Tuning issue on the CS 347

miller511 said:

Arlie,

The compression ratio of 10.47:1 is certainly a factor. I think it'll be a heat/trying to keep the motor cool issue, as well as a "gotta run premium fuel" issue.

I'm now thinking the reason the 347 motor might be being fussy with the carb I'm using is the duration of the cam (222/232) and setting the initial timing a bit higher than 10... more like 14 to 16. The Edelbrock 1406 carb is pre-set assuming you'll have 7" HG of vacuum or so, like for the stock 302 that I originally bought it for and is spec'd for cams of less than 220 degrees duration.
And apparently the long duration of my cam produces less vacuum. I'll pick up a vacuum/pressure gauge this weekend to verify where I'm at with vacuum (in HG or mercury inches) and also to check fuel pressure from the fuel pump.

Stay tuned.

Thanks again folks for the advice so far.

-Jeff

Click to expand...

Jeff,
You do need a good radiator (not the stock 2 row) for this engine. Many out there. The duration of this cam should not be a factor in your carb. The more initial you run, 12 or 14 vice 6 BTDC, the more vacuum you will realize. You should get a good MSD or Mallory. You can shorten the centrifugal to allow you to run more initial and not exceed 38 to 40 degrees of total advance. You should get a degree tape from your local high performance shop.

Both my 67 with a hipo short block and my 428 in my station wagon run Mallory unilights. My 13 to 1 compression 289 in my 67 is set at 18 degrees initial with a huge solid roller cam. My 428 at 10.5 to 1 is set at 16 degrees initial. It has a very large flat tappet hydraulic. The only draw back is with my 428 I needed a hi torque starter.

Increased duration does 2 beneficial things. It actually bleeds off compression at cranking speeds and is easier on a starter. It also bleeds off compression at lower RPM's and makes the motor less susceptible to pinging. Also aluminum heads assist in lessening pinging. Your engine can be tuned to run on 91/92 octane in todays fuel.

If you have power brakes your cam may make them a bit hard if the vacuum drops below 12 inches at idle. If you have less than 7 inches you might have a vacuum leak or need to move the initial timing forward.

Your cam and carb combo can work. It will hold back your top end power. The duration should not be any factor for this carb

Rob