Tigger 1.0 was great fun but due to the limitations of the factory engine it was time for a new build. I didn't initially plan on doing a build thread till it was pointed out that others might benefit, so here it is. Before I start though I have to thank ra2fanatic and thepenl for their great build threads. I'm sure there are others I am forgetting but my brain cloud is acting up. You'll see some similarities and some differences in regards to this engine build. Personal preferences, design philosophy and compromises all figure in to my choices and your own may differ significantly.

PISTON CHOICE:
My first decision was which aluminum alloy to use, 4032(M142) or 2168, and what static compression ratio to run. There are pros and cons for both alloys and the same goes for static compression. 4032 pistons (Mahle & Supertech) expand less with heat and so have tighter bore tolerances. This means no piston slap and less blowby when the engine is cold. (Irregardless of piston choice never beat on a turbo charged engine till its warmed up.) 2168 alloy pistons do expand more with heat and so are more likely to experience the above, but they have one very large offsetting factor in their favor. The base alloy is more flexible than 4032 and that's a very good thing. I'll draw an analogy from the wing spars of aircraft which are also aluminum. Manufacturers could choose a strong rigid alloy like 7075 but instead choose a 2024 aluminum. The reason being is the more flexible 2024 allows the wings to flex without cracking. Just the same with pistons. Under extreme loads or detonation a 2168 piston will flex rather than crack. So at this point I was really leaning towards a 2168 piston.

Next was choosing a static compression ratio of 10.5:1, 10:1 or 9.5:1. Higher static compression ratios have greater thermal efficiency when means more HP, fuel efficiency and crisper throttle response off boost. The problem in turbo applications like ours is dynamic compression ratio. As air density increases due to boost, the effective or dynamic compression ratio rises. Beyond a certain point severe detonation becomes inevitable and results in catastrophic engine failure. In our direct injection application a dynamic compression ratio of 15.6:1 appears to be a generally safe upper limit on 91 octane fuel. So without resorting to water/meth injection or very rich AFR's max boost would typically be 18 psi for 10.5:1 pistons, 21 psi for 10:1 pistons and 25 psi for 9.5:1 pistons. Each full point you drop compression will reduce max engine power by 3% but each psi of additional boost puts 3.4% more more air/fuel into the engine. I've attached a spreadsheet for calculating dynamic compression ratios as well as other variables. It comes loaded with JCW numbers but feel free to play with it.

The only 9.5:1 pistons available do not have the distinctive tear drop shape machined into the top of the pistons which optimizes atomization in our direct injection application. I'm a firm believer in efficiency and elegance in design so that's out. The 10.5:1 piston is also out since I plan on running boost over 23 psi. That leaves my choices as Mahle 10.25:1 or Supertech 10:1 pistons both of which are 4032 alloys. Hmm...what to do? What to do? I guess it's 10.5:1 pistons after all. Here's some comparison pics of the stock Cooper S 10.5:1 piston to the CP 10.5:1.
Stock:

CP Piston:

Side by side:


https://dl.dropboxusercontent.com/u/...HP%20Calc.xlsx

Next up custom rods and headaches....to be continued.

 

Subscribed!

 

I'm loving these full engine builds.

 

Thanks for doing this.

 

Connecting rod choices are currently a bit limited. My initial choice was to go with the Carrillo rods. They're readily available, light weight, well made and can probably handle upwards of 600 HP. During discussions with my engine builder however he mentioned Pauter X-Beam rods which he prefers to use in his race motors. So I did a little research and it turns out that Pauter and Crower rods generally get the nod from the big boys on heavy power builds. In addition those in Porsche racing circles swear by them. Pauter will also build your rods to your specs and are slightly less expensive than Carrillo rods but there is a lead time involved. Hmm...this gives me an idea. The factory uses 10.25:1 pistons in the JCW but combines it with a .3mm thicker head gasket to lower the compression to 10:1. Perhaps shortening the rods by .5mm will be enough to drop the compression to 10:1. So I run the math and sure enough that would do the trick.

But first things, each engine has whats called a quench gap. It is the gap between the outer top edge of the piston and the cylinder head. If you look at the attached picture you can see this area above the intake valves and below the exhaust valves. Note: The edges of the quench gap area have been slightly radiused to minimize potential hot spots.



