Street Carburetor Preference

[getZ]

Anybody got a brand preference for a street carb. It can be a manual or electric choke, but I'm pretty sure I want a choke. I also think I want four corner idling, but I don't know if I need downleg boosters or not.

 

Right now I'm running an edelbrock (carter) 750 and overall I'm not that impressed with it. Throttle response is sluggish. The combination I have on the rest of the engine is a 388 with about 10:1, dart pro1 200cc heads, 228 @.05 cam with 480 lift. This may be a bit to much carb as well since I tuned the carb with an AFM and landed up going to smaller needles and jets than what it came with.

[ozconnection]

If you want 4 corner idle and downleg boosters on a Holley, may I suggest you have a look at the 4150 HP series carb. The 0-080528-1 have the features you mentioned.

 

The calibration on these Holley carbs is for performance so they may be a little on the rich side for purely street use.

 

You mention sluggish performance after you adjusted your carb using an AFM. What were your target AFR's? Wide open throttle, Cruise, Light accel, heavy accel etc? Getting this wrong or at least not quite where they should be will have a significant effect on performance, be it economy or power.

 

You've probably helped the sluggish nature by leaning things out. Now, in conjunction with the leaner mixtures, did you bump up your ignition timing? Very rich and very lean mixtures can afford to have increased ignition advance because the fuel tends to burn more slowly at these extremes! Give that a try, adjust your ignition slowly and see how you go.

 

It's a combination thing you always gotta be aware of. "If I change that, how will if effect this" is how I work with my engines. I would hold off buying a new carb for a while. Tune up what ya got and see how you get on.

 

Good luck

 

PS, I don't have a Chevy but I do have a Holley...lots of them!!

[getZ]

I looked at a few, Holley HP, Quick Fuel and Barry Grant. I just wonderd how people liked those carbs.

 

When I tuned, I targeted 13 for an AFR, but in all fairness to the manufacturer I need to run the car more while looking at the AFM. I did not realize how different the car ran when under load versus winding the engine up in "park".

[ozconnection]

13 AFR is not quite rich enough for WOT and not lean enough for cruise.

 

I would be looking for 12.5 WOT and 14.5/15 for cruise.

 

Accel should be around 13.5 and idle should be stable at 12.5 but your cam plays a part in this too, so I don't feel as comfortable suggesting the idle mixtures. You need to play around with this yourself to make it idle properly.

 

Reving the engine without load will never give you the info that you need to tune properly. I think you know this now. You can do the tuning yourself on the road or on a dyno. I did mine on the road over several weeks of weekend testing. The AFM you have is an excellent tool to help you do this.

 

Remember the old hot rodders adage; Change only one thing at a time and run it...see what effect it has and record it. It's too hard sometimes to remember everything and whether it helps/hurts performance.

 

Cheers mate.

[grumpyvette]

http://www.jegs.com/webapp/wcs/stores/servlet/PostAddtoCart?inventoryMessage=Monday&nextAvailableDate=&jspStoreDir=JegsDirect&orderId=3513297&inventoryAvailable=Y&catalogId=10002&quantity=1&orderItemId=9144462&langId=-1&catEntryId=285202&addCatEntryId=285202&storeId=10001&ddkey=OrderItemAdd

 

good carbs are expensive but a the race demons in the 825cfm size are very easy to tune correctly

[ozconnection]

http://www.jegs.com/webapp/wcs/stores/servlet/PostAddtoCart?inventoryMessage=Monday&nextAvailableDate=&jspStoreDir=JegsDirect&orderId=3513297&inventoryAvailable=Y&catalogId=10002&quantity=1&orderItemId=9144462&langId=-1&catEntryId=285202&addCatEntryId=285202&storeId=10001&ddkey=OrderItemAdd

 

good carbs are expensive but a the race demons in the 825cfm size are very easy to tune correctly

 

Are you seriously suggesting to this guy that he run a carb like this for 'street' performance? Heck, its for a 460 big block etc and small blocks that rev to 8.5K rpm!!!

 

GetZ, you haven't told us whether its a single or dual plane setup? Engines equipped with dual plane manifolds can accept larger carbs than ones with single plane manifolds. I still think that an 825cfm carb is too big though.

 

Just my 2 cents.

[getZ]

dual plane, performer rpm.

 

I was thinking more like a 750 with down leg boosters.

[grumpyvette]

YES ID RUN THAT CARB ON A SERIOUS sbc that only spins up to about 6500rpm, IN FACT IVE DONE THAT with several 383-406 builds with good results

[getZ]

YES ID RUN THAT CARB ON A SERIOUS sbc that only spins up to about 6500rpm, IN FACT IVE DONE THAT with several 383-406 builds with good results

 

Is my combination considered serious? I would have called it moderate. This isn't only about wide open throttle conditions. I want to consider part throttle response as well.

 

Back to the original question of manufacter preferences, I was asking about manufacturer differences because I've heard a few bad things about certain brands. I didn't want to mention specifics to get biased opinions, so I intentionly did not mention the complaints of others.

