assh0l3

Just for a basis on what Im expecting for weight... A friend of mine had a coupe like minse striped for a racer, and he weighed it at 1100lbs, the only difference is I need a passenger seat and the turbo. So I think my weight expectations are inline.

As far as the power expectation, its really more of a guestimate, or a goal. I dont have anyhting to really back it up. Im just figuring Ive got all the carburation Il ever need and I can just crank the boost. Im hopint to run probably like 7psi for a while to wee how it goes and then increase it to 15 or so. I treid to use that "tubo selection for noobs" bit but it went over my head pretty quick

gsand

Hey man, My project is a blow through turbo setup, but I'm using a downdraft Weber.

I'll give you a few pointers that should help you out.

As a rule of thumb for blow through carby cars, fuel pressure should be 3-4psi above boost pressure at all times. So at zero boost you will have 3psi fuel pressure, which is pretty standard for NA carbs. 5psi boost you should have 8psi fuel pressure, 10psi boost = 13psi fuel pressure ET CETERA. Fuel pressure must be higher than boost, otherwise the boost pressure forces the fuel back down the fuel lines. Due to the design of the "carbutetor" you cannot just blast fuel into it because you will be constantly forcing the float down, and flooding it completely. Such equals the 3psi rule, so no matter what boost you are running, if your fuel is 3 or so psi higher, the carburetor will work as it is intended to (in this system too, there are MANY other issues on hand).

Your throttle shafts have to have a perfect seal. If you lose any boost out of here, it will run like ratshit and you will never ever find the solution until your shafts are sealed. Theory here, The airflow over the venturi draws the fuel at the correct mixture, but when the pressurized air leaks out of the shafts it will run very rich, because you've lost the air but still have the same ammount of fuel. Unless your shafts are screwed and you squirt a mist of fuel out of the shaft. Then your stuffed and it will still run like ----.

1 way of correcting all this bullshit, is to literally encolse your carb in an AIRTIGHT box. The entire thing. and then run airtight seals for your throttle cable, fuel lines etc. This way, the pressure around and inside the carb is the same (Xpsi), carb has its own atmospheric pressure, and runs as per normal.

Jets will need to be alot richer. You have a severe issue with using the bike carbs. Although they can be Very powerful or NA cars (as powerful as quad throttle bodies), they have issues with boost. As far as I know, the shafts and their design can handle boost fine. The problem, is that each carb (they are 4 individual carbs..) is only single throat. Now the carbs will need to be alot richer than normal to give you a good mixture under boost, but this directly means that you are going to have an EXTREMELY rich setup when you are not making boost. Get it? This is no problem with my Weber, as it has a primary and a secondary throat. Primary is setup for off-boost driving, so fairly standard jetting. Secondary opens up with a combniation of vacuum and +50% throttle. = Secondaries open when turbo kicks in. Richer jets are your away.

One more point, your distributor. It isnt electronic, old school mechanical shizzle in action here. NA cars advance the timing as the RPM's increase, to maintain a steady increase in power/constant compression. You have two systems in place, Mechanical advance which is built into your distributor (centrifigal) and Vacuum advance, which takes its signal off the intake manifold. To run boost at the best possible way, LOCK the mechanical advance, and set up boost retard.

Of course this is only a guide, and It is something you will ultimately have to work out for yourself.


Good luck

assh0l3

To handle the fuel presure I got a Mallory rising rate fuel pressure regulator, it was recomended as a low buck alternative to the Aeromotive one from (somone on turbomustangs.com). Ive also got a bosch fuel pump from an old fuelie mercedes (actually the same one i got my headlights from)

I was originally going to get the weber but the kit was a little out of my price range. Could I just set it up to be a little rich when not under boost and use some cold start injectors and a presure switch to make it up when under boost??

What would you recomend in the way of retarding the timing under boost mechanically?? Would it just work the same way the vaccume adcance does but in reverse, like would I be able to use the same mechanisim? Thats somthing I hadn't considered, I was just going to lock it and forget about it.

sohcpwr

gsand... way to go noob. Ive been waiting for someone who knows alot about turbos + carbs for awhile. Solid info buddy

ComptonsF1NEST

i think a short shifter should be at the top of ur list

4g63t_EGMonster

damn that looks like something out of an african village .. cut that sh*t down to normal size.. haha. sick looking car man reminds me of a Toyota version of the Ae86 which i will add is a sick car.. buddy has one, and with a lead foot you can make that thing do some tight axis donuts. only rpob is power. he'll be the next to hmt his car. rock on keep on the good work

assh0l3

Tell me about it, the shifter is frickin garbage. It like stirring a bowl of pool ***** with a 10ft pole. Im going to cut it down a but and move the fulcrum up a bit, and change the rubber bushings in the linkage for bearings.. That, combined with some poly motor mounts should firm it up a bit.

leed

That thing is sweet!

gsand

Thanks, noob status owns.


Astrovannin, a vacuum advance actuater will not retard under the opossite condition (boost). But, it is possible to make them work as such. I read about a man in the US who turbo'd his Datsun 1600 (err datsun 510 to you yanks, no offence). He managed to use the standard distributor, with what seemed to be simple modifications. He installed a spring inside the actuator, which held the advance arm at its maximum reach. In this siituation, the advance mechanisim is held at full advance when static. When boost is applied, it forces the arm back against the pressure of the spring. Your static timing has to be retarted to make way for the advance being held at full, obviously.

This seemed like a fairly simple design, and seemed to work very well for this guy. But it would be very tricky to set up properly, and never really be perfect. Things such as 1. Sealing the canister to handle boost, rather than vacuum with (which is far more powerful). 2. Setting the spring to operate at the boost pressure, may retard too early and make a big flatspot, or retard too late and put undue stress on your motor. The 3rd factor, is the travel of the actuator arm. This has to be very precise, because it determites the actual amount of retard is implicated. As you may know, even 1 degree can make a difference.


You then have other choices, such as retrofitting a vacuum retard canister from another car. Over the years (predominately in the mid to late 80's) many turbo cars were being produced using carburetors. A few that spring to mind is the Renault 5 Turbo, Mitsi Sigma turbo, buh, heaps more. Just rip the retard module off it, and if you know how the systems work in dizzy's, its a pretty simple thing. If you get the offset points the same as the original turbo dizzy, it it should retard the same ammount. If you are running lots of boost, I suppose you could use a manual boost controller on the boost line, to limit the booost supply.

Well I hope this helps you out a bit, feel free to shoot me a PM or whatever and I'll answer the best I can....



I was going to get a rising rate fuel reg, but a person I know has his turbo carby car set up the same way I described. I have a bosch efi fuel pump (external), with somesort of regulator that came with it, which I will be feeding directly into the carby, and then returning back to the tank after the float bowl is filled. The weber carbs have provision for this in the castings, just need to be drilled, tapped, and a hosebarb fitted.

It it means anything, My car is not running yet, the motor is being built as we speak, but I'll be posting the whole lot and progress pics/writeups along the way. And yes, I have planned for many headaches along the way