Turbocharging a 250

[Anonymous]

The Jetfire used a sidedraft single barrel version of the 2-barrel Rochester carb (itself half of a Quadrajet). In spite of the most complex fuel/air control system ever put on a production car to that point, the system was simply ahead of its time and not up to the task assigned to it. However, GM learned an enormous amount from these early turbo engines and transfered much of what they learned to the turbos of the late 70's and early 80's. For instance, even though the Buick 231 V-6 is only slightly larger than the Jetfire's 215 V-8, its turbo is vastly superior and its carb flows 3 times the CFM as the Jetfire's. So I wouldn't rely too much on adding injection to one of the GM turbo units like I have been advocating.

 

[Anonymous]

So the water injection wouldnt do much and is not neccesary with a draw through right? Wouldnt the Quadrajet assuming it's the 750 CFM one overcarburate the engine? Beacuse using the formula for cfm assuming a 5500 RPM redline and 80% Volumetric Efficiency, the cfm neccessary would be about 320 cfm, that's less than half the cfm for the smallest Quadrajet. Wouldnt the carb need alot of adjusting and tuning to get it to work right?

Also what is the lowest number of gears to run for the car? Because i would like to get a better acceleration than the one with the 2.78 rear gears. My driving hardly ever reaches the 3500-4000 RPM range, most of the time it is under 3500. What rear gears could i use to get better acceleration and still get good gas mileage with my driving habits? Maybe in the 3.0-3.25 range? Im not drag racing the car or anything it's my daily driver but i would like better acceleration of a stop light for example.

 

[Anonymous]

As Jack and I said, water injection can help these engines as you approach their boost limit. I wouldn't worry about it at the outset, though.

Slightly taller gears won't hurt the turbo, either, but again they aren't needed at first. Turbos like being loaded, so I would stick with the gears you have until and unless they prove unsatifactory. The turbo should give you the performance boost you are looking for with the gears you have.

 

[MustangSix]

The Jetfire really NEEDED the water injection because they had a static CR of 10:1. Without water, the engines quickly detonated themselves to pieces.

And in those days, car warranties were what, 6mo/6000 miles, 12mo/12000 miles? Not as long as they are today. Imagine all the ticked off customers with nearly new cars that had bad engines.

 

[Anonymous]

The Jetfire really NEEDED the water injection because they had a static CR of 10:1. Without water, the engines quickly detonated themselves to pieces.

Yeah, especially given the cat-pee they had for gas back then...

Lessee now, if the average car in 1962 came from the factory with a CR of 7.0:1, and the Jetfire had 10:1, is that equivilent to a car coming from the factory today with a 14:1 CR...and then add a turbo? Yeah, it would NEED water injection...!!!

 

[Anonymous]

Wouldnt the Quadrajet assuming it's the 750 CFM one overcarburate the engine? Beacuse using the formula for cfm assuming a 5500 RPM redline and 80% Volumetric Efficiency, the cfm neccessary would be about 320 cfm, that's less than half the cfm for the Quadrajet. Wouldnt the carb need alot of adjusting and tuning to get it to work right?

 

[StrangeRanger]

Except that with the turbo your airflow increases by 1/3-1/2 depending on boost so that 320 CFM starts to look more like 450-500. Remember you're only using the secondaries when you need them, the tiny primaries work wonderfully in "cruise" and when you need all hell to break loose it will.

 

[Anonymous]

Wow! This thread has my juices flowing! Bid on the e-bay assembly. No competition, please!

Anyone got a spare exhaust manifold? I haven't had a chance to check the yards in the area yet. My '80 has that terrible exhaust/cat manifold. I'll need something older and simpler. Any manifold suggestions from others who've been more deliberative in this process?

If I manage to put this together, I'll have an unused FPP dual out header for sale.

The Buick setup adaption harkens back to the early days of hotrodding and cobbled together improvements from assorted factory parts.

 

[Anonymous]

Tatao, according to the TurboBuick forum the turbo Quadrajet is an 800 CFM carb.

In any event, SR is correct about the interaction between turbos and carbs. Furthermore, to preclude leaning out at high RPMs, turbo carbs are designed to operate at about half their rated flow while at WOT. That way the velocity in the venturies are kept at optimum. If the velocity gets too high, fueling and cylinder filling suffer.

 

[Anonymous]

Tatao, there is a really good website on how to build your own water/alky injection kit from hardware store parts and an EFI fuel pump, all for less than a couple of hundred bucks, at http://home.att.net/~stevemon/AlcoholInjMod.html

I have to admit that I have this website tucked away in my favorites, just in case I need it for my car...

 

[Anonymous]

Well that was FUN! Got outbid on the Buick turbo setup in the last 20 seconds. Thought my ship'd come in. Just have to keep looking.

 

[66Sprint6]

Dont worry, I got outbid on so many turbos its not even funny, ones that went for like 41.00 and my bid was 40. Stupid, but Im glad it happened cause I happened to come across a guy who had a couple of the exact ones I wanted brand new and I had just made nearly the exact amount he wants for them. Im doin a Blow thru set up tho, not real keen on the draw thru, I like bells an wistles including Blow Off Valves and intercoolers. Oh well, keep up the search, if I find anything Ill post it for you.
Matt

 

[CobraSix]

Careful buying used turbos...you usually get what you pay for.

