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Step 1: Engine Basics

Below is a description of what Tim Van Setten and many of his fellow buggiers use in their rails. A turbo can be installed on any size motor so don't let the following description scare you off. Be aware though that the motor will only be as strong as the weakest link.  For a play buggy that only sees occasional abuse you may be able to get away with using your existing motor. For the highest reliability and maximum HP you're going to have to spend the money for the good stuff.

ALWAYS REMEMBER:  You must always use good gas, make sure the turbo always has a good supply of oil and do not allow the motor to detonate. These rules cannot be broken.

 

There's a lot of people with different engine configurations who just want the performance boost without having to build a new motor from the ground up. The Fuel Injection can be tuned to work with all VW's, 4 and 6 cylinder engines. The turbo is a different story however.  Generally speaking, what engines aren't suitable to turbocharge? 

First thing for a VW to convert to fuel injection is you want dual port heads. On a turbo motor, you WILL use Av-Gas, or some other very good gas. If you don't, the detonation will take the ring lands right off the pistons. You cannot cheat on good gas on a turbo motor, not even once! (There's more about AV gas on the Fuel Systems page.)

Overlap is not your friend with a turbo because of the boost pressure and exhaust back pressures of a turbo motor, keep it to a minimum. The cam still sets the personality of the engine, whether it be a torque engine or high RPM. As far as lift goes, unless your making a killer engine, the turbo will push it in just fine.

Keep the compression ratio around 8.5 to 1.  If you have a higher compression ratio to start with, just don't run as much boost. This is why it's best to build your engine for your application, street, or off road, turbo or non-turbo.

 

Why is low compression better for a Turbocharged Engine?
You make horsepower by how much air you move through the motor. A high compression 10:1 engine is more efficient than a 7:1 engine, so the 10:1 engine gives you more bang for the buck. However, because the lower compression is not as efficient, it will move more air through it. So, at 15 PSI of boost, the 7:1 engine will have an effective compression ratio of 14:1, will not be into detonation, and be moving more air, making more horsepower than the same conditions for the 10:1 engine. That engine will be in self-destruct mode, have detonation, and an effective compression ratio of 20:1!

This is why the racers only run 5:1 or even 6:1. All of this is great for a drag car, but because the static compression is lower, you will not have much bottom end torque either. So, since most of us don't drag race every place we go, a good compromise would be 8:1 or 8.5:1 compression. This way you don't loose too much bottom end for driveability, and if you don't run too much boost, say 10 to 15 PSI, you stay away from the gray effective compression area of 15:1 and up.

Remember, that the shape of the combustion area, cam, type of fuel, etc. all play a part of when the engine starts to detonate. It comes down to start with low boost, and sneak it up from there until you run into problems.

 

What should people keep in mind when building an Engine for a Turbo?
Note: You will find that you will spend more money on your transmission than on your engine. Transmissions with a turbo you'll find that the lower the gear ratio, the better and faster the turbo comes on line. We all used to run 4.37 ring and pinions and some 4.12's. With the turbo setups now, and after cleaning all the teeth off of them, we now use the 3.88's just for strength! Some use the fermic puck clutch disc, but my personal choice has been to go to the "Double Disc" setup. To date, that has been the best clutch I have ever had! You'll pay more to do it, but it will be the last clutch you put in.
The King of the Hill Motor:
What most of the buggy group has done (that let's me hang out with) has ended up building their engines like this. First they use a good case or after market one, that has dual oil relief's, and 10mm studs that do not have case savers on them. The case is drilled and tapped to accept the full flow oil mod. They also cut the cases to accept the 94 Cima cylinders while moving the studs out, and installing the case savers so that maybe just the tip of the threads show. Next  use a welded-up 82mm stroker crank (2276) from your favorite supplier, and have the case clearanced. Some go with after market rods so they can slip in a 84mm crank (2332). Assemble the bottom end, and using Super Flow heads, or to keep within a budget, CB 044 heads with the 40mm intakes, and 37mm exhaust valves works fine and keep the compression ratio to 8.5 or less. If you really want, a little porting and polishing and cleaning up the ports works great also with these heads. Setting the compression ratio to about 8.5 to one is the best of both worlds. The flywheel should be converted to the 8 dowel pins. Always use a chrome moly gland nut! Some use the stock ratio rockers, and others have used the 1.25 roller rockers. This is a personal choice because the cam mfg. specifies how much valve lift and when it will occur with what type ratio rockers. That's about it for the magic in the engine.

