The Stovebolt Site Forums The Shop Area Engine Shop 283 Exhaust Manifolds

As I assemble my 1966 SBC 283ci, I’m learning a lot.
It appears there were at least 2 different designs for the DS ram horn manifold. I bought an aftermarket (Dorman) DS manifold with the boss for the alternator bracket. When I opened the box I found a donut ring gasket piece just like the one I have on my 230ci downpipe.

So I’m guessing the 283 manifold downpipe also uses the same style insert piece (about 3” - see last 2 pictures) that I also used with my 230 downpipe. Asking for confirmation.

I don't know. I've had two 283s...one in a 1957 and one in a 1958 and neither one used anything like that insert piece you have there. The exhaust pipe was joined directly to the manifold with a donut ring gasket on each side. Must have been something used in later years?

This product is sold on EBay and seems worth every penny since it eliminates the need for the separate insert. I’d just need the 3 hole ring flange to squeeze it up against the manifold.

The original crossover pipe for a single exhaust system had the 3-bolt flanges made onto it and the donut seats were built into the pipe on both sides. Passenger's side manfolds had a flat gasket surface that the heat riser valve seated against, and the bottom of the heat riser was recessed for the donut. Some factory original donuts were made of cast iron, rather than the wound asbestos donuts that came in gasket sets. Running without a heat riser will result in really poor engine performance during warmup.
Jerry

These manifolds are repop for the 327 manifolds and have 2.5” outlets. Studs are 3” apart.
I’ll run a dual exhaust like the 1966 C10 with a 327. I’m not finding a heat riser anywhere but I’ll keep looking. Not 100% sure I’ll need a heat riser here in the warm weather of SC.
Rock Auto sells a kit for the 1966 C10 V8 exhaust but they are out of stock. I have a first rate exhaust guy near me who uses a recipe card for these old trucks and so far has been great.

New 2.5" heat risers are on Ebay, starting at $44.00 plus $16.00 shipping. 2.5" exhausts are probably too big for a 283, but they'll work OK. A 2" pipe provides better exhaust scavenging for a small engine, especially one with dual exhausts.
Jerry

I'm not finding any new ram horn style manifolds with a 2" center dump. Can I use a reducer? Reduce from 2.5" down to 2" and then 2" for the rest of the exhaust? I still need to decide what muffler to use. I think straight pipe might be annoying to the neighbors.

Lugnutz, I know you are looking at new manifolds, but what about considering good, used units? The '58-'65 3747038 casting is common, has 1.9" outlet, three studs, and can be used on either right or left side (the casting is marked RH), if the alternator mount isn't needed. If the alternator mount is needed, a suitable LH casting number is 3749965. These aren't the only 1.9-2" outlet castings, just a couple that are common.

There are a number of these castings listed on eBay, some are heavily rusted, but its not uncommon to find them in great shape, for $30-$40 each, maybe a bit more.

Maybe an option.

Doug

Cast iron doesn't wear out. I think I'd rather have a 70 year old American made piece in good condition than a brand new item made by a 12 year old indentured servant in some backyard forge in a third world country. If the gasket surfaces need a little cleanup, a belt sander and a straight edge will handle that little chore quickly. Yes, any muffler shop can install a reducer to adapt the pipe size down to 2" if you can't find manifolds that suit you. Too-large exhaust pipes on a small displacement engine slow down the gas velocity and create flat spots in acceleration at low and midrange RPM. They're great if you plan to run wide open throttle and high RPM all the time.

When I replaced a 235 in a 58 Chevy DelRay coupe with a 61 Corvette 283 in the late 1960's, I bought brand new 2 1/2 inch rams' horn exhaust manifolds for a 300 HP 327. It was a mistake.
Jerry

Used to be able to get heat risers through NAPA.

I thought I found some new 2” outlet manifolds. They are out of stock.
I already have one nice set of 2” outlet original GM manifolds, but since I’m building two 283ci engines, I’ll need a second set. I found a set locally for $60 but the DS has the boss where the alternator mounts at the front end of the manifold instead of the style I have. The local set also has a broken flange for one of the studs. Kind of a deal breaker.
I’ll search eBay again for used manifolds. I can always return these repop manifolds.

There's a good looking driver's side manifold on Ebay- - - -$40.00 plus shipping. It looks like the mud dauber nests are included for free! There's LOTS of right side ones in good shape.

(can't get the link to attach- - - -search for it!)

