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Head cooling on cylinder #5 - solutions?


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no it flows something like 21gpm constant. The LD pump is rated at 30 some at peak torque rpm of like 2400 engine speed (differnt pump speed)...

 

The pump will increase flow with increased speed. I really need to make up a pump dyno and take some readings on the pump to make a pump curve. That would solve the pump issue once and for all.

 

The Davies Craig Water Pumps are larger than the MSA, and work on variable speed as well. They perform well on some pretty strenuous applications, but they are not cheap.

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  I assume you did try to source the LD pump in Australia, I saw a thread and you mentioned you got it from Japan (?)

My thoughts on the Summary:   - The path of coolant through the L engines results in the rear of the head receiving the hottest coolant having stagnated water flow, insufficient for the he

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no it flows something like 21gpm constant. The LD pump is rated at 30 some at peak torque rpm of like 2400 engine speed (differnt pump speed)...

 

The pump will increase flow with increased speed. I really need to make up a pump dyno and take some readings on the pump to make a pump curve. That would solve the pump issue once and for all.

 

The Davies Craig Water Pumps are larger than the MSA, and work on variable speed as well. They perform well on some pretty strenuous applications, but they are not cheap.

 

 

I just bought a Davies Craig water pump. Its the 115 litres per minute jobbie that looks like a small turbo in design.

 

That 115 litres per minute is almost spot on to what you think the LD28 pump flows, 30 US gallons per minute.

 

One advantage I see is that this volume can flow at any engine speed unlike the LD pump arrangement.

 

Positioning the pump where recommended will perhaps push SOME of the water around the engine bypasses in the opposite way. Davies Craig recommend the lower radiator hose where the pump is to be fitted.

 

I'm curious to see what block coolant pressures I get with this setup. The CSR pump I have ATM produces no coolant pressure. (as far as the guage is concerned) but the 115 lpm unit really pushes out some water when tested on the bench! :)

 

I will set it up with the CSR unit in situ but turn it off for the tests.

 

I'm expecting that I'm going to be able to adjust the block pressure somewhat by altering the number and size of the lines that connect to the thermostat housing. Until I test this theory, Im really only guessing........but I'm hopeful.

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I'm expecting that I'm going to be able to adjust the block pressure somewhat by altering the number and size of the lines that connect to the thermostat housing. Until I test this theory, Im really only guessing........but I'm hopeful.

 

Don't hope for too much old boy, 'cause, like the CSR pump, no significant water pressure could be measured on my guage. It seems to me that the electric pumps just don't have enough stonk to do what I'm asking of them.

 

I've read articles where it's quoted that up to 20 hp is needed to turn the mechanical water at 5000rpm. If I read this bit carefully in the first place, I could've saved myself a lot of cash!!!!. How could an electrically driven water pump, regardless of the design, possibly compete with the stock, mechanical pump requiring that much power and give the 30 psi head of coolant pressure seen on my test guage?

 

I'm assuming that when used with a late model engine with ignition and fuel management, timing would be appropriately managed. If knock was to occur due to local hot spots in the head (nucleate boiling), ignition would be retarded. And some engine power would be lost, of course. But the deletion of the mechanical water pump would help to liberate some power so the net effect would be somewhat balanced out. When the ignition timing advances again, power will return and not be hindered by the drag from a mechanical water pump.

 

I'm waiting for the arrival of my LD28 mechanical water pump from Japan.

 

I'm also toying with the idea of setting up the pump with a smaller than stock pulley to increase the rotational speed at lower engine rpm's. Just gotta figure out how to do it!

 

Cheers!

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Does this put all aftermarket electric water pumps to rest? I can understand the challenge of both designing a large enough electrical motor and overcoming basic laws of thermodynamics (mechanical energy ->generating electrical energy-> powering a mechanical energy generating device) Does this not mean that to achieve the max 20hp output of the pump far greater HP will be drained through the alternator? Surely the only advantage to such a setup would be to provide indirectly proportional pump pressure to engine output- ie: making the pump activity fully independant and programable.

