how many MPG will porting lose compared to stock ports?
S5 turbo engine w 750cc/1000cc injectors and 13psi

previously on stock ports, this set up got 15-17 MPG, doing a regular port and re tune the ecu will net what loose ?

please, I would like real world feedback and experience, I know all of you like to front all tough like MPG doesn't matter or I should buy a daily civic hatch.
But truth is I just wanna drive my 7 everywhere cause its ******* awesome and I didn't build a ******* awesome car to sit cause its too expensive to drive when i wanna drive.

 

Ive got monster secondaries and somewhat agressive primarys. Last 200 mile trip I got right arround 26mpg @ 70-75 mph. I have done better but that was what the last tank got, am also missing both my udertrays at the moment. AFR's bounce from 14-16 at cruise. I think the bigger tires are draggin my mpg down, I had stock 16's on it.

Boost Vs Cruise are very different worlds.

Closed loop on the haltech rocks.

 

Porting is irrelevant in comparison to driving style.

 

Unless you're talking about some kind of radical porting like bridge, the port will be less of an effect on mileage than the tune.

And here's a hit: anyone with a standalone that isn't getting better mileage than the factory has a poor tune (assuming no bridgeports).

 

Youd think letting more air in the engine would throw the a/f ratio off but it does little to nothing to its fuel cunsumption. Now if you want to save some ml of gas tune the mix a bit leaner. Of course the cons outway the pros on that subject.

 

ive got a streetport with haltech standalone, i get about 27 mpg at 55mph with A/C on and a passenger. so it cant make too much of a difference. all in the tune and how you drive

 

Damn maybe I should skip being NA and go boosted

 

N/A is great to learn on.

 

but boostless is useless.

 

Its my understanding that mazda injected a bit more fuel to help the cats do a better job by making them burn a bit hotter.

Gotta love things like 6 foot by 3foot energy star tv's and auto manufacturers getting better emissions by making mpg worse. GO GREEN

 

Less fuel makes it burn hotter. [and I think produces more NOx emissions] Though Mazda did have a thermal reactor that required additional fuel on the early FBs.

 

Excessive fuel is worse for the cats. To heat the cats up you would lean it out, or do what a lot of todays manufactures do and put the cat closer to the engine right in the exhaust manifold.

 

+1. its been my experience too that the port does very little to mileage. sometimes it SEEMS like the port actually helps mileage.

 

Sorry, Rephrase, it is my understanding that on the FC's mazda had to run it a bit richer to make the cats work better for emmissions which in turn lowered MPG.

There.

Anyone have a perfect running STOCK FC that they have Cruising AFRs from?

 

Sounds right.

 

i dont think so.. at cruise, the stock ecu just runs in closed loop, so it should be averaging 14.7 afr.

some people running standalones do not use closed loop and instead tune for 15+ AFR and crazy advanced timing during cruise which can help mpg. the problem with this is crazy high EGT's.. ive seen pictures of melted exhaust diffusers and blown turbine wheels due to the high EGT's. i just keep it simple and run in closed loop and timing is around 30 deg, 0 split at 3krpm, which keeps pre-turbo EGTs under 1700F. an extra 1-2 mpg is not worth overheating your turbo and exhaust.

the stock intake/exhaust is also pretty restrictive, which can hurt mpg.

 

i've got a 76,000mile 87 GXL, and its a little tricky to explain, but basically its running in closed loop from 1500-about 3800. if you go WOT, it stays in the mid 14's until about 3500-4000, before it richens up.

the complex part is that it idle its rich, but the air pump air is being added in so the wideband reads in the 16's and the phase in to closed loop is gradual. so if you're light on the throttle you can actually be cruising up to like 2500 or so out of closed loop, the WB will be reading anywhere from 16 to 14.7, depending on the air pump air.

if you accelerate, and then back off the S4 will richen up, and then stay rich for a few seconds.

the S5's and FD's ive tested were more rigidly mapped into zones, and there were less latencies. the S5 is in closed loop from 1500-3500, unless it sees high throttle openings, it doesn't gradually ease into it like the S4. the S5 is WAY richer @wot than the S4. the S4 and S5 both start @12.2 around 4500, but while the S4 actually gets leaner and stays in the mid 12's, the S5 just linearly goes rich until it hits about 10:1 at redline

so to conclude, the S4 has a couple of small opportunities to use less fuel, but it would (and did!) require a faster ECU to accomplish this. the S5 as delivered should deliver slightly better mileage in a cruising situation