Small Block or Big Block Power for Crew Cab K30

[Mr. Lee K30]

So I found out my 400 sb had antifreeze in the oil and considering its been sitting for some while I'm looking at other engine options.  Would a 350 be adaquate for powering this beast or should I go with a 454?  My intentions with this rig is to make it a driver while doing some occasional towing and hauling. 

Specs:
Crew Cab K30 3+3
Stock th400 Trans/np203
32" Tires
4.10 Gear Ratio



 

[VileZambonie]

Why not rebuild the 400 since you've got it?

[Stewart G Griffin]

Well, coming from the stingy point of view, i would personally want to put a diesel in there.  Either a 6.2 or duramax, if the olds has been figured out, or even a caterpillar of some sort.  That would make this into a very nice machine-----you'll have all the utility and towing of the crew cab while still getting 20-25 mpg.

But if the choices are BBC or SBC only then i would go with small block.  Unfortunately, either way with this setup gas mileage will not be too hot.

i'm with vile on this and i would want to rebuild the 400 because something like this needs torque.  Or a 383.

[Redneckchevy]

383 sounds nice...But if you got the 400 why not? Sounds like the right combination of power and economy

[86 chevy silverado]

Get the 400 checked out and if you get a clean bill of health from the machine shop go with it.
Big blocks are great and will definitely do the job but at twice the cost, now with the build and later with fuel.

[Captkaos]

If you are only going to be occational towing, I would go with the 400 if it is sound.
Diesels would be a nice switch, but are you wanting that kind of project?

[Mr. Lee K30]

Swapping a Diesel would be SWEET!!! 

But right now I can't afford that.  I think I'll give the 400 a chance and take it over to the machine shop and have it checked out.  Thanks!

[Stewart G Griffin]

Ok, i saw your picture in the welcome section and it turns out that don't have dual wheels(by the way that is a pretty picture.  Not nessesarily of the truck.  i'm not saying the truck isn't pretty, but more so the scenery;  i've been to oregon once and it was pretty awesome);  Anyways, i thought you had dual wheels because it seems most crew cabs have them.  But this is actually a good thing because having those two extra wheels on the ground takes more power to turn them, adds extra weight, and not to mention having those two big fenders in the airstream probably affects mpg big time.  So, there still may be hope for you after all.

You say you plan to do occasional towing/hauling.  How often is occasional and how much and what will you be towing?  How much driving will you be doing on a weekly basis?

i feel 4.10 might be too low for this application.  Tires, exhaust, gearing and possibly cam choice i feel will be crucial for decent MPG in this truck.  I feel 15 mpg would be decent for this truck considering the size and weight.

[Captkaos]

15mpg would be dreaming on a carb'd crew cab truck.  My CrewCab with a TBI 350 got 10.5mpg on the last check, I am still checking it though.  I figured it should get about 12mpg tops.... maybe.

[choptop]

My 83 Crwecab dually got 10 mpg, with the a/c, without the a/c , on gas, on propane, up hill, down hill, didn't matter.I have learned from experience though, that it is not necassarily whether you hace a bigblock or a small block, the amount of pressure you put on the skinny pedal determines gas mileage. On my 81 pre-bigblock, I got about 12mpg. My wife drove the same truck and got 15mpg. Go figure. The new bigblock gets about the same mileage,with 540 horse available, but mash the pedal hard enough, and it gets about 7. Driving normally ( as normal as I can get) it is running aroung 14-15 mpg average. This is highway and town combined, which most of it is highway as I live in the country. If the 400 is rebuildable, I would go that route. A small block to a bigblock conversion is a pain unless you have a complete donor. The motor is drop in, but all the accessories take some redoing.

[1976Scottsdale]

I agree, keep the 400 just try not to get it too hot.  The antifreeze probably cames from a cracked head or bad head gasket.  Most of the 400's I have been around had that issue and it was rarely the lower end.  But since it is out for most of this, rebuild it all the way.  350's are great engines, but they lack the torque ur gonna need for that size of truck in my opinion.