[grumpyvette]

HOLLEY and DEMON carbs are generally much easier to tune, trouble shoot and adjust than most of the others, the demon carbs have a small advantage in that they offer more adjustments and finer mettering, now thats a two edge sword, if your a clutz it means your options allow more areas to screw up, but once youve got the basics down , the HOLLEY and DEMON carbs are generally much easier to tune correctly REMEMBER WERE TALKING A STREET STRIP APPLICATION HERE

 

let me say this, if you can follow dirrections and read plugs and do basic carb adjustments the HOLLEY and DEMON carbs make tunning the engine correctly far easier than something like a carter, quadrajet or edelbrock carb that, has less flexibility ID ALSO POINT OUT

that many "carb" problems are really related too or caused by ignition or cam sellection or intake manifold sellection choices, or matching those parts to the wrong compression ratio, rear gearing, or stall speed

 

its hardly the carbs fault if you sellect a great holley or demon carb in the 700cfm-850 range and stick it on an engine combo thats basically a collection of mismatched components and then find its difficult to get it running correctly

 

as an example,

I had a neighbor who constantly played with his classic mustang 390 ford engine, claiming his carb was nearly un-adjustable, I quickly found the problem, his fuel presure was 3 psi , his fuel filter was mostly clogged,and his ignition didn,t advance smoothly, as the rpms increased yet he cussed that carb for months, be fore calling me over to look at his car after swearing to everyone who could hear , his carb sucked!

[getZ]

when you say 825 for a carb do you mean a 750 rated at 825. That's what I was reading last night with the demons or at least what the ad was claiming.

[grumpyvette]

The Rated Cfm Is Almost Meaningless Between 750cfm-825 Cfm. The Important Factor Here Is The Ease Of Tunning And The Quality Of The Fuel Metering

 

 

 

but this may help you

 

http://users.erols.com/srweiss/calcdchg.htm

 

http://users.erols.com/srweiss/calccarb.htm

 

http://users.erols.com/srweiss/calcafhp.htm

 

http://www.rbracing-rsr.com/runnertorquecalc.html

 

http://www.engr.colostate.edu/~allan...a/effarea.html

 

http://www.newcovenant.com/speedcraf...runnerarea.htm

 

http://www.newcovenant.com/speedcrafter/toc.htm

 

http://victorylibrary.com/mopar/intake-tech-c.htm

 

http://www.geocities.com/MotorCity/T...92/vizard.html

 

http://www.bob2000.com/carb.htm

 

http://www.mortec.com/carbtip1.htm

 

http://www.rbracing-rsr.com/runnertorquecalc.html

 

http://www.centuryperformance.com/vacuum.asp

 

the question usually goes " what size carb do I need," or something similar,

4v carbs are rated at a flow rate determined with a vacume or pressure drop of 1.5" of mercury, your best power AT WIDE OPEN THROTTLE AT MAX RPMS will generally be found with a carb that lowers the presure drop or vacume to between 0.5" and 1.0" of vacume, not 1.5" at full throttle,more vacume at full throttle indicates a slight restriction to flow, now on a street car thats not going to be much if any problem, but on a race cars engine, its a sign that your potentially giving away some potential power.

lets look at your comon 600cfm carb some of you guys use, a 0.5 inches of vacume it flows only about 350cfm, at 1.0" it flows about 500cfm, at 1.5" it flows about 600 cfm , rated like a two barrel at 3.0" of vacume it flows close to 780cfm, and if you stuck it on a 600 cubic inch big block spinning 6000rpm youll pull about 6" of vacume and it would flow about 1000cfm plus!

now remember youll try to stay in the .5" to 1.5" range at full throttle, to make good power.

now some of you might notice that the flow dropped NOTICABLY once the vacume dropped and dropping the vacume at wide open throttle tends to help power, provided the a/f ratio is kept near 12.7-13.0:1,AND the engine is set up to USE the flow available to it.

VOLUMETRIC EFFICIENCY

in theory a cylinder fills to 100% full, but the limited time the valves are open and the ports restrictive flow will only allow that to happen at a narrow rpm range

your engines torque curve on an rpm scale closely mirrors the engines efficincy at filling the cylinders, on that same scale, once the cam timing and port flow become a restriction power falls off because theres less fuel /air mix burnt per power stroke, the power tends to keep going up for alittle further in the rpm band simply because theres MORE ,thou slightly less effective power strokes per minute.

at 1000rpm theres 500 intake strokes per minute thats 8 per second times the intake valve opens and closes, at 6500rpm thats 54 times a second, not much time when you think about what needs to flow thru that port in the limited time....especially if you remember that of that 720 degrees in the cycle only about 240 degrees have any useful flow potential, so you just cut even that time by 2/3rds

 

some of you may have figgured out that to get the lower vacume or restriction, youll want a larger carb or perhaps two carbs, remember were trying to get that .5"-1.0" of vacume at full throttle, and that 600cfm carb is not going to flow 600cfm, at that vacume reading but between about 350-500cfm, so if you have an engine that can take full advantage of the flow it may, and usually does require a larger carb to make max power,that 383 might require an 800-850cfm carb or two 600 cfm carbs (since you double the venturie cross sectional area with two carbs the vacume reading is generally cut to about 1/2 what it was and the two 600 cfm carbs now flow about 350cfm each or 700cfm per pair) yet the carb size is just NOT all that critical,to making fairly decent (NOT MAXIMUM POWER) simply because as the vacume signal goes up, so does the carbs flow rate, and as the vacume signal strength goes down so does the flow

RESPONCE!

up till now we are talking only FULL THROTTLE POWER, but you operate under a wide range of rpms and loads, put that larger carb on a small engine and it makes good power at wide open throttle, but it also tends to have a weak vacume signal at off idle rpm ranges and it may run like crap! so a ballance must be accepted. smaller carbs are generally more responsive, but slightly more restrictive with thier smaller venturies.

