Got the valves all set tonight. Rolled the motor to top dead center then adjusted 4 intake and 4 exhaust valves. Spun it over one time then did the remaining valves. My brother just had to refresh his memory on which order to do them in starting on cylinder 1. Didn’t have enough silicone handy to throw the intake on so I’ll pick some up along with some new valve cover gaskets before Monday. Now for my carburetor question. Carbs were phased out long before I was even born. I’ve got conflicting opinions going here. The current 650cfm Holley probably has around 500 miles on it but I bought a complete rebuild kit for it because of all the old gas sitting in it. I’ve had a number of people say the 650 won’t flow enough air higher in the rpm range to take full advantage of the new heads. One of my dads friends who has raced GM small blocks pretty intensely for years is going to come to the shop, rebuild the carb, and tune the whole thing for us. I talked to him on the phone before I bought the heads and he gave plenty of great advice. He had an 86 cutlass with a 260 cubic inch v8 and a 2 barrel years ago that he ran in the 12.00 class then built a rail dragster with a 388 cubic inch small block and a lot of nitrous. He swears up and down the 650 is just fine. He made a comment (can’t remember the exact numbers) that your average small block only needs 325cfm. When I researched my cam on the comp cams website they had a dyno graph for a 9.25:1 350 which is probably close to what I’m making for compression, a victor junior intake which is what I have, a out of the box set of iron Dart sportsman 2 heads, and they used a 750 cfm Holley carb where as I currently have the AFR’s and a 650. Peak power was made at 5800 rpm. Is it safe to say that my cam with my more modern aluminum cnc ported heads is still going to make peak power at 5800 rpm and my 650 will move enough air or can peak numbers and their rpm’s all change slightly due to the difference in parts? All though my car won’t make a large number of drag strip passes, I would rather squeeze every bit out of it while it is there. Or am I just way over thinking this for not a big difference in power?
New guy 79 factory 4 speed wagon.
- Thread starter Mighty
- Start date
My gut tells me that 650 is probably OK for your engine. If you wanted to squeeze every last bit out of your engine, then perhaps you would need to bump it up a bit; you do have good volumetric efficiency with those heads, intake, and headers. I remember Engine Masters doing some testing on carburetor size and remember they showed the larger carburetor (thought to be too big) made more power. Their older episodes may be on YouTube. In the late 70s, Holley published an equation to determine the proper carburetor size and calculated that 650 was proper for my 440. I bought a 650 double pumper and felt it was a bit on the small size for WOT in 3rd gear (automatic), but it worked just fine for the street. A 780 vacuum carburetor may have been a better choice for me.
This is my cam card, I can’t remember if I’ve posted it before or not. Operating range up to 7k rpm. The heads will work up there, I believe intake is good to around 7300? I originally planned on using the 650 but after a number of comments I don’t know now. I’ll probably stick with it. I believe the car has a cast crank in it and stock rods so I don’t want to make a ton of passes every year spinning it to 6500+.
Plan A: Use the 650; you already have it and a rebuild kit. If it proves inadequate at a drag strip, execute Plan B: change it.
Give the Engine Masters videos a go and see if they ease your mind as to which Plan to follow.
Give the Engine Masters videos a go and see if they ease your mind as to which Plan to follow.
Yea, that’s a solid idea. I don’t know anything about carburetors so I e boy a lot of reading ahead of me
Definitely recommend this, worse case you run out of air and default rich condition
Got my intake on tonight and tightened up and while leaned over tightening bolts I remembered something else I needed. Anyone know where to pick up some radiator brackets for a Malibu/gbody? I’ve got all the fan shrouds. I haven’t checked google yet, but thought maybe someone here would know
Just checked on there about 45 minutes ago. That’s where I got my body bushings. I’ll have another look but didn’t see any. I wasnt really taking my time because I decided to tear into some wiring
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