Minimalist Slant Six draw-through build...

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hellfirechrome

hellfirechrome

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Hey everyone. I have a 225 Slant Six with hyper-pak, 500CFM (detuned) Edelbrock, Electronic ignition, 904 Auto & 8 3/4 in my 65 Barracuda. It’s a real clean, rebuilt motor that purrs right now but is low on power due to elevation and, well, because it’s a stock slant LOL

I live at 6200ft+ and decided that my solution for more power will be a draw-through turbo.
Because I’m insane. I just don’t want to cam-out and mill the piss out of a great stock engine if I can do something cool for a bit of power that’s also relatively bolt-on.

It’s a vintage Rajay/Airesearch carbon-sealed turbo with the Mopar RV-style split-plenum manifold, turbo will be rebuilt before run. Manifold has a spring blowoff that will need a redirect pipe because, well, flammable A/F mixture is bad.

SO; here’s my bullet points on what I know I’ll be doing.

  • Turbo will be plumbed by T-fitting at oil pressure sender, piped down into upper side of pan for hot oil dump.
  • Turbo will be supported by brackets to the motor/mount to keep weight off factory manifold, sitting up forward of intake manifold on J-pipe from the factory exhaust (moving battery to trunk)
  • Will pull head and calculate compression, before re-gasketing head with a steel shim style.
  • Manifold will have a reed valve set added inside the plenum, to allow for draw-through from carb to intake (bypassing turbo circuit) when under vacuum.
  • Will weld-lock a distributor and run a flat (non-advancing) timing, I heard 22 degrees?
  • Will run a 2.5” exhaust all the way back, with a glass-pack for minimal back-pressure
  • Will run a live AFR gauge & boost gauge, and likely step to EFI kit if I can’t keep consistent ~14:1 AFR under boost (I know it will be rich under aforementioned bypass/vacuum idle, that’s a price to pay)

More advice is welcome... any caveats/horror stories? What else should I do? Am I missing any major steps?

Thanks in advance!
 
Bear in mind with draw through and carb you WILL need something for carb heat, like a coolant heat exhanger under the carb base. Don't know about timing, 22 may be much under boost, you need to check that out.
 
Did you read that Slant Article in Hot Rod- (Crazy like a fox) Plymouth Duster 225 Turbo. Maybe you ca gather some info. from it
 
hellfirechrome said:
Hey everyone. I have a 225 Slant Six with hyper-pak, 500CFM (detuned) Edelbrock, Electronic ignition, 904 Auto & 8 3/4 in my 65 Barracuda. It’s a real clean, rebuilt motor that purrs right now but is low on power due to elevation and, well, because it’s a stock slant LOL

I live at 6200ft+ and decided that my solution for more power will be a draw-through turbo.
Because I’m insane. I just don’t want to cam-out and mill the piss out of a great stock engine if I can do something cool for a bit of power that’s also relatively bolt-on.

It’s a vintage Rajay/Airesearch carbon-sealed turbo with the Mopar RV-style split-plenum manifold, turbo will be rebuilt before run. Manifold has a spring blowoff that will need a redirect pipe because, well, flammable A/F mixture is bad.

SO; here’s my bullet points on what I know I’ll be doing.

  • Turbo will be plumbed by T-fitting at oil pressure sender, piped down into upper side of pan for hot oil dump.
  • Turbo will be supported by brackets to the motor/mount to keep weight off factory manifold, sitting up forward of intake manifold on J-pipe from the factory exhaust (moving battery to trunk)
  • Will pull head and calculate compression, before re-gasketing head with a steel shim style.
  • Manifold will have a reed valve set added inside the plenum, to allow for draw-through from carb to intake (bypassing turbo circuit) when under vacuum.
  • Will weld-lock a distributor and run a flat (non-advancing) timing, I heard 22 degrees?
  • Will run a 2.5” exhaust all the way back, with a glass-pack for minimal back-pressure
  • Will run a live AFR gauge & boost gauge, and likely step to EFI kit if I can’t keep consistent ~14:1 AFR under boost (I know it will be rich under aforementioned bypass/vacuum idle, that’s a price to pay)

More advice is welcome... any caveats/horror stories? What else should I do? Am I missing any major steps?
Thanks in advance!
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Suggest adding an EGT (exhaust gas temperature) gauge & oil temp gauge to cluster. Shutting off a hot engine can lead to coking of oil on the bearings. The coke that forms can hurt the shaft, seals, and bearings eventually leading to oil leak, smoking and failure.

IIRC the early rustclang turbos used a carburetor. Motors would grenade on the autobahn when suddenly shutting the throttle at high speeds. Did not handle throtle transitions well.
 
I’ll add three things.
1. Stud the deck, anything you can do to a slant to improve head gasket sealing will help.
2. In this day and age a draw through setup is archaic at best. They really do not work well and are a bear to tune. Especially for drivability. Consider a blow through setup with a modern carb (CSU or similar) or just skip the hassle and go EFI.
3. Do not lock out the timing. Unless this is a race ONLY car. Run some type of timing control (MSD 6btm or similar) that allows you to keep a normal curve and pull timing based on boost.
 
Forget the reed valves. Just suck it through the turbo and put the turbo outlet right on the intake. Side draft would be nice but you wont find one big enough unless you get a big weber. You want short runners too ideally. Go for it: if you break it, just get another slant.
 
Why are you thinking draw thru but considering EFI?
 
