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Well, Sally is back in surgery. She’s sick and needs some corrective work done. But while the TPC surgeons are at it, why not make her stronger and give her some lung enhancements? After all, what girl doesn’t want bigger lungs? All the better to stay oxygenated during heavy, hard breathing while she is teaching me how to touch and feel her to the point that she feels the thrill of being on the edge of losing control. I love it when she gets out there on the edge and starts squirming and letting out those little joyful squeals. All right, all right, enough of the anthropomorphisms. I’ll keep it clean and technical, although I agree with Diverdog, I love engine porn. Plus, my wife refers to her as “the other woman” in my life and even lets me spend money on her, so life is very good.

It all started at Roebling Road late last fall. Sally and I had participated in several track events with no issues. Saturday afternoon, I noticed smoke on start up. I didn’t think a lot about it – it is a Cayman, after all. On Sunday, I was a quart low by noon and the smoke was getting worse. The worst I could think of was a possible failing diaphragm in the AOS. Then, at the end of the next to last session, I took the checkered flag and slowed for the pit. Coming up to the pit ramp, I looked in the rear view mirror to make sure no one was running me down and was shocked to see a huge white cloud following me. I depressed the clutch and the engine went to idle and stabilized. I pulled off pit road at the first exit and coasted to an area clear of other cars. By this time, the fire trucks had me surrounded. I got out of the car and looked underneath for fire and saw nothing and verified that all of the smoke was coming from the exhaust but the volume was decreasing. After I verified no fire, I removed the engine cover. Nothing abnormal on top. I jacked the car and there was some oil on the bottom. I checked the Durametrics and there were no engine codes – none at all. I started the engine. It started normally and idled normally, but when I looked under the car, there was coolant coming out of the seams in the exhaust. NOT GOOD, so I shut it down. Sally rode home on a truck and I immediately put her up on my lift to see if it were something obvious. Oil coated the bottom of the engine, but the source could not be determined. I scratched my head for a couple of weeks and decided I could not figure it out (Blown head gasket? Broken valve train? Engine should not run smoothly. And where the heck was the coolant coming from?). So I contacted my friends at TPC and described the symptoms and Mike Levitas immediately predicted D-chunk failure. Then I thought, “Well, I probably won’t work past December and I haven’t rebuilt an engine in 30 years, so I will do it myself.” After all, it is my toy and I will play with it in my own sand box any way I want to. Well, as luck would have it, my company talked me into working for part of this year, so full retirement isn’t quite here yet.

I began to weigh my options. New 3.4 block and hope nothing else is broken or compromised? Or go with a TPC 3.7?. After discussing the 3.7 with Mike Levitas and Tom Chan, I made the decision. I did not want to simply replace the 3.4 with another block with the same marginal cylinder wall strength and I have been intentionally avoiding track tires because of the oiling issues. And, when I considered the cost delta between the two engines, I decided it was worth it to go with the 3.7. I’ve also included other mods to take care of other Gen 1 worry beads and I have to say that I have developed a tremendous amount of respect for the TPC guys. Just as in the original TPC Stage 2 mod and suspension mod, they answered my questions honestly and directly. They have never steered me toward a particular solution or tried to talk me into adding something to the car. When I ask if I need a certain device on the car, I get an honest assessment which frequently takes the form of a discussion of the problem I am trying to solve and their evaluation of the value of the fix. I’ve been told more than once that they believe a certain mod will not materially contribute to the car and they would rather I not spend my money on it. I don’t think I can ask for more than that.

Okay, enough preliminaries. Let’s get into the engine porn and the decisions that went with the configuration. The data for these descriptions comes from TPC and other sources that I will identify just so I don’t do anything stupid and violate anyone’s copyright. If there are errors, they are mine and I will correct them with edits as they are identified.

Overall rebuild considerations

In discussing the options for the rebuild, we discussed the displacement, bore and stroke. The conversation started with a discussion of bore-to-stroke ratio and the design considerations that go into that. I had to study this parameter a bit and a little research revealed the following bore to stroke ratio data and the relationship of Power Density (power per liter of displacement)

Formula 1 B/S = 2.5, PD = 300 HP/L
Indy Car B/S = 1.33, PD = 190 HP/L
NASCAR B/S = 1.25, PD = 195 HP/L
Sedan B/S = 1.0, PD = 67 HP/L
Marine Diesel (big ship) B/S = 0.4, PD = 11 HP/L
(This data derived from a chart in an article by Dr. Randy Herold, “Stroke-to-Bore Ratio: A Key to Engine Efficiency” published in Under the Hood, an achatesPower blog.)
Stock 3.4 L B/S = 1.23, PD = 88 HP/L
TPC 3.4L B/S = 1.23, PD = 160 HP/L (based on my dyno run and a 15% loss)
TPC 3.7L B/S = 1.27, PD = 160 HP/L
(based on 500 wheel HP and a 15% loss)

Selection of bore was pretty simple for me. I value engine longevity as well as increased power and the 99.5 mm piston offers strength and a good cooling volume in the water jacket. Additionally, no head rework and material removal is needed and a Porsche 3.8 head gasket fits perfectly.