If there is an RPM range that the pump reaches maximal efficiency then the electric pump could be set to this without exceeding it unlike a mechanical pump.

However this appears to indicate that the electric pumps just arent up to nosh with the power output? Can anyone else confirm this...???

I've heard claims of guys running these things in track-day cars for events and such... I think this warrants further investigation!

Thank you very much for bring this to public attention, you're becoming quite the scientist!!

ing

I'm also toying with the idea of setting up the pump with a smaller than stock pulley to increase the rotational speed at lower engine rpm's. Just gotta figure out how to do it!

 

Cheers!

 

Enter machinist? I know a few around town by now, i'm getting lots of work done so we can go to pick and payless and pick up something close it shouldnt cost much to have additional machining done on my account :P... I think increasing the mechanical efficiency of the pump is perhaps the way to go given the conservation of energy paradign above?

I still have to post pictures of my cutaways and comparisons for late model heads so i'll try and have those up sooon... so busy!

 

Keep up the good work Scienctist-san!!!

 

-pete

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Don't hope for too much old boy, 'cause, like the CSR pump, no significant water pressure could be measured on my guage. It seems to me that the electric pumps just don't have enough stonk to do what I'm asking of them.

 

I've read articles where it's quoted that up to 20 hp is needed to turn the mechanical water at 5000rpm. If I read this bit carefully in the first place, I could've saved myself a lot of cash!!!!. How could an electrically driven water pump, regardless of the design, possibly compete with the stock, mechanical pump requiring that much power and give the 30 psi head of coolant pressure seen on my test guage?

 

Does this put all aftermarket electric water pumps to rest?

 

(very selective quotation)

 

Ozconnection: I cannot see that this puts electric water pumps to bed. I can see that you failed to generate any pressure similar to that seen under operating conditions in the engine, but were you running the engine at that time? Heat is Power, and Heat pressurizes the coolant of a running engine as much as the restriction on the flow impelled by the pump.

 

I would wager that a significant amount of the "energy" used to get coolant up to pressures seen in operating engines is heat energy and not mechanical energy.

 

You need to measure temperature differences between your engine at various points physical, and load/temp wise, with each setup, as well as radiator inlet/outlet/middle points etc, to make sure no variables are left out when comparing the two side by side to see if one is up to snuff with the other.

 

At least, I seem to think this is insufficient data to simply ignore the anecdotal evidence of countless users of electrical coolant circulation systems. *I* can't see any problem with my reasoning.. am I wrong?

 

Edit: I don't want to crap all over your data collection, ozconnection, nor do I have any "feelings" on the matter to push or reason to say one setup is better than the other. This is just my thoughts on the measurements you've been taking, and I may well be missing part of your point (this *IS* rather an extended conversation to review) so in other words, criticism of my own post is certainly welcomed.

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This may be a bit off the line of thought here but in the Motocross world there is a company that makes aftermarket water pump impellers. Which are made to pump coolant more efficiently and more of it. Couldnt we take apart a normal L28 water pump and press on a better performing impeller and maybe make it to tighter tolerances to the front cover and have it tested to flow more efficiently. Maybe im off base but if it works so well for motorcycles why not for a car...

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(very selective quotation)

 

Ozconnection: I cannot see that this puts electric water pumps to bed. I can see that you failed to generate any pressure similar to that seen under operating conditions in the engine, but were you running the engine at that time? Heat is Power, and Heat pressurizes the coolant of a running engine as much as the restriction on the flow impelled by the pump.

 

I would wager that a significant amount of the "energy" used to get coolant up to pressures seen in operating engines is heat energy and not mechanical energy.

 

You need to measure temperature differences between your engine at various points physical, and load/temp wise, with each setup, as well as radiator inlet/outlet/middle points etc, to make sure no variables are left out when comparing the two side by side to see if one is up to snuff with the other.

 

At least, I seem to think this is insufficient data to simply ignore the anecdotal evidence of countless users of electrical coolant circulation systems. *I* can't see any problem with my reasoning.. am I wrong?

