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500 cfm carb horsepower

General engine tech -- Drag Racing to Circle Track

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CamKing
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Re: 500 cfm carb horsepower

Post by CamKing » Sat Apr 13, 2019 1:06 pm

Racer18 wrote:
Sat Apr 13, 2019 11:31 am
Cam King- those numbers are what we have been seeing as well. I do have a 415 with your cam, flat tappet, single plane intake that made 515. Reason for my question is that I dynoed an engine for someone and it made 440 with a 4412, pulled it and put on a 750 cfm carb and it made 495. Customer was extremely disappointed in the numbers because his engine builder told him it was 600 hp :^o :lol: with a 4412 at that LOL
600hp with a 4412. Well, if you're going to lie, lie big. :lol:
BTW, if an engine is designed for the 4412, it shouldn't make much more power with a larger carb. If the engine jumps 60hp, going from a 4412 to a 750 carb, the cam is not right, for the 4412.
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Re: 500 cfm carb horsepower

Post by MadBill » Sat Apr 13, 2019 6:24 pm

Absent a CR rule, a stout 2 bbl. engine could run about three ratios more compression, thus reducing the difference. In the early restrictor plate days I understand Cup cars ran as much as 17:1. (just go easy on the throttle until the revs are up or you risk rattling it to death..)

Re the effect of 2 vs. 4 bbls., an easy test is just to make a pull with the secondaries disconnected. (It's also a good way to ensure that the mixture distribution is good.)
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Re: 500 cfm carb horsepower

Post by BigBro74 » Sat Apr 13, 2019 7:16 pm

MadBill wrote:
Sat Apr 13, 2019 6:24 pm
Absent a CR rule, a stout 2 bbl. engine could run ran as much as 17:1. (just go easy on the throttle until the revs are up or you risk rattling it to death..)








That is no joke^

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Re: 500 cfm carb horsepower

Post by CamKing » Sun Apr 14, 2019 10:59 am

MadBill wrote:
Sat Apr 13, 2019 6:24 pm
Absent a CR rule, a stout 2 bbl. engine could run about three ratios more compression, thus reducing the difference. In the early restrictor plate days I understand Cup cars ran as much as 17:1. (just go easy on the throttle until the revs are up or you risk rattling it to death..)

Re the effect of 2 vs. 4 bbls., an easy test is just to make a pull with the secondaries disconnected. (It's also a good way to ensure that the mixture distribution is good.)
For 2bbl classes, that don't have a CR rule, I ask my customers if they can run a programmable ignition. If so, they can go much higher on compression. You just have to keep the timing back, until the carb starts to restrict, then you can advance the spark, as the manifold pressure decreases.
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Re: 500 cfm carb horsepower

Post by In-Tech » Sun Apr 14, 2019 5:00 pm

That's no joke on the timing, 44 degrees was worth 70hp at 8000 so the pneumatic we had on the mag, rpm activated, was made illegal before the main. It was cool as shit to see the charge on the top end of the half mile track. Hence all the geese were crying :lol: Kinda hard to hide it when the motor is hanging oustide the chassis. :wink: That was back in the 90's, lot's of ways to do it now. But heck, I was the 27 yr old engine builder/crew chief with long hair to my ass. I wasn't liked too much :mrgreen:
Heat is energy, energy is horsepower...but you gotta control the heat.
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Re: 500 cfm carb horsepower

Post by Tuner » Sun Apr 14, 2019 6:35 pm

CamKing wrote:
Sun Apr 14, 2019 10:59 am
For 2bbl classes, that don't have a CR rule, I ask my customers if they can run a programmable ignition. If so, they can go much higher on compression. You just have to keep the timing back, until the carb starts to restrict, then you can advance the spark, as the manifold pressure decreases.
I've been setting up distributors with advance curves that do this since the days of points.
In-Tech wrote:
Sun Apr 14, 2019 5:00 pm
That's no joke on the timing, 44 degrees was worth 70hp at 8000 so the pneumatic we had on the mag, rpm activated, was made illegal before the main. It was cool as shit to see the charge on the top end of the half mile track. Hence all the geese were crying :lol: Kinda hard to hide it when the motor is hanging oustide the chassis. :wink: That was back in the 90's, lot's of ways to do it now. But heck, I was the 27 yr old engine builder/crew chief with long hair to my ass. I wasn't liked too much :mrgreen:
Yes it is. =D>

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Re: 500 cfm carb horsepower

Post by Firedome8 » Tue Apr 16, 2019 9:21 am

Is the additional advance in the mechanical or is a vacuum canaster adding the timing as the vac comes up?