The purpose of the quench gap is to create a shockwave when the piston reaches the top that forces the fuel/air mixture from around the circumference of the piston into the center of the combustion chamber. This serves two purposes in that it creates a more efficient burn and helps reduce pre-ignition. Too much gap allows more fuel/air mixture to be in the area between the piston and cylinder wall above the top ring land during ignition. This creates hot spots on the ring gaps and can lead to pre-ignition on the next compression stroke. Generally speaking most N/A engines run a quench gap of .032" with an upper limit of .060" before pre-ignition becomes a problem" With most turbo applications a looser quench gap is recommended as boost increases since air density also increases. The stock Cooper S runs a quench gap of .035" whereas the JCW with the thicker head gasket runs a quench gap of .047". So by shortening the connecting rod by 0.5mm and using the standard head gasket one ends up with a quench gap of .054". Combine this with the cooling properties of DI on cylinder temperatures and we have a winner. So Pauter rods it is with a straight cut small end to match the CP piston and racing notches for Mahle Motorsport tri-metal bearings.

The racing notch was where my headaches started. It turns out Mahle is very proud of the bearings that come out of the F1 plant in the UK. Were talking $210 for rod bearings and $230 for main bearings...ouch. Kiss me first would ya I was pretty much at the point of letting Pauter make a set of bearings for me when I came across CB-1785HK bearings made by Mahle-Clevite. These are TriArmor bearings made for a Honda B18C1 engine . They are a tri-metal bearing with a steel back shell, a copper alloy center layer and a babbit (lead/tin alloy) coating that is closest to the crank jounal. The difference between TriArmor and Tri-Metal is that in addition to the three layers TriArmor bearings also have a .003" thick teflon polymer coating impregnated with a moly/graphite mixture. The purpose of which is to protect the bearing during start-up and low oil pressure conditions. In addition when oil is present it has a drag coefficient similar to that of wet ice on wet ice. Slippery stuff there.. and less parasitic drag equals more HP and better fuel efficiency.

Unfortunately, there was a minor transcription error when the techs mic'ed the journals and the gap was .001" too small. Luckily Clevite makes a .001" oversize bearing P/N CB-1785HXK. The X denoted that the back shell are made .0005" thinner resulting in an additional .001" clearance. So now I'm waiting on new bearings to show up. Other than the bearing headaches I have to admit I seriously like the way Pauter makes the rods. I've attached a few pics of both components for comparison.





Captions should read "Come on! Give me your best shot punk." and "Please don't hurt me.". I'll let you decide which goes where...

Next up N18 heads and migraines...to be continued.

 

Your welcome sir.

 

thanks for the shoutout tigger

I'm sure your build will be epically better than mine! I have little time to consider the engine rebuild. I have an extra block lying around, but with the massive amount of hours at work, the only thing I wanna do is relax.

Cheers to you bro!

 

Great to see a build thread, thanks! I detonated hard on my first dyno run as my tune was way too lean, fixed the tune but ever since then it burns oil (about a quart every 1k). Going to tear my motor out in the winter and check it out, this thread will be a big help to me!

 

Just some random pics of the block tear down.


Builder Engine


The patient awaiting surgery.


Cylinder bores.


Bedplate

A word of advice. Be very careful when separating the bedplate. Use a heat lamp, heat gun etc. whatever it takes, and take your time working a little at a time around the circumference. If you look at the second picture above you can see the split line in the engine case. The entire bedplate is your main bearing cap assembly. There are no individual main caps like traditional engines. According to the builder if you warp it while removing it, you buy a world of hurt. Truing the bedplace could then effect your bearing seat and require line boring to correct.

 

Wow this is ****!

 

This should be interesting!

 

Where oh where do I begin to sing the praises of the N18 head. Tip #1 buy an N14. Whomever designed the valvetronic head should be smashed in the nuts. (did I say that out loud?) Seriously though the dual vanos was an outstanding concept. Fully variable intake and exhaust valve timing. Bloody brilliant! But the valvetronic function is a real pain from the performance enthusiast point of view, as is removing and re-installing the valvetronic arm springs from the spring perches. The N18 uses the valvetronic system to control load as opposed to the intake butterfly on the N14. This is accomplished by using a three phase stepper motor with a worm gear that turns an eccentric shaft. This shaft acts on an intermediate rocker arm to vary valve lift. You can see pictures of the system below.

The problem with this from a performance point of view is that any alteration to cam profile or valve lift requires altering the eccentric shaft profile or valve length. As an example lets say we installed an intake cam with 10mm lift as opposed to the factory 9mm lift cam. At idle the eccentric shaft would be rotated to reduce valve lift to lets say 1mm with the factory cam. With a 10mm lift cam installed the intake lift at idle would be 2mm. This would result in a very flawed idle as the ECU tried to compensate for an idle RPM much higher than normal. Those with experience on valvetronic heads will tell you that when performing a valve job on these you must measure the valve height when closed before cutting the valve seats and faces. After performing the valve job you must take this measurement a second time. Whatever the difference is between two must be machined from the top of the valve stem in order to keep the valve geometry the same.

