How much will my car benefit from going to an 850 Holley DP?

A friend of a friend is selling an 850 Holley double pumper for $325. Supposedly, it's brand new, in the box, never use .... The seller has a stockpile of parts that he's acquired over the last 4 decades, so even though the carb is new, it's probably 10 years old. Unfortunately, as of now, I know nothing else about the carb. Not even the model number.

I've looked at different CFM calculators online and most say I should use around an 800 cfm carb; however, Holley's website says 850 or 950 depending on the parameters I input.

So I'm just curious of peoples opinions on whether I'd see a noticeable performance difference between the QJ and the DP. Car specs are in my signature.

Thanks,

Jim

 

Sounds like a great deal..
You won't lose out even if you end up selling it.

 

x2. With your build I think you'll be pleasantly surprised.

Devon

 

The answer depends heavily on how well either carb is tuned.

 

I made a throttle ball that fits the upper bell crank location. Gives my Holley that same longer throttle throw.

 

Still doesn't really increase my gas mileage.

 

Maybe not. Throttle cable snaps on just the same. Pedal and cable range/ travel are forgiving enough.

 

Holley and others sell a bushing to reduce that 1/2" hole to standard 1/4" its just a few bucks. I like the metal ones over the plastic

 

Yep. Mine is one piece stainless. I have used the upper location on every Holley I've used.

 

I was thinking it sounded like a great deal. I think I’ll pull the trigger. Thanks for the feedback!

 

Here is my 800 Qjet and 950 HP Ultra

 

Looks like the Holley came out on top.

 

my vote

 

Scott's findings are typical of the carb swap he did, on a motor trying to make those numbers. It wants the bigger carb. He put a 950 on it. I doubt you would see the same increase with an 850. But maybe.. would have to test on your combo. If it's what is in your signature, what that combo traditionally wants is a 1000HP Holley. Assuming the iron heads are max ported, and flow at least 280/290 at .500 lift.

The crossover point where we start to see gains with the bigger Holleys is typically around 550 HP. If you making less than 500, I have not seen much, if any advantage to a bigger Holley carb, over and 800 QJet.

 

Thanks for the graph Scott and the input Jim. To be honest, I don’t know much about the car. I bought it about 3 months ago. Prior to that it had been in storage for a long time. So the info in my signature is what I was able to ascertain from the previous owner’s files and when I mapped the cam after replacing a broken timing chain. We’re slowly getting the car to run better as we find and fix problems. (I say “we” because at best I’m a backyard mechanic who’s learning as I go and I’m often seeking guidance from friends and people on this site, which is greatly appreciated.) The car seems to run pretty good now, although I think it has more in it. I was just starting to focus on the carb because the idle circuit screw pretty much do nothing and the car runs very rich at WOT. So I was trying to decide whether I should rebuild the QJ or just start fresh with the 850DP. (Hence my original question.) My long-term goal (at least for now) is to get aluminum heads, pick an appropriate cam (if the current one isn’t right), and go with EFI. In the short-term, I’m just trying to get the most out of the combo without going into the motor or buying the EFI.

 

Also, I’d like to add that I was only considering the DP because it seemed like a great deal (and I was hoping it would perform better than a properly tuned QJ).