Modifying a 3400 for MPG

[SappySE107]

I received an email and decided to copy and paste to here.

Hello,
I would like to make changes to my motor that
would increase gas milage instead of hp. On the
internet when looking up the subject many people
argue back and forth on some hot rodding subjcts
if they increase gas milage at all. Except hotter spark
most people agree but does better air flow ,higher compression,
and headers. What is your experence in better mpg's.
Thanks for your time.

[SappySE107]

What motor do you have? Anything that increases efficiency can increase mpg, but the best modifications are Tuning, Headers, and Heads. Hotter spark won't do it unless you have a single coil and distributor. Cam profile can be made for better MPG as well. Compression increases will help but only to a point, and then you have to make the motor less efficient at lower speeds to compensate for the cylinder pressure at higher RPM.

On a grand am 3400, upgrading to 3500 heads and headers plus tuning showed 5-6 mpg increase.

[SappySE107]

I have 1999 olds alero with the same 3.4l v6 as on the grand am.
Is the 3500 heads with the same 3500 factory headers what you are
talking about or are you talking about after market headers. Does port and
polishing help
increase mpg on heads. If you get the 3500 heads and use the thinner
head gasket to raise compression would raising the 9 something to 11
something
compression ratio help mpg? And what tuning do you mean? The hotter
spark I was talking about was Grantelli mpg ,close to zero ohms
spark plug wires. On the JC whitney website buyers of Grantelli mpg
spark plug wires commented on older autos it seemed to have better
mpg increase than on newer autos. And people at fuel injector
websites said that getting a newer type fuel injector( mine I think are
leaking)
with better atomization ,which newer ones are suppose to have but keep
the same lb. at same pressure as factory would help mpg.
How much would a cam increase mpg?
I know this is alot.
I really appreciate it.

[SappySE107]

You have the same setup as a grand am then, and the 3500 heads and lower with a 3400 upper would give you more power and gas milage. The headers were S&S, but we will be making some based on our J and L body design, but modified for the N body. Port and polish can help mpg but only if it is done properly. Stock 3500 and the heads i port are perfect for efficiency, which means performance and mpg.

Spark plug wires NEVER gain power or mpg unless the old wires were not working properly. Compare new vs new and its all the same.

You cannot run a thinner gasket on the 3400 without risking piston to head contact. To gain any appreciable amount of compression, you will need new pistons.

Newer injectors would help as well. I would run the 2000 and newer injectors and FPR, and tune the computer. Once I have experience with any local owners I can find, I will be able to offer PCMs tuned for the parts I sell and common stock combinations.

[SappySE107]

Ok, that should be a good start for a discussion

[robertisaar]

you didn't mention that extremely low resistance plug wires can have RFI issues?



personally, i'm pretty interested in this topic as well, i need all the help i can get with 3400lb curb weight vehicles.

[SappySE107]

Yes, I prefer better EMI and RFI protection over wire resistance. Resistance seems more like a gimmick than an advantage with todays ignitions systems.

The DIS-4 gave me 1 mpg but no power. This was with my old 3.1 MPFI grand prix, and it was comparing multiple tanks of gas with varied driving habits each time. Also compared at the drag strip for the power and ran the same times back to back to back to back.

[onefastV6]

I will be sure to post how my 3500 with the MPG cam and TOG headers works out... hoping to slap it back together yet this summer.

[19Cutlass94]

Once my car is done getting tuned, itll be exciting to see what MPG's I can pull.

But overall I think the best thing for MPG's is your right foot...

[Superdave]

In my experience (Tuning wise) there is only so much you can do for in-town mileage without hurting driveablity. If you start bumping up the SA the bucking starts with a 5 speed, Auto might be a bit more forgiving though. AE tuning helps for sure.

Highway is a different story, internally stock 3400's running $A1 have reported over 35 highway MPG with a 5 speed. LCM is a wonderful thing.

[robertisaar]

i <3 Highway fuel.

somehow, i managed to pull 38.1MPG out of the 90GP(LH0/4T60, 3.33FDR) once on a ~220 mile trip.

highway spark is a MUST when high fuel is enabled, to make up for the lower flame speed at leaner AFRs.

[SappySE107]

I saw 40 going through Texas when my car was all stock. Gearing is HUGE! The 3 speed in my cavalier is killing it for me. I can't even get 30.

[geldartb]

On a grand am 3400, upgrading to 3500 heads and headers plus tuning showed 5-6 mpg increase.

nice increase in mpg. wonder what my car get's for city/highway mpg's. i don't drive it enough on a regular basis to get real numbers.

[pocket-rocket]

This was with my old 3.1 MPFI grand prix, and it was comparing multiple tanks of gas with varied driving habits each time. Also compared at the drag strip for the power and ran the same times back to back to back to back.

You forgot to mention that number haunted you no matter what strip it was at, too, lol.

[robert 1980]

I will be sure to post how my 3500 with the MPG cam and TOG headers works out... hoping to slap it back together yet this summer.

So i guess i know why you sold me your old cam then??