Here’s a question you probably haven’t got before in your Ask Away! segments. I have a 0.060-over 283 that is now at 292 cubic inches. I just finished the short block and all my friends are telling me to put a big set of heads on this to help it make power. I can get a set of those “camel back” or “double-hump” heads—I think the cast number is 462. This is going to be a very mild 292 in my street rod and I might even add a 2×3 Rochester tri-power setup on it to give it an old time hot rod look. Any ideas?
I have actually played quite a bit with 283 Chevy engines. These are great little small blocks that were small-bore, short-stroke little blocks that seemed like they would run forever. The standard dimensions were 3.875 inch bore with a 3.00-inch stroke.
When Chevrolet needed to come up with a 5.0 liter engine for their jump into Trans Am racing with the Z/28 in 1967, they merely slipped a 283 3.00-inch steel crank in a small-journal 327 4.00-inch bore block and instantly had a 302ci engine.
But I digress.
By increasing the bore 0.060-inch on your 283, you end up with 3.935 inch bore that bumps the displacement to 292ci. The problem with adding bigger fuelie style cylinder heads like the 461 or 462 is that, while these heads increase airflow over a stock 283 head, this also increases the combustion chamber volume.
Those double-hump heads generally have 64cc chambers. The stock 283 used a 58cc chamber. The reason this is important is when we start plugging numbers into a compression ratio program—the short stroke makes adding compression difficult without going to domed pistons.
Since the 283 uses a short 3.00-inch stroke, combustion chamber volume with a flat-top style piston means you really need to make the chamber size very small. For example, a 0.060-over 283 with a 58cc chamber, flat top pistons with four valve reliefs (we’ll call that 6 cc or 1.5cc per relief), a shim steel gasket that’s only 0.018-inch thick, and a deck height with the pistons 0.010-inch below the deck produces 9.6:1 compression.
That’s a great pump gas compression ratio—likely your specs will be slightly different. Most production based small-blocks back in the day were closer to 0.020-inch down in the hole, dropping the compression to 9.3:1. So you can see that even slight changes make a big difference.
Now let’s take that 9.6:1 combination and add bigger 461 heads with a 64cc chamber. That adds 6 ccs, which doesn’t sound like much, but it has a big effect. The compression ratio drops from 9.6:1 with the 58cc chambers to 8.9:1—a loss of almost 0.75:1. That’s huge. These little motors really like compression so with a mild 292 with good compression you might make close to 275 to 280 hp.
Every point of compression is generally accepted to be worth about 3-4 percent power. So if we drop the compression by 0.75-point, let’s call that 3 percent, that’s about 8 hp and perhaps closer to 10 hp. It’s possible that the airflow increase of the larger heads will push the power back up, but the loss of compression will hurt torque throughout the entire rpm range and will also cost mileage—not that you probably care about that.
I’ve never done a straight comparison on the dyno, but I have removed a set of 462 heads from a 287 (0.030-over 283) and installed a set of 520 Power Pak castings that were lightly ported and increased the intake valve size from its tiny 1.72-inch diameter to a 1.84-inch version from a 305 engine. At the drag strip, the car picked up about 4 mph and a couple of tenths of a second. I attribute the better mph to better horsepower mainly from the added compression.
That little engine used an Edelbrock Performer camshaft (204/214 degrees at 0.050 with 0.420/0.443-inch lift) and Edelbrock dual plane intake manifold with a tuned-up Q-jet and it really ran good with a Muncie four-speed and 3.31:1 rear gears. These engines make very little torque, but decent horsepower for their size.
You can still add a set of larger port heads to these engines but you will either need to add domed pistons to improve the compression or mill the heads. Adding better pistons is the one way to go because the rule of thumb is you have to mill the head 0.006-inch to remove 1cc of chamber volume.
So to reduce a 64cc chamber down to 58cc, this is 8cc which means you need to remove 0.048-inch from the head deck surface. This is an excessive amount that will also make bolting the intake manifold on problematic and it’s almost guaranteed that the intake gasket will not seal properly because the angle has changed.
These are the details that few people pay attention to and yet they are critically important. You could take a set of old 58cc iron heads and have them machined to open up the intake valve size from stock 1.72 to 1.84 or even 1.94-inch but then you will also need to pocket port the bowl area to blend the bowl into the larger valve to take cull advantage of this swap. This is a lot of work—I’ve done it before and it will take 8-10 hours of grinding on nasty old iron.
Plus, the heads are almost guaranteed to need new guides, valves, and you will certainly want to add better valve guide seals and pushrod guide plates. By the time you are done with all that, it’s possible to have $800 or perhaps $1,000 invested in a set of ancient iron heads that might then crack. It happens all the time. Remember, these heads are over 50 years old!
World Products makes a 58cc iron head with a larger 170cc intake port and 1.94/1.50-inch valves that would be perfect. It’s not a very popular head so likely you will have to order them and wait a while, but that would be easiest way to update your 283 and not spend a ton of money.
Another approach is Trick Flow’s 175cc aluminum small-block Chevy head for small-block that features the fuelie “double hump” casting mark and would work great on your 292. The heads use a 60cc combustion chamber. Plugged into our compression ratio program, that puts your flat-top 283 at 9.35:1 which is pretty good. This will work well on pump gas.
I would also run long-tube 1 5/8-inch headers in this. If possible, try to avoid the shorty or intermediate length headers as they will hurt the low-speed torque—and with a 292 you need all the torque you can make. Ideally, I would run a set of 1.5-inch headers but these would have to be custom made, yet would really help the low-speed torque with very little loss of top-end horsepower.
As for induction, if you want the look, yes a tri-power setup is nice, but it will cost horsepower compared to even the least expensive dual plane single four-barrel intake. Those old tri-powers look very cool so if power isn’t really an issue then it’s a great idea.
Edelbrock makes a vintage looking tri-power intake manifold that even uses the old stock oil filler tube so you can run old style valve covers with no vents or fittings. The big issue will be finding three old Rochester 2GC carburetors. They are still out there but are becoming harder to find.
We’ve worked with JET Performance on various stories and they do a great job of rebuilding these Rochester 2 barrel carbs, so you might consider them as a source if you find a trio of carbs that can be rebuilt. These engines are becoming harder to find as the last 283s were built for production in 1967.
In the days when a 327 was considered an expensive engine, a favorite upgrade was to bore the 283 out from 3.875 to 4.00 inches and those engines were called 301s until the Z/28 came out in 1967. Then everybody called it a 302. One reason the 302 was rated at 290 hp was it came with 11:1 static compression and 462 “fuelie” heads that were also used on 327 Corvettes and Chevelles.
I have a copy of a set of dyno sheets given to me by Jim Travers and Frank Coon (Traco) showing a Penske 302 engine making 402 hp at 6,800 rpm for the ’67 Trans Am season. It would be fun to recreate that engine with as many close-to-original parts as possible. They were using stock stamped steel rocker arms, a transistorized ignition, and an Engle cam with a single four-barrel dual plane intake. The crossram appeared later.
Hope this will help steer you toward building that little 283 – they are great little engines that will rev to the moon!