Turbocharging a 250

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I still think a Blow thru set up would be better since you can add an intercooler and thus run a higher boost. Also it would let the fuel heat up from the compressed air.

Personally, I'm going to add EFI to my car (using megasquirt) before I go to a turbo set up. While carbs are great, I think the best set up for turbos is EFI, but that is just me.

But the Buick system is very tempting with the quadrajet.

Slade
 
Tatao, I may not get a 50% increase in power right away, but then I am not limiting myself to just half a bar of boost either. I was just saying that a stock engine should have no trouble accepting half a bar of boost. Also, my system ultimately will be LPG fueled, which will further complicate matters. In any event, I am confident that I can reach my goals.

CobraSix, I agree that for max performance one needs to go with EFI. What I was describing to Tatao was a very economical system that any handy mechanic can get up and running with a minimum of effort and cost. One of the advantages of the GM unit I am using is that it's already engineered to work with a engine similar to a 250. That factor alone will eliminate many of the hassles normally associated with adding a turbo to an old engine. FWIW, the GM draw-thru turbo completely vaporizes the fuel before feeding it to the intake log. The combination of the 'heat of compression' and the swirling action of the turbo compressor blades ensures complete vaporization and very even fueling cylinder-to-cylinder. This alone overcomes many of the drawbacks inherent in the log manifold design.

I am looking forward to getting my engine back from the shop and in the car. I can't wait to see how it runs! :)
 
I agree...I think the GM set up is a nice setup for the 200/250s. heck, if GM built it and put it on a GN, it can't be that bad of a design can it?

Slade
 
Wouldn't a J-pipe like the ones on the draw through setups be too restrictive or slow the exhaust gasses too much mainly due to the steep bend?
 
It is certainly more restrictive than a dedicated header, but there is still pleanty of energy in the form of heat and exhaust velocity to spin a turbo.

Don't get hung up on small restrictions in upstream side of the exhaust. You'll still make pleanty of boost for a draw thru application. Focus instead on lowering the backpressure on the downstream side to make sure that what you have available is put to good use.

The system Stan describes is not an all-out, end all, 1000 hp turbocraged boost design that will run at 40 psi. It's a lower tech solution that's going to be good for 6-8 lbs of boost, and a 30-40% incrrease in power from a near stock engine. And it can be done on a relatively small budget.
 
How do you hook up the carb to the turbo for the draw through? Any special thing that has to be custom made in order to hook them up? What carb would be the best to use? What about a Holley 390 with vaccum secondaries?
 
See the second picture in the Ak Miller article above? Just like that. carb is set up to feed the inlet on the turbo.

But if I were doing a low boost draw thru on a smallish engine like a 200, I think I might just find one HD8 SU constant velocity carb. That would make jetting easier and more consistent over the wide range of air volume you's see with a turbo.
 
What exactly is that thing that connects the carb and the turbo?

Would a weber side-draft carb work well or easier with the turbo or is a standard 4 bbl carb better for the setup and which one? (I dont know what carb that is you're talking about dude but judging by the name it sounds like an expensive carb)
 
Tatao, the thing that connects the carb to the turbo is called the plenum, and it allows the fuel and air to be drawn through a conventional carb, turn the corner and enter the turbo's compressor section. The photo below shows a Buick draw-thru turbo plenum with the carb removed.

<img src="http://home.earthlink.net/~rps1976/Images/Turbo/Buick%20Turbo1.jpg" border="0" width="627" height="469">
Yes, an inexpensive four-barrel spread-bore carb like a Quadrajet, Edelbrock, or Carter works with this type of plenum.
 
Wow, that buick turbo has a big gap between the turbine and the compressor. That definitly helps for draw thru applications.

Here is my question about draw thru applications. If you use a turbo with a wastegate, that effects the turbine side right? WOuld that be more desirable then a BOV since a BOV will vent compressed air and Fuel?

