Carburator question

[Hal Copple]

I'll offer my experience with the Holley's, as i have run all three.

My Windsor is stroked to 396 ci. Performer RPM intake manifold.

first carb was the silver finish 4160, had a metering plate rather than a rear metering block. You adjust the secondary "jetting" by getting different metering plates. Userful choke, etc. But under a very short (because of hood clearance) air filter, so the air down into the primary (choke) side has to make a very abrupt downward turn into the carb. Remember, at full throttle the primary side has to suck as much air as the secondary side.

Swapped in a rear metering block, cost about $45 or so, then i could more easily change jetting. But makes the carb about 1/2 inch longer, so needed new fuel lines.

Put in a 50 cc squirter, replacing the 30 cc one, but then you can only use one of the several "cams" for the squirter.

Then cut off the choke tower, to allow more air flow down into the carb. This was several hours to do right. With straight leg boosters, if you cut too much off or try to match the sculpting of the Pro, the "boosters" are a bit high to properly meter the air, which now can come around the booster, instead of vertically past it. Be careful about this with the standard straight boosters.

Then swapped out for a vacuum secondary Holley 750 HP Pro. It is very pretty, with no choke of course, and very sculped air inlets, with down leg boosters. Bob Olthoff recommended a vac secondary carb for street use, avoids some bog on throttle tip-in.

Here is what i have learned and experienced. Bought four or five Holley books, so that eventually i became comfortable with a pretty extensive Holley tear down, and learned theory of what does what on these carbs. My car ran best at low rpm street driving, with a four hole 1/2 inch phenolic spacer (for reducing carb heat with winter gas, and fuel percolation on a hot-soak re-start). An open spacer caused some hesitation on throttle-tip-in, as the RPM manifold has a separated plenum, completely separating the two cylinder heads induction. I put in road race floats.

Found that tiny adjustments in the spring loaded squirter adjustment made for big changes in low rpm part throttle tip-in, more is not necessarily better, i had flawless low rpm drivability with less rather than more squirt, i think because my car is much lighter than the usual Mustang or Camaro.

Found i don't need a choke for my starting and initial running with out a choke on any of my carbs. You can see how you like no choke by simply unhooking (and taping) the choke wires in the winter for awhile. I can start it easily in temps down to freezing (i live in SC), and ease the rpm up, and drive right off, and within a mile, the exhaust heated intake plenum works to give good cold drivability. It was no loss to give up a choke for me.

I found the lightest spring in the vacuum secondary gave more than 40 # of torque and 40+ horsepower in the mid rpm range on a chassis dyno!!! Cheap for 7 bucks!!

It also showed no trace of power curve disruption on the dyno pull either.

Found the only change that seemed to increase the feeling of power was the change to the lightest spring, and when i put on the HP carb.

My speed shop pro, very helpful to me, (he is actually a big Demon fan) told me the power of the HP probably comes from the special metering blocks used, they are definately not the ones that come in the metering block kit for a 4160. He said it is metered "very aggressively". I found each change, for some reason, seemed to increase my cruise MPG. Go figure that one. Which is why justing putting the sculpted center you can buy for about $120 may not make much difference, as the power comes from the different metering blocks, more than the sculpting of the inlet.

He told me, and i have heard first hand from several others, that sometimes a Demon is fabulous, and sometimes no matter what you do, you can't get them to run just right.

Don't change too much with any new out of the box carb, there are hundreds of adjustments you can do to a Holley, i only changed jetting on my HP, and put in a different squirter nozzle, to give a longer/ less abrupt squirt for momentary enrichment on throttle tip in. I left the squirter cam and its setting stock, etc.

For use, i occasionally spray carb cleaner down the air bleeds and thottle plates, gas slowly gums things up, keep my linkage clean. Make sure your carb plates fully open up to verticle, and yet don't over-travel and bend something. Learn what your pedal does to your throttle plates. Have your linkage perfectly adjusted.

Here is what i have found. First, thoroughly learn what does what on your Holley, so you don't make things worse with tinkering. I have sure done that before i decided to learn carb theory.

A choke is not necessary for me at all. The more power my carb modifications gave, the better my highway cruise MPG was!

All my carbs gave absolutley perfect low rpm and drag race/road course drivabilty, with never any bog or lag. By "tuning" only the squirter spring, done by going out and driving with a screwdriver and wrench, and turning the setting in minuscule amounts, made all my carbs run pefectly.

Be sure you have adequate fuel delivery, big filter you change often (lots of debris gets into the fuel with the open LeMans type of cap when you flip it to refuel. A dampened fuel pressure gage is very useful in the cockpit to see what pressure you are running and if the fuel pump can keep up on a long pull. I run AN 8 lines off a 3/8 inch hard line, all gently curved AN fittings, so maximum fuel flow is available.

The Holley Pro gave a noticable "seat of the pants" increase in power.

When i was talking to my "drag consultant" about how my car seems to be making so much more power on a cold night, he said then i must be jetted too rich in the secondary side, so that the cooler, more dense air was a bit "leaned out" and i should drop my rear jetting a bit when it warms up next summer. I am intentionally rich with 80 secondary jetting, to avoid engine risk from detonation on the long long straight at full throttle at places like VIR.

