Thread: chevy 400 build help

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For the benefit of others who may be reading this thread, I'll weigh in with some thoughts.

If I'm understanding the chevy406 correctly, he is wanting to build a low-rpm tractor motor to move a heavy pickup truck.

I agree with the choice of Vortec heads for this application due to the rather smallish intake ports (170 cc's) and their propensity to keep mixture speed up in a larger motor to aid in cylinder filling at low rpm's. I would not recommend these small heads for a 406 that will be revved higher, because in my opinion they will sign off at around 4,500-4,800 rpm's. Erik would have a better handle on the top limit of these heads on a large small block, I'm just estimating for the sake of this thread.

If the heads are going to sign off early, then it makes sense to keep the static compression low (around 9:1) so you can use a shorter cam with an operating range of idle to 4,500 rpm's in order to screw together a balanced package that will pull tree stumps.

Although the Vortec's work best with a flat-top piston, that will not be possible with a 406. You just can't make a 9:1 406 with flat-tops and that many cubic inches with 64 cc heads, so dished pistons will have to be used.

Keith Black makes a 30 cc dish piston using a 5.7" rod that would work for this combination, part# KB126 and would put static compression ratio at 9.1:1
You'll have to do the normal clearancing at the cam/rod bolt heads, pan/rod big end, and pin-end balance pad/underside of piston crown with the 5.7" rods, just like you would for a 5.7" 383. Or, purchase a reduced-base circle cam to side-step the rod bolt grinding.

NEVER TAKE THE WORD OF ANYONE ON ANY FORUM TO MAKE YOUR FINAL CHOICE OF CAMSHAFT FOR ANY MOTOR FOR ANY REASON. ALWAYS TALK ON THE PHONE WITH THE TECHNICAL PERSON AT YOUR FAVORITE CAM GRINDER.
Now, with that having been said, it's ok to listen to some of the professionals and well-versed amateurs on this and other forums in their advice on cam selection to get you close to what you should need and to tell you why. Like I said, I would choose a short hydraulic roller cam for this combination, maybe something like the CompCams 270HR grind. Operating range 1,800 to 5,000, 270* duration @ advertised, 215* duration @ 0.050" tappet lift, 0.500" theoretical valve lift with 1.5 rockers and ground on a LSA of 110*. Although this cam looks slightly large for the application, this is a LARGE small block and the cam will appear slightly smaller to the motor than it would look to a 350 motor. This cam will require a different spring/retainer combination on the heads. Stock Vortecs (GM 12558060) are limited to 0.450" lift as is. Scoggin-Dickey Chevrolet produces modified heads to use with higher lift cams.
www.sdpc2000.com

To put the icing on the cake, I'd use a slightly looser converter, something around 2,000-2,200 stall to help get the motor up on the cam earlier:

From Hughes website:
"Street Rod 2000-2200
This converter was designed and manufactured for the street rod enthusiast needing that slight edge over the O.E.M stock converter. This unit has silicon brazing for strength, needle bearings for reliability, and stator modifications for more torque multiplication."