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Cas42
04-06-2001, 07:19 AM
Pro's and Cons welcome. I'm thinking about switching out the Holley 750 dual feed for an Edelbrock 750cfm. Do any of you have any experiences with doing the same? My boat is a 78 21' Tahiti Super Cruiser with a fairly stock 454. I bought the boat a year and a half ago and the only changes to the motor(that I know of) are the cam was changed, roller rockers were added along with an Edelbrock Performer 2-0.
Since I don't know what cam was put in, the former owner told me only that it's an RV cam, I'll be changing it out also but probably not until after this summer.
As mentioned in another post, I'm only taching out at 4400 max. I'm pretty sure I can get more rpm's, even with a fairly stock motor?

Jetmugg
04-06-2001, 07:36 AM
My 2 cents - changing the carbs probably will not help, unless there is a serious problem with your Holley. You may very well want to check out the Holley internally, to make sure that it's okay, but I'm betting that it's usable. The cam swap will most likely be your best bang for the buck. You will be looking for a cam that makes the most power in the rpm range where you need it, which is currently at and above 4400 rpm. The "RV" cams are great for tow trucks, but lousy for jet boats. Forget about low end power when selecting a cam for a jet boat, what you really need is mid-to-upper rpm power. Also, don't listen too much to "car guys" with respect to camshaft recommendations, as they will tend to concentrate on low rpm torque. Many of the guys here are running very big cams by automotive standards, but they work great in jet boats.
It's also important to get the ignition timing and cam timing dialed in so that you can get the most power at the rpms's where you need it.
Steve.

jim lee
04-06-2001, 03:45 PM
Personally.. (Only in m opinion..)
I hate the Edelbrock carbs. They are just renamed Carters and I hate those too. Why? 'Cause I'm not smart enough to get the silly things to run right on anything I've tried them on.
I first tried a marine Carter on top of my Tunnel ram on my Olds. Single carb tunnel. It ran like green caterpillars. Yuch. I tweaked and fiddeled. I was able to get it -better- It actually did -ok- wide open, but anything else was terrible. It always gave the feeling that the engine was toying with the idea of dying, any second now..
They want you to drill out or add lead to counter weights and things to change how the 2ndaries open etc etc etc. Sheesh! It was too much.
So I added a pair of old used Holley 660s and WOW!! What a difference! Huge power increase and it purrs like a kitten! A very thursty kitten, but a kitten none the less!
Just to be fair I tried the Carter on another jetboat. (The familly's boat, Ford 490 with a Torquer manifold) It had a Edelbrock on there that had been hit with a chemical fire exstinglisher, all corroded. I was in a hurry and didn't want to fuss with the Elelbrock, so I put my old carter on there (Both were set to out of the box stock settings) Runs horrible! Like on the Olds, Its -ok- wide open, It idles -ok- but midrange is all rough. (granted this Ford motor is not it very good shape, and I'm no carb guy.) But I'd much rather have the Holley than the Edelbrock.
The point of my diaribe?
I have rebuildable Edelbrock, Working Carter Marine 750?, Compete jet kit, tuning instrictions, silly nut drivers assortment and a printout with all the jetting cobinations that are possible (The don't put this in the manual, I made it up myself.) And I'll trade the entire kit and cabootle for a used working Holley 750 or 850 that I can plunk onto Julie's familly boat.
So there! :-)
-jim lee
[This message has been edited by jim lee (edited April 06, 2001).]

spectras only
04-06-2001, 04:01 PM
Holley's are the simplest and easiest carbs to work with ,why change it? I still run my 1976 vintage 780 vacuum sec and only changed the gaskets once for the blue ones period.When I put a brand new 830 on my friends 460, it run perfect right out of the box. Some of my old salt boat dealers hate Holley's because some shadetree mech's wrenched on them before.Once you set up a Holley you leave it alone period.The other things you can do with a Holley is to change the metering block with a Percy unit that you can adjust the jetting from outside for different elevations.

