Attn flat top 2.8 with E31/N42 head guys

[BRAAP]

No head mods, hot cam, just bump up the CR from 8.3:1 to 10:1. That is all I'm talking about. Set the max advance on both motors just before detonation. You will find that the high CR motor produces at least 20WHP more than the motor with a stock CR. I'm not guessing here, I've made the measurements that prove this. Has anyone else?

 

Pete,

I can't argue your measured gains. They are what they are. The only possible solution I can come up with is that other factors are at play, not purely C/R alone. The math doesn’t support such a power increase.

 

At 140 wheel HP, to go from 8:1 up to 10:1, A full 2 point bump in compression, (3 tenths of point more than your bump in C/R) is a 6.5% gain in power, which at 140 WHP is a gain of 9.1 HP, not 20, especially if you retarded the timing by any amount at all. With a 20 HP gain, I believe other factors at play delivering that gain, especially if the ignition timing was also retarded.

 

Courtesy popularhotrodding.com

[z-ya]

Paul,

 

You are probably right. I didn't check the compression on both engines, and certainly the AFR on the 8.3:1 motor was too rich. I'd still like to see what kind of numbers other have seen with similar setups.

[kolonelklink87]

I also would like to see more raw data comparisons...

kudos all round guys for putting up some awesome discussion thus far. its excellent to see something so fundamental as this to engine design being debated with data and formulae rather than gut instinct and intuition

keep up the good work:icon14:

[Daeron]

Also, if I understand the entire argument behind the higher-quench heads, the ultimate extension of braap's point is that with a more ideal combustion chamber (shaved P-series) you would still be at a similar compression ratio as your 44cc N-series, but this change in cylinder head design would allow you to advance the timing further, tuning the car into more power.

 

The key element is "tuning the car into more power." More than your measured power output at 10:1 compression presently. There is power to be found with compression, and power to be left behind with timing. The cylinder head change might not itself be enough, the cooling mod might not itself be enough, the entire affair may well in fact be a Quixotic attempt chasing a theory that works better on other motors than on ours (in which case, Pete, your setup might well be preferred simply for ease of dialing the power in.)

 

The actual combustion characteristics of the different heads, and their effective contribution to detonation resistance at high compression, are up for debate. But if you could get a head/piston combo on there that gave you 10.x:1 compression and let you run 93 octane to dial in higher advance, you would see more power.

 

Edit:

Awesome Freakin Thread!!!

[htownz]

I've been racing a 1973 240Z in the 24 Hour of LeMons for just over a year now. The first car has 4 races on it.

 

It has an early E88 (E31 like) head on an F54 2.8 liter flat top block.

 

It should be around 10.5:1 compression.

 

The cam is unknown but some kind of regrind.

 

The head and intake has been ported and gasket matched.

 

SU Carbs

 

The flywheel and balancer have been lightened.

 

I run 280ZX distributor and ignition.

 

I've got an old crappy large tube Nissan Motorsports header with 3" exhaust.

 

280ZX 5 speed with 3.90 R200

 

280ZX radiator

 

When running right, it is a bat out of hell.

 

Right before seizing the motor it made a whopping 129 RWHP. We knew something wasn't right and couldn't quite figure it out. Then the motor siezed, make sure all your bearings are in right. We raced the car 20 hours with no oil to one rod bearing due to the center main being upside down. Royal Purple assembly lube is some good stuff.

 

We have had all of kinds of issues, the most recent being a blown head gasket. It looks like we may have had a detonation situation which burned the sealing rings on a couple of cylinders of the head gasket then started on the rest of the gasket.

 

In my opinion/experience, once you start running in the 10+ compression range things seem to be less forgiving.

 

The cooling systems on the early cars are less than impressive.

 

One problem on the L-Series is the ignition system. There are various systems over the years. I think the self-contained HEI type systems on the 79 and up cars are the best. They are still old. So one problem with high compression is the need for stable ignition.

 

According to Rebello, the ignition will retard at high RPM. He says you can see it on a dyno. I'll take his word for it.

 

Aside from ignition, you gotta have correct and reliable fuel delivery. Running a wideband on the track showed a lean midrange condition. The car has happier being run hard than taking it easier.

