Carb help!

Hello to all my fellow mopar brethren!!

I am building a 1050 carb w/3 circuit metering blocks on 110 race fuel from scratch and I need some help with some baseline components. My specs are:

408ci SB in my 2900lbs Scamp on 28x10.5 radials with leafs and caltracs.
10.5 to 1 comp.
550 solid lift cam
Super victor intake w/2" super sucker spacer
904 w/trans brake
8" 5500 ptc converter
4.56 gears

I leave at 3100 and shift at 6400

I currently run a 750 double pumper on 110 race fuel with the following setup:

Jets
Front - 80
Rear - 78

50cc pump front and rear

.110 needle front and rear

Notched plastic floats front and rear set with fuel level half way up sight plug at 8.5psi.

The car has gone 6.68 @ 100.75 in the 1/8 with current carb but with a 9.5" 4500 ptc converter.

So what spec parts should I use for a baseline?

Thanks
BP

Get a hold of Thumper. Maybe if you buy the parts from him, he will share some of his hard earned knowledge. IMHO, nobody has a better handle on the 4500s than him.

I did fail to mention that I am running stock volume virgin port 65cc eddy aluminum heads

First off, why 110 fuel w/that low compression. And that's way too much fuel pressure along w/backwards jetting and several red flags including a 1050 3-circuit on that motor......call me.......760-900-3895 I'll get ya going in the right direction.......

What would be your alternative to the VP 110?

@ 10.5:1 with Eddy heads, you could be running 93 octane pump premium no problem.

I've ran up to 11.4-1 on pump 93, my Dart ran 6.57 in the 1/8 @ 3260# with a 10.8-1 408.

The inconsistency of pump premium is not an option in his car.

Care to explain?.... while the owner may choose to buy race fuel, pump gasoline certainly is an option. My experience says it won’t run one lick different with one vs. the other.

To the OP: don’t think twice; call Dom (thumper).

I have a 3430 lb pump gas Chevelle racing on 94 octane running 8.84 at 150+ with a 1250 I built at 572 cubes and 11.4 comp...........

Suggest calling thumper carbs.
High octane fuel in that engine is just costing you hp.
Never run more octane than you need to stay out of detonation.
Higher octane burns slower than lower octane thus, the lowest octane you can safely burn will make the best power.

I would say I have a fair amount of experience at works and doesn’t work in competitive bracket racing. If you want to put pump gas in your bracket car, have at it. While I’m certain it has enough octane to run his engine, it will never be as consistent.

This isn’t exactly how it works. Higher octane fuel does not burn slower, it merely resists ignition to a higher capacity than lower octane fuel will. Once ignited, it burns just as fast. I’ve done specific testing with non-ethanol 93 pump premium vs 100 octane race fuel. It made absolutely no difference whatsoever in my 10.6:1 451. Over the course of 7 races, I switched back & forth day by day looking for any data variation and found zero. I do like the smell it releases better, but that’s not worth 3 times the price to me.

Fuels, gasoline, alcohol, Diesel, nitro all have a energy rating in BTU per gallon, find the fuel that will make the most heat for your application and get the AFR and tune up dialed in and go faster, no magic on that

I remember hearing that leaded fuel needs more timing due to a slower burn rate weather or not true no clue but I did add timing to my motor running 110 leaded and it did like it....

Start with straight 93 unleaded (E0) and it makes best power at X degrees of advance...

Add 10% ethanol, and you'll require more ignition lead.

Instead of adding ethanol, blend in 50% leaded fuel and your ignition timing requirements will change again.

Start with 93 E10 and then blend in 50% leaded fuel... you're working with yet another set of ignition timing requirements.

This doesn't touch on the changes to the AFR that go along w/ the changes in the fuel being used, either. Stoich for straight 93 is around 14.7; 93 E10 is closer to 14.0; 110 leaded is closer to 15.0...

My apology for stating the obvious if everyone already know this stuff...

This ties into my last post nicely. If your program demands consistency in your fuel supply, regardless of whether you're running 15:1 or 11:1 CR, that's going to have to come from buying a known product at a premium price compared to the latest tanker truck's load of fuel that ended up in the Sunoco or Shell station at the local shopping center.

I don't have to worry about it, but recognize it can be a requirement for others.

