[This article does not address MPG TUNING issues -- there is so much material to cover on that topic that we'll instead do another article on MPG TUNING in the near future. ]
The primary goal of the Mileage Master MPG long block is to sip as little fuel as possible. It will have more power than stock, but our goal is not to make maximum power, we just want to make it as efficient as possible. As with most of our “Recipes”, you can stray from our “Recipe” a little bit, but the more you stray the more you are going to wind up with a different engine than what we have designed. You can build this with Dual Port OR Single Port Heads, either is perfectly fine. We have to mention that you can do a LOT of additional things to keep increasing the MPG of your engine. But this article is intended for someone that needs a new engine, so they are going to be building one anyways. It makes no economical sense to spend $7k to build a 45mpg engine, if you can build one that gets 35-40mpg for $3k! It would take you 20 years to recover the spent $ via fuel savings. We are just assuming that you need/want a new engine, and want to focus more on efficiency and not brute power. For that purpose, we are building a 1745cc engine. 76mm crank, and 85.5mm “B” pistons.
If you’ve never torn into a VW engine, two books you may want to read prior to getting all dirty are Tom Wilson’s How to Rebuild Your Volkswagen Engine, Jeff Fischer’s How to Hotrod Your VW Engine. and for those that prefer video to books: Rick Higgins How to Rebuild Your VW Engine DVD. You will need on hand the “usual” stuff like oil, gasket set, main bearings, rod bearings, cam bearings, Curil-T Sealant, and Dirko RTV.
CRANK, RODS, and PISTONS: Use either this 74mm Crankshaft, VW Rod Journals. This crank was also used in our “1800cc VW Engine Combo: How to Build a Big VW Engine on a Budget” article, or you can use this 76mm Crankshaft, VW Rod Journals. The rods and pistons you use will be different, you have to select the crank, rods, and pistons TOGETHER to ensure they are compatible. You can also use 5.500″ H-beam Connecting Rods, also available in SCAT 5.5″ H-beam Connecting Rods; either are ok, but the H-beams cost more. Normally H-beams (H-beam connecting rods) are used in engines that turn over 7k RPMs, which is way over anything we are going to be doing with this gas sipper! Normally this crank and rod is a very unusual combination, but the way we make it work is with our Stroker 85.5mm P&Cs. This is going to make the engine STOCK WIDTH, which will save us money by eliminating expensive machining, and custom push rods and cylinder base shims/spacers.
Another variation on this engine is to use our 88mm “Slip-In” Hypereutectic Piston and Cylinder Set, but the 88mm size is only available in the “A” pin height version. If you use the 88mm “Slip-In” Hypereutectic Piston and Cylinder Set know that the heads must be bored to the 92mm P&C size, the 88mm Piston is a “Thick Wall” style, and is very large up top. Also, if you want to use the 88s (as highlighted in our 1800cc No Machining Engine Build article), use SCAT 5.394″ I-beam Connecting Rods, or even stock rods; we have Race Prepped Stock Rebuilt Rods or 5.4 I-beam Connecting Rods for these uses. If you use “A” pistons (designed for 69mm stroke crankshafts), use a 74mm stroke crankshaft, not the 76mm!
This may be confusing to you, so here is a recap to clarify it.
If you use 88mm “A” Pistons use 5.325″ H-beam Rods and a 74mm Crankshaft, VW Rod Journals. Alternative P&Cs are 90.5mm A Piston and Cylinders, 92mm A Piston and Cylinders, and 94mm A Piston and Cylinders with the 74mm Crankshaft, VW Rod Journals, using the 5.325″ H-beam Rods. Bigger bore engines are NOT going to be as MPG Friendly as the 85.5mm or 88mm bore engines will. But adding a big bore because the engine is apart, and “Why not?” are both valid reasons to do it!
If you use 85.5mm Stroker pistons, use the 76mm crankshaft, VW Rod Journals and 5.5″ rods. 90.5mm B Pistons and Cylinders, 92mm B Piston and Cylinders, and 94mm B Piston and Cylinders are also optional. Know that using the 76mm crankshaft, VW Rod Journals will require some light case machining, nothing major. If you are really uneasy about this, just go the 74mm Crankshaft, VW Rod Journals and either stock 85.5mm Mahle P&Cs, or the 88mm Slip Ins. We even have a nice Mexican 85.5mm P&C set if your purse strings are tight!
With that out of the way, know that most MPG engines use a heavy pulley and flywheel, but we believe in going the other way. Heavy flywheels take power to speed up, we want to speed up the car not the flywheel! So we are going to use a lightened flywheel. This engine uses this 13lb 8 Doweled Flywheel, you simply do not need a more expensive or stronger flywheel for THIS engine. You can also use any other 8 doweled flywheel (because the cranks above are 8 doweled) a 10lb or a 8 Doweled 18lb Stock Weight Flywheel. Chromoly Gland Nut, and run a stock clutch, nothing fancy.
You’ll find that the 76mm crank and rods, “hits” the case. Don’t freak out! Being the adventurous type, we just have to think a little bit and work through our minor problems in our engine adventure. The clearancing is so minor, you can do this in your garage, or even the back patio (if you time it so the wife is gone! ).
