Online "calculators" and cam/carb thoughts?

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motorpirate

serial mopar owner
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So, while Dany is learning the basics of Drag Racing with the stock 273 2bbl, the long term plan is a Magnum swap.
I have an '01 out of a Durango with 108K on it that i want to "fluff up" and install for her next.
What i have now:
Stock 5.9 Magnum engine
LA timing cover
Stock Magnum harmonic balancer W/ bolt on pulley
Crosswinds intake
MP elec ign conversion W/ orange box (currently on car)

When I found this thread it looked like it had my name on it!!
360 TrueStreet Magnum Build
If my intake is good for 1500/6500 RPM, The Lunati 20200715 cam (from the above thread) is good for 1200/5500 they seem a good match, right?

This brings me to "online calculators"
I can see the math being helpful as a jumping off point, but how accurate are they in the real world? (especially the ET calculators!!)

if this cam is done at 5500 RPM math says I need a 495/641 CFM carb.
Or, intake is done at 6500 RPM math says i need a 575/744 CFM carb.
If she shifts at 6000 (500 over peak, right?) I am right in the middle.
As an aside I hate Holley's, too many years fighting blown power valves and leaking float bowls on the 80's and 90's (mostly on the fords that came thru the shop) to want one on a toy meant to be enjoyed!!
I had Thermoquads on my cars in those days, and loved them, so i am thinking a Street Demon or Eddy Performer rather than a rebuilt Thermoquad with an adaptor.
is anyone doing serious performance work with either or both of these carbs?

And lastly, the ET calculators show that 370 HP and a 3400 lb car (weighed it on the truck scale at work, 1/2 tank of gas W/ dany in the seat) to run a 12.25?!?!
now i realize that she has to cut a good light, and the car has to hook (figured drag radials with the motor change) and possibly a slant converter, but how realistic is a 12 sec quarter with this simple combo??

Thanks for all the help guys.
we are going to edgewater next weekend to try the brackets there so stay tuned!!
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Well if they give points for "cuteness", she will win, but she's going to have to be fast and cute!!!:steering:
 
The math isn't very good.

I would look at a Holley based carb from BLP or even ProForm. Something with a 1.437ish Venturi. If you are blowing power valves you have other issues.

If you want to run a TQ I wouldn't say not to. Great carb. Just use it on a stock intake. It will do all you want and more.
 
It's all about a matched combo. The calculators will help you buy the right parts. That gets you closer. but it wont tell you that carb has something wrong and you lost 50 hp or that the dist curve is all wrong, causing you to put bigger carb squirters in when you should have bump the timing up 5 more degrees
 
Fiend of mine, 3rd Gen Camaro, stock 350-4, 120k mikes, 3.23 rear gears; runs a 14.2 quarter.

Realistic for you to run a 12 second quarter with your proposed build? Yes. Its mostly about power-to-weight ratio, plus getting that power to move the weight.

Carburetors - regardless which one you choose, there will be adjustments to fine tune it to your application. There is no such thing as "run perfect right out of the box." It may run "good enough." I am in the opposite camp, do not like tuning and adjusting Edelbrock / Carter carbs, just my preference. There are many people on this forum that can help you if that is your choice of carb. Any choice I'd at least run a 670 - 750 cfm.

Good luck, have fun!
 
That carb calculator tells you the smallest carb too run, not the optimal.

If it's a drag deal, put a 750 on it and go. Blown power valves are usually from backfires without PV protection in the carb. Most carbs built in the last 25 years have a check valve to protect the PV. The correction is get the tune up correct. Most people don't run enough initial timing on an engine. This causes other system to be crutched for it to run.

If you are going with an ede, just put a 625-650 on it or the 800. Stay away from the 750 IMO. The 750 has some quirks that have been hard to tune out.

The newer holley no stick gaskets are pretty nice. Scraping sucked that old glued up stuff, yuk!

Yes with good hook in a great set up, 12.20's is doable with that HP.
 
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yellow rose said:
The math isn't very good.

I would look at a Holley based carb from BLP or even ProForm. Something with a 1.437ish Venturi. If you are blowing power valves you have other issues.

If you want to run a TQ I wouldn't say not to. Great carb. Just use it on a stock intake. It will do all you want and more.
Click to expand...

