Pontiac 400 with FI and a T56 gets about 19mpg on the highway?

[sixtyfourbeets]

I had a conversation with someone from whom I may be buying a Firebird from and during the course he said he knows someone who has the above mentioned
combination and claims to get 19mpg on the highway.

Is this realistically possible? WIth those kind of highway figures would a 15mpg around town attainable?

Given the choice I would much rather keep a real Pontiac engine in a Pontiac rather than putting an LS corporate block in.

[Pontiac Chris]

I would say so, I got 20mpg with my stock 400 (670 head 067 cam) and Q-jet with a 2:41 rear gear (Richmond 5 speed 1:1 5th) turning about 2100 rpm at 70mph. I now only get 15mpg hwy as the 400 has a big cam and heads and 850 holley. Around town should be easy to get pretty close to 15mpg as you can ride the 400's torque, I shift 1st, 3rd, 5th and don't break 2500rpm when in normal traffic.

Whilst I love LS motors and have no problem seeing them in Pontiacs, there is still a cool factory to having that Pontiac motor, I have often said I'd like to switch to LS power and everyone of my friends says don't, the Pontiac is cool.

[Ron Sutton]

I had a conversation with someone from whom I may be buying a Firebird from and during the course he said he knows someone who has the above mentioned
combination and claims to get 19mpg on the highway.

Is this realistically possible? WIth those kind of highway figures would a 15mpg around town attainable?

Given the choice I would much rather keep a real Pontiac engine in a Pontiac rather than putting an LS corporate block in.

30 years ago I had a "Pro Touring" style of '77 Trans Am with a 400, 4-speed, 3.73 rear gears & low profile tires. The engine was built specifically as an "all around" street machine & VERY tuned, made 365 hp and got 16 mpg cruising at 62mph which was 3000 rpm.

EFI would make the engine more efficient in the overall rpm range & a transmission with 5th or 6th gear OD dropping rpms down in the 2000 rpm range would help bump fuel mileage considerably. So I think 19 mpg is "possible" for freeway cruising with a well tuned 400. Mine got 12mpg around town if I drove it sensibly. I would think 15 mpg is also "possible", but slightly harder to obtain than the freeway number. Of course all of this is dependent on many, many factors in the build & tune of the engine. So I'm saying what is "possible" and what is "actuality" may be different.

If you're comparing this to an LS ... the older engine is not going to compare. If you build the two engines to provide the same power, the LS will do so with much better manners, drivability & fuel mileage. I think the key is to decide what will make you happiest & build the car your way.

JMHO :cheers:

[Nicks67GTO]

Ive always heard the 400's could MPG well if you had a good tune and combo. I think it goes south fast when you go with the oversquare 4.21" stroke 455. I'm pretty sure there are guys on PY that claim in the low 20's with very mild 400's. Cliff Ruggles would be the guy to ask as hes the resident quadrajet expert/business over there and shoots everyone straight. Hes a no BS kind of guy. I think the secret is in the qjet. I'm actually considering a KRE headed 400 when I build my next engine.

[srh3trinity]

What rear gear was he running?

[sixtyfourbeets]

What rear gear was he running?

The guy may have told me during our conversation and if he did I dont recall what it was.

Could have been anything from a 3.08 to 3.22 or a 3.42.

[sixtyfourbeets]

If you're comparing this to an LS ... the older engine is not going to compare. If you build the two engines to provide the same power, the LS will do so with much better manners, drivability & fuel mileage. I think the key is to decide what will make you happiest & build the car your way.



Well, in all actuality what would make me happy is a 400 hp V8, 6 speed, RWD (or even better AWD), 4 wheel disk brake, two door sedan(or a reasonable facsimile thereof), independent all around suspension that gets about 15-17 mpg around town and 25 on the highway.
The Australians seem to have the right idea (I know 15-17mpg around town is too much to ask) however for some reason GM America is far too stupid to realize that there may in fact be a market for what I describe.
But since the niche I describe cannot be fulfilled by any domestic automaker (or foreign for that matter but the lines are so blurred that it doesnt matter) the buying public has resorted to buying SUV type things but again the marketing idiots in all the automotive manufacturers seem to be living on their own planet. The GTO and G8 was an admirable attempt which had potential but it was far too late.

So to tie this all together one of the reasons I want a pro-tourer type car is because the new Camaro has horrible all around visibility, I want one but not bad enough to sacrifice my ability to see who is on my 8 or 4 when I want to change lanes, instead I would have to count who has been in my mirrors. I do that now in my '94 Caprice but the visibility is much worse in the new Camaro and headroom was designed in as an after thought.

Sorry about going off in to tangent ranty land. I've got plenty to say about the general state of both the manufacturers and aftermarket. Like for example why did it take the better part of 10 years for the aftermarket to catch up and make some kind of LS type engine kit (headers, motor mounts) after the LS engine had been released to the public? Why is an IRS kit using existing parts (from a GTO, Camaro, CTS, G8 etc) non existent?
Believe me I would be building these kits if I had the resources.

