Finally a break in the clouds and rain here... hot and humid.

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Parked outdoors in the rain for a night and wondered why it started to feel and sound like it was down on grunt a few days later. Popped a carb cover off and had my brother hold the pedal wide open. Sure enough, the butterflies were only going to about 3/4 throttle. Confirmed linkage was snug and went after the pedals.

For shame Stuttgart, for shame... wood? C'mon now.

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Will likely be ordering the Rennline aluminum floorboards to resolve the issue. Couple weeks until the dyno to figure it out and install.

Wood is lighter and it held up for almost 40 years.

For sure, but the car has been garaged daily since at least 1986. If they were made of a nonabsorbent/no-biodegradable material from the get-go there wouldn't be a problem. Pumping them out in aluminum would have been more costly $ wise.

Catching up on a few items at a time. Intended fully to pace myself on this but hard to resist. The oil tank has been bothering me with random drops of oil and leaks when filled beyond half when hot. I suspect a spot weld on the tank mount tab to the rear has torn and dribbles oil out when tank level is high. There must have been 3-4 honest pounds of oil soaked dirt on the old tank. I did replace the level sender and gasket earlier this spring thinking that was the leak but that was not the case.

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Cleaned up the old, pressure testing replacement and old before installing. If the original tests fine then it'll get a fresh coat of paint and reinstalled.

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Great part from Rennline. Perfect fit, this is what the factory should have done. All floppy/bendy action solved. Transferred throttle stop maintaining OEM pedals/application.

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Quick lunch:

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Probably around 1k miles since the job. Might be excessive but on 4th oil change now. Next will be to synthetic.

Stacked more miles on it this weekend for a local show which was the first for the car since I took over care-taking duties.

Some entertaining local news coverage showing the cosmopolitan nature of the event:

Video - WCAX.COM Local Vermont News, Weather and Sports-

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Great gallery of the event on AudiWorld if you didn't notice...

AudiWorld.Com Gallery :: 2013

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Folks,

I'm sorry to beat a dead horse here, but this subject is near and dear to my heart. I am in the midst of building a 2.7 race motor with all the dreaded parts (7R mag case, factory 2.7RS Nikisil P&C, factory steel studs). The car is a vintage 73RS replica, so the parts that I have are what I have, and so I am going to go with them (not soliciting other parts options), however I would like the collective community's opinion on two matters.

1. Case Savers vs. Timeserts. Is there a significant difference between the two with regard to stud pull out with a mag case?

2. What is the best initial torque value for this combination? Would slightly under-torquing the factory spec be wise?

Dave

Hi Dave,

Good luck with your 73RS replica - great car.

My opinion for your situation:

1) Go with Case Savers. They have a larger root into the case and will be less likely to pull.

2) I would torque to precisely factory spec using an assembly lube on the top threads and contact surfaces of washers/nuts.

Again, best of luck,

I have no opinion on the inserts.

But I'd torque to the specification of the stud manufacturer. If they are Porsche studs, use Porsche's recommended torque.

If aftermarket, use what the seller says to use.

Torque is a substitute for what is needed in a fastener - clamping force. Clamping force is created when the fastener is stretched, and turning a nut on screw threads is an Archimedean way of stretching the fastener. While it may be that the modulus of elasticity of all steels is pretty much the same, the engineers or shops experimenting with studs have worked out what works best for their product. Some will even give you several specs - one with this kind of thread (and washer to nut) lubrication, one with some other, and another higher one with no lubrication.

If the clamping force is inadequate, bad things happen. Nuts can rotate and loosen. And heads can lift momentarily, allowing hot exhaust gasses to escape in ways not up to withstanding that.

I'd rather stretch a fastener a little more than a little less than specified.

Inserts first: CaseSavers should always be used in magnesium cases for head studs.
There are 4 8mm studs, one inside the case and three on the perimeter that should also be inserted and Timeserts work fine for this application.
The key to mag case survival is actually history. What has the previous life of the case been like. If it was case used in a thermal reactor engine (75-77 Cali), there is a good chance that it has been over heated and would make a poor choice for a performance engine. Knowing if the engine was used for racing is also paramount.

