383 carb choice
 

I am sure a few of you saw my other thread regarding my 383 stumble and I was wondering if maybe before I spent the time and effort to set up the car right if I should look into a different style/ size carb.

I am running a 650 double pumper now mainly cause I had it. But for a boat what is best? Mechanical secondaries or Vacuum? 650 or 750.... and so forth.

Keep in mind the boat is not a cruising boat. She is a little hot rod that is used for 1/2 hour blasts. Acceleration and speed are more important then fuel economy.

Chris

Call Demon's tech line. 706-864-8544. They were very helpful and nailed a TR setup for my 632. They will want lots of info about your current motor to get you the right carb. ;)

Mechanical .....vacume secondarys can shut down too quick and at high speed in a fast boat could cause it stuff the bow punch a wave ......

On my 383 which is not used for crusing either :D I am running a 750 holley vac. secondary. Its in the GM parts book. I put it on and haven't touched it since works great... But it is not a marine carb..

650 Double Pump is the way to go.:cool:

I'm using a 750 QuadraJet on my 383 with the jetting done by yours truly. It works REALLY well and has no stumble.

I would suggest looking for a vac 750... is your carb stock out of the box?

Tom

I run 600 Holley Marine vacuum secondary carbs on each of three 383 engines. One 383 is in my X-18 Donzi and a pair are in my 27 Magnum. All are propped for 4800 to 5200 RPM. I did try a 750 cfm carb on the 383 in the X-18 an found no difference in top end.

I have a fresh Marine Holley 750 Vacume secondaries for sale if you decide one that. I can set it up just about anyway you want. Has the quick change secondary springs as well.

I run a Barry Grant 750 vac secondary on my 383 in my car. I don't know what is better for a boat but I know they will tell you that you need a 650 mechanical and 750 vacuum.

On the dyno my brand spanking new 383 tried both 750CFM and 650CFM Carter carbs.

Results:
750CFM flowed a max 511 CFM at 5400 RPM and made a max HP of 398 at 5100 RPM and a max torque of 438 at 3600 RPM. Jetting was on the money with BSFC in the .45 range and FA lb/hr in the 165 range

650CFM flowed a max 503 CFM at 5100 RPM and made a max HP of 387 at 5200 RPM and max torque of 432 at 3800 RPM. Jetting was rich with BSFC in the .51-.52 range and FA lb/hr fuel comsumption in the 180 range.

conclusions: leave the 650 on for breakin and then after 10-15 hours rejet it to the 750 specs, and pick up some HP and fuel economy. This is a case where bigger insn't better....

I'm looking for 400+HP once dialed and broken in

Should push my 2400lb bow rider very nicely with the addition of a new Alpha 1 SS drive I'm getting today....... :p