4bbl Slant Intake
I can clock the carburetor whichever direction I want on this Offenhauser too. I also think it's arguable which is better where. Do you have some data to back it up? I've never seen any dyno figures on either manifold. I've always seen people say the Clifford was "better" but I'm not sure. Certainly, the Offenhauser has closer to equal length runners......for "whatever" that's worth.
Found some - knew I'd seen it somewhere...just took a while to find it again:
From
Plymouth Volare Duster / Slant Six Modifications and Performance Upgrades
Dyno Testing
You can get a slant 6 on any dyno! All you need is a
manual bell housing, clutch plate, and a place that's nice enough to actually want to dyno the motor. Dynoing ranges in price, I paid about $50 an hour. (which usually includes hooking the motor up). I spent a total of about 17 hours on the dyno (3 of which the dyno operater gave me free) and we got the motor to make 240hp and 270lbs. ft. torque, but that wasn't even near max, it was just a smooth run. I got tired of the dyno because I was out of money and the motor didn't seem to get very far in the 17 hours it was on. I would suggest on something like this is to try and tune it the best you can in the car first, then bring it to a dyno and optimize it.
1. Using only the primaries of an
850 Double Pumper and a Clifford 4-barrel intake with 28 degrees BTC and part throttle: 236 hp at 5250 rpm, 258 lb-ft at 4250 rpm. The low timing was used because the first time the motor was dynod it bumped the bearings on two cylinders.
2. We tried a 750 Dbl. pumper (primaries only) and it made 20 hp less. Also we tried a Offenhauser intake with the 850 and it made 30 hp less due to the smaller runners and plenum area.
The grooves on the intake may hurt fuel distribution, so 3 and 4
cylinders get lean while 1 an 6 get rich. I was told by some slant six racers to grind out the grooves and play around with the jetting, but I was also told to use a 600 double pumper; all in all, something isn't right, the motor falls on its face when the secondaries open on all three carbs. I suspect the fuel distribution rather than overcarburetion.
3. This time we ground out the grooves in the intake and tried a 750 vac. sec. Holley. It revved up smoother, so then we tried my 600 vac. sec. and misc. jets and it spittered. Next we tried a 750 double pumper and that didn't work either. so after 4 times on the dyno this is what we got with 92 octane gas, 23 degrees BTDC, and a 2 " spacer. The result: 240 hp @ 5000 rpm and 270 lb-ft @ 4000rpm.
It didn't want any more timing for some reason and a 2" spacer made 10 hp more than a 1" spacer.
