Drawthrough turbo setups

[dave brode]

shiftless,

You seemed to have some interest. I thought you might find this of interest.

An example of a large carb on a small engine:

http://cgi.ebay.com/ebaymotors/Aircoole ... dZViewItem

An early carb'd 231 buick [similar to the 301" V-8 transam setup]

http://cgi.ebay.com/ebaymotors/ws/eBayI ... ink:top:us

An old Corvair setup [afaik, they had no boost control: small carb limited boost];

http://cgi.ebay.com/ebaymotors/CORVAIR- ... dZViewItem



The Corvair reminded me of an old war story a buddy of mine told. He was a kid [early 70s], and his buddy had a turbo'd corvair. They wrapped the exhaust, gutted the muffler and so on, which helped [gutted muffler raised boost]. It would thump up on many hot rod small V-8 cars = much fun. He got the idea that it needed more car, so he went to work and adapted an old 4GC rochester 4 barrel. The engine pulled like a muther, but blew up during the first night of fun. No boost control on the ole Corvair. The gutted muffler and larger carb allowed the boost level to go too high for the fuel they were running.

Dave

 

[shiftless]

Hey thanks for the info. I think a 472 with two big diesel turbos and two 850 DPs would be a killer combo. A real sleeper too with a quiet exhaust in a light weight, inconspicuous car like a Fairmont. Or better yet, a blacked out, lowered, lightened 87-88 T-bird turbo coupe.  :mischievous:

 

[Darius]

Hey thanks for the info. I think a 472 with two big diesel turbos and two 850 DPs would be a killer combo. A real sleeper too with a quiet exhaust in a light weight, inconspicuous car like a Fairmont. Or better yet, a blacked out, lowered, lightened 87-88 T-bird turbo coupe.  :mischievous:

Shiftless,

Be careful with those diesel turbos. I don't believe turbos originally intended for diesels have the carbon shaft seal -- without which the fuel on a draw-through setup will wash out the oil in the main turbo bearing.  Just a thought. 

Darius

 

[dave brode]

shiftless,

Ditto Darius. As Sean and I mentioner in another thread you posted in. Afaik, the carbon seal needed for drawthrough isn't used in most diesel turbos.

Also, don't go too big on the turbos. I'd choose a compressor [or pair] that will be happy [efficient] putting out the amount of air you need for your goal. The turbine side must also be matched to the engine, or you will get too slow spool-up, or really quick spool and top end will be choked. Also, I understand that a small turbine side mated to a compressor on the large side can lead to compressor surge at low rpm [a very bad thing]

No expert here, but afaik, carbon seals can be had for some models, but perhaps not some others. If you got a killer deal on turbos that could not be used drawthrough, you could always go blowthrough carb. One 750 is probably enough for an 800 horse blowthrough setup. From what I read, an 850 is probably plenty ok for 1000.

Dave

 

[Scott]

http://www.smbaker.com/rail/monsterturbovw.html

"A dynamic seal uses a couple of piston rings, much like the rings on the pistons in your engine. As you should know, a piston ring isn't a 100% seal. There's a little gap in the ring. For a blow-through turbocharger, this is fine. The compressor will always be pressurized, and no oil will get sucked through that little ring gap.

However, when you have a draw-through setup, the carb is mounted on the intake side of the compressor. Thus, any time the throttle is closed, there will be manifold vacuum inside the compressor housing. Think about it -- most of the time when you're not accellerating, there is manifold vacuum. If you have a dynamic seal with the little piston rings, then this manifold vacuum will suck the oil out through that little piston ring gap. It'll suck the oil right into your motor, and you're engine will run like some idiot put 2-cycle mix in the gas tank. This is bad. You'll foul your plugs and upset your neighbors. The oil will reduce your octane, and you might even get detonation.

The carbon-seal, on the other hand, has a spring-loaded ring that presses against a thrust collar on the turbine shaft. There is no "gap" in the carbon seal; it seals all the way around. It'll keep that oil in there, even in the presence of manifold vacuum in the compressor housing."

 

[POTTER]

I remember Gale Banks doing a 200 mph street car (82 or up Camaro) with twin suck throughs and had two holleys mounted out in the front of the fenderwells. I wonder what they used 15 years ago. The carbs were a long way away from the intake so the stumble/lag must've been bad, but it ran 202 at bonneville on pump gas and street tires. IIRC the tubes kinda ran uphill too. Seems like fuel would tend to fall back down on de-acceleration and run out the carbs. Maybe it had small drain holes and jetting to compensate.

 

[dave brode]

I remember Gale Banks doing a 200 mph street car (82 or up Camaro) with twin suck throughs and had two holleys mounted out in the front of the fenderwells. I wonder what they used 15 years ago. The carbs were a long way away from the intake so the stumble/lag must've been bad, but it ran 202 at bonneville on pump gas and street tires. IIRC the tubes kinda ran uphill too. Seems like fuel would tend to fall back down on de-acceleration and run out the carbs. Maybe it had small drain holes and jetting to compensate.

Richard,

I remember that Banks car. As far as lag/stumble, I'm sure it's an issue, but not as large an issue as one might guess it to be. As I see it, look at many old cars, and current industrial type engines. Up draft carbs. Not quick for throttle response, but they seem to run fine. Other fellows that have done drawthroughs with air/fuel running uphill tell me it ain't bad. Some of Banks' kits had the carb quite a bit lower than the intake. We'll see. If it runs like crap, I'll convert to blow through.
Dave

 

[POTTER]

Unless clearance is an issue, I'd steer that way anyway. Seems more practical and with some throttle shaft seals, the best way to go for response and simplicity. You'll need boost advance control for fuel pressure where on the sucker you probably won't though. JMO