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K5 Is Gutless

J

jacob_coulter

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My friend and I are working on a '78 k5 blazer, and it's in great shape, with a rebuilt 350, and the 10,000 pound GCW "Trailering Special" option. The problem is, the car is an absolute dog. The car has trouble getting to 60 mph, and exceeding that speed is nearly impossible. The tires are 33 x 12.50 15 LT. The car idles and starts great, it just doesn't have much grunt.. The engine has a stock GM dual plane manifold (No EGR) with a stock quadrajet with a dual exhaust, no Cats. According to the build plate, the car has 3.73 gears.

I wanted to do some light performance mods, and wanted to see what you guys thought of this:

Hooker k5 headers
Edelbrock performer RPM intake manifold
1" Carb Spacer
Advance curve kit

I also wanted to step up the stock quadrajet with some richer metering rods/jets. Should I go up, say 2 sizes? Is there a size you guys would recommend?

Any help would be greatly appreciated. I love this vehicle, but it's almost hard to drive in normal traffic. I'm not looking for a hot rod, just some decent power.

Thanks for your time,

Jacob
 
the ign. recurve kit might help. have you checked the timing or done a basic tuneup? if the timing isnt advancing properly you'll be losing quite a bit of power. i wouldnt go switching jets unless you know the fuel mixture is off.

make sure the accelerater pump and secondaries are functioning properly. i've had both of these problems before and makes a world of difference when they're fixed. Qjet's are kinda tricky, might be a good idea to let a pro take a look at it.

new manifold would help some too, but i'd get a regular performer manifold, not the RPM. you want torque, not high rpm horsepower. you should be able to make decent power(torque) with the stock manifolds, but headers woundnt hurt.
 
jacob_coulter said:
My friend and I are working on a '78 k5 blazer, and it's in great shape, with a rebuilt 350, and the 10,000 pound GCW "Trailering Special" option. The problem is, the car is an absolute dog. The car has trouble getting to 60 mph, and exceeding that speed is nearly impossible. The tires are 33 x 12.50 15 LT. The car idles and starts great, it just doesn't have much grunt.. The engine has a stock GM dual plane manifold (No EGR) with a stock quadrajet with a dual exhaust, no Cats. According to the build plate, the car has 3.73 gears.

I wanted to do some light performance mods, and wanted to see what you guys thought of this:

Hooker k5 headers
Edelbrock performer RPM intake manifold
1" Carb Spacer
Advance curve kit

I also wanted to step up the stock quadrajet with some richer metering rods/jets. Should I go up, say 2 sizes? Is there a size you guys would recommend?

Any help would be greatly appreciated. I love this vehicle, but it's almost hard to drive in normal traffic. I'm not looking for a hot rod, just some decent power.

Thanks for your time,

Jacob
Click to expand...

From my experience, the 1" spacer won't do anything for you, and the RPM series intakes are for higher-rpm (4500rpms+) performance. The intake is a good idea but look for something milder than the RPM series - like the regular Performer. headers are a good idea too.

How's the condition of the ignition system? Maybe do a tuneup?
 
Like MTMike said, don't mess with the carb spacer. It just changes the power band characteristics, doesn't add power.

You need to do the metering rod changes in stages, not one big jump.

If you after acceleration off the line, get a higher stall converter.

Is the tranny kicking down properly?

Before spending a lot of money, you may want to do a compressoin test or have one done if you don't have the tools. Maybe you need a rebuild.
 
"Gutless" is a relative term. :) If you can't get up to 60, then yes, you likely have a real (or multiple) problems.

If it is truly lacking power it should have, then look towards things like the ignition system, rear axle, exhaust, etc.

A truck that old cannot be relied upon to currently have the axle ratio that it was built with.

A stock truck has no problem running up to 60MPH, need to figure out what is wrong with yours instead of putting $$ into things that WILL help to free up some power, but won't do anything to solve the existing problem.
 