[Stewart G Griffin]

Just out of interesting's sake when i was at the local chevy dealer on friday, picking up my speedo gear, i spotted a new silverado crew cab with the duramax engine, allison transmission, single rear wheels (not dual) and 4WD going for 52K and some change. This was the "LTZ" trim level.   If we count the destination charge, then 53K!

So basically, it's the same setup you've got (except the diesel engine) except yours was (presumably) 40-50K less.  (Are you the original owner?)  So i feel that if you can get 15mpg, you're ahead of the game.

Other MPG ideas i've picked up upon on the net recently:

1)Blocking the grill off so as to improve  aerodynamics.  Not completely of course, but like Nascar cars and trucks to the  point where the radiator still gets adequate cooling.  As soon as i install my temp gauge, i will definitely be experimenting with this idea.

2) The use of a tonneau cover apparently improves a pickup's aerodynamics up to 11%.

3) Nitrogen instead of air in the tires.

2)

[choptop]

Fuel economy is directly related to the overall efficiency of the engine. Increasing the efficiency on the engine is done by optimizing the air intake, fuel atomization, and exhaust disposal.  An engine at its peak efficency also means more horsepower. Like I stated in an ealrier post, I have an 81 3/4 ton with a 540 hp 468 that gets 14-15 mpg. The stock 350 got about the same at around 165 hp. I belive i can drop my rear end gearing to 3:73 or lower and get better mileage, plus still being able to handle the load because I have more power on tap. Some one once told me their theory on how it takes X amount of power, for this weight of truck to maintain y speed. Ok, 1st I despise algebra, second, ok, If your truck requires 100 hp to maintain 70 mph running down the highway, then ask yourself, which would possibly get better mileage, an engine with 100 hp at 3/4 throttle, or an engine with 100 hp at1/4 throttle. Now also keep in mind that thehigher power engine will use more fuel when you stand hard on the skinny pedal, but that would be your fault, not the trucks.
     As far as aerodynamics, there is onlt so much to do with a brick. Don't know if blocking the grille will help or act more like a brick wall. Keeping the truck low, not running massive oversized tires will help in this department. Not sure on the bed cover as there is too much conflicting information out there, but I think it makes a difference.
  Stewart G Griffin made the best point. At the cost difference between the new trucks and what you will have in your truck will buy alot of fuel. There is  enough differnce to put an overdrive tranny and fuel injection in you truck. I am looking at a  new truck for my company because its tax deductable, and some people don't understand the beauty in these old trucks.Any way, I figure if I got a gas that got 15mpg it would be less to operate than a deisel at 18 mpg due to the cost of the deisel engine, deisel fuel to gas difference, and maintenance. Now the deisel has its benefits if it is pulling heavy trailers constantly, but for just driving around, can't figure it,, still want it , but can't figure it.

[Captkaos]

Aerodynamics are not going to come into play at 55-75 mph.  Blocking off the front will cause the truck to overheat since that is where it is getting its air.

[Stewart G Griffin]

Obviously you can't block the grill off completely.   But, i feel that a huge grill is unnessesary for a 350;

My theory is that when chevy or whomever designed these trucks, they knew that they would be putting big blocks and diesels in there so they made the grill big to accomodate these engines.  But many other cars had small blocks, specifically 350's.  I think the best example is the camaro especially the 3rd and 4th generations.  They certainly had everybit of 350 cubes and no overheating issues even though their grill areas are rather small.  Actually, the best example is corvette. After like 84, the corvette really has no grill?

Another good example is all the S-10 conversions to v-8.  Their grill area is much smaller than a fullsize truck, yet no overheating issues.

So, i feel that, in many cases, especially with 6 cyln models, a huge grill area is unnessesary in 73-91 applications.

i'll probably start separate thread dealing with aerodynamics because we're sort of getting off topic a little.

P.S.  i was just at the chevy dealer and an older guy with a salesperson was looking at the very model i was talking about---the 53K crew cab.  So, i'm willing to bet that this truck will be sold within 3 months.  That's pretty sad or good depending how you look at it.