 

Edit: I don't want to crap all over your data collection, ozconnection, nor do I have any "feelings" on the matter to push or reason to say one setup is better than the other. This is just my thoughts on the measurements you've been taking, and I may well be missing part of your point (this *IS* rather an extended conversation to review) so in other words, criticism of my own post is certainly welcomed.

 

I hear what you're saying and I want to thank you for your thoughts on the subject Daeron! :mrgreen:

 

You may recall that when I started testing, I connected my pressure guage to a cold engine, basically because I didn't want to be sprayed with hot coolant as I did my work. But it was an excellent starting point to measure the block coolant pressures with a cold engine and then to witness the changes to the pressure as the engine warmed up and the thermostat eventually open. I recorded the values in another thread. Even when the engine was cold and long before the thermostat was anywhere near open, I saw close to 10 psi pressures @ idle IIRC. Man, to be honest with you, I dont remember seeing any pressure on the guage when the engine was turned off after normal operating temp had been reached and yes, there certainly would be coolant expansion due to heat soaking, the very reason why the radiator has a pressure cap on it!

 

But the real issue is whether an electrically powered water pump can match or be better than the stockers! I mean, I just spent a shitload of cash to find out what the deal was here and I could suggest to you all that it was the best investment since buying my Datsun. I could say that! Am I? (You already know the answer to this one mate :icon45:.) Maybe like jeffer949 suggests in his post, more work could have been done to the impeller on that CSR unit to at least look more like the stock unit. Its shape is very basic and without being too cruel, appears more like an accountants decision than an engineering one.

 

I remember quite vividly as a young boy, my dad needed a new prop for his Evinrude 70hp outboard. When we went to the boat shop to buy one, there was something like 3 different designs he could have used. Subtle differences with each one with a profound performance effect when put into the water. I could only guess that with some research on the topic, impeller selection could be be based along similar lines. Low speed pressure generator, stock replacement or high speed/rpm combinations could be offered. Hell, they could develop a VATN or centrepital clutched version for those with WAY too much time on their hands.

 

My LD28 water pump arrived this afternoon. Yes, its bigger than the stocker, but not by a lot. I guess the tip speed of the impeller is significant, so with a diameter of 75mm versus 70mm for the standard unit accounts for the greater volume of coolant passed. The length, shape and angle of 'attack' of the individual impeller vanes is the same for both pumps.

 

Get out there and test your block coolant pressure for yourself and don't just take my word for it. That goes for the electric pump boys too. Maybe I'm missing something and my testing procedure just SUCKS.......or is it just that I have WAY too much time on my hands? :) C'mon, you can do it!

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I assume you did try to source the LD pump in Australia, I saw a thread and you mentioned you got it from Japan (?)

 

I didn't even try since I figured we never got anything in Oz with an LD28 donk.

 

Most of the guys over the counter here would probably say "What's an LD28 mate?" Didn't need to go there.

 

Cheers!

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This may be a bit off the line of thought here but in the Motocross world there is a company that makes aftermarket water pump impellers. Which are made to pump coolant more efficiently and more of it. Couldnt we take apart a normal L28 water pump and press on a better performing impeller and maybe make it to tighter tolerances to the front cover and have it tested to flow more efficiently. Maybe im off base but if it works so well for motorcycles why not for a car...

 

Who are they?

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I hear what you're saying and I want to thank you for your thoughts on the subject Daeron! :mrgreen:

 

You may recall that when I started testing, I connected my pressure guage to a cold engine, basically because I didn't want to be sprayed with hot coolant as I did my work. But it was an excellent starting point to measure the block coolant pressures with a cold engine and then to witness the changes to the pressure as the engine warmed up and the thermostat eventually open. I recorded the values in another thread. Even when the engine was cold and long before the thermostat was anywhere near open, I saw close to 10 psi pressures @ idle IIRC. Man, to be honest with you, I dont remember seeing any pressure on the guage when the engine was turned off after normal operating temp had been reached and yes, there certainly would be coolant expansion due to heat soaking, the very reason why the radiator has a pressure cap on it!

 

...

 

Get out there and test your block coolant pressure for yourself and don't just take my word for it. That goes for the electric pump boys too. Maybe I'm missing something and my testing procedure just SUCKS.......or is it just that I have WAY too much time on my hands? :) C'mon, you can do it!

