turbo: blow thru vs. draw thru

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HOTMOPR said:
Another reason why blowthrough is better.. Good luck running one of these on a draw through.. Yes full size mens basketball..

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The one on the right is off a 94 dodge ram cummins..

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Last year...I had a 56 ford sitting on a 92 Dodge Dually chassis....shortened two feet...With the VE pump maxed and some scheid diesel injectors and a 64/74/14 turbo the thing would pull on 12 second cars from a roll...That was my first turbo vehicle....

Nice Cuda....whats it run?
 
going to set the car to run on E85 also.....seems perfect for the draw thru.....
 
The damage on that compressor looks like static damage - rough handling while it was disassembled.

When you tear one up @ 60,000 rpm all of the blades eat it.

A cast compressor wheel is just fine. Millions of miles have been covered with cast wheels.

Atomization? LOL. That is the job of the compressor. On a draw through any carb works great. I always had great numbers from Quadrajet carbs. We used them because they were OEM on the GM vehicles, but I ran the Q-Jet on the dyno for everything. Easy to run the secondaries really rich. Once the fuel goes through that wheel @ 60k, it is atomized.

Should run good if you clean up the turbine discharge pipe & overhaul the turbocharger. If you have a decent 650 to 750 cfm carb of some type that will be fine.

With a target of 500 horsepower that would mean about 12psi of boost & 48 lbs per minute of airflow. That assumes an A/F ratio of 11.5:1, BSFC .5 & a .85 VE You will see a discharge temp of around 200f on a 100f day.

B.
 
Mopars#1 said:
Nice Cuda....whats it run?
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With the little 88mm turbo it ran a 6.10 @120 in the 1/8 with the tires blazing all 3 gears. soft launch footbraking. So new turbo, new tires, new rear and new trans with a brake all in the works, who knows..FAST
 
bohica2xo said:
The damage on that compressor looks like static damage - rough handling while it was disassembled.

When you tear one up @ 60,000 rpm all of the blades eat it.

A cast compressor wheel is just fine. Millions of miles have been covered with cast wheels.

Atomization? LOL. That is the job of the compressor. On a draw through any carb works great. I always had great numbers from Quadrajet carbs. We used them because they were OEM on the GM vehicles, but I ran the Q-Jet on the dyno for everything. Easy to run the secondaries really rich. Once the fuel goes through that wheel @ 60k, it is atomized.

Should run good if you clean up the turbine discharge pipe & overhaul the turbocharger. If you have a decent 650 to 750 cfm carb of some type that will be fine.

With a target of 500 horsepower that would mean about 12psi of boost & 48 lbs per minute of airflow. That assumes an A/F ratio of 11.5:1, BSFC .5 & a .85 VE You will see a discharge temp of around 200f on a 100f day.

B.
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I may throw some ported heads on the motor with a new intake first.... With your experience, is it hard to run a double pumper/mechanical secondary carb with this setup? I plan on running a loose converter...
 
HOTMOPR said:
With the little 88mm turbo it ran a 6.10 @120 in the 1/8 with the tires blazing all 3 gears. soft launch footbraking. So new turbo, new tires, new rear and new trans with a brake all in the works, who knows..FAST
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Nice.....And good color combo!
 
bohica2xo

Is it still possible to get Rajay parts? I have an old "Crown" modified Corvair turbo (draw thru) on my 170 slant six. I also have a new "E" flow, with a missing compressor wheel, in the box. I removed the wheel, about 20 years ago, don't remember why, and misplaced it. Thanks for any info.
 
Mopars#1 said:
I may throw some ported heads on the motor with a new intake first.... With your experience, is it hard to run a double pumper/mechanical secondary carb with this setup? I plan on running a loose converter...
Click to expand...

Usually not an issue, as long as you can handle the jetting for a richer top end. The progressive carbs make that easy to do. Obviously you could run 12:1 A/F all the time, but that sucks fuel... I ran a Predator carb on draw through just fine.

B.
 
Charrlie_S said:
bohica2xo

Is it still possible to get Rajay parts? I have an old "Crown" modified Corvair turbo (draw thru) on my 170 slant six. I also have a new "E" flow, with a missing compressor wheel, in the box. I removed the wheel, about 20 years ago, don't remember why, and misplaced it. Thanks for any info.
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Rajay units are still supported. When used on an aircraft, you have to keep using what was approved when the engine was built.

http://www.rajayparts.com/

B.
 
EFI for the win . Draw through is not even on the table , that scenario is ridiculous and foolish in this day and age. Blow through is usually relegated to people that are afraid of EFI and are trying to cheap out and clutch to their familiar dated carburetor. .....................IMO :)
 
mean green said:
EFI for the win . Draw through is not even on the table , that scenario is ridiculous and foolish in this day and age. Blow through is usually relegated to people that are afraid of EFI and are trying to cheap out and clutch to their familiar dated carburetor. .....................IMO :)
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Yes, you are correct. I am trying to cheap out. I built this car, back in 1979, and ran it until 1985. This was before manufactures would give out their "propriorty" info. It has been sitting since then, due to life and other projects. I am putting it back together, the way it was built back then.
 
