winterfunguy

I am in the process of building a mild 350 for my 78' Cobalt 19DV which weighs in at 2810 lbs. I am expecting between 330 and 350 horsepower with the Vortec heads/ Lunati Voodo 262 cam/ 9.35 compression. I am contemplating between a 750 rochester or a 700 mercarb for now due to budget limitations. I was hoping someone could give me a baseline jetting for either of these carbs that would work with my setup. Any help is much appreciated.

wtfo

an edelbrock 1409 6000 cfm carb would be about right as it comes out of the box and probably be a smart choice for your build. I know you're on a budget, but using a second hand carb and scfrewing around with it trying to get it right can be a lot more of a pain in the neck than it;s worth... imho

winterfunguy

Thanks for the advice, I have considered this option and know that I should be using a 600-650 cfm carb for optimal performance...we'll just have to see what the budget allows for.

hunster

That edelbrock 1409 is the same weber that mercury uses. You can use the edelbrock tuning kit to fatten it up as desired. Edelbrock also has pretty good instructions on their web site. Good luck

87MagnumII

i am using a cam with almost identical specs with vortec heads for engine build, the stock springs wont work and you have to modify the valve guides and bosses on the vortecs to accomodate a larger spring and to keep the spring cap and retainer from crushing the valve seal. you may have already done this but just in case, fyi. if you need details feel free to pm me

winterfunguy

I am aware of this issue and have been told that there are some castings that will handle this cam and some that won't, depends on individual castings. I know the previous owner of these heads and he was running a cam at just under .500" lift at 6000 rpm in a mud truck with no issues of spring bind. I am going to check valve spring bind once the heads are assembled. I just got done pocket porting them and gasket matching the intake ports.

winterfunguy

I actually opted to downsize the cam a little to the Lunati Voodoo 101grind at 256int/262exh duration with .454"int .468exh lift on a 112* lobe seperation due to reversion concerns...Lunati assures me reversion will not be an issue with stock exhaust with the 101 cam.

kornegle

I bought new GM Vortec heads from Summit and used a COMP Marine flat tappet 212*/218* with about .453" or so lift. I checked the retainer to valve seal clearance and the valve seals were not completely seated. After doing that it appeared that around .470" - .480" was the maximum lift that I could use without machining. I purchased some Z28 valve springs like those used in 1970 but only used the outer springs without the dampners. This fit fine without machining and I have about #115 seat pressure. I only turn it about 5000 rpm so there is no problems so far without the dampners. I am very happy with the combination which included an Edelbrock intake, 1.5 roller rockers, and the exhaust tube to replace the bellows. About 61 mph (gained at least 7 - 8mph) on gps with a 1990 wellcraft 216 Eclipse and it weighs around 3300 without anyone in it but ready to go.