Here is something to ponder. There was no real drivability issues. Early Buicks and Pontiacs were draw through setups before EFI... I agree, stay away from the reed setup. Keep it simple and you'll have plenty of fun under 8 to 10 psi boost!
In the late 80's I built a six with forged TRW 8 to 1 pistons, ported head myself and installed 1.46" exhaust and 1.78 intake valves from Ford, .020 head gasket, ARP head and main studs, Crane "turbo" truck cam. I rebuilt a turbo used for an 81' Pontiac 301 draw through set up with a 600 Holley. Used a "J" pipe from the exhaust manifold up to the turbo. This very crude, low dollar, pile of parts withstood a high of 32 lbs of exhaust pressure to make 18 lbs of boost on 115 race gas. I added a fuel tank for the race gas and a three way ball valve to switch back to the stock fuel tank to drive to and from Maple Grove, Beaver Springs and Numidia Dragway. It usually ran low 13.0's at 104mph with 3.23 posi and sorely needed converter and trans brake but was too much money for the time. I had a lot of fun with my ugly green four door Valiant which as anyone can see was very inefficient by the exhaust pressure / boost ratio.
 
DON BURKHOLDER said:
Here is something to ponder. There was no real drivability issues. Early Buicks and Pontiacs were draw through setups before EFI... I agree, stay away from the reed setup. Keep it simple and you'll have plenty of fun under 8 to 10 psi boost!
In the late 80's I built a six with forged TRW 8 to 1 pistons, ported head myself and installed 1.46" exhaust and 1.78 intake valves from Ford, .020 head gasket, ARP head and main studs, Crane "turbo" truck cam. I rebuilt a turbo used for an 81' Pontiac 301 draw through set up with a 600 Holley. Used a "J" pipe from the exhaust manifold up to the turbo. This very crude, low dollar, pile of parts withstood a high of 32 lbs of exhaust pressure to make 18 lbs of boost on 115 race gas. I added a fuel tank for the race gas and a three way ball valve to switch back to the stock fuel tank to drive to and from Maple Grove, Beaver Springs and Numidia Dragway. It usually ran low 13.0's at 104mph with 3.23 posi and sorely needed converter and trans brake but was too much money for the time. I had a lot of fun with my ugly green four door Valiant which as anyone can see was very inefficient by the exhaust pressure / boost ratio.
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So that's the sticking point, the reed valves are really only a consideration due to the length of the hyper pack intake runners and to prevent vacuum lock upon throttle close as the above replies mentioned. I know they aren't exactly necessary, but I'm also pretty sure it wouldn't hurt. Since this intake is water-heated, just gotta make sure there's no water jacket in the split plane. Doesn't look like it.

The turbo that came with my kit is a Garrett, looks like a TO4 and does not have an internal wastegate. Since the manifold has a port on pressure side for blow off, I get to run a remote BOV and though I'd doubt that I could get to 10 pounds pressure I plan on running a 7 or 8 pound BOV with a redirect pipe and a catch can (due to AF mixture blowoff).

I have no intention of racing, but yeah it's a known working system and I think the safeguard of running a wide band O2 gauge will help me get this thing running proper. It's gonna be a budget build for sure but the rebuild kit is the wor$t part!
 
T56MaxTorq said:
Why are you thinking draw thru but considering EFI?
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Cost! If I can tune the carb for proper AFR I won't bother with EFI! But because of my elevation and the fact I travel a lot, I'd hate to have to retune every time I drive down the hill. We shall see!
 
Hi. The reed valve setups that I looked at in the late seventies and early eighties were to combat turbo lag. If I were to do it again I would install a Holley Sniper EFI on my Offenhauser 4bbl intake as a blow through, it is pricy$$ but it solves alot of problems and is tunable to boot. The turbo I used had no problem when I closed the throttle at the finish line at 5200 RPM as a draw through the carb..
 
DON BURKHOLDER said:
Hi. The reed valve setups that I looked at in the late seventies and early eighties were to combat turbo lag. If I were to do it again I would install a Holley Sniper EFI on my Offenhauser 4bbl intake as a blow through, it is pricy$$ but it solves alot of problems and is tunable to boot. The turbo I used had no problem when I closed the throttle at the finish line at 5200 RPM as a draw through the carb..
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Sounds great! Mind if I PM you sometime soon and pick your brain a bit further about how to set up my kit? Thanks in advance!
 
hellfirechrome said:
Cost! If I can tune the carb for proper AFR I won't bother with EFI! But because of my elevation and the fact I travel a lot, I'd hate to have to retune every time I drive down the hill. We shall see!
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I too live high elevation. It would frustrate me a lot if I we’re to change jets every time I do dropped or climbed a couple thousand feet. I wouldn’t leave town with it.
 
Like what you're doing. Got a /6 turbo that I'm finishing the tune. Henyee turbo from eBay. Everything you see fits under the hood and is low budget. 1974 Duster, 318 air cleaner, Fish 1 5/8" side draft carb. A 2" Fish is too big for a a 225
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Anchored turbo to block, waste gate internal. First attempt was with 2" Fish down draft but it's made for a 5.7; might work on a 5.0. posted somewhere else on 4AbodiesOnly.
 
dusted said:
before doing that I would get a timing plate limiter from 4seconds flat and you can get the total timing set. Or just get a MSD.

View attachment 1715671353
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With using that limiting plate, will the stock timing curve be acceptable (although maybe not ideal) for a 10psi Slant 6? I’m not at all shooting to squeeze every last HP out of it. Also- I already have HEI ignition.
 
The King said:
With using that limiting plate, will the stock timing curve be acceptable (although maybe not ideal) for a 10psi Slant 6? I’m not at all shooting to squeeze every last HP out of it. Also- I already have HEI ignition.
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I doubt you will have an issue. Those engines are low compression and the head isn’t very efficient. It will work well. Not sure if the limiter plate will work on anything other than a Chrysler distributor.
 
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