Im planning on a draw through 273, 360 4bbl cam, 360 intake, 360 TQ, T70 turbo. Old school all the way..no idea what Im doing but it was all free 'cept the turbo. Will mount magnum logs backwards and plumb exhaust into compressor hotside, will make a 90 off inlet to mount TQ somewhere I got room, driver fender looks OK, away from alternator. I got no inners anyway so I should have some room. I got a 65 Cuda also, seems there are a few in this thread! Will need to fab an elbow onto intake off cold side with some sort of devider in it so both banks get some charge, not just the outboard one. Bohica, chime in on some tips!
 
actually if I mount the adapter facing the front, distribution isnt too bad. Im just wondering if the front cylinders get leaned out under boost?
 
:happy1: Keep talkin guys, this is an outstanding thread fer us old coots who remember turbo's on Shelby Charger's and GLH's....
 
A blow through setup is simplistic already, why go through the hassle of turbocharging anything with an ancient 'draw through' design? It is nostalgic to say the least, but I think anyone in modern times will be disappointed with the results. Sure, we understand it is 'easier' in a sense but do you gain enough performance to justify working and 'tinkering' with something twenty to thirty years old. We still haven't factored in, you will need adequate 'high pressure' fuel system components, MSD BTM, A/F wideband setup, and all the necessities that a typical turbo build will require. Boost is boost, but with all the budget systems and widespread information today on doing it properly; I just scratch my head at these systems and their place any relatively performance oriented Mopar. Good luck regardless on your turbo mopars everyone!
 
a draw through is using a stock carb, no mods that are on the order of a blow through, ie PVCR mods, crutch BRPV's, milled air horns, carb hats, BOV's, sealed shafts, jet extensions, no chokes, uh....air bleeds, vacuum secondary lock outs, boost referenced fuel pumps, intercoolers...hmmm.. Accelerator pump seal for an edelbrock, Holley solid floats, TQ floats grafted onto an edelbrock arm ...Jeez, thats alot! but I have already been through this on my slant. Sure its old school but so is a slant and they are still getting built. Its just a thing, a simple thing. Tinkering with something 20-30 years old is about any LA out there!
 
pishta said:
a draw through is using a stock carb, no mods that are on the order of a blow through, ie PVCR mods, crutch BRPV's, milled air horns, carb hats, BOV's, sealed shafts, jet extensions, no chokes, uh....air bleeds, vacuum secondary lock outs, boost referenced fuel pumps, intercoolers...hmmm.. Accelerator pump seal for an edelbrock, Holley solid floats, TQ floats grafted onto an edelbrock arm ...Jeez, thats alot! but I have already been through this on my slant. Sure its old school but so is a slant and they are still getting built. Its just a thing, a simple thing. Tinkering with something 20-30 years old is about any LA out there!
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Most of us buy carbs built for blow through, and save others the hassle and garage time to convert theirs over. Some systems, such as remote mount don't require intercoolers as the charge piping acts as a 50% efficient intercooler. You can actually run a basic methanol injection kit and get rid of the intercooler all together on a front mount.

More power to you, I love boost regardless of which way it is done :burnout: A system like this would work great on a mild performance application.
 
Sweet5ltr said:
A blow through setup is simplistic already, why go through the hassle of turbocharging anything with an ancient 'draw through' design? It is nostalgic to say the least, but I think anyone in modern times will be disappointed with the results. Sure, we understand it is 'easier' in a sense but do you gain enough performance to justify working and 'tinkering' with something twenty to thirty years old. We still haven't factored in, you will need adequate 'high pressure' fuel system components, MSD BTM, A/F wideband setup, and all the necessities that a typical turbo build will require. Boost is boost, but with all the budget systems and widespread information today on doing it properly; I just scratch my head at these systems and their place any relatively performance oriented Mopar. Good luck regardless on your turbo mopars everyone!
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I chose to do this due to the simplicity of the system. Yea todays tech is great but a simple twin turbo draw thru set up is just as good as todays new tech. IN FACT most of the "new tech" is based off of 1950's and 60's performance that was too expensive back then to mass produce. Fat shaft turbos? roller bearings? Hugh MacInnes designed that back in the 50's on the Rajays. In fact, Turbonitics bought his patents out in order to STOP their production as they could last three times longer than any other turbo. If any of you where to get one of the books he wrote on turbocharging from the 70's, I bet a lot more people would do draw thru's. Its a lost art now, but every air craft during WWII had draw thru centrifugal superchargers "turbos in todays terms". I have one of the Gale Banks TT setups on a project trike. Gale made 1400 hp on a stock block, small block Chevy and set a LSR for a stock body car with these same draw thru turbos.

