New guy 73 suburban sbc need more torque

[BigBurb]

Hey all, new here just picked up a 1973 3/4ton suburban. It has a mystery sbc/th350, all I can see that has been done visually is an edelbrock air gap and a 1406 carb, and long tube. Sounds like if has a Lopey cam. I'm running 315 7516 toyo mts and it turns 3000rpm at 61mph.. The problem I'm having is it can't get out of its own way, sounds nasty don't get me wrong but it's timed and the carb and all has been adjusted with a vacuum gauge.. is this thing really heavy enough to slow it down that much? Please advise

[BigBurb]

Intake shot and size of rig

[rich weyand]

No.  It sounds like somebody cammed it for horsepower, which kills bottom end torque.  Very common for people to concentrate on horsepower when they actually need torque.

A 350 with a horsepower cam in a 5000+ pound truck will be a brick off the line.

Put a Comp Cams 12-231-2 (higher lift) or a 12-300-4 (stock lift) cam in it.  Change the lifters when you change the cam.  Probably ought to change out the old valve springs while you are at it, especially with the 12-231-2.  Use the Comp recommended springs.

That will give you 400+ foot pounds of torque to play with.

3000 rpm at 60 is way high.  Probably has some stupid-low gear ratio in it.

Note also that the air-gap manifold is great -- that's what I have -- it will keep the carb cool on hot days or when towing.  It will also keep the carb cold on cold days -- not so good.  You should be running the standard thermac air cleaner with an air-gap manifold.

Here's why, and how you do it with headers.  I have since got rid of the dryer duct because I found a stock replacement cold-air induction tube on the net.

http://www.fullsizechevy.com/forum/general-discussion/c10-forum/498719-induction-system-350cid-headers.html

[BigBurb]

It also runs about 2 15 deg according to the Stewart warner gauge.. just got a random thought could it be a flat cam?

[FlatBlack77]

that sounds a little hot to me

what did you set the timing at?

[LTZ C20]

Nice suburban. Listen to Rich, and do something about that throttle return spring, Rich can help there too. There was just a topic up about week or so ago about proper return spring setups.

[rich weyand]

It also runs about 2 15 deg according to the Stewart warner gauge.. just got a random thought could it be a flat cam?

That Edelbrock has a vacuum tube coming off the ported vacuum on the passenger side of the carb.  Any bet it's going to the vacuum advance?  That will make it run like crap and also make it run hot.  The vacuum advance should be off the manifold vacuum, the port on the driver's side of the front of the carb.  T it in somewhere.  There shouldn't be anything connected to ported vacuum.

[BigBurb]

New plugs and everything today.. checked the temp at each cylinder at the headers and I have two cylinders running cold, checked compression and it's low in those 2.. about 90lbs. Anyone in or around coos county have a sbc they wanna let go?

[BigBurb]

Wouldn't running manifold vacuum make it full advance at idle and then retard as throttle was applied?  That's the first thing it changed when I got the truck and it seemed to ping less at low rpm and run smoother.. am I backwards? Chevy have a retarded distributor?

[rich weyand]

A thinner mixture burns slower and needs more time, so yes, more advance the less throttle is applied.

Read the first three posts here: http://www.hotrodders.com/forum/distributor-tuning-theory-part-1-a-59033.html

[BigBurb]

A thinner mixture burns slower and needs more time, so yes, more advance the less throttle is applied.

Read the first three posts here: http://www.hotrodders.com/forum/distributor-tuning-theory-part-1-a-59033.html

Well I did according to what your link said, lost a smidgen on the acceleration but my mpg went from 8 to 11.7truck idles smoother and pings less.. guess all this time working with slogged motors made me think that is not the right way haha.. Also went thru and readjusted the valves trying to figure out why I had low compression in 2 cyls turns out I had some exhaust valves that were too tight on 2 cyls and 4 collapsed lifters. . Hard to hear with all the header leaks but she runs Soooo much better now between the 2 adjustments I made

[rich weyand]

Your temps should have come down too.

Also, what is your base timing (vacuum advance disconnected) set at?

[BigBurb]

10 deg base timing anything more she pings like crazy even on good gas.. Think it's time for me to rip the cam out and stick a good torque cam in there with some new lifters and start the tuning all over lol

[BigBurb]

Found out today its most likely the original engine... Probably explain why it is so tired feeling.. and Hauled about 1.5 cords of green alder in her between the inside and my trailer.. GUTLESS RIDE.. really need to get more gumption out of this old girl.. I do have a 99 suburban with a 5.7 vortec that blew the trans, and a 2001 with a 5.3.. thinking about a motor swap at this point

[rich weyand]

What plugs did you put in it?