Slant Six Forum

reverse cooling
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Author:  Sam Powell [ Tue Jun 17, 2008 3:29 pm ]
Post subject:  reverse cooling

I know this is an idea tht has been discussed before, but would like to get a renewed discussion going, if anyone is willing. Would reverese cooling be better for the engine, and why? Am I wrong that the coolest water hits the head first? I read in a magazine somewhere that reverse cooling will help with detonation, but I don't see how. If one wanted to do this, how would you go about getting this to work. I know on some v-8 engines, the marine version turns in the opposite direction. Is this true of the slant as well. If so, is there a water pump for marine application that turns backwards?


Author:  dakight [ Tue Jun 17, 2008 3:40 pm ]
Post subject: 

Perhaps an electric waterpump. Otherwise you'd have to not only reverse the direction of the belt drive but also get a pump designed to operate in the opposite direction. Probably not impossible but certainly not easy.

Author:  NYG95GA [ Tue Jun 17, 2008 3:44 pm ]
Post subject: 

It seems to me that the hottest part of the engine should get the coolest water; otherwise it will be hotter when it gets to the part that needs to be cooled the most, which makes little sense.

Author:  SlantSixDan [ Tue Jun 17, 2008 4:35 pm ]
Post subject: 

Much cheaper and easier way of achieving the same benefit (ping abatement relative to ordinary configuration): waterless coolant. So far, this stuff is doing exactly what it's claimed to do in my (318 EFI) truck. With ordinary coolant, I ran a factory-spec 195° thermostat and especially after I disabled the EGR, I had to be super-careful with ignition timing or ping was significant and uncontrollable. Now with the waterless coolant, I run a 205° thermostat, still no EGR, and I can't seem to make the engine ping. I gave it 2° more base advance a week ago...still no ping.

Author:  LUCKY13 [ Tue Jun 17, 2008 5:15 pm ]
Post subject: 

Sam, reverse cooling does hlep with detination. It simply cools the cumbustion chamber more which really allows more compression without detination.

I really feel there would not be much benifit unless it was for the sake of adding extra compression. One problem with the slant is the piston being so far down in the cylinder, this allows the cylinder walls to run much hotter and I dont know if the reverse cooling would help, or hurt that part. The late model 400 & 440 Mopar big blocks had the same problem with the piston down so far. They would detinate worse at 8 to 1 compression than they did with a zero deck flat top, with or without a quench pad.

I expect if reverse cooling that the engine would not get as good a fuel mileage also, unless it was able to take some extreme timing to make up for it. I really don thtink it would even help then because when I run E85 I can run so much timing that I kill the power and dont get any better fuel mileage from it, even though it still will not detinate because of the E85 and cooler running chamber.

Now if you where to run a zero deck piston, with a D- dish piston at around 11.5 to 12.5 to 1 compression, then I would think it could benifit to go to a reverse cooling setup. Or the same setup with a unshaved head and a zero deck D-Dish piston that had around 10cc dish would put it around 9.5 to 1 and with reverse cooling a turbo could be run, and still stay out of det. Until we raise the piston and get rid of all that cylinder wall showing I dont believe its going to help much, if any.

Ofcourse I may be wrong, but without testing there is not much way of saying. If I was going to try reverse cooling I would do it with a surp belt setup because that would be easy to route the belt to turn the pump in the other direction. If a reverse pump can not be had ( like the marine engine you was thinking_) then pressing the wheel off and reversing it , or installing a nother would be needed.

All in all, its main benifit is to allow more compression without det, more than it would be to allow more timing. The amount of timing needed is controlled more so by the shape & size of the chamber, although heat will change the amount needed by a little bit.


Author:  emsvitil [ Tue Jun 17, 2008 5:54 pm ]
Post subject: 

Reversing the rotation of a slant pump won't change the direction of the coolant flow.........

Slant water pumps are centrifugal (center -> out) and not paddle wheels, so a reversed pump would still flow in the same direction, but with less flow because the scroll on the output side (which is designed for the rotation of the pump) would hinder flow.

Author:  Sam Powell [ Tue Jun 17, 2008 6:05 pm ]
Post subject: 

That was all really, really interesting. Dan, can the Evans waterless be purchased over the counter anywhere? ?What happens if you need to top it off out on the road? Will water turn it into some sort of mystery glop that will clog everything? Idid not read everything on the site. What prep did yougo through when changing things over? This sounds absolutely like the thing to do. Thanks.

Lucky, I appreciated the discussion about the problem with the pistons being so far down in the hole. This makes the Evans seem like it would have even higher benefit. The slant is a detonation challenge for several reasons. The long stroke, small bore makes it prone, and now the high deck height adds to the problem.

I still do not understand how reverese cooling keeps the head cooler. I suppose maybe the entire system is more efficient as the heat is rising through the system and natural convection then aids.

