engine efficiency

[Dagostino480]

I have been searching around and this topic really can go both ways but I thought I would post and see your opinions.

Currently I am averaging about 22-24 mpg on a sohc which is great for the s13 coupe I am driving in my opinion. I have started a build on a ka24de and plan on boosting it. Will upgrading the internals of the motor be benefiting or striving the motor of its mpg. Aswell as adding a turbo will it benefit or hurt the mpg.

Heres how my brain approaches it....

uprgraded internals should run more efficient(easier) which should create less effort to get up too speed and maintain cruising speeds.

turbos should give the motor positive back pressure therefore making the enigine run efficiently.


So as long as I am not driving like an idiot my car shouldnt lose its mpg drastically. To all the turbo owners on the forum, what did you experience with your cars efficiency.

Thoughts/opinions?

[future]

If you actually drive normal it should be better turboed

[Dagostino480]

If you actually drive normal it should be better turboed

thank you for the reply,

thats what I am thinking aswell, have you noticed anything with your turbo'd car if you have one?

[future]

I don't have one. But if you have proper engine management you should but more MPGs Forsure. There is plenty of mpg threads on here

[steve shadows]

Depends entirely on tuning and quality of tuning :)

You can do magic with it...

[Croustibat]

I have been searching around and this topic really can go both ways but I thought I would post and see your opinions.

Currently I am averaging about 22-24 mpg on a sohc which is great for the s13 coupe I am driving in my opinion. I have started a build on a ka24de and plan on boosting it. Will upgrading the internals of the motor be benefiting or striving the motor of its mpg. Aswell as adding a turbo will it benefit or hurt the mpg.

Heres how my brain approaches it....

uprgraded internals should run more efficient(easier) which should create less effort to get up too speed and maintain cruising speeds.

turbos should give the motor positive back pressure therefore making the enigine run efficiently.


So as long as I am not driving like an idiot my car shouldnt lose its mpg drastically. To all the turbo owners on the forum, what did you experience with your cars efficiency.

Thoughts/opinions?

My thoughts :
You are confusing efficiency and performance.

If you turbo the car, you will have to use lower compression piston, which lowers efficiency a lot.

You need to understand that basically, a turbo engine produces efforts on opposite parts than an NA engine, meaning both have different design. For example, a turbo engine will put lots of strain on the higher half of the rod and crank bearings, whereas an NA will do the opposite. NA rods are also a lot weaker because they dont have to deal with enormous pressure increases.

Meaning "upgrading internals" = using stronger parts, which are also heavier, decreasing efficiency again.

Same goes for pistons. You are not going to put CP's assymetrical pistons with various coatings, so it will again decrease efficiency.

Lastly, the camshafts and heads have very different designs. On NA car, even stock, you want overlap. The more power you want, the more overlap you go. On turbo engines, you dont want overlap, because fresh air coming from boost will just flow in the exaust. And in the same way, the valves need to be much stronger on a boosted engine, at least the exhaust ones. Sodium filled valves are used on turbo engines, but not on NA.

Problem: most stock NA camshafts already have too much opening for a turbo engine.

This, again, will lower efficiency.


That is assuming you want a reliable engine of course. If you just do a fit and forget install without reliability, or boosting 4lbs, that is another story.

[Kingtal0n]

some data

OEM redtop engine: driving about 60-80 miles highway then re-fill the gas and divide out fuel economy.

14.7:1 air fuel ratio, turbine connected, 65MPH: 29.8mpg
14.7:1 air fuel ratio, turbine connected, 85MPH: approx 26.2mpg
14.7:1 air fuel ratio, turbine disconnected, 65MPH: approx 27.7mpg
14.7:1 air fuel ratio, turbine disconnected, 85MPH: approx 26.3mpg
15.2:1 air fuel ratio, turbine connected, 65MPH: approx 30.5mpg
15.2:1 air fuel ratio, turbine connected, 85MPH: approx 27.5mpg

possible errors include:
-I was not using cruise control so speed was not as steady as it should have been.
-fuel octane was 87 so expect mpg to be worse when using 93
-timing values are oem and therefore not optimal
-tire size and differential ratio are not OEM therefore miles was calculated using turnpike posts and not the odometer

conclusions:
Having the turbine connected while driving below 3,000rpm (around 65mph) seems to give the best fuel economy. Changing the ride height and adjusting wind resistance with creativity should dramatically improve higher speed driving fuel economy, as well as reducing weight of the vehicle and rotating mass.

I've done a similar test with two different built engine SR20DET but have yet to examine and decrypt the data because I want to do more testing first. The car I have to test is map based and fully stand-alone so I want to get timing values as well as duty cycle numbers to compare the BSFC and so forth.

The wideband I used to adjust closed loop A/F Ratio:
http://i23.photobucket.com/albums/b378/draglarry/95_redtop/th_wideband.jpg (http://i23.photobucket.com/albums/b378/draglarry/95_redtop/wideband.mp4)