Divorced choke and headers

[old cars]

Cliff. Never could understand why someone would install headers on one of those smog low performance vehicles back in the day. I would cringe when someone  drove one of those into my shop back in the day, needing spark plugs changed.

[Cliff Ruggles]

ALWAYS start with the basics. 

If your choke stays on too long verify that the pad under it is heating up quickly.

You have control of the delay (time from closed to open) by modifying the length of the rod.  Any changes made to the distance between the divorced choke pad and carburetor effect the "time" it takes for the choke to fully open.

Carboned up crossovers in the heads or manifold slow things down.

Any sort of "aftermarket" intake will NOT have the same distance pad to carb and in many cases require a longer rod just  like using a thicker carb to intake gasket would.  Aluminum vs cast iron changes things as well.

Over the years folks who installed intakes and intake gaskets had a BAD habit of using restrictors to keep some heat out of the intake, BAD idea but it was done.

I've worked on hundreds of these engines dating clear back to the mid-1970's and not in one single instance has removing the heat riser, disabling it, or going to headers made such a dramatic change in the release time of the divorced choke that I couldn't correct the added opening timing without much more than bending the stock link or making a longer one from a piece of aluminum (easier to bend that steel) TIG rod.

I will say for anyone reading this that IF I installed any "high performance" part on a mild set-up and it started a chain reaction in me having to buy more parts to correct issues it caused I would AMPUTATE that part or parts and go back to the stock pieces.

I build a LOT of carburetors for Pure Stock and FAST Class cars that use stock iron manifolds and a couple run into the high 9's over 130mph with bias ply rear tires!  I've owned and raced cars with headers and they absolutely SUCK BALLS on a small block Chevy application for the reasons I mentioned earlier. 

If they brought a LOT of power to the table I'd put more effort into using them but for at least 95 percent of the applications that get them they are WAY more trouble than they are worth.....IMHO

Folks should note here that there are a LOT of parts sold for these engines that are advertised to "make more power".  I saw earlier where a Performer RPM intake was used on a small block 400.

.....contineued

[Cliff Ruggles]

A few years back I was on the dyno with a 440CID engine with aftermarket aluminum heads flowing 260cfm, custom ground HR cam, 10.6 to 1 compression, and a factory cast iron intake.  We made 497hp and 540tq once we got it dialed in.  The shop owner had an Edelbrock Performer RPM intake in the shop and asked me to install it to "see how much power the engine will really make".  I did so, and the very next pull with NO OTHER CHANGES was 491hp/535tq!

Yes, we LOST power with the larger intake.  So how many folks buy those intakes to put on 180hp 350's and think they are making MORE power anyplace?

It's not much different with headers.  We've dyno'd a few engines swapping from manifolds to headers and even tested different headers against each other.  Sometimes you'll see dramatic improvements, sometimes none at all, and other times you stand there scratching your head and backside wondering why you LOST power?  With a really well made header compared to a poorly made one I've seen 30hp, but typically NOTHING below about 4500rpm's or so.  So even if all your efforts result in a little more top end charge, you have to weigh out the negatives with using them and make sure that your goals for improvements were stronger top end charge and that your engine has enough cam and head flow to make power that high in the RPM range.
I'll close here with this.  I'm on here to help folks solve problems and get a good end result with these things.  When I provide lengthy responses it is often to educate everyone involved and certainly NOT to be critical of the OP or what they have done.  I've been doing this well over 40 years and coming up on 20 years full time.  At this point in my learning curve I certainly don't know everything, but for sure I know what works poorly or doesn't work at all.

You'll also notice that I often go "against the grain" when it comes to the selection and use of aftermarket "high performance" parts.  This comes from DIRECT testing, not from the fancy advertising the company selling them tells me, or what I've read from Google research, other Forums, etc.....

[bob69]

Hi Cliff. I assemble all my engines. At first to save money, then because I really enjoy it. The machine shop I've been going to since the late 1970s does excellent work and the owner understands that I  like to do the assembly myself.

Over the years I've collected dozens of chevy chokes and choke rods. Not afraid to tinker with them to get the set up correct. I've taken them apart and changed the coils "clock" position and even put a 1969 coil into a 1970 housing. I'm pretty good at bending chock rods too.


Reading about your experience with headers, my first though was " been there, done that". I had the same experience in the 90s just not as bad as yours. The header eventually burned a hole in the a/c suitcase.  I removed the headers and put the stock exhaust back on.

Fast forward  to the chevelle. The old headers were very rusty and ugly.  When I put the 400 sbc in the headers were also changed. The headers were ceramic coated to reduce heat, the flanges are thicker to prevent gasket blow outs, pipes are thicker and the routing cleared the plugs and wires with no problems. Have no problems with them.

Experience taught me to check the header bolts frequently. After installation, I'd check the bolts every week or sooner on a cold engine. Always found one or two, or more that were loose. I kept doing this until all of the bolts stay tight. Surprised at how look it took to get all of them to stay tight.

I don't  understand why a header manufacturer would build a header that interfered with plugs and plug wires. Like they don't know were the plugs are? Are they designed for a sbc head with angled plugs and yet still market them for stock heads?

Before the internet, you needed to know a guy that would direct you to the correct part. Today, do a search on-line and you will find lots of feedback on user experiences with a particular part. Keeps the manufacturers and vendors honest.

[Cliff Ruggles]

Got to LOVE feedback.  It's helpful but you have to sort thru it as some of the folks bad mouthing a certain part need to get out of the hobby and never work on anything related to it again.

Kind of related but I was on Amazon recently and saw where someone gave my book a bad review and 1  or 2 stars, can't remember which.  He commented this:

"lots of history, lots of GM charts, little in the way of fixing and or modifying the Quadrajet.
Sorry I spent the money!"

Let's see, there is one chapter on "History", not a single "GM" chart in the book, and for sure that IDIOT didn't even read the book and very quickly needs to go straight back to his day job!.......FWIW....