Stroke is another matter. By doing the TPC turbo mod, I increased the load on the crank to approximately 190% of stock loads, and those loads are going higher. If I increased the stroke, I would need a different crank but it would increase the crank loads and the loads into the block. Additionally, I would have to shorten the rod to maintain compression ratio, and that alarms me more than anything because it is changing the basic geometry of the dynamic system and I do not have the data to adequately understand how the change in geometry will affect the rotational loads, vibration harmonics and resonances, and repeated loads. I trust that the Porsche engineers have done extensive analysis to arrive at the optimum block design for the geometry and loads, so I have conservatively selected to leave the stroke alone. We will handle the reduction in compression ratio (to 10:1) with piston dome design and partially mitigate the increased inertial loads by installing lighter pistons and lighter, stronger rods as recommended by Mike. That’s another reason I like Mike Levitas’ design philosophy. While always looking for high performance, he wants to change as few items as possible to achieve the project goals. I share the sentiment because I have guided numerous engineering design optimizations in military tactical jets and I know how much effort goes into executing numerous iterations to arrive at the most efficient design. I also know the risk of unintended outcomes increases as you move farther from an OEM baseline.

Here is how the engine is rebuilt with the new cylinder sleeves. First the block halves are sent to Mercury Marine. That’s right, the boat people. The boat people who also make engines for the Corvette, Nascar, and numerous other applications besides boats. They know how to build TOUGH engines. They take the block and completely mill away the top of the existing cylinder down to the web and mill a flat on the web. They then bore the bottom part of the existing cylinder. See Figure 1 that shows how the new, thicker, stronger cylinder sleeve is then inserted into the bored part of the old cylinder material. The result is shown in Figure 2. The fit of the new cylinder into the bore is zero tolerance and it is secured in place by a two part adhesive (from 3M, of course) that forms a bond that is probably stronger than either metal. That’s right! Sally’s new engine is glued together. It is actually a rather ingenious process. Boring the bottom and inserting the new sleeve allows a very precise alignment and the load bearing surface of the web lip and the clamping load of the head means that the cylinder sleeve will not move even if the thermal expansion coefficient of the block material is higher than the new sleeve material because of the adhesive strength.


Figure 1. My crude drawing of the how the new cylinder sleeve is installed in the old block


Figure 2. New Cylinder sleeve inserted into bored old cylinder.

Cylinder wall thickness: Figures 3 and 4 show the old cylinder and the new cylinder, respectively. The old cylinder wall thickness measures 7.340 mm (0.289 in) and the 3.7 cylinder wall thickness measures 8.124 mm (0.320 in)(11% thicker than stock). Additionally, the inner wall of the stock cylinder is a Lokasil (a hypereutectic Aluminum silica alloy) sleeve whereas the 3.7 cylinder is made of a Mercury defined Aluminum alloy electroplated with a Nickel-Silicon-Carbide composite that produces a very hard surface that is similar to the Silicon Carbide coating that Porsche uses on the GT2, Twin Turbo, and GT 3 engines. The primary purpose of the Nickel is metallurgical. It actually matrixes into the sleeve alloy and forms a much stronger bond than simply an electroplated coating. The Silicon Carbide forms the wear surface and is an exceptionally hard surface, second only to diamond. Additionally, it is highly oleophilic which means that it contains and retains lubricating oil. It also has a lower coefficient of friction with piston ring material, so more force goes to the crank and the net torque at the flywheel is higher. Clearly, the 3.7 cylinder wall is significantly stronger than stock, probably in the neighborhood of 60% stronger.

Figure 3. Stock cylinder thickness


Figure 4. 3.7 Cylinder wall thickness

In Figure 3, the crack propagating down the wall can be clearly seen. I am surprised that this little crack resulted in so much smoke, but I am glad it didn’t get worse. In contrast, The piston in the cracked cylinder showed only some minor scuffing. A classic D-chunk failure is shown in Figure 5. You can see how the two cracks are beginning to converge and form the classic “D” shape cyclic fatigue failure.