 

We have had an issue sucking the lower radiator hose flat. May have been an issue with the bend in the lower hose or it may have been an early sign of a leak in the system. That leak in the system being a slight leak in the head gasket.

 

We have added a second 240Z with a similar motor and it blew a had gasket right away due to an uneven block desk

 

We aslo put an N47 on an F54 block in a 280ZX 2+2. It blew a head gasket too once we got a decent distributor in it. Reliable ignition once again was a problem.

 

Aside from all that, I've seen a few cracked balancers as well. Turns out 100 ft-lb ain't really enough. I have been told to ditch the slinger and tighten to 150 ft-lb.

 

In summary, I can tell you a high compression L28 is a blast to race.

 

Unfortunately, I can not attest to it's reliability but I'll keep trying.

[ozconnection]

It seems you guys have a bit of a QC problem unfortunately....

 

Interesting read and perspective though.

 

Cheers

[Zmanco]

So one problem with high compression is the need for stable ignition.

Would you elaborate on what you mean here? Why does a high compression motor need a more stable ignition than a low compression one?

According to Rebello, the ignition will retard at high RPM. He says you can see it on a dyno. I'll take his word for it.

Was Rebello referring to the stock 280zx dizzy, or was he making a comment that a high compression L engine doesn't need as much advance at high RPM? Or perhaps he meant something else?

[letitsnow]

Would you elaborate on what you mean here? Why does a high compression motor need a more stable ignition than a low compression one?

Was Rebello referring to the stock 280zx dizzy, or was he making a comment that a high compression L engine doesn't need as much advance at high RPM? Or perhaps he meant something else?

 

It takes more energy to ionize the air in the gap of the plug in a high compression/high boost engine.

[htownz]

Would you elaborate on what you mean here? Why does a high compression motor need a more stable ignition than a low compression one?

 

Was Rebello referring to the stock 280zx dizzy, or was he making a comment that a high compression L engine doesn't need as much advance at high RPM? Or perhaps he meant something else?

 

I left out some details, a lot of details, before to try to keep the post a bit shorter. Since inquiring minds want to know, I'll give you more info. Unfortunately, it jumps around and it's loooooonnnnnnnngggggggggggg.

 

Both 240Zs have been running Premium pump gas and I think the 280ZX was the same.

 

All the cars I mentioned have been running the 280ZX distributor. Turns out you can run an 83 on the 79-80 module too.

 

The 240Z with the E31 had Petronix in a 240Z distributor but it burned the module. Turns out, if you leave power to the module with the engine off, and the exciter and pick-up are lined up, it fries itself. Didn't figure that out until the second unit fried itself.

 

So we threw in one of the spare 280ZX distributors and all three cars have been running 280ZX distributors since.

 

The 240Z with the E31, blew it's head gasket at it's first race in New Orleans due to someone getting a bit to happy with the magic gasket removal wheel on the deck of the block. Since then, it's been running a L24.

 

I am not sure what the technical part of why higher compression results in a higher probability of detonation. Just that I have experienced this. Lower compression seems to be less sensitive. With higher compression, the air fuel mixture is more tightly packed. In any case if you light the fuel earlier, it has more time to burn which means you get more complete combustion and power out of it.

 

With a Wideband installed, I have been able to observe the affect of timing changes on the Air Fuel ratio. More timing will be leaner. I am sure there is a limit to this. I saw this pretty clearly on a Chevy V8, don't recall with the L-Series being as obvious. Wideband tuning is still new to me so keep that in mind.

 

As BRAAP has said repeatedly, if you retard timing you are leaving power on the table.

 

We like to run about 35 degrees total timing. No vacuum advance.

 

The more timing we run the happier the car seems to be as long as we don't have detonation. I have not noticed the detonation without the car being under a load. It's more likely at high load and high rpm situations, like 5000+ rpms in 3rd gear on up.

 

My car was experiencing mild detonation during its 3rd race in June in New Orleans. We were basically at sea level but it was hot outside (well into the 90s). The car was running okay but hot. No one else on my team noticed the detonation just the temp gauge going up.

