800 cfm Caddy carb on a Chevy 383 Stroker

[krb90]

I have an 800 cfm q-jet, 17057235. I also have a 383 chevy stroker w/ mild street cam. Would this be a good match? I'm new to q-jets, but I've been doing some reading. The jet/rods (70/48) provide 2.0389 metering area at cruising, and 3.3175 @ WOT (if my math is right), which would seem a little lean for a 425-500 ci engine....but I admit I don't know the size of the air bleeds and how they effect. Was this carb intended for 'economy' in a larger ci engine? Do you have any advice you would give?
thanks

[Macadoo]

If it were me, I'd just plop that thing on the stroker and see how it runs.  The idle circuit may be a little rich so maybe lean out the mixture screws a little.  Run it and then check the plugs for color.
The folks on this forum (that know A LOT more than me) will need more specific info; cam specs, compression ratio, exhaust, gearing, etc.
If you haven't yet, pick up Cliff's Q-jet book.  It's a wealth of information.
Good luck.
-Mac

[krb90]

Thanks for the reply. That's the plan, I'll never really know till I put it on. I thought, since it was originally a caddy big block carb, I'd get a little feedback as to what I might expect. I haven't read Cliff's book, but I've scoured this forum, read through the Lar's paper a few times, as well as some random websites, which has got me to thinking (something I can overdo)

So can anyone offer a little insight to this: There are seemingly hundreds of jet/rod combinations. Each jet size has the same metering area at WOT, since the rod tips are basically all the same. For any given jet size, a larger rod size would decrease the 'cruise' metering area and a smaller rod would increase the area. What could someone expect comparing:
1. Larger jet with a large ratio between the 'cruise' metering area and the WOT metering area (i.e. a larger rod)
2. Large jet with a smaller rod, which would increase the 'cruise' metering area, decreasing the ratio?
3. Smaller jet with a larger rod (could be similar metering area as large jet and large rod, but WOT area would be smaller)
4. Smaller jet with smaller rod (same WOT as #3, but larger 'cruise' area

Does that make sense?

[Cliff Ruggles]

Forget metering area, it really doesn't tell you much as Q-jets are application specific and fuel delivery to the engine is far greater effected by how the carb is set up.

The big Caddy carb has tiny MAB's and rich idle calibration compared to a similar unit which would have showed up on a small block Chevy emission calibrated engine the same year.

It will delivery more fuel with 70 main jets than a 17057204 would have with 77 main jets in it.

The primary rods are also tapered and it uses an APT system to precisely locate them in the jets.  What is the secondary stamping on the primary metering rods, J, K, L, P, etc?

What are all the engine specs, compression ratio, camshaft info, etc?

Impossible for anyone to tell you anything without details.

The good news is that the big Caddy carb is a good starting point and will make an excellent carburetor for what you are doing.  Might need a little help in a few areas.  For sure get one of our SR rebuild kits for it, with the high flow N/S assembly and HP accl pump.  You'll also get the secondary plastic cam/spring, new small float, and retainer for the power piston.

Depending on the engine specs you may need some tuning parts, power piston spring, and slightly different jet/rod combo.

Test the pull-off to make sure it holds vacuum and releases quickly and the electric choke to make sure it heats up, if they are defective replace them as well.......Cliff

[krb90]

Thanks for the tips. I appreciate the forum you have here.

Truth is, I don't know many details. The motor was a crate engine, the p.o. is long gone, all I can say is that it's nothing radical. It's got some mileage on it, so I'm eventually going to rebuild it but I'm happy just to have it running at the moment. I had a chance to grab this caddy carb, kinda thinking ahead a little. But the gas hog edelbrock on it I know sucks, so why not rebuild this one now, and adjust it to whatever I end up doing later.

As far as I know the carb is all factory. I'll definitely be picking up a kit. Thanks

[77cruiser]

If it matters the gas mileage my 421 dynoed 530 hp runs 11.9 in a 4200 lb. 77 Monte will get over 19 mpg highway. So once a q Qjet is tuned you can have some cake & eat it too.

[krb90]

Awww, man, I can only dream of that kind of mileage. 10 mpg....11 on the freeway in a 3500 lb toyota pickup. Granted it's 4wd, but still....

I look forward to at least some of that