Carb Ideas?

[speedaddict]

Hey all... Well, since it's freezing here, I'm not out on the water. In the mean time I'm thinking of a new intake for my new boat. It's a 12:1 429 with aluminum cobra jet heads, and the existing cam is a 306s solid falt tappet. It has a dual plane blue thunder 2X4 intake with holley 1850 600cfm carbs. I have a hunch they are standard street jetting since the engine was put back together, and the boat sold. I'm looking at a solid roller cam, a weiand tunnel ram, and 2 holley 750 marine calibrated carbs with vacuum secondary. What are your thoughts on the carbs? Are you guys using street calibrated carbs? Marine calibrated? Mechanical secondaries, etc?? I'm trying to decide if getting some 750's off ebay and rebuilding them with new jetting. What are your thoughts? Boat is a 18' hydro.. spinning to 7k or so. Wouldn't mind having an intake that would accomidate a possible future 514+" stroker setup.
Thanks!

[AzMandella]

I"d say you are almost right on the mark.I have the same setup on my 514.Crower mech roller #22403 Advertised 300/int 310/ex duration and 654/int & 647/ex lift. 2 proform 750 vac scondary main bodys with Qwick Fuel billet metering blocks and throttle bodies on a Weiand tunnel.As far as mechanical or vacume secondaries that depends.If you are planning on drag racing competivly mechanical for sure.But if this a cruising lave racer I have found that I can get a set of Vacume secondaries to run just as well and save some fuel.but you have to put a balance tube on the secondary diaphrams and put lighter springs in it.purples seem to work great for everything.I'm turning my 514 7000 rpm with a set of Trick Flow heads that are about the same as your factory alum. heads.

[058]

BBFs like air flow. 750s may be ok but I think you are leaving some HP on the table with them. I run a 514, early CJ aluminum heads, Comp flat tappet cam, Weiand tunnel with 2 850 D/Ps and the engine feels like it could use more. The engine spins 7500 rpms in a heavy [1K lbs bare] wood deck Howard flat turning a 25% gear and a 11.5 x 15 prop. If you need to deal with alot of low rpm running such as 5 mph/no wake zones I'd pass on the roller as they usually don't like low engine speed. The exception here is the pressurized rollers, they seem to handle the idle/low rpm alot better.

[Jet City]

If it were me I would find a decent set of 750 double pumpers, list# 4779 or 7109 (I think), the 7109's can be mounted straight because they use side-hung bowls instead of center-hung. I'm very pleased with how my 650 DP's (list 4777) work on my 427.
If you plan to use Pro-Form's 750 bodies, any double pumpers from 650-800 cfm would make suitible cores as they all share the same throttle bore diameter. There's some real knowledgable carb guys around here if you need particular details.

[speedaddict]

Thanks a lot guys. I really appreciate the feedback. I think I'm really leaning to the vacuum secondary setup and the side hung bowls. Now I just need to find some.. I think I may end up buying a new pair, then putting the j vents on, and re-jettinig. Do you think flame arrestors are going to kill the airflow? I don't know how picky the law is on those if the engine is not enclosed.

[Jet City]

If you are going with vac sec carbs you may want to take a look at Barry Grant's "road demon" series, Summit part #GPT-640202OVE $289.95 EACH. These are 725 cfm and have the side hung bowls, I have not used these I'm considering a pair for an upcoming project (Blue Thunder 2x4 intake).
I'd run the flame arresters, but I wouldn't worry about the "J" vent tubes, not that big of a deal with the exposed engine, I've never been hassled about non-marine goods where I boat, may be different in your area.

[speedaddict]

Thanks Jet City.. too bad you don't need a blue thunder 2x4 for a bbf instead of an fe. The blue thunder on my 429 is what I'm looking to replace with a tunnel ram. I've given some thought to the BG carbs myself. I just don't know about the road demons though. I don't know much about those carbs, but on the demon site I think they were tuned for more mild setups with better idle vacuum.

[Jet City]

Thanks Jet City.. too bad you don't need a blue thunder 2x4 for a bbf instead of an fe. The blue thunder on my 429 is what I'm looking to replace with a tunnel ram. I've given some thought to the BG carbs myself. I just don't know about the road demons though. I don't know much about those carbs, but on the demon site I think they were tuned for more mild setups with better idle vacuum.
My Blue Thunder is for my '70 Fairlane 460 (project car), my boat is 427 Chevy (no FE's). If your looking to sell your Blue Thunder or trade for tunnel ram, let me know, I have a friend or two that may be interested. As for the carbs, I know BG doesn't recomend them for this application, but there is a guy or two on running them on 385 series engines in AC Cobra's with BT intakes, they claim with a little tuning and tweaking they work great, they don't look too different from a 4160 Holley from what I can see.
Here's a link to that Cobra thread, maybe 3310's would be a better deal.
http://www.clubcobra.com/forums/showthread.php?threadid=52726&highlight=barry+grant+725

[AzMandella]

Try Quick Flow Tech.The two guy's that own and operate them were a Holley enginiere and VP of marketing for 20yrs.www.quickfueltechnology.com/

[Sleek-Jet]

My Blue Thunder is for my '70 Fairlane 460 (project car), my boat is 427 Chevy (no FE's). If your looking to sell your Blue Thunder or trade for tunnel ram, let me know, I have a friend or two that may be interested. As for the carbs, I know BG doesn't recomend them for this application, but there is a guy or two on running them on 385 series engines in AC Cobra's with BT intakes, they claim with a little tuning and tweaking they work great, they don't look too different from a 4160 Holley from what I can see.
Here's a link to that Cobra thread, maybe 3310's would be a better deal.
http://www.clubcobra.com/forums/showthread.php?threadid=52726&highlight=barry+grant+725
Interesting....
The post at the end about BG tech is right on the money. My brother and I ran into the same problem when we were setting up his carb for a Chevelle. The BG guy kept saying the carb was to big for the cam/engine combo and wouldn't go any farther. Finally we called back and told them what they wanted to hear and it was all peaches-n-cream from then on...

[BIGS]

Hello All, addict.......if you need some help we could build you a matched set of our BIGS 750 vacume secondary carbs......wether you want bthem to sit in line with the side hung bowls or sideways with center hung bowls.....we can do the "J" tubes and have an adjustable secondary jet plate.....also we should tie the secondary covers together so they are vacume orientated to each other.....A 2 carb package deal will be made to you.....Thanx allot, Jesse @ BIGS!!
www.bigsperformance.com
home e-mail
bigs1050@charter.net
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bigperformance@charter.net

[GofastRacer]

Or you could do it the simple way!... :D :D
http://www.hotboatpics.com/pics/data/500/21Ford_Hat.jpg

[steelcomp]

I have a pair of 6109's that I'm going through right now. They've been modified to flow around 800, and are in excellent cond. $800 for the pair. These carbs are about the best running 750 TR carbs Holley ever made, and unfortunately they don't make them any more. You can mount them in line, but you'd be better off mounting them sideways. You won't starve the front jets when you nail it, and if you plan on doing any tuning, it's a LOT easier to change jets.
I have one more stock 6109 that I'd love to find a match for, so if anyone has one sitting around they might want to get rid of, let me know.
steel

[LeE ss13]

I must agree .... the 6109s are the Bomb! I ran them in a drag boat for years. (NJBA's Ski Flat class was limited to 2 - 750s). They were great. I kept them even though they are of no use in a SS boat, but I may step up to Pro Stock and play with them again.