 

We were racing a high-compression Crap Can in 90+ degree weather for 6-8 hours in a day. There are all kinds of variables in this situation.

 

I swapped the radiator with another used back up and it was still running hot. We were just managing it by running the car less aggressively. Then I got in and noticed the detonation. I dialed out some timing, the detonation went away and the engine temp was stable. Unfortunately, it felt like we had a rev limiter around 5500. That was really in the middle of the engines happy place before with it pulling well over 6500.

 

I did notice that at sustained higher rpms the lower radiator hose was flattening at the 90-degree bend near the radiator outlet. I think I noticed this while messing with the timing after the radiator swap. That may have been our temp issue but we had not noticed this problem in the previous two races. It had the same water pump and hoses from the first race, which were new for the first race. The radiator had seemed to be working fine too. I tried trimming the hose and using zip ties to improve the bend. I was at the race and did not have another hose to try at the time.

 

Talking with guys at the parts house yesterday about radiators, hoses and the Blue Devil magic head gasket repair. They said according to Gates, if you are flattening a hose, you have a leak. We were not leaking anything on the ground and did not have any noticeable coolant lose. Maybe the head gasket was compromised and we did not realize it.

 

The motor is currently disassembled and I am putting together another motor.

 

I first noticed the engine temp issue doing a practice/test and tune at Texas World Speedway in May. I don't remember having the wideband in the car. It was the first time I actually drove the car after the engine failure in February at Harris Hill Road between the first and second race and only minutes of run time after the dyno. We left the dyno and went straight to the track that day. We attributed the slight bit of noise we heard at the dyno to valve train. Less than 1 full lap around the track and the noise was worse. As we coasted into the hot pit lane, I realized the engine died. Turned out it seized. Further inspection revealed the incorrectly installed center main resulted in the seized rod bearing next to it. The center main was fine.

 

I did not drive the car during the second race due to transmission followed by clutch issues topped off with a separating strut housing. To me at TWS, the car did not seem to be making power like it did in the first race. I suspected tuning at the time but could not get the car where I thought it should have been. I do not recall any engine changes between the second race and going to TWS.

 

February was a cold race and it was pretty warm at TWS in May.

 

Everyone thought the car ran great in the second race but something was going on at TWS. I could not figure it out. Most of our time was being spent building on the 2nd 240Z and the first car seemed okay. Conclusion, we would figure it out at the track in New Orleans.

 

Additional info, I replaced the coil with an MSD Blaster coil at the track in New Orleans and bypassed the resistor. Car still ran about the same maybe just a bit better and was not pulling like I thought it should at high rpms.

 

The 280ZX with the N47 on the F54 was also having power problems, which they thought was a lean condition due to a fuel delivery problem. I think they were cutting out around 3500 rpms. Sunday, their distributor was changed for another back up and the car ran great until it blew the head gasket.

 

I changed my distributor out after the June race and the car was pulling much better at MSR Houston during the Texas Z Party two weeks later. I still did not feel like we had the power of the first race but the car was better than it was in New Orleans. It was one of the faster cars at the TZP. The temp seemed okay but I did notice it creeping up a bit late in the 20ish minute sessions.

 

So two cars running 280ZX distributors had power problems, which appear to be related to some part of the ignition system contained within the distributor assembly. Both cars ran fine with no load but stumbled under a load. Maybe this is some kind of module problem. I haven’t figured this out yet.

 

During a tuning session before the 4th race, the stock temp gauge showed high engine temps under mild loads. When checked against my infrared, engine temp seemed fine. Under hard loads while using the wideband, the engine temp was fine and our A/F seemed okay. When we started making some milder laps looking at lines around the track was when the temp started going up and we were a bit lean too. We saw increases in engine temp in the twistier parts of the track, which immediately came down during hard loads on wider turns and the straights.

 

The lean condition indicated by the wideband seemed to correspond with the temp going up.

 

More info, we have to run straight water. The gauge exceeded 220 but there were no signs of excess pressure in the system. The infrared temps looked fine. Conclusion bad gauge or sending unit, the gauge is pushing 40 years old now. So I added another half turn on the carbs, if I recall correctly. That was the last session we ran that day.

