Throttle Body Injection, or Multi-Point Injection for fuel economy? 1

[REDlinesDOTcom]

Based upon the question in the subject, which fuel injection arrangement would you expect to yield best results for fuel efficiency?

I'm going to leave this open for discussion, then I'll post the results that I have come across on more than one occasion.

 

[kenvlach]

REDlinesDOTcom,
Re "Final drive on the Si appears to be 4.25 vs. the DX having a 3.89 with 1-5 gear ratios being the same."

Running the smaller engine slower at the same highway speed should give this relation, assuming same volumetric efficiency:
DX mpg = (1.6/1.5)x(4.25/3.89) x Si mpg
= 1.16538 x Si mpg
Checking your results, 31.8 Si mpg vs. current DX 39.6 mpg,
gives DX mpg = 1.16538 x 31.8 = 37.059 mpg.

You should get the average over several tanks of gas for an accurate number (Best: use the same pump & stop at the automatic shut-off). Also, cars get better mpg as broken in (friction reduces) and this continues until start losing compression (rings & valves). Varies by engine, but maybe generally best mpg from 50,000 to 150,000 miles. Also, warmer weather helps mpg -- thinner air requires less fuel, although less power.

I suggest verifying the 5-speed gearbox specs. If it's the close-ratio, performance box, switch to a wide-ratio, exonomy box for lower engine RPMs at highway speed. [Or, even the wide-ratio 4-speed]. The EPA estimated highway mpg for the 4-speed is better than the 5-speed, so the engine must be capable of same highway speeds while turning about 6% slower.

 

[kenvlach]

Look at some 1995 Honda Civic data (from fueleconomy.gov):
HB VX 4 cyl, 1.5 L, Man(5), EGR/4-VLV (FFS), 47 (city) 56 (hwy),
(model?) 4 cyl, 1.5 L, Man(5), EGR/2-VLV (FFS), 42 46,
(model?) 4 cyl, 1.5 L, Man(5), (FFS), 34 40

[maybe you can figure out model with engine data & the 'Fifth Generation...' info below]
FFS = Feedback Fuel System (usual FI w. fuel & oxygen sensors),
EGR/4-VLV -- EGR (?)usually means exhaust gas recirculation,
VLV probably variable lift valves.
I think the VLV's are versions of Honda's VTEC-E, the 3rd listing is earlier VTEC engine, maybe same as the 1991.
VTEC-E description:
"Honda's next version of VTEC, VTEC-E, was used in a slightly different way; instead of optimising performance at high RPM, it was used to increase efficiency at low RPM. At low RPM, one of the two intake valves is only allowed to open a very small amount, increasing the fuel/air atomization in the cylinder and thus allowing a leaner mixture to be used. As the engine's speed increases, both valves are needed to supply sufficient mixture. A sliding pin, which is pressured by oil, as in the regular VTEC, is used to connect both valves together and allows the full opening of the second valve."

http://en.wikipedia.org/wiki/VTEC#SOHC_VTEC-E

Honda probably set up the 1995 Civic HB VX w. VTEC-E to run at pretty low RPM at highway speed, thus in economy mode, to maximize the MPG (56). So, final drive gearing probably also lower.

Also, look at a few 1994 Honda Civic EPA mileage nos.
Honda Civic HB VX 4 cyl, 1.5 L, Man(5), (FFS), 47 56
Honda Civic 4 cyl, 1.5 L, Man(5), (8-VALVE) (FFS), 42 46

Fifth generation (1992-1995)
"All DX and LX models used the D15B7, while the CX had the D15B8 and the VX had the D15Z1 (VTEC-E engine). The EX and Si trims had the more powerful D16Z6. The SiR was equipped with the 1.6 L B16A1 with VTEC."

http://www.reference.com/browse/wiki/Honda_Civic

A bit surprising that the 8-valve engine (obviously not a VTEC-E!) got 46 MPG rating.

Anyway, some target MPG's for you.
Lots of luck.

 

[globi5]

Throttle body injection could have a small advantage over Multi-point injection, if all fuel is evaporated before reaching the combustion chamber and thus improve and accelerate combustion (higher peak temperature at TDC).

 

[r2800]

All things being equal multi point is better in power,economy and emissions and in injector location within the span of the inlet tract this then allows the throttle body to have a simpler location due to the absence of fuel pipes, although throttle potentiometer and other sensor wiring etc may still have to be accomodated.
The other advantage over single point is the absence of raw fuel condensing on the inlet manifold walls and causing unequal mixture distribution within the manifold just as in the good old days of carburettors this being exagerated by throttle position and the vapour pressure of the petrol being used.Perhaps the only advantage is cost, in europe we got over that some years ago,funnily enough there now appears to be a resurgence in this form.

 

[AnythingDynamic]

Porsche has just unveiled her version of DI which, apparently, is to be used in all her V-8s (see current issue of *Exce11ence*.)

The claim is that DI affords better mileage, more power, and less emissions.

Rather elegant -- even by Weissach standards.

 

[FoMoCoMoFo]

if these were 2 identicle engines, on dynos, in steady state conditions, I would bet on tbi.with a long intake you would get good mixing and more evap time and cooling but in the real world port inj. probably wins for the reasons stated above. comparing 2 different cars and engines no matter the similarities does'nt tell you much in relation to your question. Happy motoring.