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Discussion Starter · #1 ·
Heres the problem I have ;
I'll admit Im at the point to where i dont know what i want :confused:
my vehicle;
1978 c20 2wd 3/4 w/ 355,th400 3.73
my engines;
.060 over 400sbc in pieces all machine work done
newly aquired 454 rebuilt (stock) 781 heads minus carb (5000 MILES)
roller 350 needs rebuild
olds 403 stock
the small block i have in is cursed cant keep it timed or tuned and i get like 8 mpg even though i have like 25-30000 miles on it and still no real power
freshly aquired 062 vortecs with 2.02 valves (they may be 2.05)
with perf rpm intake, scorpion roller rockers 1.5, and pushrods
do i;
put the vortecs on the 355 i have now for more power?
put together the 412 for the torque? WITH THE VORTECS (i need torque for the hauling/towing)
put the 454 in but the mileage wont improve
sell all and have the roller 350 rebuilt for the efficiency/mileage gain?
put the 403 olds for the different "wow factor" i know the other engines wont get much better mileage but if i have the power thats ok yesterday i put $20 in gas drove 45-50 miles and am on E again and the engine is a dog it has 600 elec edel carb,edel perf intake and performer cam .204, .214. .420. 420 lift with stock 76cc heads and manifols i just got a rebuilt 400 trans and put in a summit 1700-2100 stall convertor HELP WHAT TO DO?????? HELP FELLAS :confused:
 

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I would not build an engine to chase milage if you're trying to save money, you'll never be able to save money. If you need an engine using an SBC would be the eastiest/cheapest approach. A .060" over 400 is NOT a good canidate for a towing rig IMO, the cyl. walls are too thin. A 350 or 383 with no more than .030" over would be more durable and not give up too much in the tq department. Run the 400 crank and rods in a std. bore 350 with 350 pistons for a cheap stroker combo. Vortec heads and a small roller cam would help as well, so would 1.6 rockers (cam lift is usally real low with rv cams and 1.6 rockers can help take advantage of your heads porting). You want to get your tq peak as close to 3,000 RPM as possible, which is actaully quite low compared to most 350 builds.
 

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I'd second the recommendation from ap72, and use the roller 350 block and vortec heads. If you want to spend a little more, make it a stroker 383 with the same heads. If you pick a moderate lift roller cam, you should be able to make good power without killing gas mileage.

Bruce
 

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a heavier truck is heavier for a reason, and this isn't a race car, sounds like a hopped up farm truck. I agree that Gen III/IV stuff is great, but by the time you're all set and done its not as cheap. Why stop at a 5.3 though? I'd atleast go to a 6.0L, they're getting pretty common.

A well built 383 with a 400 rod will be pretty cheap to build and give him enough tq, next step from there would really have to be a diesel or a nice big block- but that can't be done for less than $1500, a 383 can go well below that if you plan it right.
 

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Discussion Starter · #6 ·
THANKS BROTHERS my thoughts were all pretty similar (no towing with a .060 over 400) to throwing the crank and rods into my 350 now to just having the roller rebuilt to the 4.8-6.0 lq4 engines
as to selling the c20 it has sentimental value and is/was a farm truck my father used it to haul produce to market and i use it to deliver wood pellets now.
sorry back up my father put a diamond plate flat bed on it back in the late eighties so yea it prolly does weigh 6000 (8 feet long by 7 ft wide.)or so 1/4 mile times were never intended but a litter more snort would be nice as it sits now i can hardly pull the grades with 2500 lbs in the box or towing 3000 lbs OH YEA I will get it alligned and rotated/balanced that wont hurt
So sell the 454?
truck is very solid and pretty decent shape I am restoring it while i work with it
 

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All that is OK. Just don't expect good mpg with that truck.

bad mpg can be justified with no truck payment and lower insurance rates for a paid off truck (liability only). Do the math, it will make you feel better. Saving 500/month for a new truck and 75 for insurance buys lots of gas

A really heavy truck needs a big engine and gears. A 454 will also get 8 mpg but will at least move the truck. My 454 gets 8 to 9 in town and 12 to 15 on the highway (depending how fast I drive). But my LWB truck has a 3.08 gear, th400 trans, and weighs 4400 pounds (full tank, spare, adding sound proofing, and me in the truck). Runs high 14's at 96 mph

if you do a lot of highway driving then maybe a gear vender OD setup would come in handy. with an OD, you can go to a 4.11 gear for extra power around town.
 

