30MPG is the Goal

[Gary]

I use my '72 1900 wagon as a daily driver for 8-9 months a year and average between 20 and 24 MPG for a 40 mile round trip commute. It's an automatic with non-working A/C. 32/36 Weber. Low comp. engine was "rebuilt" not to many miles ago.

I pulled the head off to fix an oil leak (late style head gasket used on an earlier setup) and got to thinking about ways to increase it's gas mileage. I'm looking for ideas or comments on how to get it to a 30 to 35 MPG level using a combination of conventional parts and tricks.

Here's what my thoughts and questions are so far:

Cyl. Head - I'm replacing the head with a 1.5 head. Should I use a stock solid or hydraulic cam? Don't want to get into any wild porting, but are there any areas on the intake side that should be cleaned up?

Fuel system - Carb (Solex or 32/36 Weber) or '75 Fuel injection?

Exhaust - Sprint with a 2" pipe?

Cooling - Electric fan or '75 clutch fan?

Tires - I have a set of 185 (?) x 14 that I can put on.

Excess Weight - The only A/C parts left on it is the under dash unit. Rear seat is out I do not plan on dieting and losing 50 pounds so that is not an option.

Throwing some ideas out to see where this goes.

[oldopelguy]

Tall, skinny, properly-inflated to slightly over-inflated tires are the first place to start. Second place is new top quality synthetic lube in the trans and rear axle. Third is top quality synthetic grease for the front wheels and u-joints.

It might be worth slipping a quart of type-F ATF in with the new tranny fluid to firm up the shifts some. That's an old trick for firming up GM transmission shifts, though without knowing the condition of your trans it's hard to know if it would work well, not work, or damage something.

I would suspect that for the best possible fuel economy you would want to use the EFI manifold and injectors and such but swap to an aftermarket computer like an SDS unit or a Megasquirt that runs off either a newer hot wire MAF sensor or a MAP sensor. A more sophisticated injection system should allow for better fuel economy if it's dialed-in correctly, or at least more tuning options to get towards more mpg.

[neuropel]

Gary,
I've had a similar goal in mind for a long time (with a manta) but haven't made much progress other than accumulating parts (I keep getting sidetracked with other projects). I can't help but believe that going to a modern, fully tunable EFI system would make a big contribution. I'm planning the Sentra SER throttle body/Opel EFI plenum setup with a megasquirt, and try to tune the engine for economy. Several years ago when I dumped a 4 speed and installed a 5 speed in a GT I was getting 30+ MPG using a well-tuned Weber 32/36. I could never break 25 mpg with the 4 speed, but my commute was all highway. My experience with the automatic has been even worse gas mileage. I'm wondering if there are strategies to porting an Opel head that would improve economy? Certainly skinny tires help, along with a good ignition system and appropriate exhaust. It'll be interesting to see how others may have approached this challenge. I'd like to see just how high the mileage could go with the 1.9L.

Todd K.

Edit - Also, what about cam profile? That's a pretty cheap way to drastically alter an engine's performance, but I've never heard us mention optimal profiles for economy.

[West Coast GT]

I recommend breaking your approach into two areas. Let's say something like:

• Big expensive gains
• Small inexpesive incremental gains

Big expensive gains would include converting the car to a five-speed manual transmission. Rebuilding or overhauling the engine to keep the combustion chamber tight. Then move on to advanced modifications such as EFI and engine management systems.

Small incremental gains would include good wires/plugs, electronic ignition, synthetic oil, your tall skinny tires. And wax the hell out of the car to make it as slippery as possible.

Meanwhile:

• Re-arrange your commute to find the route with the fewest stop signs / traffic signals. Shift your start time so you follow after the heaviest commute period, but before parents/students are driving kids to school. Come home after the evening commute period. Try to optimise the daylight time so you don't use your lights.
  
• Install a vacuum gage on your A pillar and pay attention to it.
  
• While you're waiting to install EFI, convert your automatic choke to manual.
  
• Back into parking spaces and your driveway rather than nose-in. At home, park in your garage and install a block heater.

[jeff denton]

Gapless piston rings!
Long connecting rods!

