30MPG is the Goal

[GTJIM]

..and don't forget the thread about using a tiny bit of Acetone in the fuel too.

http://www.opelgt.com/forums/general...tone-fuel.html

.. and the grooves in the head!

http://www.opelgt.com/forums/general...n-chamber.html

though it might be better to put the groove in the piston top - rather than 'hack' into a 1.5L head ... :O

[opelnut10]

Originally Posted by hrcollinsjr Quote: Originally Posted by opelnut10 Lock the dist. plates and make it full mechanical advance take it to someone with a dist. machine and play with the springs and weights until you get it at full advance at 2800RPM. WHY on a nearly stock engine would you want to disable the vacuum advance mechanism? Limit total mechanical advance? Yes! Harold

Because by making it full mechanical advance YOU control the curve not some 35 year old vacuum pot that has had more use than a banjo string, not to mention problems associated with vacuum hose fitment. If timed correctly the mechanical advance dist. will improve fuel mileage, and I believe than is what this thread is about.

[madhatterpdc]

If you are able to justify the fuel savings over say, 47 years, you may want to look into having a camshaft designed according to the Atkinson Cycle

Atkinson cycle - Wikipedia, the free encyclopedia

The Atkinson cycle may also refer to a four stroke piston engine in which the intake valve is held open longer than normal to allow a reverse flow of intake air into the intake manifold. This reduces the effective compression ratio and, when combined with an increased stroke and/or reduced combustion chamber volume, allows the expansion ratio to exceed the compression ratio while retaining a normal compression pressure. This is desirable for improved fuel economy because the compression ratio in a spark ignition engine is limited by the octane rating of the fuel used. A high expansion ratio delivers a longer power stroke, allowing more expansion of the combustion gases and reducing the amount of heat wasted in the exhaust. This makes for a more efficient engine.

This would sacrifice power output throughout the rpm range, perhaps below an acceptable threshold. A small turbo, coupled to a variable flow valve to increase gas velocity at low RPM would counteract any power losses entirely.

Mileage may vary.

[hrcollinsjr]

Originally Posted by opelnut10 Because by making it full mechanical advance YOU control the curve not some 35 year old vacuum pot that has had more use than a banjo string, not to mention problems associated with vacuum hose fitment. If timed correctly the mechanical advance dist. will improve fuel mileage, and I believe that is what this thread is about.

So I've thought incorrectly all this time that vacuum advance on a street engine improved economy?

Harold

[opelnut10]

Originally Posted by hrcollinsjr So I've thought incorrectly all this time that vacuum advance on a street engine improved economy? Harold

I don't know if your thinking incorrectly, I can only speak about what has worked for me. Every Opel that I have ever owned has had the dist. locked and the advance reworked to put it in quicker on a stick shift car and slower on the automatic. My wife drove a 75 FI Manta with an automatic that was getting 22-23 MPH before the dist. modification and with no other modifications made it went to 25-27 MPG. You have to have a dist. machine and play with the springs and weights in order to achieve the right curve and you have to time the car at TDC by static timing it, with the engine off.

[hrcollinsjr]

I did a quick google search on vacuum advance helping fuel economy and came up with this:

Vacuum, Timing and Fuel Economy: in Non-Computer Assisted Engines

--------------------------------------------------------------------------------

Publication:Lousiana State University Date:1993
GOALS:
To understand the relationship between vacuum and ignition timing and to identify the cause of reduced fuel economy.

OBJECTIVES:
For non-computer assisted and some partially computer assisted vehicles, the student will:

1. Learn to identify the ignition system's vacuum sensing device.
2. Acquire the knowledge in order to test for a faulty vacuum sensing device.
3. Calibrate, for optimum fuel economy, a vacuum sensing device (when possible).

