Primary Jets and Rods

[flashcad]

Hi,

I'm sure that the info that I'm about to ask has been answered a few times in this forum, but I don't know quite where to find it.  So, I thought that it might be easier if I just asked in a new topic.

My question is this:  I've heard that, generally speaking, if you subtract the size of the primary metering rods from the size of the primary jets and the difference is right at .030", then that's a decent setup.  Is this true?  If not, what's best for a streetable, strong setup?

Here's my carb:
Q-Jet #  17057253 from a 1977 Olds 350, or possibly a 403.
Electric choke.
Non-CCC.
Read in an article by Lars Grimsrud that despite the "3" at the end of the carb #, this carb is for an automatic trans.
Stock primary jets, primary rods, and secondary hangers.  .073 on the primary jets, I believe.  Primary rods= .  Secondary hangers= .

My car:
1970 Monte Carlo SB 400, 2bbl., 265 HP, Auto Trans. and A/C.
Stock engine/ no mods

I would like to increase my HP decently and also get a little better MPG than what the 2 bbl. gives me. I'm not trying to build a race car by any stretch.  What I'd like is a setup the way GM would have done it in 1970 if they had decided to put a Q-Jet on the SB 400's.  As far as I know, all they ever put on these engines were 2 bbl. carbs. I also want to keep the car looking fairly original, while incorporating carb features like the electric choke, so I'm looking for a SB GM 4 barrel intake from a year close to 1970.  I'm not a complete purist, though, or I'd try to find a 1970 carb.  I suppose, though, that the main reason I want to use this carb is because it is the one I have, you know.

Anyway, I don't want the car to bog or hesitate or backfire, etc., so I thought I'd see if any of you had any suggestions for this particular carb on this particular car. Maybe the carb doesn't even need the jets, etc. changed. I really don't know. I do know, though, that the mid-late 1970's gave us some gutless dogs, performance-wise, so I'm pretty sure something is needed. I've owned a number of cars with Q-Jets and loved them, but I'm pretty new with changing the internals of a Q-Jet. I'm trying to learn, and I've learned enough to know that this site is the best place to be.

Thanks,
Flashcad

[Cliff Ruggles]

The carb you have will work fine, but it is not the best set-up for what you are doing.  The front inlet and long fuel housing shove the fuel line right up against the thermostat housing, and why Chevy used side inlet carbs for that application.  A shorter housing will help that situation.

The Olds carb came with 73 jets, 49K rods, and CV secondary rods from what I can remember.  I would get one of our rebuild kits, and use our 44 tapered rods in place of the 49K rods, for better control of the part throttle A/F with the APT system.  The stock CV secondary rods are fine, as is the stock hanger.

Idle system will be adequate for what you are doing, give it a good rebuild with good parts, changing the primary rods, put it in service, and go back and make changes if/as needed.

I would get one of our electric choke kits as well, so it will work fine on any stock or aftermarket intake that you end up with.  I would use a stock iron intake, they are excellent units, even the later EGR versions......Cliff

[flashcad]

Well, I ended up in Wichita last weekend and picked up a cast iron, non-egr manifold, # 346250. It has a date code of F-5-8, which should be June 5, 1978. Different sources on the internet list its applications as either 305 or 350 SBC in a pick-up truck or on a Mercruiser inboard boat engine. Either way, it has no egr provisions, so that works. I didn't have this manifold # on my list of possibilities because I wasn't looking for anything newer than '72 because of the egr. When I saw the date code, I thought 1968, but that wasn't right because those manifolds would have had the oil filler tube in the front, like on a 327 or 283. Then it dawned on me that trucks and boats were much less restricted by pollution laws. So, anybody out there looking, do your homework and make a list. Don't buy off eBay on one of these either. I picked this one up for $25. The cheapest on eBay now is $75 with $50 shipping. That's nuts.

Because you mentioned the fact that the fuel inlet line might hit the water neck with my Olds QJ, I hunted around until I  found a 90-degree adapter to make the carb more like a Chevrolet QJ. It's called a Banjo Adapter, and it's brass.  I also saw some red and blue anodized adapters, but that's too flashy for me. For folks who want them, though, they're out there. 

Anyway, I also picked up an air cleaner from a 4BBL SBC that should work just fine. So, with the jets and rods you recommended, I should be in business.

Thanks for your help, Cliff. This setup should work.

[Cliff Ruggles]

Those are excellent intakes.  Never seen one of those 90 degree adapters.  We usually go to AN lines fittings or tap the front of the fuel filter housing for NPT threads.  Makes going back to steel lines pretty easy.

The short fuel filter housing for your carb gets the fuel line far enough away from the thermostat housing to easily route a fuel line to it, and leaves more room if adapters are going to be used.....Cliff

[flashcad]

Thanks Cliff!  I'm trying to figure out how to post a picture on here, and when I do, I'll get that adapter up here so you can see it.

I'm glad to hear that you like that manifold. I wasn't very clear in my original post, but I intended to use cast iron all the way. Even though it won't be "right," it'll be close, and generally, if someone points out the faults in some car of mine, I just say, "That's nice. Where's yours?"  And, with a '70 Monte, most people don't have one to compare. I just wanted it to be reasonable enough that people would ask if it was stock. I think I will have accomplished that. And I do thank you for your suggestions.

Flashcad

[flashcad]

Okay, let's give this a try. I think this will work.

Here is the 90 degree adapter:  It looks like something you could piece together at a hardware store.