GM had MANY warranty issues with the flat top, no valve relief pistons in the Tri-Five years, even in the non-performance, 2 barrel carburetor engines. I can't imagine why anyone would risk damage from valve to piston contact. I say relieve the pistons. It used to be that it could be done using a modified stock valve and a bare cylinder head. Head bolted down with the cutter valve, and an electric drill used to relieve to make cuts in the piston tops; then remove head, change valve to another position and repeat the process. That was done until ALL pistons had been cut. I "helped" to do a 265 once in the mid 60's, and it took a while! The cam manufacturers used to sell the cutters to do the job also. You should also use HD valve springs! There's going to be some guys against doing it this way, but that's how it was done up until at least the later 70's. Not much material is removed from the piston tops, and most guys did't worry about the slightly lighter pistons relative to the factory balance. Other wise, swapping pistons is the only other alternative; unless you care to rebuild the engine after you over-rev or miss a shift, and wing the engine. JMO. Butch/56sedandelivery. When I typed this up last night, I could't think of the "term" used in doing this. Well, it hit me this morning, "FLY CUTTING" the pistons! Butch/56sedandelivery.
A 283 with flat tops and a D 30-30 is gonna be a dog around town anyhow, too much cam for the low compression of non popup pistons, if it doesn't have "power pack" heads at least
This is a fact. I have a 283 bored .040 over with flat tops and am running a 350hp/327 cam (the old 151) with power pack heads. Stock 4 barrel manifold and an old Rochester carb. No fancy head work, just stock stuff and around town it felt like I was hauling around a 5th wheel trailer. Rear end gear, tire size, and so many other variables come into play when putting together a 283.
I don't know if I'd flycut cast pistons. My sister had a 57 283 powerpak and the crank broke at the last rod journal. I replaced the crank with a new forged one, installed a 151 cam and new lifters and put an AFB on it. 3 on the tree with 3.70 rear and it ran great until it pulled a rocker stud. first item on sbc build is screw in studs.
I've done the same on a few 5.0 mustang engines, push clay down in the ring land, cut the relief, pull out the clay, turn the engine over on the stand and flush the cylinder with brake cleaner. In the car i'd just use the clay, shop vac any shavings before pulling the clay out.
i know this is heresy butwouldnt it make more sense to use a cam with a lessor amount of lift and duration..something that will build more cylinder pressure and avoid pistons and valves kissing??just my 2 cents..be great,mark.
The studs pulling out could also be partly because of piston-to-valve contact. As far as the lift relative to the true flat top pistons (no valve reliefs), even the STOCK 2 barrel carburetor engines had this problem. Being that the pistons are cast is of no concern, the fly cutting is't that deep; virtually all factory cast pistons now have 4 valve reliefs; some are cast in, some are machined in. I say, NO higher than stock lift cam with 55-57 style, stock pistons in 265/283 engines. Butch/56sedandelivery.
I believe you are all correct. 283's need gear and compression to run. They make a nice cruiser, but do not saddle it with 3500 lbs and highway gear, or you need to look into a 307 2bbl. Mine below 4,000 RPM has me looking to drop a gear virtually falls flat,
A Duntov '30/30' cam is a relatively low lift cam. Somewhere around .447 or so. I'm not sure you would need any extra relieving for the pistons to clear. That being said, the 283 with that cam really needs some compression and stiff gears to run right. r
Not on the early engines with no valve reliefs. Even the lower lift Duntov cam caused interference problems when guys stuffed them into a '55-'57 2 bbl engine.
