Is it worth it in fuel consumption? I mean cost, headache, work and so.

Right know I get 12 mpg at 65 mph with my carbureted combo(Pro system 1000hp). 489 bb 570 hp th 400 9.5" converter around 3000 in stall 3.73 in the rear.

Would i save much gas using efi on same combo?

Marcus

Depending on your highway RPM you might be better off with an overdrive transmission or a Gear Vendor unit.

Or just tune your carb with an a/f meter, you can get the same results as an EFI unit - but it will take a lot more of you're working it out than a computer. EFI units are trying to keep the car at 14.7 ratio, with a carb you can make it higher if you want, and bring the gas back in at WOT when you need it.

or buy a little kia for your daily driver and leave the velle in the garage except for when you want to play.

I love my little commuter, getting 34 to 36 mpg on it

Well, I also have a 454 but with EFI and 5-speed manual. A few years ago I drove 2 tanks at 75-80 mph (road trip Dallas->Kentucky) and averaged 20.7 mpg.

Car is a '71 Vette.

Mark have you checked your mpg we have almost identical engines. What ratio does your rear have?
Berto just wanted to know if efi is really worth it or if Im better of using the money on something else?

I usually tell people if the only reason they want to go to aftermarket EFI is fuel economy increases, don't bother. Not enough justification.

If you want fuel economy, get an OD trans.

Or swap in an LSx drivetrain with an engine that is very efficient as-is and get an OD trans with it.

Or tune the carb better if it is that far off.

12mpg with that combo at 65mph isn't too shabby to me.


I love EFI and wouldn't run a carb, but if fuel economy was all I cared about, the advice I give above is what I'd say.

Mark have you checked your mpg we have almost identical engines. What ratio does your rear have?
Berto just wanted to know if efi is really worth it or if Im better of using the money on something else?

I won't bother doing the math, but take an increase of 12-14 against how many miles you drive that car a year and see what it says.

I get about 18 on the highway, windows down, 70mph. I get an average of about 13mpg's tooling around, having fun, etc. If I'm on it a lot that goes down, obviously.

I have a 3.42 rear and a GV overdrive unit. Thing that surprised me was just how often I'm in the idle circuit, which is where I see the gains. I've bumped my idle circuit to 15.x AFR and it has a huge effect on how far I can go on a tank of gas.

With an OD, you'll be mostly on just the idle circuit from what I've seen cruising. Most people don't seem to think that.

Mark what mods have you done to your carb? Your total with od 2.50? Think with od I be closer to your mpg.

I have a 3.42 rear with .22 reduction from the GV - more like 2.70 if I'm calculating right. A regular OD tranny has a steeper OD, so you might be close.

Carb from ProSystems was dang near perfect right out of the box. What surprised me was how really small changes to the idle screws made a large difference in A/F ratio - like 1/8 turn on all 4 screws can drop your A/F ratio a full point to point and a half. I was NOT expecting that.

So really, to get the mpg all I did was lean out the idle circuit. I run low 13's AFR while accelerating, and right at 13 WOT. Only 1 more thing to do for now, I need a higher # PV so I don't go too lean before the mains come in. I have it, just haven't installed it yet.

I have played around a bit with this... setup is '68 El Camino with 402 BBC, 236/242 @ 050 .610/635 lift HR cam, Ede angle milled EFI heads, Ede RPM-Air Gap intake, Ede 600 carb, headers, 3" dual exhaust, and 3.31 rear gears. Figure about 26.5" rear tire.

My baseline was about 8 around town and 11 MPG down the highway.

Added a TKO 3550 with a .68 (methinks) OD 5th and pulled down a 13 highway. Dropped the RPM from 3000+ at 70 MPH to 2000 at 70 MPH. I used to cruise at 60-65 MPH due to the highway RPMs and now cruise at 70. Huge noise reduction on the highway with the lower RPMs too.

I spent some time tweaking rod/jet in the Ede carb with the target of bumping up the cruise AFR for economy. The actual AFR varies widely dependent upon vacuum/load and going much above 15.0 or so would result in some bucking under certain lean load conditions. Backed off a bit, eliminated the bucking, and achieved a 14 to 15 highway.

So my experience so far has been that there is more benefit in gears than AFR.

However I still think there is a couple more MPGs left in there with an EFI tune because I can get closer to the edge with better control and predictability.

One feature to look for if you go EFI is wide band O2 support. In particular many systems now have a target AFR table that you can configure. The beauty of this is you can configure a light load cruise AFR of 16-17 or even higher depending on what your engine can take. Then as load increases walk it down to 14.7 AFR. And finally for full load WFO operation optimize the AFR for best power from your engine (varies from 12.5 to 13.5 plus or minus). All under closed loop operation (this is where the EFI computer uses O2 feedback to adjust injector pulse width and thus fuel, you could think of as self-tuning operation).

or buy a little kia for your daily driver and leave the velle in the garage except for when you want to play.

I love my little commuter, getting 34 to 36 mpg on it

lol x2

Going to say a 700R4 with electric locking converter would probably cheaper and better gains. I went to a 6speed manual and installed a wideband. Had a th400 with 3k stall also, and was around 12mpg. Now it runs right around 20mpg highway. In town also went up which was suprising due to a heavy right foot.

Using a vacuum advance can help on freeway, as can lighter wheels. The gearing and stall you have is mostly for around town/racing however.