Im with everyone else on this one. The 350 in your blazer should turn those tires with no problem. Something else is the problem here. First, put a timing light on it and check the timing. Then check the cap, rotor, plugs, wires, etc. Then check the fuel filter, fuel pump, and carb to make sure they are all in correct working order. Then check the compression. Then check the gear ratio in the rearend. Like someone said before, in a truck that is that old, you can never tell what gears are in it until you check. Are you sure its a 350? The 350 shares the same block with the 305 and its sometimes hard to tell the difference. Im asking because I know for a fact that even a stock 350 can have plenty enough power. My brother has a 79, and when he first got it, the engine was worn out, it had 35's, and 3.08 gears and the truck had no problem moving to 60. I have an 87 with 37's and 4.56 gears, and it has plenty of power. Something is definitely wrong with your blazer. I suggest checking everything that you can possibly think of to find out what it is. Buying headers, an intake, and putting some new heads on are great ways to give you more power. But you need to get it producing its power at 100% before you try to cover it up with these mods. Just my $.02.
-Harrison
 
blocked exhaust??

Checked the cataliytic converter to see if its clogged??--some Y pipes have been known to collapse internally where they are double walled,choking the exhaust flow...this is a big cause of power loss,along with all the usual tune up and carb possibilities..you need to have plenty of air going IN too--hows the air filter?? :crazy:
 
Sounds like something is amiss in the motor. Even with a fouled cylinder, I was still able to get moving and moving along pretty good. Gas mileage sucked and had the wonderful aroma of fuel when I stopped, ride spitted and sputtered but once she was above 70 or so, it smoothed out. If you are relying on the speedo, make sure it is not wrong as you have bigger tires and it will cause the error if it isnt compensated for.
 
There is something wrong for sure! my dads 70 blazer with a stock 307 would pull his beast around without any problems. Your 350 should pull your blazer around just fine. First off is it bogging, missing or just no power? have you checked the plugs to see if they are rich or lean? since you have dual exhaust you might need to rejet, might be a little lean now. Is the distributor the original one, whats it from? A revurve would probably help. Have you replaced the fuel filter, checked to make sure no fuel line are bent? Clean air filter? How about the exhaust is the muffler(s) plugged, any of the pipes kinked?
I would find out why it has no power befor I spend any money on performance parts! When you do get to modifications, I would start with headers, and rejet. The stock manifold should be fine till you get to 250hp or start messing with cams the stock intake should have more torque below 2500rpm than the aftermarket intakes. After this I would run the performer RPM Q-jet (I have found the rpm is just as strong as the performer in lower rpms and pull harder in upper rpms) I have not tried the brand new performer but looks like it might be a good choice. When changing the intake this would be a good time for a cam swap also.
Good luck
Shawn
 
Cliffy472 said:
Or you could just buy my cadillac engine tranny and transfer case and call it DONE!

472ci
Bored 30 over
Shaft style rocker set-up
Aluminum intake
Performance cam (specs unknown)
Heads milled slightly (specs unknown)
Oversize, stainless steel, swirl polised valves
Port matched intake to heads; and heads to (the exhaust it had on it)
Double valve springs
Compression is estimated at 9.5:1

Estiamted 500hp and 500ft lbs!

Has approximately 500 miles on it.
Runs on pump gas, prefers mid or high octane. I usually ran the low
85-87 (depending on which station I stop at).

Includes everything from the carb to the starter. The alternator,
power steering pump, fuel pump, dist, wires etc..etc...

The only thing NOT INCLUDED is exhaust. All I have is two driver side
manifolds which is what I used for my application. This motor is DYING
for some headers and professional exhaust.

Asking $2,000 firm.

Regrettably I don't have any pictures of it. But since
it was in a 4x4 it's not super nice. It's just a motor from the outside;
all the good stuff is inside!!

H-303-659-9991
C-303-946-2562
Ask for JD,

I'm located in Brighton, CO. That's 80601. I cannot ship/deliver it;
pick-up only
Click to expand...

nice spam..... :(
 
my truck lacked power ,and it was the muffler pushing against the e-brake cable so check everything
 
i have a 86 that once had a weak 305 and 33's with 3.42 in the rear and it will still go over 90, granted it took 5 miles to get there, it ould still go. check the timing, plugs, and plug wires first off. IF you have a fried wire that is misfiring its hard to tell at idle on a stock motor, but it will kill performance. I had it happen to me once and after I took it to a mechanic i felt like a retard for not checking the them myself.
 
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