Twincam running to cold?

[M100]

The convection cooling directly from the head at partial throttle is so high that the thermostat is not even opening. Honest to gawd this is what is happening when the ambient temperature gets down to 10C or below.

But 10 deg C is a typical english summer day

I don't run my car right through the winter but I'm sure there are definitely days in the year when I've set off from home when it's been around 10 deg C and had no problem getting the car warmed up.

After ripping a hole in my sump last year I had been considering a sumpguard of some description but I'm wondering if it might be worth considering a permanently fitted undertray that keeps up sump temperatures and restricts the airflow out of the engine bay (working along the lines that the most effective way to keep up engine temps on a single seater is to tape up the radiator *exit* ductwork - not the inlet)

[type26owner]

John,
The airflow through the front drill. Whether it goes through the radiator core or around the outside it matters diddly squat. No real heating of the air passing through the core happens until the thermostat opens. It never does get there on my engine with a 90C thermostat. Even if you have a lower temperature thermostat installed the exhausted heat flow from the radiator will be much less because of the law of thermodynamics. Heat only flows from high to low and with a 70C thermostat the efficiency is so low in efficiency passing the heat off into the air that it's working about equal to the head's cooling rate only. This just makes the overcooling AND the overheating worse. The engine temp will get stuck at 70-80C and I freeze cause the cockpit heater only makes this worse. Only if I close the heater water flow off will the engine finally climb up to barely 90C. The difference of 15-20C warmer water circulating through the heater has to be experienced to be believed. According to the good old laws of thermodynamics this makes perfect sense. None of this stuff is intuitive unless you've got an engineering degree or in my case had the on the job experience.

Chris,
If Lotus kept the same opening size in the front grill for every version of the Elan then 40sq/in of area blocked off will be magic size. Trust me.

M100,
That's why you guys in the UK should be very concerned. I'm taking a different route to solve this. I'm going to add loop of tubing into the top tank of the radiator and pass all the engine oil through so it gets heated up to the water temperature. Then going to partially insulate the oilpan to reduce the heat loss from the air blowing past it. The reason not to stop all the airflow from the bottom is simple. The alternator will burnup from overheating. To keep the alternator alive where I live I have to add a heat shield between the exhaust manifold and the alternator. Also an air deflector which hangs 1/2" below the chassis to force cool air to the backside of alternator when the car is moving. Since I've done these two mods the alternator has not died since.

Wish I had picked up on this trick when I still had the Maserati Biturbo. They would get cooked sitting within inches of the turbo and be toasted and die everytime about every four months.

My optics stuff usually gets cooled down to 77Kelvin (liquid nitrogen) or 4K (liquid helium). Ironically, the cooling capacity is very small at those temperatures since the gradient is never very large if you can possibly help it. Better know what you're doing or you'll screw the pooch.

[john.p.clegg]

LOUVRES:- this could be the answer to the problem,just like on the front of the Rolls-Royce,a louvre panel attatched to the radiator(so as not to restrict air to the intake filter) operated from inside via the redundant locking choke knob????
John

[john.p.clegg]

P.S. Keith
I am sure Mr Vizard reckoned that 72 was the best operating temperature?
John

[M100]

LOUVRES:- this could be the answer to the problem,just like on the front of the Rolls-Royce

A mate with an old Rolls-Royce has this arrangement but the thermostat operates the louvres via a multiplier linkage.

Keith, along your tube in a radiator idea have you looked at the laminova heat exchangers? I've retrofittted one to the Elise and it warms up and stabilises the oil temperature very quickly as well as speeding up coolant temperature rise (car runs all the year round)

[type26owner]

John,
That's one guy's opinion. Just because they wrote a book does make it true. Are the dyno sheets specifically testing differences of the engine operating temperature only included in the book? There is plenty of evidence on the web from modern day race engine tuners that's not the case just that it's not from running a twinkcam so it's not conclusive.

If running the engine that cold was good for making horsepower the good old Nascar boys would be strippping off all that tape from the front grill in a second. Gotta laugh when the annoucers claim it's for the aero downforce. Yeah right, a couple of squares inches oneway or the other is even noticable.

Rohan,
Have you any conclusive dyno data to share in this regard? You have established credibility and I would believe you.

[type26owner]

M100,
That unit is expensive, too long and has the wrong size water fittings IIRC. I bought the VW and the Ford water-to-oil-intercooler to try and fit those in the space available. I gave up for various reasons. This problem is a real bugger. The intercooler is definitely the way to go. It protects the oil from running too hot or cold.

The folks that sell the wax linear motion actuators laughed at me when I told them I was interested in buying just one. They would but it was hideously expensive. I could not figure out to adapt a regular thermostat one and not make it a major project. They lack much force. I'd love to see a picture of your friends version.

[rgh0]

Keith

I have never done any properly controlled dyno tests on my Elan to try to identify an optimum operating temperature versus hp. Just too hard to control on a rolling dyno especially with the relatively small radiator I run. At university 30 years ago, I did some engine dyno work which on the rather conventional 1600 cc push rod GM ( Holden Australia) engine of the day involved showed no difference over a 70 C to 100 C operating range for the individual engine involved but I would hesitate to translate that to a general conclusion.

From a theory I cannot see why any temperature in a 80 to 120 C range would be preferred either from an engine HP or engine life perspective. Under 80 C and the oil will stay to cool to properly drive off volatiles, over 120C you risk boiling the coolant. In practice an individual engine may give a little more or a little less hp over this range depending on type of oil used or clearances in the engine and how well the air intake is isolated from engine bay heat but I dont think you could predict what was the right temperaure in general from this as it would be very sensitive to each individual engine build. I dont believe it is possible for Vizard to conclusively sat 72C was the best temperature for a twin cam without specifying the oil used, build tolerances and engine bay installation details.

In practice on the track I see no difference in my lap times with engine operating temperature. My track time are very repeatable within a tenth of a second on most tracks. On a 15 degree day versus a 40 degree day my engine temp will vary at race speeds from 85C to 110C. Despite this engine temperature variation I see no difference in my lap times so I conclude no significant hp difference or at least a hp variation that is similar to other subtle variables driven by ambient temperature such as tyre grip or air density.

I think the biggest difference you would see in practice is that with a bigger radiator to enable lower engine temps you will have more drag which will affect high speed performance. The tape on Nascars and the high temp small radiators F1 cars run is all about drag minimisation. The faster the track and lower the ambient temperaure the smaller the radiators the F1 cars run to lower drag. That is why I have stayed with the original sized small radiator just with 3 core rows versus the orginal 2. This runs with the thermostat fully open at race speeds and 170 hp. The engine temp floats with ambient temperature over an acceptable operating range, thus I conclude I have the smallest practical radiator for my car and use ( I am not going to change radiators with trackspeed and ambient temp like the F1 guys !!!)



regards
Rohan

[type26owner]

Rohan,
Thank you!