Re: 5.3 or 6.0 in my 1970?
 

I don't know guys. The trailblazer has the 6.0 and we get around 13-14 mpg. I think it would be a little better in a lighter (less than 6k lb) truck. It scoots the Trailblazer along pretty quick, I couldn't imagine the speed in a swb truck weighing in around 3800lb. I think i would spend the extra money on the 6.0 if you are really after power. If you are wanting mpg I would get the 5.3 just because it would be cheaper initial purchase and the gas would be cheaper also. Just my opinion though.
Shawn

Re: 5.3 or 6.0 in my 1970?
 

I'll chime in on the gas mileage thing just for reference. My last tank was about 60% highway at about 70-75mph. I got about 13.5 mpg. This is with the 6.0L, 38x15.50 tires, and 5.13 gears in a heavy ass Suburban. I gained about 2 mpg with the 5.13's vs 4.10's that I used to have. I would highly recomend the 6.0 over the 5.3, so much more potential for cheap.

Re: 5.3 or 6.0 in my 1970?
 

Did you switch to the 5.13s after the tires? In theory, lower the rear end ratio allows for better MPG, lower cruising speed. But of course, on larger tires and the stock ratio the engine could be killin MPG to spin the larger tires.

Re: 5.3 or 6.0 in my 1970?
 

For whatever it is worth…. my 5.3L Z71 Hoe averages around 18 MPG but it doesn’t see many miles. It pretty much only hauls my skinny butt and 30 lb suitcase and laptop bag back and forth from the COS airport so it only sees highway miles.

I am often amazed how much power the 5.3L doesn’t have in a Hoe with 3:73 gears. Living at 5,000 ft elevation doesn’t help much. It feels like it needs one more gear in the trans to make the powertrain work in symphony. First gear acceleration is decent, second gear okay but the 2-3 shift the 5.3L and 4L60E falls flat on it’s face. I swear there are toe nail marks in the floor mat just to keep up with traffic.

One of the most annoying things with this powertrian combo is when I encounter this particular large hill I often encounter when the cruise is set and the trans downshifts from 4th to 2nd gear and the RPM’s jump wayyy the hell up. The 5.3L sounds like the pistons are swapping holes at that point. The RPM jump always scares me to so find myself tapping the brake pedal to release cruise and relax the engine. I am not impressed with the power that my 5.3L delivers in a SUV anyway living at high altitude. Maybe in a lighter truck it would be adaquate.

I actually hate this damn Tahoe and want to off it for a Poncho G8 but my wife really likes it and it is 5 payments from being paid off so I guess we are stuck with it for a while. SUV’s aren’t worth 50 cents in resale right now anyway.

Re: 5.3 or 6.0 in my 1970?
 

liked mentioned, if you want more power go 6.0, but mileage is the same, i went from a 5.3 > 6.0 in my 2001 ext cab with 4.10 and still get 15city/19highway, also with a 3200 converter that flashes at 3900, guys let me tell yo this, these new GENIII motors are awesome but you wont believe how much better you can make them if you have them tuned better with like HP tuners or EFI live, if you have them tuned right you can get a whole lot of power out of these motors and more gas efficient....

just to give yall at idea, my truck with the 5.3 went 13.2@99mph and then i swapped to a 6.0 and went 12.43@106, my trucks raceweight is 4700lbs, so I cant imagine a setup like this on a 1000lb lighter truck? which the 5.3 would perform awesome aswell.. these both motors have aftermarket cam only, both are stock heads....... i am also almost getting ready to put a 5.3 in my 68', i found a 2006 5.3 complete longblock with accessories, and 4l60e for $1000, can let go of a deal like that,,,,

Re: 5.3 or 6.0 in my 1970?
 

exactly!! deals are out there. i got a 2004 5.3/4l60e complete for $800 had 20k on it. runs perfect!!

Re: 5.3 or 6.0 in my 1970?
 

THat is the kind of prices I am finding also. So that sounds about right. You figure with all the other things necessary, you could probably get away with getting one all buttoned up (fuel tank, motor mounts, tranny mount, driveshaft shortened, etc) and running for around 1500.00 if you do all the work yourself and can figure out the wiring yourself. You can barely get a rebuilt 350 long block from your local engine builder for that (not talking crate motors).
Shawn

Re: 5.3 or 6.0 in my 1970?
 

I used the in cab tank, made adapter plates, used stock motor mounts, stock trans mount, stock trans crossmember, etc.... haha

Re: 5.3 or 6.0 in my 1970?
 