 

So before the 4th race at MSR Houston in October, we changed the lower radiator hose to a 280Z lower instead of a 280ZX lower which we thought would solve the flattening at the bend in the hose. May have done some additional tuning (I can't recall) and installed a new temp sender and an additional mechanical temp gauge. The two gauges seemed to be about the same but I trusted the mechanical gauge more so maybe the old gauge is still okay.

 

Everyone was happy with the power during practice and for the first 30-40 minutes of racing under green. Then the temp started creeping back about 45 minutes into the race. It would heat up in the slower part of the track but come back down under hard loads again. This is just freakin' baffling!

 

We struggled all day to keep the car under 210 degrees. I wanna say it was still pretty warm in October.

 

The 2nd 240Z running an L24 and 4 row radiator barley saw 140 degrees.

 

The 280ZX did not run the October race.

 

Back to the E88/F54 car:

 

At the end of the day Saturday, the oil looked good, no signs of water. We did not even need to add any oil after 7+ hours of racing. At some point we noticed very small bubbles in the radiator. That was a sign of a leaking head gasket. A compression check showed we had very low compression on 6, lower compression on 3 or 4. We were maybe around 180 psi on the good cylinders where we have been closer to 210 psi on the initial build. We figured the high engine temps had hurt the rings and the head gasket was compromised. We did have to come in and add water at one point in the afternoon cause the motor was not cooling down. We figured it went into the overflow tank. The car stayed cooler under heavier loads than it did under milder loads.

 

We decided to try the Blue Devil instead of changing the head gasket since we figured the head would need to be machined to get a good seal from the head gasket. The gasket only seemed to be mildly compromised. Initially, the Blue Devil seemed to stabilize the engine temp as it idled for well over an hour at a steady 180 degrees.

 

Well, we should have changed the gasket.

 

In the morning I replaced the plugs and changed the lower radiator hose to one with a spring. The car sounded good and we sent it out.

 

Almost immediately under race conditions the temp went up and would not come back down. We parked the car within 15 minutes. I took it out right at the end of the race to take the checker. It seemed fine until we had a Yellow followed by the virtual stop of coming in after the Checker. The temp skyrocketed and I couldn't get it down. It probably hit 240 waiting in line to come off the track.

 

After the race, the oil looked like a milk shake. It looked the Blue Devil even got in the oil and left little bits of grit. Did I mention we should have changed the head gasket Saturday night?

 

So where do compression, ignition, temp and head gaskets collide? I haven't quite figured out the chain of events but they seemed to have come together and had a field day in my motor.

 

There is a chance the FelPro gasket we used after the engine seized did not properly seal. A Stone gasket with Copper Coat will just about glue the head to the block. A FelPro gasket does not appear to benefit from Copper Coat.

 

Back to retarded timing and engine RPMS:

 

As many other people have posted, they want to run 35+ degrees of total timing. Say they set it around 3000 RPM.

 

That would seem fine and all but the timing can/will retard at high RPMS, say 6000 and you will not be running the 35 degrees you set at 3000. That's what I gathered from the info I got.

 

So the retarded the timing should decrease the odds of detonation. So why was I getting detonation?

 

I don't know about all that for sure since I do not have a way to measure timing with the engine under load at high rpms. I can measure A/F with the wideband at high rpms and that seemed fine. We seemed to be getting a good burn.

 

So one issue seems to be that the total timing should be set closer to the red line. I haven't tried this yet. The motor is currently in pieces.

 

It is my understanding that just about all distributors retard timing at some point. Some may be worse than others. A distributorless ignition system is probably more stable and reliable but I have no personal experience with that.

 

The theory on my engine’s failure is this: we experienced detonation for some reason in February. It compromised the sealing rings around the cylinders in the head gasket. Overtime the cylinder combustion slowly burned away at the rest of the gasket. Cylinder 6 got to the cooling system first. This began to pressurize the cooling system. This was where I think our engine temps problems started. It was a slow process so it did not initially seem like a catastrophic failure like the other two cars. The 280ZX literally shot water right out the side of the motor and all over the car.