Valves: One interesting thing about heads we found with the turbo engines is that some people have taken and made both valves the same size. Rumor has it that they are different sizes to keep the vacuum signal high to keep the carb happy. Anyway, the one's that have made both valves 40mm are very fast and an interesting side effect is they say it takes longer to heat up the motor. They seem to run cooler.

Cam: On naturally aspirated engines that run high RPMs, usually there is a lot of overlap because the air doesn't start moving instantly. By opening both valves at the same time, it gives the intake a head start and helps to flush out the cylinder of the exhaust. The exhaust by now is a column of air that is already headed out the pipe and helps pull in the intake charge. On turbo cars, this valve overlap will allow the increased cylinder and exhaust pressure to flow backward into the intake.

Much has been written on Camshaft theory. Unfortunately most of the published research is done for non-turbo or carbureted engines. When you have a pressurized intake system and exhaust back pressure from the turbo, much of the existing theory goes out the window. The following links may give you some insight into normally aspirated camshaft theory.

Camshaft Selection
Camshaft Story
Basic Camshaft Science

Some turbo cam grinds also wait with opening the intake valve until the piston is already headed down. This is because on a boosted engine the exhaust back pressure can be as high as 30 PSI. The intake pressure under boost is only 15 PSI and will be blown backward. By waiting until the piston has started downward, the cylinder pressure drops and the trick is to open the intake valve just as the cylinder pressure is crossing 15 PSI (in this example).

Good high performance cams for naturally aspirated engines will have a intake and exhaust duration of say 270, 280, or 288, 298 etc. Notice the exhaust event is longer than the intake. On turbo grinds, it is always shorter, say 270, 260 (intake, exhaust), or 275, 255.

On turbo VW's, reports are coming in that the Engle 110 turbo grind has better bottom end than the Engle 120 turbo grind. The turbo grind 120 loses bottom end but trades it for top end RPMs.  This is all "Seat of the pants" scientific evaluations. Hopefully somebody out there has done some "Turbo" cam comparisons. I have used a regular Engle 120 and have had very good success although I would recommend a turbo grind if you are building a new turbo motor.

Engle Turbo Cams Part Numbers:

Engle 110: TCS-10 284 deg advertised .430 lift(in) 112 lobe center 276 deg advertised .420 lift(ex) 112 lobe
Turbo cam street/strip good idle-low compression.

Engle 120: TCS-20 294 deg advertised .435 lift(in) 112 lobe center 284 deg advertised .430 lift(ex) 112 lobe
Turbo Drag race only/large cc-low com

Rod Length:  What's the difference in the length of the rods and what effect does it have on an engine?  After doing a lot of research, here's what I found. First, a stock length rod will make good bottom end torque because of the thrust angle relationship to the crank. The piston speed is much faster for a given RPM compared to a longer rod. The long rod motor has 3 things going for it. First, the piston speed is slower because the thrust angles are less. Second, because the thrust angles are less, it can spin the crank faster. And third, the reason a long rod engine makes more horsepower than a short rod is because the piston is at the top of the cylinder longer, so the combustion pressures have more time to push on it. Just things to consider when building up an engine. Short rod = Good bottom end torque and mid range. Long rod = Good mid range, excellent high RPMs.

