400 rwhp and 20+ mpg?
 

What's the best way to go about 400 hp to the tires and still get 20-30 mpg? SBC or ls?

Re: 400 rwhp and 20+ mpg?
 

LS will get you close to that, although I'm not convinced it is possible to get 20+ mpg. These trucks are bricks moving through the wind. My '68 stepside with 5.3/4L60E achieved about 15-18 depending on driving conditions.

Re: 400 rwhp and 20+ mpg?
 

Look into vehicle weight and RWHP to see if the physics works.

Re: 400 rwhp and 20+ mpg?
 

My 347" LS dynoed 445rwhp and has knocked down 25mpg on the highway. But it's in a Camaro, which is considerably lighter and more aerodynamic.

The best path for 400rwhp and 20 mpg in a truck is LS and "hypermiler" driving techniques!

Re: 400 rwhp and 20+ mpg?
 

I understand everyone wants better gas mileage and HP , I want a super model who loves to cook and clean house and is happy to wear a potato sack and never spends any of my money . Ain't gonna happen ! I've seen guys try to do it and spend $1,000's on mods to be fuel efficient when they could have just paid the price of the fuel and buy a beater mini truck to get to work every day instead of driving their COOL truck and hating to feed it .:chevy:

Re: 400 rwhp and 20+ mpg?
 

Well you won't get the horsepower but if mileage is what you want my dream is a swb truck with a cummins 4bt

With the right gearing and a manual trans 25+ shouldn't be an issue

Re: 400 rwhp and 20+ mpg?
 

I would look at a 4.8 LS with a turbo. Couple it with a 6-speed auto. You could get there with the right gear out back-and have a screamer when you wanted it.

Re: 400 rwhp and 20+ mpg?
 

My Datsun 280z makes 428 RWHP LS6 w T56 manual and will knock down 27-28 mpg all day but weighs 2640lbs. My 1971 RS Camaro will get 27 MPG if you act right with and it makes 606 RWHP with a magnacharged LS6 with 5 speed manual both have 3.70 gears so even in a truck 20+ would be very realistic but only LS powered and FUEL INJECTED

Re: 400 rwhp and 20+ mpg?
 

Well put!

Re: 400 rwhp and 20+ mpg?
 

I would love to know how everybody achieves these high mpg's! I have owned a FEW 5.3 trucks and a 4.8 truck and always avg 13-14 mpg. Maybe 16-17 on all highway. Maybe I drive faster..
All the cummins guys claim 20+ mpg and I have had 2 24 valve 5.9's and a 6.7 cummins and even though the display shows 17mpg, on paper it always came out to 12-13 mpg.

OP, Big power+fuel efficient= LS. No doubt the LS based engines will beat the sbc in every aspect.

Re: 400 rwhp and 20+ mpg?
 

I still have one of those 150 MPG carbs if anyone's interested:>)

Re: 400 rwhp and 20+ mpg?
 

20-30 mpg? :haha:

Modern midsize trucks can't even achieve close to that.

Even with a fuel injected LS and OD, expect 12-14 around town and 17-20 highway depending on your driving style/habit (and rear end gear!). Anything over 60mph on the highway and you start to lose mpg with these trucks (huge bricks).

The older Cummins with a manual can absolutely get mid 20's. My uncle has owned a 94 Ram reg cab longbed with a cummins for probably 15 years now. He hauled my 67 from NY to SC for me (rode with him) and hand calcs (GPS verified) showed 17 MPG with a 2500 lb trailer and 4K pound truck. He regularly gets low to mid 20's unloaded on the highway. I have read the newer ones are way up on power, but emissions (and the sheer size and weight of the newer trucks!) have killed economy.

Re: 400 rwhp and 20+ mpg?
 

stick shift and a conservative right foot go a long way
20's can be a stretch with higher hp

Re: 400 rwhp and 20+ mpg?
 

^^^^this is about the best advice you'll get. If you have 450 plus hp it's doubtful the truck will get that cuz you'll always be on it lol.

Re: 400 rwhp and 20+ mpg?
 

