Q-jet, spacer and ancient C3B intake...mileage discussion

[Brad54]

My daily driver is a '62 Suburban (okay...by the end of this month, it'll be a daily again: The rear end housing ate itself, and it turns out the Dana 44 is very, very rare in the '60-'62 trucks. But I digress).

right now, it pulls down 18mpg on the highway with bad aero (going to work on a few things), .73:1 overdrive manual trans, 3.55 gears. Engine is 290-horse GM crate engine (dressed to look like a vintage 327). Out of the box Edelbrock 600cfm carb, Edelbrock C3B intake, stock (and old) HEI distributor, 2-inch rams horn manifolds. Open element Speedway spun aluminum air cleaner (with the drop base somewhat like the K&N Flow Control air cleaner assembly), and a 1-inch 4-hole carb spacer.

Immediate changes will be 3.42 gears, front end rebuild, close-off some of the aero problems (filler panel between front bumper and cross member to keep air from stacking up under the hood, short unobtrusive chin spoiler behind front bumper to clean up air from under truck, and close off the unused part of the grille opening).

I'm not willing to give up the Edlebrock C3B intake at this time.

I'd like to hear from anybody who has or is running a Q-jet style carb, with economy in mind.

It seems someone once told me a Q-jet to square-bore adapter kills performance and is just bad. Any thoughts? Does anybody know this to be the case?

With the drop-base air cleaner and spacer, I can camouflage the carb and keep the look I'm going for.

I'm not looking for people to say "Yeah, you should get X-mileage improvements." Mainly, I'd like to know if anyone has done anything along these lines and liked it, or if they did it and it turned into a boondoggle.

Substitute "C3B" for "Performer RPM" if it makes you feel better. I realize nobody (yet) is going to have the numbers for the old C3B.

-Brad

[squirrel]

Re: Q-jet, spacer and ancient C3B intake...mileage discussion

What's your question?

Anyways, getting 18 out of that thing is great, I'd be afraid to change anything

[Brad54]

Re: Q-jet, spacer and ancient C3B intake...mileage discussion

What's the matter? You don't speak overly-caffeinated gibberish?

Does a spread-bore to square-bore carb spacer kill any performance or economy gains? In other words, would any gains made by running a Q-jet be wiped out by putting it on an adapter and running it through an intake NOT designed to work with a spread bore? Lots of guys have used Q-jets on square bore intakes, I have not. For those guys, were they disappointed with the results, or were they happy with them?

Is swapping to a spread-bore worth the hassle and expense, from a fuel economy point of view? I drive it 15K+ miles per year, so at these gas prices, improvements will pay for themselves--IF they're actually improvements.

I do love that it gets the mileage it does now, but I'd really like to wipe the eye of everyone who thinks old cars and trucks aren't practical or economical, and do it with a carb and smart building.
-Brad

[squirrel]

Re: Q-jet, spacer and ancient C3B intake...mileage discussion

Oh, I see. I missed the part where you said it has a 600 edelbrock carb on it now.

If you have a free qjet to experiment with, have at it! Be careful with the adapter to make sure it's sealed well to both the carb and intake. I'd be surprised if you gain anything, though.

[Freiburger]

Re: Q-jet, spacer and ancient C3B intake...mileage discussion

I don't think that the Q-Jet cares too muchif it's on an adapter.

Sidebar question. Brad, you saw my C4B and mentioned your C3B. Are you sure the C3B is not designed for an old Holley three-barrel? If so, that would be really cool.

I'd like to head from someone who runs a three-barrel.

[squirrel]

Re: Q-jet, spacer and ancient C3B intake...mileage discussion

I've been wanting to find one for my 61, but that's a long term project....

I do know a guy in town who raced his 66 Chevelle when it was new, and he ran the 3bbl and did well with it. He recently put one on his 80s 496 powered Suburban, just for fun. They're out there...and making a comeback....

from a 1971ish JC Whitney catalog...




(quite the thread hijack)

[Brad54]

Re: Q-jet, spacer and ancient C3B intake...mileage discussion

I don't think that the Q-Jet cares too muchif it's on an adapter.

Sidebar question. Brad, you saw my C4B and mentioned your C3B. Are you sure the C3B is not designed for an old Holley three-barrel? If so, that would be really cool.

I'd like to head from someone who runs a three-barrel.

From what I've been able to dig up, it's like this: There are actually at least four versions of this intake: The C4B (Chevrolet 4bbl), C3B (Chev 3bbl) and C3BX. From the pics I've seen, I can't see a difference in the C3BX.

The C4B I have has a 4-hole carb base. The runner lay-out LOOKS poor, because it has very long and very short runners, rather than more evenly spaced runners. The one you have has that runner lay-out. To me, it looks like it's going to have lean and rich cylinders.

The C3B I have on the truck has an open carb base with a divided plenum, much like a Performer. It has a notch in the plenum to clear the Holley 3bbl throttle blade. You can see the progression of this intake to the Performer. The high and low sides of the plenum floor are reversed, compared to the C4B I have, and the runners are much more even in length. Biggest difference I can see between this intake and the Performer is that the Performer is taller, by a couple inches, easy.
Here's an ebay link to a C4B with and open base, divided plenum, no notch for the 3bbl carb. http://cgi.ebay.com/ebaymotors/EDELB...spagenameZWDVW

My C4B has the same runner lay out, with a 4-hole carb mounting pad.(So there are two versions of the C4B)

My C3B has a similar plenum (with notched divider), but the top-side runners leave from the passenger side, giving them a much more equal length. This required changing the plenum floor from the intake shown in the link.

I have no idea what sets the C3BX apart, but that one is out there too.

With the notched plenum, I found your intake shoot-out very interesting, when you machined the plenum. The C3B doesn't have a notch nearly that big.

-Brad