Dear Stealth: Burn rates and evap rates DO matter, its not just the heat produced but, how fast the fuel will burn completely.
There are hundreds of articles on this by a plethora of Manufacturers and racing programs.
We are in the age of some pretty exotic fuels as the additives get more and more complex.
We did dyno testing on our known 512 /10.75 /trick flow heads engine to find out what fuel it liked and, yes, race fuel is certainly most consistent, but the engine made best power at 93-95 octane.
100 octane lost 15 hp, no timing adjustments or carb adjustments would bring that back.
110 race fuel lost almost 25 hp.
89 OCTANE was down as well, even with pulling a little timing, but down less than the 110..
When we talked to VP RACING FUELS we were told that the 93/95 octane fuels do, indeed, have a faster burn rate than the higher octane "simple fuels" .
If we were to go to oxygenated or more exotic ( very expensive ) fuels we could pick up a little power as they do, indeed, have faster burn rates .
We were looking for ways to offset the really bad air quality we have in Texas these days and that is only going to get worse as our humidity levels are going to continue to increase year over year- Da values will only increase.
Its normal in summer here to be at a track 500 ft above sea level but Da at 3500-4000 ft thus, we are constantly looking for ways to offset that, the water molecules displacing oxygen in the air.
Of course Vp recommends a fast burn oxygenated fuel thats correct for the compression ratio/cam profile etc.

Still a bit reluctant on those fuel because of the extra maintenance program required and Dom hasn't put out much info yet on working with these fuels.
All that to say, ( sorry for the long post) every time i talk to Vp racing fuels, burn speed is something they bring up .
Its not nearly as critical in 6500 rpm engines as it is in 10-12 k rpm engines but, is indeed, part of current fuel technologies as far as im told, literature we receive.

Hope this is of some small help.

from Vp Racing fuels:

Too Much Octane

You may have heard the following: “don’t use too high of an octane fuel or you will lose power.” This is a half-truth. Having a fuel with too high of an octane will not cause your engine to lose power. The problem is that the popular components used to make the octane of a fuel higher slows the burn rate and a fuel with a burn rate that is too slow can result in an engine power loss. Of course, that is just typically what happens and it does not hold true for all fuels. As an example, VP Racing Fuels worked with the Scranton Brothers and their turbocharged Pro Class Celica throughout the 2002 season to develop a new fuel blend. This blend was designed to provide 120+ motor octane with the quickest burn rate possible. The result was the VP Import blend which produced six percent more power in the Celica than VP Racing C16.

Energy, Burn Rate and Vaporization

Let’s say we have a fuel that keeps our tune-up from experiencing knock. From this point, we would want to find a fuel that packs the most energy, has a compatible burn rate and has a vaporization characteristic that allows for peak performance.

Racing fuels are essentially blends of anywhere from three to 50 components. According to Steve Burns of VP Racing Fuels, “Putting together a racing fuel is like putting together a salad. There are different types of lettuce, olives, tomatoes and dressings. A great salad is one that complements the engine combination being used.”

Some fuel components add energy value to the fuel, some components are good burn accelerators and some components help vaporization. In general, energy values of different racing fuels are usually within three-to-five percent of each other. The burn rate and vaporization characteristics of different fuels are more likely to vary from fuel to fuel. Burn rates need to be fast enough so that all of the air-fuel mixture can combust in the cylinder. If the burn rate of the fuel is too slow, energy will be lost through the exhaust valve. As engine rpm increases, the amount of time that is available for the burn to take place is reduced. In that sense, a fuel that works well in an engine that revs to 6,000 RPM, may not be the best fuel in an engine that revs to 10,000 RPM.

As for vaporization, here is the ideal scenario: The fuel would enter the combustion chamber as a liquid. The reason you would want it in liquid form is that this would not displace any of the air that could potentially make its way into the cylinder. However, when the intake valve closes and the compression stroke gets under way, all of the fuel should change from a liquid to vapor state. With the fuel in a vapor state mixed with the air in the cylinder, the air-fuel mixture can be ignited and a high percentage of the charge will go from reactants to products.

Love my VP-101 OXY Unleaded fuel.............

I'm guessing thats the HP101 , 3.77 percent oxygen ?
Man, please tell me more about your results with that?
Thinking of trying it on the Duster's 511.
Any problems with hurting pumps, carbs , lines etc?
If YOUR loving it, i'm thinking of trying it even though 100 octane lost power on the dyno, but thats a dry room, no air flow through a hood scoop etc.
Plugs look good i'm assuming?
Slight jetting change????