LESSON/INFORMATION:
Ignition timing is the single, most critical adjustment for a gasoline engine. Assuming the engine is in good mechanical condition, there are no vacuum leaks, and the fuel mixture is correct, then the ignition timing can affect the net power yield from the fuel. Improper timing can significantly change a vehicle's mpg. Three types of timing are used for gasoline engines. They are:

1. Static timing;
2. Mechanical (centrifugal) timing; and
3. Pneumatic (vacuum) timing - mechanical.

Each has a specific purpose.

1. Static timing establishes a physical relationship between engine crankshaft position and the distributor. This is fixed and should not change. Basic and initial are terms also associated in the static timing.

2. Since fuel burns at a relatively fixed rate (i.e., time to burn is in milliseconds), then the faster the engine runs the earlier the fuel must be ignited so that the millisecond time frame will remain constant. Thus, mechanical timing advances are used. A device, usually a centrifugally activated weight control balanced by a spring, advances the timing proportionate to engine RPM's. The faster the engine runs, the more timing advances. This is true up to approximately 2,700 to 3,500 RPM's. Mechanical timing is critical to acceleration and power response in a gasoline engine. This timing is added to the static timing.

3. The third timing, pneumatic (vacuum) - mechanical, provides an extra measure of timing over and above static and any mechanical advance. The vacuum advance extends the burn cycle even longer so that all the heat energy may be absorbed by the pistons resulting in more power yield per measure of fuel and more mpg. The sensing device is a spring offset, vacuum activated diaphragm. This diaphragm receives its vacuum signal from the carburetor or intake manifold. In many vehicles this signal is modified by the transmission gear selector position, by coolant temperature sensor(s), by vehicle speed sensor, or by combinations of the above. Early computer assisted vehicles retained the vacuum advance system but employed the computer to modify the signal to the diaphragm, thereby optimizing the system performance.

Total advance is the combination of initial, centrifugal, and vacuum.


Vacuum advances are sensitive devices. By design, vacuum advances are spring offset to give zero advance. Only when a strong enough vacuum signal is present will it advance the ignition timing. The higher the vacuum signal, the greater the timing advance. High vacuum signals are indicative of low engine loads at a closed or nearly closed throttle position. At idle, when the throttle is almost completely closed, vacuum is highest; however, during idle, no vacuum signal is present at the vacuum advance. This is accomplished by tapping the vacuum for the advance system above the throttle plate. Excessive vacuum advance results in part throttle ping and a loss in mpg. Insufficient vacuum advance results in poor part-throttle response and a loss in mpg. Notice both insufficient as well as excessive vacuum advance results in a driveability problem and a reduction in mpg. Many drivers try to correct the part-throttle ping by purchasing higher octane fuels. This may fix the ping problem but mpg will still be reduced (See Fuel Octane Selection Guide.) Some technicians attempt to fix poor part-throttle response by advancing or retarding the static timing. This may correct the part-throttle problem, but basic, wide open, and near wide open throttle positions will have excessively advanced or retarded timing. This could result in an extremely hot combustion chamber temperature and long term, severe engine damage may result. Worn cylinders, cracked piston rings, burned valves, worn valve guides, damaged piston ring lands, or holes in pistons are some of the possible long term engine damages that may occur with excessively advanced static timing. Again, owners may compensate for the pinging noises by purchasing higher octane fuel. The result is the same, lower mpg and wasted energy. (See Fuel Octane Selection Guide.) High combustion chamber deposits, low fuel economy, or poor power output can occur with retarded engine timing.

The correction for each of these problems is a complete, systematic, diagnostic approach using the manufacturer's recommended procedures and specifications. Static timing must first be set properly. Mechanical advance may then be checked and finally the vacuum advance checked. If the distributor fails any test, it should be removed for repair, recalibration, or be replaced. Prior to disconnecting a distributor's vacuum advance system, always check hose routing, system sensors, and soundness of the hoses and connections. Ultrasonic vacuum detectors or propane detectors are good diagnostic devices for locating leaking vacuum lines and connections. Improper hose routing, by- passing system sensors, failed system sensors, and/or leaking hoses account for significant numbers of malfunctioning or poor operating vacuum advance systems.