 

Assuming my head gasket failed due to detonation, what caused the detonation? A carb issue or maybe an igniton issue?

 

This is a massive amount of information that I have struggled to process. It is giving me intellectual indigestion. Enjoy.

[letitsnow]

It sounds like you should try a few things, water wetter, drilling/tapping above 5 and 6 and returning them to the thermo housing(look at the sticky) and maybe knocking the compression down just a bit. The first two are relatively cheap and probably worth a shot just to see.

[ozconnection]

 

Too common for the L-6 to have to back off ignition timing due to the compression ratio. I have been preaching for some time that the power lost due to the retarded ignition timing to keep it from rattling, for greater than the power gained by the bump in compression ratio. Gain of maybe 7-10 HP max for the compression ratio bump over the paltry 8.3:1, but over 20+ HP lost in retarded ignition timing! open chamber L-6 heads, (E88, N42, N47), have their optimum non octane limited spark advance in the 38-42 degree range. If you can't get 38 degrees total ignition advance above 3500 RPM at WOT, (N/A), with E-88, N42 or N47 head because it is rattling, you are laving HP on the table.

I'm not saying that 10.4:1 comp ration can 't be done and still have adequate ignition advance, it has been done but most of those combination rattle and and can't run full ideal ignition advance.

 

In short, I do not endorse L28 builds with flat top pistons and E88, N42 N47 heads for ANY street application unless a thicker head gasket is used to drop the compression down to below 9.7:1 or so. If flat tops are is on your must have list, then I recommend the P79 or P90 head.

 

Great summary!

 

I tried your suggestion of advancing the timing and it seems that I was already 'at my best' with a static of 15 degrees, 35 total. Any more and the engine would rattle when I was deep into the throttle. Did I notice any power gains? Well I did a G-Tech test and there were no changes detected by the instrument. Personally, I felt that the engine had a little more torque at part throttle but that didn't translate into quicker or faster times over the 0-100km/h sprint or 0-400 metre run.

 

To be totally honest, the advance that you were suggesting seemed somewhat ambitious but I'm always open to reasonable suggestions and this one was quick and easy to try out. Oh well, didn't work. Just curious though, what temperature thermostats do you run with the amount of advance you suggest?

 

You also linked this idea to a thread that talked about cylinder head/engine block coolant flow. I just couldn't find much reference to coolant pressure inside the block and head. I mean, the radiator cap will release at about 14 psi but the pressure in the block and head channels should be optimally higher at arounda 30 psi. The combined use of 'restrictors' and varying the water pump speed (great if you can use of one of those electric L series water pumps) could potentially be the key in reducing the speed at which the coolant travels around inside the engine and the restrictors helping to adjust for block and head coolant pressure. The correct coolant pressure AND flow will drastically help to stove off the formation of steam pockets, the cause of local hot spots and detonation. If that still doesn't quite keep the engine temp. stable, time to add a larger radiator. The cooling system will then operate close to or at maximum efficiency, regardless of the engine speed (with the electric pump).

 

How many people have attached a pressure guage to the coolant passages inside the head or block to see what they are and adjusted them to get 30 psi or so??

 

How many people have played around with water pump pulley sizes to get the water pump to spin at its 'best' non cavitational speed? Has there been a change to a different harmonic balancer with a differently sized pulley, changing the 'ratio', either slowing or speeding up the water pump speed?

 

I have a few things on my 'to do' list for next weekend it seems. Can't wait to discover if work needs to be done to something that I assumed to be right in the first place!! Maybe then I'll be able to run 42 degrees total advance (or 10.5 or more compression with a different cylinder head).....who knows??

 

Top thread, this is really thought provoking!

[BRAAP]

Great summary!

 

I tried your suggestion of advancing the timing and it seems that I was already 'at my best' with a static of 15 degrees, 35 total. Any more and the engine would rattle when I was deep into the throttle. Did I notice any power gains? Well I did a G-Tech test and there were no changes detected by the instrument. Personally, I felt that the engine had a little more torque at part throttle but that didn't translate into quicker or faster times over the 0-100km/h sprint or 0-400 metre run.

