Aloha, I have a 460 with ported D0VE C heads, a torker 460 intake manifold, stock rockers and lifters, and a mild lunati cam thats maybe one or two sizes over stock. The motor unfortunately breathes through stock exhaust manifolds, and a 500 cfm q-jet. I feel like the motor isn't really living up to its full potential. Could the carb be holding it back, or am i expecting too much? My stock 400 with a two barrel felt stouter than this 460, Especially in the low end. Am I missing something?

 

I would think for that motor a 750 cfm carb would be more suitable. I've ran q-jets before and they are awesome power houses when tuned right, but if your certain about the cfm capabilities I think that a larger carb would definitely be in the cards. However if your experiencing low end lag I don't believe the carb would explain that considering the flow would be impacted at higher rpms. I would look at that cam you put in, depending on the set-up it may have increased your performance from mid to high rpm and you lost out on the low end?

 

I've never knew that there was that small of a Q-jet. For some reason I thought they all were 750-800. Not sure why just did. I think it's mainly becasue your set up is all over the place. Your stuff needs to match to one another. You have a parts bin motor basically. The specs on the cam would help. Also ditch the carb and exh manifolds for a set of headers and at least a 750. That torker intake is a single plain for mid to high rpms. Which contridicts the 500 carb you have with the mani's.

 

The motor originally had headers, but I couldn't get them to fit. So I bolted some stock manifolds on it. Here is another strange thing (to me anyway). If I close the choke to about halfway closed, it will pin you back in your seat once it gets 1800 RPM, does this suggest that perhaps the carburetor is a little lean?

 

That sounds weird to me. It would make sense you would be running lean for this to happen.

 

Q jets are only available in 750 to 800 CFM's. There is not a 500 CFM model.

Which timing chain set is this engine running? Hopefully the cam is installed straight up or maybe even slightly advanced, depending upon the lobe centerline.

If your choke has to be closed in order for the engine to run, it is terribly lean and needs to be adjusted.
How does this engine idle? This lean condition would indicate a potential vacuum leak. Poor performance could be the result of a bad vacuum leak.

Is this engine using a "turkey pan" intake gasket or standard gasket? Turkey pans can leak once in a while if used with aftermarket aluminum intakes, and not tightened down in the proper sequence. Many leak oil at the "China Wall" in certain situations as well.

Does this engine consume oil? I ask because once in a while the vacuum leak can be under the intake in the lifter valley. This is tough to troubleshoot, and can cause this same issue.

 

Thanks for confirming this, I swore that was true too, but I've been wrong before and didn't want to post anything false.

 

No the truck idles great, probably between 550 and 650 rpm
YouTube - 1979 F150 Start and Drive
It just doesn't really have as much power as it should unless the choke is halfway closed. And I have to have the engine revved around 1800 before it really starts bringing on some power. It doesn't use oil. And I have no idea which gasket it uses. I have not had to have the intake off. I think the 9 inch rear may have 3.23 gears though. So that may be why it doesn't seem to have much power down low.

 

I am glad to know the carb wan't available in 500 cfm.

 

You need a dual plane intake. That will help your low end. A BETTER carb( like demon or holley) and headers. I agree with 93F22A6 in your combo of parts is not real good. Motors have to be built in sync from top to bottom

 

So there is nothing fishy about the truck being stouter with the choke closed?

 

It's definitely fishy if the truck is stouter with the choke closed. That could be caused by anything, including your giant open plenum intake, which has such low flow speeds at lower RPMs that your fuel will probably be coming out of suspension, requiring you to "supersaturate" the air mixture by closing the choke halfway. Or you could be horribly lean with a smallblock carb calibration. Perhaps keeping the choke closed is actually keeping your manifold vacuum up- your parts-bin motor there might not be able to handle a full intake charge at low RPMs.

Are you using an adapter on that Torker intake? 'Cause that's a squarebore intake, all QJets are spreadbore, and if you're not using an adapter, then you're not using a QJet. I've only ever seen adapters to put a squarebore on a spreadbore manifold. You can turn them upside-down, like I've done on my truck, but then you run into funny gasket issues and you could have a HUGE vacuum leak you're not accounting for.

I agree with zak8tac, the QJet is an excellent carburetor when tuned right, and they came in 750 (most common) and 800CFM (sometimes 850 on a special performance package).

I've only ever heard good things about DEMON carburetors as well, same with the Truck Avengers.

 

It's not the intake. The old single plane = only mid and high rpm power myth is being proven as just that with dyno comparisons against dual planes.

From the evidence we have here, it seems that the carb is not tuned properly for the cubic inches of the engine.
The 460 moves a much larger volume of air through the venturis than a 5 or 6 liter engine that the Q jet probably came from, and it needs to be tuned for the 460 by someone who knows what they're doing. Or, you need to read up on Q jets and do it yourself.

An important point about the intake/carb baseplate mismatch has also been made. If the Qjet is sitting on a square bore intake base, or one of those cheesy adapters, you could have problems there too.

Take some up close pics (IN THE DAYLIGHT) of the carb/intake setup from sides and front.

 

It is sitting on a cheezy baseplate. But I will look into tuning it up to better suit the 460.

 

I still believe that this thing has a vacuum leak. The mention of a spacer / adapter is undoubtedly a problem. THese Q-jets have an interesting gasket and accomodations for the heat crossover which leaks all of the time.
YOu may also have a vacuum brake (small canister on the side of the carb) that is responsible for the operation of the choke, and these can also leak and cause fits.
Not too sure how you get the choke to open or close when you want it to. Perhaps knowing which year carb you have or whether or not it has a manual choke. Most common is a vacuum over bi metalic spring version.

The symptoms sound as though the spring for the primary power piston is not functional, or missing. This may permit the piston to sit at rest and never lift when the throttle opens off idle. The spring lifts the piston when the engine vacuum is low, and the engine is not pulling enough vacuum to do it by ltself. This is a critical calibration for Q Jets, and unless you are a fairly decent tuner, you may not even recognize the parts that I have mentioned. Understanding the Q-jet can be interesting. It is not an easy carb to tune, and can be rather difficult. These work well once they are dialed in, but can put gray hair on your head in no time.