Thread: Head Help

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i have a sbc 406 with eagle forged crank,eagle forged rod 5.7,kb pistons,compression is 10.5.xr288-10 cam..236 intake,242 exhaust,110 lobe @.05,edelbrock performer intake,holley 750 mech secondaries......i currently have the jegs aluminium heads 180cc intake,72cc combustion chamber, 2.02 intake,1.6 exhaust.......this motor is just not making anykind of power like i think it should.....should i change the heads and if so what should i get? i just think i need to be making more power. how does this setup look or what should i change to make power. any input will be appriciated.

Welcome to CHR!

I’m going to make some assumptions and ask you a few questions. I’m assuming your 406 is a 400 SBC bored .030 over with a stock crank. You didn’t say what type of pistons you have so I’ll again assume a dish and add 4cc to my calculations. I’ll also assume that you’ve had your block decked and C/L is squared to the mating surfaces with deck clearance of .010. Those numbers with a .042 head gasket will give you 10.5:1 compression ratio.

You said your heads were from JEGS – they sound like Dart 127211. If your block was a true 400 SBC did you have the steam holes drilled (and are you using 400 gaskets)? These heads do not come drilled and thing will heat up and may have already damaged (at the very least) the head gaskets.

Not knowing what your transmission is, or your rear end gears it’s somewhat difficult to bring hard advice to the table but here’s my first impression.

Your cam is too big. Lift on the exhaust side is .540 and unless you’ve had the heads reworked, your springs will bind on anything more than .520. The duration is also a bit long for this setup. For raw duration numbers at .006 of 288/294 you’ll be disappointed below about 4,000RPM. If you’re running an automatic with a stock stall converter your car probably feels like a real dog unless you punch it at 3,500RPM but even then, you may not like the results if the exhaust valve springs are binding up.

I also think that the 750 mechanical could be problematic as well because everything opens up at WOT regardless of your vacuum situation.

Address my assumptions, tell us about your ride, i.e., vehicle, transmission, stall converter, rear-end ratio and we can give you a few more hints.

Regards,
Glenn