340 dyno chart thoughts
I'm thinking for now I would use a mech.
Mechanical will work fine. The Carter M6866 is a stock replacement but IF the free flow fuel volume posted on the S*mmit website is correct, then that not keep up on full throttle 1/4 mile run. A 340 with a cc280 cam will need about 28 gal/hr peak. You can calc the exact number for your engine at any rpm since you have the lbs/hr from the dyno data. Just divide by 6, it will be close enough for this purpose. The nice thing about the M6866 pump is the max pressure (aka cutoff pressure) 5.5 psi
Carter's M6902 may be a good alternative. There seems to be some internet talk, for whatever its worth, that the cutoff pressure is over 7psi. That would be a problem if true. However they were originally set with a spring that relieved pressure at 6psi, which most carbs can handle.
The M6270 carb is 7.5 psi and definately would need a regulator.
I've had good luck with a Holley mechanical, 12-360-11, 110 gph series, no regulator.
so.. based on my setup if i were to change the cam which hydraulic one would you recommend. and what size of carburetor to go with it? i assume if i wanted more power from my engine later on these 2 things would be the best place to start. everything else should be fine?
My opinion is spend time on tuning what you have. Looking at the dyno data, the manifold pressure didn't go up during the runs. However the AFR dropped .4, so get that flat and then work it for max power. Whether max power is going to be at 12.5 or 12.9 or something else only will be found by testing. Use the same fuel if possible. Take it to the drag strip and have fun.
i have a question about the ld4b that i have on the engine. this intake has smaller ports then the 340 intakes. is the full chamber smaller on the ld4b or is it just at the opening where it enters the heads? i ask because i was told he port matched the intake to the heads so would that not make it the same as the ld340 intake or no?
The LD340 has bigger runners than the LD4b. I did very similar to you, same cam in a 340, had a Street Dom port matched to the 340. Now have a different cam in it but with the LD340 intake. In retrospect would suggested using the 4b without porting up, but its too late. Small runners help on the street (autocross rally, etc) by keeping velocity up at lower rpms so less fuel drops out and less volume needed to keep the walls wet. The discontinuity of the intake to head port *might* have helped reduce reversion at idle and low rpm (ie under 2500).
For the rpm range this cam gets happy at, I'd not use a plain ole performer. The Ld4b was a good choice for street/strip, the only one that might do better at both lower rpm and higher rpm is the Performer RPM . If you start trying taller intakes, keep an eye on hood clearance.
As to your initial question, Since it was mostly a break-in excercise, keep the data as a baseline.
If there were some weird divergences on the VE, BSFC, Fuel to AFR etc, then that would be a flag for something being off. The EGTs and the spark plugs will let you know if the WOT distribution was fairly even.