But my best drag strip quarter mile, run on a cold night, with a prepared track, (ideal circumstances) was still with the original, unmodified carb under a small air filter!!!

In summary, you can indeed get fine drivability and excellent performance with any appropriate sized Holley, but for me, the power seems the best with a slightly tweaked HP 750 on my engine, on an RPM intake manifold.

Don't waste time spending a lot of time and money on trying to modify a 4160, use it right out of the box, or move up to a Pro Holley HP.

I can trundle along at 1000 rpm in fifth, and accelerate in fifth with no hesitation nor stumble. It can't get better than that.

[Mr.Fixit]

Originally posted by Cobra #42
Sorry to disagree with your comment about not using a dyno with fuel /air & EGT measurement mr. fixit, but I wonder how one can read a plug at every rpm range from idle to redline ??

Guys have been making more HP than you ever will, prior to EGT probes or multi-gas analysers. Idle is easy, you can put a vacuum gauge on it, or just go for highest idle speed by trimming out the idle mixture screws, then re-adjust idle speed at the throttle blades. After that, run it hard for 1/4 mile, push clutch in and kill motor, coast back to the pits then pull plugs and inspect. Once you get the plugs looking good, you will have to most likely adjust the squirter/pump cams, and make fine adjustements to the transition circuits. Adjust for as little gas as you can in all the perameters, without turning your plugs ash white or having any stumbles in any rpm or condition, these things run too rich most of the time reguardless. The problem with dyno tuning a carb is the dyno puts a different load on the engine than the car will, you are fine tuning it for a condition unlike it's home in the car. The dyno tune will be close, but you probubly just paid somebody a few hundred dollars at least to do that tune to it, so you won't want to change his work. There's more to fuel curve tuning than looking at sparkplugs or reading the monitor attached to the smog machine, you must use your ears, eyes, nose, and "seat of the pants" to determine under what conditions you need more or less gas. The instinct is to go more gas, but you should try for less gas until it stumbles, then richen it up until the flat spot goes away. But by all means, if you really want to, run EGT probes in you car's headers, you will get an important measure of what's happening in the combustion chambers, and buy them from Exhaust Gas Technologies in anaheim CA.

[glasssnake]

I have a sugestion for your carb delema! you can send your carb to this company and give them your motor specs cam ect and they will set your carb on a flow bench. take it out of the box and it will be right. first off I have used many holly carbs they are nice to work on and ajust, but I have seen many straight from the plant that had the rong parts in them. so even if you get a new carb I sugest getting it checked by the pros. Now on the co pilot thing get in the summit book and they have fuel fragrances that will make it smell rilly nice for her. apples,cherry,groovy grap ect by manhattan oil If interested in that carb @ me be more than happy to hook you up . Mark Check my pics to see one

[Flyin_Freddie]

Hey, 347...I'm running a Performer dual plane, with 1/2" phenolic spacer under my Holley 750-HP, and a 1/2" aluminum spacer on top between the carb and air cleaner. I'm running a FoMoSpo 14" round air cleaner with a K&N filter. The engine would perform better with a 1" phenolic spacer...even better with a 2" spacer....but I'd have to butcher my hood and I don't want to sacrifice the original hood look.

Mr. Fixit...you're right about the differences between the 4150-HP model Holleys and non -HP models. Indeed, there is a huge difference in the metering and overall quality of the carburator. Bottom line, at least in this area, you do indeed get what you pay for. You can spend $250 or $600 .... one is a good carburator, the other is a GREAT carburator. And your tuning explanation is exactly the way I remember it... drive ... stop ... pull the plugs and read 'em ... adjust something and go do it again.

Not meaning to take anything away from anyone elses preferred carburator, be it Barry Grant, AED, Street Avenger, Speed Demon, Road Demon, Carter, Quadrajet....or Staniframitz...which ever one seems to work best in your application....

[Cobra #42]

No fixit , I don't pay anyone , I have a Dynojet in my shop and we use it on every car in the place. Try tuning a turbo 1000+ HP Honda 4 cylinder, by looking at the plugs Kenny Tran 8.59 *New National record Sport Compact Hot Rod class is one of the guys I work with.

[Mr.Fixit]

Tuning for forced induction is a whole different can of worms. Except a roots blower with a pair of Holleys on top, that's still relatively easy. Any serious (re: not a street rod, but a racecar) blown or turboed engine deserves EGT probes in it's headers to keep that investment in one piece, and make all the power it can. It is all to easy to make great power, just in time to find out you burned holes through the tops of all your pistons.

[Jack21]

Which manifold for a carb'd 351W? You have two choices, Edelbrock Performer RPM, and Wiand Stealth. I'm using the Ede, but I can't say that one would offer any advantages over the other.

Opinion. The Ede air gap would be a good 3 season intake, but miserable to live with in the winter as an daily driver.

Carb. Am using a Holley 700CFM double pumper (4778). Came with 69 primaries, and were way too rich for roller motor (CompCams retrofit hydraulic roller 224/224 - .533/.533) and roller rocker arms. Roller cam pulls 15" - 16" vacuum at idle. Running 64 primaries presently. 78 secondaries have been left untouched.

