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Old 02-01-2010, 06:49 PM
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Will adding a 1 inch carb spacer affect carb tune?

Hello guys I have not been driving my truck which is a chevy s10 with a 350 sbc and I just had my carb tuned good but had to put a set of new plugs in cause of being gas and oil fouled from swapping out a couple of different carbs to get a good one running nice. The carb was tuned nice and good and did not have any issues with a constant miss till plugs got bad.

Ok I put a 1 inch 4 hole spacer on to have an extra vacuum hookup source for my pcv and I have noticed that while cruising around at 1900 rpm I seem to have a very slight and very faint miss. I don't have any miss at idle or while driving through town just when I am going at a steady 1900 rpm. Could the carb spacer be causing the carb to be doing this?

I read from somewhere that a carb spacer can affect your A/F mixture ratio but I don't know what affect my spacer would have. Would it actually help with my mixture and make it burn better or not? I have not noticed any difference with it being on there just the miss I was wondering about. Wires and everything else is new and the wires are just 8mm stock replacement type.
Thanks guys
Eric

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Old 02-01-2010, 07:54 PM
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Not saying it couldn't but I've added and removed spacers many times and never had it adversely effect the carb or cause a miss.
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Old 02-02-2010, 10:37 AM
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Quote:
Originally Posted by eric32
Hello guys I have not been driving my truck which is a chevy s10 with a 350 sbc and I just had my carb tuned good but had to put a set of new plugs in cause of being gas and oil fouled from swapping out a couple of different carbs to get a good one running nice. The carb was tuned nice and good and did not have any issues with a constant miss till plugs got bad.

Ok I put a 1 inch 4 hole spacer on to have an extra vacuum hookup source for my pcv and I have noticed that while cruising around at 1900 rpm I seem to have a very slight and very faint miss. I don't have any miss at idle or while driving through town just when I am going at a steady 1900 rpm. Could the carb spacer be causing the carb to be doing this?

I read from somewhere that a carb spacer can affect your A/F mixture ratio but I don't know what affect my spacer would have. Would it actually help with my mixture and make it burn better or not? I have not noticed any difference with it being on there just the miss I was wondering about. Wires and everything else is new and the wires are just 8mm stock replacement type.
Thanks guys
Eric
Maybe, manifolds don't do a good job of supplying every cylinder with the same mixture ratio nor amount of WOT flow. To properly set up a carb monitoring the overall fuel ratio in the exhaust stream is an inadequate approach, rather each cylinder needs to be monitored separately and the carbs jetting set such that the leanest cylinder is correct. This will make the rich and correct cylinders more on the rich side but there isn't a lot that can be done about that without going to a carb per cylinder or fuel injection. The miss you're experiencing is most likely a cylinder that's a bit on the lean side.

A carb spacer can cause these kind of problems, they change the flow pattern of mixture exiting the throttles which can effect the cylinder to cylinder fuel distribution. They increase plenum volume which can effect the signal on the booster. They increase the distance from the valve to the venturi which can affect the wave tuning effects at the venturi and booster.

Sometimes these affects are good, so that's what the advertisers use to sell these. But sometimes the affects are bad, which doesn't get mentioned in advertising claims. You have to think of these things as a tuning tool, some set ups like 'em, some don't care one way or the other, and some don't like 'em.

Understanding that you're using them as a vacuum source rather than a tuning tool. If you can find a cylinder running richer or leaner than the others by looking at the spark plugs you could adjust the jetting. Sometimes a multi strike spark box can overcome these light load misfires as well.

Bogie
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Old 02-02-2010, 10:48 AM
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I went from a 1" to a 2" without the slightest problem.
Just a better responding carb and smoother acceleration.
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Old 02-02-2010, 11:15 AM
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Taken from the Knowledge Base & NHRA

Racing Technology
Tuning with carburetor spacers

by Wayne Scraba


The art and science of tuning headers
Most people think of carburetor spacers as simple horsepower-increasing devices. But that might not be completely true. Certainly, in some cases they can be used to increase engine power levels, but, more important, they can be used as a sophisticated tuning aid. Spacers often provide an increase in top-end power, but at the same time, they can reduce bottom-end power as well as mid-range torque. Typically, power gain comes from increased plenum volume, but that's not the complete picture.

