Improving Engine Efficiency & Performance

[torq455]

31 mpg

[Rhedalert]

in a v8 with tuning. sure. the problem with comparing an engine with 2 more cylinders and more cubic inches per cylinder is whatever effect happens on it, the lesser engine will have a lesser effect. they say a K&N filter adds up to 15 HP on a 454. well, on a 305, it might be more like 8. then our 3x00's, maybe 3?

i was hoping for more mileage with my headers, but didn't see any gain. though, with my FDR of 3.05, at 65 MPH i turn ~1950 RPM. light throttle at that rpm won't need a high flowing exhaust.

What do you average on the highway for fuel economy?

[Bones]

A high flowing exhaust isn't nessesarily important but a low-backpressure exhaust is because any extra pressure pushing down on the piston during the exhaust stroke robs power from the flywheel. Likewise a header that scavenges the cylinder well at cruising RPM will create a small vacuum in the cylinder which helps accelerate the intake into the cylinder so that less power is lost filling the cylinder. Of course if it scavenges too well or the camshafts overlap period is long some of the intake charge can be sucked right out the exhaust port, which is good for horsepower, but it obviously doesn't help fuel econemy.

I'd say that less exhaust gasses left in the cylinder also means that the intake charge is less poluted. This could mean less ignition timing may be required, or it might allow the EGR system function better by reducing intake vacuum more. It gets a bit complicated to work out all the variables and figure out what works best at this point, would probably take a bit of experimenting with the tuning to figure that out but regardless I think reduing back pressure would help econemy.

that's my $.02
-Mike

[IanSzgatti]

light throttle at that rpm won't need a high flowing exhaust.

but i'll bet it's good when you pound on the pedal like a red-headed step-brother

[torq455]

in a v8 with tuning. sure. the problem with comparing an engine with 2 more cylinders and more cubic inches per cylinder is whatever effect happens on it, the lesser engine will have a lesser effect. they say a K&N filter adds up to 15 HP on a 454. well, on a 305, it might be more like 8. then our 3x00's, maybe 3?

i was hoping for more mileage with my headers, but didn't see any gain. though, with my FDR of 3.05, at 65 MPH i turn ~1950 RPM. light throttle at that rpm won't need a high flowing exhaust.

[Rhedalert]

Headers are known for a couple extra MPG's in the F-bodies (after tuning) and the LS1 already has decent flowing stock exh manifolds.

Nice catch on the 3500 vs 3400 VE! I haven't been able to find 3500 bin files to check that out.

[IsaacHayes]

Yep many things that improve performance can also improve mpg since it's more efficient. Now somethings like a really hot cam can hurt MPG. I wonder how much mpg headers are worth?

[IanSzgatti]

to help the 3x00 you need to increase VE....thats about all you can do with the engine untill you start getting into areas that would require extreme modifications.

I just wanted to say that threads like this are awsome because they are a pool of knowledge all brought together by each member, and it enlightens and educates. It always impresses me; the amount of knowledge in theory some of you have.

To keep in line with the topic, I agree with the statement I quoted. Since the 3400 is a conventional "air pump", then the ease of which it performs has a lot to do with the pumping of the air. Now my little story...

Before I did my exhaust, I would cruise at around 70 km/hr until OD kicked in. Once it did, I would try to maintain that low rpm/low vac condition throughout cruising. When coming to gentle rises, the car would downshift with the slightest increase in throttle.
Now that I have changed the muffler and added a short high-flow "performance" catalytic converter, I can take the same gentle rises and maintain that low rpm while slightly increasing throttle pressure.
I suppose a little higher rpm would produce more power, thereby reducing pulse width or something, but then your still getting more rpms anyways... so i'm not sure which is more benificial. I am out of things to say that make me appear to know what i'm talking about, so I will stop at this point.

[onefastV6]

I think the design improvements in the 3500 heads may help... part of the reason I think when I was running the 3500 top end, that I was getting better mileage.

The attached excel spread sheet shows the stock 3400 VE table for a 02 Grand Am compared to a stock 3500 VE table for a 04 malibu.

