1.6 NA Giles vs non-Giles fuel economy comparison

[overdrivegear]

Hypothesis: Giles equipped engines require different gearing to realize increased fuel economy.

I have two 1.6 NA's and here are the specs for each:

87 Cabriolet w/ diesel conversion:
Hydraulic lifter engine
Giles IP
Giles 135 BAR injectors
Stock 1.8 gasoline exhaust with Cat. delete
AGS transmission w/ 0.71 fifth, 3.94 diff (2500 RPM @ 60 mph)
Stock wheels/tires 175 tire width

85 Golf 1.6 NA (2-door)
Solid lifter engine
Stock BOSCH IP
155 BAR injectors w/ Merc nozzles
Stock 1.6 NA exhaust
ACH transmission w/ 0.71 fifth, 3.94 diff (2500 RPM @ 60 mph)
81 Rabbit steel wheels 155 tire width

Other controls in the experiment: both use same weight oil, similar road trip for both cars, similar temperature conditions.  Both cars are driven on highway/interstate 55-60 mph, coasting out of gear down long hills, etc.

In the Golf, I never get less than 50 MPG, even driving on mountainous highways.  Currently, my record MPG is 56.7 (GPS distance confirmed) but the average is 52.

In the Cabriolet, the best I've been able to do is 46.6 MPG driving 50-60 mph on highway to the Atlantic Coast and borderline hypermiling. 

I think I have to go to a transmission with 3.67 diff plus the 0.71 fifth to drop RPM and get some better economy.  Anyone else care to weigh with their experiences and why I'm seeing 10 mpg lower in the Giles car.  Shouldn't it be the other way around?

[Mark(The Miser)UK]

Swap the pumps and injectors over as a 'heart and lungs' transplant keeping their timings identical, and see if the economies swap, or remain with the vehicles.

[Vincent Waldon]

2X... Lots of differences between your two test subjects and so a heart-and-lungs transplant is the best approach scientifically.

You don't mention timing, but even if it is the same it will actually be quite different due to the big difference in breaking pressure.  Pump wear may be different as well...which also impacts real-world timing.

[745 turbogreasel]

Nothing has worse aerodynamics than a convertible...

[R.O.R-2.0]

cabbys are heavy, theres no roof to use as structure, so they put all the structure in the pan.

weigh both cars, report back..

i bet the actual weight will shed light on things..

[coke]

Also too, not sure if you changed the 5th gear in your ACH and AGS transmission, but they both have a 0.75 fifth gear, not 0.71.

Tire size will change the RPM at a given speed too.

Does your Giles pump smoke bad under a heavy load? I noticed on mine I had to turn down the full load stop screw some. It was really pumping out the soot at 3/4 throttle or so going down the road. Thats just wasted energy going out your tailpipe.

All in all, Giles has said more than once that with his pumps, your economy should be the same if not improved, as long as you aren't trying to put out a cigarette butt on the floor board when you drive it.

I noticed too you're using 155 bar injectors with Merc nozzles in your stock setup.  I'm no injector guru, but your setups aren't similar enough to do an accurate economy comparison, imho.

[overdrivegear]

Obviously this is not scientific because there are way to many variables and not enough controls, but just for rough comparisons with engines with the same displacement, gearing, and driving on similar chassis I would not expect a variance of 20-25% biased in one direction.  I'm ruling out aerodynamics since the two cars have very similar C_dA's and the fact that there isn't a whole lot of difference at the speed that I'm driving.

I'm going to start looking for an ASF or ACN trans, pop in a 0.71 fifth and improve my highway cruising and see if that does anything.  With the added torque of the Giles setup and cruising at 60 mph, I wouldn't think this would be a problem.  I'll swap out the IP and injectors before I do that though.  When it gets to be spring and I'm not losing so much heat to ambient, I guess I should see an increase to the 50 mpg range in the Cabby.

The thing that I'm very intrigued by is the injectors.  My Golf with the stock IP, 155 bar injectors w/ mercedes nozzles runs cleaner, quieter, and smoother than the hydraulic lifter Giles set up of the Cabriolet.  I replaced the head gasket in this golf recently and examined the internals by using the merc nozzles; absolutely pristine and no carbon build up.  Just wiped it down with a rag.  Imagine that.

[Mark(The Miser)UK]

The only way to keep variances the 'same' is to do as I said in post #2.

There is no substitute, period.

[R.O.R-2.0]

Also too, not sure if you changed the 5th gear in your ACH and AGS transmission, but they both ahve a 0.75 fifth gear, not 0.71.

Tire size will change the RPM at a given speed too.

Does your Giles pump smoke bad under a heavy load? I noticed on mine I had to turn down the full load stop screw some. It was really pumping out the soot at 3/4 throttle or so going down the road. Thats just wasted energy going out your tailpipe.

All in all, Giles has said more than once that with his pumps, your economy should be the same if not improved, as long as you aren't trying to put out a cigarette butt on the floor board when you drive it.

I noticed too you're using 155 bar injectors with Merc nozzles in your stock setup.  I'm no injector guru, but your setups aren't similar enough to do an accurate economy comparison, imho.

difference between .71 and .75 is about 40 rpm @ 70 mph..

and the merc nozzles, and 155 bar injectors could be some reason..

[coke]

I was simply pointing out he indicated he had a .71 fifth, when the AGS/ACH has a .75. The difference in RPM at 70 is actually around 160. Probably not enough to notice a huge difference.

[8v-of-fury]

I would like to point out your losses as a fault of the merc nozzles. They have been proven to not work well with our precups (injector spray points the wrong way, doesn't atomize properly). So less efficiency right there.. Meaning you inject more fuel to get the same performance from them.

Why run merc nozzles? Last I checked there wasn't a shortage of the proper nozzles designed for these cars.. Lol

[overdrivegear]

I would like to point out your losses as a fault of the merc nozzles. They have been proven to not work well with our precups (injector spray points the wrong way, doesn't atomize properly). So less efficiency right there.. Meaning you inject more fuel to get the same performance from them.

So, in other words there should be an even larger discrepancy?  Remember, the Merc nozzles are on the car getting the BETTER economy and running smoother (despite being solid lifter vs hydraulic). 

As for the 5th gear, I swapped both of them out to be 0.71:1. 

Don't get me wrong, I don't think there's anything the matter with the Performance Diesel stuff; it's absolutely awesome.  I'm just skeptical at this point about getting significantly better economy over stock.  Getting below 50 MPG makes me cry. 

[8v-of-fury]

Sorry about that, I misread the post when I replied on my phone.. You sincerely have a weird scenario.. LoL

I get 49-51 in my N/A with 60% being hwy and most of that at or above 115km/h

[R.O.R-2.0]

i get 48mpg with NO OVER DRIVE..

GC trans .91 4th gear, 3.89 final drive..

this thing just HUMMS going down the road.

i think i got better mileage with my 4A tho, it had .70 4th gear, and a 3.94 final drive.

[8v-of-fury]

Not to mention the difference in 5mpg is the teensiest (yup teensiest) amount. I'd be glad with anything over 35 for a combined city/highway/WOT romps