No towing power, any one have this problem?

[mtdave2]

I just bought a camper rated at 4000 pounds. I was having trouble maintaining 65. the slightest of hills slowed me way down. I had the pedal almost floored to keep it at 65 on flat road. To say the least im a bit pissed, I had put the vortech heads on in hope of solving my power problem. Perhaps im just wanting too much out of the truck

Perhaps ill play with the timing a bit, and maybe go back to my original carb..


Here is the tread on the engine build
http://67-72chevytrucks.com/vboard/s...d.php?t=304830


Btw, the gear vendor rocks when towing.

[dan42]

You might change your fuel filter too - just a thought.

[71tahoe]

Fouled plugs, timing, bad plug wires, vacuum leak, poor coil connection.

[mtdave2]

its the orginial bottom end of the motor, we took it apart to change gaskets and seals, everthing looked good so we left it.

the top end got the heads, intake, roller rockers, and the cam above.

now i have added the below.

new plugs, accel wires, high pro coil, cap, rotor...aka new ignition system,

no vacuum leaks,

took the valve covers off, no sign of flat lobe on cam.

rebuilt the th350, shift kit, th400 converter.

having my org qjet rebuilt..

this is really starting to piss me off, this truck should be burning the tires off.

[dan42]

Is the exhaust system appropriate for the engine setup you have? (i.e, too big, too small, etc.)

[mtdave2]

ya, it has dules with a xover pipe and magnaflow mufflers. good thought though..

[Old Chevy Mech]

If you are nearly floored at times, did you verify that your linkage is allowing full throw of the throttle? If it is, are the secondaries opening?

What rear end is in the truck?

[Boog]

Dave I quickly looked through your posts and it looks like you have the GM HEI on it updated with new coil, cap and wires. That's good stuff. What condition is the mechanical and vacumn advance in on that unit? If the mechanical advance is somewhat siezed up it will definately be sluggish and drink gas. Also the HEI has to have a 12 volt power supply if that hasn't been changed already. How clean are the spark plugs running?
Yeah you are right your setup ought to be running great with plenty of power.

[mtdave2]

mechanical advance is in good shape, i played with different springs, everything moves freely.

when i replaced the plugs, they all looked ok. nothing out of the normal.

compression was 165-175 , vacuum running at 16.

idle is nice and smooth, and it drives and shifts fine.. just no grunt

[pumpkin]

What cam are you using? Whats the outside temp? Whats the gears in the truck?

[mtdave2]

cam http://www.jegs.com/i/Comp+Cams/249/12-235-2/10002/-1

head
http://www.jegs.com/i/GM+Performance...58060/10002/-1

411 rear end

[mtdave2]

carb rebuilt.. nice to have the orginal one back on.

still no power..

guess it may be time to take everything back apart. perhaps i can find wtf we did wrong....

really have no idea what elese to do here.

[brothers69c-10]

You may have used a th400 converter, but that may not still be enough. I have the same problem with my truck. I have a stock th 400 torque converter in place which is it about 1200-1400 stall on my truck. Looking back through my engine components and the powerbands that they are for i need almost a 2500 stall converter to get the power out of my truck. I figured this out also by putting the tranny in 2 instead of drive and i couldn"t believe the power at the high rpms.

[69GMCLonghorn]

Dave, I'll almost guarantee that your timing is not dialed in for your cam. Everything is probably functioning correctly, but it's just advancing enough or at the right time. If you have a timing light that measures advance, you should be running right around 40° of total advance in that thing. I had the same problem with my rig. I didn't know how to re-arch the distributor so I had someone else dial it in. I ended up with so much low end power that the tranny bearing were grunting in pain!!

[mtdave2]

Originally Posted by 69GMCLonghorn

Dave, I'll almost guarantee that your timing is not dialed in for your cam. Everything is probably functioning correctly, but it's just advancing enough or at the right time. If you have a timing light that measures advance, you should be running right around 40° of total advance in that thing. I had the same problem with my rig. I didn't know how to re-arch the distributor so I had someone else dial it in. I ended up with so much low end power that the tranny bearing were grunting in pain!!

i was convenced of that too... with the light, im at 11 btc at idol. 2000 rpm it jumps to about 25-30 mechanical, with the vac adv its 35 or 40.

i

[El Jay]

What's your rear gear?

[69GMCLonghorn]

Originally Posted by mtdave2

i was convenced of that too... with the light, im at 11 btc at idol. 2000 rpm it jumps to about 25-30 mechanical, with the vac adv its 35 or 40.

i

Ok, so maybe you need to set the timing the "ghetto" way... Bump it up until it pings, then back it off about 2-3 degrees. You can probably get another 5° out of it before it pings.

[clinebarger]

Lugging 10,000 pounds around at 65MPH is asking alot from a small block

[1FAST68]

Originally Posted by mtdave2

i was convenced of that too... with the light, im at 11 btc at idol. 2000 rpm it jumps to about 25-30 mechanical, with the vac adv its 35 or 40.

i

When you said 25-30 degs at 2000 is that what the light is saying? You should have close too 36-40 without the vac adv plugged in.

Also is you timing tab correct with TDC?

[69GMCLonghorn]

Originally Posted by clinebarger

Lugging 10,000 pounds around at 65MPH is asking alot from a small block

It's not a light load, but in my other truck, I know my dad and I went over the scales at the dump at over 13,000 lbs... and that was with a 307, not even a 350.

[clinebarger]

Originally Posted by 69GMCLonghorn

It's not a light load, but in my other truck, I know my dad and I went over the scales at the dump at over 13,000 lbs... and that was with a 307, not even a 350.

I agree its possible, but with a camper being taller than the truck catching all that air its hard to maintain high speeds with im guessing 300-350 ft.lbs.

[68C15]

what is your RPM at 65? you mentioned a GV overdrive.

there's no replacement for displacement. you can achieve this 2 ways. build a bigger engine or wind up the 350 more.

[capev86]

camshaft....is it a low rpm/rv type grind or a high rpm only piece of junk better suited to a honda than a work truck? back in the mid 80's my dad replaced the 350 in his 72 burb with a 305 out of a 77 monte carlo. he put in a camaro oil pump and an rv grind cam. we hauled our 71 holiday travel trailer all over the place with that little engine....a 305 has the same stroke as a 350, just more efficiently sized pistons. the mechanic/friend that did the job reinstalled the stock q-jet and put in hei. that and a cheap dual exhaust and it ran great. had stock 3.73 gears in the back.

ignition......gm's love dialectic grease.....my dad's current 87 tbi burb has that problem every year or so....not running bad, just absolutely no power...period, so he has to take it apart and grease it up....knowing that ahead of time could have saved $500.

done carefully, occassional towing gets the most out of any engine.....the extra heat generated will burn out all the carbon deposits. the original 350 out of my dad's 72 burb was clean as a whistle when the mechanic took it apart to rebuild it for another project....because we used it to tow the trailer for a short while before the engine swap.

[PanelDeland]

On the timing issue.There may be another problem you haven't discovered.It's very possible that the original Harmonic Balancer is on the engine and the rings may have slipped giving you a false reading(on timing).Just another thought.

[68C15]

^^^^^
and a good one at that