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Thread: Engine opinions Please for OlBurb

  1. #1
    Carb and Points!
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    Engine opinions Please for OlBurb

    I am an new member and I am trying to decide which engine to install in a 1988 3/4 ton 4x4 suburban that I have owned for 15 years. I had decided to us the L31Hd create engine from GM Performance http://www.jegs.com/i/Chevrolet-Perf...30283/10002/-1 but after reading on here I found some issues that I am not sure I want to tackle. (1) I was planning on using a carb intake and a tbi adaptor plate after reading this great response to a simple wtb ad I am concerned with the cooling issues http://www.gearhead-efi.com/Fuel-Inj...ntake-Manifold any further feedback is appreciated. (2) although I have not pulled my computer yet I assume it is a 7747 and everything I have read says 7427 is far superior. Also I found a post by dave w ("The 93 ~ 95 TBI computer with Red / Blue connectors is 8192 Baud / 64K PROM. The early TBI computer is 160 Baud / 4K PROM. The 93 ~ 95 TBI computer with Red / Blue connectors is about 51.2 times faster and the PROM has 16 times more memory. Don't tell anyone about the Red / Blue TBI computer, prices might increase. The Red / Blue TBI computer is the secret to an AWESOME TBI system" ) I assume this is a 7427 is that correct? Switching ecms either repin or adaptor is a lot to swallow for a tuning novice. My question is can the 7747 be tuned to operate the vortec motor with the tbi until I gather the courage to tackle the swap. (3)The suburban has a 700r4 and 410 gears do you think the vortec L31 is worth the extra effort and dollars for the increased HP and torque (which I have gotten several answer to exactly what those numbers are!) verses a properly tuned engine that came in the truck stock. http://www.jegs.com/i/Chevrolet-Perf...68758/10002/-1 I planning on doing fuel pump upgrade, crossover pipe, headers and O2 either wide band or heated (we will save that for a later debate) Thanks for your time and patients Jim

  2. #2
    Super Moderator dave w's Avatar
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    There are many opinions on what makes a good engine upgrade, cost vs. performance. The '7747 is adequate enough to run a L31 TBI engine, with a custom tuned PROM Chip. The '7427 is MORE than adequate to run a L31 TBI engine with a custom tuned PROM Chip. Some "export only" built after 1995 L31 TBI vehicles used the '7427. ... I had very good results (cost vs. performance) when I helped a co-worker rebuild his 1989 5.7 TBI engine using all stock parts except for the L31 roller camshaft and roller liter upgrade. Very few changes were needed the '7747 PROM Chip to get things dialed in. Heck, the stock 1989 TBI PROM Chip ran decent with the L31 roller camshaft and roller lifters. It's hit and miss on upgrading the stock 5.7 TBI engine to roller camshaft, some 5.7 TBI blocks are ready for the roller camshaft upgrade, some ARE NOT! ... dave w

  3. #3
    Carb and Points!
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    Thanks dave I bit the bullet today and ordered the vortec motor. It makes me feel better that you were able to get one up and running with stock tbi chip.

  4. #4
    Super Moderator dave w's Avatar
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    I was not able to get a Bone Stock L31 Vortec engine using TBI to run correctly with a Bone Stock 1989 TBI Chip!!! ... .... I was able to get a COMPLETELY BONE STOCK Rebuilt TBI LO5 5.7 liter TBI engine with a Vortec Roller Camshaft upgrade to run decent with a stock 1989 TBI Chip. ... Two very different engines!! ... I want to 100% clear, YOU WILL NEED A CUSTOM CHIP for a Bone Stock L31 Vortec engine using TBI!!!! ... dave w

  5. #5
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    Bubble busted !!! I decided to go for it and deal with what ever comes along. I have been doing more reading and looks like I have a lot to learn!!!! I have a great group of friends here to help who have computer, machine and mechanic skills. although none of us have tuned any thing before. It will be a fun project!!!!

  6. #6
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    Reading that other thread, the OP wrongly equates taking coolant from the rear of the heads on a Vortec as something related to the coolant bypass path.

    Hopefully you're referring to post #17 by 1project2many. Basically, you just have to provide some means for some coolant to circulate in the engine with the thermostat closed. You can connect a dedicated hose between the intake passage under the thermostat to the water pump and that allows the coolant to circulate even with the thermostat closed. If you connect the heater core between the intake manifold and the water pump port then it will also work as a bypass as long as you don't have a valve that blocks the coolant flow when you don't want heat. In any case, allowing for this bypass has nothing to do with requiring the intake manifold to have coolant flow from the rear of the heads.

