paulmoore

First off let me say that this is a street/strip engine 383 stroker that makes 500HP. On my last dyno tune, the engine put down 419HP and 430TQ to the wheels. I currently have an Edelbrock 1407 model carb on there now that's a 750 CFM, manual choke, mechanical secondaries unit. Needless to say, my dyno tuner told me that he could pick me up another 10-15 Rear wheel horsepower by switching over to an 850 CFM Holley double pumper. He also told me that it would help with my bog issue(when my Eddy carb goes WOT and the secondaries kick open the motor bogs cause it runs lean due to no accelerator pumps on the secondaries). Needless to say, I think that an 850 CFM carb is too big for my engine, but this guy has been tuning drag cars and carbs longer than I have been alive, so I tend to respect his opinion. Anyways, seeing as how this engine will be on the street, there are a few criteria that must be met. power brakes is a must for me along with the PCV system. It needs to have all the vacuum ports as well. From what I see the classic Holley double pumpers do not come like this(by looking on the Jegs site anyway) and won't be ideal for me. Then I found this carb here...
http://www.jegs.com/p/Holley/Holley-...57757/10002/-1

I am looking at part number 510-0-82851. It has all the stuff I need to run my everyday accessories, but is still a double pumper with true mechanical secondaries(not that secondary air door crap the Eddy carb has) Just curious to see what you guys think, and if anyone has run this carb specifically and if it performed well or not. Thanks for any opinions on this, Paul M

Confuzed1

iTrader: (4)

Looks pretty much like your standard double pumper carb to me - maybe with an additional vacuum connection or two, and it's shiny. They don't explain much about thier "special metering".

My carb is pretty much an HP series carb, it has one small connection for full vacuum, one for timed vacuum, and a big port on the rear for my power brakes. My PCV hose used to go to a fitting on the intake like most cars I know of. Do you currently have both the PCV AND power brake connections going to your Edelbrock carb?

paulmoore

Yeah, I am a little worried about the Special metering thing too. I am hoping that the carb still has some sort of ajustability with it when it comes to jets and all that. One of my friends has one of those NASCAR Holley carbs on his Ford and it has no choke, its an 830 CFM unit, and doesn't have replaceable jets so I don't know how they ended up tuning the thing. But as far as the Edelbrock goes, yes I do have BOTH the power brake booster and PCV hooked up right now. The port on the rear of the carb goes to the brake booster and on the front of the carb there is another big port on the front that goes to the PCV valve on my driver's side valve cover. You can see it in this picture here....


I don't really care about the looks. I am going for functionality and what will net me the best power gain and still let me drive on the street, and I hope this one will do it for me.

heff17

iTrader: (1)

Ive got the 750 version of this carb and its great. It went 530hp on an engine dyno at 6500 rpm and it was just a 355 with bowtie heads. It has plenty of ajustability, you can change jets on the front and back, powervalve up front, it even has removable air bleads up top where the venturi are. All around a good carb, i wouldnt trade mine for anything else.

84 z28

I say go mighty demon.

bluegrassz

iTrader: (3)

I have the same 750 version on my stock bore 350. I just have to let it warm up for a few minutes because of no choke, but other than that its great. I drive mine on the street and track. The vac lines work great.

You should pick up maybe a couple of tenths in the 1/4 also.

Confuzed1

iTrader: (4)

That typs of adjustability exist on most performance carbs. Same on the Mighty Demon carbs also with the addition of idle-eaze.

The only diffences in the one you posted is the addition of the extra vacuum port (which is nice) , and the special metering. I'd say go for it if the vacuum connections are important to you.

If not, I'd look at the Mighty Demon 825 cfm general competition carb. Either is a good choice though.

EDIT: BTW...Nice ride heff17 - Love the color!!

five7kid

iTrader: (14)

Hardly. No choke tower, replaceable air bleeds, 4-corner idle, stainless steel throttle plates, notched floats (for jet extensions), fuel bowls that can be plumbed from either side.

