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[blown540flattie]

I need a little help. I am have been building a blown bbc motor. I have a couple of questions on the spark and injection setup. Here are the specs on the engine, bbc 540, 11.5-1, 14/71, bird hat w/port setup and msd mag. The motor hasn't been assembled completely yet. What is the pully ratio, timing, spark plug and gap that I should start with. I am a little new to this and i nedd a base line to start from. Thanks for any input!

[Fiat48]

I'll try to help but need more info. When you say pulley ratio..I assume you mean drive ratio for the blower. I am going to assume this is a "lake boat". A 14 is so big and pumps so much air that I would think 1 to 1 (or straight up) drive would be plenty for you. Timing is 34 degrees no matter what you run. Locked out distributor (no advance) is best. Less than 34 degrees causes exhaust temperature to rise at a rapid rate. More than 34 you run risk of hurting parts. I am speaking from experience here.
Sparks plug gap depends on ignition system. Magneto's like .018 to .020 gap due to weak spark at cranking speeds. But I have never run the MSD so somebody else may know. I hear they are very powerfull so you may be able to run wider gaps than Mallory or Vertex mags.

[HighRoller]

This may sound like a stupid question,but is that 11.5-1 the static compression ratio?If so,and your turning a 14-71 blower you might want to consult a professional engine builder on the boost and injector setup.I'm no expert but you might end up with 14 or 15-1 final comp ratio and that is no picnic especially on a mechanically injected engine.VERY tempermental.Is this going in a pleasure boat???

[Fiat48]

Don't know if this will help in your expectations of performance but here it goes. I just returned from a first race with my Cole 5/8" runner bottom Blown alcohol Flatbottom. Engine specs: 475 cubic inches, 12.5 static compression, Brodix heads decently ported, decent but not perfect 6/71 blower, Birdcatcher hat, 80A pump,34 degrees timing, Mallory super mag III. 32 gears and 11 X 16 menkins prop. Heavy weight boat. Best was 125 mph with an 8.50 e.t. with the blower driven at 2% over, 58 nozzle and a 75 main jet and no high speed. Still much tuning to do but capable of 128 to 130 I would say and 8.0's or high 7's.

[Dimarco Kid]

Fiat, I assume no trans in your boat, right? That thing runs hard!
D Kid

[Fiat48]

She will run harder next time. Sponsor stepped up to the plate and said "Get the best block, crank and dry sump system money can buy and I will pay for it." Soooo....Dart Big M splayed cap 4.500 bore..Lunati Blower crank and here comes 509 inches. Hope to be complete by Dexter race.

[Snowboat]

Fiat48. I have a couple of questions. You say 34 degrees no matter what. I thought if I ran at 28 I would have more low end torque and be a little less worried about detonation. I have been using AR 13 plugs, figuring that the electrode would start to deteriorate in the case of suprise detonation, and cause it to miss and save the engine. I had been gapping them at 032". I have a Don Zig mag, locked out. If I tighten the gap and increase timing will it still start like it does when its at 028" with 032" plugs? 460 Chevy, Bowtie heads, 6/71 10% over, 14 max boost, solid roller, 680 and 698 lift. Its on a medium weight 18' Biesemeyer flattie. Thanks for any advice.

[Snowboat]

I was surfing the Hunt Magneto site and they recommend .015" to .020". You are right again. Still would appreciate an answer on the timing. I'll tighten up my plug gap and I bet it'll start great. It started OK before, but I wasn't really happy.

[GofastRacer]

Fiat48:
Don't know if this will help in your expectations of performance but here it goes. I just returned from a first race with my Cole 5/8" runner bottom Blown alcohol Flatbottom. Engine specs: 475 cubic inches, 12.5 static compression, Brodix heads decently ported, decent but not perfect 6/71 blower, Birdcatcher hat, 80A pump,34 degrees timing, Mallory super mag III. 32 gears and 11 X 16 menkins prop. Heavy weight boat. Best was 125 mph with an 8.50 e.t. with the blower driven at 2% over, 58 nozzle and a 75 main jet and no high speed. Still much tuning to do but capable of 128 to 130 I would say and 8.0's or high 7's.You're there!!, time to hook up the "high speed"!!... wink

[GofastRacer]

Fiat48:
She will run harder next time. Sponsor stepped up to the plate and said "Get the best block, crank and dry sump system money can buy and I will pay for it." Soooo....Dart Big M splayed cap 4.500 bore..Lunati Blower crank and here comes 509 inches. Hope to be complete by Dexter race.You lucky SOB!!!......