 

Awesomeness on a stick, I just couldn't recall if you got a cold weather baseline pressure reading. One of my STRONGEST of my strong points is catching little stupid details that *can* slip through the cracks, and that is all I was trying to do (in addition to making sure *I* wasn't missing or forgetting something; obviously I was.)

 

I am very well aware that the impeller (propeller) shape, size, pitch and number of blades has all SORTS of subtle and varied effects, but I am wholly ignorant of all those subtleties and thier impacts.

 

I still want to say that the anecdotal evidence of hundred of electric water pumpers suggests some hole* in this, somewhere, but I never really thought I would be one of those guys anyway and this thread has almost certainly cemented my opinion on that.

 

 

*"Some hole" may well be a bunch of track cars using the pump (an the engine equipped with it) in situations that many many of us would call "limited use," which would mean there is NO hole.

 

 

 

Years ago, when I was still in school, my teachers always loved me because I asked excellent questions either for anchoring the subject matter in "reality," or expanding the subject matter ever-so-slightly beyond the scope of our present text or curriculum. I definitely also posted my query hoping to see if anyone was around who could school me about it with some encyclopedic post explaining why just about everything I've ever thought was wrong. :2thumbs:

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In short, Daeron made the same mistake 1FastZ did when making the statement 'the cap gives you pressure in the system, the pump only makes flow'...

 

As Oz mentioned, there is 10posi in the block at idle BEFORE any blanket pressure adds to the NPSH at the inlet to the pump. The pump imparts flow, to be sure, but the flow against the RESTRICTION of the thermostat or orifice or block internals causes that flow to diffuse into PRESSURE. Block pressure will be close to 40+ psi at speed. This is cold. Blanket pressure will add to this directly.

 

It is THIS pressure that combats the spot boilling phenomenon. Our heads are particularly prone to this in some way, as even with STOCK engines it's not unheard of to get runaway overheating in SoCal on even moderately temperate days with only a bad radiator pressure cap.

 

There is a reason Electromotive ran 3 bar + blanket in their big horsepower car, it fought that phenomenon quite effectively. The pump will add even more pressure to that. It's the differentiation between static pressure (the cap) and dynamic pressure (that imparted by the flow of the pump meeting restrictions.

 

Understand Electromotive increased the flow capability of the engine some 300%, and ran a 3 bar pressure cap. It's like the discussion on boost. Sure, you can boost to stratospheric levels and make 300hp at 15psi. Or you can port your head and increase flow to get 300hp at 8psi. If you have adequate blanket, and a properly flowing block and head, the electric pump may be all you need. But short of that static blanket, you will need the mechanical pump to force the flow and MAKE dynamic pressure where it's needed (in the block and head) to combat spot boiling and the results shortly thereafter.

 

The 'hole' you are thinking of is the addition of blanket pressure. Go look at some high dollar people running electric pumps in CONSTANT SERVICE (roadracing, not drags or short sprints) and you will find very high pressure radiator caps on their cars. They have the flow, and in this case the cap pressure is their insurance against spot boiling. If you run a standard cap, likely there is the possibility that you can run into problems with the lower flow of the electric pumps.

 

Wasn't GM using an electric pump on one of their V6's? If they have optimized the cores for flow, and were attentive to casting surface finish, this may be possible to do---when the OEM's start doing it, the technology has come of age for durability and warranty consideration. Till then, it's limited usage on lower output mills.

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Thanks for that. The information on the site is a bit light on but it seems that there are people out there doing some R & D. I guess it wouldn't be too hard to improve on a 45yo design. The shape of that impeller on the web site is so different from what is on the end of the 'modern' CSR WP, it's ridiculous!!

 

I believe the impellers are press fit onto the shaft of the stock water pump. Putting on another aftermarket impeller shouldn't be all that hard to do.

 

Moving lots of water at lower rpms could be the design criteria for one model (towing, stop start city driving, chronic overheating) another design could push water well at high rpms for racing engines. Then the owner of the vehicle could buy the most appropriate design for their engine.