Ems, interesting observation. I guess one would have to completely redesign how the pump works, with a remote electric pump of some kind. It hardly seems worthwhile.


Author:  SlantSixDan [ Tue Jun 17, 2008 6:12 pm ]
Post subject: 

Sam Powell wrote:
Dan, can the Evans waterless be purchased over the counter anywhere?

A scattered few places, but it's not a commodity item.

What happens if you need to top it off out on the road?

Top it off with any propylene glycol based coolant (there are many; this is a commodity item) then drain and fill back up with Evans as soon as you can.

Will ater turn it into some sort of mystery glop that will clog everything?


What prep did yougo through when changing things over?

Drained block and rad thoroughly, blew rad and heater core out with compressed air, filled with Evans, burped air from system, brought engine to operating temp and carefully let off system steam a few times. A lever-type rad cap would've made this a bit easier, and a 4-pound cap would've removed all need to futz with it at all. Evans Waterless operates at low/no system pressure (its boiling point at atmospheric pressure is 375°F); a 4-lb cap is plenty adequate and allows any steam from residual water to exit the system. You do want to be running a coolant recovery tank, and the 4-lb cap you select needs to be a double-seal type (upper and lower) meant for use with a reserve tank.

I still do not understand how reverese cooling keeps the head cooler.

With the conventional system flow, the water flows from the radiator to the water pump, into the engine block, and then up to the cylinder head, and then from there it goes back to the radiator to be cooled down. So by the time it gets to the combustion chamber, it's already been heated up quite a bit by the engine block. With reverse cooling, the coolant goes from the rad to the cylinder head, and then down to the engine block, so the coolest coolant (rather than the hottest) hits the cylinder head.

Author:  Dart270 [ Wed Jun 18, 2008 6:42 am ]
Post subject: 

From my experience and learning, I expect the small bore and long stroke make detonation less likely due to smaller area chamber, and also allow less timing advance for complete burn (more efficient). This is why the 225 likes 25-30 deg total mech advance for max power. My guess is this would also make the 0.180" piston-deck height less of a problem.

Personally, I don't see that the 225 is detonation prone since I am running 10.5:1 comp with 91 octane gas and running it hard that way. I ran about 500 miles full bore around VIR 2 weeks ago on pump gas. This is with 0.170" piston-deck and stock cast pistons and about 250 crank HP.

I cannot comment on boost detonation yet. I agree that a zero deck piston/rod design will be an improvement. Tilley's turbo motor has made 600 HP on 95-98 octane with a stock-type 225 chamber head, albeit zero deck.

I would like to try the waterless coolant in my '92 360 Ram van. That thing likes to ping and it's 8:1 or so.

Sorry to sound confrontational, but it bothers me when people try to solve "general problems" that may only be particular to a person's individual buildup. I put the manifold distribution "problem" into this category also. I agree it is not ideal, but in 99% of all cases, it is not an issue for performance or durability.

All that said, I think the reverse cooling could help detonation issues. You would need an external electric pump, which are easily obtainable and seem to be reliable (about $250-300 from Summit?). The block deck is very thick (~0.400 or more), so pistons 0.180" down in the hole shouldn't affect the cylinder cooling much - just a guess there.

I assume you are still getting detonation after switching plugs, Sam? I am puzzled why your motor should detonate with relatively mild timing, boost, and performance, along with H2O injection. It is conceivable there is something about your air plumbing or turbo that is creating heat?



Author:  Sam Powell [ Wed Jun 18, 2008 9:30 am ]
Post subject: 

All my stock slants were detonation prone. They would go into detonation hysteria at light throttle, and it was always tricky to get it tuned so this did not happen.This experience dates back to my earliest slant, which was in 1972. I have had several stock slants in this car, and they exhibited the same tendency. I have a long, ten mile pull coming up 270 towards Gaithersburg out of DC, and it seemed to put just the wrong amount of vacuum and lack of power valve opening to get it into detonation. The longer I drove up the incline, the worse it would get. I have lived in this house, and made this drive for 32 years now. And I have done it with a slant powered car most of the time. Maybe I should have said, stock slants with mild cams and factory timing curves are detonation prone.

My understanding is that the flame front travels across a small bore in less time than a large one, and thus does not need as much timing to get the best burn possible. If the piston being down in the bore creates a hot spot at the top of the cylinder bore, that could possibly contribute to this. Others with stock slants I have discussed this with relate the same experience.

The purpose of this forum is to expose ideas to more than one line of thinking. Just because I have asked a question does not mean I am lobbying fore or against a given position. NOT knowing is the first step towards knowledge. Did your comment, Lou, feel confrontational? You should always feel free to state your position without getting upset about it. There is always room to talk about these things and get other's points of view, experience, education, etc. without getting bent out of shape over it. If you think someone is wrong, feel free to share your knowledge and opinion. But you don't want to shut down honest, open minded inquiry.