Some might argue if I want all the things I describe I should buy a BMW/Audi/Subaru thing, if I wanted to change my timing belt every 50000 to 100000 miles on the interference engine I would but thats not my cup of tea.
I had a Volvo 240 handled great with Bilstein shocks, but that 50k mile belt change interval got boring very quickly I would not describe a 240 as reliable if like clock work the belt breaks.

I hope I dont get in to too much trouble for this.

[Ron Sutton]

I hope I dont get in to too much trouble for this.

Oh you're in all kinds of trouble. You just wait buddy! :rotfl: :rotfl: :rotfl: :rotfl:

[srh3trinity]

FWIW, I scored a used G8 GT and it is a fantastic car. I can knock down 23-24 with mostly interstate and a little city. Certainly not a two door and it is heavy, but I really like it for a DD.

[dobie6982]

+1 for Stephen. I have one and love it. Easily hangs with just about anything out there on the interstate.

[sixtyfourbeets]

FWIW, I scored a used G8 GT and it is a fantastic car. I can knock down 23-24 with mostly interstate and a little city. Certainly not a two door and it is heavy, but I really like it for a DD.

I am so very close to breaking down and breaking my bank to buy a G8 GT. The only thing that bothers me a lot is maintenance down the road.
I know if I build the car myself, the wiring and all that junk I can fix it myself without being forced to go to a shop.
I'm not building a garage/trailer queen, I'm looking to build a rough and ready daily driver that will get parked on the street and exposed to the elements.

[nekkidhillbilly]

actually the the 73 catalina dad almost bought a few months back pulled 18 mpg all original

[tazzz25906112]

Ran a 1970 Firebird Formula 400 with a built 455 60 over and e heads with an Edelbrock injection system in front of a keisler 5 speed and 342 gears across America from TN to Vegas in 2009.... I was averaging about 19-20 miles to the gallon....

That all said,,, the LS is definitely on average roughly 25% better in the same application as experienced by me.... If your building a pro-touring ride the LS is the answer for me.......

[rustomatic]

When it comes to mileage, it's gears, not so much the injection part. Aerodynamics also play a part, but most old cars don't have much here, unless you're doing a Superbird (not the cheesy thing at Denny's). My 40 year-old Dodge 4x4 with 37-inch tires does about as well (for mileage, in the low teens) as the average new full-size, with a cheap Summit 600 carburetor; granted, I rarely exceed 65 miles per hour. My Falcon will do 20 mpg on the freeway, doing 70 or so; this is largely due to the 5-speed and fairly freeway-friendly rear gear (2300 rpm at 70); it has a very mild 5.0 roller motor, though, not 500 horsepower. The big torque in an old Pontiac non-big block can take you far here...

[Jeremy]

Very doable. I run a 400 with 068 cam and a tremec 5 spd. With Holley projection and 3.23 could get 24 mpg with the ac on at 75. With an edelbrock carb and 3.73 rear, I get 20. If the roads hilly and a 55-60 speed limit, I get better mileage with the 3.73. Around town is 15-17 no matter how I drive it.

[sixtyfourbeets]

Very doable. I run a 400 with 068 cam and a tremec 5 spd. With Holley projection and 3.23 could get 24 mpg with the ac on at 75. With an edelbrock carb and 3.73 rear, I get 20. If the roads hilly and a 55-60 speed limit, I get better mileage with the 3.73. Around town is 15-17 no matter how I drive it.

So if a Pontiac 400 with a Holley FI system may be able to yield about 20mpg on the highway would it stand to reason that a 1968 Cutlass with an Olds 350 and the same kind
of Holley FI with a 200 4R trans may be able to yield slightly better MPGs?

I ask this question because a 1968 Cutlass with a 350 and 200 4R has become available locally.

I realize that the LS would be the best overall option and it is my first choice but I also have to consider cost effectiveness and time as well hence I am weighing
all options that may be available.

[Scott Parkhurst]

It's all about rpm. If you can gear it to rumble down the road at 1400 rpm or so on the freeway, decent fuel economy is possible. It's all about the right combination. My wagon gets 20+ with a T56 and 3.89:1s on the highway.

[Jeremy]

I agree its about rpm. I think I dropped the mpg due to the rear gear swap not the change to the carb.

[Takid455]

I run 455 (474) pushing approx 540 hp, 3.73 rears, T56, EFI and yield 17-18 hwy (85-90) and 12-13 city/ town. 20 def possible if velocity remains 65-75.
This is in a 78 T/A tanking the scales at 4300# w/ driver, pass and luggage/ crap. Car is 3900# alone.

[boodlefoof]

I'll second going with original Poncho power. I'm putting a stroked 400 in my Tempest.