No of course bigger is not better. From my experiance the opposite is usually the better option. That bieng said I probably just made a mistake, but the price was right. So my car is an 86 cutlass with a ten and a half to one 383 sbc, full roller, aluminum heads, 3.55 gears, with a munci for speed. I origanly ran a 650 double pumper on this set up and the car really responded well to having mechanical secondaries, but it was a swap meet special I should of left at the swap meet. I'm pretty competiant at these carbs, and this one would not clean up at idel. So I finaly switched it for a 750 vacuum secondaries. Which runs very well, but it lost some of its punch. So the power to wieght of the car coupled with the manual trans does kinda call for a mechanical secondary. So an 800 main body came available to me for cheap so I bought it. I have all the other parts to build it right. So I guess my question is do I have a chance at making this work or is going to be way to big. I'm gonna try either way but I'd still like to hear your opinions.
Holley carb bigger is better right
- Thread starter 86judge
- Start date
- Status
Well I once ran a 950 on a 10:1 327 sbc with good results. Not saying the mPG didnt suffer and ran a little rich. What your building will mostlikely work just fine. Its all in the jetting of carb really. Imo.
I think Super Chevy magazine did a carburetor comparison, I originally found it with google. Anyway, they had a pretty stout SBC on an engine dyno and had a stack of Holley 4 barrels and kept swapping them out and running the motor up.
What I remember was the difference between a 650 CFM and a 750 CFM was one horsepower! The 390 was weak and the 1050 was rich but other than that they were all really close. I'll see if I can find the article.
What I remember was the difference between a 650 CFM and a 750 CFM was one horsepower! The 390 was weak and the 1050 was rich but other than that they were all really close. I'll see if I can find the article.
It all depends on what you are doing with your setup. With a 383 a 650 Holley will be a little undersized, but give you better throttle response off idle and part throttle response. It will run out of carb around 6400-6500rpm. A 750 Holley will be the center of road with decent performance across the rpm range and will vary by how it is tuned, gear ratios, and vehicle weight. A 800 or larger will do really well from 1/2 throttle up, but not very responsive off idle. As for mechanical vs vacuum secondaries, mechanicals are better suited for the track since they are controlled by throttle position regardless of speed or engine load. Vacuum are best on the street and for economy because they adjust for engine load and speed.
What kind of intake, heads and whats the cam specs?
The the cubes and air flow all directly relate to carb size.
Bigger isnt always better. The right size is the best option.
Im running a 1000cfm 4150 on my 383. That doesnt mean u should.
The the cubes and air flow all directly relate to carb size.
Bigger isnt always better. The right size is the best option.
Im running a 1000cfm 4150 on my 383. That doesnt mean u should.
You hope you guys know that the HP line is kinda false advertising when it comes to cfm.
The 950HP is Holley's version of a well worked over 750.
The carb shops used to take a 750 with it's venturi diameter of 1.375" and mill the choke horn completely off then smooth the main body.
The standard 750 base plate has a bore size of 1.6875". They would replace it with the 850's base plate that has larger 1.75" throttle bores, then use thinned shafts, and button head screws.
That is exactly what the 950HP uses with a little nicer main body.
If Holley were to use the flow numbers they use for their other carbs it would only flow around 830cfm.
Yes, a standard 850 does flow more than a 950HP.
In some cases people have bolted on a regular 850 and got more horsepower than their 950HP because the engine liked the larger venturi diameter of 1.5625".
It presents less of a restriction to the cylinders and introduces a greater amount of atmospheric pressure to the cylinders.
The 1000HP is Holley's version of a worked over 850.
If Holley were to use the flow numbers they use for their other carbs it would only flow around 870cfm.
The great thing about the HP series is that nice main body, and if you get the right one you can tune alot of the circuits instead of just changing the main jets.
Another thing to think about is that if you have Annular boosters, they don't add cfm, they actually take away from it because their large size creates a restriction in the flow path.
They do enhance bottom end torque a great deal but tend to run rich at the top end. You have to be able to tune the high sped air bleeds to compensate, changing the main jest doesn't do that.
