The motor is a 350 bored .060" over, flat top pistons, small tube headers into a 3" pipe, stock heads, XE256 cam, Performer intake. The Q-jet used to be on my LG4 305, and wasn't running properly because my car no longer had a computer to control the fuel mixture and whatever else it controlled on the Q-jet. So I found a rebuilt Holley 750 to put on, and installed a new 5.5 power valve in it.

What I'm not impressed with is the fact that the motor will barely spin tires from a dead stop, and is pretty weak on torque, about the same as my old LG4. When I had the Q-jet on, even with it being out of tune and flooding real bad, it still had a lot more torque and would burn the tires all day long. So can anyone give me an idea why the Holley performs significantly worse than the out of tune Q-jet?

 

Probably, it's even worse out of tune. Totally not calibrated to match what the motor wants, or worse.

Follow the "Holley Tuning" sticky at the top of this forum, then come back and let us know if it's any better. Rebuild it (new gaskets & power valves, complete cleanup in solvent, all worn or damaged or non-original parts restored to original, etc.) first, before attempting to tune it. Like anything else, not alot of sense tryong to fine-tune something if it's broke, or if it even MIGHT be. Make it perfect first.

Might have something to do with

whichever ones you happened to end up with. "Stock" for a 350 covers ALOT of ground; from legendary muscle car ones, to deep smoggers from the 70s, to Vortecs, to TBI swirlies. The word "stock" is altogether worthless as identification except to the extent that it means "not aftermarket".

 

Well, I can give the Holley back to the guy I bought it from and get my money back. I know another guy with a non-emissions Q-jet that I can rebuild. The only problem with that is it's a Q-jet, and I'll probably have a time tuning it. Since I have the Holley already, I'll probably just try to take care of it.

 

What stock heads? Some of those "stock heads" are good for 150 hp on a good day, regardless of what you bolt onto them.

Since you're gonna have to tune and you already have the holley, you may as well roll with that. But I will say a 750 is WAY too big for that engine. With that cam you may not even need bigger than a 600, especially with stock heads. That will cause tuning issues for sure if it's a double pumper.

 

That carb is probably isn't helping for such a mild setup. I'd go with a 600-650 if I were you and you'de probably notice a large difference in responsiveness.

 

I used that same cam in my 305 and it was tiny. You have too much carb for that basically stock 350.

 

"car no longer had a computer to control the fuel mixture and whatever else it controlled on the Q-jet"

What about the timing? The computer controlled that too. If you have the old computer controlled distributor still in there, that is a big part of your problem.

 

Mine are off a '69 Corvette which came with 370 hp from the factory.Great heads,and the matching block to boot.

 

Find yourself a 4177 Holley 650 DP and you will be a very happy camper....

 

Sure, so are everybody else's; there's at least 15,000 times as many sets of those in existence today, as there were in 1969.

Not saying "they're not", only, that if you didn't SEE THEM COME OFF OF IT or have other objective proof such as AT LEAST the casting number and date, and you're just quoting what the PO told you, well,,, .... ,,, ....... ...... ... Here's what happens when you believe the PO. https://www.thirdgen.org/forums/tech...ing-block.html

You do the math.

Post a casting number and we can help you identify them. That may well be part of the reason for your disappointment.

Meanwhile, I'd suggest first repairing and then tuning on the Holley, before giving up on it. Also, posting its list # might possibly offer a clue.

 

I'm not the original poster,I never said anything about being dissapointed.I have researched all the casting numbers and know as well the original car the engine and heads came from.Also I don't have a Holly.I think your entire response was supposed to be directed at the original poster, drumminfoolz

 

Those old horspower numbers are SAE gross horsepower, not modern SAE net horsepower. Thast 370hp is under ideal conditions with a big single plane intake and headers. Also with probably higher compression and leaded gasoline of that era. Modern heads are far, far better. Iron L98 heads are probably better.

 

So, why did you bother posting that monkey-spank in HIS thread? How will telling us all about YOUR heads provide HIM with useful information? What benefit was that toward answering HIS question? Or were you just trying to confuse everybody that was trying to help HIM?

 

That is a more important piece of info than what heads are on it.

 

Agreed. The computer controlled HEI has to go away when you ditch the computer controlled carb. An older mechanical/vacuum advance HEI is the usual drop-in replacement in these situations. Relying on the old computer controlled distributor to run the timing once you ditch the computer controlled QJet system will result in very lackluster performance (super weak timing curve) and a pathetic slug of a torque curve.

 

I was told about possibly having too big of a carb by a guy I work with. The problem with that is I'm gonna have to keep what I have or trade it because of financial issues. I adjusted set my TV cable and floats, which helped a lot, but I know there's still some things on the carb that I need to take care of. I have a vacuum advance HEI distributor, and as far as carb and head numbers go, I'll try to post them as soon as I can.

 

Is the carb bigger than you need? Probably. But, it should still work. We now know you have the right distributor. Now, lets hear about the timing? Where is it set (initial, total, with vacuum hooked up, etc.)?