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fred70

Regular Contributor
"I'm a new member that is

"I'm a new member that is going to need HELP!
I am going to acquire a 34 Luhrs in the near future, that is going to need a little work. Port engine locked up,
snow.gif
Starboard was blowing steam
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when last run about 2 years ago. Been setting dock side in salt water for 2 years.
Rebuilt engines on there way , but
Q. 1) What to do about the Q-jet carbs. Rebuild, sh** can, change over to Edelbrock, go EFI? (Other than the post Fuel Injection on a 454 cid http://www.marineengine.com/discus/messages/12489/170426.shtml ) , I haven't seen anything else.
Of course it is a captive cooling system, but I will be using it 100% of the time in 100% fresh water.
Q. 2) Leave it Freshwater, or convert it to Raw water cooling?
Q. 3) What about Exhaust manifolds & risers,
I know that they will need replacing, so give up some opinions , Osco? Barr? OEM? Sierra? or a I see them from anywhere between $180 - $340 per side. Or maybe something like a pair of http://www.cpperformance.com/detail.aspx?ID=2825 for $600.
The boat is only 1239 miles away from where I live, but I'm told that I can get it any time I want. Any body got a low boy?
I'll only be using her occasionally (20hrs or so a season) because of other summertime activities that I do with other family members (Fastjeff knows what I'm talking about). Sad but I dough that I put 15 hours on my 245 Slick Craft last season.
I've got some time , so I'd like a lot of opinions.
Thanks"
 
"Hi there, if you're gonn

"Hi there, if you're gonna drop the money on 2 rebuilts now is probably a good time to throw on the cooling system. Even in fresh water, it will allow the engines to run at a more consistant temperature, which is will give you better performance overall. That said, you dont need to, boat will proably run fine anyway. As for the q-jets.. they seem to have a bad rap here, but why change them if you dont know anything is wrong with them. Granted, sitting for 2 years isnt good for them, but they might be ok anyway. Its all about time and money, if you have the time, rebuild them if your comfortable doing so, if you have the money, slap on a couple new qjets just for kicks. As for the risers.. ask al, he's had lots of fun with that sort of thing.."
 
"[b]From the Holley web site[/

"From the Holley web site
www.holley.com


<font color=""ff0000"">QUESTION</font><font color=""000000"">: How do I tell what size carb I need?</font>
<font color=""0000ff"">ANSWER</font><font color=""000000"">: You take the engine cubic inch and multiply by the maximum RPM and divide by 3456. If you have an automatic transmission you will need a vacuum sec. carb, a standard transmission can use a Double Pumper carb.</font>

So let's work that out ... (assuming a 5500 RPM redline)
(CID x MaxRPM) / 3456 = CFM
(454 x 5500) / 3456 = 722

Manipulating the formula mathematically ... we should be able to determine the max RPM (under ideal conditions) for a 600 CFM carb

MaxRPM = (CFM x 3456) / CID
MaxRPM = (600 x 3456) / 454
Max RPM = 4567

I don't think that I COULD see that at WOT Jeff.

Fred 156-M

P.S.
more questions answered on the link
How do I adjust the mixture screws on my carburetor?
How do I tell what size power valve I need?
Where do I hook up my electric choke?"
 
"Fred:

you need to adjust t

"Fred:

you need to adjust the CFM formula for Volumetric efficiency - usually 0.85 is a good number for a factory, mass-produced engine."
 
"I here you MakoMark,
I thin

"I here you MakoMark,
I think what your saying is that a production engine ISN'T going to need all of the cfm from the formula, but optimally, a ported & polished head & intake might, Right?

So you don't think that the carb people at Holley are intending the use of the above formula for production street / marine engines.

Hmmm, very interesting, & possibly true.

Opinion or fact, Mark?
And where did the 0.85 come from?

thanks
Fred 156-M"
 
"I see now , the Holley formul

"I see now , the Holley formula would be perfect if you were moving a noncompressible (say water for instance), but being less air can occupy the same area (partial vacuum). I think I understand where your coming from.

When I started, it was like this
cid .X. rpm. / 2(4 stroke)/ cim>cfm = cfm
454 X 4000 /..... 2 ...... / .. 1728 .. = 525

OK, its the same thing.


Fred 156-M"
 
"Fred:

The VE phenomena is

"Fred:

The VE phenomena is fact; the 0.85 factor appears to be a consensus opinion. The VE is supposed to follow the torque curve for a given engine. The only positive way to define yours is to rent an instrumented dyno and take you engines to that facility.

The point was to show there is more than enough capacity of a 600cfm carb to sit atop a marine big block. contributors to the "VE < 1.0" are many, besides the compressible air."
 
"Keep in mind that "we&#34

"Keep in mind that "we" are mainly interested in cruising power, not all out racing power. THAT is what really decides the carb sizes. A vacuum operated 4 barrel is running on the primary barrels ONLY during plane off. Therefore, a two barrel carb of 300 SCM would be enough get the job done. During cruise, only heavily loaded boats would need more than the primary barrels to maintain plane.