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This is also very true. My grocery getter mazda 3 doesn't get any better then 30 mpg highway. I doubt any full size truck comes close to 30 mpg downhill. Though I see the big three try to claim otherwise. Trying to get 30 mpg in these trucks when new factory trucks can't is like saying we know more then the engineers at gm,ford etc. We all would like better mpg and there's ways to improve most times but being realistic is also key.

Re: 400 rwhp and 20+ mpg?
 

Bone stock LS1/4l60E with 3.73 and a 29" tire. I've never done better than 22.5 MPG highway and that was driving like a grandma, probably with a tail wind :lol:

Truck weighs right at 4000 lbs.

400hp and 20mpg can probably be done, but it wont be easy and likely wont be under "normal" driving. I'd still go LS if I were you - just keep your expectations reasonable.

Re: 400 rwhp and 20+ mpg?
 

I agree. If I drive it, it seems to drink fuel. Where people claim 14 - 16, I get about 12 with the same setup. When I am feeling cheap, I drive my Honda that gets 65 to 75 MPG - I even hit 86 one time.

Re: 400 rwhp and 20+ mpg?
 

Show us how that's done.

Re: 400 rwhp and 20+ mpg?
 

My Duramax gets about 22mpg on the highway empty, and with a tune you'd probably be able to get 400hp to the rear wheels... ;)

Re: 400 rwhp and 20+ mpg?
 

Well I know nothing about diesels, though I could maybe go to school for it, I'm either going for engine building or metal fab but I could always go for diesel tech also, will probably put a dmax or Cummins in a lifted truck if I ever build one.

Re: 400 rwhp and 20+ mpg?
 

I have a 72 C20 with 350 and TH350 trans......I'm running an edeljunk carb.....I'm getting 10-11 mpg 95% city driving only with short driving distances.

I was a bit disappointed at first, but then I remember my 99 tahoe got about 12-16, and my 2010 GMC truck got 13-17 so it's really not bad for a 42 year old non-fuel injected brick rolling down the road...

I'm calling BS on anyone that is claiming they are getting more than 15 or 16 MPG with a stock configuration 67-72 truck with city driving....im not saying it's impossible but very hard to achieve.

Re: 400 rwhp and 20+ mpg?
 

Ah Guys ? the OP is 17 , Unemployed and doesn't have a truck yet . He came to the right place to learn how to build one eventually ...:smoke:

Re: 400 rwhp and 20+ mpg?
 

Not only were you pulling the trailer and the weight of the truck but probably also had to fight the crappy are dynamics of the 67 as well!

When it comes to these trucks I feel as long as when I tromp down on the gas that thing feels like it just lost 700 pounds and starts to fly down the road, I would live with 15 in the city or over. There's always a price to pay in our case owning a c10 means you'll never know what good gas mileage feels like... Or you can find out what semi good gas mileage is but you'll have to spend a couple thousand for an LS.

Re: 400 rwhp and 20+ mpg?
 

I have the truck, just not to where I can work on it. So I'm gathering parts and ideas to bust ass on it when I get it to the shop

Re: 400 rwhp and 20+ mpg?
 

Good ,this is the place to learn and get help ,Now lets see what truck your starting with .:wop:

Re: 400 rwhp and 20+ mpg?
 

Can't upload pics from my phone unless its a fb message so.....kinda stuck there

Re: 400 rwhp and 20+ mpg?
 

I have an '83 K20. I swapped the original anemic 350 for a Tuned-Port 350 from a '90 Corvette w/ aluminum heads. It has 3.42 gears and a 700R4. I have had it since it had 42K miles. It always got 14 city and 17 highway. With only a change to TPI, I went to closer to 17 city and 20 highway (empty). Now I "only" have 300 or so horsepower, but the TPI has a lot of bottom-end torque. It feels so much better loaded on the hills.

Re: 400 rwhp and 20+ mpg?
 

My 600 RWHP 78 Malibu has gotten 26 on the highway at 70mph. This is with a 200-4R and a 3.42 rear end. It's a turbocharged Buick V6.:metal: I would probably go with a stock cammed 4.8 or 5.3 and add a turbo/intercooler for an easy 600 at the rear wheels. Don't go overboard with a cam and that combo should get at least 20 on the highway in these trucks if you keep the gear ratio around 3.42.