In those days the power valves were all about the ethanol in the gas. Im sure Holleys are the go to in racecar world, I just spent too many hours scraping gaskets on them to be interested.
As to the original manifold, I have Magnum heads, so my manifold choices were Eddy Air gap (wrong bypass fitting for LA timing cover) or Crosswinds.
Both are square bore so thats why I was leaning Street Demon.
But I could maybe be convinced on the Holley if no one on here uses a Street demon for anything but a street carb...
 
motorpirate said:
In those days the power valves were all about the ethanol in the gas. Im sure Holleys are the go to in racecar world, I just spent too many hours scraping gaskets on them to be interested.
As to the original manifold, I have Magnum heads, so my manifold choices were Eddy Air gap (wrong bypass fitting for LA timing cover) or Crosswinds.
Both are square bore so thats why I was leaning Street Demon.
But I could maybe be convinced on the Holley if no one on here uses a Street demon for anything but a street carb...
Click to expand...


Wasn't thinking magnum. Forgot that part of your post. So yeah, that OE cast iron intake won't help you.
 
Holleys are nice because they are quick to work on. And their base low-speed circuits are rich enough to work on a wide variety of combos.
I like metering rod carbs, cuz I can put a pretty lean low-speed circuit in there, and go for the big fuel economy numbers.
Back in the 60s and 70s, Chrysler amassed such a huge empirical data base of P/W and ET information, that they published it for all to see. Ima thinking the calculators echo that data. I'm not a racer so can't speak to their accuracy.
But do bear in mind that there is a huge difference in ET when street trim is involved, more often than not;over a second. So while your P/W may indicate 12.0@111 Mph with SS suspension, actually getting that 12.0 could represent several thousands of dollars. More likely is a low 13. Possibly a high 12. and SS suspension is more than slicks and gears
But I just gotta say; IMO, any 12 is a funtaaaaastic time.
 
Nice setup.... Cam choice is nice . I would look at a 625 or a 750 Street Demon carb series ,depending on converter and gear .
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And forget the slant converter you mentioned, spend a few dollars on a custom built converter, it will make ALL the difference in the world.
 
Cope
Well in my case;
the first time, it was the A833/3.55s and BFG streets,the 292/108 cam, suspension lowered and sprung for speed bump hammering, and drifting in the corners. My 60 fts were heavy into the 2.2s and she trapped at [email protected]/ best of 4 . That 109 indicates 385 hp at my 3650 pounds and should have a minimum ET of 12.2 So I lost .7second with most of it in the 60ft . With 3.55s, 109 is about 6900 in 3rd gear, so some of it may have been there as well.
The second time 4 years later,IIRC
she trapped 93 @ 7.92/ best of 4, shifting at 7000, now with a 230 cam, 4.30s and 325/50-15sDRs and still in the heavy 2.2s,lol. This was on a short track so no 1/4 available.
Mr Wallace converts my 93 to 115 in the quarter which, now at 3467, converts to 422 hp and should have a minimum ET of 11.4.
But my 7.92 converts to 12.55. So this time I lost 1.15 seconds to chassis set-up, with again .5 likely in the 60ft. I still had the same street suspension as I had had 4 years previous, but now with DragRadials and gears. But some of that was also lost in the engine, as I was still shifting at 7000,lol..

I'm not a racer so cannot speak to what those guys run for suspension other than what I read, or see. So Ima thinking I would have to swap out my; 1.03 bars , dual mainleaf rear springs, the HD street shocks,maybe the power steering, the heavy frontrunners, and the lowered ride height. I just don't care that much about ET. But I was ecstatic with the 93trap. For me, just knowing the car's potential was/is enough.
I don't normally mention the ET with my 93trap cuz you know it is pretty slow for 93,lol
 
Thanks AJ!

I enjoy math, just not on paper. I like math with a square, a saw an a bender.

One of these days I'd enjoy picking your brain on some things.
 
It doesn't take much suspension to get your et to match your mph in a 12 sec car. My Satellites best et was 12.35 at 106. 3800 lbs. Super low budget low comp, hyd cammed, iron head 440. Car still had its factory 318 t bars. Only suspension mods : I added a full leaf on each side . Chopped the bottom leaf in half pointed forward on the drivers side. Two half leafs on pass side. A couple of clamps on the front segment of each spring, one right behind the axle. Flipped front hangars to raise the front spring eye and lower the car. adjusted pinion angle with shims. cheap shocks. 8/75 3.23, 10 inch converter that flashed between 3500 and 4000. 28 x9 ET Drags. I didn't have frame connecters on the car at that time , but I recommend them for ALL Mopars , race or street. Proper torque converter is key. More important than gear ratio, IMO.
 
