V8 fuel economy

[greasess]

5

[greasess]

I have a vortec 4800 in the car right now. I originally chose the 4.8 because of it's stout bottom end. The first picture is of a chamber that I had welded up on the plug side and shaped like a figure 8. The added quench area should improve the engine's detonation threshold allowing for more compression with a given octane fuel. This chamber should also push more of the burning mixture into a smaller area at TDC allowing for a faster burn that will require less timing and allow less heat energy to escape through the head. I have 2 sets of heads prepared like this. One of them can be seen in the second picture. The intake port walls were left rough after porting. My thinking is that this should improve fuel atomization because of the added turbulence. The third picture is of the "somender singh groove". After the engine is together without the groove I'll get a baseline and then take the heads back off, put the grooves in the chambers, resemble, retune and test again. The groove is supposed to increase mixture motion/turbulence. I'm also going to make a set of headers with anti reversion cones to improve scavenging and decrease pumping losses. I plan to do all this with 93 octane fuel at first and eventually move to e85 when it's time to turn the boost up. The engine has 9.5 to 1 compression now with what I think is a 58 cc chamber. I haven't done a cc check on the finished chambers yet but I hope I can get close to 11 to 1. All this turbulence and chamber motion along with a faster burn and less optimal timing should allow me to use significantly less fuel and actually make more power. The car has a 6 speed manual with a .5 6th gear, 3.50/1 rear gear ratio and 315 35 r17 tires and that puts me at 2,000 rpms at 90 mph.

[Frank Lee]

"More power to you"!

I was looking through the EM Garage for vehicles above 40 and 50 mpg... many three cylinder 1.0 m/t gas cars, hybrids, and diesels fail to crack 50 mpg. You have your work cut out for you.

[greasess]

I know that aero mods like a boat tail and things like eoc would really help me achieve 50 mpg but I want to do it without any of that. I would really like to hear what cripple rooster thinks of this. While doing research on google about ethanol and cr limits I always come across your posts.

[greasess]

I think I do have my work cut out for me but I also don't think the smallest engine is always the most fuel efficient. At 65 mph my engine is only turning about 1400 rpms. How fast does a 1.0 liter have to rev with factory gearing at 65 mph? Did you know that double the rpm quadruples the amount of rotational friction an engine experiences? I forgot to mention that I'll also be using reverse flow cooling and a propylene glycol based coolant that will allow me to run coolant temps at 240 F further increasing atomization and reducing chamber hotspots.

[Frank Lee]

4800 @ 3.3" stroke @ 1400 rpm = 770 ft/mn piston speed

1.0 @ 3.03"stroke @ 3000 rpm = 1515 ft/mn piston speed

Yup the 4800 would be turning quite slow- actually by some accounts too slow while the stock geared 1.0 is above it's best range of 1000-1200 ft/mn at 65 mph.

You aren't going to get 50 mpg at 65 mph either.

[greasess]

What speed do you think I may get my best mpg at and why?

[Frank Lee]

Search "optimal piston speed" for probably the best engine rpm range and for aero, the slower the better. Most American vehicles with automatic transmissions are said to get their optimal mpg at about 45 mph, a little above converter lock-up.

[greasess]

When I got 33 mpg I was on the highway between Pinellas County and Orlando going about 80 mph.

[greasess]

My car's DC is supposed to be .34 so it's average I guess. I wouldn't mind doing aero mods that aren't visible but I just can't have a boat tail on my car. I feel like that would be a crime.