So for N18 heads the best you can do without modifying the eccentric shaft is port and polish the head and perhaps install aftermarket valves with undercut stems. None are readily available off the shelf at this point. So your best bet is to remove one intake and exhaust valve and send them to someone like Ferrea or a similar company to have custom valves made. If your going to go this route be advised you will need to upgrade your valve springs which Supertech makes for the N18 to prevent valve float. Reason is because the aftermarket valves are heavier since they are made from solid stainless as opposed to the factory hollow sodium filled valves.

Here's a picture of the N18 valve train. The exhaust cam is at the bottom, the intake cam is in the middle and the eccentric shaft is partially hidden by the spring perch at the top. These springs at the top press against the intermediate rocker arm and hold it against the intake cam.


Here's a breakdown that may make it a little clearer.


Another picture with the intake and exhaust cams removed. The gear to the bottom left is attached to the eccentric shaft and is what is turned by the worm gear on the valvetronic motor.


A few more pictures of the intermediate rocker arm and eccentric shaft. The regular roller rocker arm is underneath and runs from the top of the valve stem to the hydraulic lash adjuster.



As you can see the intake tract from the factory is as rough as hell. Not good for VE. Most numbers quoted for volumetric efficiency on the N14 and N18 are .87. Plugging various dyno runs into the excel file at the beginning of this thread also produced the same number. Some are of the opinion that there is no need to port and polish a turbo charged head. In fact nothing could be farther from the truth. A turbo charged engine will benefit very much from an increase in VE. In our application an increase in VE from .87 to .99 which is easily achieved can result in a 30+ HP increase.

Before:


After:


Here's the exhaust port after polishing.


And finally here's the head after port/polishing when returned from the machine shop. Ready for re-assembly.


There's a lot to be gained from these heads especially in the deep pocket and seat area. What can't be made are huge gains in cross section through the rest of the ports. Because the way the head is cast the ports have less than 1/4" of material in places. Removing too much will result in a cracked head. So if you plan to have this done make sure you take it to someone who knows what they're about. On a side note I do plan on experimenting with the head from Tigger1.0 to evaluate the feasibility of altering the eccentric shaft profile for a higher lift cam. So perhaps there may be some good news on that front down the road.

 

Looks like my ports before they got coated. Good job on the port work. Really nice.
That's the valve train in an N18 motor ?!?!
Holy cow! Is there some serious monkey motion gone on in those heads. WOW !!

 

Thanks I'll pass that on to the guy that did it. His bread and butter is porting Lotus heads. I didn't have time to do it all myself and just did the upper train tear down and re-assembly so he could fit it in his schedule.

 

Well the last week has been a total bust on the engine build. There's been a nasty flu bug going around and guess who got it. Good news is everything should start cooking again Monday when he gets back. Can't wait to drop the new engine in. Of course then comes the breakin period before I can accomplish much on the tuning front. Per the builders recommendation the first 500 miles will be done with conventional oil as the rings will seat better. Then 1500 miles on full synthetic before next oil change and base dyno run.

On the tuning front I hope to post some pretty good information and a comparison between 3 very popular tuning options with dyno runs and data logs for each. I'm not expecting to be surprised by the final outcome but you never know.

 

Interesting, but it makes sense since you wouldn't be wearing much of anything with full synthetic especially with more robust upgraded internals.

Get well soon.

 

What kind of numbers do you hope to see tigger ? I got some emails from nick at manic about the exhaust as to what he found on a dyno.

 

Hell anything north of 250 HP would make me happy. Now having said that, ideally I'd like to see 270+. I know Nick has tuned an auto to 300 HP so it is possible. 242 ft.lbs of torque at 6500 RPM would do the trick and that's still below the 250 ft.lb design limit of the auto. Not sure what percentage of safety margin was used during engineering but I'd be surprised if it can't handle 275 ft.lbs without ill effects. Funny you should mention that as it's the next subject I'm about to post about. I'd love to hear if his observations correlate with what the math says after I post it.

 

love all the shiny things, cant wait to see more!

 

I've had two separate PM's recently about exhaust size in relation to a KO4 turbo. So I thought I'd post my research and thoughts on the subject. There's a bit of math involved so grab a cup of coffee or some nice 18 year old scotch if you prefer lol.

The most common question is 2.5" or 3" exhaust on our cars and the short answer is that for most of us it doesn't matter. Let me explain why. In most N/A cars the largest restriction in the exhaust is the catalytic converter followed by the muffler. So a free flowing exhaust can make a pretty big impact. In our application however, the biggest restriction is caused by the spud shoved in the tail pipe commonly known as a turbo charger. Nothing else in the system comes even remotely close for generating back pressure. At 1.5 bar of boost pressure the pressure in the exhaust manifold is about 2.5 bar. That's 36 psi which is a hell of a lot of back pressure and is one reason why turbo's run with less valve overlap than N/A vehicles.

