Give that slant some more MPG

[SixBanger]

Hello Guys!


The health of the slant seems fine. I want to keep this. But I'm looking to improve the performance of the engine. I am willing to spend a few hundred dollars for an upgrade.



The goal is to drive the car more economically. A smoother or faster acceleration is desirable.

Now the average fuel consumption on LPG is between 12-14 mpg. It runs and drive fine now. I also have no impression that it is too rich, though I say so myself. However, it starts easily, even now with the colder weather without using the choke.

I have seen that it is possible to improve this towards the 22 mpg.
This gives a bit of a guideline. Of course this differs. It would be desirable if the car runs more economically on the motorway. Here I drive around 60-70 mph on average.


My car is fitted with , to my knowledge, a standard super 225 slant with a 'European' camshaft (244° intake, 244° exhaust, 26° overlap, 0.416" lift).

What is a sensible upgrade for the slant to improve fuel economy and some bottom performance?

I was thinking to install a programmable ignition system for adjusting for both fuels. But maybe someone have another ideas or experience?



All tips are welcome. Thank you in advance!

 

[Dr Lebaron]

I dunno, my bone stock 2bbl can get 22mpg with no A/C and 17-20 with A/C but there is idle time not shutting the A/C off.
Running 94 non ethanol.

I did a lot of driving this summer and kept refilling the car noting the mileage.

 

[Dr Lebaron]

This makes one killer /6.
Hard to find kit.
KIT PERFORMANCE CLIFFORD MOPAR 225 CI | Moteur, Pièces de Moteur | Lanaudière | Kijiji

 

[Oldiron440]

This is your best bet for fuel economy and performance on a /6 or stockesh 318.

The Clifford intake would be nice with this along with a good set of headers.
This is a Holley kit but FITech makes one also but I've heard that the Holley kit's are more compleat.
Of course a free flowing exhaust after the header is needed also.
The addons will improve efficiency and make more power, two for one.

 

[Dr Lebaron]

He has everything including headers.

 

[SixBanger]

22 mpg seems great! A huge difference then. But I don't have driven lot on petrol, so I can't give an idea what the consumption would be.
May I aks, what is your setup Dr Lebaron?

In these engines with carburetors, the adjustment is made by reducing the evaporator. This is arranged rather ungainly. It does not really provide a smooth and idle gas mixture at all engine speeds and loads. In addition, the mixture of propane and butane has changed as it gets colder outside. And the LPG delivers less power. Interesting is that LPG is beating (octane 104-107 ish?)
The new injection systems do ensure better consumption and power.

But I have to say, maybe I can check the CO content at a garage.

 

[SixBanger]

The EFI from Holley is a beautiful system! Fully programmable + monitor of div parameters. But since I mainly drive on LPG is not that convenient. I mainly run on petrol to keep the fuel system kind of fresh and as a backup I could give up LPG on problems.
Maybe add sometime in the future.
Or... Are there any aftermarket/other car throttle body that fit the original intake?? Modify the intake is no problem. Than I could try to fit an mega squire on this powerplant. So also tuneable ignition timing.

Like the stuff of Clifford!
Especially the inlet and outlet set. What is the difference between that Weber carb. and the current crankcase 2 bbd? More cfm?
But interesting how much would his set of extra power deliver when you look at crankshaft power? 170-200 kp ish?

 

[Oldiron440]

The Weber looks like a Holley 2300 but Its not.
I had a Weber 2v carb on a vw that worked like half a 4v. It had a primary and a secondary.

 

[Charrlie_S]

To all the posters saying go Fuel injection, the OP is running Propane. None of those FI systems can handle Propane.
In my opinion, raise the compression on the engine (stock is less he 8-1), to take advantage of the high octane rating of propane. I would shoot for about 10-1. Should be able to get that just by milling the head. Then adjust the advance curve in the distributor to optimize everything.

 

[SixBanger]

Okay thanks for info!
Increasing compression ratio is a good idea.

I myself have not previously adjusted an original distributor in terms of vacuum and mechanical advance.
The car is from '77. I have read somewhere that it has no mechanical advance. But that this is regulated in the corresponding ignition ecu. Is this correct?

If you read these articles there is a lot of torque and economy to achieve with the adjustment of the original distributor.

