Fuel Ain't Pumpin'

PostPost by: type26owner » Mon May 09, 2005 8:24 pm

Matt,
With a 10psi radiator cap the boil over temp is around 120C if my memory is correct. Best to run the engine at between 90 to 105C for lots of reasons. I have a 90C thermostat installed. The fan switch MUST be set to switch off at temp slightly higher then the thermostat opening temp. Having the fan switch try to cool below the closing temp of thermostat is a recipe for disaster.

I can talk you through the tuning of the Webers. Spitting is caused by the mixture being too lean or the timing is retarded or both.

I assume you're based in GB. Presently I must block off 40 square inches of the front grill to get the engine to warm enough to open up the thermostat here in Cailifornia on a chilly day. Little wonder Lotus downsized the radiators in the later cars since they are seriously overcooled. You'd only know that if you've got a good background dealing with the laws of thermodynamics. The aluminum head directly radiates most of the heat away at the heatload generated at a steady cruising speed on the freeway. I'm going to rig up a cable to open and close the louver. Right now I have it velroed into place on the front grill and it's a pain to remember I didn't install or remove the damn thing after I'm already strapped in.
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PostPost by: steveww » Mon May 09, 2005 8:40 pm

Hmm.... Interesting TTR says that 70C is the best operating temp for max power.

My twinc has a "summer" thermostat in it which is 74C IIRC. Even on a cool day (10C) the engine runs at thermostat temp whilst crusing. The temp soon rises once stuck in traffic. I have installed a large rad with 10" electric fan. The fan cuts in a 84C IIRC. Never seen more than 90C stationary in traffic on a hot (33C) day.
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PostPost by: type26owner » Tue May 10, 2005 1:31 am

Hey Steve,
Hmm.... Interesting TTR says that 70C is the best operating temp for max power.

But that's just one guy's opinion. Is he an expert in Thermodynamics? Where is the supporting data? Having blind faith in anything that is claimed by one individual is kind of a farfetched notion for me to take very seriously. There is abundant data from credible sources which leads one to believe that simply is not true. A credible source is likely one which is not trying to sell you anything BTW.

I don't have any hard data either from a dyno. Just seat-of-the-pants feedback stuff. Bet I'm within just a few percent of extracting all the available power with my crude feedback ways of tuning though.

How many cfm does your fan provide? Do you have a shroud which forces air past every cooling tube in the core?

My dual fans provide 1300 cfm and the shroud forces air to flow past ever square inch of the core. When there's extra heat to remove when the temp goes above 100C high capacity is essential.
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PostPost by: steveww » Tue May 10, 2005 5:50 pm

Well I guess his considerable sucess in racing a preparing Lotus racing cars counts for something. Practical experience is often a lot better than untested theories. I have read in performance books that cooler engine temps give more power and hotter engine temps give cleaner emissions. Can't lay my hand on the book at the moment, I guess I will have a dig through my library tonight.

The 10" fan is just attached to the rad, no shroud but certainly moves enough air to keep things cool. The rad is aprox twice the size of the original S4 rad and is situtated right down in the nose to catch the air. Last time out on a trackday the temp only when slightly about thermostat temp after a 20min session, ambient temp was aprox 18C.
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PostPost by: type26owner » Tue May 10, 2005 11:50 pm

Hey Steve,
This subject is really impossible to argue with any certainty. I'm just relating my observations from empirical testing and guessing as to the reasons why it's true. Ignore it if it bothers you.

How about if I reframe the basic premise a bit so the advice that TTR gives actually applies and is correct? If you still have a stock cooling system with only an air flailing fan mounted on the waterpump pulley with the stock cooling efficiency then installing a 70C thermostat makes good sense. That provides the largest capacity to remove the waste heat to prevent a boilover when operating the engine at maximum power for an longer period of time. I'll agree to that. It just adds a little more specific heat capacity.

Is your radiator a newer style cross-flow or even a double pass type?
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PostPost by: steveww » Fri May 13, 2005 8:37 am

I know what you are saying. With the old standard rad and 74C thermostat the engine typically ran at aprox 90C i.e. the temp was determined by the cool capacity not the thermostat setting.

The new rad is similar to the old standard rad only a lot bigger in all directions.

I can't remember where I have read about engine output vs coolant temp but I am still looking. It will come to me eventually. However I am sure that the real world difference in output of 70C vs 90C is only 1bhp or less :unsure:
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PostPost by: type26owner » Tue May 24, 2005 3:12 pm

Hey Steve,
I've been doing more homework on this subject of engine temperatures. What I've found is there is a possible advantage to running the engine at a lower temperature to lower the onset of detonation at full power. It's entirely possible that a higher power output can be obtained by doing this. The compression ratio and the fuel are the big factors as to whether this is necessary or not. Along with about several hundred other influences too. The advance curve of the standard twinkcam is very mild though and it's easy to back off the total timing to suppress any badness.

The 11 to 1 air/fuel mixture I'm currently running should actually promote detonation since the fatter the mixture, the faster it burns. Presently with my 104hp engine I'm not having any detonation problems which would force me to install a cooler thermostat.
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PostPost by: steveww » Tue May 24, 2005 7:37 pm

I am glad you have confirmed my memory on this subject. I knew I had read somewhere that lower temps give more power. However as you say and I have already mentioned I am sure the effects are slight.
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PostPost by: marcfuller » Tue May 24, 2005 9:22 pm

There is no simple answer of one temp value or range for max power. Our beloved twin cams are heat engines which gain in efficency with the highest combustion temp and lowest exhaust temp possible.