I don't know of any Holley that doesn't have replaceable jets. Your friend's carb might not have replaceable air bleeds, might have a secondary metering plate instead of metering block (not likely).

The "Street HP" are metered for street/strip rather than strip-only, that's all that means.

Confuzed1

iTrader: (4)

The lack of a choke was already mentioned by Bluegrassz. Maybe I should've said - your typical HP series Double pumper to be more exact.

Thanks for clearing that up 5-7....

paulmoore

These are the kinds of responses that I was hoping to hear. Actual people who are using this carb and like it. I think that this carb will work very well for me, and am seriously considering getting it very soon. Fully adjustable stuff is really nice and having the ability to make more power is a plus too. I still tend to lean on the fact that the 850 might be a tad bit too big but I guess they can compensate for it in the tune. I have not had this thing to the track yet because it is still a work in progress but I can tell you one thing; after the 700R4 and 3600 stall went in(and the TV cable was adjusted decently) this thing gets! Spins all the way through first gear, bangs 2nd still spinning the tires halfway through the gear and then chirps third. That's with a 9 inch Ford rear detroit locker and 3.90 gears with 315/35/17's out back. With some slicks, this should be a fun little ride, and I can't hardly wait! Thanks for all the input by the way!

Confuzed1

iTrader: (4)

I think it'll work well for you Paul. I'm running a Pro Systems 750 carb on mine, (Basically a 4150 HP Holley) and I've ran a Speed Demon on it also. Both great carbs.

Once you get it on the dyno, they should be able to set the idle A/F mix, and jet it for WOT. I'm running a 9" rear also with a True-Trac. Wish I had the rubber you have under yours! Sounds like a nice ride you have!

five7kid

iTrader: (14)

CFM = CIDxRPM/3456. That's for a single plane intake, dual planes can use a little more carb.

So, 383x6000/3456 = 665 CFM. A 750 should be fine. An 850 will hurt you in the lower RPMs and on the street. You might gain a little bit of peak HP with an 850, but you won't be faster on the track. And, you can't tune to compensate for too much carb.

Confuzed1

iTrader: (4)

That's pretty interesting. I wonder why Demon has a 825 cfm carb listed for a well prepared 383 - 415 cube engines (5423010GC) when only 665 CFMs are required? I realize it's not 850 cfm's, so are those carbs designed for a dual plane intake?

Demon has a carb selection guide on their website too.

EDIT (Holley does too)

bluegrassz

iTrader: (3)

I vote for the 850 only if you are trying to get all you can out of it at the track. For everyday and some track events go with the 750.

I was running a 750 3310 VS Holley with the choke removed, rear metering block, notch floats, Quickfuel Adjustable VS. I swapped to my 750 Street HP and picked up .15 in the 1/4. I have the PCV system hooked up now which I needed. The pressure from the motor was pushing oil out the breathers.

If you have room, run a phenolic spacer also. It will cut down on the heat building up in the carb.

paulmoore

Yeah, that was one of the major concerns that I had about that carb(or any 850 CFM carb for that matter). I sat down and ran all the numbers for the CFM requirements and all that and came out with the same numbers that you did which is why I was skeptical. It's just that my dyno tuner has been doing this for a long time and when he tells me I should make more power with the 850, I would really like to believe him because he has enough experience to back it up. I also understand that max power at the strip vs street driving are two different animals altogether, and it is really hard to find a seamless blend of power and streetability. Oh and I am using a dual plane intake manifold. I am running the Edelbrock Performer RPM Air Gap, and unfortunately I don't have any extra hood clearance to run any kind of spacer, not even a 1/2 inch one. The cam isn't that big, it's just a COMP hydraulic roller retrofit .520/.540 236/242 110 LSA 106 IC with the AFR 195 heads. Everything flows very well and I have no complaints about any of that except for my Edelbrock carb. It leaves alot on the table in terms of what I want the car to do/perform...

bluegrassz

iTrader: (3)

Im running a RPM AIR GAP with a dropbase air cleaner, 2" filter and a 1/2 in spacer under a stock 92 camaro hood with blisters. Were the HP doesnt have the choke tower, it doesnt hurt airflow as bad. At the track, I dont run the air cleaner anyways.

