Engine opinions Please for OlBurb

[dave w]

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

[OlBurb]

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.

[dave w]

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

[OlBurb]

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!!!!

[lionelhutz]

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.

[Fast355]

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.

[lionelhutz]

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.