Vortec heads- cold weather issues?

[77 K20]

So I installed a GM HT383 in August of 2014. I've been thru 2 winters with it so far and it runs like crap in cold weather. Pretty much anything below 37 degrees or so. It will start ok but then cough sputter and shake while at idle and at low speed. There is also hesitation right off of idle also. However once it is fully warm it runs great.

I've run 2 different quadrajet carburetors on it and am now running a Edelbrock TBI fuel injection unit on it. All of them behaved about the same when cold. The fuel injection is the best out of the 3, but still pretty lousy.

I used to think is something was wrong- but now I'm thinking that maybe it is just by design? I have read that for some reason votec heads do not have an exhaust crossover passage for the intake manifold to warm them. I'm thinking this is why my old 400 ran so much better when it was cold. Would you guys agree with that?

The 383 has a GM performance 12496820 manifold which is rumored to be made by Edelbrock.

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How much would another intake manifold help to make the engine run better when cold? Edelbrock makes one for vortec heads:

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Of course Edelbrock is going to recommend this manifold- as they said the GM manifold won't work well because it is a spread bore manifold and the TBI unit is a square bore. I'm currently running an Edelbrock aluminum carb adapter on it.

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Before I used the above adapter I ran the one below and it ran worse. I'm thinking because it pretty much made the dual plane intake manifold into a single plane.

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So just wanted to pick your guys's brains and see what you thought. Getting sick of spending money on it, and now that it is getting to be summer I won't worry much about it for 6 months or so.

Of course in hindsight I should have skipped the TBI unit and maybe bought a multiport setup for even more $$$ instead. But my dad's 1987 K5 Blazer with TBI on it ran great in winter. I stupidly thought the same would apply here.

 

[77 K20]

Or the other thing that has been bothering me- I keep reading how when GM made the vortec heads they changed how coolant flows thru the heads and intake. And some say you need a coolant bypass hose to allow warm coolant to open the thermostat and flow along the bottom of the intake manifold to warm it up. Others say just running a hose from the intake manifold to the heater core and then to the radiator is all it needs...

I bring this up because I have a VDO coolant temp gauge that reads the temperature of the head and the temperature goes up to 190 degrees then swings down to 170 degrees every 15 seconds while driving on the highway. The thermostat is 180 degrees (as per GM recommendation).

 

[crazy4offroad]

Interesting, if it were a design flaw with the heads the late 90s trucks would act like that too but they don't. Mine does take forever to warm up but never put much thought into that, since it's not a daily driver. I think you may be on the right track about the warm water bypass tube. I'm subbing to this thread to see what the answer turns out to be and if it is a bypass tube, I want to know how it routes. By the way those 2 intakes look identical, I wouldn't waste money on another.

EDIT: a short google search turned up this image for a bypass water tube for Vortec engines. I don't think my intake has that port, and I don't think my waterpump does either. So it might take some creative modification to route one in.

 

[77 K20]

Interesting, if it were a design flaw with the heads the late 90s trucks would act like that too but they don't. Mine does take forever to warm up but never put much thought into that, since it's not a daily driver. I think you may be on the right track about the warm water bypass tube. I'm subbing to this thread to see what the answer turns out to be and if it is a bypass tube, I want to know how it routes. By the way those 2 intakes look identical, I wouldn't waste money on another.

EDIT: a short google search turned up this image for a bypass water tube for Vortec engines. I don't think my intake has that port, and I don't think my waterpump does either. So it might take some creative modification to route one in.

I've spent the last 8 hours reading about vortec heads, intake manifolds and cold issues. From what I've read so far vortec heads on an older Chevy small block is a horrible idea if you live somewhere cold. The intake manifold stays cold for much longer time than the older intakes with a exhaust crossover in them. This was never an issue with the vortec engines that GM made as they used a CSFI fuel injection system (think multi-port) which sprayed the fuel right at each cylinder. Thus they didn't suffer from "wet manifold puddling syndrome".

Both of the manifolds I posted above would have the same issue- the manifold will stay cold and puddle fuel under the throttle body. Apparently GM/Edelbrock must have noticed this and then made a manifold that has externally plumbed hot water crossover passage. Some say this isn't as good as the exhaust passage as it takes longer to heat up, but it is better than nothing. Unfortunately this feature is only on the RPM series manifold. My engine is for low RPM torque...

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Apparently GM used to run coolant under the TBI unit also years ago to help keep fuel suspended in the airflow.

 

[crazy4offroad]

I read some on the site that pic came from and they concur the exhaust passage is the best way but the water passage is next-best-thing. From what I gather if you have a heater core hooked up that is the same thing as the bypass. It just takes longer for the coolant to heat up and make a difference. They also claimed the heads get crazy fluctuations in heat until the thermostat opens which is sometimes why they crack so easily. I'm wondering if a cooler thermostat would speed up when the engine straightens out. The thermostat just has a minimal opening temp, and the optimal operating temp is always going to be whatever is normal for the vehicle except in extreme sub-zero temps. An electric fan setup may help with that though. Short of going full MPFI it sounds like the Performer RPM may be the only "better" option which may still be similar to what you have now and minimal if any improvement. And I understand what you mean about its compatibility with a torque-leaning engine though, it just sounds like there's no perfect answer.