Full flowing the case is recommended with turbo engines.  To full flow a VW case you plug the oil exit hole in the case where the pump pushed the oil into.  Then you change the pump cover to one that has an oil exit fitting. Now ALL the oil for the motor will flow through this fitting, through an external oil filter (and maybe a cooler if needed) and then back to the case right at the main oil galley. You drill and tap a return fitting at the case plug just to the left of the crank and just above the oil pump.


Above picture shows line from pump on bottom, and case return line above.

Warmup Reminder: You're now going to have more pressure in the filter and oil lines so it's even more important to use the right viscosity oil and to let the engine reach operating temperature before driving.

Oil Filter: Use a high pressure full flow filter such as the FRAM HP1. The typical automotive oil filter has an oil pressure bypass inside. If you want 100% of the oil filtered you need to use a full flow oil filter.

Pressure Sender: An interesting idea stolen from the off road circuit is that the oil pressure sensors seem to fail more often when mounted on the engine. The extra vibrations seem to do them in. They mount the pressure sensor on the remote oil filter where it does not see the engine vibrations.

Oil: At full throttle, the turbo can spin at speeds upwards of 100,000 RPMs. At these speeds it's going to need a constant supply of oil to lubricate and cool the bearings. It will have a small supply line going into the top (1/8" pipe thread)  and a larger return line coming out the bottom (1/2" or 5/8"). You can supply the turbo with oil by adding a "T" fitting at the oil pressure sending unit on the engine (next to the distributor.)

Why the bigger return line? After the oil goes through the turbo bearings, it's going to get whipped into a frothy lather.  It's important that this large return line be allowed to gravity drain back into the case at a point above the oil level. This will allow some time for the oil and air to separate. You can return the oil into a valve cover, or into the old fuel pump hole. It never-ever "T"s back into the oil lines!!!

Oil Pressure: Wire the oil pressure sender to a loud horn. Something that's loud enough to overcome the noise of your eyeballs rattling at the top of that monster hill. With the higher RPMs, full flow, and bigger oil pump it is possible you could run out of oil at the top of a hill. Depending on your application, it may be necessary to increase your engines oil capacity through the use of a deep sump or dry sump. That decision is something you have to make yourself. I can say this though, your engine will run without oil for a certain period of time. (Don't test this though!) Because of the high rotational speeds of a turbo under boost, it will fail quicker than your co-pilot can say "What was that noise?"  so keep it oiled.

Oil Type: The science of oil and oil types is enough to fill a book so don't expect this paragraph to answer all questions for every engine application. You want to use an oil with an SE or SF classification. This classification has antiscuffing agents that turbochargers like. Watch out with multi-viscosity oils. The polymer additives in these oils do not like the heat of the turbo bearing very well. In a street car with a really hot turbo, these viscosity additives can aid in oil "coking" which means that after you shutdown the engine, the oil will bake itself into charred clumps in the turbo's bearing housing. In a buggy, the turbo will typically be exposed to open air so it will tend to stay cooler than it would be in a closed engine compartment so oil coking is not as much of a problem. Whenever possible avoid these multi-viscosity additives and use the proper straight grade oil (SAE 30, etc.) If your climate requires you to use a multi-viscosity oil, then use the smallest range of viscosity necessary. One more thing: It should go without saying that you should change your oil often.

 

Further Reading:

FAQ on Motor Oils
Speed-O-Motive Service 1 - Quench Depth and Detonation
Squish What it is and how to check it
Rod Length article

Ignition and Combustion Tech Faq

A Quick Look At My Engine Ideas
- intake & exhaust runner, cam
Standard Abrasives - DIY Cylinder Head Porting Guide

Automotive Calculations
Aircooled.Net, Inc. - Deciding to Build a Type 1 Performance Engine
The Causes of Internal Engine Knock, and How to Eliminate it. By Ray T. Bohacz
Intelligent Engine Mods

 

Intro ] ReadMe ] Basics ] [ Engine Basics ] Intake ] Injectors ] Fuel System ] Controller Wiring ] Test & Tune ] Turbo ] Exhaust ] Parts List ] Methanol ] Carbs & Turbos ] My Installation Guide ]

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