OK. Back to your original question. The early turbocharged engines where the Olds 215 V8s starting in 1962. They used a large single barrel Rochester side-draft carburetor. You will need around a 61 mm turbo for use with a 350. The compressor outlet would be bolted right to the intake manifold. You would need something like twin Weber side drafts to supply enough airflow for a turbo 350 and that would not be cheap. If you used a 4 barrel carb, it would sit above the turbo inlet on a 90 degree tube which would put the carb pretty high. Would there be a hood clearance issue? Paul
1978-83 Buick V6 used a 4 bbl Q-jet with the turbo. The raised hood bulge provided clearance for the elbow atop the carb which led to a remote air filter. Turbo will need seals to keep the 'wet' mixture from leaking out of the turbo.
Thanks Walt I remember that combination now that you mentioned it. I was in the middle of editing my post when you replied Paul
Draw thru can be made to run fine, but it does take more work than a blow thru. I have a turbo-charging book somewhere where a guy has a 292 inline six T04 draw thru in a 32 coupe. It runs in the 10's. It's not strictly or even mostly a drag car either. The blow thru came to dominance because it was more simple to set up and tune. One problem the draw thrus can have is fuel puddling. That is where the fuel falls out of suspension and puddles on the intake floor. IIRC, the cause is the fuel air mix gets very cold. It even leads to icing of the intake/plenum. That is why you see water lines run to the plenum. Using water taken from the warm engine, you can prevent the freezing and puddling. Something else to remember is that you have to create the throttle linkage for the arrangement.
Old International Scout 80 models could be ordered with a draw through turbo setup on the 152 cubic inch engine. If you want to talk about a simple setup that worked, that was it. I'm pretty sure those trucks had about 8 moving parts all together. I don't know how much horsepower it realistically added to the car, but they were a little more potent than the N/A versions.
I think the freezing up was more likely to happen in alky engines than it was with gasoline, but that might just be me mis-remembering. The puddling is a definite side effect of the "fuel tuning problems" I mentioned earlier, thanks for bringing it up! :beer
I decided to double check by breaking out my Turbochargers by Hugh MacInnes book. The puddling even happened with gasoline engines. I can only imagine how alky would do. Another book with some good info on draw thru turbos is Super Power from S-A Design.
Freezing? I'm not driving this car in the cold. How can an intake get that cold when it's on top of a hot engine??? And what conditions would make the fuel puddle? Hood? Who needs a hood when a sawzall is so much fun. Ha ha! If I were to do this the turbo is going right on top of the intake with the carb on a short 90 degree bend. As close to the turbo as I can get it. Any ideas on the sweet stall speed for the torque converter?
Temps at or below 60 degrees would allow it to happen. I think humidity would play into it too. It definitely has some advantages over blow thru. I strongly suggest the books I mentioned previously. While they are old, it was pretty good stuff even then. The car I mentioned was a 1937 Coupe, maybe a Chevy. It had an adjustable boost controller and would drive like a pussycat on the street, but become a monster on the strip. 10.70 in the 1/4 with a T04 turbo. Supposedly Hot Rod Magazine had a feature on it sometime in 2001.
If you are serious about this project then here are some things to consider. You will need a carbon seal on the compressor side of the turbocharger. When the turbo is making boost and the throttle plates on the carb are suddenly closed, there will be a high vacuum that can suck the oil past the standard seal. Fuel puddling, at low rpm, can happen in the low spot of the compressor housing or any uphill section in the intake manifold. Single plane manifolds work best because the runners are downhill (unlike the dual plane) and single planes have better distribution. Yes I realize there are no "off the shelf" single planes available for the 350. I know they cost a lot more but the ball bearing turbos spin at any engine rpm and will help with fuel puddling. They also spin up a lot faster than the journal bearing turbochargers. We had both Turbonetic and Precision 88mm ball bearing turbos and they would spin if you blew on them or as soon as the starter was engaged. Keep the engine compression ratio at 8.5 or less, not only because there isn't any intercooling, but also when the engine shifts at WOT under max boost, the engine rpm suddenly drops and the boost pressure will spike possibly causing detonation. It takes a little time for the wastgate to respond and for the turbo to spin down. The better way of controlling pressure spikes is with a bypass valve from the intake manifold back to the inlet side of the turbo. As far as the cam selection, just like N/A, if the heads are stock (not ported) you will want to focus on the low end and figure 5500 rpm as the cutoff. That puts the intake duration at 218 degrees or less. Because of the restrictive exhaust ports, the exhaust duration can be more that the intake if you want to help the power on the upper end or the cam can be a single profile if you want to have all the focus on the low end. It also helps to have higher lift. The main difference is to try to minimize the valve overlap and use a lobe separation angle between 112 and 114 degrees for low boost. A converter stall around 2500 rpm will help spool up the turbo. Paul
Where would I get a turbo with a carbon seal? And I know this is off subject but would an eaton m90 supercharger be big enough for a 350? I found a killer deal on 1. And I might get it of outs enought.
Back in the late 1970s we started using draw through turbo systems on the Kawasaki 900 and 1000s using Rajay turbochargers. I believe all Rajay units were carbon seal but they are no longer produced and hard to find<o></o> If you are buying a new turbo, then you need to ask the supplier if you can get it with a carbon seal. If you are getting a used turbo then you will need a carbon seal rebuild kit or get one rebuilt with a carbon seal from one of the many turbo rebuilders. Having one of the rebuilders do it is a good plan because the turbocharger should be rebalanced after being re-assembled. The M90 supercharger would have to be driven 3 times the crankshaft speed in order to produce 7 lbs of boost on a 350 cid engine and you would have to limit engine rpm to less than 5000 rpm not to over rev the supercharger. The MP-122 H is a better match and is set up with a 4 barrel carb flange mount on top of the supercharger. Paul