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Re: 500 cfm carb horsepower

Post by Tuner » Wed Apr 17, 2019 12:08 am

Firedome8 wrote:
Tue Apr 16, 2019 9:21 am
Is the additional advance in the mechanical or is a vacuum canaster adding the timing as the vac comes up?
Mechanical. Depends on specific application, but usually advancing 1 to 2 degrees per 1000 above 3000 or 4000 RPM up to above engine maximum RPM, so mechanism does not hit a mechanical stop.

An additional bonus is the the weights and springs advance mechanism acts as a centrifugal pendulous absorber, reducing torsional oscillation in the distributor drive, such as from the oil pump.

Using vacuum advance to add timing at less than WOT load, such as during yellows, reduces exhaust and water temperatures. Obviously, the vacuum advance setup varies per engine specifics, compression ratio, cam timing, carb restriction, intake vacuum, etc.

Because the common electronic ignitions which use mag triggered distributors eliminate the potential inaccuracy of points there really is no reason to avoid vacuum advance. The key is the "correct" vacuum advance (degrees per in. Hg.) for the application.

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Re: 500 cfm carb horsepower

Post by Tuner » Wed Apr 17, 2019 4:21 pm

Tuner wrote:
Wed Apr 17, 2019 12:08 am
Firedome8 wrote:
Tue Apr 16, 2019 9:21 am
Is the additional advance in the mechanical or is a vacuum canaster adding the timing as the vac comes up?
Mechanical. Depends on specific application, but usually advancing 1 to 2 degrees per 1000 above 3000 or 4000 RPM up to above engine maximum RPM, so mechanism does not hit a mechanical stop.

An additional bonus is the the weights and springs advance mechanism acts as a centrifugal pendulous absorber, reducing torsional oscillation in the distributor drive, such as from the oil pump.

Using vacuum advance to add timing at less than WOT load, such as during yellows, reduces exhaust and water temperatures. Obviously, the vacuum advance setup varies per engine specifics, compression ratio, cam timing, carb restriction, intake vacuum, etc.

Because the common electronic ignitions which use mag triggered distributors eliminate the potential inaccuracy of points there really is no reason to avoid vacuum advance. The key is the "correct" vacuum advance (degrees per in. Hg.) for the application.
Poor choice of words in the second sentence above.

I should have said it more like this: An additional bonus is the advance mechanism weights and springs act as a centrifugal pendulous absorber, isolating the torsional oscillations of the distributor drive shaft, such as caused by the oil pump, from the trigger (reluctor or breaker cam).

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Re: 500 cfm carb horsepower

Post by Firedome8 » Wed Apr 17, 2019 7:41 pm

Tuner wrote:
Wed Apr 17, 2019 4:21 pm
Tuner wrote:
Wed Apr 17, 2019 12:08 am
Firedome8 wrote:
Tue Apr 16, 2019 9:21 am
Is the additional advance in the mechanical or is a vacuum canaster adding the timing as the vac comes up?
Mechanical. Depends on specific application, but usually advancing 1 to 2 degrees per 1000 above 3000 or 4000 RPM up to above engine maximum RPM, so mechanism does not hit a mechanical stop.

An additional bonus is the the weights and springs advance mechanism acts as a centrifugal pendulous absorber, reducing torsional oscillation in the distributor drive, such as from the oil pump.

Using vacuum advance to add timing at less than WOT load, such as during yellows, reduces exhaust and water temperatures. Obviously, the vacuum advance setup varies per engine specifics, compression ratio, cam timing, carb restriction, intake vacuum, etc.

Because the common electronic ignitions which use mag triggered distributors eliminate the potential inaccuracy of points there really is no reason to avoid vacuum advance. The key is the "correct" vacuum advance (degrees per in. Hg.) for the application.
Poor choice of words in the second sentence above.

I should have said it more like this: An additional bonus is the advance mechanism weights and springs act as a centrifugal pendulous absorber, isolating the torsional oscillations of the distributor drive shaft, such as caused by the oil pump, from the trigger (reluctor or breaker cam).
Thanks, my dist. tester maximum rpm is aprox 5500 what method do you use to set up curve ? I have considered modification to increase the rpm limit.

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Re: 500 cfm carb horsepower

Post by Tuner » Fri Apr 19, 2019 2:22 pm

Firedome8 wrote:
Wed Apr 17, 2019 7:41 pm
Thanks, my dist. tester maximum rpm is aprox 5500 what method do you use to set up curve ? I have considered modification to increase the rpm limit.
Obviously, stronger springs, but the exact approach depends on the design of distributor advance mechanism, Ford, Mopar, Bosch, GM Delco, or whatever. It isn't simply stiff springs, the geometry of the mechanism has significant influence. The shape of the advance cam is the critical detail in Delco and others that utilize a cam to modify the leverage acting on the springs. The cam has to be a specific shape to achieve the high RPM slope in the advance curve, whereas Ford and Mopar distributors can be setup with a high RPM curve with suitable heavy springs.

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