467-Ratman

In about a month when its time to put the Vette away for the winter I want to change my cam. Its a Crane PowerMax 296-2, 236\246 duration at .050 and 553 /571 lift. The curent power band is 3000 to 6500, No matter what we seem to do with timming and carb adjustments the motor is just plain lazy untill it hits 3 grand. My problem is I figured with all of the cubes of the BB it would be fine around town, but it is very sleepy. Looking for ideas on a power band that would be lower and give a better idle with a max rpm of about 5800 or so. Thanks!

The Money Pit

Your combination looks perfect to me cam wise.Are you running a carb spacer?If I were you,I'd borrow somebody's Q-Jet,or smaller Holley to see how the low end feels.Seems like a carb problem you have,not a cam.Mine idles rough,but pulls fine as soon as I touch the gas.Most of the time I intentionally hit the gas slowly,so as not to break loose the tires.
What is your advance curve like.The stock springs took almost 4000 rpms to give the full advance in my HEI,but now it's all in by 3000.

If you're set on the cam swap,I ran the Comp XE-274 in my current 406 and thaught it idled like a stock cam,and it did pull into the high 5000 range.

467-Ratman

I have been fooling around all summer with the 850DP and it seems to be ok now, but I still think as you do its a little over kill. I talked to the people at Edelbrock and Barry Grant and they said go with a 750, better around town driving with good top end. I think my combo of big cam and big carb is killing me?

The Money Pit

Another thaught I had was that your intake ports are too big.This could also contribute to a soggy bottom.When I built my 406 I intentionally sized the intake port small.I ran a 350hp cam in a 327 once,and loved the throttle responce,so I used the 170cc port size,and extrapolated the size the 406 would need to maintain the same ratio of ports size to engine size.The 327 hit 7000 rpms,and by golly the 406 can too with only 195cc runners.

I realize you're running a BB,but physics is physics,SB or BB.

467-Ratman

Yeh, with my Merlin heads the intake runners are 310cc, lots of air moving around for sure! I guess the car belongs at the dragstrip.....Live and learn!

Larry3x2

Hydraulic rollers are the way to go. See my post on dyno results. Flat Tappets give up too much due to long acceleration ramps which affect low end vacuum and throttle response. LSA's under 112 will also move the power band up and lose bottom end capability

69 N.O.X. RATT

I would not give up on the current combo yet, it is not that wild. One thing you may want to look at is the timing, how much initial are you running ? A stock setting won't do. If you move the initial up to 20 or so and then max 36-38 all in by 3000 you will be surprised how much it wakes the bottom end up.

Don't worry about that 850 I run a 1000 on my 454, with a much bigger cam than you have and it gets around town pretty good :yesnod:

The only thing I might change would be the heads, some big ovals would help the bottom end, without killing the top end too much. An Edelbrock Rpm Air Gap would be a great manifold for your combo.

467-Ratman

My friend told me what the specs where and I think he said my intial timming was 18 or 20 plus the vacuum advance for a total of 40. It seems to start ok when hot and the idle is actually pretty smooth?

Les

Unless your compression is low you should be able to make that combo run real strong. I'm running 9.5 to 1 w/ a flat tappet solid lifter Ultradyne that's very similar- .243/.251 duration & .586/.601 lift. Even when you account for the valve lash it's a bit more cam than you have and it's in a 439 inch motor. I also run a modded carb that's rated at 1040 cfm. With this combo low end throttle response is almost too good(if there is such a thing). I don't know enough about your heads to be sure, but I just don't think that's it either.
At least check your timing to make sure the advance is coming in fully & early enough. I really wouldn't give up on the cam yet. My last thought is on the cam install- did you have it degreed at that time?

Flareside

Sounds like you have a place to start looking for the problem. If you really have 40 total with the vacuum advance, then something isn't set right. You want the 38-40 total before the vacuum advance kicks in. Like the others said, get your initial to around 20, then get another 20 coming in via the mechanical advance, then get the vacuum working (probably adds another 10-15).

fireball

With the 4 spd and that rear, do you spend much time below 3k rpm? I'm curious because I was thinking of raising my power band higher in the rpm range. Right now mine is from about 2,500 to 4,500 - so when I shift I'm already half way through my power band.