If I sit here in my own little world, not sharing, not asking questions, and not digging any deeper than what I read on line or in a magazine, I won;t learn as much, and the community will not be enriched.

The slant six is a different kind of machine from most, and some if not much of what you read in the mainline car hobby magazine will not apply. That is why this forum is invaluable to the slanters,and your info is especialy valuable. I remember reading a Hot Rod build up of a slant (at least I think it was Hod Rod), where they were disappointed in the results. Their conclusion was that the slant did not offer much potential. Any slanter who read this could see what was wrong, and that they put together a very poor combo for a slant. They just matched cam, induction, rear and tranny very poorly for a slant. . Any one of our built racers would have dusted them off easily. The point is, without the discussion and sharing that goes on here, many of us mortals would be building our slants poorly too.

To go back to the discussion at hand, I think the mild stock cam,and the lean jetting in a stock slant make it more detonation prone. From what I have seen and read here on this forum, slants like big cams. Which most of us will be a little reluctant to jump into. But apparently slants thrive on big cams. Your '64, which has a big cam, and runs great, and gets decent economy.

The problem with this game of engine building is that it is hard, and expensive to try every combination of parts on a given drive train. How do you know what cam to put in a certain buildup and drive train combo if you don't have someone elses experience to lean upon? Especially when you are bilding an engine that does not follow the same rules as a mainline SBC.

At the time I was putting the turbo engine together, I did not know what cam to go with. No one else was real sure either. Since I was building what I thought would be a daily driver, I thought mild cam, custom ground for turbo would be OK. Looking back on it, I would do more research into turbo cam profiles for small bore, long sroke engines, and maybe reduce the compression ratio. But if what I have now can be fixed with some creative thinking, such as waterless coolant and short reach spark plugs, I am going to try that first.

The short reach plugs did help with the detonation, but it does not seem to idle as well. I can hear some misfires at idle. I would like to solve this problem with other fixes if possible. I am currently designing a new intercoler set up. I have purchased the new one ,and am working out the plumbing. I am also open to trying to reduce the compression ratio with a thicker gasket if that seems practical. That is, if it creates enough reduction in compression in to make it worth the time and effort.

Thanks for your thoughts. I am not at all discouraged. I am enjoying the process of trying to "fix" the detonation problem.


Author:  Sam Powell [ Wed Jun 18, 2008 9:39 am ]
Post subject: 

Would not the thicker deck make it hotter and not cooler? It seems as if the thick deck will retain the heat, and that coolant cannot get in touch with as much metal when it is thick.

Sorry about the long, long response. I am on vacation, and have lots of time on my hands.


Author:  Dart270 [ Wed Jun 18, 2008 12:06 pm ]
Post subject: 

Hey Sam,

I am not at all feeling like your question was not valid. You should definitely be asking these kinds of questions.

My response was partly motivated by the "general consensus" ideas I think are over quoted and under supported, IMHO. Sometimes these things touch a nerve. My apologies.

That is quite interesting that you had detonation issues with your stock Slants. I guess mine have never stayed stock for very long, but the stock ones never had detonation issues I recall. I do remember hearing pinging in some cases, but I don't see that as a damaging effect, unless excessive. You actually want to have a little pinging for best mileage, IIRC, or at least be right on the edge. I have also mostly had 68-down Slants with richer jetted carbs stock than 70s models.

I do believe that the stock Slant timing curve was not very good for all around use and had too much mech advance with not enough vac advance. The mid-late 70s distributors were better on this.

The thick deck may make it hot, but I don't expect a big difference between the reverse cooling and piston-down-the-hole being substantially hotter than normal cooling situation. I'm no expert here, just a thought.
There is water on the head side of the deck too, of course.

Glad to hear that the plugs helped. My guess is you may have to retune mix and timing at idle to correct for the different plug character.

Hmmm, one big difference between your motor and other turbo 225s is that they are mostly near zero deck motors. The others I can think of are around 9:1 or a bit higher. Jess could be on the right path here.



Author:  SlantSixDan [ Wed Jun 18, 2008 12:45 pm ]
Post subject: 

Dart270 wrote:
I do remember hearing pinging in some cases, but I don't see that as a damaging effect

I disagree — I think any amount of pinging is to be avoided. When you consider what causes the "ping" effect, it becomes pretty clear that it is not something you want to tolerate, even just a little bit. I could be more sensitive to the issue on account of running several aluminum-block 225s, but just because an iron 225 is stout enough to withstand a lot of pinging, doesn't make it OK.