I’m not going to say you didn’t see the results you’re claiming........ but I will say this.......

In 30 years of dyno testing, I have never seen a loss like that by running race gas, no matter how low the CR of the engine was.

Unless........ the race fuel was stale.

If you had fresh 93 summer blend, and a sealed 5 gal can of VP c12....... and dynoed the two back to back on a 600-700hp TF headed 10.75:1 BB stroker with a known good carb on top...... fuel curve and timing all sorted out for the 93, then drained the fuel cell and carb........and dumped in the fresh c12.........it’s not going to lose 25hp.

Not here anyway.

The only time I’ve ever seen any kind of significant difference in power from swapping fuels(assuming they have adequate octane for the combo)....... is going from a non-oxygenated fuel to a heavily oxygenated fuel.
Like, from c16 to q16.

My experience has been that losing 25hp going from pump gas to race gas on a build like that would not be a typical result....... at all.

No problems except for, lowet et's, higher mph and tire shredding torque......

Thanks Dom.

Hi Dwayne: Dyno operator predicted the results within a few hp and vp confirmed the results were within their files as well.
Changing timing did offset some of it, but we couldn't make up the losses.
97 Degrees outside temp, 60 percent humidity - lousy hot/humid day.

carb/timing all dialed in etc.

On the race car 511 , switching from regular old 110 race fuel to c12 and adding 2 degrees of timing- car picked up just as Vp predicted , i think we cut .02

Could we be talking about the differences in being in lower mean altitude and in very hot /humid climate compared to there?

Im certainly confused as to why your dyno experience ( which is more than mine ) would be widely different than we see here.
Jessie ( engine builder chebby guy that owns the local speed shop and is at the dyno often ) confirmed that he see's similar inn playing with fuels/engines at the same dyno.

So, i'm really confused on the differences.

For instance, we tried c16 in the race car and it fell on its face .

Very interesting to say the least.

Dom: Im gonna try some this year then and see if it will allow us to stay closer on our number in the heat of the year when water displaces oxygen in our air.

Rusty, it’s certainly possible the weather contributes to the different results.
I’ve never run the dyno in the type of soup you guys are stuffing with down there in the summer.

Also, not all race fuels are created equally........ and I’d never bother trying to run c16 in a 10.75:1 motor.

But frankly I’d be absolutely shocked to lose anything even remotely close to 25hp by swapping from 93 to c12 out of a sealed can(I’d be pretty surprised to see that type of combo even lose 5hp).

That would be my suggestion for the next time you go to the dyno with something that’s at least 10:1 CR.
Pick up a factory sealed 5 gal can of c12....... and retry the test(if you’re so inclined).

I know of several people who have used several different brands of the lower grade race fuels(like VP Red for example), that got less than stellar results. Although I don’t know if those tests were done using fuel from sealed cans of not.

I can tell you this....... a lot of race fuels don’t keep well at all once the seal has been broken....... so if you’re not testing fuel from a container with a freshly opened seal....... imo you’re leaving the door open for misleading results.

Dwayne: Thats very interesting as we get our fuels from a local parts store or Jessie's and they both just pump from the 55 gallon barrels , never gave a thought about getting stale fuel with race fuel.
Might be a valid reason for re-testing.
The c16 from 110 and c12 was on the 13-1 motor.

i know nothing about weather up there in the summer but, here, its bad , huge water per cubic ft of air just kills us on displacing oxygen.
On the other hand, when it starts getting cold and we get a good, dry, north wind for 14-20 hours, that track at 500 ft above sea level will have Da's at 1100 ft below sea level and i can up the jets a good bit.
Down here, for index racing, you have to run at least a tenth under during cold/dry air in order to run your index from late May through September.

i still say burn rate is very important and running the wrong fuel for the compression/cam is a mistake- at least down here.

On the 13:1 motor, what was the original fuel you were running?

He was running 110 , Vp stated we were on the ragged edge on compression /fuel, said we should go to C12 which lined up with what the dyno operator had stated.
Car didn't like anything more than 34 degrees of timing - at all.
We tried it and picked up power and, it would take a little more timing, which also helped.
Well, if a little fuel change is good,,, so, we tried some 16 - car did Not like it .
This engine has pistons about 14 up out of the hole.
Our best runs are on the C12, 35-36 degrees of timing in the heat , 34 when its cooler /dryer.