 

Anyone interested? :)

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Here we go again making terribly flawed comments about a design that is old is somhow inherently flawed because we all know something NEW is automatically better than something old.

 

NOT TRUE.

 

I have discussed this with JeffP regarding the possibility of sourcing rebuildable seal/bearing packets for the pumps, and then having LD impellers 5 axis machined out of Stainless Steel. This would give us a pump that is basically 'lifetime'. The cost would be astronomical, but the advantage of 5 axis cuts over raw cast has been proven that you can get more flow simply due to the smoother surface. In some cases, the limitation of the castings is such that you can flow more because five-axist cuts allow for a thinner blade than otherwise possible, giving more physical clearance for the pumped medium to flow.

 

Other than metallurgical advancements (stainless steel) and more precise machining (five axis versus cast) you will see that water pumps today sold by OEM's are very similar to pumps sold 50 years ago.

 

You will also notice commercial pumps sold today are very similar to what they were 100 years ago. This stuff is basic engineering. There are no tricks here, you have a VERY versatile pump which millions of yen of development time went into to give best performance under various conditions. If the boys at Electromotive were able to cool a 1000hp turbocharged monster using an unaltered LD28 pump----er.... just exactly where do you think it has shortcomings?

 

Since I just gave a basic class to some operating engineers and roating equipment folks in Brunei this past Wednesday and Thursday, my brain was scratched back on the basics of impeller design. I tried to 'quote' the photos above, but unfortunately the 1mpbs (advertised) line here at the hotel is not cooperating.

 

Basically lets look at the two pumps and their differences. The LD pump impeller is larger in overall diameter. The LD pump has a larger center opening (or 'eye'). In centrifugal pump design this points to basic delivery changes. The eye (or impeller) diameter dictates flow---the larger the center of the eye, the more flow the pump will produce. In turbo terms this is referred in some circles as your 'volume tips'---when you get a rub in these areas your capacity goes down though you still normally make natural surge point like the machine did before the rub. Seond, is the pressure tips---or outer diameter. The larger outer diameter dictates more pressure. A rub or clearance in this area will mean lower surge point (earlier cavitation, at a lower pressure inside the pump).

 

The LD has both a larger eye, and larger outder diameter to the impeller. Meaning it has both more flow, and is capable of producing more pressure under identical conditions as the non-LD pump.

 

The biggest contributor to any of this is CLEARANCES. If you don't have optimal clearance from the vanes to the pump volute, or casing, your capacites go all to hell. Clay up a pump and check your clearances and you will see they are WELL wide of optimal for best pressure production. They may work at lower pressures and higher volumes, but tightening them slightly (tricky to machine when it's all assembled, eh?) can make for boosted performacne. Build a pump dyno---take a 5HP engine, belt it up to a pump mounted to a front cover, and give yourself some pumping capacity from some old 200L drums. I think you will find the 5HP pump will be a little shy once you start spinning it up there, but by simple experimentation with clearances you will see visible flow characteristic changes and resulting increases in pump horsepower requirements.

 

You are chasing a red herring here, you are going after parts without understanding how they all work together. The design is sound, how it is presented in a mass marketed package is what needs to be addressed. Again, Electramotive used stock Nissan Pumps, but they did not leave the blocks, heads, theromstat, etc alone. They optimized flow, and ran a belt driven pump. If it cooled their beast, it will cool yours.

 

Custom impellers? Really with the flat performance curve you will find this impeller design has, you are oging to see it's not required. It's not a high tech design like a turbo impeller. It's a centrifugal pump. Talke a look a gorman rupp, worthington, flowserve, dresser rand, sunstrand, any of the big manufacturers out there. Get into their design engines and compare the impeller design sizes with what they have for commercial offerings. you aren't going to change the world using the stock front cover. You wanna sling a completely independent pump housing off one side of the engine, then you may accomplish something. But working with the stock stuff will be an exercise in futility until you start gaining a grasp of the interplay between the impeller and casing clearances at a minimum. Impeller design IMO was optimized long ago. It's just so many people look for a short-one-shot magic bullet solution rather than sweating the details of proper flow management of fluids through the engine they miss the answer that is there in front of them. The pump is not the problem, guys. It never was.