Torque specs: Like Walt says, fasteners should generally be torqued to the manufactures specifications. In the case of head studs, it will ensure proper preload during the critical warm up and running stages.

One more question. Would it be a good or bad idea to use the top-side air deflectors with a mag case? The long ones on either side which cover the case bolts and the bottoms of the cylinders (as used on the aluminum case motors). Again, this is going to be a race-only motor.

Thanks,
Dave

The top side tin is a design enhancement specifically intended to divert much needed cooling air from the cylinder base to the top fins and cylinder heads. As I stated earlier in the thread, heat in the cylinders is concentrated in the top fins of the cylinders as they try and pull heat from the heads. Diverting the air to the top is indeed a benefit worth pursuing.

Dave,

Just adding on - I know you said you weren't looking for parts suggestions. I would recommend the thermal barrier coating for piston tops, combustion chambers, valves, exhaust ports and inside the headers. These coatings seemingly work well to limit heat transfer into the heads so you can make more power and also as we now know have less thermal expansion and stress on the case as a result.

Henry,

I was specifically wondering if the top side tin would be exacerbate the head stud pulling issue with mag cases, since they block cooling air from the exact area of the case into which the head studs are fastened.

Dave

The case operates at the temperature of the oil and gets little or no cooling from the fan. Install proper CaseSavers and control the engine temp and head studs pulling is a non issue.
Cheers

I know what you're trying to convey here but a quick fact check ...

The oil temp and case temp are different. They're close at operating conditions but different. They tend towards an equilibrium due to the surface area they share in contact with each other. The case temperature is also very different depending on location of measurement. The temp of the case at the base of the cylinder is not the same as the bottom near the seam where it washes with the breeze. That has been my observation with the infrared thermometer.

I believe Chris posted the temperature/ fatigue data earlier in the thread for magnesium. It's fairly strong to a certain temp and then drops quickly.

Been running 93 octane since taking ownership of the car. 1st tank of 91 octane running through now and not a difference noted from 93. No pings or detonation above 80F ambient with 91.

Really need some sort of knock detection/measuring means to determine if there's detonation going on. Can't always hear or feel it.

+1 Intake noise alone can be too loud to hear it until real bad with carbs.

Agreed, audible means of knock detection aren't reliable with the human hear in the breeze. Options:

1) A Bosch 3 wire knock sensor can be hooked to the microphone jack on a laptop computer for recording and playback analysis. I have access to this setup but normally use only on the dyno.

2) Spark plug inspection. Plugs look perfect on this one.

3) Aftermarket knock detection system...

An aftermarket sensor can easily be hooked up with an SCR diode to "latch on" when knock is detected and be done on cheap. This route allows conversion of an existing light to be knock indicator (such as low fuel light)

Detonation is generally a function of extreme conditions.
The test of an engines propensity to detonate is to load the engine under less than ideal conditions.
High cylinder pressures along with piston dome and chamber shape combine to create the arena. Add to that a sustained load or increased temperatures and detonation can occur.
You can generally tune around these issues but that means a loss in performance.
Make it run rich or lightly retard timing and the issue can be masked.
You can only determine the propensity to detonate by tunings for maximum predictable performance and loading the system.

What's interesting is on these older engines without knock control for ignition timing optimization is that your tuning window for the best performance without detonation will be highly dependent upon environmental factors. Modern engines retard ignition in the presence of detonation on the fly in everyday driving situations normally when using low octane fuel. The use of premium octanes in these same Camry/Subaru/Audi/VW street creatures will realize less "timing pull" adjustment due to the presence of less detonation based upon fuel quality alone.

These older fixed ignition curve engines don't adjust at all on their own. Setting the static ignition advance one way or another may indeed be necessary depending on your extreme environment if the fuel and other factors remain unchanged and you wish for the maximum performance the engine may possibly deliver safely. Anyway you cut it with fixed advance systems, you're going to be leaving performance on the table compared to a knock sensing ECU system. That's the nature of the beast.

