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Thread: WTB: GMPP TBI / Vortec Intake Manifold

  1. #16
    Fuel Injected! devind's Avatar
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    Quote Originally Posted by dave w View Post
    The link to the 1227747 ECM to 16197427 PCM http://www.gearhead-efi.com/Fuel-Inj...out-Directions!

    The simple easy way is to use a Plug-n-Play adapter. See pic below. R.I.P to the 1227747 that donated it's connector.

    dave w
    Thanks Dave,
    Apparently in your opinion this is a worth while up grade!

    I have seen on here how many more tables you have the ability to tune with this PCM. It makes since that it would be a better engine control not sure I even have a good handle on the 7747 yet. But there again I never thought I would even close to where I am now with the 7747 so maybe I can learn the 7427 too.

    What was the 7427 PCM originally used in?

  2. #17
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    I donít know exactly what the deal is but is has something to do with the water flows through the Vortec heads.
    The deal is this: In the old coolant path water could circulate from the forward portion of the RH head, through a passage in the head gasket, into the block, and out through a 5/16" hole into the coolant pump. Inside the pump this coolant was routed to the inlet side, and the pump would circulate the coolant back through the block. This helped ensure some warm coolant reached the thermostat so the 'stat would open.

    As the need for cleaner emissions increased, faster warmup times and better vaporization of fuel became more important along with reducing variation int intake air temperature. Later carburetor and TBI intakes routed coolant from the front of the intake, under the throttle body or carb, and back to the heater hose fitting. Coolant would circulate through the core and return to the pump or on some HD trucks, to the radiator. This routing also provided a faster and more accurate heat signal to the thermostat so it would open properly. Coolant always flowed through the heater circuit and if a restrictor wasn't in place, it could cause overheating as radiator performance began to decrease. In my experience the restrictor is always found at the manifold side (outlet). Although the bypass circuit is still present in the heads, some of the TBI truck blocks do not have the 5/16" hole in the RH side of the block for the bypass circuit. Its been a "gotcha" that guys have had to watch for since the late '80s.

    With the '96 and newer 5.7, GM decided to approach faster warmup and consistent temps in a completely new way. They did away with the bypass circuit in the heads and the block and replaced it with a much larger bypass circuit connected externally from the manifold under the thermostat to the water pump. This alone is nothing new. In fact, the Chevy smallblock was one of the few engines that didn't have a large, external bypass circuit prior to '96. But what was new was that the bypass circuit flow was now linked to coolant flow through the radiator. As the thermostat opens to allow coolant out of the manifold to the radiator, it also closes the passage that leads to the bypass circuit. In this way, temperature in the block is encouraged to stay at the same temp as the thermostat opening temp.

    When installing Vortec heads on an older engine, you don't have the advantage of either bypass circuit. The old internal ports aren't present in the head and the external passage doesn't exist. Consequently there is no "flow path" for warm coolant to get to the thermostat and cause the wax pellet inside to expand and open the 'stat. Drilling a small hole in the stat allows coolant to flow directly past the 'stat so warm coolant will arrive eventually. The trick to this is in two parts. First is drilling a large enough hole so the back of the block and the heads don't overheat before the thermostat gets the signal that it's time to open. Second, on a street vehicle used in cold weather, the trick is to drill the hole small enough so the engine can actually warm up and provide heat.

    A second method to ensure some warm coolant gets to the 'stat is to connect the heater to a port as close to the 'stat as possible. Ensure there's no heater shutoff valve on the heater circuit and the 'stat will usually get a strong enough signal to open in reasonable time. If heater flow is blocked, however, there's a good chance the engine will overheat because the 'stat will no longer be exposed to coolant that's at the same temp as what's in the head and block.

    The third method is to plumb an external bypass into the manifold. But the problem here is twofold. If the external bypass circulates between manifold and pump it tends to reduce cooling ability in summer. If the external bypass circulates between manifold and radiator it tends to reduce engine heating in the winter. In either case the bypass should be sized to only allow the minimum amount of coolant necessary to make the thermostat open. 1/2" and 5/8" openings are not appropriate for this bypass.

    I have tried forcing a warm thermostat closed before. I do strange things like that sometimes. It takes a fair amount of force.

    I have run Vortec heads on an older engine, and I have a non-stock intake that I intend to install on a Vortec engine in the future. I am very seriously considering making a spacer like in the picture which will allow me to use the stock Vortec thermostat and be machined for the same type of bypass circuit flow control. Of course projects around here move slowly these days who who knows if it will happen. But it seems like the cleanest and most appropriate solution.