[opelwasp]

I also had high lift low duration cam that seemed to help gas mileage. 252 adv. dur. with .420 lift.

If I recall I was getting 34 mpg with .30 over high comp pistons and a pacesetter header.

[73Manta72gt]

check the fuel/air ratio with
Gastester Digital Exhaust Gas Analyzer | Automotive Diagnostics | Northern Tool + Equipment
or similar and change jets if needed.

Make sure your choke is fully open when hot and working properly.

[Rionart]

Install a piece of 2x4 under the gas pedal!

[opelbits]

Depending on what comp. ratio you get with the 1.5 head, a 5 speed may not work well. You drop your rpm, but will it have enough power to pull an overdrive? Flat tops, at least, or maybe do the 2.4 stroker bottom with the stock head and a good cam.
I'd say look for torque rather than hp. Anything that keeps the rpm down will help alot. The further you have to push the pedal down to achieve the performance you want, equals more rpm and gas.

Keep the windows up, aerodynamic mirrors, 3.18 rear end, lose the roof rack, front airdam, and maybe lower it a little.

Whatever you do, keep from having rev the motor to much.

Maybe someone else can answer this, is there an advantage to using an earlier small runner intake manifold for economy purposes?

[michaedo]

Best bang for the buck is replacing all the fluids with synthetics.
I realized a 6% gain with my big block pickup after changing out
the diff, trans, and engine fluids.
Could be good for a couple miles a gallon towards your goal.

[BQS4]

Actually, I have a stock 75 F.I. Sportwagon, with roof rack, airdam and huge fog and driving lights. It was an automatic, till I switched it over to a 5-spd and it got 33 mpg at an average of 70mph when I went to and from Carlisle last year. Oh, it has pertronix ignition

[heimue]

I assume Gary has this wisdom anyway, but maybe for some younger kids around here: The most efficient way is a defensive driving style. Don't spin the tires when leaving the red lights, don't race the rice cooker next to you. Speed up slowly, get off the gas when going downhill. Look forward and get off the gas approaching a red light or stop sign. Sounds boring? In morning and evening commuting I DON'T CARE!

Dieter

[Paul]

Gary,

From recent experience, I found the larger intake valves coupled with modest porting gave better economy and power. Bumping up the compression will also make a difference. However, I don't know for sure which method of increasing the compression ratio yields better economy results: low comp pistions with a 1.5 Head or flat top pistons with a 1.9 head.

My guess is: it will take more and higher skilled porting work with the 1.5 head than with the 1.9 head to achieve the economy results you desire...........

Also, I recommend changing over to synthetic fluids and greases as Jeff suggested.

A front air dam will help aerodynamics.... as well as reducing height of the car.... if the rear of the wagon is lower than the front, from saging springs, the front will catch too much air under the bumper...

Also, you need to restrict some of the air through the radiator/engine compartment as well as this make up about 20% of total drag.

[RallyBob]

ICyl. Head - I'm replacing the head with a 1.5 head. Should I use a stock solid or hydraulic cam? Don't want to get into any wild porting, but are there any areas on the intake side that should be cleaned up?

Compression is a huge factor in mileage. The 1.5 has smaller valves than the 1.9, so unless you are changing the valves I wouldn't port the head.
Hydraulic cam is a better choice IMO, the specs are milder.

Fuel system - Carb (Solex or 32/36 Weber) or '75 Fuel injection?

Factory EFI definitely makes more power, but even according to Opel, the mileage was not as good as with a Solex. I'd only go EFI if I could use modern injectors and ECU, the stock Opel 1.9 injectors are way too big, they're sized for 160 hp on an 80 hp engine!

Assuming you go the Weber route, keep it a 32/36 and jet accordingly for economy, probably 125 primary main jets FWIW.

Exhaust - Sprint with a 2" pipe?

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

Cooling - Electric fan or '75 clutch fan?

Electric for me. And if you drive mostly interstate it will never even turn on.

Tires - I have a set of 185 (?) x 14 that I can put on.

165/80-13 would be best, run at max pressure.

Excess Weight - The only A/C parts left on it is the under dash unit. Rear seat is out I do not plan on dieting and losing 50 pounds so that is not an option.

