SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: renegade on July 17, 2011, 05:23:09 PM
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Here my question, is 2 750 carbs to big for a 10-1 compression 468 ci olds. or will 2 500 carbs work better?
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Here my question, is 2 750 carbs to big for a 10-1 compression 468 ci olds. or will 2 500 carbs work better?
On a tunnel ram you may get away with the 750's, but two 500's IMHO would work mo betta O0
GT
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Depends on cam, headwork, exhaust, oil pan size, and drainbacks. TIMINATOR
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the heads are stock ka and the cam is a 496 280 duration. pistons 60 over forged trws.miladon high volume oil pump with a 6 quart oil pan.with 1 carb 750 it turned 5000, with the 2 750s it turns 4800. went 2 stages leaner on both carbs and had to put in 1 stage hotter plugs in..in think its to much for my basic stock set up. but it sure looks good with 2 carbs sitting there.
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the heads are stock ka and the cam is a 496 280 duration. pistons 60 over forged trws.miladon high volume oil pump with a 6 quart oil pan.with 1 carb 750 it turned 5000, with the 2 750s it turns 4800. went 2 stages leaner on both carbs and had to put in 1 stage hotter plugs in..in think its to much for my basic stock set up. but it sure looks good with 2 carbs sitting there.
Are these 4150 or 4160 carbs? Big difference in this case. The other things would be what'd the plugs look like? IS this a tunnel ram deal or just a dual quad lo pro intake? IF they are 4160 Vac secondary, I would be looking for a vacuum leak causing the RPM drop and primary/secondary jetting from reading the plugs. Sounds like a hot enough cam, if the valve springs are up to snuff and not allowing "float", makes no sense to lose RPM. IF 4150 Mechanical Double pumpers, well, then can easily be stovepiping the engine. In other words, WAY too much CFM.
The only other thing I'm going to toss out there is WHY a high volume oil pump, in general, and ESPECIALLY on an Olds with only a 6 qt pan?
Ray
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the heads are stock ka and the cam is a 496 280 duration. pistons 60 over forged trws.miladon high volume oil pump with a 6 quart oil pan.with 1 carb 750 it turned 5000, with the 2 750s it turns 4800. went 2 stages leaner on both carbs and had to put in 1 stage hotter plugs in..in think its to much for my basic stock set up. but it sure looks good with 2 carbs sitting there.
To be able to support the twin 750's, that poor Olds would have to turn in the area of >6500 RPMS to even be close.... :screwy: The twin 500's would be closer to the magic 5,200 RPM, still awfully high for the Olds :-\
Without extensive oil side enhancements, you are playing with a time bomb running an Oldsmobile that hard...
Most Berkeley style jet pumps perform and load the best at <5,500 RPM...(Just my humble opinion).
You can turn them much faster, but proper loading, proper bearing and wear ring set up and attention to details need to be addressed...(Think "throwing a lot of time and money at it")..
My neighbors little Tahiti has a 455 with a Wiend tunnel that has two 650's with a progressive linkage set up and it runs right to 5,100 RPM with a Berkeley A like it is set up with a governor.
Never really a problem until the oil heats up.....(no paint left on the oil pan :screwy: )...Then has major breather losses.
We have installed oil restrictors, flow limiting pushrods, modified stock pan, stock passenger car oil pump (Low volume with a 100#bypass) and hogged out the block on the oil passages...I think it has flat top pistons, but can't remember, something is telling me 10:1 compression, but could be FOS.
GT
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believe it or not the olds has 8 seasons on it turning 5000 with just a blue print and balance job.the carbs are edelbrock 750s the intake is a 064 edelbrock dual quad with 2 4 in spacers 4 hole.exhaust is over the transom bassets. spark plugs look good now like i said i had to put a hotter plug in.
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I run a tunnelram with 2 750s. It runs good. I've been told a couple of times to "ditch the second carb" and "why some much CFM?".
I talked to a guy that owns a carb shop and he said he would change the annulars(?) and make them about 650.
This motor has had this combo for a long time and has worked. I just have never had the time, money or knowledge to try something different.
10:1 468 also. Holley double pumpers.
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what rpm do you turn with 2 750s troller dave
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what rpm do you turn with 2 750s troller dave
About 4900. cam is a Mondello JM 25-28.
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About 4900. cam is a Mondello JM 25-28.
By dropping the bore size of the carburetors and picking up some more velocity through the venturies I would be willing to bet you pick a little something up...Any chance you have some vacuum numbers at WOT? I bet they are way too low.
Just a thought.
GT
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No vacuum #s. I wouldn't even know how to take vacuum readings. Like I said, it works and I don't like to mess with it.