86 GMC K1500 Crate 350-Adding HP without Removing Engine

[poboy73]

I purchased this truck after a recent restoration and love the truck, however the new crate 350 they installed lacks the HP that I would like to see. It is a show truck and daily driver in the summer so doesn't have to win at the track but I would like it to have more pep than a Cavalier. With that I am not trying to get 400HP for under $500, but wanting to keep the current engine and just maximize it's potential without going overboard where a new engine would make more sense. It only has 1000 miles on it right now.

Adders to the base crate engine that I can see are the Edelbrock Performer (0-5500 RPM) and has a Q-Jet 795CFM carb. The rest of the engine specs are below:

The 12681429 engine remains our most popular crate engine of all time! This is a great entry level replacement engine for older cars and trucks, and a great basic street rod engine. All of the parts in this engine, including the block, are Brand New!
Specifications:
Power: 250 HP @4300 RPM, 350 ft. lbs. of torque @ 3600 RPM
Displacement: 350 CID, 5.7L
Bore x Stroke: 4.00” x 3.48”
Compression Ratio: 8.5:1
Recommended Fuel: 87 Octane
Block: Cast Iron, 2 piece rear seal, 4-bolt main caps.
Crankshaft: Nodular Iron
Connecting Rods: Powdered Metal Steel
Pistons: Cast Aluminum
Camshaft: Hydraulic Flat Tappet
Cam Lift: .383” Intake / .401” exhaust
Cam Duration @ .050”: 194 deg. Intake / 202 deg. Exhaust
Lobe Separation: 112 Degree
Cylinder Heads: Cast Iron, 3/8” pressed in rocker studs.
Combustion Chamber: 76cc
Valves: .194” Intake/ 1.50” Exhaust
Rocker Arms: Stamped Steel, 1.5:1 Ratio
Valve Springs:3911068
Balance: Internal
Maximum GM Recommended RPM: 5100
Ignition Timing: Base 10 degrees BTDC, 32 degrees total
Cylinder Head Notes: 7 Bolt style Exhaust Flange Standard, 85' and prior intake manifold bolt pattern. Perimeter bolt style Valve Covers. This head is very similar to the old #882 castings from the 1970's.

I am new at the engine stuff so I am looking for ideas that can be done without pulling the engine out for now. The previous owner had the following ideas but when I checked with Summit they weren't necessarily in agreement. Looking for others inputs.

Headers 137Y
http://www.stans-headers.com/gm_headers.htm
with dual 2.5 exhaust. Currently has manifolds with 3" single exhaust.

Camshaft
https://www.summitracing.com/parts/cca-cl12-268-4/overview/make/chevrolet

Heads
Not sure on this but have read vortec or Edelbrock Performer heads are good options
http://www.edelbrock.com/automotive/mc/cylinder-heads/chevy/performer-sb.shtml

I am sure I am missing things as I have never done this before but I would like a positive experience and be able to work on this in the shop with my son. Not sure if a top end kit/total power package makes mores sense given my experience but open for suggestions.

Thanks

 

[crazy4offroad]

I wouldn't go with stock Vortec heads, your cam lift would be pretty limited. Summit has good reviews on their branded Vortecs and can handle up to .520" lift. With the combination of heads, cam, headers, intake, carb and a nice air filter you'll be surprised how much power you can get out of one.

 

[echo7bravo]

Before investing anything.....Have you dialed in your timing and gotten your carb adjusted to it's fullest potential? I've seen numerous engines weaker than puppy piss simply because the timing was off a hair or the carb wasn't leaned out enough.

 

[poboy73]

I had the carb and timing adjusted last summer in the local shop. I recall the carb needed some adjustment and it did run better after the changes. I haven't brought it to a performance shop and have them do anything on the dyno or anything like that.

 

[4WDKC]

I wouldn't go with stock Vortec heads, your cam lift would be pretty limited. Summit has good reviews on their branded Vortecs and can handle up to .520" lift. With the combination of heads, cam, headers, intake, carb and a nice air filter you'll be surprised how much power you can get out of one.

Stock vortecs are rumored to handle up to .550 lift with the correct spring, I had mine set up for .520 no machining. New ones are better route to go you wont have to waste time pulling and having them checked for cracks, they come ready for .450 lift (IIRC) and have screw in studs already. Switching to vortecs would up your compression to around 9.5 probably requiring 91+ octane.

Also your cam isnt very big dont expect alot of power from it, the specs are similar to the vortec 350 and they had their timing retard 4 or 6 degrees and were rated at 255 HP 330 tq.

 

[poboy73]

Thanks for the replies, so is the comp cam I am considering a good choice or would you recommend something else?

 

[Jrgunn5150]

What's your gear ratio and tire size?