Aerodynamics matter more at a constant speed than weight. Once the weight is in motion it doesn't matter as much. Get a front air dam from Pete Anastopoulas (hope I didn't butcher that too much Pete!), it will help.

I'd lose the automatic and go 5-speed, the automatics have about 300 rpm worth of 'slippage', and the engine is always revving higher than even a 4-speed. They also eat up a lot of power and create heat, hence drag. I've never gotten 'good' mileage from an automatic Opel, and I've driven 3 of them as daily drivers over the years.

When I drove my Ascona from CT to Mid-Ohio racetrack back in 1995, I got 28.5 mpg for the entire trip. And we all know the Ascona is a brick aerodynamically. That was with a Getrag 240, 3.89 gears, very wide tires (245/50 -13's!), and 300 lbs of stuff in the trunk (spares and luggage), and a constant 72 mph for 11 hours each way. Oh, and the engine was the same one I loaned you for your old blue wagon, with a 38 DGAS and ported intake, so it was making 97 hp instead of 65 hp stock. Considering the extra weight, aerodynamic and frictional drag (tires), and the addition of 50% more power, it wasn't too shabby. And that car was only rated for 24 mpg from the factory...

Bob

[RallyBob]

From recent experience, I found the larger intake valves coupled with modest porting gave better economy and power. Bumping up the compression will also make a difference. However, I don't know for sure which method of increasing the compression ratio yields better economy results: low comp pistions with a 1.5 Head or flat top pistons with a 1.9 head.

The 1.5 head with the flat tops!

The bigger intake valves help because the Opel head design over-scavenges on the exhaust side, and thus uses more fuel (dumping it out the tailpipe).

My guess is: it will take more and higher skilled porting work with the 1.5 head than with the 1.9 head to achieve the economy results you desire...........

Same ports, just different valve sizes. If the valves are 'big', then the 1.5 head gets trickier thanks to shrouding.

Also, I recommend changing over to synthetic fluids and greases as Jeff suggested.

Yes, big difference overall. I remember the first time I switched to all synthetics in an Opel: Engine oil, tranny oil, rear axle, and front wheel bearings (all Redline mind you). The car was actually noticeably easier to push around my shop!

[opelnut10]

I use my '72 1900 wagon as a daily driver for 8-9 months a year and average between 20 and 24 MPG for a 40 mile round trip commute. It's an automatic with non-working A/C. 32/36 Weber. Low comp. engine was "rebuilt" not to many miles ago.

I pulled the head off to fix an oil leak (late style head gasket used on an earlier setup) and got to thinking about ways to increase it's gas mileage. I'm looking for ideas or comments on how to get it to a 30 to 35 MPG level using a combination of conventional parts and tricks.

Here's what my thoughts and questions are so far:

Cyl. Head - I'm replacing the head with a 1.5 head. Should I use a stock solid or hydraulic cam? Don't want to get into any wild porting, but are there any areas on the intake side that should be cleaned up?

Fuel system - Carb (Solex or 32/36 Weber) or '75 Fuel injection?

Exhaust - Sprint with a 2" pipe?

Cooling - Electric fan or '75 clutch fan?

Tires - I have a set of 185 (?) x 14 that I can put on.

Excess Weight - The only A/C parts left on it is the under dash unit. Rear seat is out I do not plan on dieting and losing 50 pounds so that is not an option.

Throwing some ideas out to see where this goes.

The 1.5 head will take your compression ratio to about 9 to 1 however I would use the larger 1.9 valves in it to help it breath better, you have to have the hardened seats installed on the exhaust side anyway, The head is a 3 bearing head and unless you are going to get a cam re-ground for it you are stuck with mechanical lifters. 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. All the other advise about tire pressure, syn. lubes, exhaust system and a 3:18 gear will help as well. Lastly you heve to drive it like you got an egg between your foot and the gas pedal and start and stop smoothly.

[Gary]

Thanks for the inputs. My commute is ~32 miles highway and 8 miles city. Only one route is available.

Actually, I have a stock 75 F.I. Sportwagon, with roof rack, airdam and huge fog and driving lights. It was an automatic, till I switched it over to a 5-spd and it got 33 mpg at an average of 70mph when I went to and from Carlisle last year. Oh, it has pertronix ignition

Interesting numbers Gene and that was with it loaded to the roof!