Figure 5. Classic D-chunk failure

I’m not a fracture mechanics expert, but the failure must originate at an imperfection on the top of the cylinder wall. One crack starts and the net bending moment causes a second crack to initiate at another weak site. In Figure 5, the second crack originated shortly after the first, as indicated by the symmetry of the crack curved path. I’ve seen pictures of other failures in which the primary crack curves down and across the cylinder before a nearly straight crack aligned approximately along the bore completes the “chunk”.
Compare the thickness of the cylinder walls in Figure 3 to the 3.7 block in Figure 6.


Figure 6. 3.7 Cylinders

Besides the obvious wall thickness, another item to notice is the slightly decreased water passage thickness which may cause cooling concerns, but I was assured that there have been no cooling issues.
So there it is. Take a 3.4 block, machine out the old cylinder sleeves and replace them with larger, stronger cylinders, and the probability of a D-chunk failure is drastically reduced. Worst risk mitigated.
All right, all right, I know I promised you engine porn and then gave a long engineering discussion, so here it is. Let’s start with the pistons.


Figure 7. Piston perspective

Figure 8. Piston top

Just look at these things. Aren’t those curves beautiful? The skin tone is perfect. The domes perfectly shaped and a skirt short enough to be very enticing. As soon as I saw it I wanted to insert a rod and start making it go up and down. Yum………. Okay, already, I’ll get my mind back to the hard core technical stuff.

The pistons are manufactured by JE Pistons and are billet machined non-silica 2618 aluminum alloy. You can clearly see the valve reliefs. The shallow grooves in the top land are designed for better cylinder wall oil coating and the rings are materially matched to the cylinder coating. The wrist pin is made from chromoly steel and weighs darn near as much as the piston. I inserted the wrist pin through the pin bore and it took about 3 lb of force to keep it moving. When the pin got to the opposite pin bore, there was no indication at all of any off-center condition. It simply guided into the bore perfectly centered. These things are obviously very precisely machined.
And now the rods.


Figure 9. R&R Rods

I always wanted a rod like one of those, and now I have 6!!! Sigh. The rods are H beam (vs I beam stock) for stiffness and strength. They are machined from billet 4340 Chromium-Molybdenum steel (Chromoly)hardened alloy. Exactly the same length as stock. What is not to like about a rod like that? I am sure Sally loves it and I an sure she is thanking me for not shortening her rods.

All right, it’s time to wrap this up. You guys who love engine porn, its time to stop drooling on the keyboard. All of this cool stuff is installed in the engine and the engine is being built back up to get ready to go back into Sally.

There have been some other things going on in parallel. A Guard LSD is in the tranny. An X51 oil cooler that is 30% larger than stock. An LN Engineering half quart sump extension. Bodymotion ITC Racing spec Power Steering cooler kit. And a GT3 master brake cylinder (20% larger than stock.

And lastly, I am putting Sally on drugs. The TPC surgeons are getting ready to run the lines for a permanent IV to inject her with meth – Methanol, that is. More technical details to follow. I’ll close with a picture of the Man, Mike Levitas putting together Sally’s long block.
Smile, Mike, this is going to be fun!!



For those of you who desire a purely technical discussion, this post is included in the Articles section sans the anthropomorphisms.
 
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Discussion Starter · #2 ·
Sorry for the link failures. Trying to get it fixed.
 

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Discussion Starter · #4 ·

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Cayman The Destroyer!
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Very nice engine porn! And a great explanation of the hows and whys. I'm sure you are really going to enjoy Sally's new get up a go!:cheers:
 

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Thank you. My project is not nearly as daring as yours. It will be interesting to see how the Methanol works out in a Gen 1 car. I haven't played with Methanol for over 40 years when I put it on my Olds 442 to get more advance. Metering was an issue and what I remember most is that the carb would ice up on hot, humid days because of the heat of vaporization of the Methanol. Back then I was crazy and stupid. I am proud to report that some of the stupid has been cured.
 

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I think the meth injection is a great way to go. I may do the same in the future since only 91 or 100 octane is available here. At $7 a gallon 100 octane gets old quick. I'd rather tote around jugs of meth to the track
 

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I had that thought when I started investigating. Cars limited to 91 Octane should benefit more than cars with 93 octane available. And ditto on the cost savings. The last time I put 110 into my car, it was $18/gal. With the way TPC schedules the injection (as a function of load), I anticipate that I will get somewhere between 100 and 110 octane for less than $5/gal. And, as you know, the turbo cars drink more fuel than NA cars. In Sally, I would get about 9 mpg on the track. After Stage 2, it was closer to 7.

