Mpg challange updates?

[redinjuns]

Tdi golf is back, or you could put a pd150 in the Spit I think those are rated at 150hp/ 270ft/lbs. They also mount longitudinally so it would go in relatively easy. There are a few Miatas running with them.

Do it for the children.

[Loren]

I gave serious consideration to putting a diesel engine into the Spitfire when planning my engine swap. Ultimately, opted not to. The Yaris 1.4D would have been ideal, but I didn't want to have an oddball not-available-in-the-US engine in my already oddball car. Not much else that's available in the US seemed like a good fit.

The TDI Golf is still too big. I like a car that tips the scale well under 2500 pounds... hard to find these days. (even the Yaris is nearly 2400)

[redinjuns]

Jetta > 3400
Plus 2 kids and a sled full of toys
Still pulled 47.2 up I-75/I-20 from the fl state line to Birmingham.
I-40 headwind slapped me back to 44ish.

[FoxHondaRider]

I alway decelerate so I can stay moving until the light turns green again to go. I mean most times your going to have to stop. But a good bit I can keep rolling and by the time the other cars accelerate I'll be right at there pace to accelerate up to the speed limit without having to idle or go from a stop.

[Loren]

Not looking to pick a fight or argue, but why do you say that "You really don't want to get into 'compression braking' to decelerate."?
I just see it saves my brakes and fuel.

When you downshift gently to keep your revs up and gain the benefits of DCFO, you're not hurting anything. The wear on the clutch is almost nothing because the engagement is smooth with no torque applied (either from the engine to the drivetrain, or from the drivetrain to teh engine), the wear on the engine is negligible, and there is no risk of doing any engine damage from over-revving because you're taking it easy. But, that's not really "compression braking" if you do it right. Your goal should normally be to have the car in a gear that keeps the revs fairly low to provide LESS resistance to your coast and allow you to coast further while maintaining the DFCO condition. (note that if you're coasting downhill at speed for a good long ways, it's actually more conservative to shift to neutral and take the fuel hit for letting the engine idle and extend your coast longer, but that doesn't happen much in FL)

If you're downshifting with the intent of compression-braking, you're going to put a lot more load on the clutch and the transmission. A hard downshift is just like a hard launch or a hard upshift, it's hard on the equipment. You also risk over-revving if you get careless, and that can trash an engine in a hurry.

The main thing is simply that brakes are a lot cheaper and easier to replace than clutches! But, there's a time and a place for everything. If you're driving through the mountains, going downhill, and just trying to maintain a speed without too much gravity-induced acceleration, it is quite appropriate to put the trans in a lower gear and let the engine braking regulate your speed. But that's quite a different thing from trying to use the engine to SLOW the car in normal driving.

Back to "efficiency" driving: Aggressive downshifting to slow the car is no more beneficial than using the brakes. In either case, you're scrubbing off momentum that could carry you further. You're turning momentum into heat either in the brakes or in the engine. The true economy would come from getting off of the gas sooner (when possible, of course) and coasting further rather than braking (either by engine braking or by using the middle pedal). Every extra fraction of a second you can spend in a DFCO coast rather than idling is going to improve your MPG a little bit.

[Loren]

Nah, not really too far off-topic. Good discussion.

[FoxHondaRider]

Best I was able to get was 32MPG. Let me tell ya it took some very carefull driving! Now this was with an automatic, with a manual I could have shifted lower. Still I was accelerating so gentle and slow, I wouldnt pull out quick into those open slots in traffic and mainly I didnt go any faster than the speed limit. It felt good to get gas mileage in the 30's but damn it wasnt easy. I made it 2 tank fulls 31 and 32MPG before I started driving more normal not going so slow and saw high 20's.

[steveyjr1982]

I was able to knock off an average of 38.2mpg in my regal on a recent trip to orlando which isn't too bad.

[P057]

25.065 mpg last time i made a 90% interstate road trip. Not really admirable numbers, but i was beating on the car almost every chance i could get, and drove 80mph the whole way.

The key to good mpg for me is 60ish mph. Any more than that and it makes a big difference. Maybe those speedy highways or expressways would be ideal for me with their 65mph limits.