Removing the cat will definitely help and can net 10 to 15 HP. As the air exits the exhaust turbine the airflow is as turbulent and messed up as a soup sandwich. It's spinning around with vortices and eddy's everywhere when it reaches the cat. If you ever had a chance to look at the internals of our cats you'll note that the cells the exhaust must pass thru are stacked tightly together and are perfectly straight. This forces the air to be suddenly straightened at the same time it is required to come into contact with a great deal more surface area. This creates a lot of parasitic drag and back pressure. Removing the cat makes the single biggest difference in the exhaust and is pretty much mandatory if you want to see 270+ HP.

Ok back to the exhaust, lets calculate back pressure differences between 2.5" and 3" pipe taking into consideration CFM and exhaust temp. I'll use numbers from a JCW as a baseline then we can go from there. The first things we need to know are the CFM going in the engine and the exhaust temp as it comes out of the turbo. We don't care what it is forward of the turbo because we've already determined there's a lot of back pressure there we can't do much about. A JCW is pushing about 27 lbs/min or 333 cfm into the engine at about 114 degrees Fahrenheit. The exhaust temp after the turbo is pretty damn hot and varies based on load so we'll use 1550 degrees. You have to convert these to degrees in Rankine and divide them to get an expansion ratio which is multiplied by the cfm entering the engine to arrive at the cfm exiting the engine. The air cools rapidly losing volume while passing thru the exhaust system but we will ignore that for the moment so we can calculate pressure loss through a 2.5" and a 3" pipe. We're also ignoring mufflers at this point but will return to them later.

Pressure drop in compressed air is airflow in cubic meters per minute times 7.57 to a power of 1.85, times the length of the exhaust in meters times 10 to the fourth power, divided by (the inside diameter of the exhaust in mm to the fifth power, times max pressure in the system in kg/cm squared). So well use 1175 cfm, 10 feet of exhaust and 36 psi as our initial pressure. The pressure drop for a 2.5" exhaust pipe would be 0.82 psi and 0.33 for a 3" pipe. Less than a half of a psi difference between the two. Keep in mind this is downstream of the 36 psi of back pressure created by the turbo itself. Not a hell of a lot of difference there.

Muffler design however can make a more marked difference in back pressure. If the muffler is a convention design like this you can see how it can generate back pressure.

Whereas a straight thru design will look more like this and obviously generate less.


My personal choice was to go with a Magnaflow muffler as they are a straight thru design and I do so love their sound. None of that raspy, bee's in a can sound you hear emanating from the rice rockets running around. Just a nice deep rumble when tooling about. Once you get into it however others will know this is not your Grandma's Mini.

If we scale the HP numbers above up to 250 HP and 300 HP at the wheels thing start to look a little different. You end up with a pressure difference of 0.67 psi at 250 HP and 0.87 at 300 HP. So unless your planning on running 300 HP or higher you should be fine with a 2.5" exhaust if it's a free flowing design.

There's a few other reason why you don't want too large of an exhaust in a turbo application. The first relates to wastegate function. Our cars use an internal wastegate. Which means that it functions as a differential air valve between the turbine and the exhaust system's back pressure. With an exhaust that is too free flowing the ability of the wastegate to control boost in very high boost situations can become affected resulting in momentary boost spikes. Normally these are difficult to see on a boost gauge as they are short in duration. The second reason you don't want an exhaust that is too free flowing is you will lose bottom end responsiveness. When the exhaust flows too freely the exhaust gas temperature is lower at low RPM generating less boost resulting in lower torque. On the flip side this pays a dividend on the high end by keeping exhaust temps in a safer range when your really pushing it. And one final tidbit to note. A 3" exhaust will, all things else being equal, be louder than a 2.5" exhaust.

 

awesome thread....thanks Tigger!

 

subbed. So much info that everyone on these forums needs to know and understand.

 

I'll send ya a pm.

 

+1 I'm in the car service business and this is valuable information to me

 

Glad to spread some wealth. I've learned lots here at NAM. When I sold Pepper my 1st Gen and bought Tigger I thought I understood turbo charged cars lol. Then I joined NAM and quickly realized how much I didn't know. I'm still just scratching the surface. Mucho respect for those that paved the way especially the tuners that have proven their skills. Being able to safely tune requires math that make the pressure loss formula above look easy.

Oh on the subject of exhausts. Here is my DP waiting to be reinstalled after ceramic coat. For those that are ecologically sensitive my apologies about the lack of a cat. I promise to go hug a tree later to make up for it. ;-)