Well there you go! Do you have any trouble with fuel starvation going around corners when the gas in the tank is low and sloshes away from the fuel pickup?

Re: 5.3 or 6.0 in my 1970?
 

Guys,
How much does a 1970 C10 Short weigh? I am going to go with a 6.0l with a 4l80e trans. I think i am just going to get a tune for it and install a cam in it. My wife has a yukon with the 6.0 and it moves! I am sure my little 70 is way lighter than that beast. There was someone on ebay that had pretty good deals on motor combos, but he does not have any 2WD applications. I will continue to look! I am bound to get a good deal on a 6.0 with todays gas prices. How aggressive of a cam can i install (good street manners) in a 6.0? Any suggestions on cams?
You guys ROCK!

Re: 5.3 or 6.0 in my 1970?
 

I have a 5.3/4l60 e in the garage and I am not too far away, interested?? PM me. What everyone is using as the measuring stick isn't necessarily realistic in that one the older truck is about 2k lbs lighter, you'll strip a bunch of emissions crap off of it, and the motor will be (should be anyways!) tuned to do away with the craptastic OE tune that is used to help GM avoid warrantee work, so low rev limiter, terrible shift point/perf, etc, etc. A 5.3 with a 6.0 cam and a tune plus stripping the crippling tune and a 5.3 ought to kick 300-350hp to the tires, right??

Re: 5.3 or 6.0 in my 1970?
 

Yes I switched the gears after the tires. The motor was just lugging too much with the 4.10's. Now I'm about 2400rpm at 70mph and the motor is hardley working, it's great.
As far as a cam, you can go as big as you want. "Good street manners" is a relative term. My truck now has a .551"/.551" 210/218 114lsa cam and it drives great. Little bit of a lope, but not much. Some people think it's too lopey. I'd actually like to go a little bigger. My last Trans am had a .595/.605, 234/240 114lsa cam and it was perfectley streetable too, in my opinion. It's all a matter of opinion. Your limiting factors are going to be valve springs ( stock are only good to about .500 lift ), and needing a higher stall converter if you go real big on the cam.

Re: 5.3 or 6.0 in my 1970?
 

Guesstimate at around 4000-4500lbs, give or take a few hundered lbs. I forget what they said last time I asked.

Re: 5.3 or 6.0 in my 1970?
 

dont usually let it get to low, been to just below a 1/4 and didnt have any probs.......

Re: 5.3 or 6.0 in my 1970?
 

Do you have 1 ton running gear? If I go over 70 mpg my mileage REALLY falls off, between 70-75 I only get a little over 11mpg.

Re: 5.3 or 6.0 in my 1970?
 

Hey boost not to get off topic but I would have thought that gear swap would have cost you mpg, by the way I'm getting about 13-15 overall with 33s 6.0, 4L80 and its hard to keep the foot out of it

Re: 5.3 or 6.0 in my 1970?
 

Yes and no on the 1 ton running gear. I have a 14 bolt rear and 3/4 ton Dana 44 front. One of these times I'll try being a little more patient and try to keep it under 75mph on the freeway. I'm sure my mileage will increase noticeably.
TyJ- Normally the gears would have hurt mileage but I was on the extreme end of wrong gearing. On the freeway the motor was only turning about 1800rpm. When you factor in the awesome aerodynamics of a lifted Suburban, light weight of 38x15.50 tire, and our high elevation it was a little much for the motor. Unless I got up over 70mph or about 2k rpm, there was just too much load on the motor for the converter to even lock up. So that's just wasted rpm. Now with the rpm's up higher where the motor was designed for, I barely have to crack the throttle open to maintain speed. Any time you can take load off a motor, it will use less fuel.
FWIW, when I forst did the motor swap, it was bone stock and I had 1/2 ton axles and 35x12.50 tires and only got about 10mpg average. The added power of the cam swap and especially new gearing helped my mileage considerably.

Re: 5.3 or 6.0 in my 1970?
 

Wow what a great thread! This was kinda what I was looking for when I started this one in the 99+http://67-72chevytrucks.com/vboard/s...d.php?t=304525 $1700. swaps? Hmm Maybe thats a cheaper route then me getting a new/used truck...nah!!!

Re: 5.3 or 6.0 in my 1970?
 

Where are you guys finding these motors so cheap the lowest I have found is $3500.For the 6.0 and trans

Re: 5.3 or 6.0 in my 1970?
 

bigger is always better!! here's my 6.0 waiting to go in my truck... i paid a little too much for mine, but i'm a compulsive buyer, i saw it and i bought it... but who cares; i got what i want.