turbo: blow thru vs. draw thru

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Old thread, but any updates on the blow thru vs. draw thru discussion?
 
I don't see any negatives to bein sucked or blown. It's all good with me.
 
Dejavu, I just took a walk and my neighbor 2 doors down has a cherry black Turbo Trans Am. I knew the old fart had an 81 TA but I didnt know it was a turbo as it always has the cover on it.
 
pishta said:
Dejavu, I just took a walk and my neighbor 2 doors down has a cherry black Turbo Trans Am. I knew the old fart had an 81 TA but I didnt know it was a turbo as it always has the cover on it.
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They were really nice cars, but dammit they were slow.
 
As a side note- you can pick up the entire draw through T/A 301 turbo system on ebay for $200-$300.

Might be interesting to see if it could be adapted to a SBM.
 
YY1 said:
As a side note- you can pick up the entire draw through T/A 301 turbo system on ebay for $200-$300.

Might be interesting to see if it could be adapted to a SBM.
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Hmmm....gonna go search eBay now....
 
...and this thread recently got a LOT more important for me.

Believe it or not, I found an almost complete mazda rx7 twin turbo setup in my warehouse dumpster!!

I'm pretty sure of how it got there as one of the tenants builds import drag cars and he has 3 rx7's one with an enormous aftermarket turbo.

Therefore, I suspect there's nothing wrong with the one I found other than being too small for someone's liking.
 
IMG_20170729_183727.jpg
 
Big turbos have their place, but like carbs and port sizes, bigger is not always better. there is alot to sizing them, but free is always good!
 
Another question: When your full on boost in a draw through and you let off the gas, ie hit the traps and take your foot OFF the gas, where does all that suction go from the wheeling compressor? I can imagine that it would pull the guts out of whatever is left in the fuel bowls through the idle slot creating a very lazy (if at all) deceleration...? I see the wastegate but I dont see a blow off? And if you blow 'in' the intake (vent to atmosphere) thats just not right. Rethinking......:wtf:
 
No different then a carb without turbo. And remember the turbo doesn't keep spinning at full rpm. When the throttle closes, exhaust voluum goes way down, and the turbine/compressor slow down.
 
On a draw thru, the closed throttle blades are also choking the compressor, slowing the turbo speed, too.
 
T56MaxTorq said:
On a draw thru, the closed throttle blades are also choking the compressor, slowing the turbo speed, too.
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That fast thought? Thats alot of kinetic energy spinning at up to 130,000 RPM...and you still have the idle transfer slot. I would think that would create a huge vacuum draw on the carb, but I guess decelerating a V8 from 7000 RPM is about as taxing on the throttle blades and idle circuit. OK, back on track....
 
Just about every major auto manufacture has released a draw thru system at one time or another. None of them had a problem with deceleration. That can't always be said for acceleration thou...

Carbon seals are installed on the turbine shaft to control the oil flow when the throttle blades are closed. The vacuum draw is enough to draw oil into the intake pass the bearings.
 
kesteb said:
Carbon seals are installed on the turbine shaft to control the oil flow when the throttle blades are closed. The vacuum draw is enough to draw oil into the intake pass the bearings.
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Yep, that is one reason, MOST turbos available in salvage yards are not good for draw thru. They were used on blow thru, and don't have the proper seal. Some turbos do have a replacement seal set available that is compatable with draw thru.
I used a 1966 Corvair Spider (Rajay) turbo on my 65 Valiant 170 engine, back in 1979.
 
IIRC those 301 pontiacs were draw through and so is my rx7 setup.
 
Yes they were. I have a Pontiac system on the shelf. There was also a Buick system. And I think the early "K" cars were draw thru with a carb.
 
And I have a Buick setup from a '81 Rivera, which has a different outlet then the Regal setup.
 
YY1 said:
As a side note- you can pick up the entire draw through T/A 301 turbo system on ebay for $200-$300.

Might be interesting to see if it could be adapted to a SBM.
Click to expand...

I've wanted to adapt one to a Slant.
 
T56MaxTorq said:
On a draw thru, the closed throttle blades are also choking the compressor, slowing the turbo speed, too.
Click to expand...

That's how it works. Everything slows when the throttle blades close.
 
Well, I got a Holset HX35W and a new HX40W. I guess I struck out as neither have a carbon seal even available. Plus looking at the plumbing makes me think a blow through is more compact in its function, no big carb hanging off the side of a snail at a right angle...but I suppose either is possible. O ring a Carter Accelerator pump with the marine app part and your good to go. I used to have a compressor map comparison website where you plug in your data (limited) and you get a few choices but its 401 now. anyone got a good plug in site? Half the java sites dont work anymore.
 
Update from 2013. Got the trike up and finished, tagged and legal. For all the nay sayers, 5.3 chevy with twin Gale Banks draw through turbos through a 650 Holley 4150. I’ve made upwards of 24 psi a few times at the cost of engines ($250 junkyard motors) experimenting to get it right. Running 7-10 psi now. Drive it almost everyday and out run everything from Vetts to Hybusas’. This setup was making over 1000 horsepower on a 302 Ford in 1970’s and now it powers my trike. It can be done today if you spend your time researching correctly and apply yourself. I hope those of you that run a draw through setup experience much fun and a many a grin making others look stupid when running them down and passing them. I give most cars three tractor trailer lengths and bike two. Close the gap in seconds!

4708E531-89C0-4F60-9186-BF3F284F5FCF.jpeg
 
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