Slade
 
Good observation, Slade. These old Buick turbo housings are longer than a modern "cartridge" turbo housing, which gives more options for mounting. In the photo below I have labeled several parts. The compressor outlet has a tap on its side to send boost pressure to the wastegate actuator. The actuator has a spring loaded diaphram inside of it and a rod from the diaphram to the wastegate itself. As pressure builds inside the compressor, it places pressure to the right side of the diaphram (in this photo). When the pressure hits about 6-8 psi, the boost pressure begins to push the diaphram to the left, and the rod opens a turbine section bypass (wastegate) to reduce the exhaust pressure on the turbine wheel, maintaining a maximum of about 8 psi boost.

<img src="http://home.earthlink.net/~rps1976/Images/Turbo/BuickTurbo1.jpg" border="0" width="638" height="477">The neat thing about this very simple setup is that the spring can be shimmed or changed to raise the pressure at which the wastegate begins to open. Or even MORE simply (and cheaper), a "bleed" can be added to the boost sender line to reduce the boost signal to the wastegate actuator, again to raise the boost point at which the wastegate begins to open.

By now you guys should understand why I am so enthusiastic about these old GM turbos. They are DIRT CHEAP, adjustable, and thoroughly engineered.
 
CobraSix
A wastegate is universal, it can be used on wet (draw-thru) or dry flow (blow-thru) applications. Popoffs are limited to dry flow.

Popoffs have the advantage of dumping pressure without slowing the turbo, so it remains spooled up. A wastegate necessarily loses some RPM but this loss can be minimized with control design.
 
yeah...I see your point. I know about the waste gate trick. We do that on our Turbo Volvos. We actually have a screw that can adjust pressure at which the wastegate actuates. From the looks of the system, it seems that the orientation of the plenum can be changed so better facilitate adaption to an inline 6.

hmmm...maybe I'll tinker with one for the Aussie Head...

Slade
 
What's the maximum boost for one of those buick turbos? Im thinking using a 10 psi boost for my engine. How realiable are those used turbos. I took a look at the one on ebay and I was wondering if it would still work well being it's used and old. In case the turbo is too beaten up, what would need to be changed in order to make it work like new again? What's the A/R ratio for one of those buick turbo's?
 
There is always the risk that the turbo is trashed, Tatao. I have two of them (one for a spare), but bought them only after inspecting them in person. They both spin freely with no more than a few thousanths of end play, and after purchasing them I immediately oiled the bearings. I will tear them down and rebuild them using a turbo rebuild kit (about $60) before installing them on my engine. The a/r is stamped on the side of the scrol. Send the seller an email to ask him for the a/r, plus the model and serial numbers off the tag. Ask about the end play, if the unit spins freely and if there is any visible damage to the blades. If he won't provide the info, look elsewhere.

Edit: Oops, sorry I fogot to answer your question about max boost. I think 10 PSI might be about max with a stock log head, but that's just a guess. VERY mild porting and bigger valves would probably raise it a little, plus better exhaust, etc.
 
One other consideraton on a 250 that will limit your boost is the fact that these engines have no quench at all. 10psi is going to be a lot without doing something to fix that, even with the low CR.
 
Would water injection help cool it down a bit? I saw this link to a site where it showed a homemade water injection setup which mainly consisted of a water bottle with filters and a hose with a needle at the end that went into the hose going to the carb's vaccum port. That way as vaccum was created for the distributor's vaccum advance it sucked water. The bottle had to be placed below the carb so gravity wouldnt overfeed the carb with water and ruin the engine completely.

Would water injection help at all? If it does would that setup work because if it's a draw through setup and the water is sucked by the carb, then the water would evaporate when the air is getting compressed. Would the evaporation during the compression stage have a cooling overall effect for when the mixture goes into the combustion chamber or would a more expensive water injection setup need to be used?
 
Water injectio will help. Do a google for 1963 Oldsmobile Jetfire turbo. One of the reasons that model failed in the marketplace was due to people forgetting to fill the water bottle and destroying their engines.
 
Yeah, a 50/50 mix of methanol and water (or just water) can help stave off detonation, which is a limiting factor with our non-squish head design. OTOH, water/methanol injection generally doesn't help as much with draw-thru systems as it does with blow-thru systems. That's because draw-thrus are already very efficient at extracting the heat of evaporation out of the fuel. As one increases the boost pressure with these turbos, the usual route is to fatten up the secondaries. This accomplishes the same thing as injection without the drawbacks of such systems.
 
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