So the question becomes - if you can tune for a few more degrees of advance living in New England than they can tune for in the deserts of Nevada, do you do it? Sure, it's free hp. I actually have a few different tunes I've saved for my megasquirt car for different environmental conditions and octane ratings. If I'm driving across country at 70mph with nearly no load then I don't need to spend the money on premium fuel the whole way as I won't be taking advantage of the anti-detonation qualities of the fuel in the absence of load. I have an 85 octane ignition curve that I load into the computer on that car for long trips; the general rule of thumb for tuning ignition for octane is 2-3 degrees of advance for each fuel grade reduction from pump premium at max torque. So if your max advance is 35 degrees with 93 octane, you would run 29 degrees with 85 octane. Does it reduce power? You betcha.

You tune for your environment in which you operate the vehicle. A car tuned in the deserts of Nevada may have less aggressive timing than one tuned in the crisp air of a cooler climate. Tuning to the point where detonation occurs isn't how any professional tuner worth their salt tunes. You get on the dyno with these fixed curve engines and you set your air to fuel/carb tune. Next, twist your distributor to find MBT and quit. Simple as can be. Should I add more timing if I don't find detonation under the most demanding conditions that the engine ever encounters? Not necessarily as you want to leave a little wiggle for changes in the weather and variations in fuel.

Do I need to load my engine into conditions that it won't see ever during regular or race operation? Only if you want to rebuild it sooner rather than later. There are many dyno tuners (non-inertia equipment) who will overheat the system and damage the drive-line unnecessarily and still speak with great confidence with a wake of broken rigs. When would you ever make a 30 second pull in 3rd gear? Last I checked, there wasn't a highway up Mt Everest. If you track your car then find the longest straight away and find the duration in time at WOT, add a couple seconds and use that for your tuning target with a competent operator.

For this application - the 2.8L overbore iron cylinder experiment with thermal barrier coatings and cylinder head heat sinks on a street driven vehicle: There is no detonation using the same ignition advance as the engine had with the Mahle RS spec bits. The operating conditions are everyday New England; long hills both up and down, winding cracked up roads and temps from 50-90F and humidity all over the place. Does it need to operate under conditions of Phoenix International Raceway? No because it's not used there. I don't imagine I would ever be able to speak with confidence on this combination under Phoenix International Raceway conditions as I don't plan to take the car to the desert at any point in the future. The performance is flawless for where the vehicle resides and the purpose it serves. Would the performance degradation match that of aluminum cylinder engines when put into the sandbox? Unknown. I don't the desire to truck the car 2700 miles to find out right now... come February when I have cabin fever I would probably be ready. :D

This thread started with the proposition that a "new" direction for building 2.7 mag case engines could be achieved by ignoring previous quantified results,
then using engineering theories and scientific observational to test and verify the results. Now what we get is "good enough for who it's for". Really?

I wonder if it's "good enough" for the most Porsche enthusiast?

We used materials data not just theories. The results are good thus far. Are you trying to move the goal posts? Sorry, the engine is working as intended. I'll continue to post feedback on the results as the build ages and wears.

What you did was cherry pick generic data and tried to extrapolate "fact" outside the realm of specific application, ignoring all the data and consensus that didn't fit your theory.

I'm not moving goal posts or anything else. I'm just commenting on the quantum change in demeanor.
From an arrogant, attack based, overbearing "with my experience and plethora of world class engineering consultants, I can change the world" to "aw shucks, it seems to be good enough for me".

I was told this wouldn't work. Guess what? It's working.

Game over- Turbo_Pro goes to the ignore list.

Question on your material expansion discussions. Laymen terms please.
What tests have been done under the loads and temperatures that they will be exposed to. Does the expansion and contraction remain the same when under compression for the cylinders, and tension for the studs, or are the expansion and contraction rates the same loaded and unloaded.

Hi there,

I'll try my best.

A larger coefficient (such as aluminum) means a given material grows more in ALL directions per temperature generating a higher force relative to a lower coefficient metal (such as iron). It's actually pressure, but you can get force by multiplying the pressure by the area being compressed. In an over simplification, the ratio of the diameter of the fastener to cylinder must be adequate to resist the force generated by the thermal expansion of the diameter of the cylinder material when unlike materials are used. This is easiest to imagine 2 dimensionally for me on a horizontal plane while ignoring weight of components.