    I don't know if noise in the heater core would be an issue for me. I have an older Toyota pickup and those are notorious for making burbling noises in the heater. But adding the criteria of "no heater noise" to the solution makes it more challenging and more fun to work out.
    Last edited by 1project2many; 11-25-2013 at 05:09 AM.

  3. #18
    Fuel Injected! devind's Avatar
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    Quote Originally Posted by 1project2many View Post
    The deal is this: In the old coolant path water could circulate from the forward portion of the RH head, through a passage in the head gasket, into the block, and out through a 5/16" hole into the coolant pump. Inside the pump this coolant was routed to the inlet side, and the pump would circulate the coolant back through the block. This helped ensure some warm coolant reached the thermostat so the 'stat would open.

    As the need for cleaner emissions increased, faster warmup times and better vaporization of fuel became more important along with reducing variation int intake air temperature. Later carburetor and TBI intakes routed coolant from the front of the intake, under the throttle body or carb, and back to the heater hose fitting. Coolant would circulate through the core and return to the pump or on some HD trucks, to the radiator. This routing also provided a faster and more accurate heat signal to the thermostat so it would open properly. Coolant always flowed through the heater circuit and if a restrictor wasn't in place, it could cause overheating as radiator performance began to decrease. In my experience the restrictor is always found at the manifold side (outlet). Although the bypass circuit is still present in the heads, some of the TBI truck blocks do not have the 5/16" hole in the RH side of the block for the bypass circuit. Its been a "gotcha" that guys have had to watch for since the late '80s.

    With the '96 and newer 5.7, GM decided to approach faster warmup and consistent temps in a completely new way. They did away with the bypass circuit in the heads and the block and replaced it with a much larger bypass circuit connected externally from the manifold under the thermostat to the water pump. This alone is nothing new. In fact, the Chevy smallblock was one of the few engines that didn't have a large, external bypass circuit prior to '96. But what was new was that the bypass circuit flow was now linked to coolant flow through the radiator. As the thermostat opens to allow coolant out of the manifold to the radiator, it also closes the passage that leads to the bypass circuit. In this way, temperature in the block is encouraged to stay at the same temp as the thermostat opening temp.

    When installing Vortec heads on an older engine, you don't have the advantage of either bypass circuit. The old internal ports aren't present in the head and the external passage doesn't exist. Consequently there in no "flow path" for warm coolant to get to the thermostat and cause the wax pellet inside to expand and open the 'stat. Drilling a small hole in the stat allows coolant to flow directly past the 'stat so warm coolant will arrive eventually. The trick double. First is drilling a large enough hole so the back of the block and the heads don't overheat before the thermostat gets the signal that it's time to open. Second, on a street vehicle used in cold weather, the trick is to drill the hole small enough so the engine can actually warm up and provide heat.

    A second method to ensure some warm coolant gets to the 'stat is to connect the heater to a port as close to the 'stat as possible. Ensure there's no heater shutoff valve on the heater circuit and the 'stat will usually get a strong enough signal to open in reasonable time. If heater flow is blocked, however, there's a good chance the engine will overheat because the 'stat will no longer be exposed to coolant that's at the same temp as what's in the head and block.

    The third method is to plumb an external bypass into the manifold. But the problem here is twofold. If the external bypass circulates between manifold and pump it tends to reduce cooling ability in summer. If the external bypass circulates between manifold and radiator it tends to reduce engine heating in the winter. In either case the bypass should be sized to only allow the minimum amount of coolant necessary to make the thermostat open. 1/2" and 5/8" openings are not appropriate for this bypass.

    I have tried forcing a warm thermostat closed before. I do strange things like that sometimes. It takes a fair amount of force.

    I have run Vortec heads on an older engine, and I have a non-stock intake that I intend to install on a Vortec engine in the future. I am very seriously considering making a spacer like in the picture which will allow me to use the stock Vortec thermostat and be machined for the same type of bypass circuit flow control. Of course projects around here move slowly these days who who knows if it will happen. But it seems like the cleanest and most appropriate solution.

    I don't know if noise in the heater core would be an issue for me. I have an older Toyota pickup and those are notorious for making burbling noises in the heater. But adding the criteria of "no heater noise" to the solution makes it more challenging and more fun to work out.

    Excellent information and much appreciated!!!
    Thank You for time you must have spent to put all of that together.

  4. #19
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    Thank You for time you must have spent to put all of that together.
    You're welcome. It's the result of years of learning.

