Slant 6 MPG Upgrades?
Good chance you have 3.23 rear gear ratio on that early push button shift A Body.
What's the car, what size engine?
It gets to the point when you lean them out so far there is not enough Power left to keep up with today's traffic at 70 mph + out on the freeways.
Yes, currently 3.23. With overdrive of .78 final drive ratio, my effective rear end will be effectively 2.5 without sacrificing torque for acceleration. Once I get up to a nice cruising speed it'll drop down the RPMs, making up for fuel inefficiency in the city.
The car is a 64 dart with a freshly rebuilt and mildly modified 225. Milled slightly, ported, and a mild cam. The car can accelerate no issue and maintain speeds of 70+ without being all out. I've cut, by my estimate, a little over 100lbs in switching to more modern components in the engine bay, and less mass to move is less fuel spent accelerating. Realistically I've cut about all the weight I can while keeping the car comfortable, I'll probably relocate my battery to the trunk to make the back-to-front balance better.
Parasitic loss is what I'm worried about. The direct mounted fan is (relatively) heavy and induces, by most estimates, a 10-15hp loss. On a stock 225 that makes 145hp that's around a 10% loss in efficiency, which translates to less of the energy from the fuel being used to propel the car forward. I'm just having trouble finding a thin enough electric fan to mount direct to the radiator.
One of the huge fights you have, which people don't take into account is FUEL. Alcohol --izz--eeed fuel --you need more of it, and the more alky content, the more fuel you need.
I have ready access to no ethanol fuel here in the south, same price as premium/high octane where I am, around $4.
what are you willing to invest?
lest say you go from averaging 20 to 25
and lets say you driver 25 miles to work
now, you are putting 250 miles per week on the dart, thats 14000 miles per year
at 20 MPG that is 700 gallons
at 25 MPG that is 560 gallons
so you'd be saving 140 gallons per year
lets say it runs about 3.50 a gallon, thats $490.00
that $490 would be what we call "return on investment"
what does aussie speed want for their services ? one years of savings?
a new pump and lines, thats another year
add a fitech, and sparker, another two years
im not trying to rain on your parade, but if it were me, id spend that disposable income on fuel...or boost
boost might be the best way to go to increase your MPGs aswell
I'm looking at $4-5k including the GVOD, which itself is roughly $3k.
You make a great point about ROI based on a commute of 25 miles. At that point it would take me almost a decade to "pay back" what I spend. However, I do a good number of road trips. Whether that's Athens or Alabama or down to the beach, and that's where a lot of the miles add up. That can be anywhere from 1500 to 2000 miles a year, plus miscellaneous driving around town. Lets say all told thats 16500 miles.
At an average of 19 miles a gallon (have moved to the city since I last drove the Dart, still do a lot of highway miles, but an increasing number of city miles as well) that translates to ~869 gallons of fuel a year.
At an average of 25 miles a gallon (a low, but believable estimate of what I want to achieve) that's 660 gallons/year.
That's become a savings of 200 gallons/year which at current prices is about $800 saved per year, let's say I spend $4500, I make my money back in just over 5 and a half years instead of almost a decade.
But that's aside the point - I'm in my early 20's and this car is 60. It's been nothing but fun for me, and I vastly prefer driving it to any modern car. I want to drive it until it's at least 100 years old if I can, so long-term, a few thousand dollars up front should be well worth it, even if it doesn't pay off in the immediate future.
What MPG are you shooting for? Have you looked into what the slant guys are getting with the Sniper EFI?
When you compare a modern engine to the slant there are several technologies that allow higher efficiency (MPG's) and power over the slant 6. Higher static compression, control over dynamic compression, EGR or exhaust re-breathing systems, more efficient chamber design, multiple valves, better flowing intake & exhaust ports, Spark plug location and reach better intake tracts and exhaust systems all help.
If anything ditch the 904 with GV and get a T5 manual from a 87-93 5.0 Mustang. Reducing rotating mass off the engine is a win to a point.
I'm shooting for high 20's MPG as a mix of highway/city with probably 80%+ of my driving being on the highway. If I could hit 27 I'd be plenty happy.
I wish I could ditch the 904 and switch to a small standard trans with OD built in. I like the push buttons too much to get rid of, and am willing to suck up the loss in efficiency there to keep them. I also know that the vast majority of my cost is going to come from trying to make up for that loss with an OD unit for the 904. I didn't buy this car cause I like my wallet I guess, lol.
Sell your intake. Gill Welding can help you out with any of the engine related items. Call them. David and Bryce are fine fellas.
For a hair over $500 they'll modify one to accept injectors and send it back with a fuel rail as well. I really oughta call them and see what system they know plays well with the /6 since they've been messing around with fuel injection on it for a while.
I was gonna say something about being "worth it" what you're looking to spend for what you get out of it in return... The more you have to pay to "have" done for you the less worth it this becomes. The more you can do yourself or with the help of a buddy for beer money, sort of thing the more feasible it becomes.
And your statement about lower rpms = more mpg doesn't always hold true either. There comes a point where you are lugging an engine. When I had my wrangler with it's 4.0 inline 6 and 5 speed (all stock) with 3.07 gears and 235/75-15, it didn't like being run in 5th below about 60 unless I was rolling downhill. Which was worse with the 31/10.50-15s I had in it for a while.
I like electronics. Once I get a feel for what's required of the build and can get high-quality components, I can do the EFI install myself and set it up. A lot of the good ones are self-tuning so once I get some basic target data, it'll attempt to achieve that.
The issue I have with
a lot of the electronics made for our older cars is that they're low quality. It seems like a company found a good product, took a picture of it, and then recreated it without any testing or verification that it works.
On your second point, absolutely. Too low of RPM won't be efficient for the engine. With my current tires/trans/rear end, I go around 3200 (I believe, been a minute since I did the calculation) RPM at 75mph. I'd be dropping to around 2500 for the same with OD. A carburetor that's outputting an ideal A:F while city cruising isn't necessarily outputting the ideal ratio while highway cruising, and vice versa. A system that can adjust itself as it drives can create a close to ideal mix at every RPM, which means it can be happier when it drops into overdrive, as well as while its driving around the city.