The 950HP is Holley's version of a well worked over 750.
The carb shops used to take a 750 with it's venturi diameter of 1.375" and mill the choke horn completely off then smooth the main body.
The standard 750 base plate has a bore size of 1.6875". They would replace it with the 850's base plate that has larger 1.75" throttle bores, then use thinned shafts, and button head screws.
That is exactly what the 950HP uses with a little nicer main body.
If Holley were to use the flow numbers they use for their other carbs it would only flow around 830cfm.
Yes, a standard 850 does flow more than a 950HP.
In some cases people have bolted on a regular 850 and got more horsepower than their 950HP because the engine liked the larger venturi diameter of 1.5625".
It presents less of a restriction to the cylinders and introduces a greater amount of atmospheric pressure to the cylinders.
The 1000HP is Holley's version of a worked over 850.
If Holley were to use the flow numbers they use for their other carbs it would only flow around 870cfm.
The great thing about the HP series is that nice main body, and if you get the right one you can tune alot of the circuits instead of just changing the main jets.
Another thing to think about is that if you have Annular boosters, they don't add cfm, they actually take away from it because their large size creates a restriction in the flow path.
They do enhance bottom end torque a great deal but tend to run rich at the top end. You have to be able to tune the high sped air bleeds to compensate, changing the main jest doesn't do that.
Thanks for the replies. I knew from the start bigger wasn't better. I just figured that it would draw in anyone that had working knowledge of carbs.
Mathmatlicly speaking a 750 is what it should have. I just want a mechanical secodaries carb. I perfer them, they fit my driving style. And speaking of my driving style idle and cruise speed isn't realy it. Lol. The main thing I was trying to figure out was if it was going to work at all or if it would kill the air veleocity completly. I've just never ran anything that big. So I was looking for someones personal experence on a street setup, but I'm sure its no different then the many motors I've pulled 750 carbs off of because once you put a dress up kit on any small block it needs a 750 double pumper. Lol(side note: you guys notice how many vaccume secondaries are bieng advertised as double pumpers on craigslist) I was kinda suprised at how many people don't know what they own. But any way
I haven't even touched the carb yet. We just got done building our new house which we moved into a week before christmas. So its been a little hectic here. But as far as the cars setup the gear and cam is getting changed before spring, but it still isn't going to require an 800. The runners in the head are not large enough to move that much air and I'm not turning enough rpms to move that much air, but if I get enough mid range response out of it. Which is what I don't like about my vaccume secondary carb. I'll probably run it for awhile, but it will ultamitly be a 750 double pumper. If I don't go fuel injected first.
So just so everyone isn't confused about my opinion on carb size. BIGGER IS NOT BETTER!!!! It gives you volume not velocity which takes cubes or rpms to compensate
Mathmatlicly speaking a 750 is what it should have. I just want a mechanical secodaries carb. I perfer them, they fit my driving style. And speaking of my driving style idle and cruise speed isn't realy it. Lol. The main thing I was trying to figure out was if it was going to work at all or if it would kill the air veleocity completly. I've just never ran anything that big. So I was looking for someones personal experence on a street setup, but I'm sure its no different then the many motors I've pulled 750 carbs off of because once you put a dress up kit on any small block it needs a 750 double pumper. Lol(side note: you guys notice how many vaccume secondaries are bieng advertised as double pumpers on craigslist) I was kinda suprised at how many people don't know what they own. But any way
I haven't even touched the carb yet. We just got done building our new house which we moved into a week before christmas. So its been a little hectic here. But as far as the cars setup the gear and cam is getting changed before spring, but it still isn't going to require an 800. The runners in the head are not large enough to move that much air and I'm not turning enough rpms to move that much air, but if I get enough mid range response out of it. Which is what I don't like about my vaccume secondary carb. I'll probably run it for awhile, but it will ultamitly be a 750 double pumper. If I don't go fuel injected first.
So just so everyone isn't confused about my opinion on carb size. BIGGER IS NOT BETTER!!!! It gives you volume not velocity which takes cubes or rpms to compensate
- Status
Similar threads
