Dear UDHarold:

I had a 406 sb, DartII heads, 10:1, 1 5/8" headers.
Induction is antique Rochester FI with 2 air meters.
Cam is CC street roller with 255@.050, I think 172*@.200, symetrical lobe, 110 LSA.

Although it made 455 RWTQ on Bob Stiegemeiers dyno, the HP was dismal. Bob said my experience was typical of Dart's exhaust port. Fuel curve was pretty good and I know 455 is a big number for NA 406.

I've purchased AFR 210 heads and I'm concerned that I may be over-cammed with the new heads. The Rochester causes about 20 cfm drop in airflow compared to bare heads. Intake length is near 14 1/2", about the same as a tunnel ram.

A 7000 rpm limit should allow me to take advantage of the 3rd and 4th hormonics. Do long runner manifolds like more or less LSA? Should I go with a shorter cam and forget about hormonics? Should I dump the Rochester and go with a Victor Jr.? I have read these old FI's had a double torque hump and I'd like to find it. Heaven is a big, bold torque curve. Car is 3400 lbs. Th400 was stalling @ 4400, was built for 3500 but made more torque than builder thought it would. FI is an original Bill Thomas unit. Would much appreciate your advice for a cam. This is my first experience with really good heads on this engine. Would the dyno printout help?

Thanks for your time.

kirkwoodken,

It all depends on whether or not you want to keep the Nostalgia look. The Rochester's air passages are a little small for a 10:1 406, that would easily make over 500 BHP around 6500. The 210 AFRs will support over 600 in a 12:1 engine, with a little port work.
If you have to have the Nostalgia look, a wider LSA will work better. If you change to a Victor Jr, a tighter LSA is better. To drive on the street, use either my 501B8SBLUN, which is 287/295 at .020, 254/295 at .050, .582"/.582" valve lift, and 108 LSA, or my favorite, the 501C2SBLUN, which is 288/296 at .020, 255/263 at .050, .626"/.626" valve lift, and 109 LSA. The 501C2 may need screws in the rear rims.....
The SB in the grind numbers just means Small Base Circle, which you will need for a 5.7" or longer rod.
Both of these cams have wide flat torque bands, and if the length of the FI runners cause 2 torque peaks, they'll be there.
The 501C2 in 12:1 355s has over 420 ftlbs from below 4000 to 7200......

UDHarold

Harold seen as these FI units are basically controlled by manifold vacum signals how will the cams you listed differ from each other. I know someone told me that you need a cam that has X number of inches manifold vacume at idle for the rochester units to work well but i cant remember who it was that told me or what the vacume number they said it needed.

You currently have a Comp Cams that is 255 at .050, 110 LSA. The 2 of mine are 254 and 255 at 050 on the intake, and I know my 255 thinks it is only a 252 at .050. My 2 cams should have vacuum very similar to what you have now, within 1" or less. I know my 2 idle at under 1000 in 355s with Victor Jrs and 750s, I'm sure a 406 will lower that slightly.
I do not know what vacuum a Rochester FI needs to properly meter fuel. A 750DP needs about 74s/84s to make 576 BHP in a 12.5:1 210 AFR-headed 355, 1 3/4" headers, very conservative dyno.

UDHarold

Thanks a heap for the advice, Harold. The Rochester is much like a Hilborn with a pill whose size could be regulated by vacuum. Venturi vacuum adjust the flow to the nozzles, as does manifold vacuum. The main control diaphragm works on as little as 1/8" water column vacuum. Manifold vacuum is bled into the control diaphragm for idle control. Getting enough signal for idle is no problem, much easier than keeping carb throttle plates in the transfer slots! Stiegemeier thinks the Rochester should only cost me about 50hp over a Victor. I think throttle response is better than a carb. And I like to make old junk work. I'm trying to build what the Corvette engineers wanted in the cars in 1963.

Is a 4-7 swap worth considering for insurance against 5-7 cross fire?