 

To be totally honest, the advance that you were suggesting seemed somewhat ambitious but I'm always open to reasonable suggestions and this one was quick and easy to try out. Oh well, didn't work. Just curious though, what temperature thermostats do you run with the amount of advance you suggest?

 

….

Top thread, this is really thought provoking!

 

I can't say for sure this is true, but I do feel that the knock from the advanced timing is limiting your power gains past 35 degrees. If the knock could be subsided to allow a little more timing advance, I think there is a little more power left o the table. At 35 degrees already, probably not much more left, but possibly enough to be measurable, probably not enough to feel.

[ozconnection]

I can't say for sure this is true, but I do feel that the knock from the advanced timing is limiting your power gains past 35 degrees. If the knock could be subsided to allow a little more timing advance, I think there is a little more power left o the table. At 35 degrees already, probably not much more left, but possibly enough to be measurable, probably not enough to feel.

 

I can feel the difference at part throttle only, but nothing much changed at WOT. (Can a G-Tech tell the difference between 125 and 130 rwhp, for example when pushing along 3200lbs of Cedric!? )

 

I'm curious about the thermostats because of the amount of temperature variance there is between the ones I've seen (and used) for L engines. 161, 171 and 181 degrees F are available to me here in Sydney. I'm currently using a 161 degree unit. My factory temp. guage stays just on the cool side of halfway. The others move the dial to midway with the 171 thermostat and to the hot side of halfway with the 181 degree thermostat.

 

My point?

 

Can you put in a different temperature thermostat and notice a performance difference to the engine? Should the high compression guys who are having knock issues play around with different temperature thermostats in an attempt to be able to run with more total ignition timing?

 

Hmmmm, I seem to recall from my own experiences on the dyno that I had a hot (181 degree) thermostat in the car when I put out my highest power figure a few years ago. I changed it some time later and didn't really give it too much thought....until now!!

 

Hmmm, its not too late for me to find some this afternoon........

 

What do you guys think?

[BRAAP]

I have always ran the 160 F thermostats in my L-series engines and even my performance Small Blocks. I have no proof or theory to support that as the way to more power other than I remember reading Smokey Yunicks work from years gone by and recall he said that cold water and hot oil always made the most power, so I followed that advice and applied to my engines.

 

In the case of the detonation sensitive L-series, they seem to be more tolerant of fuel quality, and ignition advance when they are colder vs hotter, for that reason I would lean toward running a colder thermostat. (Sort of follows along my theory of the coolant flow not being adequate in the head so cooler coolant in the head should help to reduce detonation?)

 

As an aside, in the late '80' and through the mid nineties, (maybe even still today with OBD-II?) privateers were finding that running colder thermostats in their factory EFI cars of the time was allowing the engine to run colder which forced the ECU to run a little richer and in the case where ignition was also controlled, the ECU ran a more aggressive ignition timing as well, which showed up as more power i.e. fuel and spark maps for normal operating temp was emissions based and very conservative during the OBD-I era, and forcing the engine to run colder would allow the ECU to run slightly more aggressive maps. Not sure what this bit about late '80 EFI cars has to do with this topic as we already have control over the fuel and spark timing, just thought I'd throw it out there.

 

Sorry for the tangent, I get gabby after a beer..... or two.

[ozconnection]

I like to challenge convention and will ask the question: Does a cooler thermostat benefit the running performance of the engine?

 

OK, the way I see it is a cooler thermostat opens at a lower temperature. At that point, water is allowed to circulate through the radiator etc. The temperature of the coolant at that point is less because it hasn't had as much time to scrub off as much heat from the engine. But probably more significant is that some of the coolant pressure needed to keep the engine from forming steam pockets is released by the thermostat opening 'early'.

 

So, can one assume that by increasing the opening point (temperature) of the thermostat, there is more time for the coolant to absorb the heat from the engine whilst also maintaing a higher coolant pressure in the coolant passageways around the block and head?

 

Or does it make a difference at all when the thermostats are open in both cases?

 

I managed to also find a 190 degree thermostat. Seems I got it a bit wrong, the 160 degree unit is not listed as a stock temperature thermostat.

190 degree cold climates

180 degree normal

170 degree tropical climates.