Here is a photograph of a case half that has been clearanced for a 76mm crank and rods. You will find similar when you put bearings on the your crankshaft and set it in place in the case to check, it WILL HIT in these spots. Make SURE that when you are doing this you push the crankshaft all the way toward the flywheel. When the flywheel is on it will pull the crank this way, if you have the flywheel off the crank can “float” to a position it will never be run in, and you’ll be clearancing places you don’t need to, and will end up clearancing twice as a result of your error!
Simply mark the spots that hit with a sharpie and take the crank back out. Make sure the crankshaft is pushed all the way toward the flywheel. When the flywheel is bolted up it will hold it in this location, you do not want to clearance the wrong places because the crankshaft floated toward the pulley (where it isn’t when the engine is assembled and running)! Now, how you clearance the case is up to you. You can use a Dremel but that will take some time because the Dremel is puny. The easy way to do this clearancing job is to grab a hand held grinder with a 4 or 5″ wheel, and work over the areas that you identified with the marker. Don’t worry about making it pretty YET, just lay the metal on the case back until the crankshaft and connecting rods clear. You’ll probably have the crankshaft in and out 10 times. Remember while you do this to wear safety glasses because of the flying chips, AND also remember that you are grinding on a magnesium case. Magnesium is extremely flammable, so make sure you keep the grinder moving, don’t work on one spot for too long, it will get too hot.
Once the crank is rotating in the case without issue, do the other case half. Once that one is done put the connecting rods on the crank, and lay it back into the case. The trick here is to only clearance what you have to. When the engine is actually assembled, the small end of the connecting rod will be held “Centered” by the piston and cylinder. But we don’t have that, and if we did we couldn’t see, so now what? Here’s our trick!
RUBBER BANDS: Put these over the outsides of the 4 head studs, but slipped through the small end of the connecting rod. This trick will center the small end of the rod while you slowly rotate the crankshaft to check for rod/case contact. You need .030″ of clearance. Check and grind until it rotates without interference. If it hits on 1 cylinder, you can assume it’s going to hit on all 4, so clearance all 4 the same way in the same relative locations. When it clears smooth out the sharp edges from your work, and that the case had before you got it! You don’t have to clean it yet, we are still in the “Mock Up” stage.
Now put the P&Cs on (you don’t need the rings for this part of the job, and measure your deck height. You want your deck height to be between .040-.070″. You’ll need 85.5mm Cylinder Base Shims for the 85.5mm and 88mm Slip In P&Cs. selecting the thickness that gets our deck height in our .040-.070″ range. If you don’t have a deck height tool, you can use this Deck Height Measuring Tool. You can use a dial indicator or calipers if you are careful too! Remember, you want a deck height of .060-.070″. It will likely be smaller than this when you mock it up, do some quick math and figure out which set of 85.5mm Cylinder Base Shims you need to put between the case and cylinders to get there. Smaller deck heights are better if you have a choice.
Next, do some quick math to figure your compression ratio out, we are going to build this engine at a target CR of 9:1 for a really efficient use of the fuel! For example, a 1745cc engine with .060″ deck height needs 46cc combustion chambers in the heads, as one combo to achieve 9:1 Compression Ratio. If we have .070″ deck height, we need 44.5cc in the heads for the same CR. We will make the heads match the engine and deck height, since we are doing the heads last. Your goal is to just get the engine’s deck height between .040-.070″. Get the deck height within range, then we will make the heads have the chamber volume we need to get the CR dialed in.
Now you can take the engine back apart and drop the
Crank Gears, Keys, Spacer, Snap Ring
Off at the balance shop. We need this thing to PURR, vibration is wasted energy. This is money well spent! Remember at $5/gallon the paybacks will be swift. When your parts come back, clean everything and start final assembly. Use Curil-T for the case sealant, and Dirko for the cylinder base shims.
For our camshaft, there are not a lot of good choices for a MPG cam. We feel that most cams are designed for “power” instead of MPG. The biggest issues we have are that most aftermarket cams have too much valve lift to be “efficient”. Lift is for power, NOT MPG. We want a gentle cam, with a very mild lift, so we can use soft valve springs. This reduces friction, and is super easy on parts. Fortunately, CB Performance has just the cam we want! We have chosen the CB2231 Camshaft, it has the duration we want, and has very moderate valve lift. Basically ANY really mild cam will work fine. SCAT C20 Camshaft is also a candidate. You could also use the CB 2229, 2230, or 2280 “Cheater Cam”. The CB 2280 Cheater Cam is what was used in the CB Mileage Motor engine article in HVWs (which we had never read until this article was half written).
