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Any DRAW-thru turbo setups here?
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Author:  polkat [ Sun Mar 27, 2011 11:09 pm ]
Post subject:  Any DRAW-thru turbo setups here?
I'm looking at all sides of the turbo idea, so as the title says; has anyone here built a draw-thru slant 6 turbo setup? What was your setup and any pics?

Thanks!
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Author:  1974duster kev [ Mon Mar 28, 2011 1:16 pm ]
Post subject: 
Charrlie has a draw thru setup i was looking at it when i picked up a timing set from him. I'm my humble opinion if your going carb blowthrough is the way to go, draw through is non intercooled plus various other reasons but it's still cool as all with alot of different builds.

Kev
Author:  Doc [ Mon Mar 28, 2011 2:00 pm ]
Post subject: 
Here is a early Buick draw-thru set-up on a SL6.
DD

Image

A "work-in-progress" shot showing the turbo mounting:

Image

Image
Author:  polkat [ Mon Mar 28, 2011 4:13 pm ]
Post subject: 
Nice setup Doc. That small manifold that the carb is sitting on; did you make that, or borrow it from something? Has that setup actually been run, and what if any carb mods did you do?
Thanks!
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Ebony Cams
Author:  Doc [ Mon Mar 28, 2011 4:44 pm ]
Post subject: 
The intake manifold is a factory SL6 cast iron 1 bbl manifold with the carb's mounting boss machined-off. The other "small manifold" is factory early Buick. ( they ran a carb the first few years)
This turbo system cam right off a 84 Buick and went right onto the SL6 and it will produce 10 lbs of boost.

This set-up has blown-up 2 factory Slants... with-out much trouble. (broken pistons)
My guess is higher RPM detonation is causing the failures, that needs to be addressed in some fashion (water injection?) or else... this set-up is just a "hand grenade with the pin pulled". :shock: :evil:
DD
Author:  bigslant6fan [ Mon Mar 28, 2011 5:39 pm ]
Post subject:  ,
You need a turbo with special seals to withstand the vacuum of a drawthru set-up. You also need a larger carb,so it can flow enough to prevent vacuum from building at the base of the carb,and turning off the power circuit.Let's do a roll call on sucessfull STREET driven drawthru vs blowthru set-ups. I,d just forget the idea.
Author:  polkat [ Mon Mar 28, 2011 9:25 pm ]
Post subject: 
I don't see any particular advantage of a blow-thru over a draw-thru. According to the books I've read (McInnis and others) and the people I've talked to, draw thru's work just as well as blow thru's if properly built, and fuel delivery and carb mods are far easier on a draw-thru. Also, the Buick GN 3.8 carbed turbo units (what I'm also planning to use)already had the seals needed.

So Doc, what could you have done (or what did you do) about damaging the pistons (which I assume were stock)? Every stock engine/turbo build I've read about that went to 10psi boost had no piston trouble!
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Author:  emsvitil [ Mon Mar 28, 2011 11:17 pm ]
Post subject: 
I think an advantage of a draw thru carb would be that it would handle a rapidly closed throttle more gracefully and you DON'T need a blow off valve in the intake plumbing.
Author:  GunPilot [ Tue Mar 29, 2011 7:53 am ]
Post subject: 
One downside is, if you run an intercooler then you have fuel/air mix in it. One backfire and it's a grenade. I could see fuel puddling problems too as the charge cools and the fuel condenses out.

Looking at Doc's pictures my first impression is how hot the intake air would be. I think I see the heater hoses run over to that manifold to provide a liquid/air intercooling effect. Still, if the coolant is 195 then what would the air be?

I don't have enough experience (yet) to speak authoritavely on the subject; however, the draw thru looks like it has a lot of problems to overcome.
Author:  Charrlie_S [ Tue Mar 29, 2011 10:16 am ]
Post subject: 
Do not run a charge cooler with a draw thru turbo setup. As was stated it is a bomb waiting to go off, if there is an intake backfire. The cooler will be full of fuel and air, KABLUIE!!!!! The hoses on the manifold under the carb in the photo of the Buick setup is to warm the air/fuel mix, between the carb and the turbo. I had to add that to my setup. Before doing that, at idle the manifold would get "frosty" and the fuel would puddle, then slug to the engine as a rich mixture. It was imposible to get a good idle, with the mixture going rich/lean/rich/lean.
My opinion:
Draw thru is easier to to fab up.
Blow thru is better, turbo just handles air.
Port fuel injection is better yet, as the turbo just handles air, and tuning is more precise.