A draw thru turbo mixes the air fuel better and will require a smaller jetting

draw thru's super cool the air fuel mixture so cold it will freeze the intake track, that's why an intercooler is not needed, in fact, you have to ADD heat via a cross over intake with heat risers in the heads, or coolant thru the turbo intake.

draw thru's reduce the vacuum under the carb so well that a SMALLER CARB is used. AKA a stock 350 would use a 750 cfm carb as a factory performance engine, the same engine with a draw thru would need a 650 cfm and make twice the power.

I have several of the books from Huge MacInnes on these set ups and I can hardly wait to get it running. Took me 6 months to find all the correct parts to put it together correctly. A 40 year old aluminum Holley with none of the threads stripped out is near impossible to locate today.
 

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pishta said:
Im planning on a draw through 273, 360 4bbl cam, 360 intake, 360 TQ, T70 turbo. Old school all the way..no idea what Im doing but it was all free 'cept the turbo. Will mount magnum logs backwards and plumb exhaust into compressor hotside, will make a 90 off inlet to mount TQ somewhere I got room, driver fender looks OK, away from alternator. I got no inners anyway so I should have some room. I got a 65 Cuda also, seems there are a few in this thread! Will need to fab an elbow onto intake off cold side with some sort of devider in it so both banks get some charge, not just the outboard one. Bohica, chime in on some tips!
Click to expand...

Find the Huge MacInnes books from H.P. Books from the 70's on ebay. READ THEM as to the intake designs needed and why. You can fry an engine if the intake is not done correctly on a draw thru set up. You will know more about turbos than most people that have been using them for 20 years. Those books are a god send to anyone doing draw thru turbos. You want the ones from 74 and 77 and you will see where todays new tech comes from.
 
bohica2xo said:
The only turbochargers we used were Rajay units back then. An E flow Rajay on a 350 cid engine would push 10psi plus with a 1.0 A/R ratio on the hot side.

We ran a looser 1.3 A/R on the big blocks. Back then it was common to size a turbocharger to max out with the engine to build a system that would work without an exhaust wastegate.

Gale used a dogleg intake with a pad for the carb that put the top of the air horn below the centerline of the compressor on some truck installs. That was ok for a smallblock, but on big block it was restrictive with that short turn in to the compressor inlet. we saw icing on those manifolds, especially the one with the carb near the passenger side headlight.

Most motorhome kits had a higher carb mount. Which setup does your friend have? Which turbocharger, Garrett TO4B or Rajay E series?
B.
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A draw thru turbo NEEDS the dog leg to break up the swirl produced by the turbo and induces turbulence to keep the fuel in suspension, if it did not have the 90 degree bend, it would sling the fuel out of the air and onto the walls in the intake tract and then lean destruct by melting the pistons very very quickly as the fuel will pool up in the intake. As in the end of the driveway. It can not be a 90 degree tube or pipe, it needs to be a flat wall square 90 to stop the swirl produced by the compressor scroll as it leaves the turbo housing on a single turbo set up. TT set ups can have the compressor outlets face each other and basically blow against each others outlet to create the turbulence needed to break up the swirl. Yes these designs are restrictive for a normal NA engine, but that's not what we have or are trying to build with the draw thru system. Those restrictions mean nothing when its under pressure from boost.
 
mean green said:
EFI for the win . Draw through is not even on the table , that scenario is ridiculous and foolish in this day and age. Blow through is usually relegated to people that are afraid of EFI and are trying to cheap out and clutch to their familiar dated carburetor. .....................IMO :)
Click to expand...

So I guess to you, building a 40 year old car with 10 day old parts is better than actually trying to build a 40 year old car with 40 year old hot rod parts. hhmmm. Where is the challenge in that. Finding a 40 year old draw thur turbo set up and making it work correctly seems more of a hot rod thing to do than just picking a part out of book and ordering. As for your EFI, it was done in the 40's on Allison aircraft engines. Port fuel injection with an analog computer. In fact most all of the new tech was done in the 1920's thru 1940's
Supercharging 1870,s
compound supercharging
turbo supercharging
electric supercharging 1929
4 valves per cylinder
roller cams
sodium filled valves
port fuel injection
speed density fuel management 1944 (aka analog computer)
water meth injection
No2 injection
blow thur carb supercharging
blow off valves
intercoolers
long ram intakes
etc,etc,etc

Almost all this tech today came from Allison aircraft engines (V1710) and Rolls Royce from 1920-1947. Any of this can be found on google patents search.
 
366396


Great thread! Thanks for sharing so much of the finer points on draw through set ups. I am a believer.
 
mrproffitt said:
So I guess to you, building a 40 year old car with 10 day old parts is better than actually trying to build a 40 year old car with 40 year old hot rod parts. hhmmm. Where is the challenge in that. Finding a 40 year old draw thur turbo set up and making it work correctly seems more of a hot rod thing to do than just picking a part out of book and ordering.
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Yeah, I agree.
It's easy to dress up and look like a hot rodder these days. It's just a little more difficult to actually be one...
 
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