Turbo Boost and FE

[Backtobasics]

2 things to consider between a N/A and turbo motor. One is negative, the other is positive.....

1. exhaust restriction. The manifold is normally very short, creating restriction, plus the restriction in the body of the turbo, the restriction of the propeller, and any addition angles and turns that the exhaust must overcome to exit the into the exhaust system, plus the lost velocity that was used to turn the turbo hot side. Negative
2. Heat. Compressing air raises the temperature, hence the use in performance applications of an "Intercooler" (aftercooler), to remove heat. The additional heat on a turbo application, regardless of the the boost pressure, helps to atomize the fuel better, for a more efficient combustion efficiency. This is a built in hot air intake, so to speak. Positive

Ultimately, The heat from the turbo should help to overcome the restriction of exhaust, but it is a tight battle.

[ShadowWorks]

I have driven a turbo charger car for years also a 2 litre turbo, I thought I knew how to get the best FE but I didn't, I always assumed the turbo had to be in its efficiency range which on my engine would be 4.5k rpms, bad for FE obviously.

I honestly believe I have figured it out now, I am gentle in 1st and 2nd gear and I open the throttle a fair amount, not WOT but not chocking the intake either, in 3rd gear I look at my vacuum gauge and make sure that its at 0 or atmospheric pressure, the engine speed is low and the turbo begins to spin at 1.5k but I change gear before or on 2000rpms as this is the most efficient range in my fuel table, so I basically keep my throttle open but the engine speed below 2000rpms, what ever the turbo can do in that range has helped my FE because I got 160 miles from 3.7 UK gallons or 17.1 litres of fuel, when before I was getting 80 miles from the same fuel!

Keep the engine speed down but get the turbo working is the trick, if you can lean your fuel system I recommended that as well, turbo cars run extra rich under boost conditions, I hope to experiment with this idea this week.

[AlainB7]

My wife have a Hyundai Sonata 1992 with a 4g63(mitsubishi 2.0l) and 3 speed automatic FWD 3 speed + overdrive + lock-up.

My Galant VR4 also have a 4G63 but Turbo and 3 speed automatic AWD + overdrive witout lock-up.

Both car have similar FE but The Galant made a bit better with about 5MPG more. But It is Turbo without lockup and it's AWD. So if the galant was FWD with a lock-up, it will do better FE. Both car weight almost the same.

But if I dont run at low trottle FE will rise up, full trottle @ 25 psi of boost, i'm about 375HP at the wheel! Not good for FE

In 4g63, the compression ration of turbo and non-turbo engine is different.

[GasSavers_Dust]

One thing that is being missed here I think, but was covered on the ecomodder site, is fueling.When in boost, the fuel pressure will rise. The effective compression ratio will also rise.

As as anecdotal aside, several turbo mustang guys have noted increased MPG from their turbo bolt-ons.

I think a 9.0 CR with a low compresion turbo, or a turbo with some meth or water added would be the best of both worlds.

[AlainB7]

Originally Posted by Dust

One thing that is being missed here I think, but was covered on the ecomodder site, is fueling.When in boost, the fuel pressure will rise. The effective compression ratio will also rise.

As as anecdotal aside, several turbo mustang guys have noted increased MPG from their turbo bolt-ons.

I think a 9.0 CR with a low compresion turbo, or a turbo with some meth or water added would be the best of both worlds.

For me. 43 psi base pressure and 68 psi of fuel @ 25 psi of boost.

For shure compression ratio is different from a NT vs Turbo 4G63.

1G 4G63 NT: 9.0:1 (192 psi compression)
1G 4G63 T: 7.8:1 (164 psi compression)
2G 4G63 T:8.5:1 (168 psi compression)
Galant 92+ 4G63 NT: 9.8:1 (220 psi compression)

[GasSavers_BEEF]

I'd love a 1 liter turbo 3 cyl.

talk about the best of both worlds. gas mileage without boost and enough tail to get out of the way with boost.

[DRW]

Originally Posted by BEEF

I'd love a 1 liter turbo 3 cyl.

talk about the best of both worlds. gas mileage without boost and enough tail to get out of the way with boost.

That's the rub, how much fun vs. how much FE?
Certainly a turbocharged engine is the right way to push both ends of the envelope. But there's still a limit to how much power you can get and still keep good FE. I'd like to see what a 3 cylinder 1 liter engine could do with direct injection and compound turbocharging. Maybe add an electric motor to make it a hybrid, and setup the engine so it can run as a generator when needed.
What would you guess? Maybe 75mpg and 250HP?

[AlainB7]

DRW, explain me how you get 46 to 53 mpg with your big Laser?

You almost make the FE of my VX with the set-up of my Galant that make 19 mpg...

[Dalez0r]

Originally Posted by AlainB7

DRW, explain me how you get 46 to 53 mpg with your big Laser?

You almost make the FE of my VX with the set-up of my Galant that make 19 mpg...

No offense, but your galant's aero looks like this:




It's also an automatic, does that torque converter lock up at cruise? Or does your high stall converter slip constantly? That would annihilate your fuel economy.

[AlainB7]

Originally Posted by Dalez0r

No offense, but your galant's aero looks like this:




It's also an automatic, does that torque converter lock up at cruise? Or does your high stall converter slip constantly? That would annihilate your fuel economy.

This car is modify to drag, fnot for FE.
For shure I know that my AWD, Automatic, High stall and no lock-up don't help my FE, but I am not at my first DSM.

I had a 92 NT, 90T, 91T, 95T, Elantra swap 4g63T.
Even the Elantra(1000 pound less than the DSM) can't do best than 35mpg and it was MT FWD.