You actually want to have a little pinging for best mileage, IIRC,

This was GM's public-relations spin in response to large-scale dissatisfaction with how their thrown-together feedback-carbureted CCC emission control system of the 1980s "worked". I have a hard time taking it as anything more substantial than yet another of the many imaginative whoppers GM have told over the years.

Do keep in mind that the slant-6's combustion chamber, even the '67+ "revised" chamber, had little or no active, scientific engineering applied to it. The engineers' accounts of cylinder head development describe the chamber as "the general shape of a wedge, used as cast". It works OK, but it is definitely not optimal and is certainly ping-prone. These days, combustion chambers get a whackload of careful engineering, simulation, testing, etc. It's one of the reasons we once again have high-compression new engines on the street.

Author:  Dart270 [ Wed Jun 18, 2008 1:55 pm ]
Post subject: 

I certainly would not assert that the Slant chamber/head design is optimal. I am well aware that it was not developed with modern design principles, CAD, etc... Having used such principles myself for magnet and mechanical oscillator designs, I know the power in such methods.

However, I think the Slant head has much more potential than most people suppose, both for power and mileage.

For example, many people here complain about poor HP due to head design, but there are NA engines 300-370 HP on gasoline with a ported stock-type Slant head.

Personally, I would LOVE to have a new Slant head design in aluminum with nicer chambers and ports, but such efforts have failed so far.

I thought I had heard the "little pinging" also from JB Heywood of MIT, a prominent engine design scientist/engineer. I could be remembering wrong. Ideally, I think you want to be on the edge of pinging, but not actually pinging. Thus, if you have mild pinging on some small fraction of combustion events, you will be at the edge. It will be hard to make ALL combustion events ping free unless you are substantially away from the edge. Again, I am not an expert here, but I would think you would maximize cylinder pressure and thus power per unit fuel (thermodynamic efficiency) when you are on this edge.

As for high compression, I think strict computer control of ignition timing also has a lot to do with the ability to manage that on pump gas. Variable valve timing (drool) is great for that too.

Just some more blabbering... :D


Author:  LUCKY13 [ Wed Jun 18, 2008 2:07 pm ]
Post subject: 

You know Sam, that is something I have never give thought to. (big thick deck of the slant).

So will that thick deck retain more heat, or aid in better cooling?

The big blocks with the low piston would instantly drop 20 degree in temp, and the burn in the chamber was much better after changing to a piston that was closer to zero deck with a quench pad. The power and the fuel mileage would be incressed a hugh amount.

I am think the deck will retain the heat, then reverse cooling even with a low piston may just help. Or atleast it would seem it should, the head probably has a lot to do with the temp of that deck because of all the contact area. But there is a lot to all this and will it help, or not, may just have to be tried to know.

With the cooler water hittting the head and that deck first before the cylinders add all there heat it would seem it should have a hugh effect.

The piston up farther in the cylinder only allows the heat to be used in the combustion chamber instead of getting into the water system from the cylinder walls. So not only do you get rid of that surface area ( top of cylinder wall) but if a proper quench pad is used the area of its size is eliminated also, there forth the heat is used in combustion, and not going into surface walls (as much).

Heat in the cumbustion chamber is a funny thing, you need it, but only enough to complete combustion. Anymore than needed starts building up in the surface area's around the chamber and promoting det. The more heat you force into cumbustion the better the burn, and less timing can be used ( which makes power ).

Really agian I think this may be the reverse coolings best time of helping, when you have forced all that heat into a smaller more localized area, that area needs the extra cooling ( mainly around the valve seats) from the cooler water going there first before it soaks up heat from other parts of the engine. We use alot of that extra heat we forced into the chamber, but we cant use all of it (alteast not yet anyway) so it builds up in these area's we forced it into.

I know with the reverse cooling one thing you will noticed is oil temp will raise. Telling me that the water removes so much extra heat from the top of the engine, that it doesnt cool the lower part of the engine as well (which the reverse is happening with regulor cooling) becuase its already hotter. So the oil ends up having to removing alot more heat. Which is one of the oils jobs anyway. When reverse cooling, a exturnal oil cooler is a must and should be meantioned.

Controlling heat is one of the real important parts that many race teams put alot of time into, not only how to keep it under control, but when and where to use it also. Its not a easy subject with easy anwsers, and may infact hold the key to many of the more effeciant engines out there.

I do plan to try reverse cooling on my street engine when I up the compression to 13.5 to 1 ( with E85). I finally reached 20 mpg with this stuff, but it was through lower timing, and not higher timing that got me there. My thought where that having direct control over the combustion chamber temp with the reverse cooling I will be able to use the T-Stat to set the temp at whatever level gives best power or economy depending on the goal at the time. There should be a temp level that works best for each. If this results in a hotter running engine that I need to cool off then the oil cooling will be used.


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