I am beginning a engine buildup and i'm not sure which to use if i am wanting about 400 rwhp which would be the cheapest to build using stock heads??

 

The best thing to do in the long run is to get your heads reworked. Heads are where most of the power is to be had. Later, if you want to make improvements, you already have good heads to work with instead of having to fix them up. Stock heads will not support very much lift.

I am making 410 HP at the wheels on my 383 running thru an A4

 

Simply put, with the same parts, the 406 should almost always make more horsepower. The 1/8" larger bore will allow both larger valves and allow the valves a little more room. Plus its got an extra 23 cubes. Since the 383 and 400 use the same unique crank, balancer and flexplate, costs should remain close. Only difference in cost would be the pistons. However, 400 blocks are harder to come by, and the heads need steam holes machined into them if not already equipped. Roller cams usually make more power than the flat tappet counterparts. Hydraulic roller 350 blocks are common, and a good base for a 383. No factory hydraulic roller 400 was ever made. Conversion kits are available, but are quite expensive.

BTW - You'll NEVER achieve 400rwhp on either of the 2 engines on stock heads. (without boost or nitrous)

 

simple... 406

 

I vote 406.....400 blocks are not that hard to find, and it only cost me $20 to have steam holes drilled in my aluminum L98 heads. The only downfall is that you are stuck with a flat-tappet cam, but the extra torque provided by the larger bore is very nice

- Justin

 

Won't the flat tappet cam be noiser and possibly fool the KS into thinking there is knock? I have never had one to check out so I cannot say for sure but that is just a hunch. Someone tell me if I am wrong.

 

406 with any aftermarket heads. If you're going to scrap a 400 block to get the crank and build a 383, just build the 406. If you buy an aftermarket stroker crank, then build the 383 since 350 blocks are easier to find. GM stopped making 400 production blocks in 1979 so the blocks are getting rare. Next best thing is any aftermarket 400 block such as a Bowtie block.

Cubic inches need air to fill the cylinders. Factory heads are very restrictive. When you look at all the work that's involved in machine work and parts to build up some factory heads, it's cheaper to just buy aftermarket heads which will be better right out of the box for less money.

 

No. Knock sensors were around years before the introduction of the hydraulic roller cam. You might be confusing the hydraulic flat tappet that is being referred to with a mechanical flat tappet, which may cause problems.

 

400 production was from '70 to '80, not '79. They are still fairly easy to come by yet. My vote is for the 406.

Also '85 and '86 TPI 305's and 350's have hydraulic flat tappet cams from the factory. So no problem with a flat tappet cam and a Knock Sensor.

Martin

 

......so the big debate between the 383 & the 406 goes on! Look for this
to have 100's of reply's...... anyway, I'd go with the 406 but DON'T go with
stock heads! I have a .060 over 400 {415 I believe?} that put out 438 HP & 499 TQ. on a flywheel dyno. It's got AFR 195 heads with 2:05 intakes & 1:625
exhaust valves, headers, cam duration at .50 is 224 intake & 234 exhaust with 520 lift, flat top pistons with 9:75 t0 1 compression. If I did it again I WOULDN'T
go .060 over on the bore. Now I'm putting this motor in a '32 Ford and I want
to put a 8:71 GMC on it and wish that the cyl. walls had more 'meat' between them! The dyno guy said that it would help to go with a bigger cam, then it'd put out a lot more HP & wouldn't lose much, if any Tq...... Anyway, HEADS are what make your POWER!!! Bill.....