hello, long time reader...first time post. I am rebuilding the .030 over 283 that my buddy ran in now my 31 model A. He ran trw l2149/48 pistons with double bump heads (64 cc gives a 9.7 cr) and L79 cam. I am thinking about running a set of 1973 corvette heads (880545 because I own them) 2.02_1.60 with factory screw in studs and guide plates...these heads are 76 cc chambers. Will there be enough compression? The crank is at the machine shop and i dont know how the pistons sit in block for depth. I have read that the 2.02 valves in the small 283 valve needs to be limited to .450 lift is this true? The picture here (excuse the greased bores and dirty heads) shows the cylinder and valve placement. Also open to camshaft recommendations. 1931 model A weighs 3k with a full load of gas and me on a good day. 3.70 rear axle ratio with a 25 inch tall tire. Running a modified wc camaro/s10 tail T5. Looking to gasket match an old C4b intake and run a Carter competition 500 cfm, hei, sprint car headers. Looking to out perform the orginal build. 5500 rpm max. Thanks in advance, crew dawg Paul
If you're looking to outperform the original build, why are you trying to go to such large chamber heads? With big chambers and big valves it will most likely be a dog. If you want better performance, you need to go smaller in chamber, not larger. 2.02's are pretty big for a little 283 if you're wanting to stay below 5,500 rpm. You will probably be better off with smaller valves and chambers.
Thanks, I am a little concern with the 9.7 cr. I have a fresh set of 1.94 double bumps but they don't have screw in studs and guide plates like the l82 heads.
The reason for limiting lift with a larger intake valve on a 283 is that the valve will hit the top of the cylinder bore. Even with a 1.94 intake you may need to grind a relief in the top of the bore for valve clearance, depending on lift and head gasket used. The L69 305 H O used a head with larger than 283 intake valves and better ports than original 283 heads and made 9.5 cr with flat top pistons. (1983 -'86 F-Body L69: GM PN: 14014416 int: 1.84/ exh: 1.50, 58cc chambers, 178cc runners, Flat Tappet) These are considered the best Chevrolet head for the 283 since the valves are sized to be optimal with the 3.875 bore without causing intake valve shrouding. If you need more compression, Summit still sells pop up pistons for the 283 that are very similar to the original Corvette fuel injection engine pistons. I think they start in .030 overbore sizes. Tom
If you want better performance than the original build, how do you expect to do that with less compression ratio? Decide what you want. Is that a reliable 87 Octane engine? Are you okay with running 91 with more compression? My machinist is going to put the 305 valves (1.84/1.50) on my Power Pak heads so that I'll get the nostalgic look but better valve sizes and not too big for the little 283.
In my opinion, 39deluxe made a very good recommendation using the 305, 416 heads. They're relatively inexpensive, I paid $100 for a pair for a 283 I built. Unless you're out to build some fire breathing 283 I think the 416 heads will serve you well and with their small combustion chamber will give you a decent compression ratio. Something to keep an eye out for when selecting pistons is something that has a taller compression height so the piston doesn't end up way down the bore at top dead center. Some "rebuilder" pistons have a shorter compression height to accommodate for blocks that have been decked. Maybe you have already used a compression calculator, but if you haven't do a search for compression calculators online. A good one will ask for bore, stroke, piston style (whether dished or domed or flat), gasket thickness, deck height (distance piston is down the hole at top dead center), combustion chamber volume and maybe a couple other things I'm forgetting. Good luck with your 283 build! Lynn
Thanks for all the great input. I completely agree with 305 heads being a good solution. I should have stated my desire to run the parts that I own. Thanks again. Let's say I run a 64 cc 1.94/1.5 double bump head. Who has a camshaft recommendations for 9.7 cr? I have a set of speedway aluminum double bumps in 2.02/1.60 but that raises the valve shrouding-cam limitations question
The most basic question (default) to ask is, what are your plans for this car. The L79/327 engines' cam was paired with 11/1 pistons, it never was intended to be a world beater, but it is still one of the best engine combinations to come out of GM. I don't have experience with this cam in a 283 but there have been hundreds of people say it makes a sweet combination for a street engine in a light car, especially with a 4 speed as Chevrolet never paired the L79 engine with an automatic transmission. In my opinion, shooting for a compression ratio in the 10/1 range in a 283 with the L/79 cam (or equivalent) would make a great lowbuck engine. As important as anything is that the distributor should be checked on a machine to see where the advance curve is at. An experienced guy will know where to set it but he will need to know the vehicle and environment it will be used in.
