Thread: 400 engine combo what will it do?

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Hello Tony. I welcomed you on your initial thread and am pleased to see a rodder from the other side of the pond and to trade ideas back and forth.

I am what you might term the resident self-proclaimed math rat here on CHR. I take great delight in crunching numbers because to me, numbers are the definitive answer to any problem.

Now, with that explanation aside, I'll take a shot at your combination. I have to agree with the others that the heads are a little bit on the large side according to a rule of thumb I use. (CID x 0.5 = intake runner volume) for a street motor. For a more agressive motor, (CID x 0.55). Your heads fall right in the middle of this and in my opinion, can be made to work on the street with enough cam, static compression ratio, converter and gear.

When cam grinders post the operating range of a cam for a SBC, they are using the most popular motor used for hot rodding, the 350 CID motor. A cam which seems about right for a 350 under certain operating conditions will appear more tame when bolted into a larger motor such as your 400. Your 294S (I'm assuming this is the Comp 12-224-4 cam) is not necessarily too big for a 400, depending on operating rpm's, but it is too big for a static compression ratio of 9.5:1.

In order to generate good cylinder pressure (BMEP), the intake valve must close at a certain point commensurate with the static compression ratio built into the motor. The 294S cam would work well in a 10.5 to 12.0 environment. I figured the 0.050" tappet lift valve events of the cam based on information given on the Comp cam card. They are: intake opens 18* BTDC, closes 50* ABDC. Exhaust opens 58* BBDC, closes 10* ATDC.

Using the DYNAMIC compression ratio calculator on the Keith Black Piston site, I calculated your DCR at 7.63:1. Tony, this is leaving quite a lot on the table and I think you'll be disappointed with the performance characteristics of the motor. There are three scenarios:
1. Increase static compression ratio to more closely match the intake closing point of the cam and bring DCR up to 8.3 to 8.5. Install 3000 stall converter. A SCR of 10.5 would generate a DCR of 8.41 with the 294S cam. I might even be tempted to raise the SCR to 11.0 if I knew the motor had a good tight squish of 0.035" to 0.045" and that good fuel was available to prevent detonation. That SCR would generate a DCR of 8.8. You'd also need pistons with a large, flat area on the crown to mate up with the squish pad on the underside of the cylinder head in order to generate a good squish. Aluminum AFR's are recommended to use the Fel-Pro #1003, which is 0.041" compressed thickness, so the piston deck height would have to be zero or very near zero in order to create the necessary squish. I don't know what heads you have. You just said aluminum.
2. Decrease cam timing with an earlier intake closing point to more closely match the available 9.5 SCR and bring DCR up to 8.3 to 8.5. Install 2500 stall converter. A cam which closes the intake valve at 35* ABDC @ 0.050" tappet lift would generate a DCR of 8.4 with the available 9.5 SCR. Problem here is, the motor would run out of cam before it ran out of heads.
3. Bolt in a 3000 stall converter with the present configuration and hope for the best with your 7.63 DCR.

I don't intend to sound mean-spirited here, but perhaps that's why the motor was for sale.

If you'll post a detailed list of parts and dimensions, I'll be glad to run your combination on my DynoSim software and publish the results.