LOL!
Jerry

If you don't want/need the alternator bracket on the manifold just cut/grind it off...that leaves you with the donut bevel.

If you're not installing a heat riser you can use the left side manifold on the right side so the donut gasket works on that side as well.

Mike B

Yes, using a LEFT side manifold on the RIGHT did occur to me. That might be why I see a lot of right side manifolds for sale on eBay, but without a left side mate.

I’m still on the hunt for a second pair. I have a good lead.

If you need a generator/alternator bracket for the driver's side, it's a very simple matter to use a piece of angle iron and a couple of pipe nipple spacers to adapt a passenger's side (right, not left) manifold for use on the driver's side. Right/left is always supposed to be described from the driver's seat, not the front of the vehicle. I've made several of those brackets, particularly when I wanted to mount the charging system on the passenger side for some reason.
Jerry

My eBay purchase arrived today. The selling point was that it included the blank heat riser as part of the deal. I’ll remove the old threaded studs and install new. I don’t see any cracks in the manifolds, so I think my $96.30 which included shipping was well spent.

Take notice how the DS manifold has threaded holes on the end for the alternator. Vendors sell the correct bracket. Here’s a picture of a 1966 C10 283 with the same manifold/bracket setup. Last picture shows same style bracket with the alternator.

Oh, well- - - -at least I tried! Good luck!
Jerry

I’m confused by your comment. You said I should get 2” outlet original GM manifolds. So I did!

I also said you need a heat riser.
Jerry

Yes, and I thought this WAS a heat riser from the eBay pictures. At least I can assemble things now for the run stand. Can’t you see I’m trying?

A heat riser has a spring, a flap valve, and a counterweight to route exhaust gas under the carburetor during engine warmup. On a V8, there are passageways through both cylinder heads and the intake manifold to facilitate the gas flow to the carburetor until the bimetal spring relaxes and the gas flow and the counterweight pushes the valve open. That open hole has none of those things, and is used by people who don't think the engine designers who went to a great deal of effort to build the system knew what they were doing. The standard excuse that "I'm in a warm climate" doesn't take into account that exhaust gas is somewhere in the 1,000 degree F. range or more.

This is the correct heat riser for a 2" pipe manifold- - - -ignore the "Corvette" designation. There are others on Ebay for lots more money that just say "2 inch".

https://www.ebay.com/itm/224312028645?hash=item343a09ede5:g:aUMAAOSw7Ilf-49p

Jerry

Depending on the application some 283's did not have the heat riser, I was surprised to find mine did not have it from the factory. 1957 2 ton Low Cab Forward, 283, single exhaust.

Anyone ever come up with a manually operated heat riser? The inline 230 heat riser flap is notorious for failing, and of course the owner doesn’t know because it’s one of those items that gets neglected.

The 1931 Buick straight 8 I worked on in the mid-1970's had a manual heat riser. It also had an updraft carburetor, I believe. Buckshot, since the big rigs with the 283 ran more or less full throttle against the governor all the time, the exhaust generated plenty of heat under the intake withuot a restriction on one side.
Jerry

I'm a bit late to the conversation. But I just picked up a set of chinese ramhorns. they are very light! compared to the original set that I have.

I’m returning mine to Summit Racing. I thought they were decent for the money, but these original GM manifolds are 2” whereas the Dorman manifolds (China) I bought from Summit Racing are 2.5”.

On a hard pull at high RPM on the dyno, I've seen original equipment rams' horn manifolds glow cherry red all the way from the heads to the exhausat pipe flanges. Headers get so translucent you can see the flames dancing around inside the tubing. I wonder what those Chinese repops would look like during a full throttle run up sometning like the Grapevine hill in California? That's 6 miles of 6% grade. or at least it used to be when I was trucking there back in the late 1970's.

Big block Chevy motorhome engines had a bad habit of cracking exhaust manifolds (and heads) from the stress of pulling those big shoeboxes uphill. I've done some road testing with the engine cover off at times, and the orange glow from the exhausts is pretty impressive on a long upgrade.
Jerry

Yep, used to see that all the time at the short track stock car races. Brings back good memories.

I've measured exhaust port temps on small block round track engines approaching 2,000 degrees F. No wonder headers burn up spark plug wires!
Jerry

Back in my beer delivery days we had 366's, 427's in medium duty trucks and 454's in a couple of one tons, manifolds would glow red when we would pull into the barn, the medium duty engines were bullet proof.