Gary,

A front air dam will help aerodynamics.... as well as reducing height of the car.... if the rear of the wagon is lower than the front, from saging springs, the front will catch too much air under the bumper...

Also, you need to restrict some of the air through the radiator/engine compartment as well as this make up about 20% of total drag.

One of Pete's air dams is already installed.

How would you restrict the air flow?

Compression is a huge factor in mileage. The 1.5 has smaller valves than the 1.9, so unless you are changing the valves I wouldn't port the head.
Hydraulic cam is a better choice IMO, the specs are milder.

Factory EFI definitely makes more power, but even according to Opel, the mileage was not as good as with a Solex. I'd only go EFI if I could use modern injectors and ECU, the stock Opel 1.9 injectors are way too big, they're sized for 160 hp on an 80 hp engine!

Assuming you go the Weber route, keep it a 32/36 and jet accordingly for economy, probably 125 primary main jets FWIW.

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

Electric for me. And if you drive mostly interstate it will never even turn on.

165/80-13 would be best, run at max pressure.

Aerodynamics matter more at a constant speed than weight. Once the weight is in motion it doesn't matter as much. Get a front air dam from Pete Anastopoulas (hope I didn't butcher that too much Pete!), it will help.

Bob

Excellent points, Bob.

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.

Distributor has been reworked.


Thanks, guys.
I will be keeping the automatic and will not be going into the lower end of the engine at this time. So the dished pistons are staying. (I am gathering up parts now and will be building up a stroker motor for my GT at some point)

Here is my plan based on the posts so far;

• Stock 1.5 head with a stock grind hydraulic cam. (might use roller rockers for a test)
  
• Sprint manifold to 2" pipe with the 2 1/2" over-axle.
  
• Going to keep the 32/36 for now and plan to switch to a megasquirt F.I. system later. (F.I. gas tank is already in the car)
  
• Switch to an electric fan. (need to hit the "search" button here. I know this has been discussed)
  
• Switch to a separate trans cooler to try and keep the tranny temp lower.

BTW, Gene - No roof rack! At least not a permanent mounted one. I have a vintage basket style rack when the need arises.

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

I'm sure more questions will come up but it is good to get it all in one thread.

[Bill Hoffmann]

I don't know what the situation in the Northeast is, but you may find that where you buy fuel can make a difference. I avoid filling up in the Chicago metropolitan area if possible. They use blends that are more eco-friendly but definitely affect mileage. If I fill up in rural areas I find my mileage can be around 5% better. One clue that you're getting the "good stuff" is that the pump nozzle lacks vapor recovery hardware.

[Gary]

I don't know what the situation in the Northeast is, but you may find that where you buy fuel can make a difference. I avoid filling up in the Chicago metropolitan area if possible. They use blends that are more eco-friendly but definitely affect mileage. If I fill up in rural areas I find my mileage can be around 5% better. One clue that you're getting the "good stuff" is that the pump nozzle lacks vapor recovery hardware.

We get that oxygenated gas from October to ~March over here. Mileage usually drops during that period.

[GTJIM]

You can use either a 3 or 4-bearing cam in the 3-bearing 1.5L head - the 'spare' lobe just hangs in the air and the other three are in the same relative position on the two types of cams.

Look in to getting one of the old Isky 'Mile-a-More' hydraulic cam profiles ground on to an Opel cam - or one of the other manufacturer's 'Economy' grinds - might be worth a trial.

My 1991 Auto Senator gets near 30mpg on the open road at 100kph because it has a four-speed overdrive auto with a lock-up convertor - better gas milage than a 5-speed manual! I am tampering with trying to fit a 4-speed OD Aisin-Warner auto trans on to my GT motor - just for the convenience of an auto with good gas milage.

I have a suspicion that it is better for gas milage to use a stiffer gear set in the diff because 3.67 or 3.89:1 ratios give greater torque multiplication than 3.18:1 or 3.44:1 ratio - and so the motor does not need to be worked so hard to get acceptable performance with lower throttle openings - both with manual and auto transmissions with OD to lower the ratio when at cruise speed.