Jeff"
 
"I hit 4600rpm WOT (light

"I hit 4600rpm WOT (light load in the boat) with a bored 454 and a smallish flame arrestor and the 600cfm edlebrock. Size of these carbs is a non-issue. If your wanting a drag boat and need to turn 8000 rpm, get the big one.
yawn.gif
"
 
"Jeff,
I think you mis spoke

"Jeff,
I think you mis spoke here "A vacuum operated 4 barrel is running on the primary barrels ONLY during plane off." I think you meant,.... A vacuum operated 4 barrel is running on the secondary barrels ONLY during plane off..

OK I guess what I was afraid of was running into an issue similar to what I had with my SlickCraft, when a heavy load was on board, (having to positioning 3 passengers forward into the front of the cabin until up on plane). I often thought about taking off the 195hp 2 bbl. intake & installing the 225hp 4 bbl. setup.
I've been on this 340 Luhrs in question & seen it struggle to get up on plane with the existing Qjets (always being blamed as the culprits). Now I realize that the engines were NOT kept up extremely well, but with electronic ignition, they shouldn't need a lot. I'm also aware that the bottom may have need attention too, but thats not going to be an issue any more, as it is going to be a hoist kept, fresh water boat.

Do you think that the 4 bbl. would have been beneficial in my situation on the Slick, or would it have been a non issue, as the engine RPM didn't achieve the levels requiring the cfm that a 4 bbl. could provide?

Dave, & makomark, I'd be extremely interested in a vacuum gauge reading when your at WOT / 4,600 rpm mark with that 600 cfm.

Fred 156-M"
 
"fred:

the last set of dat

"fred:

the last set of data I have was when i reset the power piston operating point (the 'before' factory setup). it only goes to 3200.this is raw data and wasn't integrity checked. I also don't have the after sheet in my book.

rpm vac gph vac gph
1000 16 2 15.5 2
1400 12.5 4 14 4
1800 10 7 11 6.5
2200 8.5 8.5 9.5 8.5
2600 7 11.5 7.25 12
2800 7 12.75 7 13.5
3000 6 15.5 7 14
3200 5 20 6 19

Also, of significance, in the notes, was that this was done during the exhaust swap out; ie the merc center riser style manifolds were on, along with the stainless 4" elbows but we haad to 'reduce' them to fit the existing 3" hose. A handwritten note on the back of the data sheet says air valve starts to open around 3200 (5" of vac) and is fully open at 3600 (2-3" vac)."
 
"Fred:

A vacuum operated fo

"Fred:

A vacuum operated four barrel--like most Holleys--runs on the primary barrels unless there's enough vacuum to pull the secondaries open. On plane off, when you mash it, there is initially not enough vacuum. It's not until the motor starts to "conquer" the load that the secondaries start to open.

Holley makes a selection of springs to make this happen sooner or later. The trick, to prevent a big old bog, is to DELAY the opening of the secondaries until the motor can handle it. The Edelbrock, by comparison, has a straight mechanical linkage that yanks them right open. To prevent a bog, they also have a "flip over" plate that slowly opens up as the motor picks up.

Jeff"
 
"What I was looking for Jeff,

"What I was looking for Jeff, is a confirmation (by way of a vacuum reading) that the the 600 has enough cfm flow to amply support the 454 @ 4600, I under stand that they will run on a 600 cfm or even a 2 bbl.
My guess would be that IF w/ a 600cfm @ 4600rpm, the intake vacuum was still @ 3.5 in, then the 750 may be useful from time to time.
Once locked into the 600 you can't stretch it, but its like I tell anyone that's reserved (sheepish) to take out one of my race boats "Full throttle is an option. You don't have run it there, but the boat will easily handle it, if you chose to do so."
For the extra $25 a carb., at I'd hate to make hasty decision that I'd regret later.
I'm blind to the disadvantages of running the 750. Lets here some.

Fred 156-M"
 
"As I understand it, the Edelb

"As I understand it, the Edelbrock 750 has larger secondaries only, so you cold have your cake and eat it too.

Jeff"
 
"Sorry Jeff
here's what t

"Sorry Jeff
here's what they say at
http://buickperformance.com/carter.htm

To determine Carter AFB carb flow, measure the butterfly bores and use the table below:



CFM......Venturi Diameter.......Bore Diameter
.........primary.. secondary......primary..secondary
--------------------------------------------------------
400... 1 1/8 ...... 1 1/4......... 1 7/16 .... 1 7/16
500... 1 3/16..... 1 1/4 ........ 1 7/16 .... 1 11/16
575... 1 1/4...... 1 9/16 ....... 1 9/16 .... 1 11/16
625... 1 3/16.... 1 9/16........ 1 7/16 .... 1 11/16
750... 1 7/16.... 1 9/16........ 1 11/16.... 1 11/16

Fred 156-M"
 
"Rats! Thought it was the oth

"Rats! Thought it was the other way around. Oh well.

I'd still go with the smaller carb, for gas mileage.

Jeff"
 
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