 

What those bike kits are giving you is an impeller like what we ALREADY HAVE in the L-Engine to replace cheapo stamped sheetmetal pumps that OEMS like to put out there these days. It's apples and oranges. The bikes have a pump design that is not optimized, our engine does. Look at that impeller in the last link, and compare it to the photos of the LD and stock L engine impellers. Because a Chevy has a bad pump design doesn't mean a Chrysler does as well. Same goes for bikes and Datsuns. Pump clearances can be addressed first, without putting on an impeller that is investment cast (slightly smoother and more precise shaping)---the ultimate pump impeller will be a SS Five-Axis Milled design and you will pay accordingly. But what will you get for that cost? Not much if you don't FIRST address tip clearances. And once you do, ask yourself the question "with all this new pressure and capacity, do I really need to improve further?"

 

At some point, this becomes a tossers game. Use your head more, and then TEST. Mental gymnastics only work if the mat you fall on isn't covered in broken glass...

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Hi Guys,

 

I have read through a fair amount of this post. Is there a problem with JohnC's #28 cap to prevent hot spots in the head?

 

I am not sure how JohnC determined #28 to be right. That's not a real common cap to pick up.

 

This post has gone on over 2 years with 18 pages of posts. I have read some of it but by mo means all of it.

 

The LD28 pump looks interesting as well.

 

I currently race a 240Z in The 24 Hours of LeMons and have had a 240Z driver.

 

Back in the later 90's my driver was a 72 with a L26. I live in Houston, TX where it's hot and humid most of the year. The old 240Z with its stock cooling system did okay most of the time. The only time I really had cooling issues were on 90+ degree days sitting still in traffic with the A/C on. I was in college at the time so I was far from wealthy, I not wealthy yet for that matter. The car probably could have used a new radiator but didn't leak so it seemed okay to me at the time.

 

The early 240s just weren't designed with air conditioning and real hot weather in mind. As long as the car was moving and getting decent airflow across the radiator, the car did okay.

 

So I am not sure what everyone is doing with these cars that demands such exotic cooling system modifications.

 

The car I am currently struggling with is the LeMons Z. It's a 73 with a small chamber E88 (like and E31), a C cam on an F54 block. We ported the intake and head. We run 280ZX ignition, 34 degrees total timing and 3-row 280ZX radiator along with a Nissan Motor sports header. I gutted a 180-degree thermostat so it's just a restrictor plate now.

 

A side note, I hope to dyno the car since it's only non-stock part is the header to see what kind of power you can make on stock L-Series parts.

 

I am running an early 240Z harmonic balancer now, which is smaller than the later ones. I opted for that because I was concerned the water pump might be cavitating at high RPMS and the smaller balancer would slow it down. I have done no testing; it's just a concern.

 

We tend to keep the car above 4000 rpms and try to do so for a full tank of gas. Refuel and do it again for up to 8 hours. That's the goal, it just rarely happens that way.

 

This post along with the posts about high compression L-series motors and ignition timing have all collided in my motor.

 

Along our journey down the path of endurance racing a cheap Z we have hit a few speed bumps. Many of which seem to be installer error from working on the car in the middle of the night. So some problems have been self-induced.

 

At this point we have built a second car with a similar motor.

 

Both cars have blown head gaskets. The second car blew its gasket early on in its first race due to an uneven block deck. The engine got swapped out and has not been put back in.

 

The first car has run 4 races and we were fighting engine temps for several races with a lot of head scratching.

 

After our fourth race and a definite head gasket failure, we discovered the gasket sealing rings were burned on #1, #3 & #6. Cylinder #5 is fine. I believe the failure is due to detonation. So I am not exactly sure about the idea of local hot spots on #5 resulting in detonation and head gasket failure.

 

I knew we experienced detonation during the 3rd race, I heard it. I am just not sure for how long or exactly why. We retarded the timing which cut our power and power band (like BRAAP says) but the temp steadied. We were getting unexplained varying timing readings too.

