I was wonder how good of gas mileage can you get when you have a large street port? Also would you get better gas mileage than regular stock ports on stock ports but polishing them?

 

It will be worse.
Good gas mileage is not in the vocabulary of an Rx7 owner..But FUN IS!
..and I think Zoom-Zoom sounds a hell of a lot better than saying: Veeee taaaaaaakkkk"

 

Haha true. Im looking for the brapping. Im planning to daily a large streetport with half bridge.

 

I think there should be an Equation for this.
The Hole in Wallet is equal to the Size of the Port!

 

not exactly, porting can in fact increase mileage but only when you open everything up.

stock cars generally run about 20-21.5mpg highway, my turbo increased to 23.5mpg highway when i deleted emissions, added free flowing intake and exhaust as well as street ported it. reason being you can lean out your fuel trims while keeping the engine under less stress to maintain speed without all the factory parts. my car also has a 70 trim MP turbo and makes roughly 325whp when the throttle is mashed.

if you have no way of adjusting fuel trim you won't notice any of those benefits.

my engine is also tired, quite. at roughly 250k miles on the engine shell components(although rebuilt it was years ago before i had shelves of parts to choose from or resurfaced housings). basically borderline retirement at 90psi of compression on the S4 turbo II engine.

 

i get 19.5 mpg at 60 mph for 4 hours, im 6k into my stock rebuild

i get avg 12-14 mpg, when i boost here and there, and its my daily driver

16 city if i stay off the turbos completely

I have stock twins though, would a single make it better?

 

a single will get rid of most of you bottom end power. the stock twin only kicks to the large side at 4500rpm if i'm not mistaken (someone correct me if i'm wrong). so the theory is your gonna lose power and probably fuel milage since you would have less airflow. the turbo is a obstruction and without it supplying air you are not going to burn all the fuel entirely which is pretty much a waste of both fuel and power. the better a engine breathes, in the full range of rpm's, the more power and fuel economy you are going to get. well thats the theory as far as piston engines go anyway, so i may be off base as rotary engines are different and i have a little knowledge on them. i'm sure if i'm not 100% correct on this someone will chime in. if it were me i would just get a better intake manifold, a free flow exhaust, uprgade the turbo mani, k&n intake, and give it a regular full tune up. just my $0.02

 

O ok I see. My friend has basicly the same setup as me but he has an fd and I have a carburated fc and he gets like 10 miles per gallon.

 

It's all relative to how much your right foot weighs. You can get 22 if you want it, but I've gotten 10 as well. All depends on how you like driving your car.

 

Ok so I just have to stay in low rpms for better mpg.

 

my example was at 80-85mph, with 100mph jaunts here and there to pass slow moving vehicles.

it's mainly just how well you tune the car. even a bone stock FD should get about 22mpg on the highway(just did it in an FD i delivered 500 miles. but it did have an M2 intake, downpipe and catback with stock main cat).