Thread: Convert to reverse flow cooling

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Hello there, back after a longish pause in building due to all sorts of stuff

Is it possible/adviseable to convert an older Chevy engine (Gen I) to reverse flow cooling? As reverse flow cooling seems to be the better choice for this style of engine and I'm planning to do a total rebuild of my engine anyway I thought I might as well change the flowdirection. A bit of money is on hand.

The engine is in a daily driver truck, got 492 heads with big valves on it, Edelbrock intake and 600cfm carb, a Comp Cams Extreme Energy cam (mild roller), and headers. Flat top hyper Pistons.

I'm not looking for power, but I'm planning on running it with LPG (autogas), so I'm looking to raise the CR a bit (to around 10.5-11, LPG has 110 octane).

Is there an "easy" way to convert the flow direction? As it's a 28 year old car I'm not going to put an LT1 in it
But will putting on a reverse drive water pump, changing the thermostat and swapping the hoses be enough? I have a machine shop and can build my own parts, like a thermostat-housing for an outlet-thermostat after the water pump...

Has anybody tried this?

Thanks a lot,

Max

I like your style Max –

Possible? Well, years ago Smokey Yunick developed and built reverse-flow system for some of his Trans-Am race cars – but then again Smokey had pretty much unlimited resources. Several independent engineer / engine builders have toyed with reverse cooling but as you already know the LT1 was the first “mass-produced” engine with reverse-flow cooling.

There are differing opinions on the effectiveness of reverse-flow cooling. It would appear to be better than standard-flow systems but it certainly requires additional engineering to make it work properly. In a “standard flow” engine the coolant is typically boiling somewhere in the engine – more than likely in the coolant passages within the cylinder head as this is the hottest point the “coolant” comes into contact with. The temperature of the interior engine walls surrounding the combustion chambers are far above the boiling point of any known coolant. The coolant directly in contact with the back-side of the combustion chambers, particularly near the spark plugs and exhaust valve seats, turns to vapor. This forms a turbulent natural convection where the vapor forms bubbles that collide causing a condition known as “nucleate boiling”. This condition is not harmful as long as the vapors are continually moving and not allowed to accumulate (like when an engine runs cry – very bad things happen). Under normal engine operating conditions, the coolant flow rate is sufficient to move the vapors along while continuing to flood the area with a steady stream of liquid coolant. As the liquid hits the vapors, any of the above mentioned “bubbles” that may have formed condense back into the coolant stream.

If a steam pocket forms, the vaporized coolant may prevent the flow of the coolant to that area of the water passage and a hot spot will develop on the inside of the chamber. This condition can cause detonation and potentially lead to engine failure. Vaporized coolant cannot transfer heat as efficiently as liquid coolant so in essence, it acts as an insulator, allowing the temperature to go into the stratosphere.

In a reverse-flow system, the coolant flow not strong enough to expel the vapor from the cylinder heads down through the engine block and out to the radiator. The vapor, instead, will remain trapped around the cylinder head, where it will become super heated and in all likelihood - melts your engine.

GM came up with a solution to this problem. They vented the cylinder heads where coolant vapors would normally collect. On the Gen II engines, these vents are on the rear side of the cylinder heads. Steam and trace amounts of liquid coolant escape through a banjo fitting into a tube that goes into the coolant overflow reservoir. The opening of the banjo is small enough to limit liquid coolant from flowing through it, but allows steam to easily pass. As the steam travels through the little hole in the banjo fitting, the pressure drop and it condense to a liquid state as it returns to the overflow reservoir.

So to “convert” from standard to reverse flow cooling, you’ll have to have the steam holes and a means to regulate / restrict the passage of steam vapor and fluids. You’d also need to capture and return to the cooling system.

Picture of how an LT-1 Reverse Flow (from GM Manual)

Regards,
Glenn

Good post Glenn!! It would seem however that designing and building a reverse flow SBC would be just reinventing the wheel.

With somewhere north of 90,000,000 yea thats right 90 Million Small Blocks built. That the cooling system works pretty good just as it is. While I personally never want to see anyone stifle experimentation this just may be the least productive place to put that experimentation to work. But then again....................