 

My guess is that if I were to use the 190 degree thermostat, my engine will warm up more quickly. Less wear can only be a good thing.

 

Engine oil needs to be around 95 degrees celcius minimum from what I understand. To me it kinda makes sense to keep the coolant close to oil temperature when not at WOT for a streetcar. Then when you open the throttle up, temperature of the oil is where you want it, it hasn't cooled off from slow rpms and closed throttles/low loads.

 

I'm willing to try this out during the week. After the change, I'll see if I can't advance the timing further. Call it an experiment if you like. The thermostat cost me AU$13.00, about US$11.70. That's not much!! Coolant and gasket I already have.

 

Cheers!

[Daeron]

So, can one assume that by increasing the opening point (temperature) of the thermostat, there is more time for the coolant to absorb the heat from the engine whilst also maintaing a higher coolant pressure in the coolant passageways around the block and head?

 

Or does it make a difference at all when the thermostats are open in both cases?

 

Point: Colder water absorbs heat more rapidly on contact than warmer water. the greater temp differential, the greater rate of heat transfer.

 

Point: Any thermostat, or even a thermostat gutted into being simply a restrictor plate, acts as a pressure differential point in the cooling system. The pressure is higher "before" the thermostat than it is in front of it, because the pump works against this restriction and is pushing water through the engine into the thermostat housing, through the restrictor. So even wide open, at a colder temperature, a thermostat in the housing is MUCH more than pulling the thermostat altogether.

 

Now, my thinking is, I run the lowest T-stat I can find (because I have read the points braap made above, made by MANY others, and also because I live in S. Florida. Its 83 degrees out right now on December thirteenth in the rain at 2 AM.) and use the coolant with the highest rate of heat transfer that is practical in the situation. That Thermostat, even when wide open, restricts things enough that the constant flow of my water pump (often at high RPMs) is inducing plenty of pressure at the high point, which is the system BEFORE the thermostat.

 

I don't know how much weight you want to put in my experience; I said "practical" about coolant before because most of my L6 miles driven and owned are on a bone stock N42/N42 L28E and "practical" meant "water. I can always flush the thing out, and its gonna get rebuilt eventually anyhow." But my points stand.

[ozconnection]

I was, until recently, an OH&S officer at my work. One poster I put up on the wall I remember particularly well.

 

Oxygen + Heat + Fuel = Fire

 

Remove any one of these and the fire cannot exist.

 

Sure the spark plug initiates the 'fire' in our engines, but what happens to that fire following initialization? The chamber has just been blasted a relatively cold charge of air/fuel and the spark plug fires for only a fairly brief period of time. To continue the combustion process, heat is needed in the chamber. What temperature (and pressure) is best at that point?

 

To investigate this, I'm suggesting we play with not only the ignition timing point but also the surrounding ambient temperature (and pressure of the cooling medium) around the combustion chamber to try and get to where we want to go.

 

To quote the characteristics of other engines is taking a shortcut to potential misinformation. We need to explore the characteristics of our engines for themselves. Even if I find my ideas to be heading in the wrong direction, at least I can say I've done it the Aussie way and "Given it a shot!' Friends, what do we have to loose by trying?

[Zmanco]

I'll throw one more thought out on the thermostat issue: how will the engine be run? If it's just an occasional burst of WOT on the street, then I can see the benefits of a lower temp thermostat. But if it's sustained WOT, such as on a road course, then I don't think it matters without other changes to improve airflow through the radiator. The stock setup, regardless of which radiator is used, is likely to see the water temps rise above any of the thermostat temps being discussed after a few laps. Once the thermostat is fully open, the temperature at which it opened no longer affect the final steady state operating temperature.

 

I used to run a similar setup with .030 flat tops, N42 and mild cam and couldn't exceed 35 degrees total advance, and on track days, had to run an ignition table where I retarded between 4k and 5k about 5 degrees or so. With the 4 core MSA radiator I routinely saw water temps in the 210+ range by the end of 20 minutes track sessions with ambient temps in the 90s. I added an oil cooler and that brought them down a few degrees (typically around 204 - 206 max). I didn't have an oil temp gauge, but expect the oil temps saw a much larger drop. My point is that it would not have mattered which thermostat I ran as the cooling system was limited by airflow (or lack thereof) through the radiator.