It is important to remember that even a slightly mistuned engine will deliver poor fuel economy. Optimum fuel economy may only be achieved when timing is optimized.

[Opelkurt]

Originally Posted by opelnut10 I don't know if your thinking incorrectly, I can only speak about what has worked for me. Every Opel that I have ever owned has had the dist. locked and the advance reworked to put it in quicker on a stick shift car and slower on the automatic. My wife drove a 75 FI Manta with an automatic that was getting 22-23 MPH before the dist. modification and with no other modifications made it went to 25-27 MPG. You have to have a dist. machine and play with the springs and weights in order to achieve the right curve and you have to time the car at TDC by static timing it, with the engine off.

Of course the '75 fuelies didn't even have vacuum advance; just vacuum retard....

-Kurt

[hrcollinsjr]

Originally Posted by Opelkurt Of course the '75 fuelies didn't even have vacuum advance; just vacuum retard.... -Kurt

For emissions not performance or mpg.

Harold

[Opelkurt]

Originally Posted by hrcollinsjr For emissions not performance or mpg. Harold

Quite right.

-Kurt

[lewdawg]

Earlier in this thread a member posted this website from northern tool.

Gastester Digital Exhaust Gas Analyzer | Automotive Diagnostics | Northern Tool + Equipment

Another member I know is having issues passing emissions on a 73 GT and I was wondering if this inexpensive tool would help in tuning her car to pass emissions?? Any help would be appreciated.

[hrcollinsjr]

Originally Posted by lewdawg Another member I know is having issues passing emissions on a 73 GT and I was wondering if this inexpensive tool would help in tuning her car to pass emissions?? Any help would be appreciated.

What I did years ago to get a '85 Ramcharger w/headers and no cat(s) to pass. Tuned the Ramcharger set the timing a little low, made sure the gas tank was almost empty and added the cheapest octane booster (making sure the key ingredient was alcohol), pulled the PCV loose and let it suck clean air, and the last thing was to pull the air filter about a block before the emissions testing station. Immediately after taking the emissions test I filled up with gas to dilute the octane booster to the proper mix. Make sure the booster has been in long enough to reach the carb. I added it to the tank the day of and drove the few miles to the station. I passed for several years until the turkeys started doing VISUAL inspections. I transferred a plate from another vehicle and bought a new truck the following year.

I would do similar for the GT. Hopefully they have electronic ignition, set the timing to factory specs and hook up the vacuum retard, see if it will idle with the PCV hose pulled from the valve cover, add the octane booster, and remove the filter.

There are some fuel additives that you can buy that promise you will pass or your money back.

Personally, any state that makes you test a '73 car is just wanting money. Move to TN and don't talk about how much better the place was that you moved from and we'll be glad to have you.

HTH,
Harold

[Gary]

Originally Posted by RallyBob Definitely! And the 2.5" over-axle pipe will give it about 4 more ft lbs of torque, which certainly helps economy.

The pipes are at a muffler shop. 2" pipe to a 16" flowmaster, 2 1/2" over the axle to an Ansa dual tip resonator is the plan. Is 2 1/4" pipe to the muffler too much for a stock engine?

I may have him make up one for my GT while he is at it...

Originally Posted by Gary New question: Valve timing - Stick with stock setting or advance/retard the setting?

The head is on and I'll be working on setting the timing tomorrow. Any thoughts on this? I have a cam gear drilled out to RallyBob specs and a master linked timing chain so i can be flexible.

While the intakes off, I'll put in the F.I. hose fitting and a GT oil pressure sending unit.

While this is all apart, I may replace the fuel line from the gas tank. With F.I. in the future plans, should I use 5/16 or 3/8? Same diameter for the return line?

