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Old 10-29-11, 08:48PM   #1
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Join Date: May 2005
Location: Spokane Washington
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Default Twin Turbo 400

Hi Everyone, I am a long time lurker and I have been gathering info on a turbo build for my car but I haven't seen this particular question.

I have always wanted to do a twin turbo on my car but I want to be able to drive it anywhere so I am not going to go too radical on the horsepower.

So my question is: Would the stock cast crank be able to hold up for 8-10 psi of boost? I have in mind 600-700 horsepower at the flywheel.I know this would be a perfect time to put a 4.25 crank in it but I am wanting to stay lower on the cubes to self-limit horepower lol. I like to go around corners so that is what the car is set up for. I really don't have the desire to put a rollbar in it for the times I would take it to the track-1 to 2 times a year. So I am shooting for 11.50's with a suspension not optimized for drag racing.

Here is my set up now and what I wish to change in the future:

1967 Firebird
1968 400 from a GTO originaly a 265 horsepower now maybe 300 on a good day
turbo 400 transmission stock except for a B&M shift kit
stock torque converter
B&M Quicksilver shifter
12 bolt rear end with 2.73 gears and a posi
Herb Adams VSE suspension including front and rear swaybars solid body bushings and solid bushings in the upper and lower stock control arms
Power disc brakes from a 1970? buick Skylark
Power steering box from a 1986 Camaro
5 leaf rear springs-stock set up for a big block Camaro
Cyclone 3 tube headers
Flowmaster 2 1/2 exhaust

Proposed changes:
17 inch wheels for bigger brake clearance
13 inch front disc
12 inch rear disc
Frame connectors-weld in
5 speed Richmond transmission
2.56 gears
Rebuild the tired 400 to include stronger rods forged pistons stud the mains upgrade to 4-bolt if needed
87 cc Edelbrock heads
Hydraulic flat tappet cam-Roller would be nice but not sure is needed at this level
Buy needed turbo parts from Jeff including headers for twin set up
Any fuel system upgrades-it will be carburated
Would like to intercool but will do meth injection if I run out of room

Now I realize that I could make the needed power with one turbo but I am pretty well determined to go with the twins. I want to retain the power steering and might go to hydra-boost for more room in the engine compartment. I have owned this car for 34 years it is my first car and I enjoy driving it. I have been to Hot August Nights in Reno and the Cache Valley Cruise in Logan Utah. I want to be able to build it and drive it with out worrying about breakage (within reason-I know it's not a perfect world lol)
I know the turbo 400 would doo better with the turbo's but I had a 4-speed in it when I first started driving it years ago and miss the clutch terribly lol.
I used to be ASE certified years ago but no longer do it for a living so I do know my way around a wrench fairly well. I also tore the car all of the way down to the frame in the early 90's so there isn't a part I haven't touched.

Sorry to be so long winded but I figured too much info, in this situation, Is better than too little. Right now I am gathering info so I can start saving the money (or sell a child lol). Thank you for the info, David
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Old 10-29-11, 10:24PM   #2
70 bird
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Location: Taylor Mich
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So my question is: Would the stock cast crank be able to hold up for 8-10 psi of boost?
Stock crank should be fine, My 455 cast crank has seen up to 15psi. more than a few times without any problems. Pontiac cast cranks are pretty strong just keep the rpm's down and it should live a long life, stock cast rods are another story, there junk so get a set of aftermarket h-beams.
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Old 10-29-11, 10:41PM   #3
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Join Date: Feb 2005
Location: simsbury CT
Posts: 5,717

Yes Id agree

Just watch the radii on the journals that helps strengthen the stock crankmines been good for a long long time now

Im sitting here w the power out from the storm
Roads blocked by downed trees in both directions. Playing Uno w my 5 year old by candle light lol
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Old 10-29-11, 10:56PM   #4
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Location: Spokane Washington
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Playing with your 5 year old is a lot more important than answering my question lol. But thank you. I have a lot more questions now that I have a path I can go. But thet can definatly wait. I hope the weather treats you well but for your 5 year olds sake I hope the power stays out for awhile. Enjoy your time. David
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Old 10-29-11, 11:00PM   #5
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Location: Spokane Washington
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70 bird thank you. That is one of the reasons I want to go turbo. I like the idea of low revs for this build but to still have loads of power. Of course my dark side wants to build a 7500 rpm 400 that won't run below 3000 rpm and pulls 3in of vacum at idle lol. David
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Old 11-05-11, 10:09PM   #6
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Location: Austin, TX
Posts: 108

You may want to keep that turbo400 tranny. I have a hard time watching my tachometer when the boost hits. I probably short shift my super T10 at 5500 most of the time due to keeping my eyes on the road and not the tach. An automatic would leave one less thing to worry about, theoretically.
1976 Bandit 455 T-top
One of 110 made.
One of a very few still around...
twin turbo
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Old 11-06-11, 12:44PM   #7
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Opnwide, I agree. I will probably have the turbo 400 in it at first anyway. Since I will be doing the build in stages. I do the best I can to not have the car down for very long ever since the 3 year hiatus for the frame off lol. But when I first put the car together in 1978 it had a four speed and I really miss the driving experience. I will keep all of the auto pieces in case nostalga is a liar lol. BTW I love your car. If I didn't have mine I would be wanting a 75-78 Trans Am since those were the hot car when I was going to high school. David
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