Reverse-flow cooling in ZR-1

[hand_coder]

I was just asked about the cooling system of the ZR-1. The questioner pointed out an article where a "reverse-flow hybrid cooling system;" was listed as a engine specification. The article is dated February 1988, so it was discussing the 1989 ZR-1 which never made it to production.

The ZR-1 press release I have, dated March 15, 1989, did not mention reverse flow despite devoting 2 1/2 pages to the cooling system.

Did the production ZR-1 feature reverse flow cooling? Was it part of earlier ZR-1s and then dropped from production? An inquiring mind wants to know!


Regards,


Paul Pollock
WebCars! Webmaster
http://web-cars.com

 

[Rob]

Paul,

To the best of my knowledge, the LT5 engine did not have reverse flow cooling. RFC didn't appear on the Corvette until the introduction of the 1992 LT1 engine.

 

[LT4man]

I was told the ZR-1 had a form of the reverse flow cooling which found its way to the LT1/LT4 engines. The LS1 also has a derivative of the reverse flow cooling system.

GM is very good as far as research & development. They also share this info with other GM car lines.

SAVE THE

 

[hand_coder]

a form of the reverse flow cooling

I'm curious: what do you mean when you say "a form of reverse flow cooling?

In the press release dated March 15, 1989 they talked of relocating the LT5's thermostat to the inlet side, resulting in a "more constant temperature since it is sensed immediately at the engines inlet". Is this a form of reverse cooling?

GM is very good as far as research & development.

I agree and I often think that they don't get enough credit in this area, which is unfortunate.


Regards,


Paul Pollock
WebCars! Webmaster
http://web-cars.com

 

[Hib Halverson]

"Regular" flow cooling, ie: "regular" as in the SBC and the BBC, is the coolant enters the block then flows around the cylinders and upwards into the heads then back to the radiator. In those engines the thermostat was at the outlet.

"Reverse" flow cooling, most notably on the Gen 2 SBV8s (LT1, LT4, L99) fed coolant to the heads first. Coolant then flowed into the block and finally out of the engine. The coolant went through the thermostat twice, once on the way in and a second time, on the way out. On the way in, it heat controls the thermostat and on the way out, it's routed either to the radiator or back to the engine.

Neither the LT5 nor the Gen 3/4 V8 family have reverse flow cooling. They do, however, have the thermostats located at the engine coolant inlet rather than at the outlet.

The LT5 also has a coolant bypass that prevents coolant pressure from rupturing or the radiator at high rpm. There's a spring loaded valve that opens when the pressure differential across the radiator reaches a certain point. The open valve allows coolant flow to bypass the radiator.

The statement above that the LT5 had a form of reverse flow cooling that was later adapted to the Gen 2 V8s is not correct.

 

[hand_coder]

Hib:

Thanks for an excellent reply, I think we now know the answer.

One question tho:

Coolant then flowed into the block and finally out of the engine. The coolant went through the thermostat twice, once on the way in and a second time, on the way out.

Does the coolant go through the same thermostat twice? Possible I suppose, but I'm having a hard time visualizing it. Or are there two thermostats?


Regards,


Paul Pollock
WebCars! Webmaster
http://web-cars.com

 

[LT4man]

Actually, I believe it was Dave McLellan who told me about the ZR-1 and the LS1 having some features of reverse flow cooling.

You might want to take it up with the Chief Engineer of Corvette from 1975-1992! :L

I was having a conversation with him at MAM's Funfest last year. We were speaking about reverse flow cooling systems. He was the one who brought up the ZR-1 and then moved the conversation to the LS1.

My point is this, Hib. Technology is NEVER a new idea. Ideas that have been around for some time are reinvestigated. Ideas that come from there are tested and validated. What we call NEW technology is something that has been around the block several times before we (the general public) actually have a chance to experience the information.

Just thought I would straighten out the incorrect information in this thread.

Carry on!

SAVE THE

 

[Hib Halverson]

Regardless of what Mr. McLellan may have said, neither the LT5 nor the Gen 3/4 engines have reverse flow cooling...if we are speaking in a definitive sense. Yes, they may have a "feature" of the Gen 2 V8's reverse flow system, ie: thermostat located at the engine's cooling intake rather than at its outlet, but neither of those engines have coolant going to the heads first and the block second, which is the only factor in describing their cooling system as "reverse" flow.

As for the question about the thermostat in a Gen 2 V8 (L99, LT1, LT4)...there's only one thermostat. My understanding is it sits in two cavities. On one end of the 'stat is the wax-filled "pill" that expands and opens the thermostat valve. That pill is in the first cavity which is exposed to coolant outlet flow. In the second cavity is the thermostat valve which controls coolant inlet flow. Again, I'm not an expert on Gen 2 thermostat engineering but I believe that's how the coolant temp control system on that engine works.

 

[Aurora40]

I think the technical term for the LT5's system is "Bizarre Flow Cooling". The stuff flows all over the damn place.

 

[Hib Halverson]

I think the technical term for the LT5's system is "Bizarre Flow Cooling". The stuff flows all over the damn place.

Seems that way, huh.

Actually, if you take the heater plumbing out of it, the system is pretty simple. There one inlet, with a thermostat controlling the flow, and there are two outlets, one for each head. The inlet connects to the bottom of the radiator and the outlets connect to the top of the radiator. That's all there is to the basic LT5 cooling system.

Early in development, GM found at high rpm and high coolant flow, pressure in the radiator, due to it's restriction, would blow the rubber seals between the side tanks and the core. GM did not want to design a specific LT5 radiator, so the solution was the radiator bypass which opens when the pressure differential across the radiator reaches a certain level. This bypass valve is part of the thermostat and, when open, allows coolant to flow, from junction of the two outlets, down to the inlet at the thermostat housing.