Why would anyone want to use a .030/.030 Duntov cam? They weren't any good for anything but hearing the clatter of the wide lash. A 350 hp 327 cam would run circles around it on the street and at the track. Now add 30+ years of cam technology and the word "relic" is almost laughable. If your serious about making any engine perform the way YOU want get on the phone with one of the current cam grinders (Comp Cams is my favorite), tell them what you got and what you would like to do and let them recommend a grind. All of the cam grinders have help tech phone lines and the people on the other end know what they are doing. They DON'T want you to be dissatisfied with their product so why not bring the millions of dollars worth of research they have invested to bear on your project. Frank
Ah, Frank, you know it's cool to rattle through the Burger joint parking lot on Friday night with your lifters rattling like an old Texas snake. And you get to kill every Saturday morning adjusting the valves again. At least the second part held true for me with the 30-30 cam in my T bucket. On needing the valve notches in the piston when running that cam, not only yes but HELL Yes unless you want a batch of bent valves. I got the task of replacing valves and touching up the seats on a couple of sets of heads off Chev V8's that guys here in town stuck one of those cams in in the early 60's when I was in high school auto shop. The cams were also about 30 bucks at the local Chev garage parts department and the parts guy usually kept two or three on the shelf along with a couple sets of finned Corvette valve covers.
In 283 speak.........that hot Duntov was called a 0.012 - 0.018 "Twelve Eighteen" cam, solid lift at somewhere around 0.398 lift by Solid Lifter. Might have to find an operating cruise night at a Dog and Suds for anyone to remember... the old 30-30 was a .480" lift solid with long duration more of the 327 cam of 60's and early 70's street speak. But none to big. The 350HP 327 Hydraulic....short 0.447 lift long duration seems to run good in what ever you put it in. I believe it is the most copied cam spec in history if my memory serves me right, look at any cam maker, they all make a 0.447/0.447 320 duration ish cam. Put the above with some Vintage Mickey Thompson 327 pistoles.....below..
The are great cams considering they were using the stockish springs, pushrods and studs. They also make a decent amount of power while keeping pretty reliable. Now there are better cams these days but they aren't designed to go 200K miles(much of it under warrenty) on a GM valvetrain. Most of the modern warm cams these companies sell only see occasional drives by old farts or full on racing. Something also to consider, most modern cams are also tailored to 350/383's these days and the smaller motors are an afterthought. Smaller motors have different demands cam wise due to the ratio of air flow vs CI. For example take the 383, it has the same bore/valve size as the 302 chevy, do you guys think the same cam would run the same in both?
The 097 cam that came out in 1957 lash I .012 E .o18 lift I.393 E .399 in 283s in 62 and 63 327s the valve lash was I .008 E .018 the 30-30 cam in 1964 .455 lift
lots of good info here. A 30-30 in a 283 will be doggy and the pistons need to have reliefs to be safe. An 097 is a better choice in a 283 and will idle better but still not much below 750-800 RPM and about 14" vacuum. I have one in a 57 fuel injected 283 with a 3spd and 3.70 posi and it is *****y and has the "sound" but as many have said there are much better cams today-still a fan of the 097 though.
Probably wants to be traditional? .....Everyone runs the 400jr in flatheads cause they like the sound and they work decent...I get it.... The L-79 is still sold a lot ! All the company's usually market it as the "R/V cam" I think the opinions are right on the 30-30 being too much I understand the 302s don't actually start making any power till about 4,000rpm FYI the 12-18, the 30-30, and the L-79 are all still made by sealed power ... Most rebuilder cams have a L-79 offered and they are cheap , usually around 100.00 for cam and lifters
Anouther option ive heard with the 097 is to run 1.6 rockers, it gives is a faster opening and highter lift, it takes it from a .400ish to close to a .500 I believe
My '55 Chevy I built in 1969 was a '67 Chevelle 283 Power pack engine. Stock bore and pistons, with the factory flat top and fly cuts. I put a pair of old 1.94 heads on it, and the Duntov 30-30 cam, with a dual plane aluminum Offy intake, and dual AFB's. I ran a 4 speed and 3.90 rear gear ratio, and never felt the "doggy" reaction some guys keep talking about with this setup. It pulled hard down low, and even harder right up to 7k with plenty of power. If the 30-30 was such a doggy cam, why would Chevrolet have used so many of them in cars designed strictly for street applications? I know there are better choices today, and I haven't used a 30-30 cam, or similar specs in years, but they were and are a great cam for a high winding short stroke engine like a 283, with the right heads, intake, and gears.
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