WTB: GMPP TBI / Vortec Intake Manifold

[devind]

It's amazing that the Edelbrock pump can make enough pressure at the thermostat to keep it closed. I've tried to muscle t-stat's closed before and they generally have a fair amount of pressure. Plus the pump isn't anything more than a splash type pump, like a TBI pump with much greater clearances. But I guess .08 in sq of opening added to the 'stat made a large enough difference. How did you determine pressure was forcing it closed?

All you need to get the 'stat to open is enough warm coolant to provide a signal. Ever look at the front of an Olds 350 / 455 intake? I'm really surprised none of the manufacturers have built the bypass in using that method and a different coolant outlet and supplying a block off plate if the bypass isn't not needed. Wishful thinking, I guess.

People get excited about drilling holes and tapping the manifold for a bypass but why not use a thermostat spacer? http://www.behrents.com/c/Cooling-HousingThermo.html


No, the pump doesn't lend itself to easy drill and tap procedures.

Do you have a restrictor on the heater hose from the inlet pipe?

I don’t know exactly what the deal is but is has something to do with the water flows through the Vortec heads. Since the 1996 and newer Vortec blocks did not have the bypass on the passenger side of the block at the water pump mount, apparently the heads have a little different design as well. Also when you are trying to muscle the T-state you were probably trying to open it. When in the intake the water is actually pushing against the back side trying to close it.

I ran the same pump with the TBI heads for several years and never had a problem.

It wasn’t until I rebuilt the motor and went with the Vortec heads that I started having this problem.

I thought I might have something else going on. It wasn’t until I found the thread on the Tri-5 forum were guys were having the problem with their Ram Jet engines which also run Vortec heads that I knew for sure I was diagnosing the problem correctly. Some of those guys were running standard stock pumps and still having the same issue. Most guys just say they run the T-state with the bypass holes in them and never have a problem. But with EFI I want the water temp to be consistent.

I’m not sure about the heater hose fittings. They are the same ones that I ran with the TBI heads. I was actually thinking about that the other day when I noticed it making the funny noises. I was trying to remember were the smaller one goes. If I’m correct the smaller restrictor fitting actually goes on at the water pump to create some back pressure and help keep pressure build up in the heater core. Does that sound correct?