 

[crazy4offroad]

One thing that just hit me when I posted that would be the heat riser tube to the air filter can. It may be a funky thing to set up but I bet it would work. If you run headers though it may have to take something custom fabricated. The cold air being drawn into the intake would keep the intake ice-cold, possibly to the point of frosty cold. The heat riser tube would get "warmer" air into the mix quicker. Maybe have a valve hooked up on it you could control with a manual choke knob or something. Just an idea.

 

[bucket]

The stock truck Vortec motors did use a bypass hose from the water pump to the manifold.

 

[77 K20]

So for now I'm not too concerned about the 20 degree coolant temp wanderings... I'm going to order another 180* thermostat and drill a small hole in it this time. As far as a coolant bypass I'm running from the intake manifold to the heater core and back to the radiator. This will keep coolant running until the thermostat opens up.


My main concern is how do I get this engine to ever run decent when it is cold? I live 40 miles from Canada and this is my daily driver year round. Winter time can get very cold. The intake manifold I have now is plumbed to use an EGR on. Since there is no exhaust passages in the vortec heads for this GM tapped into the driver's side exhaust manifold and ran a metal line up to a port on the front driver's side of the intake manifold. Exhaust then runs thru the intake manifold to a block off plate right next to the spread bore carb mount on the passenger side.

Running exhaust thru the manifold would heat it up quick. Is there a way to run exhaust thru the manifold but not actually dump exhaust into the plenum? I circled the EGR ports in this picture:

So from what I understand is GM routed exhaust into the port circled in green. It then runs under the manifold over to the EGR valve itself (which I don't have- there is a block off plate there) which is circled in purple and red.

This is where I don't know how an EGR is plumbed. Does the exhaust enter the EGR valve at the purple circle and wait for the vacuum to be applied then it routes it back into the red circle and thru the intake where it comes out the blue circle? How could I manually control an EGR valve? Maybe have a switch on the dash and use it like a choke. Turn it on when it is cold, then shut it off later. Or is this a dumb idea?

Or screw the whole EGR thing and buy the RPM manifold (for another $250 bucks) with the hot water ports under the carb/throttle body area. This will probably provide more even heat for both banks of cylinders. I had read that someone thought in theory you could run exhaust thru the same passage. But how would you do that? Tap both exhaust manifolds and run a line on each side up to the intake manifold? But then there wouldn't really be flow right? It would be dead headed?

Ugh.

 

[bucket]

On my '69 and '70 Impalas, I have the aluminum intakes installed with gaskets that are using the little block off plates for the heat crossover. They both always ran fine in cold weather. The '69 was even my DD when I was younger. It has an old dual plane Holley Dominator on it. Can't remember what's on the '70, I think it's an Eddy Performer. I don't know how the coolant flows in either of them.

 

[77 K20]

I'm thinking there must be a difference in older style intake manifolds vs the vortec intake manifolds. I just called my dad who has a 1979 GMC K15 with aluminum heads and an old style (12 bolt) intake manifold. His runs great in winter with his heat crossover blocked.

The things you find out after the fact. Wish I would have done a LS 6.0 swap instead.

 

[foamypirate]

I'm thinking there must be a difference in older style intake manifolds vs the vortec intake manifolds. I just called my dad who has a 1979 GMC K15 with aluminum heads and an old style (12 bolt) intake manifold. His runs great in winter with his heat crossover blocked.

The things you find out after the fact. Wish I would have done a LS 6.0 swap instead.

The grass is always greener. I spent so much on my 6.0L swap that I had thoughts here and there along the lines of "shoulda just bought a built big block", haha.

 

[DoubleDingo]

You see that threaded hole on the left front of the GM intake? You actually circled it in green in another response. You need to have a bung hole welded into your driver's side exhaust and plumb a pipe to that hole to warm up the intake under the carb. I don't have a GM 383, but I did swap over vortec heads and used that same GM intake, and have the same cold running issues you mentioned. When warm it runs great, but stumbles and stalls until is gets warm in the winter months. I haven't added the exhaust tube to the hole mentioned, but I'm sure it would help heat the intake, since it was designed to do just that.

 

[77 K20]

You see that threaded hole on the left front of the GM intake? You actually circled it in green in another response. You need to have a bung hole welded into your driver's side exhaust and plumb a pipe to that hole to warm up the intake under the carb. I don't have a GM 383, but I did swap over vortec heads and used that same GM intake, and have the same cold running issues you mentioned. When warm it runs great, but stumbles and stalls until is gets warm in the winter months. I haven't added the exhaust tube to the hole mentioned, but I'm sure it would help heat the intake, since it was designed to do just that.

I wonder how much heat would transfer up as there wouldn't be flow since the other side of the manifold is blocked off with a plate. Or the trapped air that is in the line and manifold would just simply heat up? This would be the most simple and easy idea yet...

 

[DoubleDingo]

Shortly after installing the vortec heads on my truck, and running into this cold running issue similar to what you're encountering, I searched and found an EGR pipe that has insulation wrapped around it to keep the gasses hot up to the intake. I don't know if they're available anymore, and I can't even recall where I saw them, but I believe that will definitely help you get the intake warm under the carb even with the block-off plate on the other side of the intake. It's worth a try either way. The only other thing I could think of to help, would be to heat the block during the night so it's warm instead of cold upon first start of the day, but that doesn't help after work when the engine is cold again, unless you also plug in the block heater while at work, which most people can't do.

 

[77 K20]

Looks like the EGR tube is $112:

https://www.rockauto.com/en/moreinfo.php?pk=6309531&jsn=__GIX__3__