[wrench459]

Originally Posted by Gary I may have him make up one for my GT while he is at it... The head is on and I'll be working on setting the timing tomorrow. Any thoughts on this? I have a cam gear drilled out to RallyBob specs and a master linked timing chain so i can be flexible. While the intakes off, I'll put in the F.I. hose fitting and a GT oil pressure sending unit. While this is all apart, I may replace the fuel line from the gas tank. With F.I. in the future plans, should I use 5/16 or 3/8? Same diameter for the return line?

Crud we need more details.
The head your using is a 1.5 right? stock valves,ported?
Then theres the bottom end what size pistons,stroke
Oh questions ..that needs to be answered
1/4 inch return line should be fine .. do you have a fuel well in the tank?
Its all about the total combination.

[Gary]

Originally Posted by wrench459 Crud we need more details. The head your using is a 1.5 right? stock valves,ported? Then theres the bottom end what size pistons,stroke Oh questions ..that needs to be answered 1/4 inch return line should be fine .. do you have a fuel well in the tank? Its all about the total combination.

Stock 1.5 head, not ported, Standard hydraulic lifter cam.
Std. bore, low comp pistons. (PO had the engine rebuilt by "the most reputable rebuilder in NJ" )

I put a '75 tank in it last year.

[RallyBob]

Originally Posted by Gary The pipes are at a muffler shop. 2" pipe to a 16" flowmaster, 2 1/2" over the axle to an Ansa dual tip resonator is the plan. Is 2 1/4" pipe to the muffler too much for a stock engine?

2" is all you need up to about 140-150 HP. Bigger would not be better in this case.

The head is on and I'll be working on setting the timing tomorrow. Any thoughts on this? I have a cam gear drilled out to RallyBob specs and a master linked timing chain so i can be flexible.

Advanced cam will make more torque where you need it. 3 degrees works well. A stock Opel cam is 1 degree retarded from the factory, assuming the chain is fresh, and the block and head are not milled. So you may need a 5 degree bushing to get a true 3 degrees of cam advance.

While this is all apart, I may replace the fuel line from the gas tank. With F.I. in the future plans, should I use 5/16 or 3/8? Same diameter for the return line?

For EFI, 5/16" hard line (or high pressure rubber) feed, and 1/4" return is fine.

Bob

[Gary]

Originally Posted by RallyBob ...For EFI, 5/16" hard line (or high pressure rubber) feed, and 1/4" return is fine. Bob

Thanks once again, Bob.

I read somewhere that the new ethanol mix in gas is not friendly to rubber hoses when the car is not used regularly and sits for long periods so I'll be going with hard lines. I won't be driving on salted roads so I guess aluminum tubing would be ok.

[namba209]

Just as info for you Gary, I've got a high pressure pump (70 psi) feeding the fuel rail on Willit? The surge tank overflow, pump bypass and bleed, and the fuel rail all dump into a #4 (3/16" ID) stainless line back to the tank and it works just fine.

[Gary]

Thanks, Ron. BTW, the first season of John from Cincinnati is going to be repeated on HBO starting March 31. Maybe this run will generate enough ratings for a second season and bring the production $$$ back to Imperial Beach.

[namba209]

Could be Gary, but the motel they used next to the taco stand is being sold, so I guess all the work the players did was for naught. I would like to see a sequel, just to see who John tries to help next go around. Maybe some of the druggies that are on the beach. It appears to be a thriving business at the men's room by the pier. I do know the Sheriff's Office liked them being here, the officers got extra pay and the department picked up some loot too, for traffic control. If you remember the huge circular antenna array, what we call the elephant cage, that's where Willit? spent 8 years after I blew the third engine in it. It belongs to the Navy Seals now, they use it for a training facility. The township of Coronado wants it, so they can build a golf course. We don't have enuff of them, yet. Only 125 in San Diego county, not counting the 4-5 on military installations. Yeah, bring back John From Cincinnatti, we need the income to fix up this burg.