The molecular structure of the metal determines the coefficient of thermal expansion we used. The expansion rates are observed and held in academic circles the same as the boiling point for water is; the experiments/tests are done for materials and indisputable by science. When you have a fastener with adequate strength which is stronger than the cylinder then the force will be transmitted to the fastened ends/anchor material which is the magnesium case.

The expansion rates remain the same but the force will be greater with aluminum cylinders and a non-dilavar stud when loaded due to differences in temperatures and material expansion rates. With iron used as the cylinder, the force on the case material is greatly reduced due to the lower coefficient of thermal expansion between the stud and cylinder.

I only took a few minor engineering courses in college, and never took the Strength of Materials course, unfortunately. So with that said.
I understand aluminum expands more than steel with temperature. What I am curious to is the force exerted by the different materials at operating temperatures as they expand under pressure. I would think steel would operate at a higher temperature than the aluminum since it dissipates heat slower, so that would have to be taken into account when measuring expansion of both. I am curious if even though aluminum will expand more, does it exert the same pressure per unit of expansion, or does the density or molecular structure compress or deform more under load, thereby reducing the pressure in the more heavily loaded direction and would distort in the less loaded direction, sort of like rubber would squeeze outward under pressure. Would steel transfer the same, or more force even though it expands less since it may be less prone to that distortion, than aluminum?
Other things I think about are the effects of the head and base gaskets. All the air cooled Porsche engines use soft copper base gaskets. Wouldn't this mitigate the expansion to a degree by compressing the softer copper. I would also think some engines used head gaskets which would also offset the expansion to a degree, whereas ones like the 3.2's used no head gaskets, so would this then increase the effect of cylinder expansion on the studs and anchor points in the case over ones with head gaskets?

I had the same question early on. The strength of the thermal expansion force/pressure is equal for metals but of course melting points differ. The greater expansion of aluminum means it will be generating more force than iron under the same temperatures well below the melting point/fatigue/yield limit. This is evidenced by the early mag case engines with iron cylinders not exhibiting the same failure rate of case threads as the later mag cases with aluminum cylinders. Heat being a byproduct of the combustion process, the amount generated of which depends upon the power output and efficiency of the engine. The iron itself doesn't cool as well as aluminum by the nature of the material. This is why we added thermal barriers as well as the heat sinks to the alloy valve covers.

The base gasket is copper and softer than the other metals- it is also expanding when heated rather than yielding under the forces and compressing; I suspect rather than for setting deck height alone, it was intended to hold tension during the thermal cycles of the rest of the cylinder and head stack in order to prevent leaks.

I have seen what Andrew describes...on old Beech B18 aircraft.
The radial engines (the cylinders) actually grew in diameter at the base where they connect to the crankcase...because the steel bolts were not as forgiving as the cylinder material.
When the engines were disassembled...the diameter of the cylinders were different from top to bottom of the radial.
You had to be careful when re-assembling...if you put a small jug in a big hole...you had a massive oil leak!
Also the engine would be way out of balance because of the sideways walk of the jug.
Metal expansion is a problem yet to be solved...we do the best we can...and hope we get it right.
Bob

Are the Supertech head studs really $800? :eek::eek:

Lapkritis; I was planning on ditching my 2.7 after a quick search on head studs/heat reactors etc. But now, I'm not so sure. You seem to have got really good results that you are happy with for a reasonable amount of money.

Supertech are $637.00 on Pelican - comparable pricing to Raceware, ARP, etc.

The ARP are available under $500. That said I would not hesitate to use or recommend the Supertec stud for the additional features in design over the ARP, specifically the thread on the head end. If you have ARP in hand then they are perfectly suitable.

I couldn't be more satisfied with how this performs as a street car. I have a few more catch-up repairs on the car now that the engine is sorted before I would feel confident in taking it for a track day. I'm away from home on travel for at least a few weeks as of yesterday so I'm not sure a track day will happen this fall.

Just replaced the shifter coupler thanks to Ed Mitchell at http://WWW.thecouplerwhisperer.com

Huge difference as you can see from the dead coupler I removed:

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The sway bar socket end links in the rear need to be replaced and some tired front wheel bearings also need attention. I have the Rennline tow hooks to install to replace the stock bits. The parts are in-hand just need to find the time.