The use of these cams lets us use stock valve springs, which keeps stress and friction down. We will equip the heads with Bugpack Chromoly Retainers for reliability however, the stamped steel stock retainers are unreliable and just too sketchy. We also carry an Economy Chromoly Retainer Set for those with a really tight budget! Courier Valve Adjusters or Elephant’s Feet are also recommended but not required, you can use stock adjusters, even lash caps are optional because of our conservative valve train! The only reason we can do this is we are only lifting .330″ at the valve, so we can also use stock push rods! The Gentle Valve Train also allows us to use 1.1:1 Ratio Stock Rocker Arms, or retain your stock arms and add Bolt On Rocker Shafts, which are completely optional and certainly not necessary for a mild build like this. You must get it out of your head that you need “more valve lift”, so forget 1.25 or 1.4/1.5 ratio rockers.
You can also either use a Straight Cut Cam Gear for minimal friction, OR if you have some old parts lying around you can use a 36hp Cam Gear, with the matching 36hp Crank Gear. The 36hp gear sets have half the gear pitch of the 40hp-1600cc gear sets, for less cam thrust. If you don’t want every last .2mpg, don’t worry about these cam gear selections, just use a stock or basic bolt-on cam gear, it’s really not a big deal.
For our oiling system, use this 21mm oil pump. Bigger pumps are NOT NEEDED, and in fact incur a lot of pumping losses that rob precious HP that is better used pushing the car through the wind. We are also going to use Z-rod 10-30 Synthetic Motor Oil. Thicker oil is just going to chip away at our efficiency. Full Flow Filter Kit for Type 1 is always a good idea, to keep the dirt out and keep this thing running for years with minimal wear.
For cylinder heads we are using our L3 Cylinder Heads, fly cut to our 46cc chamber size to dial in the CR. You can also use Stock Cylinder Heads, don’t be afraid to take them apart and give a quick “fluff and buff” with a die grinder and sanding wheel. Just smooth the edges up. Clean it, then re-assemble and lube. A good valve job is a wise move, if you can’t do it bring it to a head guy or machinist that can!
Single Port Head Owners: follow the same cam guidelines above, knowing you will be running either the stock carburetor, or dual 1bbl carburetors. Single ports are great torquey reliable engines, and they will drive like a different engine if you put a better flowing exhaust, and a set of dual 1bbl carburetors on there.
For the exhaust system, in previous articles you had a lot of options, but for this engine you do not. Because we are going for efficiency, we MUST have a 4 Into 1 Street Header. We try to cut financial corners where we can (we are cheap too!), but in this case the stock muffler has to go. You can retain stock heater boxes, or you can switch to J-pipes if you do not need heat. You can use either a Single Quiet Pack Muffler, or our personal favorite the Hide-a-Way Muffler. HOWEVER, if you are going to use a center mount carburetor (stock, or Progressive), you must get our Pre-Heat Upgrade to the header. We need as much heat to the intake manifold as we can get. By doing this we’ll be able to jet the carburetor LEAN, knowing that all liquid fuel is vaporized, and the cylinders won’t know they are lean! It will actually burn it instead of unburned fuel making it’s way to combust in the exhaust system. Heat on the intake is your friend! If you have dual carburetors, the Pre-Heat Modification m modification is not needed on the 4 Into 1 Street Header.
Ignition: An Aircooled.Net SVDA Distributor, or a Pertronix SVDA Distributor are a must for really wringing out top MPG. A Mallory Hyfire VI-A CDI Ignition is also nice, but not required; we’ll cover this more in the tuning article that comes later.
CARBURETOR(S): If you are using dual carbs, don’t be stupid. This is a MPG engine, if you start trying to wring HP out of this, your MPG goals are toast and you just wasted a bunch of your time and money. Focus on your goals! If you have a Single Port, either run the stock carb or get Dual Weber ICTs. If you have a Dual Port enigne we feel you have 3 options.
1) Stock 34-3 Dual Port Carburetor. This will work great, and believe it or not, the stock carburetor will get better MPG if you put a larger venturi in there! This is to prevent the carburetor from turning the main circuit on so early, we want to cruise on a lean-tune on the progression circuit. We’ll cover this in more detail in the 2nd part of the MPG series, but the Stock 34-3 Dual Port Carburetor is fine. Remember, you must have as much pre-heat as possible if you use this!
2) Progressive Weber Carburetor Kit. This allows you to run a lean tune on the primary barrel, but retain a “Power Tune” on the secondary for when you need it. Most progressive kits have a poorly designed intake manifold but this Deluxe Progressive Kit is outstanding.
3) Dual 36mm IDF Weber, Dual 40 IDF Weber, or Dual 36 DRLA Dellorto. All of these are excellent. Bigger carburetors will be too large for this MPG engine, so are not discussed. These carburetors are the ultimate MPG carburetors.
That’s pretty much it for our actual engine. The actual tuning of this engine and the actual engine building techniques will be covered in another article, that information will also be able to be applied to “normal” engines. Tuning will mostly focus on the jetting and adjustment of the carburetor(s).
If you have any comments or questions, feel free to give us a shout. If we have missed something or we are not clear on a topic and you mention it (e-mail is best), we will edit this article incorporating your suggestions to make it even better. We also LOVE to hear from those of you who have built and drive this engine. Let us know how your build goes, and how it works out driveability and performance wise for you!
Thanks for reading….Aircooled.Net
Article Written 4/1/12