Getting idle mixture right has been an exercise in adjusting secondary idle opening, while positioning primary butterflys into proper location with primary transition slot. Have not resorted to drilling holes into primary butterflys...yet. Replaced secondary idle screw with Allen head setscrew that can be adjusted with engine running. Close, but no Cigar.

Contemplating replacing Holley with Demon 650 double pumper. Virtually all the published info I've seen lately use Demon carbs replacing the age old Holleys for better street (and track)performance.

Comments???

[DAVID GAGNARD]

Guys;

Holley's own formula for determining carb cfm size for any given internal combustion engine goes like this;

Maximum RPM x cubic inches divided by 3456...assuming that given engine is 100% efficent....

Example; My 351-W-----6000 rpms x 358 cu in=2,148,000 divided by 3456= 621.52 cfm needed for my engine assuming it is 100% efficient,Assuming it is at least 90% efficient,I would now only need 559.36 cfms to operate it at it's max potential.

I have run everything from 600cfm Holleys with vac sec. to 715 Marine Holleys to highly modified 750 holleys and the best,fastes,and quickest at the 1/4 mile was an Auto Zone rebuilt Holley 600 vac sec for a whopping $150.00.......

David

[scottj]

There is another formula for sizing carbs; 1.3-1.4 cfm per horsepower on gas and 1.2-1.3 cfm per hp on alky. When you get into application specific modified carbs they refer to carb size as throttle plate dia and venturi dia anyway.

Re: Demon vs. the age old Holleys- I know the Demon is all they write about in the hot rod mags and as a result every other car at cruise night runs one, but they are almost non-existent at race tracks. By race tracks I mean circle and roadracing, which is much more demanding than drag racing when it comes to fuel curve management. At race tracks, Braswells are the standard by which all others are measured. The Holley HP was designed by Dave Braswell to be a production carb with the advancements of his custom modified carbs. The HP makes higher peak power, broader overall power, and has better throttle response than any past Holley. The only 4bbl carbs that meter fuel better than the HPs are the modified HPs and only the good ones. I'm not going to bad mouth Demons, in fact I had a 825 cfm race Demon on the Cobra for 83 street miles and it had good drivability. I also ran the Demon on a circle track car and in both applications a Blake modified 4150(non-HP model) was the same as the Demon and a 4150 HP had better drivability and throttle response than either.
Scott

[bly]

Thanks for all the great responses to my post. The carb I have Is a 4150 model I beleive, I purchased it off e-bay, seller said the number was #4779. supposodly rebuilt and dynod. I bought it for 150.00. Installed it, started car and the secondary accel. pump cover started pouring out fuel. removed cover to install new gasket and found diaphram to be old and crusty replaced, (so much for it being rebuilt), then found two screw holes on fuel bowl to be stripped causing leakage, helicoiled, leak stopped. ran engine again, noticed a constant drip coming off of primary boosters. Pulled off again took to performance shop to be rebuilt (90.00) Put back on ran, same accel. pump cover leaking again. took off, heli coils pulled out. Took back to perf. shop and they replaced the bowl for no charge. Put back on, leak gone, tuned carb, shut motor off and noticed fuel leaking out of primary boosters again. Tried to adjust floats to stop leak, no help. I also put some of those clear float bowl sight lenses on, one broke off and now that leaks. Im done with this carb i belieive, I coould've bought a new one almost for what i have spent on this one. I am thinking of a new 4150 650 DP. If I do get new, Is anyone interested in the 750 I have, Will be relatively CHEAP! Thanks again for all your input. Bly.

[Flyin_Freddie]

Hell, why don't you just take it off, empty out the float bowls, clean it all up and everything and ...

USE IT FOR A DOORSTOP!

Or....buy another one off ebay, chain them both together, and use them for wheel chocks....

Even better.....attach a heavy chain on the carb and use it for a boat anchor..

Man....I feel your pain...I'm sorry for your wasted time, effort, and money. I hate it when something I bought as a bargain turns out to cost more than it would have to just buy a new one...HATE IT!

Be sure and go back to ebay and 'rate the seller'. Let everyone else know what kind of merchandise this seller has had for sale so no one else can be burned like you were.

At the risk of sounding opportunistic, I have a Holley 4160 750 cfm double pumper for sale in the Club Cobra FOR SALE section. Electric choke, vacuum secondaries, lightest weight secondary spring, etc. I'll personally guarantee it won't leak, and cause the problems you have already had. This one was working when I removed it from SPF #770 last month, and was put in the same box as my new 4150 750-HP came in. I know, I know.....I'm sounding more and more opportunistic....I agree. But, I'm not going to use it...if you can, then I can save you some money...if not, that's okay by me, too. I'll just leave it in the box and it'll wind up at some swap meet in the next few months.

Let me know if you're interested. I work for FedEx, so I can have it to you tomorrow if you'd like.

[Mr.Fixit]

If it is continually dripping fuel from the boosters, I would take the well plugs out of the metering block and clean out the metering block. There may be some debris or a poorly machined passage in there. Or just put a new metering block on the primary side and see what happens.