was just wonder the specifics of turbocharging a carborated engine without running it too lean, heard talk once that you need to build a box around the carb, any info or pics would be appreciated
yeah get a box to put the carb in,vortech makes em,and i think turbonetics,this keeps pressure inside and out side equal,lot less problems as a carb works under va*** not pressure,get a rising rate fuel press. regulator, and an msd btm6al box,match a turbo to your engines displacement, some plumbing and your rippin. iv done on the cheap if you look hard enough, you can find this stuff used. not for the beginner, but not that hard,i suggest searching the web for blow thruogh turbo and such as it would take me 5 years to type every thing about this, stay away from draw threw setups,unless you like complication in your life[turbo ****ing thru carb] its an idea from the50s,and just because its old school doesent make it good hope this helps [qyuote=rodknocker]was just wonder the specifics of turbocharging a carborated engine without running it too lean, heard talk once that you need to build a box around the carb, any info or pics would be appreciated[/quote]
you don't NEED to enclose the carb. the main issue with carbs, is leaky throttle shafts. normally not a problem, but under pressure, you'll have an air/fuel mix blowing out through the throttle shafts. an easy solution is to dis***emble the baseplate, and drill some small holes that intersect the throttle shaft holes, now would be a good time to rebush them too. the most common way is to drill straight up from the gasket surface, and drill the gasket and manifold to match, then tap the manifold for a pipe fitting, you then tap off your pipe from your turbo to the carb to pressurize the shafts with straight air instead of air/fuel mix, still leaky, but not leaking fuel vapor into the engine compartment. other than that, make sure that your carb isn't one of the oddballs that has the float bowl externally vented, if it is, you'll have to seal off the vent, or do a similar modification. IMHO it's a pain in the **** to have to remove part of a box to access the carb for adjustments, and you can't do it with the engine running under boost. do a google search on "blowthrough carburetor modification" or some such and you should come up with some how-to's. as far as running too lean, that has nothing to do with how the carb is fed by the turbo. if you're gonna mess with boost, it's cheap insurance to invest in a wideband O2 meter to get the tune right, they're not "cheap" but a helluva lot cheaper than a grenaded engine.
[/quote] Draw-through setups are not as bad as they are made out to be. You just need to stay away from a long cold intake tube after the turbo to avoid fuel dropout. Another problem is the turbo seals, because now you are putting fuel across the compressor. Draw-throughs are still used in industrial applications and roots-blown engines are all draw-through (pretty much all).
vortech sells a box, or you can go the other ways and have a headache. pressure box makes it easy, they have a full right up on it. procharger has the stuff too, just replace blower with turbo in the instructions. if you can tig aluminum you could make one cheap. just have a bead on the pipes to prevent blowoff.
It's not quite as simple as boxing the carb and blowerizing the motor... a carb setup to run at atmospheric pressure is designed to deliver a set amount of fuel based on the vacuum signal generated by the motor attempting to fill empty cylinders during the intake stroke. When the motor is force-fed, the fluid mechanics inside the carbie change; an atmospheric carb setup will not provide enough fuel for the motor. The enrichment circuit, main jet circuit, and accelerator pump circuit will have to be revised (enriched) to match in increase in m*** flow thru the carbie. Also - when you go to forced induction, the fuel pump pressure has to be boosted to overcome the pressure inside the carbie. Fuel level is a function of float level and fuel pressure - a 5# pump ain't gonna feed a 7# boosted carb! Finally - the fuel injection folks have figured out the way you eliminate turbo lag is to retard the snot outta the motor - this causes a fuel burn in the pipe between the exh manifold and the turbo (downpipe); you'll want to recurve the dist to provide min initial edvance and allow the boost to spool up the motor. The o2 sensor is a great tuning tool - yeah, it's high tech, but LOTS cheaper than a cooked motor! Back in the 80's, we had fun with the turbo guys as aftermarket turbo kits would most likely eat their motors with more than 30 seconds of WOT operation. Teeny motors wound tight = holed pistons! Modern engine management eliminates this potential, but there's LOTS to be learned which can be sucessefully reverse-engineered onto a carbie setup. And no. You don't necessarily need a box; a hat will work as long as the float bowl pressures are equalized.
Man, your question is so open-ended that you'll never get what you want in one piddly thread. You need to do some research and maybe follow in the footsteps of some guys that have been there, done that. Go to this site and register, and find out if anyone has done something similar. All the tips above are valid, and another concern is using stock floats in the carb; some of them will crush under boost and then you're gonna have a helluva problem. There is a local guy that runs a Fairmont with a pretty straightforward single turbo setup through a Holley into a 302, and it runs 9.8s @ 130-something MPH. Pretty damned impressive.
Da Tinman is right C&S has the fastest blow through turbo'd car and the fastest blow through supercharged cars on the drag strip. They can build you a street carb. Call and ask Roger what you need. This not a job for newbys. They can send you a carb that will be perfect right out of the box. msmbob
Put the carb before the turbo. Not as efficient, but...no funky tuning, no ugly box, to leaky throttle shafts, no linkage or choke issues, no taking box apart to tune, in short, tons easier to work with.
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