However I am staying with my "Corvair" draw thru, at least for now.
PS: I also have one of the Buick carb setups on the shelf. Maybe someday :)
Author:  Doc [ Tue Mar 29, 2011 10:51 am ]
Post subject: 
Quote:
...So Doc, what could you have done (or what did you do) about damaging the pistons (which I assume were stock)? Every stock engine/turbo build I've read about that went to 10psi boost had no piston trouble!
I get the "Turbo bug" every now-and-then, put a system together, work on the "issues" until the engine dies... then swap back to a N/A set-up and toss the turbo stuff back on the shelf...
I learn new things every time...
At this point, I think EFI is the way to go when using a turbo.
Can I get a carb fed turbo system to work on the street, long term... may-be.
I would have to build a dedicated turbo engine, using stronger piston and paying closer attention to the compression ratio.
I would have to do a lot more specialized tuning and figure-out a way to hear / see any high RPM detonation or lean-out condition.
If I stick with a carb. fed system, then I need to get more familure with the carb that came on this Buick system I currently have or switch to a boost referenced Holley carb. (I know Holleys pretty well)
These "one-off" Turbo systems just take some time to sort-out and get right... hopefully you can do that before blowing-up a bunch of stuff.
DD
Author:  1974duster kev [ Tue Mar 29, 2011 12:18 pm ]
Post subject: 
As far as not having to buy a BOV for a draw through they are cheap and sounds cool so having one has been a plus for me, and as charrlie said that his draw thru wasn't easy to tune either so i really think the tune is going down the same road either way lots of trial and error, and for the intercooler i think is a major draw back if you can't use one that intake charge gets mighy hot, which would help detonation happen. The only solution that i could think to cool the charge besides meth injection would be maybe an outside coolant such as a water mister dowsing the hot pipe :lol: You could use heat sinks also to draw the heat from the pipe maybe? But then you may have fuel puddle issues if your intake isn't cooking i don't know after thinking i just dont see the advantage to a draw thru. Did draw thru style or blow through come around first? i'm assuming draw thru is the old school way of turbocharging right?

Just thinking out loud
Kev
Author:  polkat [ Tue Mar 29, 2011 5:33 pm ]
Post subject: 
Well, the main advantages to a draw-thru is that the carburetor(s) don't have to be sealed, or the PV valve boost referenced (unless you want it that way), plus the standard fuel delivery system can be used. The travel of the fuel mix can be kept short if designed right. True, there's usually no room for an intercooler, but I've seen a lot of non-intercooled blow-thru's that run just fine.

However, I've read elsewhere that a stock (in good shape of course) slant 6 will hold up just fine to about 10psi of boost. But here, Doc describes lots of stock piston trouble at that amount of boost. So what's the full story there?

In fact, there is so much disagreement about turbo build details on the web that it's hard to trust everything you read!! How much boost will a (good) stock 225 handle?
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Author:  Shaker223 [ Tue Mar 29, 2011 6:07 pm ]
Post subject: 
Quote:
In fact, there is so much disagreement about turbo build details on the web that it's hard to trust everything you read!! How much boost will a (good) stock 225 handle?
I had almost 30 full throttle dragstrip passes and another 15-20 Chassis dyno pulls at between 20-30 psi of boost. Additionally, I put 2000 street beat miles on the car before a piston failed.

The 225 is plenty strong. As with any engine, it's all in the tune. 10-15psi on the street should last a long time in my opinion.
Author:  1974duster kev [ Tue Mar 29, 2011 8:45 pm ]
Post subject: 
Ya buddy :) i'm hoping mine lasts awhile since its my daily driver hopefully with the aid of meth i can make it hold up to some substantial boost.

Kev
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