    Do a Google Images search for "Vortec engine bypass hose" or something similar and you'll find lots of pictures of bypass hoses, both in stock form and on performance built engines. It seems most guys get away with a 1/2" bypass hose or using the heater as a bypass just fine.
    Last edited by lionelhutz; 02-08-2017 at 10:58 AM.

  7. #7
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    Quote Originally Posted by lionelhutz View Post
    Reading that other thread, the OP wrongly equates taking coolant from the rear of the heads on a Vortec as something related to the coolant bypass path.Hopefully you're referring to post #17 by 1project2many. Basically, you just have to provide some means for some coolant to circulate in the engine with the thermostat closed. You can connect a dedicated hose between the intake passage under the thermostat to the water pump and that allows the coolant to circulate even with the thermostat closed. If you connect the heater core between the intake manifold and the water pump port then it will also work as a bypass as long as you don't have a valve that blocks the coolant flow when you don't want heat. In any case, allowing for this bypass has nothing to do with requiring the intake manifold to have coolant flow from the rear of the heads.Do a Google Images search for "Vortec engine bypass hose" or something similar and you'll find lots of pictures of bypass hoses, both in stock form and on performance built engines. It seems most guys get away with a 1/2" bypass hose or using the heater as a bypass just fine.
    You do not need a bypass of any kind on a stock TBI cooling system. The heater already bypasses coolant from both sides of the heads back to the radiator if you run the GMPP intake. I never ran a bypass on my old G20 van with the TPI Vortec setup. Just used a later model 4 port heater diverter on it plumbed in line with the throttle body heat. Worst case scenario you drill a couple 3/16" holes in the thermostat. I like running drilled thermostats anyway as it helps keep the engine temperature more stable.
    Last edited by Fast355; 02-08-2017 at 12:58 PM.

  8. #8
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    Quote Originally Posted by Fast355 View Post
    You do not need a bypass of any kind on a stock TBI cooling system.
    YES, YOU DO. The engine needs some means to circulate the coolant from behind the CLOSED thermostat back to the inlet of the pump. Call it what you want, heater core, throttle body heating passages or whatever, something needs to be in place to allow the coolant to circulate. When you drill holes in the thermostat you are using the radiator as the bypass.

  9. #9
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    Quote Originally Posted by lionelhutz View Post
    YES, YOU DO. The engine needs some means to circulate the coolant from behind the CLOSED thermostat back to the inlet of the pump. Call it what you want, heater core, throttle body heating passages or whatever, something needs to be in place to allow the coolant to circulate. When you drill holes in the thermostat you are using the radiator as the bypass.
    I am talking about adding one to what already exist via the heater core. On the carbureted 350 Vortec I built, it had the bypass hole and passageway in the block. I simply drilled the Vortec head for the matching hole and had an internal bypass as well.

  10. #10
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    Quote Originally Posted by Fast355 View Post
    I am talking about adding one to what already exist via the heater core. On the carbureted 350 Vortec I built, it had the bypass hole and passageway in the block. I simply drilled the Vortec head for the matching hole and had an internal bypass as well.
    Yes, the bypass uses the heater core exactly as explained in my post and the referenced post. You muddied up the requirements for a bypass by posting the "you do not need a bypass of any kind" statement regardless of the intention. On a Vortec engine (not just using the heads but the newer block too) there MUST be an external coolant loop in place to perform the bypass function.

    The OP also asked about NOT running the GMPP manifold.

  11. #11
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    Quote Originally Posted by lionelhutz View Post
    Yes, the bypass uses the heater core exactly as explained in my post and the referenced post. You muddied up the requirements for a bypass by posting the "you do not need a bypass of any kind" statement regardless of the intention. On a Vortec engine (not just using the heads but the newer block too) there MUST be an external coolant loop in place to perform the bypass function. The OP also asked about NOT running the GMPP manifold.
    That depends on what water pump you use. The Vortec block I built had the passageways and with the older water pump, simply drilling the head provided for the correct coolant bypass. Actually if you simply use the Vortec heads even on an older block it will block off the bypass!

  12. #12
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    Thanks everyone for the feedback but Jegs called to verify order and I was so confused I chickened out on the vortec and changed my order to a Lo5 engine that came stock in the old burb. It will be much cheaper and faster to get going again. I know it is not close to as good an engine but it has been sufficient for years.
    I may try some tuning on it and get some experience and at a later date try the vortec and sell the lo5

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