More Power For Your Leaning Tower: Add 14-Horsepower To Your Slant 6
Gallery: Distributor Recurving for Improved Fuel Economy

This seems to me nice as the first improvement step.

 

[SixBanger]

But I saw that it is also possible to install a Megajolt system as programmable ignition. Coupled with an EDIS-6 and a trigger wheel and crank sensor.

Megajolt/E MK2 | Autosport Labs

What I can see in this way is the biggest advantage that the advance curve over speed and vacuum is electronically adjustable. And that an ignition curve can be realized for both LPG and petrol. In addition, this ignition would give a somewhat stronger spark.

I could only find out on a number of forums that this was applied to a slant. Maybe someone has experience with this?

 

[Charrlie_S]

Okay thanks for info!
Increasing compression ratio is a good idea.

I myself have not previously adjusted an original distributor in terms of vacuum and mechanical advance.
The car is from '77. I have read somewhere that it has no mechanical advance. But that this is regulated in the corresponding ignition ecu. Is this correct?

If you read these articles there is a lot of torque and economy to achieve with the adjustment of the original distributor.

More Power For Your Leaning Tower: Add 14-Horsepower To Your Slant 6
Gallery: Distributor Recurving for Improved Fuel Economy

This seems to me nice as the first improvement step.

That vehicle should have mechanical and vacuum advance in the distributor. However when the Propane conversion was done, that may have changed. The ecu (Mopar 4 or 5 pin) has nothing to do with timing.

Those are good articles. But remember, if you do the distributor mods first, you will need to redo them, after doing most any other mods, especially raising compression. Also remember the engine will want a totally different timing curve running on Propane as compared to petrol. The procedure to modify the distributor will be the same, but the numbers will be different.

 

[Charrlie_S]

But I saw that it is also possible to install a Megajolt system as programmable ignition. Coupled with an EDIS-6 and a trigger wheel and crank sensor.

Megajolt/E MK2 | Autosport Labs

What I can see in this way is the biggest advantage that the advance curve over speed and vacuum is electronically adjustable. And that an ignition curve can be realized for both LPG and petrol. In addition, this ignition would give a somewhat stronger spark.

I could only find out on a number of forums that this was applied to a slant. Maybe someone has experience with this?

There are several aftermarket ignition systems that could be used on a slant six. I can't comment on any of them, as I have never used them. I believe in the "KISS" theory (Keep It Simple Stupid).
BUt you are correct about needing two different curves. One for Propane, and different for Petrol. However you stated you use Petrol, just in an emergency, so I would set the ign curve for Propane.

 

[SixBanger]

Thanks for the info and your input!

 

[Charrlie_S]

Just a FYI. I don't have experiance with propane systems on street cars, but I have worked on propane powered industrial equipment. I also have a Impco propane system on the shelf, and a new Rajay turbo, that I had planed on putting on a street driven 170 cid slant six. Never got around to it. Been sitting there for 30 years.

 

[BudW]

Do you mainly drive on highway/freeway or mostly city driving (or about a 50/50 mix)?
BudW

 

[SixBanger]

Hey Bud. Currently I mostly drive city driving (70/30). But I will soon be using it for daily transport with my other employer. Then I use the highway more, more direction (40/60).

 

[Dr Lebaron]

What's the speed limit over there?
Mine just cruises along real nice in the 80/90/100kph, but on the Daytona 401, if you're not doing 125+, then you are in trouble.

I feel sorry for my 110 hp with A/C on at those speeds.
Really working that worn motor.

 

[SixBanger]

Here the maximum speed varies on the motorways of 100/120/130 km / h.
I drive here mainly around 100-120 km / h. I myself notice that it runs fine at any of these speed. Around 110+ the ride is a bit smoother.

I must say that the engine rotated fairly low speed with the standard three-speed gearbox and diff. I did not have measured the speed or water temperature jet. But I can not see that he possibly overheats at these speeds. Not even last summer with +30 degrees Celsius.

Compared to my previous car, an opel commodore. This one also 6 and ran on LPG with a four-wheel drive, I avoided the highways as much as possible. Ran too high revs when drive faster than 100 km/u.

 

[SixBanger]

I feel sorry for my 110 hp with A/C on at those speeds.
Really working that worn motor.

Maybe, a worn engine also has less mechanical loss... Perhaps this will result in more favorable consumption?..
And the slant in my car has not break in after 40 years?