The system I will be talking about will be "blow through". What this means for those of you that do not know, is that the turbo force feeds air into the top of your carburetor, puts it under pressure (boost). The basic differences between a blow through turbo and a draw through turbo is that on a draw through system, the carb sits before the turbo charger. The turbo "draws" gas and air from the carb, the gas and air go through the turbo and then get crammed into the engine. I personally prefer a blow through system for off-road cars, so that is what I am going to spend most of my time talking about.
I'll start off with a very important part...the turbo. Turbo sizing is important. I mean...you can't just go and yank a turbo off of a Semi and bolt it on your 1300cc...well, you could...but it's not something that "SHOULD" be done. Sticking with the budget minded guy who does not want to pay to have a turbo custom built for his car...I will loosely recommend junkyards and e-bay. I am not going to go into the science behind how to select the right turbo for your engine...It's pretty long and drawn out and I feel it would bore most of you to tears and make you lose interest in a turbo project. So...if you have found a turbo and want to know if it is too big or too small...drop me a PM and I will tell you. Now...here is a short list of cars with turbos to look for in a wrecking yard.
The turbo's from these cars will work if you have an engine between 1600 and 1835cc's.
Mazda's built before 1991 such as the RX7, MX6, 323 and 626.
Mid 80's Mercury lynx.
Ford Thunderbird turbo...I think the years were like 87 and 88 but not positive.
Subaru's are good for turbos.
Mid 80's to 1990 Chevy spectrum.
Isuzu had a few as well...but they slip my mind.
90 on Ford fiesta.
Pontiac 2000
Pontiac sunbird.
That's just a very small list of cars you can rob a turbo off of that will work for VW's 1835 and under.
Now...If you built a 1914 or bigger....the list of turbos you can scrounge is HUGE...I will go through a few of them..but can't cover all.
Volvo.....740, 760, 850, V70, S70, and 940.
Late 80's to mid 90's Chrysler with 2.5 and 2.2 liter engine.
Mitsubishi Talon and eclipse.
Saab, good for turbos and intercoolers.
Nissan 300ZX.
Mustangs.
The list goes on and on...you get the picture...there are plenty to choose from and I will be happy to help any of you when that time comes.
Now...lets say you found a suitable turbo. You are now going to have to spin it, which means an exhaust header with a flange for your turbo. You CAN just get an Tri-mill off-road exhaust and weld the proper flange to it so your turbo will bolt up...This will work...BUT...if it's a cheapy...it won't last long. The turbo makes exhaust run HOT, it also puts a lot more pressure on the gasket mating surfaces...so it will blow out gaskets, it can take off ceramic coat or turn it brown, chrome will bubble off and turn blue etc. The thin wall tubing of your average tri-mill was not meant for that kind of heat...so eventually, it will get weak and most likely break. There are a handful of companies that make turbo headers. They have nice thick flanges and most of them are up to the task. CB performance makes a pretty decent turbo header, and a nice clean design. As a matter of fact...when I build a turbo header...I stick really close to the CB design...I use thicker wall tubing and heavier flanges...because I overkill most things that I do...but for your average guy...the CB header will work just fine. Mine are a few bucks more than this one...if you like overkill.