Timer
04-06-2001, 04:17 PM
spectras only, where can I get info on the Percy unit?
I have 2 Holleys with the bowls facing each other. Could you still change the jets from the outside with the Percy setup with this arrangement? Thanks.

spectras only
04-06-2001, 10:40 PM
Timer , I have to call the local speedshop tomorrow to find out the manufacturer's address.I beleive the jets were adjustable from the top [ I hope ].Let you know when I found out.

Cas42
04-06-2001, 11:10 PM
thanks for all the input guys. The Holley I have seems to work ok although it does drink a lot, maybe too much since 15 gal will last about 1 1/2 hours without skiing. I'm going to pull it apart this weekend to see what size jets and power valves are in it.
When I bought the boat, I got the original carb and the one that's on it. The original is a 780 dual feed but since the air horn was cut off, I decided to use the 750. I kind of like the use of a choke.
Right now I'm a little in between on what I want to do with the boat, I guess I'm a tweener. Anyway, I'm not interested in building a real go fast (yet), just want to make the most of what I have now....make sense?
The only thing I'm not fond of with this boat is the Panther jet. My old boat had a Berkeley and it just seemed to be a much better pump. I was also able to easily disconnect the pump, put a hose to the water inlet and do all the fine tuning in my driveway. I'm not able to do that with this boat/pump.

Squirtcha?
04-07-2001, 05:28 AM
Cas42
Check out this article. I found it very useful when I rebuilt my Holley last year.
http://www.fordmuscle.com/archives/1999/12/holley/index.shtml

Cas42
04-07-2001, 08:27 AM
thanks Squirtcha, I'll be using it too

spectras only
04-07-2001, 11:45 AM
Timer, get the Summit Racing catalog, go to page 85.There you'll find the Percy's metering block.The price is between 75-81 US$

Timer
04-07-2001, 01:26 PM
Thanks, spectras only.

HighRoller
04-07-2001, 03:14 PM
Yep,holley is the simplest,most adjustable and best running carb by far as long as you keep junk out of them.Dock gas will have who knows what in it so make sure you have at least one each of a fuel seperator and fuel filter on your boat!!The Holley needle and seat assembly is especially sensitive to garbage and can get stuck.I recommend a cannister(Holley HPG)right out of the fuel tank then a small inline between the fuel pump and carb.The water sep would be before either of these,of course.As a sideline,has anyone experimented with using a Demon carb on a boat?They work great on race engines,seems like they would be a perfect jetboat carb??

Cas42
04-07-2001, 11:15 PM
well, I was going to post the size of the jets I found in the Holley but I never got around to pulling it apart. I got a little sidetracked by putting in a new stereo system with a 400w amp.
I figure it might be the only way I'll be able to blow away another boat.
Holley specs to follow soon

ODDD1
04-08-2001, 05:26 PM
Cas, definately do the cam.....you need to get more air thru the motor to make more power...which means more rpm. The motor will not breathe well at higher rpm with a RV cam.

mister460
04-09-2001, 08:21 AM
A big block Chev motor usually has a steel crank in it especially if it's in a boat. Does it have rectangular ports? Cause if it does it should turn at least 6500 rpm in stock form. Oval ports it'll spin 5 and a half grand reliably. Trust me, the internals are strong enough and the oiling system is adequate. As for carbs, listen to everyone else and stick with the Holley. Cams, go big. Really big! Just make sure your valve springs and rocker arms are up to snuff. For duration try about a 230 deg @.050 retarded 4 degrees. Should make sickening power above 3200 rpm. Not much below however. But who cares if your boat will pass everything but the gas pumps, right? Well, that's my three bits. Any questions, just e-mail me.

Cas42
04-09-2001, 07:48 PM
<<I have rebuildable Edelbrock, Working Carter Marine 750?, Compete jet kit, tuning instrictions, silly nut drivers assortment and a printout with all the jetting cobinations that are possible (The don't put this in the manual, I made it up myself.) And I'll trade the entire kit and cabootle for a used working Holley 750 or 850 that I can plunk onto Julie's familly boat.
So there! :-)
-jim lee>>
How about a 1978 780 with the air horn ground off, vacuum secondaries that needs rebuilding?
Oh yea, dual feed with the chrome gas line included.

