Just kind of doing some searching and reading.

Recently changed my plugs and was astounded by how black they were! I currently run a 1850 4160 600cfm Holley and plan to do the 4150 conversion to get my AFR ratio right because it has to be pig rich. Noticed last night I looked like a freight train (with back barrels open) while a following car illuminated my richly burning exhaust. Also, I know that it's not oil burning :-)

My question is, can a 600 cfm 1850 Holley use the carb main body from a 3310 750 Holley to increase airflow? This seams like the way to go as I can get a used 750 mainbody for cheap and could piece that and my current carb together. The throttlebody would also have to be changed?

Would the bowls also have to be changed? I also don't want to have to spend a year increasing passages .001" at a time to make it not stumble etc if I will have conflicting contrictions.

Just curious if there are any carb gurus out there.

Ben T.

 

No carb guru's here, I guess. . .

What's up, Ben?

Mike

 

A bigger throttle plate may increase flow slightly, but the venturi in the main body has the most effect on flow. Any modifications to the carb may require substantial tuning. I haven't done his exact mod on a 600, so I cannot tell you the exact changes required.

Anything that changes the velocity or pressure drop through the carb, will also change the tuning requirements. This is what pulls the fuel from the passages into the airstream.

Basically on any V8 high-performance engine, you can use more carburetor than a 600. The carb you have is a mild performance type carb. By the time you upgrade to different metering blocks, buy gaskets, jets & spend time getting it right, you may be able to sell the carb & buy one more suited to your application.

You did not state what the application was so I cannot recommend an alternative.

Hope this helps.

 

Lonnie, he's running a GM 330 hp crate motor. It's the 350 cid, 9/1 compression, Vortec head, 212/222 cam motor with 1 5/8" LT headers in a truck.

I've heard of a similar modification involving a 750 with an 850 baseplate. After alot of machine work and hand porting, the final product flows around 870 cfm, but has the booster signal and, thus, response, of a 750. But, as you said, calibration must be done from scratch.

Mike

 

I have seen some 750's with 850 base plates. Yes these do work well, but are reworked considerably. This typically costs in the $300+ range for custom reworks with different boosters etc. These mods are less common (except in serious race type applications) since many manufacturers are making performance carbs in numerous configurations.

You are generally better off with a vacuum secondary carb in a truck. A 750 vac secondary Demon should be a good complement to this engine or any of the Holley variations. I assume you still have the dual plane intake on the engine. A double pumper (mechanical secondary) variety can work well, but is more sensitive to overcarburetion on a heavy vehicle.

The Edelbrock carbs are also responsive & very tunable but I do not have a lot of experience using them so I cannot recommend one in particular.

 

I would also like to point out that a dual plane intake will need a larger carb than a single plane.

With a single plane, open plenum, each cylinder has access to all venturis. But, a dual plane intake only gives each cylinder access to half of the carburetor, so venturi velocity is higher.

If it were mine, I'd do a 750 vacuum secondary and never look back.

Mike

 

There are a lot of parts that can be mixed and matched. My 850 has a large venturi and a large baseplate. The Holley 950HP has a similarly large baseplate but a smaller venturi. It's really just has an 850 baseplate with a 750 body but doesn't have a choke horn so it can flow more air.

There's more to a carb than just the baseplate and venturi size. There are many different metering blocks available. You always hear about someone who doesn't like Holley carbs because it never ran right or was always a pig on gas. Chances are they had a carb that wasn't designed for their application or it was so worn out or out of tune. Even looking at all the 750's available there are many differences between each.

Pick up the book Super Tuning and Modifying Holley Carburators published by SA Design. Jegs and Summit carry it. It's invaluable when you want to start modifying the carb.

My carb has been heavily modified. It's been converted over to alcohol and uses Demon float bowls.

Most of the time a stumble is lack of fuel. The engine needs a rich mixture when the throttle is opened suddenly to compensate for the lean condition of the open butterflies. This is accomplished by the accellerator pump and squirters. If the pump shot isn't enough or the squirters are too small then the engine isn't getting enough fuel and will stumble.

 

Mike,

I accept paypal if you'd like to fund such an effort. All signs are pointing to the 750 and in hopefully not too long I'll get to bolt a nice 3310 to my dual plane.

I think a nice 3160 would certainly be unique too. Do you guys remember that carb? That's the 3-barrel Holley with the single massive secondary opening that measured 1.75 x 3.625".

I think I'll just wait to pickup a nice 3310 then add the secondary metering block and perhaps try to find pickup a proform mainbody. I mean, I just saw the stock 3310 mainbody go for $40 on ebay. I would certainly be willing to spend $60 for the Proform piece.

Also, I agree with the 600 Holley being less than optimum.

...these parts and the help of Engineermike reading the wideband and I should be good to go.

Stephen, I have that book in my library. It makes a good reference.

Thanks for the info guys. I think I'll just try to sell the 1850 600cfm that's on my motor and apply that to get a nice 3310.

Ben T.

 

You can't bolt a 3310 main body into an 1850. Lots of reasons why, but the main one is that the 600's smaller throttle bores won't line up where the 3310 main body meets the 1850's lower throttle body. There will be a nasty "step" there, not to mention the idle passages and stuff won't line up, it'll leak all over the place, have vacuum leaks, etc. Your typical nightmare.

