black wire is the output with respect to the ground, and the 2 white wires are for a heating element (like on an electric choke) used to heat the sensor faster.
-Finally, some imports and most universal replacement sensors have 4 wires combining the ground, sensor output, and the wires for the heating element. Some even add an additional fifth wire for a 2-stage heating element.

For cheap guys, like me, the easiest thing to do is install nearly any oxygen sensor and hook up a multimeter to the output and the exhaust pipe.If you don't already have a multimeter, you should get one, and even the $7 analog ones from Walmart will work fine. Your output is going to be, like Bob hinted to, not a quickly changing and quick responding item, but it will be useful. Draw yourself up a quick table, and take the car for a drive. Keep steady engine RPS for enough time to get a stabile reading and mark down wheather it is rich or lean at that RPM. Vary your speed some and keep track of how the sensor responds throughout the engines operation range. It should be easy to spot where the engine goes from rich to lean or vice versa, and you should be able to dial-in the jetting with a lot fewer intermediate steps.

Those newer imports, Like Bob's Subaru, use an additional sensor with a much larger spread of voltage either side of the proper ratio. These new O2 sensors are therefore much more precise, and they also happen to be quicker acting, both of which make the cars computer able to use them more for instantanious tuning. They are also more in the $250+ range instead of the $45 or so for most other new ones.
 

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Discussion Starter · #15 ·
Very informative and helpful reply, thanks. Just how does one install the O2 sensor? Drilling and tapping a hole( I assume the O2 sensor is threaded and screws in) on a thin walled exhaust pipe seems it would be difficult to do, and I can't imagine a good seal would be made. Drill, press and weld a threaded insert or boss (we call them PEMS in the electronic industry) into the exhaust pipe that the O2 sensor would then thread into?
 

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Threaded adaptor

Most of the Hi-Po catalogs (Jegs, Summitt, etc, even JC Whitney) sell an O2 mounting "button". Its a threaded adaptor (round OD w/threaded ID) that you weld to the exhaust pipe... after a hole has been drilled. The sensor just screws into it.

HTH
Paul
 

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Just me but...

My own favorite for mounting the O2 sensor is a kit from Dynatech that includes a threaded "bung" to weld to the exhaust pipe, a cap to thread into it, and a check valve assembly to use the hole for a pan-e-vac system. This allows you to use the exhaust as a mild vacuum source for removing gasses from the crankcase, which is supposed to free-up some power. Almost every top fueler uses some variation on this system, so it must work, right?

I don't know how much power it will really yield, but puting crankcase blow-by out in the exhaust makes a lot more sense to me that putting it back through the engine. Besides, the kit is $15.99 from Jegs (part # 329-85-100950) and you can always opt to use just the plug and not the vacuum fitting.
 

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Discussion Starter · #18 ·
Just what I was looking for, thanks. I can now buy all the bits and peices needed, and plan out what I want for the custom 2" exhaust system that I'm going to have installed in the spring.
 

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Discussion Starter · #19 ·
Well today I finished modifying my recently aquire '75 Sprint exhaust manifold as per some suggestions from the ClassicOpel board. Removed both of the webs and the boss on the center runner. Painted up great, looks pretty nice. My ported intake manifold is done too, I've got no more winter projects left. I need spring (warmer garage) to start installing this stuff.
 

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About 2 years ago, I was in search of the head pipe for my Sportwagon, this is also the same pipe for the Manta and the Sedan. I was looking all over the net in Europe trying to find a source, while I had my friend at Midas scour their vast inventories and see what comes up. As luck would have it, I found a place in Germany to get the OEM pipe, but, Midas turned up a pipe from the Canadian division. I bought both pipes and when I got them side by side, I noticed a few differences. Even though the flanges are the exact same, and both pipes have all the proper bends, the one from Canada was different in that when the two parallel tubes come down from the mounting flange, it only goes about 15" before they connect back into one. It also has an O2 fitting down stream. The OEM is like I have always seen, the two tubes parallel for about 3' ending up well under the car before they join. Is there any signifigance in this difference? Bob?
 
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