The manifold dilemma
Using a single-plane intake manifold as an example, you must first realize how a single-plane intake manifold functions. Generally, a single-plane intake includes a large, centrally located plenum that has reasonably straight runners leading from the plenum to the port entries in the cylinder head. In this configuration, a large common plenum is under the carburetor. According to the experts, this common plenum allows each runner and cylinder intake port combination to draw from all four carburetor venturii at wide-open throttle. As the partially vaporized air/fuel mixture leaves the base of the carburetor venturii, it forms as four individual mixture streams. When each of the cylinders places a demand on the plenum chamber, these mixture streams, or in some cases portions of the streams, physically bend in the direction of demanding runner/port entry. The mixture "streams" combine to form a single "mixture river," which flows into the runner, eventually feeding the cylinder that is making the demand.

Moroso Performance Products points out that the beauty of a single-plane manifold configuration is that it allows each runner to withdraw a larger volume of air/fuel mixture during the available induction time span. Unfortunately, life isn't always simple — and neither are intake manifolds. As each cylinder withdraws a charge from the plenum, the mixture streams are forced to change direction constantly. Creating more havoc inside the manifold are pressure pulses that travel backward from the cylinder into the manifold runner and eventually into the plenum. And some engine combinations have more of this reverse pressure pulsation than others. These constant directional changes in the plenum along with pressure pulses can create a healthy amount of turbulence inside the plenum.

The cure
Moroso notes that some single-plane intake manifolds are designed with a very short-turn radius coming out the bottom of the carb venturii into the respective entries of the intake-manifold runners. When the carburetor is moved up — most often with a spacer — the velocity of the intake charge is reduced, which in turn allows the previous mixture streams to make the bend around the corner, or short-side radius, easily. In certain applications, a short, 1/2-inch spacer will work, but in other cases, the manifold design dictates a larger spacer.

It doesn't take a rocket scientist to figure out that the addition of a spacer effectively increases the distance between the carburetor and the floor of the plenum. Because of this added distance, the carburetor signal is weakened. And when the signal is weakened, a larger jet or jets in the carburetor will be required. Carburetor spacers designed with four separate holes tend to recapture the velocity of the mixture stream that gets lost when an open carburetor spacer is installed. In simple terms, more exit velocity in the mixture stream creates a stronger carburetor signal than that found with an open spacer. Generally, the jet size will still have to be increased when a four-hole spacer is used, but not as much as with an open spacer.

How much spacer should you use? As a rule of thumb, single-plane intake manifolds seem to respond best with larger spacers — two inches in height and larger. On the other hand, most dual-plane intake manifolds work best with open spacers with a height of between 5/8-inch and 1 1/2 inches.

The market is filled with dozens of spacer styles and configurations. Some spacers are manufactured with insulating materials. These spacers decrease the amount of heat transferred from the intake manifold to the carburetor throttle plate and main body. This reduces the fuel temperature inside the carburetor. Naturally, the result is a denser fuel charge to the manifold, which in turn creates more horsepower.

Spacer materials
Believe it or not, plywood can be an ideal material for constructing carburetor spacers. The thin layers of laminated wood, bonded with resin, form a natural heat sink. For example, a wooden Moroso spacer features top-quality hardwood plywood with a sheet of phenolic resin-impregnated paper bonded to both sides. This creates a durable product that can be used in drag racing, circle track competition, or on the street.

Plywood spacers are easy to modify to suit a given manifold for optimum performance. On the other hand, phenolic spacers are constructed from an advanced material similar to plastic that can reduce heat conductivity 10 times greater than aluminum for a much denser air/fuel charge. Obviously, aluminum spacers are still widely available. The advantage in aluminum is that it can be easily modified for a given application. The disadvantage is that in some cases, an aluminum casting can be porous. Because of this, several manufacturers now offer billet-aluminum spacers CNC-machined from 6061-T6 material.

