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57 260hp carb

"unless its got the stop screw

"unless its got the stop screw on the air valve, its rated for 750. That said, you'll never need it."
 
"When I was at Mercruiser trai

"When I was at Mercruiser training the instructor told the class that they were 625 cfm...........

Besides a 750 cfm on a stock 350 is to much.

Aslo the Holley 650 spread bore is a direct replacement for the rochester, Of course with some cable bracket modifications for the throttle cable....."
 
"That's what rochester rat

"That's what rochester rated those casting at...agree, the engine will never need it.

That's one of the better feature's of the Q-jet, it will only flow what is needed by what's under it."
 
"MARINE ROCHESTER Q-JET Remanu

"MARINE ROCHESTER Q-JET Remanufactured 4-BBL Carburetor 650-CFM, Restore Your Confidence In Your Engine Start-Ups and Performance. Used On Small Blocks, GM (Chevy) 305 & 350 Cu. In., (5.0 & 5.7-Liter Engines), Replaces Sierra #18-7615 & 18-7615-1, If Needed Order Flame Arrestor Part# 18-7231 And Rebuild Kit # 18-7095. Note: Crusader applications order part number: 18-7607-1 (1782403) see below on this page. NOTE: Some OMC engine applications may require throttle arm modification.



From a remanufacture internet store for marine carbs.....even though it says 650 the actual is 625 per mercruiser spec.

In fact the instructor said ALL rochesters used were 625 cfm even on the standard 454 bigblocks!!!

Allthough I would think a 750 cfm carb would be better suited for a 454.

Just the messenger not the manufacturer!!"
 
"Unless its a hand built, hi-p

"Unless its a hand built, hi-perf part (read that as standard, GM mass produced and delivered to the OEM), it will be pretty standard.

I've haven't been to East Brunswick in a long time so things may have changed, but I can't find a flow spec in any of the merc factory service literature I have....

When you get to the remans, you'll find most don't use the original style castings...most have "marinized" the post-'76 style casting (newer APT type) and then applied a generic calibration curve to them. What they spec their stuff at is TBD."
 
A standard Q-jet (750)

A standard Q-jet (750) would be fine for the original configuration or the latest 5.7 crate engines.
 
"It would be a waste of fuel f

"It would be a waste of fuel for a stock cam shaft and stock heads no matter vortec or standard.

If you were to plug in all the data for a 350 ci engine into a formula to determine what cfm carb is best for that motor it would give you something in the ballpark of 425 cfm.


Using such a small carb is not practical on a 350 and thru development and a lot of trial and error 575 cfm to 650 cfm work best based on specifics used in the engine. (stock to mild) (NOT WILD)

Many many street cars have used and continue to use the old 600 cfm holley 4 barrel on small blocks and they supply more than enough fuel and air for most set ups.

I feel running a 750 would work but you would be running rich.

I have the exact same engine you have in my boat.
1987 4bbl rochester

It is what it is and there aint no more unless you spend and biuld it out, At that point, have a engine biulder/tuner decide what is the best carb for it.

JMHO"
 
"you can go to google books an

"you can go to google books and search for doug roe rochester carburetor flow ratings - should show you the chart on page 108.

GM put them on tiny engines to huge engines - they are adjustable in terms of max flow. the engine can't pull in more air than it needs unless it has mechanical assistance - turbo, etc. The ratings are for MAX flow. Unless you run WOT all the time, most people run on the primaries only. In a q-jet, these are much more efficient than most designs and, when properly set up, will deliver excellent 'drive-ability' and economy.

It was the standard carb for decades on just about every marinized GM engine sold. They didn't start to disappear until the 90's, when GM pulled the plug based on their 'business case' studies."
 
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