Slade

 

[66Sprint6]

Very Very true,
Also, if you find a used for cheap, it will need a rebuild, even if in good condition I would get it rebuilt before using it and that will become costly quick. I think its almost better to look for one thats already been rebuilt or is brand new and pay more for it right now. I got lucky, but I almost won a few others and then realized that buyng the kit to rebuild it alone was more than what I would have paid for the turbo and then both would equal more than a rebuilt or new model. So I held out for a bit ( I know, hard to do, lol) and waited till I had enough money for a new one.
Matt

 

[Anonymous]

How many jet sizes richer should the secondaries be on a vaccum secondaries carb that is going to be used with a turbo be it either draw through or blow through? I want to run about 10 psi of boost, the car is going to be my daily driver so i dont need that much boost. The highest I might go would be 15 psi. Would 10 psi of boost be safe to run on a draw throught setup? would 15 psi be safe as well? Would the richer jet sizes for the secondaries on a carb still be used on a blow through setup?

 

[xctasy]

In my opinion, if the carb flows 250 hp then it'll do a 250 with 10 pounds boost. But it needs to be able do meter out very small amounts for a 231 type application at idle to before boost sets in. This is a metering rod issue.

Any turbo will need a wider range of settings. Richer secondaries and the total amount of primary fuel flow in cc/minute must be enough to flow the peak power you are looking for.

For 250 hp, total flow needs to be around 1500 cc/minute with around 300 cc/min each jets for the front (600), and the balance for the back(900 from two 450 cc/min jets.

But a Qjet is a tough nut to crack. Rochester Reproductions did there homework with this gem. There are literally hundreds of metering rods, hanger and jet combos. It took me four weeks to crack Holley jetting combos, and a few days to crack SU combos. With the Qjet, it could take months.

The Buick 231 Turbo guys will have it cracked. Get a good repore on there websites, raid the info, and share the wealth. Chevy six cylinder guys should take note. Your 250 I6 Turbo set-up could become a benchmark for others to follow.

 

[80broncoman]

A carb that flows 400 cfm max can flow 800cfm when air is forced thru at 15psi this is why smaller carbs work well with blow through system.
But remember one thing fuel pressure must be higher than boost pressure or when the float drops you will push fuel back to the tank!!
Jim

 

[Anonymous]

Tatao,

I have no real experience with blow-through carb'd turbos, but from what I've read, one should expect to start with normal primary jets and plus-2 on the secondaries. FWIW, I also HIGHLY recommend using a pre-turbo pyrometer to monitor your exhaust gas temperature. You will want to jet the secondaries enough to keep max boost temps below about 1250 F. And as 80broncoman notes, with a blow-through setup you will have to ensure that the carb's fuel bowl and the back side of the fuel pump receive boost pressure. Otherwise the engine won't run at all under boost.

Draw-through turbos are another matter altogether. If the carb is too small you'll have to jet it up, but then it won't run right at partial boost (it will be too rich). The answer is to grossly oversize the carb to assure proper fuel pickup in the secondaries while under boost. Buick used the 850 cfm carb (with standard jetting) from their 455 GT engines on their '78-'82 turbo 231 engines -- a carb that would be ridiculous on a normally aspirated 231.

One last point...you are planning to use this on a Ford 250, right? As has been said elsewhere, running more than about half a bar of boost (~7.5 psi) with any log-headed engine may be out of the question without extensive modification of the engine. Start with low boost, amigo, and build up to what the engine can safely stand. Good luck!

 

[CobraSix]

for blow thru, Holley I believe makes a carb with the proper boost referenced internals. For a blow thru, you'll also nee a high pressure fuel pump. You'll need a fuel pump with approximately 4-5 psi more then your desired boost pressure right?

The carb sizing makes since. Think of it like this: a 231 CI engine with 1bar of boost (14.7 psi) will use the same air and fuel as a 462 engine. you are cramming twice as much fuel and air into the engine. AT least in THEORY.

so a 250 running at 10 psi, should need the same air/fuel requirements as an engine sized around 420 CI. So maybe look for a carb for the 429CJ.

Am I way off here? Basically, a turbo is just an adjustable engine size device. cruising around town? only need 250 CI? no boost. Hauling arse...need 400 CI? There you go...10 psi.

My 2.3L volvo @ 14psi runs the same power as the mustang GT 4.6L V-8. Probably the best example I can think of.

Slade

 

[Anonymous]

Guess I'll be going with a draw through setup. Too much money for the blow through. A turbocharged engine has 100% VE right? So using 5500 RPM as a redline on the cfm formula, I would need approximately a 400 cfm carb. If a 231 Buick used a 850 cfm carb, then 400 seems not enough for a 250. Would a 600cfm carb with vaccum secondaries get the job done? I want to be conservative so i wont overcarb the engine. If that carb is OK would i need to put richer jet sizes for the secondaries?