need help selecting a carb
 

Im in the middle of building a new engine for my boat and need some help choosing a carb. I am replacing a 1987 260 hp 5.7L with a 1997 model 350 block with Vortec heads. I am using a edelbrock performer rpm intake, forged flat top pistons which will put the CR around 10:1. the block has been decked, cam degreed, and crank balanced. the cam kit I am using can be seen here:

http://sdparts.com/details/gm-perfor...parts/12480002

and my boat can be seen here:

http://www.concordboats.com/Magnum-II.html

should I rebuild the stock Qjet or junk it and go for a holley??
would 750cfm be to much? any thoughts on best carb for best top end performance would be appreciated.

http://www.jegs.com/i/Holley/510/0-8...oductId=743728

750 might be a little too much for only 350 cu.in.'s.

if you go to holley's website they have a calculator to find out what size carb you should go with, i believe you put in your max rpm and cubic inch and it will tell you what cfm carb you should run. as for what carb holleys are great carbs and easy to tune, q jets are great also if you know how to set them up and they can be fast and efficent.

A Holley 650 should be plenty.

a good tuned 650 or 675 would be great. something with mechanical secondaries of coarse.

i have pretty much the same set up and put a 650 holley electric choke and dual feed got it at allstate carb on long island they run them on a engine on a dyno to your rpms and adjust everything so when you get it put it on and go great people and prices

Ditch the quadrajunk holly much better they dont call them that for nothing

I have a brand new test ran 750 holley carb in the box if your looking for a deal one one.

I built a real similar combo but with ported Vortecs for my 19'6" Ebbtide 10 years ago. I used a 750 vac secondary Holley with great success. I always buy carbs that are alittle big so I can upgrade the long block and not buy another carb. That Ebbtide would run 72mph on the gps! I turned it 6000rpm with a 23" prop. The hull was WAAAY over powered, kinda unstable. Call BS if you'd like, but that boat suprised a lot of people! I think you will be pretty happy with you selection.

My brother is running a carter/merc 750 off a 454 mag on his 355 w/vortec heads. The boat runs great with it!

thanks guys for all the input!! im leaning towards the holley 650 qjet replacement, im thinking it has vacuum secondaries. somebody mentioned earlier to go with mechanical secondaries. was wondering about the pros and cons of mechanical and vacuum secondaries

transition into seconderies is alot smoother and no lag

I have a similar combination but with aCOMP marine 212*/218*,.450" lift flat tappet cam. Are you sure that off road GM cam has low overlap to prevent reversion? I kept the stock Quadrajunk and it seems to fine. 216 Wellcraft Eclipse went from 52 - 53 gps to 60 -61 gps after the heads, cam, intake, etc.

Go for the Double Pumper
 

I vote for the Holley.

I like the 600 CFM Mechanical Secondary set up for that boat. The throttle response will be very crisp and you have complete control over the secondary action. The next step up with Mech Secondaries is the 750...which is too much carb for the motor.

You want to keep the velocity up as high as possible to keep it crisp.

My brother has a similar set up in a Formula F3 355/Alpha GenII w/ a 600 Double Pumper on a Edelbrock ES Square Bore Performer.

The throttle response is like NOW and he can plane the boat and then back off and cruise on the primaries. Very sweet set up.He gained 5 MPH over the Q-Jet and saved about 10%~15% on the GPH (once he started driving it like a SANE person)

I wouldn't run 750's on a SBC unless it was a 383...too much air flow at RPMs under 5500~6000 for a 350...makes it sluggish.

ended up going with a 650 marine demon, havent fired it yet but i will let you guys know as soon as it warms up in april!!