tyler72

Well, I got the 347 together and going again finally. I also got the little C4 all tied up and working really well too. I now have about 150 miles on them. My question is pertaining to the engine. It pulls really good all the way up to 5000 rpm, and then it is like you hit the nitrous or something (which it does not have). It freaking screams at like 5200+ rpm! But, the transition isn't smooth. I mean, when it hits that rpm, it just suddenly begins to scream! Like Vin Deisel hitting his "NOS" in Fast and the Furious. Like it will set you back it the seat even more. My question is why is this? I wish it would pull more smoothly throughout the rpm rang instead of just wham bam at 5200. Do you think it could be that the secondaries are opening this late? It is a vacuum secondary 650 CFM Demon carb. What about the timing? It is set at 18 degrees base, and is an MSD pro billet ready to run with vacuum and mechanical advance. I just want to know if there is anything that I can do to check and see why it starts puling this hard just all of a sudden at 5200. It I could get it to pull that hard all of the time (or at least at like 4000 and get stronger on a smoother note) then it would be waaaayyyy wicked! Anybody got any ideas???

If anybody is curious, the cam specs are as follows: Valve lift Int/Exh: .555/.570 Adv. Duration Int/Exh: 284/291 Duration @.050 Int/exh: 238/245 Lobe center: 110

Jfsram

Place a paper clip on the secondary linkage. Fix it so you can tell if it moved. Now drive the car. Go wide open throttle up to 3000, then 4000, then 5000, then 5500. If you don't disturb that clip until after 5000. Then it's what you suspected. Your secondaries are opening too late.

Holley has an assortment of secondary springs in a kit. Keep changing to a lighter one to make it open earlier. You will know when you've went too light when the car bogs.

With the distributor you are running. Base is only for that, base timing. You must confirm total mechanical timing with vacuum disconnected. With the engine running high rpm, like 3000rpm or more. It should be at 30 or more deg of timing. Then fall to 15-20 at idle. Plug in the vacuum advance and don't be surprised to find it running at 40-50 + deg of timing. Not to worry, at full throttle the vacuum drops and you will be back to your 30 or so deg of timing.