[QUOTE="motorpirate, post: 1972142310]
So, while Dany is learning the basics of Drag Racing with the stock 273 2bbl, the long term plan is a Magnum swap.
I have an '01 out of a Durango with 108K on it that i want to "fluff up" and install for her next.
What i have now:
Stock 5.9 Magnum engine
LA timing cover
Stock Magnum harmonic balancer W/ bolt on pulley
Crosswinds intake
MP elec ign conversion W/ orange box (currently on car)[/QUOTE]
While I’m not a fan of the crosswind intake, use what ya got. But I rather suggest dumping the orange box in favor of a Chrome box or a FBO box, a revenator or a ready to run MSD or Pace Performance ready to run. Same as MSD.

When I found this thread it looked like it had my name on it!!
360 TrueStreet Magnum Build
If my intake is good for 1500/6500 RPM, The Lunati 20200715 cam (from the above thread) is good for 1200/5500 they seem a good match, right?
Click to expand...
A copy can engine build is the best for of flattery. Do it and thank the builder who did it first.
Otherwise, the parts, rpm wise, yes there a good match.
This brings me to "online calculators"
I can see the math being helpful as a jumping off point, but how accurate are they in the real world? (especially the ET calculators!!)

if this cam is done at 5500 RPM math says I need a 495/641 CFM carb.
Or, intake is done at 6500 RPM math says i need a 575/744 CFM carb.
If she shifts at 6000 (500 over peak, right?) I am right in the middle.
Click to expand...
Stay away from in line calculators. They can be misleading and confusing as well as Contradicting.
A 5.9/360 on the street or strip can use a 750 carb very well.


As an aside I hate Holley's, too many years fighting blown power valves and leaking float bowls on the 80's and 90's (mostly on the fords that came thru the shop) to want one on a toy meant to be enjoyed!!
I had Thermoquads on my cars in those days, and loved them, so i am thinking a Street Demon or Eddy Performer rather than a rebuilt Thermoquad with an adaptor.
is anyone doing serious performance work with either or both of these carbs?
Click to expand...
Use what you feel best about using.

And lastly, the ET calculators show that 370 HP and a 3400 lb car (weighed it on the truck scale at work, 1/2 tank of gas W/ dany in the seat) to run a 12.25?!?!
now i realize that she has to cut a good light, and the car has to hook (figured drag radials with the motor change) and possibly a slant converter, but how realistic is a 12 sec quarter with this simple combo??
Click to expand...
Go into the racers forum and the stickies up top are in track ET’s. Each thread has many combos. Big and small block, stock stroke and strokers.
Read carefully. Pay attention to the cars weight IF they listed it like they should have done.


Thanks for all the help guys.
we are going to edgewater next weekend to try the brackets there so stay tuned!!
Click to expand...

Staying tuned!

OH! There is a fella here that has run a stock 5.9 into the low 12’s and he basically (sort of kind of) copied the MP 360/380 create engine.
Now! IIRC, he used the Comp Cam equivalent roller cam, a Edelbrock RPM-AG W/Edelbrock Magnum heads....

IF that member would step up (if he reads this of course) and list his parts..... you’ll be in great shape.
Then again, he might already be in the 12 second thread in the racers forum!
 
I have found the horsepower to weight to et calculators to be pretty accurate. I have run both holley based carbs and my current 800 avs eddy. Ease of adjustment goes to the eddy. Number of ways to adjust goes to the holleys. I think the 800 avs would be fine. It also allows for room to grow when she inevitably wants MORE power! I agree with going to a custom convertor. I have been very happy with my PTC convertor spec’ed by John Cope. Car weighs 3578 with a fat guy in it.
 
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I just plugged my info in the moparts calculators. It says the car should run 11.84 with 425 rear wheel hp and 3578 lbs. it has run 12.02 at 115.02 the difference can be attributed to my small rear tire and only a 1.71 60’ most 12.0’s are going to have much quicker 60’s
 
But that is the problem with online calculators!
A Newbie will take this information go to the dragstrip, and fail, and then wonder why.

As with most things, it is easier said than done.
 
Online carb calculators are way off. They actually pretty accurate on how much cfm passes through your engine. But the problem is the way carbs are rated don't match up to the formula. But it's pretty easy to pick the carb from what known to work. For most hot street sb a 750 cfm is gonna be your carb. Big displacement or full race probably go up to 850 + cfm and low power or small displacement 650 cfm. I think you would have to have a pretty small engine and under 200 hp to go under 600 cfm.
 
IMO, 273 is right.
Ma MoPar gave a general carb listing on what size to use for what you were doing. It is a great starting platform.
 
The online calcs say my dirt track 383 needs about 780 .....my carb guy sez 830 to 850. Maybe 900 if i jump my rpms to 7500. I believe him more than the calculator.
 
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