http://www.cbperformance.com/catalog.asp?ProductID=308
So you have the turbo, you have the exhaust...What now? Well....a carb would be a good idea. Since I am somewhat on the cheap theme...let's go with a single down draft, center mounted 2 barrel. Such as a Weber IDF 40 or 44. A Dellorto DRLA 40 or 45. Both carbs will need basically the same things to have pressure blown into them. There are MANY mods you can do to a carb to deal with pressure...but most of you guys are not going to be running 15 to 20 pounds of boost. So your basic mods are all that will be necessary. First...you will need a pressure hat that goes where your air cleaner used to. This will be what you hook your turbo into. http://www.cbperformance.com/catalog.asp?ProductID=310
Next...there are some things that people run into when trying to pressurize a carb. Many of them get discouraged and give up...However, these problems are can be addressed pretty easy. One (and this is a biggy) Most of you know that your Weber or dell carb should be ran at around 3 pounds of fuel pressure to run correctly. That is still true. BUT..when your turbo is spooling up and on boost...your carb is pressurized and so is your float bowl. So lets say you are trying to push fuel into you float bowl at 3 pounds of pressure...but the float bowl has 7 pounds of pressure in it...well, obviously you are not going to be able to push three pounds of pressure into a 7 pound of pressure bowl...it just won't go in. Okay...now what...I mean...you can't crank you fuel pressure up to 8 pounds because when your engine is not on boost and your carb has no pressure in it, the 8 psi will over power the needle and seat and will just flood the carb. SO.....what you need to do is increase your fuel pressure as boost increases. You need to keep your fuel pressure slightly above that of the pressure in the float bowl. What you need is call a boost sensitive fuel regulator. This is how it works.... You set it up just like pretty much any other regulator, you dial it in so your carb is being fed 3 pounds of pressure. Then you hook this regulator into you boost pressure. So you run a line from your pressure hat, turbo or ducting to this regulator. When you build 1 pound of boost, your regulator reads this and increases fuel pressure accordingly. So if your fuel bowl is pressurized with 7 psi, your regulator knows this and has increased your pressure enough for fuel to now enter your fuel bowl. http://www.cbperformance.com/catalog.asp?ProductID=581
Your average electric fuel pump only sputs out about 5 psi. So when you need 10...that just ain't going to fly. So...you can buy a Holley pump for fuel injection...(over 100 bucks) OOOOOOOORRRR...you can go back to the wrecking yard and look for this specific pump......Ford trucks with fuel injection, a lot of Lincoln, crown vics and such from the late 80's came with a fuel pump that will work just great with a blow through turbo. It is referred to as the E2000. You can skip the wrecking yard and pick up a new one at the parts store for around 70 bucks (usually with a warranty). The pump will look like a long fuel filter and will have E2000 stamped on the side of it. It was used on a lot of Ford cars and trucks with fuel injection...and it's what you need.
You have now taken care of getting fuel into your boosted carb the correct way...Now what about jetting? Jetting a blow through turbo carb can be a pain. The problems come, when up on top end and under max boost. Here is the problem, your car is now being force fed air, so with more air, you obviously need more fuel, so a bigger main jet. Sounds simple enough right? Well...no, it's not. The problem is...once your main jet is large enough to run the right fuel mixture when on boost...it's then WAY too big for lower speeds when off boost. Not an issue in a race car because your throttle is pretty much shut or open. But on a car that needs to be driven at all speeds, it needs to be addressed. When your idle jet makes the transition to the main jet, your car won't be on boost yet and will go VERY rich. You deal with this by using the correct emulsion tubes. These e-tubes are specifically for turbo charged blow through carbs. They allow you to run a big enough main jet and not flood out when off boost. http://www.cbperformance.com/catalog.asp?ProductID=520
There is GREAT detail I could go into here about jetting and how it works...but I will just stick to what parts you need and why, for now.
We have now worked out the problem with the main jets (pretty much) but what if you want that extra bit of fuel shot in while under boost? That is where a thing called modulator rings comes into play. They look like a small velocity stack and bolt in place of where a velocity stack would. They are little rings (as the name suggests) and they are normally 1 to 2 mm smaller than the venturie in your carb. What the mod rings do is create an extra high pressure spot above your main jets when you are under boost. What this does is send more pressure to your main jets, so they spray fuel with a higher pressure. Kind of an over simplification...but that is the general idea. Mod rings are kind of difficult to find these days with the sizes you need...So I have began making them myself in different sizes. I charge 30 bucks a set.
There are a lot of other nickel and dime things left and little secrets that I will share with you guys as we go. But right now...you have just got "the scoop" on the black magic part that most seem to keep to themselves. Feel free to ask any questions...I know that this is new to most of you...so there are no dumb ones...Also...go take a read over at my Forum (forced induction) there is a lot of great info over there.