[merlot566jka]

op engines are fairly comon in the navy used to generate electrical power and propulsion.

opposed piston engines are made by fairbank-morse. they are manufactured in virginia. they sound odd, vibrate and are very complex.

what does this have to do with this thread? things tend to get off topic here and thats when the good info comes out.

to help the 3x00 you need to increase VE....thats about all you can do with the engine untill you start getting into areas that would require extreme modifications. those modifications would almost render the engine a completely different animal.

[Rhedalert]

It's my understanding that pumping losses are very high at part throttle and cruise speeds vs WOT and high RPM. That can be observed based on engine vacuum readings. Since we're talking engine efficiency improvements and for people looking for that extra MPG, we have to assume most of the driving is done under part-throttle, be it city and/or highway environments. So in order to reduce pumping losses, generally you want the throttle to be "more open" without adding additional load, and still maintain a given speed. This can be accomplished by (in theory)

- Dropping the drive ratio. If you need, say, 50 hp to maintain 65mph on the highway, you could achieve this at 15% throttle at 2500 rpm, or 25% throttle at 1500 rpm. The 1500 rpm/25% throttle has the advantage of less frictional loss due to spinning slower, and theoretically lower pumping losses due to the wider open throttle. Just throwing some numbers out there but obviously we'd need a dyno chart showing real values, to see if the engine would be within the powerband.

- Smaller engine. This wouldn't be an answer here but for arguments sake, a larger engine may only need 10% throttle at 2500 rpm while a smaller but otherwise equal engine would need 20% throttle at 2500 rpm to maintain the same speed. This would be a pumping loss reduction.

- Variable displacement, same reason as above. One might even suggest injecting larger amounts of inert (exhaust gases) into the combustion chamber to effectively "reduce displacement"





The only part of that video I disagreed with is how he seemed to explain the internal combustion engine inefficiency was due to "unburned fuel out the tailpipe". At least as far as gasoline engines go, I can't see this being the major cause. How much more BTU energy is lost from the cooling system vs the BTU content of this supposed unburned fuel? It seems to me with modern engines, this can't be the case, since the air/fuel ratio is precisely controlled at stoich under normal conditions.

[Canyonero]

With the gas prices on the rise and not wanting to spend money on another vehicle, I am brainstorming ways to make the 3400 and 60*V6 engines in general more efficient.

I think the physics talk was much less of a digression than this line on theoretical internal combustion engine design.

[Bones]

When you combine a larger compression with 2 pistons, its not a gimmick. What you are saying, is the design itself doesn't allow for any more energy to be used. You said that you need to use more of the heat...well doubling your stroke on 1 cylinder by using 2 pistons instead of one does that. It uses more of the energy from that one combustion event than a single piston would.

Not sure I'm following you... I think compression ratio in current diesel engines is already optimal. More compression creates more heat and not much else, at least that's my understanding. The only possible advantage I'm seeing is that not having any heads reduces the surface area of the cylinder so they'd dissipate less heat, which could lead to a significant improvement, but still nowhere near the "80% efficiency" that they claim. It would take testing to see if there are worth-while improvements. Plus you'd have to develop some kind of valves to work in the cylinder walls (unless we're talking about a 2-stroke diesel which I gather are much less efficient due to having to run a big blower along with port timing compramises)

I don't think that the results would be a very big improvement, and I'd rather see development go into one of the 6-stroke designs, but that's just my opinion. Without a lot of testing there's no way to know for sure.

[SappySE107]

Anything off vacuum will improve efficiency a great deal. Less work for the motor and it gets over 100% volumetric efficiency.

When you combine a larger compression with 2 pistons, its not a gimmick. What you are saying, is the design itself doesn't allow for any more energy to be used. You said that you need to use more of the heat...well doubling your stroke on 1 cylinder by using 2 pistons instead of one does that. It uses more of the energy from that one combustion event than a single piston would.

[Bones]

Getting back on topic....

I don't see a TURBO on you list of areas to improve A senicible (read: small) turbo with a proper camshaft (short duration, negetive overlap) can actually improve fuel econemy, not to mention give you lots of extra torque. The small turbo will choke the motor so you won't be able to turn a lot of RPMs, and the whole thing is likely to cost you more than you'll save on gas, but hey....TURBO! haha