spectras only
04-09-2001, 09:13 PM
refering to mister 460, the only BBC that you can trust having steel crank is a 1970's genuine LS6 [I'm talking about older boat application].If you looking to turn over 6000grand you better have steel crank because Chevs have smaller journals in the main and connecting rods than BBF.I have a 429 Cobrajet in my 20 Spectra and a 454 LS6 in my 24 Spectra.The Ford has beefier crank and doesn't turn as fast as the Chev and the rod angle is less steep than the Chev.The LS 6 you can crank up to 7000RPM if it's an unmolested original.Forged pistons and rods,dual springs 3/8 pushrods,solid cam and with the rectangular port heads.I had my Spectra for nearly 25 years and did experiment with timing , different impellers and nozzle setups.Despite the fact engines produce more bottom end with TDC timing, jets prefer to benefit from retarded settings,ie;4 to 6 degrees. By retarding the timing, the powerband moves up to higher RPM where the prop guys usually start walking away from jets.With the retarded timing one can feel the engine start pulling stronger over 4000 RPM. With a BB engine jet engines rev almost instantly anyway hence big torque[between 480 500ft pounds]I run 4750 RPM with a "AA" impeller, 780 Holley vacuum sec, 72 primary, 85 secondary jets. We run my friend's warmed over 460 19 Spectra 6600 RPM "A" impeller, 830 Holley vacuum secondary with 84 primary,92 secondary jets.By the way both Spectras[20 and 19] has the original points distributor with no problem what so ever.The 24 Spectra has the MSD system [looks cool].

squirt
04-09-2001, 11:12 PM
spectra I'm going to run a 427 bbc with rectangle port heads. I know these motors rpm well. You say your running an ls6 but you have your rpm at 4750 with an AA impeller. Since I'm new to jets my question is do you not want to use "more" of your motor? I thought rpm was good? or is it best combo of impeller size vs torque? These are answers that will help me select motor components thanks Don

spectras only
04-10-2001, 07:47 AM
squirt,Yhe LS6 is in my24 v-drive boat,the 429 ford that I'm getting 4750 in the 20foot jetboat.I'm getting 5000RPM[stewart warner tach]in the v-drive boat with a big 14x13 3-blade cupped OJ prop , 4%overdrive.Your 427 should spin 7000 also as my friend's 66Corvette does.

Cas42
04-11-2001, 07:10 AM
well, I did it. I pulled the Holley off the boat and took it apart last night. The primary jets are 72's with 76's for the secondary's. The power valves are 7.5's. After reading through a couple of websites regarding Holleys, both of the websites hinted that 6.5's would be a better choice?
I measured the vacuum to be about 17.5.
Vacuum leak and fuel consumption....
Do any of you have an idea what effect a vacuum leak has on fuel consumption?
The reason I ask is, as I was examining the carb after removal, I found a hole in the base plate. Since I found the little tube with a cap on it on the manifold, I'm guessing it's a vacuum port for whatever.
I don't know when it fell off but I'm guessing it was before the last time I took the boat out.

Jetmugg
04-11-2001, 07:41 AM
Cas42:
A vacuum leak is never good, but I don't know how to express it in terms of fuel consumption. The jetting, however, sounds lean to me. I'm not a carb expert, but there are some good carb guys here. By comparison, my Marine Power 454 came stock with a 750 vac sendonary Holley, and 86 jets, front and rear. You may be able to get more rpm's simply by changing jets to some larger units.
Steve.

spectras only
04-11-2001, 08:08 AM
Cas , when you have a vacuum leak the idle gets rough.The tube on the carb you mentioned should be the vacuum gauge hook up, and the big tube for PCV hookup.Consumption will be high at high RPM regardless of your jetting.Rule of thumb,if you can keep your jetboat on plane between 2800-3000RPM that's where your best economy will be.6-7 GPH at 3000, 20-24GPH at wide open!The 780 Holleys work best with 72 primary, 86 secondary.And yes, go for 6.5 or 4.5 power valves.As I mentioned in previous posts, the best result I got from a Holley 830 vacuum secondary marine carb for a big block.
[This message has been edited by spectras only (edited April 17, 2001).]