  5. #20
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    Bringing this one back from the dead....My L31 brand new short block is at the machine shop, I've just had it pulled it apart to double check all the clearances, had the the block decked to reduce the quench area, have had the balance checked and will be fitting the new roller cam.
    The Vortec heads have been machined for screw in studs and guideplates and are ready to be bolted on.
    I will be using the GMPP TBI/Vortec intake manifold and when done the engine will going in my 94 G20 van (yes it's the same motor I started working on a couple of years ago)
    Anyway I've been doing a lot of reading about the external coolant bypass required for the Vortec heads with non factory intake manifolds and the description above is the best I've seen after many hours of searching.The way the factory Vortec thermostat closes the bypass as it opens makes a lot of sense but unfortunately aftermarket manifolds aren't designed to work like that.
    I've checked my new L31 block and the coolant bypass hole from the front of the block does enter make a turn and come out on the block deck so coolant would flow through it, is there any reason why I just can't use the head gasket as a template and drill the missing coolant bypass hole in the Vortec head?
    I will be using a standard counterclockwise rotation TBI water pump which unlike the Vortec water pump has the passage for the coolant bypass on the passenger side.
    My factory heater hose does exit out the rear of the intake manifold and after a bit of tracing out looks like it eventually returns to the radiator, it passes through a tee that diverts coolant to the rear heater core and then up to the heater control valve which without pulling apart I assume it either sends coolant through the heater core when required or if it's closed bypasses directly back to the radiator.
    From what I've read elsewhere by having the heater hose from the rear of the manifold effectively returning to the radiator you don't need the external coolant bypass plumbed at the front but the factory TBI heads still used the internal coolant bypass passage so would it hurt to do the same as the factory setup and just drill the coolant bypass hole in my head?
    Last edited by Kitch; 01-15-2017 at 01:19 PM.

  6. #21
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    Sorry, I can't figure out why the spacing keeps disappearing after every sentence? It looks a mess....

    Figured it out, for some reason I needed to go into general settings and change the message editor interface!
    Last edited by Kitch; 01-15-2017 at 01:23 PM.

  7. #22
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    Honestly I did a different approach on the last Vortec I built for a carb application. I have had numerous OEM Vortec blocks that had the bypass hole in the block cast and machined into it. Only the matching opening in the head surface was cast over. I drilled the Vortec head for the bypass passageway. Internal bypass with no external plumbing or drilled thermostats.

  8. #23
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    Thanks Fast, I figured that drilling a hole in the head for an internal bypass should work but in the hundreds of different posts I read most people were running external bypasses or drilling holes in their thermostats. Oddly I only found one post were someone mentioned making it internal but they didn't give much detail.

  9. #24
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    With the GMPP TBI/Vortec intake manifold I won't be running an external EGR connection and I'll be blocking off the EGR port on the manifold, does anyone know where you can buy a threaded fitting to block of the EGR entry into the manifold? I was also thinking of plugging the two EGR holes in the plenum floor, to me it looks like fuel could enter the redundant EGR cavity under the manifold?

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  11. #26
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    Hi Hog,

    Thanks for the reply.
    I was going to make my own block off plate, I actually needed the pipe hole plug for the intake manifold.
    Your part numbers helped me track down the part I needed http://www.jegs.com/i/Chevrolet-Perf...56596/10002/-1
    Now I just need to find one from somewhere were the freight is less than $43...

    Cheers

    Andrew

  12. #27
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    Quote Originally Posted by Kitch View Post
    Hi Hog,Thanks for the reply. I was going to make my own block off plate, I actually needed the pipe hole plug for the intake manifold. Your part numbers helped me track down the part I needed http://www.jegs.com/i/Chevrolet-Perf...56596/10002/-1 Now I just need to find one from somewhere were the freight is less than $43...CheersAndrew
    It is actually a hydraulic fitting size. Might be able to track down one local. I tracked down a cap for the EGR port on my Thorley headers when I converted to the Marine intake. Been a while but I want to say it is a JIC fitting.

  13. #28
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    Just wanted to chime in and say thanks for a great thread. Bookmarked!

    I am fighting through this right now. Drilled holes in my tstat this morning. I drilled 3 holes at 3/16" diameter. Still having issues. Things are fine for awhile (hovers around 195) but after running more than 35-40 minutes the engine can't cool below 215. Doesn't get above 225 though. Very strange. I have another thread going on that and once I figure that issue out I will come back and post the solution here. Starting to think my heater core is plugged or connected backwards. FWIW there is no heater control valve on my truck. Not sure if that matters.

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