anyone want to help pick a cam for a smogger BBM

[1931s/x]

so i was planning a cam swap and possibly port a set of heads and go to an rpm intake. i just had a timing chain failure, so maybe ill do it now rather than later over the winter. low compression mid 70s 400 somewhere around 8.5:1, i put a steel 383 crank in to run it in front of a stick, honed, new rings, bearings, a cam that is close to a factory hp cam http://www.summitracing.com/parts/SUM-K6400/ , a rebuilt set of 906 heads decked to clean up and the steel shim head gaskets, performer intake, headers and 3.73 gears.
the car is a cruiser its not a strip toy i put over 5,000 mile son it this summer. id like to have a little more power, i have overdrive that knocks my highway cruise rpm down to 1500-1800. hughes has a line of whiplash cams that are supposed to build cylinde rpressure and work real well with the smoggers but they mainly talk about the choppy idle they have. i dont care how it sounds, i want it to work well. i dont really want it to sound like an 11 second car and only go 14s. i know you can make pretty good power with these things, but have to give up some driveability characteristics.

[Ron Ward]

That engine combination sounds a lot like the one I used to have in my Road Runner. With that low compression and the overdrive rpm range, you won't be able to use a really big cam. I would recommend something similar to the Mopar Performance .474/280 hydraulic cam P4120235.

You didn't mention which carb you were using, but I would not go very big with this combination. Keep it around a 600-650 CFM and make lots of bottom end torque. Those short stroke 400's need all the grunt they can get.

On a separate note, due to the large diameter bore of these engines (4-3/8") they really dig nitrous. A small system (150 hp or less) ia a ton of fun and will wake that sucker up on demand. Make sure you have plenty of fuel pump and don't go with a bigger system as those cast pistons won't like it.


Ron

[1931s/x]

i have a 750 holley vs on it now. sitting on my shelf i have the fest ez efi for it. i did have an nos thermoquad on it at first but i was having some issues with it, but when those secondaries opened it was like and animal. the holley is boring compared to it, and i said if i could get the thermoquad working well without sending it out to someone, i wasnt even going to do the efi. right now i can get 20 mpg on the highway if i drive normal and i think the compression is holding me back from getting any better.

[boxer3main]

you got some good centered stuff in it now..
remove the shims and drive it.

[1931s/x]

huh?

[Scott Liggett]

Comps Xtreme Energy cams have fast opening ramps that help build cylinder pressure which helps with low compression motors. Keep it on the smaller side. A big cam with tons of overlap and duration will kill low end torque and mpg.

That cam you listed has the same specs that is in my Monte's 350. It's really mild in that car.

[Huskinhano]

Not for nothing but I'd look to a vendor that specializes in MOPAR cams. Mopars are blessed with tappets that have a larger diameter then just about any one else. You could get a flat tappet cam that'll have a much quicker opening and closing events mimicking a roller cam that'll perk up that low compression motor.

The problem with generic cams is that they use Chevy profiles because they are the most common on everything. Chevys have one of the smallest diameter tappets that limits how quick a ramp can be and also the profile are geared for what works on Chevys, not Fords, MOPARs or anything else.

[Stich496]

the bigger lifter is not a + anymore with the new oils,,

[Ron Ward]

What issues were you having with your Thermoquad?


Ron