Hey all,

I hope this is not in the wrong section.
I have an opportunity, to go from a RB 6port intake and a 600 Edelbrock to a stock S4 Na EFI setup. This is my main question: can the EFI be upgraded over time?
and will i be able to blast the tachometer into the heavens with the Stock EFI stuff?
Will my fuel economy be better than the 11.2 MPG that I am getting now?
I am totally blown away by my carbureted setup, I just want to be able to actually not have to have at least $200 in gas for a 280 mile round trip just to enjoy myself.
My buddies have said that the EFI FC intakes can kill at least 20 to 45 horsepower??
I eventually want to upgrade the EFI to future things but if i am sitting at a comfortable 150 HP then that is just fine for me. Oh yeah, btw this is in a 1981 FB S model.


thanks,

Tim

 

the major difference between the S4 intake and the RB intake is that the factory intake is longer, this will move the power peak to a lower RPM. this should help the mid range (2000-500rpm), but you might loose over that

the mileage is a function of the tuning of the carb, it must be really rich when you're just cruising/idling. the factory ecu is more like 18-20mpg

 

I did this swap in my 79 with the stock port, stock ECU S4 NA. I can't comment on power difference as I have never run the carbureted version. I do know that I'm getting about 26mpg highway and closer to the 18-20 around town as stated by j9fd3s. The truly nice part about the EFI is driveability. No bogging, smooth power band, nice idle (on stock ports anyway), no grenading mufflers, and you don't have to worry about fuel slosh in the float bowls when pushing it hard in a corner. If you want to push the EFI or if you have a ported engine you'll need a good stand alone ECU and some time with tuning.

 

11.2mpg... How foulded are your plugs?

I get about 15mpg in town. I do drive like a bat out of hell though. On the highway, if I'm docille, I'll get about 20 or so.

 

Hey guys thanks for the info!

I have decided to stick with the carb for now.
Quingdao: I checked my numbers and I incorrect.
I am getting about 14mpg i think i am getting around 150 miles to a tank on an 1984-85 12a gas tank which i believe, is 16 gallon max.
J9fd3s: thanks or the info that helps.
GySgtFrank: thanks too! that gives me better idea now.
my next purchase shall be wide band O2 sensor and gauge.

thanks much and i will keep all posted

 

The Edlebrocks have a nice feature; if you keep your foot out of it, the metering rods will stay down in the jets and limit fuel usage.

 

Instead of guessing your tank size. Fill up to the brim -> reset the trip -> drive -> then refill to the brim and get the fuel used inbetween your fills from the secont fill.


Do you pre-mix? Too heavy a mix will kill millage.

 

Thanks for the info.
I have a confirmed 16 gallon tank and am getting a way better bit of milage than I thought.
I do premix as well right around 1 ounce to a a gallon of gas, since I drive my car very hard.

Thanks for the info tho.

 

Being a owner/driver of a S4 EFI powered car, I would say keep the carb. The early EFI system Mazda used on the FC is mediocre at best... Ide rather run a weber tuned by a 3yr old than the S4 EFI system

 

Thanks for the perspective. I have a weber DCOE and the RB upper manifold to fit an S4/S5 lower manifold. Think I should give this a try on my 6 port?

 

With the right jetting and venturis that should be a blast to drive. Do it!

 

Sounds like a better choice than EFI.

 

its a bit quicker, and there are less pieces to find

 

Id steer away from the holley if youre faint of heart. Its costly to build one right for the rotary, and RB most did not properly prepare ANY of the holleys Ive bought from them in the last 10 years, so either pay a pro to build one on a dyno, or go with the above mentioned weber 2bbl options...


** Just noticed you said you wanted to run an Eddy 600, in which case should be awesome. But why the eddy? The new demon carbs are extremely precise and highly responsive to tuning.

http://www.summitracing.com/parts/dem-1900/overview/

Inexpensive too, and some local shops have already started boost prepping them with great success.

 

The only real perk of the stock EFI system is the direct fire coil and non-linear spark curve. The only way to achieve this running a carb on the S4/S5 13B set-up and a non-standalone spark controller would be to run a carb, delete the fuel injectors, and plumb the stock VAF/MAF to a carb, as the computer bases almost all of ignition timing on RPM (CAS) and calculated airflow (VAF/MAF) and load (TPS). Luckily, the S4 EFI specifically is a very rudimentary design and doesnt really know or care if any auxiliary controls are there or not, all it needs to run w/o CEL codes or fail-safe mode are the basic engine sensors... S5 is a little more picky and needs to see working emissions controls

 

That sounds pretty rightious. I might look into this as the turbo car progresses. I don't like this electronic distributer.


Garrrrrr Thread pirating

 

I see. Fortunately it has a direct fire setup already (DLIDFIS). Think I should just go with the Weber DCOE and call it good?

I should have access to all the jets and air bleeds from when PercentSevenC was experimenting with boost. He said all it needs are some 36mm chokes, but now I'm thinking since this is a 6 port, I might want to keep the current 40mm chokes. Less parts for me to buy! Thoughts?

Oh and I have an update about the PO's carb vs EFI position: he decided to keep the carb for now.

 

go 40! 36mm is for piston engines! (eww)

 

Ok thanks! Less stuff for me to buy! I could actually test run it after the exhaust is built.