 

http://www.carcraft.com/techarticles/0304_intake_manifolds_contrast/index.html

 

http://www.superchevy.com/technical/engines_drivetrain/induction_poweradders/sucp_0612_big_block_tunnel_ram_intake/index.html

[dr_hunt]

Anybody got a brand preference for a street carb. It can be a manual or electric choke, but I'm pretty sure I want a choke. I also think I want four corner idling, but I don't know if I need downleg boosters or not.

 

Right now I'm running an edelbrock (carter) 750 and overall I'm not that impressed with it. Throttle response is sluggish. The combination I have on the rest of the engine is a 388 with about 10:1, dart pro1 200cc heads, 228 @.05 cam with 480 lift. This may be a bit to much carb as well since I tuned the carb with an AFM and landed up going to smaller needles and jets than what it came with.

 

Quite the opposite. Your getting good signal and it's pulling alot of fuel so you needed to lean it out. If you had poor signal then you'd have to richen it up.

 

The downleg boosters work wonders on the street.

 

I have never seen an engine pull negative vacuum. IMO they won't do it unless your going down hill in gear.

 

1.5 inches of mercury is a lot more than 1.5 inches of vacuum which is usuallymeasured in relation to water.

 

They are not the same units.

 

Flow ratings mean nothing IMO. Buy a custom Da Vinci, C&S carb, the rest are pretty much all sales hype. I have never been impressed with BG. Nobody that races seriously and makes big HP in circle track uses them.

[getZ]

Quite the opposite. Your getting good signal and it's pulling alot of fuel so you needed to lean it out. If you had poor signal then you'd have to richen it up.

 

 

 

I think you are referencing the needle size? I should rephrase what I meant, numericaly smaller not physicaly smaller. It was off the little chart they give you with the carb. Anyhow it gave me better control of the airflow ratio and gave the plugs a nice brown instead of black, so yes I did lean it out.

 

I like your taste in carbs, but I don't want to spend $700 bucks on a carb. I'd like to keep it more in the $500 range, besides I don't think I qualify as a serious racer, it would only be the occasional run what ya brung type racing and a bit of bracket racing.

 

Nice pics grump. I should finish reading everything you posted before the years end. Work is actualy slow and boring so I have time.

[Pyro]

I would just use a holley 3310, 750 cfm with vac secondarys. A cheap, durable, and easy to tune carb. Plus they get much better mpg than a double pumper.

 

my z ran 11.7's at 120 with a 3310, rpm intake, 292H compcam, 200cc darts.

 

and 10.7's and 135 with a 175 hp n02 shot. also 6.9 at 110 in the 1/8

 

et's were slow for mph because i use gmt5 5 speed and i shifted it really slow so it wouldn't blow up.

 

also had 11:1 cr, 362 cid (3.55 stroke x 4.030 bore, zero deck), full length headers, dual 2-1/2 pipes with hooker aerochambers, r200 3.90, 26 x 8 mt drag slicks, 71 240.

[getZ]

Thanks for the reply. I landed up getting a Holley mech secondary HP 750. Mileage is not that big a concern, throttle response, smoothness and tunability are bigger concerns. I may get a chance to dyno it against the old edelbrock soon.

[getZ]

Got the car started again tonight and there is no comparison between the edelbrock and the holley HP. In a nutshell, you get what you pay for. Idle quality, throttle response and secondary opening (not exactly a fair comparison a vacuum secondary vs a mechanical secondary).

My only complaint might be a cold startup without a choke. We shall see again tomorrow since the carb comes filled with some kind of solvent.

 

I was really impressed with the throttle response, it wasn't that for off from the fuel injection! It may still need a little tuning, but overall I think I made the right decision and I did my share of consumer confidence in spending, at least for the month....

[dr_hunt]

Got the car started again tonight and there is no comparison between the edelbrock and the holley HP. In a nutshell, you get what you pay for. Idle quality, throttle response and secondary opening (not exactly a fair comparison a vacuum secondary vs a mechanical secondary).

My only complaint might be a cold startup without a choke. We shall see again tomorrow since the carb comes filled with some kind of solvent.

 

I was really impressed with the throttle response, it wasn't that for off from the fuel injection! It may still need a little tuning, but overall I think I made the right decision and I did my share of consumer confidence in spending, at least for the month....

 

 

Cool!

[ozconnection]

I'm also happy that your machine is running well