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Ted Guldemond
09-30-2003, 10:30 AM
I'm looking for advice on initial jet sizes for a Holley 750 cfm square bore carb on a sbc 383ci. The Holley tech line recommended 76/80 which sounds somewhat rich to me??? Any suggestions would be greatly appreciated.

Rootsy
09-30-2003, 10:54 AM
get the list # off of your carb, go to holley's webpage and grab the pdf that has all the carb list numbers and how they came setup originally... grab the info for your carb and i would start with the stock jetting and tweak from there... chances are she will be a little fat as advertised... (better rich than lean from holley's standpoint)

4150 or 4160 holley? mechanical or vacuum secondries? jets fore and aft or just on the primary side?

76/80 is probably gonna be a wee bit fat for a 750 and your motor(but very difficult to just guestimate) but within probably 2 - 4 jets sizes...

my 600cfm 4160 runs 66/72 on my 350.. it's really close and the stock jetting was 68/70...

gotta love O2 sensors right about now...

BUIZILLA
09-30-2003, 02:39 PM
Without knowing what cam & exhaust you have, I am just guessing on a starting point...

With that being said, I would go 72 and 76 for starters, maybe end up at 74-76. 80 is way too fat for a 5000 rpm motor.

Also, use 8.5 PV's in the front and 6.5's in the rear.

Jim

Let us know.

Ed Donnelly
10-01-2003, 05:26 AM
Buy a set of speed blocks. That way you can make all the jet changes you want. without removing the fuel bowls. No muss,no,fuss.You can even change jets with the engine running...Ed

Rick
10-01-2003, 10:18 AM
I've been on the jetting journey. 5000 RPM 351's 350 hp Holley 750's. I am putting in what I believe to be the final jets, and I am ending up with 74's front and rear. I like my ceramic inside the plug to look like they are coated with pencil lead dust. It's time consuming and can be expensive if you start very far off. Good luck Rick wink

Ted Guldemond
10-02-2003, 08:20 AM
Thanks for the jetting suggestions. If it helps the cams specs are 222 degrees int./230 exh. at .050 lift and .509" int./.528" exh. lift. Carb is a 4150 with vacum secondaries originally from a 454 omc cobra. Heads are vortec with 2.02/1.60 valves, deshrouded combustion chambers. Exhaust is crusader marine to 4" through the transom. (The crusader manifolds have about 3" of individual exhaust runners per cylinder and they were free.) The I/O is a volvo 280. The boat is 2600 lbs. (19ft St. Tropez). Thanks again.