400 with 305 heads

Just picked up a set of 305(614) heads done by C&J clylinder head exchange,1.94 intake valves,milled to 55cc, 520 lift springs,screw in studs.I plan on putting them on a rebuilt 400 with a stock short block and dish pistons,a480/480 lift comp cam.A turbo 350 trans with a 2300 stall converter and 3.73 gears in a heavy 72 el camino. The thing I'm not sure about is if the cam is to much on the high RPM side for the heads.If any one has tried a combo like this or has any input please let me know before I waste time and money. Thanks Wayne


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we did this same thing years ago, and honestly, I wouldn`t waste my time on them, if the chambers were not deshrouded the larger valve will only choke the flow more. The small runners won`t support upper rpm operation and it`ll fall flat on it`s face at 4000 RPM. We bolted on a set of Dart II`s after the 305 heads cracked, the difference was incredible, it picked up a lot of power and would haul A**! The cam choice isn`t bad at all for a 400, we ran one bigger than that and you could barely tell since it loped little at idle, 400`s take bigger cams well.

I also did this same combo for a customer. It did not make good power. He later went to some ported 882's and reported a very big power gain. This was in a 1/2 ton pickup.

Drop the heads in somebody's lap who isn't clued in and go with a better set, which would be just about anything else. Even a set of stock 350 heads would give you better performance. 305 heads on a 400 is just not a performance enhancing move.

305 heads are best left on 305's they fall on their face on 350's let alone 400's.

O.K. thanks for the info,seems like its been tried with poor results to many times,I still don't seem to be doing the math in my head right,I'm thinking that the 400 is a lot lower RPM motor and the bottom end torque would be great and with a small amount of port clean up 4500 rpm would be plenty THANKS for the imput,Wayne

I have a set of reworked 305 heads on my 350. They have been ported and 2.02 valves put in. It runs real good for being in a big car. I wonder how much they are holding the engine back if any?

The 2.02 valve are so shrouded in 305 heads they prob'ly don't breathe much better than the 1.84's. You'd be surprised at now much you are losing compared to a set of proper, good 350 heads. Even a set of old fuelie 1.94's would be an improvement (not that I recommend them much, anymore. Any aftermarket head is an improvement over them).

It is true that the 400sb was designed to be a low end torque motor but what you have to remember is that even while living at low rpm a 400 needs to breath alot more than a smaller engine specifically a 305. The is the reason that you can get away with more radical cam shaft designs and larger heads while still retaining a fairly street able engine.

To begine with the 305 heads need to be drilled for the steam holes.


Tazz


Rat Rods Rule!

keep the stock 400 heads, they flow a lot better than the 305 ho heads. more than likely the 400 heads are 993's & they are decent heads.

On a larger bore 400 I would think a smaller combustion chamber with large valves would flow pretty nicely. Valve shrouding? I dont think so.

A nice port job should do the trick for mid-high RPM use.

But since I'm not too big a chevy fan nor stuck 305 heads on a 400 before I could be wrong here.

Also I would think the smaller CC yielding a higher compression ratio would yeild more gain than loss.

i put a set of 614's on a 350. it didn't run worth *****... the runners are to small to flow what the 400 needs.

I said port them

But they are tinny, arent they

THEY WHERE PORTED. the runner's are just to small to get any power out of a big motor. they would work on a 327 as long as you didn't turn it hard ( oner 6,000 rpm)