Re: 400 rwhp and 20+ mpg?
 

I have a couple Harley's that run 80 all day long and pull 35 mpg Doesn't mean a whole lot when we're talking '67-72 Trucks !:chevy:

Re: 400 rwhp and 20+ mpg?
 

That sucks when a VW Jetta diesel can do the same thing...lol. However, the Harley would take the *coolness* factor.

Re: 400 rwhp and 20+ mpg?
 

20 mpgs IS do-able with todays technology. The money needed is up high. "It costs to go fast how fast can you afford to go" we are talking about running 93 octane, electric cooling fans, electric water pump, aluminun vortec style heads (all those things just give a slight percentage increase it adds up though), electronic fuel injection kits (they claim 4-6 mpg gain), thats for the a small block style engines.
There are multiple ways to skin a cat though.
-4.3L is an option with turbos done right you should see good mpgs not driving like you stole it
-Or even a mild 5.3L (any LS style motor) conversion
-Youll need to look into a 6 speed manual transmission (t-56 trans is a good choice for that) but rear gears will need to be changed accordingly
The new epa laws kill mpgs on new vehicles.

But you wont be able to get higher 20 miles per gallon without computers and TUNED CORRECTLY

cant wait to see pics and to hear about this build

Re: 400 rwhp and 20+ mpg?
 

if you wanna play you have to pay ! Period , We can all complain about what it costs to feed the monster but only you can decide if it's worth the effort /time and expense if not buy a jetta and drive slow in the fast lane while texting !:lol:

Re: 400 rwhp and 20+ mpg?
 

you guys are missing the mark... the trick is torque, torque is where it's at. If you can increase torque, it takes less effort for the engine to turn larger wheels. By increasing wheel size, and you can cover more distance per revolution of the wheel. This means you need less revolutions to cover the same distance, which means you need less revolutions of the engine to cover the same distance. Less revs of the engine means less fuel used. This is why diesel trucks with bigger tires get descent gas mileage. My brother has a 05 dodge diesel with a fast fuel, edge juice, and 37's and on the highway he gets about 25mpg because the engine is running about 1800 rpm at 80mph

The torque can be achieved by increasing volumetric efficiency, or increasing stroke.

Re: 400 rwhp and 20+ mpg?
 

Yeah well .... that diesel will be watching my tail lights fade away with my 572 and Muncie fuel eating fire spitting leave you boys on the porch good ol chevy horse power at 5 miles to the gallon and a grin on my face all the way to the next fuel stop ! Go buy a prius and quit complaining about what real horse power cost ! Go big or go home ! ... if you have to worry about what it eats go small and stock ....:lol:hmmmm there is a 650 super charged chief motor out there ......20 gallon gas tank 40 gallon reserve sounds about right ,it's only money you will make more or you'll go 6 cylinder ? I heard Wizzer makes a good motor ?

Re: 400 rwhp and 20+ mpg?
 

I would love to catch you out on the street with my 27 mpg datsun

Re: 400 rwhp and 20+ mpg?
 

You better watch out for those diesels....they can be very fast too. Bigger isn't always better like many old school guys think. I've tore up plenty of big block *pure race cars* at the drag strip with my air conditioned, power windowed, cruise control...etc 3500lb Malibu. It's sooo fun when a they find out a V6 done put a whooping on them and still drove home on the street! :haha: It sounds like a bumble bee but it WILL sting when provoked...haha.

Re: 400 rwhp and 20+ mpg?
 

I would love to catch you out on the street with my 27 mpg datsun

Re: 400 rwhp and 20+ mpg?
 

As someone else said, 400rwhp (500 at the crank) and 20mpg isn't going to happen with a carburetor and an *old school* small or big block chevy engine.

Re: 400 rwhp and 20+ mpg?
 

To do what haul extra gas when I need it ? :lol:

Re: 400 rwhp and 20+ mpg?
 

Let me know when your ready ! NOTHING beats a worked 572 with a good driver and a good suspension .