Those short tires are a mileage killer since like Rob said the final drive ratio is so low. Either put 3.23's in it or much taller tires on it. The 3.23 gears will help the mileage more than the tires cause taller tires weigh more so the drag from them is greater. Taller tires have the advantage of getting better traction but if that's not a problem I'd go with the 3.23's. Naturally any taller gears (or tires) will cost you some take off umph so keep that in mind. The converter, if it's a decent one doesn't really hurt the mileage as bad as some think as long as it's not slipping bad. If you go with a stock converter you may have trouble getting it to idle decent in gear at stop signs with that cam plus it'll lose a ton of take off.
I spent good money for a converter and had it custom built for my car. Now if I switch to different gears or tire size how is that going to affect the converter? I understand that I will loose some performance by swapping to different gears or taller tires, I just dont want it to be sluggish. As for a stock converter I had one in my car prior to buying the custom converter and you are correct I couldnt get it to idle very well and take off was embarrassing. Im pretty sure the kid on the tricycle whooped my butt at the stop light.
Like Cannucky, I get far better mileage from my stroker but I also run 3.55's with 28" tall tires. When I keep my foot out of the 750 double pumper it can knock down 16 mpg. Even gear heading it I rarely see less than 12. Last fall I drove it 40 miles to the track, ran twice, drove home and checked the mileage and it got 14.5 mpg. Ran a 12.24 in the 1/4... As you can see fair mileage is achievable even with a hot car.
So are you turning about 2600rpms at 60mph? I was debating about switching to a 235/70/15 tire and maybe 3.23 gears.
Even though your plugs might look ok on color the air/fuel ratio could still be off enough to affect MPG quite a bit. Install a wide band O2 sensor and you can watch what's happening. I put one on my Cuda and tuned the carb and it now gets 4-5 mpg more than it did and it's faster. Timing can make a huge difference in fuel mileage so if it isn't dialed in do so. If your distributor doesn't have vacuum advance get one that does. Shoot for 20-22 degrees of initial timing with 34 total and about 15 degrees of vacuum advance at part throttle. Tune the timing first then the carb cause timing affects air/fuel ratio
Im sure that I need a good tune, and it was already determined that I need to switch back to my stock jets to give it a try about my hesitation problems, which is another thread. I cant go that far advance with my initial timing. I need to have my dizzy curved, the person I got it from used it in his drag car so it has the light weight springs. I started at about 18* initial and when I reved it I went up to about 42*. So I backed it down to 15* and now Im at about 38* total. Again, totally different problem for sure but not contributing to my gas mileage.
The suggestion of installing a OD trans sounds great until you look at the cost. If you drive a lot (at least 8000 miles a year) you'll recover the cost of installation in a few yrs. but if it's a weekend cruiser/hot rod it could take 15+ yrs. to recover the cost. I'm not knocking it, just looking at it realistically.
Ya, its just not a possibility for me. Tires and gears are though.
205-70-15 is just a tick over 26" tall so it's taller than the original tires were.
I would move to a vacuum secondary carb (if you don't already have one) and make sure everything is tuned correctly.
The 670 is a vacuum secondary carb. But I need to tune it all properly, I just suck at tuning and not sure Im doing things correctly.
I think you have more MPG in what you have. The big problem is this is a new build and your right foot is working very hard to keep a smile on your face.
Isnt this the truth!!!
A different trire would be my first move. A GVOD would be my mech fix of choice.
What does GVOD mean?
727, 2800 stall converter
3.73 gears
the two mileage killers.
you could switch it to manual shift. Not a option
you could switch to 2004R and all that rigamarole to get a lock up converter Not a Option
you could swap the rear to a 3.23 Is a Option
if it was my money i'd do a passon 5 speed (has overdrive), keep the 3.72 rear
http://www.passonperformance.com/images/stories/passon_documents/Passon_5-Speed_Flyer_2010-11-18.pdf
but you will need pedal setup from a salvage yard, bell housing, clutch, flywheel (external balanced 360 is different than internal balanced) etc etc etc
so the summary answer is $$$ or drive it like it is
I will take those gears when you are ready to swap! 4.56 gears with a 4000 stall here, talk about bad 'mileage'... LOL
Having lots of fun for now but want to tame it down for sure.
For sure! We can work something out...Since you are close and all! Hell if you know how to tune a engine better than I do, come over, have some beer, and we can chit chat etc...
Keep in mind that unless you drive the car quite a bit it is going to take a very long time to recoup the $$ it takes to make any sort of major changes...especially the one that was mentioned about a Passion 5 gear. How much does he want for the box, 4k or so is what I seem to remember seeing some where. By the time you buy all the necessary parts you will be over 5k.....how long is it going to take to "save" that money in fuel costs? Sure, there are a few folks here that will tell you that you can find a complete pedal assembly/flywheel/clutch assembly for $300....but I have never been that lucky....
This is so true and the real reason I will not spend the time or money on swapping to a OD trans. I only drive this on the weekend because of collector plates. I would love to be able to go on a day cruise and not worry about how much Im spending on gas, considering I fill it with premium, or how far the next station is.
3.23 isn't that much of a difference from what you have now, still vote spare 2.94, and big tires as the best option here. :angel5:
http://www.ebay.com/itm/Mopar-8-8-7...Parts_Accessories&hash=item27e4d35367&vxp=mtr
Thats a good deal on a R/P. Im still curious as to the largest size tire that can fit in the opening? I have about equal space from the tire to the front rocker area and the inner lip to the sidewall of the tire.
If you have a tight converter you should have no issue with slip cruising a few hundred RPM below stall. Try it out, use a tach and see what your RPM vs speed is at compared to what your cruise would be with new gears, and compare with this tool. Rev it a little while your there to see how tight everything is.
One thing the builder of the converter mentioned was. "I set your converter at 2800 rpm of true stall, and str is set at 2.40. You will have perfect street manners, and a great wide open throttle launch." So Im curious if I switch gears or tire size what happens to my converter since it was built for this application?
Play with this to get an idea, and measure your tire from center of hub, to ground to get accurate size.
http://vexer.com/automotive-tools/speed-rpm-calculator
That is cool! Thanks