 

We were dealing with several cars at that race too. The first car was not perfect but it was better off then any of the other cars we were dealing with so it probably did not get the time it needed to properly understand and resolve it's issues. It did finish the race though.

 

That race was in New Orleans in June. To say it was hot was an understatement but I do believe we were below 100 degrees that weekend. At high temperatures like that, we expected higher engine temps too so that did not help with analyzing what was going on.

 

I was concerned that the high temps may have caused the air to be thin enough to give us a lean condition, which would promote high engine temps and detonation too.

 

Getting back to the general implication of this thread is detonation occurs from local hot spots in the head that is caused by suspected cooling problems, particularly on cylinder #5.

 

In our case, we are running around 10.5:1 compression which increases the probability of detonation due to tuning. Which gets into issues brought up by BRAAP about timing and head and block combinations. With 34 degrees of total timing, the car just flies. If we go lean, we can have a problem. Those are factors that affect engine temp along with the efficiency and functionality of the cooling system itself.

 

The 280ZX distributor is probably the best stock arrangement we can run but they are old and reliability is questionable.

 

While we do not use the vacuum advance, I wonder if it wasn't moving around a bit and causing our timing problems.

 

After our race in New Orleans, I replaced the distributor with a reman and our power seemed a bit better and our timing readings were more consistent. I still swore we had more hesitation in the mid-5000 RPM range and the car wasn't pulling like it did in the first race.

 

During our 4th race we realized a very odd phenomenon. The car stayed cooler at higher RPMS when the car was run harder.

 

During a test day to check the car out and do some wide band tuning before the 4th race the car seemed to stay cool enough but we did get some variation in temp. It heated up a bit in the slower twistier parts of the track and cooled down under harder accelerating loads. It was leaner in mid-range RPMs than at idle or during high-RPM heavy loads. This occurred more often in the twistsier parts of the track. This is the reverse of what is expected.

 

We did not notice this much until we took some slower laps looking at proper lines around the track. Then we started getting a bit hot on the stock temp gauge.

 

The infrared thermometer showed much lower temps than the stock gauge and we weren't boiling over or anything. The stock gauge was way up though. Our conclusion, either the sending unit or gauge was wrong. Conflicting data makes it real hard to figure out what's going on. We did not run any more sessions that day.

 

Later we replaced the sending unit and installed a second mechanical temp gauge. Ran the car a good while and everything seemed fine.

 

It's like the boat in the driveway; it's always perfect in the driveway. Get to the lake and something seems to have gone south along the way.

 

During the Test & Tune for the race, we are running 25-30 minute sessions with no problems.

 

Once the race started, the engine started getting a bit hot about 40+ minutes into the race. You start finding lots of issues don't occur in a 30-minute sessions when you try and do an enduro.

 

Further disassembly and inspection led us to discover broken ring landings on cylinder #6 and the magic head gasket repair stuff in the crankcase. The Blue Devil not only failed to repair the leaking head gasket, it looks like it got into the oil and damaged the bearings too.

 

Broken ring landings plus the burned sealing ring are both indications of detonation in #6. That was the cylinder that finally burned it's way into the cooling system.

 

We have resurfaced the head. Swapped to a different short block, just because I got a better one. Replaced the rings and bearings and basically rebuilt the motor.

 

We put the motor back in the car last weekend and discovered one of our crappy back up radiators was not functioning so well. It got swapped for another old radiator that appears to be cooling properly.

 

Yesterday we took the car to the track to test it out. We kept the RPMs below 5000 for break-in. With a #20 radiator cap, 3- row 280ZX radiator, 180 degree gutted thermostat, OE style water pump and small early style harmonic balancer we ran a pretty steady 165-170 degrees. We ran about 4-6 30-minute sessions, I didn't count them.

 

In case this matters, we run a hose from the rear of the head to the thermostat housing and no heater core.

 

The only cooling problem we had was when the lower hose got to friendly with the alternator fan and cut the hose. We swapped the hose and everything was fine.

 

Hopefully we have nipped our problems in the butt. Only time will tell.

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