 

[poboy73]

305/70R17 Ridge Grappler
4:10

 

[henrym]

I purchased this truck after a recent restoration and love the truck, however the new crate 350 they installed lacks the HP that I would like to see. It is a show truck and daily driver in the summer so doesn't have to win at the track but I would like it to have more pep than a Cavalier. With that I am not trying to get 400HP for under $500, but wanting to keep the current engine and just maximize it's potential without going overboard where a new engine would make more sense. It only has 1000 miles on it right now.

Adders to the base crate engine that I can see are the Edelbrock Performer (0-5500 RPM) and has a Q-Jet 795CFM carb. The rest of the engine specs are below:

The 12681429 engine remains our most popular crate engine of all time! This is a great entry level replacement engine for older cars and trucks, and a great basic street rod engine. All of the parts in this engine, including the block, are Brand New!
Specifications:
Power: 250 HP @4300 RPM, 350 ft. lbs. of torque @ 3600 RPM
Displacement: 350 CID, 5.7L
Bore x Stroke: 4.00” x 3.48”
Compression Ratio: 8.5:1
Recommended Fuel: 87 Octane
Block: Cast Iron, 2 piece rear seal, 4-bolt main caps.
Crankshaft: Nodular Iron
Connecting Rods: Powdered Metal Steel
Pistons: Cast Aluminum
Camshaft: Hydraulic Flat Tappet
Cam Lift: .383” Intake / .401” exhaust
Cam Duration @ .050”: 194 deg. Intake / 202 deg. Exhaust
Lobe Separation: 112 Degree
Cylinder Heads: Cast Iron, 3/8” pressed in rocker studs.
Combustion Chamber: 76cc
Valves: .194” Intake/ 1.50” Exhaust
Rocker Arms: Stamped Steel, 1.5:1 Ratio
Valve Springs:3911068
Balance: Internal
Maximum GM Recommended RPM: 5100
Ignition Timing: Base 10 degrees BTDC, 32 degrees total
Cylinder Head Notes: 7 Bolt style Exhaust Flange Standard, 85' and prior intake manifold bolt pattern. Perimeter bolt style Valve Covers. This head is very similar to the old #882 castings from the 1970's.

I am new at the engine stuff so I am looking for ideas that can be done without pulling the engine out for now. The previous owner had the following ideas but when I checked with Summit they weren't necessarily in agreement. Looking for others inputs.

Headers 137Y
http://www.stans-headers.com/gm_headers.htm
with dual 2.5 exhaust. Currently has manifolds with 3" single exhaust.

Camshaft
https://www.summitracing.com/parts/cca-cl12-268-4/overview/make/chevrolet

Heads
Not sure on this but have read vortec or Edelbrock Performer heads are good options
http://www.edelbrock.com/automotive/mc/cylinder-heads/chevy/performer-sb.shtml

I am sure I am missing things as I have never done this before but I would like a positive experience and be able to work on this in the shop with my son. Not sure if a top end kit/total power package makes mores sense given my experience but open for suggestions.

Thanks

You don't need a carb bigger than 600 cfm for an engine with that small an output, 600 cfm will probably be good up to 400 hp

 

[Jrgunn5150]

305/70R17 Ridge Grappler
4:10

Well that's reasonable.

The cam you are looking at is reasonable, part of the issue is the 8.5:1 compression ratio of your engine. It's good to run 87 octane, but not so good for snappiness.

A swap to Vortec heads would bump it by a full point to 9.5:1 or so, give or take some variables, but would require a new intake as well.

A 200 dollar set of springs and retainers on Vortec heads will let you run up to a .550 lift cam with no machine work.

You can probably pick up 75-80 hp with the whole shebang.

FYI, the 250 crate engine you have, and the 290 hp I have used, are the same except for the camshaft. So you can pick up 40 hp with just a cam.

How far you want to take it only really depends on how much money you want to spend. Personally, I'd swap cams and leave it be.

 

[poboy73]

I am confused trying to understand the cam specs. Is the comp cam listed above ok to use with the stock heads on this engine or is there a different one you would recommend if I don't replace the heads


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[Honky Kong jr]

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[poboy73]

Love that movie

 

[shiftpro]

The low compression is the limiting factor. A bigger cam will have less effect on low compression than something with say 9.5 to 1.
More research required... about the heads? Do you have a good machinist (engine builder) close by? Before swapping heads I would
consider modding your current heads. Put in a larger exhaust valve and open the bowls. Shave as much off to raise compression.
Again, you need a competent machinist to determine how much can be milled off the heads. Not all heads can tolerate getting shaved.
Casting is too thin. For example I think Vortec heads are to flimsy to mill down enough to make much difference.

Just build another engine, and your currnet engine can serve as a backup or for another project. Stroke a 350 or *** it go BB! You said you want more power...

 

[shiftpro]

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One for the car and one for the party?