Hello, I am planning a 400 build.
Stock 2 bolt 400 block popped out to 406
Flat top pistons with an Eagle rotating assembly, Forged crank, and forged aluminum pistons
Dart 200cc aluminum heads with a 72cc combustion chamber.
Weiand Xcelerator intake.
Holley 750 cfm carb
Summit Inch and a half headers
Summit 00172 cam. .450 lift intake and exhaust. 214 lift intake and exhaust 106 LSA
Going to be blowing into 2 and 3/4 Magnaflow exhaust
Compression should be around 10.25 would like to run 87 octane.
Hoping to be around 350hp

Thanks, Sean

 

Reduce your compression. No need to be that high - will just be detonation prone. Especially on 87. Stick to around 9 to 9.5. High compression doesn't add much performance. My 350 with 195cc heads and 8.5 compression (for power adder) makes more than 350 brake HP at the crank. 300 at the wheels with a FIRST TPI manifold.

Headers are too small. Get some Dyno-Don headers that are 1-3/4"

Keep your fuel injection. Go with a FIRST manifold.

If the bores look good and measure ok, don't bore it over. 400's already have thin walls. Run stock size pistons and don't touch the cylinder walls with a bore or a hone.

GD

 

Ok, thanks. The 400 I'm looking at is already punched out so there's not much I can do to help that. But I actually wish I could lower the compression but I really don't want to use dish pistons and with a 72cc head, the compression is roughly 10.25. And I really want to do the carb way. 86 being the last 1st gen sbc I wanna run kinda old school. And the TPI never ran right for the short while till it blew the head gasket lol. Could always go the 350 route too but displacement.

 

Not running right is a function of skill. TPI isn't that complicated. Putting a carb on it is entirely unnecessary and frankly it's a hack that ruins the value of these cars.

I have dished forged pistons - what's your issue with them? I have well over 350 crank HP on 350 cubes with dished pistons at 8.5:1

I would skip a bored over 400 personally. Too much potential trouble.

GD

 

Ok thanks for the info

 

Regarding your compression ratio, what values did you use to arrive at 10.25:1? Piston to deck, head gasket? What length connecting rods?
While 10.25 isn't unmanageable in and of itself (particularly with aluminium heads) that's a very short cam you've selected and that could prove problematic. 400 CID can swallow up quite a bit more and still be entirely streetable.
I would ask why the flat tappet? I understand the cost perspective when moving on to a retro-fit roller however I will say from having experience with an engine that's ingested a cam and lifters, it's a false economy.
If a 406 isn't making at least 1 HP/CID, then you're not really trying.

 

I actually bought the cam originally for a tame 350 but then this 400 came up so I was maybe thinking of using it.

 

While the tight 106 LSA is arguably a good choice for 406 CID (although just about any company you go to for a recommendation will not suggest that tight), the short duration and early intake valve closing point is going to drive up compression pressure. Perhaps unreasonably so as GD pointed out in post #2.
I look at it two ways:
The first is with 10.25:1, (and this is something you'll have to confirm as the numbers I ran for your SCR don't quite stack up) and a cam for that compression. That spec will push the peak HP numbers higher up the RPM scale than the Summit cam would provide. Those heads will support 500 HP and in a 400, that RPM would come in at less than 6000. The cam spec would be such that peak HP is developed at that speed.
The second option is if you keep that cam, then I'd say pull some of the SCR out of it. With the smaller cam, peak HP will fall in at a lower RPM and naturally be less than the higher SCR/larger cam combination.
The combination of the higher CR and the small cam could produce something that, in my experience, is problematic.
That's for you to decide.

When it comes to spec'ing a cam, you have to have determined all of the variables like gearing, converter, weight, application, etc.
For arguments sake, if I were building a 406 with those heads and was targeting the most torque (application notwithstanding), the cam would be something along the lines of 284/284 on a 106. With 10.25:1 , this would keep some of the compression pressure in a range that would be manageable on the street. Overlap is a very workable 72 degrees. Even then you'd have to be sure of the state of tune.

There's still the matter of the flat tappet vs a roller too.

 

Ok thanks I'll keep this in mind