hows ur mpg? for all you boosted guys out there

[no_doz]

not going diesel-im just not paying 50% more for the fuel just to get 30% more economy

[torq455]

you can get better mileage with a lot of bottom end, tall gearing, and low rpm operation. just swap in a turbo diesel with a 2.56 FDR.

[z284pwr]

I had our TGP to 22MPG with 75% freeway/15% spirited city/10% tuning. I was getting it better and better until it had issues this past December. I shouldn't hope upon it but I really do hope the cam is going flat so we can put in a better cam, with more torque, cruise is right above where it starts making any power so going up any hill it downshifts at least one gear. Heavy TGP with a GT3076R and a horrible bottom end torque cam doesn't go very well at 4400ft and hills

[no_doz]

so could i supercharge a v6 or get a 3.8sc & get great mileage (with my foot out of it) with a very tall rear end gear ratio-rather than modifying the trans itself?

[RedZMonte]

wow, id never run a car at anything lower than 12:1... thats rich as hell redzmonte...

i think its like 12.5:1 at which peak torque can be found usualy with a/f ratio...

HAHA i know.. i need some fine tuning. But it still makes great power and for over 2yrs hasnt blown up....

S

[93grandprixse]

wow, id never run a car at anything lower than 12:1... thats rich as hell redzmonte...

i think its like 12.5:1 at which peak torque can be found usualy with a/f ratio...

[Canyonero]

Torque and gearing, read here: http://www.carmagazine.co.uk/News/Se...ontent-block=1

[RedZMonte]

I am currently getting the same as stock.. 24mph mixed (hwy/city) on 7psi. I am running pretty rich, if i get some more tuning time in i think i can get +2 or 3mpg and make a little more power.. Im currently seeing about 10:1 a/f mixture...

[bszopi]

The current engine is just insane. You can read about it on their website, www.theoldone.com . Check out the engine on the engine dyno, and it's efficiency...



Yeah, I'd say it gets it done...

This is still my favorite (although it is a 4-cyl import). 1.55L making 487hp and running low 11s in the quarter. Yet it gets 23-27mpg in the city and 33-36mpg on the highway.

That article is from several years ago and the engine has been redone since then. I don't know the current power its making, but it is one hell of a beast.

27 psi, let's see, 14.7 psi makes that 1.55L more like 3.1 L and another 12.3 psi of boost totaling 27, makes the 3.1L about 6L worth of symbolic displacement by the amount of air moved. That's about like having a built small block 400 on tap in that little car.

Note the high compression ratio with high boost and he could probably get even more mileage out of it with a 3 series final drive instead of that 4, but that's not what it was built for.

[bszopi]

This is still my favorite (although it is a 4-cyl import). 1.55L making 487hp and running low 11s in the quarter. Yet it gets 23-27mpg in the city and 33-36mpg on the highway.

That article is from several years ago and the engine has been redone since then. I don't know the current power its making, but it is one hell of a beast.

It's really not that complicated and technical. It's all about efficiency and gearing. Best scenario to date I'm aware of is a 9 sec quarter Turbo LSx Corvette, with 27 mpg hwy according to the announcer at the track and if I recall correctly it has an LS engine stroked to 427 cubes, I'll have to look for the video to confirm it.

If you build, cam and gear the engine for its best efficiency at hwy cruise speeds you will get exceptional mileage in everything you drive compared to the standard compromise settings for vehicles in its class. That's why VVT helps so much, instead of a best all around fixed cam, you have a system that gives you the best cam dynamics over a broad rpm range. Advanced for low end grunt, retarded for high end performance. The engine also has to have a proper power to weight range. A lot of the high mileage imports are light in weight.

If custom gears for your tranny were easy to come by and practical, you could run circles around the factory mileage achievments by optimizing the drivetrain to your requirements. From the factory they have to decide on a medium that includes everyone and dependability over all extremes. The EPA decided the 14.7:1 AFR ratio for emissions purposes. Higher ratios would yield better mileage otherwise. As high as 16:1 or more for some engines during cruise.

The 3800 is not exceptional at all, it happened to receive better gears for economy because it had the extra power needed to still provide a performance feel despite the economy gearing. Put the 2.8 and 3.1 on that same transmission and you will see a tremendous improvement. Recall that the early 2.8 and 3.1 rarely found itself attached to a 4 spd automatic and ran 1:1 with the 3 spd and still managed as high as 30 mpg in some cars, the 5 spd did not have economy ratios like those that could be found in the 4 spd auto.

Again, the car has to be built as best all around performer or it may not sell as well, so the weaker engines get shorter gears so they can keep up with the bigger engines in exhchange for less than best fuel economy. The aluminum head motors when placed in Fieros unless you screw it up usually mean an automatic 30 + mpg. Some are getting up to 35 with the 2.8L.

[no_doz]

very true-why the other day i was researching the high tec japanese engines & came across things like the b16b making 180 hp at 1.6l! and a toyota 4a-ge with 5 valves per cylinder & 162 hp at 1.6l!

considering that stock 3400's made at the same time make 170-180, although the v6's make a lot more tq. what ive been thinking pretty hard about is how these high tech japanese engines are designed & how much power they create with so much less displacement because of the whole flow/efficiency combination, as well as things like compression & etc... & some of these make lots of power for their size. like the nissan 350z-3.5l v6 making 280-310 or so hp stock, almost the exact same bore & stroke characteristics-4 valves per cylinder-dohc, etc... if a 3.4 dohc had the head done (any reshaping needed on the heads & porting-valve job, etc...), gasket matching, headers, the works-if the internals were made light & the compression was raised to the same as the 350z-the only real thing stopping you is a very small amount of displacement & the intake/cam-& if a supercharger was used then 70% of that intake tract is gone & replaced with pure unadulterated boosty goodness-then some very serious power could be achieved. what im wondering is if a digital boost controller was used to keep the boost way down under normal driving conditions by just letting most of it go via the wastegate-could excellent gas mileage be achieved & lots of power when needed?

[torq455]

the newer 4-bangers have more research and technology in them. VVT, more efficient heads/combustion chambers, intake design--variable as well, cam profiles, and now direct injection, work together to make a nice healthy flat torque curve. my 2.0 91 Sunbird had ~130 ft/lbs @ 3200 rpm. newer 2.0s easily have that at 1500 rpm, thus making them more efficient. in turn, more lowend torque allows lower rpm operation with an OD tranny. also have to mention: newer cars are more aerodynamic as well. i never would have believed a 2.0 engine (cobalt SS) turbo, not only would get 260 HP, let alone 260 TQ @ only 2000 rpm, but to get 22 mpg city and 30 mpg highway? no way!

[no_doz]

does all that torque really mean that much for gas mileage? and if so how do these little 1.x 4 cylinders pull around heavier cars with good mileage (2.2 in a 3050lb honda car, 30 mpg if not brought into vtec) & etc...? and what if that kind of tq was in a car that weighed around 2400-2500lbs & awd-wouldnt the potential for mileage be a LOT better if the vehicle was driven mildly? also using a digital boost controller to allow for less boost in order to get better mpg-how well does this work on a supercharged engine?