RS

I eliminated all of that on my LS 7 and replaced them with bleeders. So when I'm replacing the coolant I just bleed off all the air as the engine warms up. I haven't had any cooling problems with this system. So I guess you could do the same with yours.
Ken

ken, please post up pictures of you bleeder set up

Originally Posted by gassersrule_196

ken, please post up pictures of you bleeder set up

If you go to my thread, One Way To Build A '32 Hyboy, it's all in there.


I just went back threw my build and can't find it. I will take some photo's of it tomorrow, sorry.
Ken

Thanks for the post! Helps me out a lot. Seems like it's going to be difficult.

The thing is: I live in Germany and the amount of good cylinder heads I can muck around with is limited

My engine is currently running on LPG (that's a butane/propane mixture very common here in Germany, as prices on regular gas are about $8 per gallon )
LPG costs half as much, has a higher octane rating and burns more efficiently, but it also has a much higher burning temperature (and higher octane = more compression possible = more efficiency = even hotter). So in regular heads I might get cooling issues (haven't so far, but I've only put 5k mls on my gas system). So with my new cylinder heads (got another set of 492s) I've polished the combustion chambers and exhaust outlets (less surface area = less heat dissipation into the coolant passages) and the underside of the valves. The heads are getting hardend exhaust valve seats, too.

So the next issue would be to reverse the coolant flow, but on the other hand that would be a load of work. I've thought about water injection as well, but that's not street legal here in Germany, and this is going to be a daily driver.

So I just thought maybe there's an easy way to do it, but I guess the Gm engine engineers new what they were doing building it that way... And if they bust 100 engines in a series of tests till they get it right they wouldn't care, but I (and my wife ) would care...

I'll have to think about it. I'll let you know if I try to do it And I'll never tell anybody it I fail

Max, Thanks for the post, and Glen thanks for your excellent overview of what's involved reworking an engine for true reverse flow. I think that there are lots of people (I was one) that are a little bit confused about reverse flow cooling due to the different water pumps out there for the older engines that are tagged "reverse flow" when they are really "reverse rotation" to account for the serpentine belt. For those, like on my SBF, the "reverse flow" pump flows the same as the "regular flow" pump, but the impeller is curved the other way for reverse rotation.
I've read some about Smokey Yunick's super efficient engines, mostly back when he was doing things and had articles in Popular Science, but I think I may dig a bit deeper into his history. He was a brilliant guy.

Yup - I remember "Say, Smokey" in Popular Science as well. Smokey was certainly one of the greats - no real formal education yet he had several patents and numerous automotive innovations.

See the article at http://www.legendsofnascar.com/smokey.htm for a lot of information on this automotive giant.

Of course you could just use an LT1 block and heads with gear driven water pump---we do about3-5 of them every week or two and have shipped them all over the globe .

If you want more info PM me and I'll have my son Corey get in touch with you

Jerry Clayton

Originally Posted by gassersrule_196

ken, please post up pictures of you bleeder set up

Here ya go. This is how I did it. When I first started my car I immediately new I was going to have a heating problem. I didn't want a upper radiator hose so I had my radiator made with two radiators side by side with a common tank. That way both the inlet and the outlet could be out at the bottom of the radiator. I'm telling you this because my bleeding of the cooling system was a extreme problem. If you do it on a conventional system it is very easy to do. I have two radiator fill caps, one in my cowl vent and one in my grill shell with a bleeder next to it mounted in the tank. another bleeder in the right front head of the motor. so now it is simple to get all the air out of my system. I fill the radiator from the cowl vent, that fills the block and part of the heads on the back side of the thermostat. Then I fill the radiator under the grill Shell, this fills the front side of the thermostat. Put the grill shell on and start it up. leaving the cap off in the cowl vent , so I can add more coolant as needed. when the thermostat opens and It now has full flow I just keep pushing on the bleeders on the motor and on the radiator tank until I get nothing but coolant. Add coolant along the way as needed to fill the system, no hot spots.
When I tear the car apart to paint I have stainless bleeders to get rid of the steel ones.
Ken

Wow - that's innovative and certainly make your ride unique. I always like to see the "one off" approaches that hot rodders tend to come up with.

I'm curious - do you mostly run highway or a lot of cruising with stop and go?

Again, great idea!
Glenn

Thanks Glen, It has about 900 miles on it and I would say about 150, miles were on the highway.
Ken