vortec heads on 350

[77 K20]

Thanks for the great post Mike.
Again another advantage of propane btw. This gas never drops out of suspension and thus you can use a tunnel ram on the street with no problems, just saying.
Back to the Great Vortec heads, instant 40 hp.... probably best to go with aftermarket at the end of the day, and gain 50 hp.

Yes, the power out of them is very nice. I just wanted him to be aware of the cold weather issue. I did a ton or research and never heard about that- seems everyone that did it was from Arizona, Florida, Texas, southern California.

If you have an engine block heater that does help a lot. And once it warms up it does run great...

I spent probably a year being confused on what was happening before I figured it out.

 

[rpcraft]

Keep in mind the one disadvantage no one ever talks about with vortec heads... COLD WEATHER!!!

Vortec heads and the intake manifold got rid of the exhaust heat crossover tube that is below the carb. This was removed as vortecs moved the fuel injectors to closer to the valves. They wanted to make the intake as cold as possible for more power with denser air coming into the engine.

Now if you live in a cold climate and run a carb fuel likes to drop out of suspension when it suddenly changes direction. What you end up with is puddling of fuel right under your carb. GM makes a intake manifold for vortec heads and a carb but there is not "waffle pattern" under the carb. A waffle pattern or ridges along the plenum there help get fuel airborn again. Fuel can rise up to the top of a ridge and then lets go and flies on down to a cylinder. Kinda helps a bit.

At temps of about 40 degrees or below I noticed that I had a miss and the engine couldn't run quite right. It can take a long time to heat soak the intake enough for it to start running right (I have a 10 minute drive on the highway doing 65 and at the first stop light it would still run like crap).

I bought an edelbrock intake manifold that has a externally plumbed heat passage in it. It runs coolant thru it. Still runs like crap when cold, but will warm up much faster. BUT: when I installed my first manifold I went thru a lot of coolant. Every time the engine heated and cooled it would drink coolant. I found small PUDDLES of coolant inside the plenum. Edelbrock refused to believe me even with pictures. I replaced with a SECOND intake manifold and the SAME thing happened. I was so pissed at that point I added a tube of alumniseal and dropped my radiator cap from something like a 14 psi one to a 7 psi cap. Haven't used a drop of coolant since. Perhaps it would be possible to pipe exhaust thru that plenum instead...

And lastly, they say vortec heads need an external coolant bypass otherwise you get hot spots and boiling. With the GM manifold I didn't do the bypass and could watch my coolant gauge go from 180 to 215 and back to 180 every 20 seconds or so on the highway. Replacing the thermostat did nothing. Plumbing up the heat passage worked as a coolant bypass and then evened the temperature right out.

Maybe you could just get some motorcycle heater grip strips or somethign similar and attach them to the bottom of the intake for heating when it is cold outside?

 

[77 K20]

Maybe you could just get some motorcycle heater grip strips or somethign similar and attach them to the bottom of the intake for heating when it is cold outside?

I thought about trying to fill up that plenum in my manifold with coolant and use a TDI glowplug threaded into one side to heat it... or some electric heater type thing. (VW TDI engines did use glowplugs for coolant also)

Never came up with anything.

 

[Rusty Nail]

Lol

 

[1983ChevyK30]

oh, i never knew that about the vortec heads acting like that in the cold, okay its settled. shes getting a big block. what size head gasket do the 454s come with? i could just put a thinner head gasket in to help bump up compression. how to the big blocks do for gas mileage? i know its bad but how bad? and the reason i ask about the clutch swapping over is because i just replaced the clutch thats currently in it like 3 months ago, and what is the compression ratio of a stock 454 truck motor with 781 heads? im not 100% on the year but i can get the code off of the back of the engine if needed to determine comp. ratio.

 

[SquareRoot]

[QUOTE="1983ChevyK30, how to the big blocks do for gas mileage? i know its bad but how bad?[/QUOTE]

Make you want to buy a Prius kinda bad. Lol

 

[idahovette]

[QUOTE="1983ChevyK30, how to the big blocks do for gas mileage? i know its bad but how bad?

Make you want to buy a Prius kinda bad. Lol[/QUOTE]
NO FRICKIN WAY!!!

 

[1983ChevyK30]

How much would a thinner head gasket affect my compression ratio with stock pistons?

 

[DirtyDYT]

how to the big blocks do for gas mileage? i know its bad but how bad?

9 mpg city or highway with a carbed 454, SM465, and 4.10 axles. ‘85 K30 cab and chassis with a 12’ flatbed.

what is the compression ratio of a stock 454 truck motor with 781 heads? im not 100% on the year but i can get the code off of the back of the engine if needed to determine comp. ratio.

The engine is a Gen IV and that’s what matters for finding parts. I can’t recall the exact compression ratio by year but I’m pretty sure it’s around 8:1.

How much would a thinner head gasket affect my compression ratio with stock pistons?

You can go from stock .039” gaskets down to .020” but I’m not sure what sort of gains you might see. Someone else will probably chime in with that info.

Edit: Here’s a CR calculator for you.
https://www.campbellenterprises.com/Race math calculators.htm

 

[rpcraft]

NO body gets a big block and is concerned about gas mileage... You think you had bad mpg's before just wait, lol...

 

[SquareRoot]

NO body gets a big block and is concerned about gas mileage... You think you had bad mpg's before just wait, lol...

Exactly. If you have to ask, you can't afford it.

 

[Rusty Nail]

Exactly. If you have to ask, you can't afford it.

This.

 

[4WDKC]

[QUOTE="1983ChevyK30, how to the big blocks do for gas mileage? i know its bad but how bad?[/QUOTE]

it depends on the build o f the engine a stock 190 smogger 454 is bad on gas, a huge cam high rpm is going to be bad on gas also. something to consider also is that my stock 350tbi/700r4 truck only gets 10-12, is 454 mileage really that much worse?

 

[Paladin]

Don't worry about the gas mileage, shoot the moon! Walk on the wild side and all that! It's only money going down that intake and your kids won't appreciate it anyway when your gone.

 

[Shorty81]

My 454 block is dated 77. It has been bored .060 and stroked to a 496 using a Slip White rotating assy. Compression is 10.6:1. Running 781 heads. It runs great with 93 octane.