So how can spacers be used to improve performance? The folks from Moroso provide this theoretical example: You have a car that hooks. It works well, turning the tires slightly during the rollout. Everything is fine until you're up against a track that's greasy after the launch pad or provides conditions that resemble a mine shaft. Typically, the car still hooks reasonably well, but on the 1-2 gear change, it turns the tires heavily (in this case, assume that the engine rpm is brought down to the torque peak on the gear change). The e.t. goes away, and so does the consistency.

Now what? It's a tough situation to "tune" out. None of the normal tricks work because they kill the launch. That's where a spacer can be used. Add a spacer or increase the spacer height and increase the jet size by a couple of numbers. The launch will remain almost the same, but the increased plenum volume helps to shift the torque peak and peak horsepower upward. Because of this, the engine isn't dragged into the meat of its torque band during the gear change and it doesn't turn the tires. The result? A quicker e.t. and a bunch more consistency.

That's but one area where spacer tuning can work; however, there are dozens of other tuning applications, especially those where you have to tune to the engine, the car, the track, or the atmospheric conditions.

One final item to consider when buying or testing carburetor spacers is hood clearance. If the carburetor air horn is moved too close to the hood, then the airflow and fuel metering can become restricted. If the airflow is restricted, you simply won't be able to take advantage of the spacer.

Are spacers for you? That depends on your application, but if you don't tune with them, you could be missing out on some easy e.t.
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Old 02-02-2010, 11:24 AM
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and spacer info from the BG carb site tech articles:

http://www.gnetworks.com/v4files/bar...h%20images.pdf

what intake and cam are on the motor????
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Old 02-03-2010, 06:36 PM
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Hello guys man thanks for all the great info. Well my engine is a Chevy 350 with a edelbrock rpm performer and my cam is a crane powermax hydraulic roller with 222/230 @ 50 duration with 510/520 lift with 5 degrees of overlap at 50 duration and a 112 LSA. My carb is a holley 1850s 600 with 69 jets in the front and 75 in the rear and 31 size squirters. The carb runs excellent on my engine but the last set of plugs got fowled from previous carb issues and my stupid pcv sucking up oil but another post as well.

I put a new set of plugs in the other day and they looked nice and clean after a nice highway run and some town driving. Color was grayish color on porcelain part with a few specs of tan showing as well. I don't think the missing is coming from plugs cause they are new and at WOT there is no surging and did not have any previous misses at cruising but now at 1900 2000 rpm I do. Its like a constant miss but nothing major. Hope that helps out.
Eric
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Old 02-04-2010, 10:52 AM
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does it miss at constant 1900 in park in the garage? (no load conditions)

use the throttle linkage idle rpms adjust screw to set it to constant 1900 and then go listen all over the truck for where is it coming from...
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Old 02-04-2010, 03:12 PM
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OP.. I am experiencing a similar miss too,kinda, mine is between 1400-2700rpm and is almost a periodic very short stutter, this occurs at a set/held RPM between 1400-2700.. Acts like a faulty spark plug/lead/boot or a crack in the dizzy cap. Mine does not do this under hard accel or WOT and appears worse or more noticable when cold/cool. I beleive its carb tuning or in my case I have purchased the incorrect series of carb for the amount of duration within the cam..as of now I have a BG Speed Demon 750cfm mech 2nds..

Combo:72 Chevelle(heavy bamf) 355cid SBC,10.5:1, iron heads big valves, Comp cam 253*@.050 with .544" int/ex set @ 0*, Magnum 1.5 roller tips, Vic Jr intake, Demon 750, MSD Pro billet dizz, MSD 6A, MSD SS Coil, MSD 8.5mm wires behind it is a TH350 w/minor upgrades, 3800rpm stall..10bolt rear.