Get the 750 Street HP. With the choke tower removed and contured venturies I think they flow just a bit more air than a regular 750 dp. You wont be dissappointed.

Your combo has more cubes, larger heads and slight more cam than I. I get good signal with my carb and intake, yours should be a strong runner.

You wont get max HP numbers on the dyno with it, but it is a great combo. Now if you went with a Vic JR intake, more cam and a 850 street HP, then you could see some top HP gain, but you will lose down low and not be as streetable. The great thing about the RPM airgap is it pull through the entire powerband. Its like having the best of both worlds in intakes.

paulmoore

Sorry to be bringing this thread back from the dead, and I'm sure that you guys are tired of reading my posts but I have been doing some thinking and am having a really hard time coming to a decision. I will most likely be calling Holley sometime this week about my engine combo, and see what they have to say about a carb size recommendation. In the meantime, I'd still like to hear what you guys have to say, I've been here long enough and value your opinions. I have run into an issue with my engine after the 5 speed to automatic swap. It seems that having a torque conveter bolted to the engine is loading my engine and causing the engine vacuum to be a good bit less than it was before. I used to run 9-11 inHg at idle with the stick and now I only have 5-6 in Hg and it isn't enough to run my power brake booster. Anyway I will be waiting until after the Holley goes on and it's tuned to see if it will help vacuum, and if it doesn't an electric vacuum pump goes on for the brakes only. Something that I remembered about when I had my car dyno tuned the last time: the K&N substack. When they were changing the metering rods and such on the Eddy carb, they ended up leaving the substack off. and after a few passes they didn't understand why it lost 20RWHP and my AFR's were messed up. They put the substack back on and it returned to normal. Now, I don't necessarily buy into the whole adding CFM thing, but it goes to show that the substack did do something. Possibly sped up the airflow to increase metering signal or reduce turbulence? Anyways, I had some other thoughts and figured that I'd throw them out there and see what you guys think about these...

1. If for any reason my dyno tested rear wheel horsepower drops below 400HP(due to the extra load of the converter), I will be very upset(sorry just kinda **** about that number!). In that case, I MIGHT jump up to a 1.6 ratio roller rocker. I have 1.5's on there now, and have plenty of piston to valve clearance to swing them. My .520/.540 236/242 cam would end up being a slightly larger .555/.576 xxx/xxx(I know they don't change actual duration, just duration under the curve). Would the extra airflow from the 1.5 rockers justify any increase in carb size?

2. The substack. If the 850CFM end up being too big and hurts my lower RPM power, would the substack help it? By it's nature wouldn't the substack help speed up the airflow into the carb and help with the metering signal, and/or part throttle driveability? My engine makes a ton of torque down low, and I don't mind losing a LITTLE BIT of torque to make upper RPM horsepower.

3. My max engine RPM limit. In one of five7kid's posts he gave the formula for CFM assuming 100% VE. In that equation he plugged in a 6000 RPM limit. My engine makes peak horsepower at 6500 RPM. I know that it isn't that much more RPM but it does make a difference, and when plugged into the equation again you come up with...

383x6500/3456=720.34 CFM

Once again, that is assuming 100% VE

I think it all boils down to what I am prepared to accept as streetable. For the most part, I built a race engine and put it in a street car. I really can't expect it to act like a street car. Well, have any thoughts? Fire away!!

Confuzed1

iTrader: (4)

The second quote is from me in an earlier post, and I'm sticking with that. My #2 pick would be a Holley 750 HP, although I don't believe you'll notice any increase in "streetability" between the two.