The maximum difference of these temps is, as Keith points out, dependent on many things - just a few of the "several hundred"; air/fuel mixture temp, fuel octane, compression ratio, combustion chamber design and metallurgy, cooling system.

The key is a high combustion temp (without detonation before top) AND a low exhaust temp.
-Marc '66 Elan DHC (36/6025)
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PostPost by: mark030358 » Tue May 24, 2005 11:01 pm

Steve,
Where did you get your radiator from? and how much? Not a TTR ally one I trust.

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PostPost by: type26owner » Tue May 24, 2005 11:04 pm

Hey Marc,
What I was hoping to achieve by elevating the temperature was an increase of the fuel mileage. If there was any improvement it was very small. However what I noticed is the heat flow through the engine is all wacky. Rather then deal with these issues the 70C thermostat was installed. I'm just trying to bring my engine up to present day best practices.
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PostPost by: marcfuller » Wed May 25, 2005 5:21 am

Hi Keith,

It made sense, increasing thermal efficency is a way to power. But as you have pointed out, that big hunk of soft alum moves a lot of heat around in different paths which can sometimes negatively change the ratio between combustion and exhaust temps. No way to tell on this stuff ahead of giving it a try. Without tremendous testing assets, your observations are much better.

Trying to bring the TC with all its old parts and design up to anything near present day standards is difficult if not impossible. But your efforts to try to find improvement and then document for us your experience is one of the best things in this board and helping to get my Elan running. Thanks.

I was just trying to point out to anyone reading the thread that coolant temp alone is a poor proxy for engine efficency and max power output.
-Marc '66 Elan DHC (36/6025)
http://www.lotuselan.us
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PostPost by: steveww » Wed May 25, 2005 5:50 pm

Where did you get your radiator from? and how much? Not a TTR ally one I trust.


Not a TTR rad but from a chap in Kent who had a load manufactured. However this chap has now switched over to ally and put his prices up but still less than TTR but only just. See his ad in the current Club Lotus mag. I have also seen some ally rads for the Elan on ebay. There are also a number of modern ally rads that will fit e.g. VW Golf rad. Contact me off list and I will go through all the options with you.
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PostPost by: rgh0 » Thu May 26, 2005 10:13 am

Design engine operating coolant temperatures tend to be set by the design of the radiator side first. How much temperature difference between the water in the radiator and air through the radiator do I need to remove the required heat is the key question for a designer. A 10 or 20 degree change in water temperaure here is very significant. Formula 1 cars run high coolant temperatures in order to enable them to run small radiators with low drag. The smaller radiator in the later Elans will have a lower drag than the larger radiator in earlier cars and the cars have a slighlty lower overall drag coeeficient. The smaller radiator was also cheaper which is really why the change was made.

The next issue is to design an engine coolant temprature and circulation rates so that the components in the engine receive adequate cooling from a mechanical and materials design sense and you dont get uncontrolled thermal expansion or materials being overheated. This was pretty much a try it and see process when the Elan was designed, now days its subject of precise computer modelling before a car is built

Thirdly in these days the impact of coolant temparatures on the emissions especially during wam up is a consideration. For the leans tis ha no real consideration as emission during warm up was not a real consideration even for the late USA cars

Finally the small potential impact of coolant temperature on the thermal cycle of the engine and detonation characteristics would be considered. The range of 20 deg C we are talking about here is virtually insignificant and many other design elements such as combustion chamber design, coolant passage layout and flow have a much greater impact on the heat flow in the combustion chamber than the coolant temperature itself. The impact of coolant temperature on Elan power output relates more to the effect of engine coolant temp on intake air temperature and losses due to changed frictional drag rather than combustion thermal efficiency

Rohan
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PostPost by: Leo Leentvaar » Sat Apr 07, 2007 6:40 pm

This forum is just great, fill in a key word and off you go!! :D
Upon reading this thread I had my first Elan light bulb moment. :idea:
I suppose there's many more to come, so brace yourselves :P

I just took delivery of the Elan Sprint yesterday and although the guys in the shop gave it a good work over, I had to call the AA last night as the car seemed to struggle with fuel and came to a halt. Despite the fact that the mechanical pump was checked and received a new membrane, it was the culprit. After a lot of checking the AA man was able to muster an electric pump which was fitted in the boot and connected to the battery using an inline fuse.

One of the things that occured to me was the fact that the pick up of the Webers was a bit hesitant when throttling more than 1/3 down. The guys in the shop thought the dip was due to the carbs.However the dip was gone once the small emergency pump was running.
It brought a smile back on my face at 2.30 AM and experiencing the fact that these cars are such a hoot to drive when set up properly.

So this Saturday morning I ran to my specialist and got myself an SU electric pump with low pressure and a pressure stop (just like in my MGB)
I wired it with a feed from the contact/igintion switch and earthed it to the battery with a fuse. just three seconds of clicks of the pump to prime the carbs and presto we've got noise!

At least the fix should get me mobile for the Easter weekend. Afterwards I'll decide either to fully replace the mechanical pump with a new one or to go electric and make a more permanent fit of the pump.
At present I tend towards the electric way.
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