According to BG my intake "signal" is too slow, the "Speed Demon" series does not have the appropriate metering capilbilties to overcome this.. My main issue is a NASTY off idle bog that I have adamently tried to tune out, with others and BG's assistance.....BUT..I do beleive that my miss/periodic stutter is due to this. BG recomended as a band-aid to install a 1" thick 4-hole spacer to speed the signal up, but it didnt cure it..helped..sort of. Dont know if Holley Carbs could ever suffer from this or not...Just a thought..

Wheeew...

My timing is set @ 18*base, 32* all in by 2400rpm, im still playing with timing as this build is still fresh.
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Old 02-04-2010, 04:04 PM
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Generally...upsize jets.
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Old 02-05-2010, 08:54 AM
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Coletrane,,,
lose the Victor Jr open plenum and mount a dual plane...

open plenum=at low rpms, the one piston that is on the intake stroke is trying to pull a vacuum from the entire huge intake cubic area in a very short time window and both carb primaries are exposed for air leakage...

dual plane=piston pulls from only half the total intake area volume and due to the divider wall under the carb the piston is pulling against only one carb primary worth of leakage...

the victor and your cam choice is a "race only" rpms operating range configuration...

carb cfm is correct (basically)

Last edited by red65mustang; 02-05-2010 at 09:04 AM.
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Old 02-05-2010, 08:58 AM
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Quote:
Originally Posted by red65mustang
Coletrane,,,
loose the Victor Jr open plenum and mount a dual plane...

open plenum=at low rpms, the one piston that is on the intake stroke is trying to pull a vacuum from the entire huge intake cubic area in a very short time window and both carb primaries are exposed for air leakage...

dual plane= pulls from only half the total intake area volume and due to the divider wall under the carb the piston is pulling against only one carb primary worth of leakage...

your cam makes for next to no HP/TQ at low rpms/low Hg due to valves timing and the Victor is making it beyond tune-able
Keep the Vic Jr. A dual plane would not match the rest o the parts well, if anything step up to the Super Vic. You need a carb swap, as already indicated by the tech's at BG.
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Old 02-05-2010, 09:23 AM
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AP,
I re-worded my post (lol,,,as always...)
his choice,,,
he can have more power over the whole rpms range with a dual plane for "street manners" or just have a small percent more power at the HP peak with a open plenum...

off the top of my empty head illustration:
victor at 1900 is 60HP/170TQ with his cam(????)
dual plane is 90HP/220TQ (????) at 1900 due to higher HG=better velocity and cylinder fill and more better results per rpms with more rpms versus the victor...

not until the motor rpms actual total cfm exceeds the dual plane capacity will the victor actually make more power...

a compromise choice can be a RPM style dual plane which has a small part of the divider wall removed so it does behave like both types...
1900=75HP/200TQ???? with the RPM

edit: I checked my numbers "guesses" against my analyzer and they are in the ballpark,,,,rough numbers only because I don't have head spec's....

Last edited by red65mustang; 02-05-2010 at 10:07 AM.
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Old 02-05-2010, 12:24 PM
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eric32

i dont know if all these people are gay-but ...disconnect your vac., advance crank your timing up - and have a good time!!!!! your combo needs alot of timing. i had this problem w/a low comp. 327 untill i dissed the vac. adv. + cranked the timing to 40!!!
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Old 02-05-2010, 05:26 PM
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Well to answer a few questions asked it only happens under load while driving through town or highway in normal driving. Hard acceleration there is none. I also have a slight miss at start up but it goes away after a few minutes. I got my carb tuned very well for idle and I used my vacuum gauge to do so. My timing is at 16 degrees with vacuum plugged off and I have a total of 32 total by 3000 rpm.

My plugs are brand new and it did it the very first time I drove it with the carb spacer on. I am thinking either its a very very faint light surge at that rpm from being just a tad to lean or the plug wires doing something. My cap is in excellent shape as is my coil etc. I have a new one setting aside and I might put it on once the weather breaks and see what it does.

I also only have a set of stock type plug wires and plan on getting something better then 20 dollar wires. Only got them cause I kept burning plug wires and boots and have finally fixed that problem. It seems to me the carb spacer is the culprit and I may have to go up one more size in jets on the front.

Eric
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