4150/4160 style carbs from 650-800 CFM all use the same throttle bore diameters, however, and so it's easier to play "mix-n-match" when you're in that range.

One of my favorite conversions for the street is to start with a junkyard/swap-meet 3310 (I pay about $60 each for them), rebuild it back to stock specs (Holley has a PDF on their website with all the stock calibration specs- or you can email me and I'll tell you) and then do a 4150 conversion to a rear metering block (instead of the plate) and a quick-change vacuum secondary spring kit. Total cost- maybe $130, and it's better than any NEW 3310 vacuum secondary carb costing 3 times as much.

 

Daman, that's exactly where I want to go. Get a 4160 3310 and do the 4150 conversion to it, but instead of adding the quick change vacuum secondary housing add the adjustable one. This way I can adjust it until I just start to get a vacuum reading at 6000 and then back it off a little bit. I say this because I need a spring in between what comes in the Holley kit. I either get vacuum on the topend or a lean spot. Right now, I've traded my vacuum for a lean spot around 2900. At least this way they fully open.

Anyway, pretty much the same thing you were talking about.

Your sig says you are the last remaining qjet tuner on earth. I have a q-jet if you want it. If you can ship me a 3310 for close to the price you say you buy them for, PM me. You can have the rochester if that's the case!

Ben T.

 

Ben, I appreciate the offer but I don't trade carbs except in special circumstances. Qjet for Holley I'll sometimes do, but I have Qjets coming out my ears.

The springs in the Holley quick-change kit are usually plenty close to eachother in my experience that you don't find one works well and the next one down has serious problems. If you go too light on the spring it generally bogs about 10 feet down the road from where you put your foot into it. It bogs when you nail it and then it recovers and hauls butt through the rest of the gear. An area to look at is the check-ball in the vacuum diaphragm assembly. It's like the "regulator" that SLOWLY admits vacuum into the vacuum chamber to work against the spring tension. If it's not working correctly (or has been removed) you will find that you must use a very heavy (strong) spring to stay out of a bog. Compromising high RPM airflow, obviously.

Generally, if it's going to lay down on you it's going to do it as the secondaries JUST START to open- not midway through the gear unless it just wants fatter jetting or you're outrunning the fuel supply (fuel pressure isn't keeping up).

Most 3310s on most motors can take a spring as light as the YELLOW without a bog, unless the motor's got a big cam and the torque converter is too tight or the ignition timing isn't reasonably close.

What kinda WOT vacuum are you seeing through a run?

 

Everyones right about the 600 you cant interchange body with 750. Base plate has smaller bore size and metering plates are also calibrated to 600 cfm ,it wont run right. If your af ratio is rich first start with your powervalve make sure you have the correct one for your vacuume signal . The number on the powervalve should be half of what your engine vacume is at idle in gear with vacume advance disconnected. From there work with your jetting to further improve your af ratio.

 

I have a double pumper question now. It looks like I might could get a 650 double pumper and use and AED 850 cfm base plate on it.

This should get me adequate airflow, good response, and nice topend power.

What do you guys think?

A nice used 650 with the choke horn cut down to the venturi top and this,

http://aedperformance.com/Accesories.html

The AED baseplate is most of the way down... and also $180 too!

I think this might make a good combo in my 4200 lb truck. I plan to drill & tap the mainbody for changeable air bleeds and am counting on having to modify all sorts of things,

pvcr, bleeds, jetting, etc.

Give me some input please.

Ben T.

 

Ben, the throttle plates/bores are not the restiction in a Holley. Stock holleys use the same 1-11/16" throttle bores from 650 to 800CFM. The restiction is the venturis themselves. That's what Holley fiddles with to get the higher airflow in their carbs. A main body change to something with larger venturis is the way I'd go if looking for more airflow. Of course, once you change things you've now pooched the stock calibration and you'll need to fiddle with jets/bleeds to get things back to "sanity." You might consider how much time/effort you can spend dialing things back in after a main body change before you go that route. You might ask the manufacturer of the aftermarket main body for their recommendations for a "baseline" tune to get you started if you go this route.

End of the day..... you could work a little harder to find a higher flow Holley at a swap meet/junkyard and then you could just look up the stock calibration specs on Holley's website for it. I recently scored an 800 CFM double pumper for $25 at a swap meet. Guy thought it was a 650. He was wrong. I was armed with better information and "stole" it from him for cheap. He never knew the carb was worth more than what he sold it to me for. I HIGHLY recommend dowloading the Holley PDF off their website. It's got almost all the list numbers for their carbs, CFM ratings and calibrations specs. I carry this list around with me at swap meets when looking at carbs so I know what I'm buying before I buy it. The guy selling it doesn't know what he's got about 50% of the time.

If you do buy a swap meet carb I have additional information about them (metering block numbers, pump cam specs, etc.) that are NOT listed in the PDF file. In short, I have almost everything you could want to know about them to make sure they are correct and complete before you start serious rebuilding/tuning efforts.

That being said, I'll remind you that I've long been known as a Rochester QJet bigot- they're my bag. But remember that just beacuase I say that I don't have any use for Holleys doesn't mean I don't know how to make one sing.