Twin Turbo 401 Nailhead

[63'Riviera]

hey. So i know there is not much as far as after market performance parts for nailheads but i wanted to be the first to try something. A Twin Turbo blow through system. I was going to use the stock exhaust manifolds and just get them bead blasted and acid dipped so they're like new and those would be the turbo manifolds. Im having the heads rebuilt and ported im looking to dramatically port them without getting too close to water jackets. I was going to run the Mutha Thumper cam and roller rocker set from TA performance also a dual 4bbl intake with two holley carbs. So if any of you can help me with a few questions

1. How much should i port the cylinder heads to compensate for the extra air fuel mixture
2. what fuel should i look at running with it
3. should i get completely new gasket set for engine and forgged connecting rods?
4. an if you have any other knowledge with turbonetics or have been interested in the subject before

thanks a lot

[Dr. Frankenbuick]

hey. So i know there is not much as far as after market performance parts for nailheads but i wanted to be the first to try something. A Twin Turbo blow through system. I was going to use the stock exhaust manifolds and just get them bead blasted and acid dipped so they're like new and those would be the turbo manifolds. Im having the heads rebuilt and ported im looking to dramatically port them without getting too close to water jackets. I was going to run the Mutha Thumper cam and roller rocker set from TA performance also a dual 4bbl intake with two holley carbs. So if any of you can help me with a few questions

1. How much should i port the cylinder heads to compensate for the extra air fuel mixture
2. what fuel should i look at running with it
3. should i get completely new gasket set for engine and forgged connecting rods?
4. an if you have any other knowledge with turbonetics or have been interested in the subject before

thanks a lot

1 - The point of turbocharging is overcoming limited intake tracks with forced induction. Porting will increace effiency and reduce inlet the tempature some, but is not critical to a successful turbocharged system.

2 - 93 octane or E85 if you have it local. These wil provide great power and won't have you chasing after race fuel.

3 - Yes, you will need a gasket kit. You already have forged rods and a forged crank in your 401. Forged pistons with a compression ratio that complements the camshaft are critical to the torbocharged system ( your cast stock pistons will not hold up anyway). Big cams with lots of overlap are not good for a turbocharged system. They can cause "blow through" that forces part of the intake charge out the exhaust port when both valves are open during overlap, or "reversion" where the exhaust pressure built by turbo pushes exhaust gasses back into the cylinder when the both valves are open. Neither are good for performace. Many hot turbo cams are much like the ones in your stock vehicle.

4 - Call burtonmachine@charter.net at 509-860-3370 and ask for Mark. They are making turbo kits for the 455 and 350 Buick. I think they would like to get involved in a Nailhead project. You may also want to consider an intercooler to make the engine more powerful, durable and able to maintain continious application of the turbo.

[kitabel]

"reversion" where the exhaust pressure built by turbo pushes exhaust gasses back into the cylinder when the both valves are open

This is pretty much always going to happen with anything less than a full developed race system.
The backpressure is typically about twice the boost: 10 psi in the intake manifold = 20 lbs. of exhaust backpressure.

[63'Riviera]

dr.frankenbuick,

thanks a lot for the info i will give that guy a call and see if he can further extend my knowledge. I bet you know that there is not a huge selection as far as aftermarket cams for a 401 nailhead. What would you recomend to compliment the turbo system? And yes i was going to use a intercooler for the system. Also do you think i could convert the stock exhaust manifold into the turbo manifold?? I can bead blast them and clean them up so the flow will be good. I was thinking 2 50mm or 60mm turbo or 2 Garret t4's which are pretty standard

[Dr. Frankenbuick]

I kind of like this cam: http://schneidercams.com/284Hnailheadhydraulic-1.aspx. It is not perfect, but with a 108* intake centerline and a 112* lobe seperation it yields a 7.75:1 dynamic compression ratio from a 10:1 static compression ratio piston. That a very good dynamic compression ratio for pump gas. I could not find anything with more lobe seperation, but 114*-116* would be better.

[kitabel]

i could convert the stock exhaust manifold into the turbo manifold

If you can weld cast-iron it's worth a try.

[wkillgs]

Accelerated Motion offers a 'turbo' cam for the Nailhead:
http://www.amotion.com/amcams.html#14841
It has 0.466" lift, 216 degree duration, and 114 degree lobe separation.
Another option would be a stock replacement from Sealed Power....0.440" lift, 209 degrees duration, and 114 degree lobe separation.

It's not necessary to chose a cam with high lift (over 0.500") when using the roller rockers....the extra ratio of the rockers will add approx 0.050" extra lift over the stock ones.

Forged pistons are gonna be expensive....figure at least $800, maybe $1000.
Better connecting rod bolts are recommended....ARP bolts for a 455 will fit.
The rest of the engine should hold up fine if you keep boost under control, have a good ignition setup with boost retard, and use good gas.

[Dr. Frankenbuick]

Accelerated Motion offers a 'turbo' cam for the Nailhead:
http://www.amotion.com/amcams.html#14841
It has 0.466" lift, 216 degree duration, and 114 degree lobe separation.

Walt, I like that cam for a turbo, but wish it had more lift. Roller rockers will cut into a turbo budget pretty good. I am not sure what happened to the OP, but we may have it built for him by the time he returns.

[66larkgs]

run a set of t60 with .81ar and those puppies will spool up fast... i dont know how those old cast iron ones would hold up.. alot of people love the cast iron turbo manifolds due to they handle all the heat but i would look into using a gd set of sbc turbo headers and than modify them to fit your nailhead.would be a little labor but easier than making your own. if i change my turbo setup on my 66 lark with a 401 thats what i am going to do. it will look cherry .. setting up the oiling system would be easy because it is right thier, might need a oil restrictor to take down pressure. run a modfied oil pickup tube, intercooler, two blow off valves, two wastegates, boost reference fuel regulators, and a boost reference ignition 6btm, that will be a safe setup and very easy to tune. start to detonate and turn down the knob for the timing, you have settings from 1-3 degrees of timing it will pull out for every 1lbs of boost.

paul
66larkgs
401 turbo nailhead