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Discussion Starter · #8 ·
one of my buddies down the road has a tremec and a quick change rear end i can buy but that lotsa work too so i guess i shoulda started a poll as to what engine just have the roller block rebuilt with those vortecs thrown on and a comp rv cam?
 

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first try getting your current engine to run right.

tell me about your ignition timing.
initial timing?
total mechanical advance?
how much from the vacuum advance?

how do the plugs look?

what is the cranking pressure on all the cylinders?
 

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boyd1on said:
one of my buddies down the road has a tremec and a quick change rear end i can buy but that lotsa work too so i guess i shoulda started a poll as to what engine just have the roller block rebuilt with those vortecs thrown on and a comp rv cam?
Tremec and the quickchange aren't even close to being strong enough for use in this truck. The tremec would work in a hot rod 1/2 ton, but the quickchange is too weak even for that. QC's are made for light 2400 lbs or less race cars, not 6000 lbs tanks.
 

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Discussion Starter · #11 ·
Thnx 454c10 um the timing is difficult to figure cause i dont have a timing tab on it anymore(dunno why cant remember) and I am gonna do a compression test some this week hopefully tomorrow (wednesday the 16th) so we'll see where that sits then ill check the plugs while im at it but as far as the timing and tuning i go by hear and the gas peddle and just adjust the screws on the carb till she sounds right and doesnt smell rich any suggestions?
this is why im such an olds guy every one ive ever had just ran so strong it blew my mind and got good mileage to boot oh and ericnova72 i was kidding about the tremec and quick change it woulda been nice but naaah
 

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you really need a timing tab. what is the diameter of the balancer?

http://www.summitracing.com/parts/PRO-66109/

ignition timing can really effect mpg and power.

should also check for true TDC with a piston stop. Pull all the plugs, screw in the piston stop into #1 spark plug. Turn the engine over by hand slowly and gently until the piston hits the stop. mark the balancer at that point, then turn the engine the opposite direction until it hits the stop again. Mark the balancer again. The 1/2 way point between the 2 marks is true tdc.

A low compression mild cam 350 with smogger heads needs about 12-15 degrees initial timing and 37 to 40 total from the mechanical. Then the vacuum advance should add another 12 to 15. So driving down the highway, timing should be around 50 degrees.

I also recommend plugging the vacuum advance into a manifold source. this will make the engine idle in the 25 to 30 degree range. You should also get an adjustable vacuum advance canister for the hei. crane makes one and is also sold at summit racing.

Then, you need to start to tune that carb.

incorrect timing and a bad carb tune can easily drop a 12 mpg truck down to 8 mpg and lose power at the same time.

You could also be having cam issues. cams can go flat and kill power and mpg. If everything else checks out, then look at the cam. pull the valve covers. start the engine, and look of any rockers that aren't moving as much and the others.

what carb is on the truck now?
 

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Discussion Starter · #13 ·
edelbrock 1406 wich is a 600 cfm electric choke sitting on an edelbrock performer intake should i put the marks on the same side of the balancer? ive never heard of that measure before ill admit timing has always been a weakness of mine and i know its about the most important too
even though you described it to me im still not getting it on how to tell the degrees :confused:
 

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Discussion Starter · #15 ·
WOW Thank you SSEDAN64 thats really teamwork i love the brotherhood here I am cutting some wood today(weather starting to get nasty here in Wisconsin) then I will read all the info tonight then apply the new knowledge tomorrow,once again thank you :D
 
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