Keep the heads on it now. By double bump do you mean like a like a 461 head with 194 intakes ? If so run them. Add screw in studs or pin the existing ones. Thousands of pretty hot SBC built with out guide plates or screw in studs . I'd keep the compression vs 2.02 valves and screw in studs and guide plates you likely do not really need . Put/ save your corvette heads on a flat top 350 or 383 build were you will gain more and they will make good compression ratio. Lot better cam choices than the old factory offerings. That said if you own the parts on a budget then pick the best combo with what you have . The 305 head mentioned is interesting.
Excellent insight. I have run the l79 hydraulic cam in a warmed over 283 with the accel hei distributor and a manual transmission. I will look at a modern version of the l79 from comp cams for this 283. Thank you
The heads and style cam you have now are very hard to beat in that engine . A good 283 with those heads and that cam should be all you want for the street in that chassis . The power to weight ratio is excellent,,,,it should run like a stripe-edd ass,,,,(That’s a zebra in country language ),,,,,lol . Tommy
Thank you, comp cams offers a "modern" version of the l79 hydraulic cam. I will steer this build toward the double bump 1.94 heads and add screw in studs and guide plates. I appreciate your input
I'm all about running what you have. At 17 I trusted an older friend to help me build a 327. I scrimped and saved my money, bought a cam, intake etc for a 327, and agreed to use some 441 large chamber heads. What he gave me was my parts on a 283. It was an absolute Turd. I pulled it and put and years later put double humps on it. It came alive, and became a more pleasant combination.
Thanks, this engine was built in the 80s. The last owner red lined it a lot. The 1959 steel crank is balanced to a T. The block was line bored and the connecting rods reworked and the best bolts in the day added...I am leaning toward the comp cam modern hydraulic version of the L79 camshaft. I appreciate your input
Thanks, I appreciate your input...I guess I need to pay homage to this old school build and do her up right
Thanks, I was looking at the larger valves and improved volumetric efficiency. With all the great input on this forum, I will steer my build toward running 64 cc double bump 1.94 heads. Thanks again
Thank you, I am looking to add heat to my hot rod...I know I can't be the fastest in the valley but I can try lol. Thanks again
I'd be shocked if that 283 will be over 9:1 CR with those 76cc heads! Even with flat top pistons it will likely be down around 8.5:1 CR, and kill whatever power you add in cam, etc. on the build. I'd see if you can trade those to a machine shop for a pair of 1.94 heads, or even power pack heads that can have larger seats installed and setup for 1.94 valves. Your engine will appreciate the smaller 59-64cc combustion chambers, and bring some life to the build.
I don't think this type of build needs screw in studs and guideplates but in case you don't know it, hardened pushrods are required with guideplates.
Thanks, the pistons I am using are early corvette domed pistons. 11 to 1 cr with 58 cc heads. 9.7cr with 64 cc heads. I agree the 76 cc heads are low compression. They are fresh, 2.02 with screw in studs and guide plates...weighing my options. Thanks for your input, I appreciate it. I am leaning toward the 64 cc #291 64 cc double bumps I have
The 3-7/8" 283 bore ( even .03" O/S) may shroud the 2.02s significantly. A REALLY good valve job and a little short turn smoothing might help a smaller valve head a lot. As would the right exhaust. And of course a well tailored igntion curve. Discussion on the C$B intake - https://www.jalopyjournal.com/forum/threads/edelbrock-c4b-whats-the-real-scoop.857992/
This model A was an orginal hotrod from the early 60s, they took 2 model A frames and welded them together for a box. I added a 17 gallon fuel cell and double firewalls around the fuel cell, trunk and firewall...I have an aircraft background lol...crossed the scale at 2760. I reinforced the frame, added a lot of cross members and went thick on sheet metal
You have to get into the mid 60's how to modifiy your 283 articles on these deals and if memory serves right, 39Delux hit it spot on in post 5. It isn't just the valve being shrouded, it is the valve hitting the top of the cylinder wall on a 283 with 2.02 valves and any real lift on the cam. There were in depth articles in magazines back then. You had to clearance the top of cylinder wall next to the intake valve. The other thing is that most of those 283 engines that were modified that way ran 11.5 or 12.5 pop up pistons with the heads with the 2.02 valves just as you would need with those "Corvette" heads.
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