[BRAAP]

One other point I wanted to bring up that other Z owners have also noticed is, just prior to the engine temp reaching normal, that is when the car felt the strongest power wise. Granted, can't trust the butt dyno, but every L-6 Z car I have owned I noticed this. On the initial start in the morning, just before the temp temp needle reached mid way point, the car felt stronger than it did when at full operating temp, that was also another reason I ran as cold a thermostat as I could find, trying to replicate that.

 

I like to challenge convention and will ask the question: Does a cooler thermostat benefit the running performance of the engine?

…

Would be interesting to learn what the current wisdom is regarding coolant temps. My thought is that whatever the current wisdom is probably applies to the modern engines which might not carry over to the old L-series due to it's overall coolant flow design, coolant passage surface area surrounding the available heated surfaces, etc...

 

 

My guess is that if I were to use the 190 degree thermostat, my engine will warm up more quickly. Less wear can only be a good thing.

!

 

The hotter thermostat should not warm the engine up any faster than a cold thermostat. They are both closed when cold, the colder thermostat just opens at lower temp than the higher thermostat.

 

Rate of engine warm up is another topic.

The OEM designs the engine and its cooling system to get the engine to full operating temp as soon as possible, mainly for emissions reasons, and also for passenger comfort reason in colder climates, etc, My knee jerk reaction to that concept from a machinist/engine builder standpoint is quickly heating the engine up, (that heat emanating from the combustion chambers and radiating outward from there), would put more thermal stresses on the engine being as it is made out of more than a few different materials and even different alloys of a particular type of metal that expand and contract at differing rates and amounts, i.e. aluminum will not only conduct heat quicker than iron, but also grows more, i.e. aluminum pistons in iron bores, etc., (one of many reasons why we were taught not to hammer on a cold engine, including cold oil doesn’t flow as freely to the bearings/valve train, etc), on the other side of the fence, modern engines are wearing far less than their older design counterparts, mostly due to more precise control of the fueling, none the less, modern engines seem to going longer before requiring an overhaul. Though I would still be hesitant in trying make changes to the cooling system of the L-series to make it warm up quicker. Modern engines are designed with the quicker warm up in mind, the L-series was designed around how quickly it currently warms up. Those design parameters might be different, then again, might not.

 

I think I am starting to get too far off topic here. My apologies for the tangents guys.

[Tony D]

I have always ran the 160 F thermostats in my L-series engines and even my performance Small Blocks. I have no proof or theory to support that as the way to more power other than I remember reading Smokey Yunicks work from years gone by and recall he said that cold water and hot oil always made the most power, so I followed that advice and applied to my engines.

 

Same as what I read. Talking with the Electromotive guys, they said they overbuilt the cooling system, and paid a penalty for it (more weight for exchangers, etc) but they NEVER had a DNF that was cooling related. Their statement was 'you can always cover a cooler, but if you get hot during a race, you're screwed!'

 

Note the S20 head, LY head, and even the FIA L-Series heads had a totally different cooling passageway setup with a street driven setup. These were engines designed for high specific output and racing from the factory. The LY24 was over 300HP, the S20 in racing form was 340+, and the FIA heads... well the LY was quoted as around 5% more power, so I can only figure the FIA head was a response to that same level of power (300HP).

 

Cooling is a bear, and always overlooked. Nissan recognized the requirement for a different setup to keep these aluminum heads cool under continuous racing environments. There are improvements to the head that will allow considerable flow increases for cooling, they just need to be implemented, and in most cases people aren't willing to put that much into a head for a street car. For a LeMons car, all that cam is likely overkill. A stock low compression L28 was eating the field for 8 hours in Reno, and was competitive at Thunderhill the year before.

 

As for rate of heating, look around many pit areas and see if you find oil heating blankets on the oil sumps (or on wet sump pans)---hot oil is what you want, the rest of it will handle itself pretty quickly on the warmup lap. But that oil needs to be hot NOW when you start the engine! But we digress...