My old cam was alot like the one you're running now (236/242, same lift - Comp XE288HR) - I ran it in my 408, and it was on the fine line of what I'd consider "streetable" myself. But you should have more vacuum than 5-6 at idle...I had 11-12 on mine with my initial advance set at 21 BTDC. It loped (idled) at around 900 rpm's.

I'm sure other opinions will follow (5-7...where are you??)

paulmoore

Wow, see to me that's a little excessive. My engine has about 18 degrees of inital advance, and the rest comes all in at 2400 RPM. At 3000 RPM i have 38 degrees of total timing. Not sure if I can go any more than that, but I am running 93 octane and my idle speed is just a tick over 750 RPM.

paulmoore

Ok guys, sorry for the double post that I am about to make. I was stumbling around the Holley site and came across an interesting .pdf for the proper carb selection. I had to save the file, open it in paint and modify it to save it as a jpg, but hopefully it will load...



Anyways, as you can see the image from Holley asks for torque converter stall speed and engine size. I am not sure what to make of this chart. If you plot the points on the graph like I did for my combo,(383 CID with a 3600 stall converter), and keep the diagonal line going all the way to section C like they say, it puts me in the 1050 dominator range which I know is nowhere near what I want or need, and would be way too big for me. The horizontal line that you see on the spec sheet is calling for just a little bit less than an 850 CFM carb. It seemed to me to be a more accurate way of what my engine details required but I could be wrong. If I am right though, I am actually surprised that it ended up being that close and not closer to the 750. I am not sure of the validity and/or accuracy of this chart seeing as how there are so many more variables out there to consider when choosing a carb for your engine. Factors like vehicle weight, rear end ratio, compression, cam size/overlap, max VE, etc. all play a big part in it as well. So, whatcha think? Shed any more light on the subject, or am I just beating a dead horse!?!?!?

five7kid

iTrader: (14)

That chart is intended to show you how "small" of a carb you need to avoid bog off the line. With 3600 stall behind a 383, a 1050 wouldn't bog.

It is not saying how big of a carb to put on your engine.

Confuzed1

iTrader: (4)

Not excessive at all. All depends on where the engine likes to idle at, and it's typical to need more initial advance on a bigger duration cam. It's all how you set up your distributor. That's why they come with different springs, stop bushings etc.

-Did you try going to the Demon site? They have a selection guide that's alot more straight forward than Holley. Good luck!

paulmoore

Well, I managed to talk to the guys at Holley today and they gave me some pretty good information. I gave them the usual shakedown of all the info about my motor, and my previous dyno tunes. The fact that the Edelbrock made more power with the substack was most likely due to a restrictive choke horn area, and the fact that the metal that forms the choke tower as well as the choke door all take up space that air could be flowing through. He also advised against getting the 850. He explained how the intake velocity would be slower at the lower and mid range RPM's and that it could hurt power down low. He also said that putting a substack on the 850 *might* help with the airflow into the carb, but that I wouldn't notice a large upper HP difference with it. The 750 would be a better choice as it will allow for better metering/fuel delivery, a more stable idle, and will have no issues supplying my engine up to 6500 RPM, even if I decided to do some other engine upgrades later.. He also said that I could use the substack on the 750 if I wanted, but not to be disappointed if it didn't make any more power. Basically, I would only be using it as a *what if* kind of tuning tool. So I guess that's it. A Holley 4150 Street HP will be in my future here pretty soon along with all the associated fuel lines and stuff. Thanks to all of you guys who have put your in. I just really like doing alot of research before I buy my parts. I understand that most people see things on tv or magazines, like powerblock, or hot rod magazine. They see something advertised tht it will do X, and drop the cash for it. Once they get it installed they find out that the part wasn't all tht great. I would rather talk to people that have the parts, and have experienced first hand any issues or if it worked the way it was supposed to. So thanks to you guys for giving me some guidance.

bluegrassz

iTrader: (3)

Let us know what kind of numbers you get with it. I knew when I bought my 750 street HP that it might be slightly large for my 350. But I plan on going bigger in the near future and didnt want to have to buy another carb .

Good luck and your welcome.