I also want to think about a Methane/water mixture. I've read some technical articles that a 50/50 mix produces slightly less power but results in significantly lower EGT and an overall cooler running engine. One way Methane increases power is by cooling the air going into the cylinder due to heat-of-vaporization extracting heat from the inlet air. This results in more air/fuel mass going into the cylinder and thus more energy when the mixture ignites. Mike Levitas is considering putting Meth on a car in lieu of an intercooler. It makes sense and would save the weight of the intercooler and third radiator.

Anyway, there are yet a few discussions to be had. I will almost certainly stick with 100% Methane because my car is not equipped with enough instrumentation to understand the trade-offs of water/Methane mixtures.
 

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All this talk of Methane injection creates an image in my head of some tube running from the bottom of your seat to your intake and someone handing the driver a bowl of beans... just sayin...


Oh and you can get free Methane injection by driving on the surface of Titan...
 

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All this talk of Methane injection creates an image in my head of some tube running from the bottom of your seat to your intake and someone handing the driver a bowl of beans... just sayin...


Oh and you can get free Methane injection by driving on the surface of Titan...
As usual Ken has been eating plenty of beans!
 

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It took you a month to think of that reply? :taunt:
Ken, I know part of the deal is I must read all of your posts within 24 hours but some times I miss a few:banana:
 

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Love the photos, tech, and rebuild. Thanks for sharing. I'd hate to ask what all of this is costing you. But I'm interested because I feel that this is a something that I would want to do.
 

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Ken KG, aside from the flatulance advancement kit postulated by one bean driven Mr. Ken K-Man S, just kidding Ken! it actually might work! It has been one of the most enriching posts I've read, please keep posting, fascinating build. I'm really curious to see Sally put together and struttin' her stuff. You have to understand, us lesser mortals, we cringe at the thought of a flat six torn asunder and manhandled like Oscar Meyer baloney in an elementary school cafeteria. No doubt Levitas knows what he's doing, nonetheless the visual aspect is amazing and frightening at he same time! Lol! Follow up with Ken and his FART* (tm) kit, good for at least 25 bhp ( depending on burrito octane rating)

*Flatulence Advacement Retrofit Tuning (tm)
 
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Admittedly late to find this thread, but what a great read! all the background on the 3.7L particulars is great. Despite owning one, I'll admit to not knowing much about it. Until now.

Love to see more 3.7L Stage 2 TPC turbo's!
 

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I had that thought when I started investigating. Cars limited to 91 Octane should benefit more than cars with 93 octane available. And ditto on the cost savings. The last time I put 110 into my car, it was $18/gal. With the way TPC schedules the injection (as a function of load), I anticipate that I will get somewhere between 100 and 110 octane for less than $5/gal. And, as you know, the turbo cars drink more fuel than NA cars. In Sally, I would get about 9 mpg on the track. After Stage 2, it was closer to 7.

I also want to think about a Methane/water mixture. I've read some technical articles that a 50/50 mix produces slightly less power but results in significantly lower EGT and an overall cooler running engine. One way Methane increases power is by cooling the air going into the cylinder due to heat-of-vaporization extracting heat from the inlet air. This results in more air/fuel mass going into the cylinder and thus more energy when the mixture ignites. Mike Levitas is considering putting Meth on a car in lieu of an intercooler. It makes sense and would save the weight of the intercooler and third radiator.

Anyway, there are yet a few discussions to be had. I will almost certainly stick with 100% Methane because my car is not equipped with enough instrumentation to understand the trade-offs of water/Methane mixtures.
Kenkg,
Where do you get the information that a Meth injection on 91 oct will yield a 100+ rating?

Jose
 

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Very interesting modifications:
1.May I ask you why you chose billet conrods? Billet conrods are inheritendly weaker than forged con-rods, so my question is why didn't you choose some custom made forged conrods from carillo or similar.
2. Can you give a number for the weight savings using your pistons and con-rods?
3. Oil consumption: Once finished I would love to get some information on the actual oil consumption of your engine.

Good luck

Andreas
 

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Kenkg,
Where do you get the information that a Meth injection on 91 oct will yield a 100+ rating?

Jose
Jose,
I don't know that Kenkg actualy ment that the meth will increase his 91oct fuel to over 100oct+ but it does have the same cooling effect that running a higher octane would have thus allowing you to push the engine's capability that only race fuel would allow. The caveot is that now you put the motors life in the hands of a glorified waterpump if you do not have a fail safe mode incase you cannot supply the meth/water while the car is under boost.

Meth inj is amazing and i will be utilizing it as well. It prevents detonation and lowers your IAT's dramaticaly. But will not set it up to be dependent on it meaning that if my meth inj fails it will only result in lower hp not blown motor. However you can always tune with meth and get thoes extra ponies left out but I'm not much of the gambling type...
:hilarious:
 
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