Guys,
I'm getting inquiries from fast bracket racers & TD racers about which way to go.
Applications: BB engines, methanol, single carb blow-thru or dual carb supercharged, almost all are in dragsters.
While happy with the power, some of my blow-thru/pro-charged racers are complaining a little about consistency, particularly with weather changes while my supercharged guys are not. Both are happy with their performance (E.T./MPH).
Thoughts?
Carb'd Procharger vs Supercharger...
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Re: Carb'd Procharger vs Supercharger...
Mike,
Lacking accurate words to explain the happening, consider this. It seems to me, the "natural flow" of air and fuel is by low pressure from under the carb. That was the original design/concept. Whereas "forced flow" from the top is outside the original concept. As you explained, blow through makes good power but there must be some unnatural or disturbing even the makes the fuel distribution and droplets inconsistent. I have no science to back this up, just what seems reasonable to me. I have noticed the fast TD are roots supercharged.
Lacking accurate words to explain the happening, consider this. It seems to me, the "natural flow" of air and fuel is by low pressure from under the carb. That was the original design/concept. Whereas "forced flow" from the top is outside the original concept. As you explained, blow through makes good power but there must be some unnatural or disturbing even the makes the fuel distribution and droplets inconsistent. I have no science to back this up, just what seems reasonable to me. I have noticed the fast TD are roots supercharged.
Larry Woodfin - Team Woodfin Racing - Owner, Woodfin Automotive
Re: Carb'd Procharger vs Supercharger...
The 2 systems do not provide the same RPM vs. boost curve. Positive displacement blowers are generally linear, centrifugals produce boost ~ the square of RPM.
This means that exact launch technique, shift point, etc. are a larger variable with a centrifugal.
This means that exact launch technique, shift point, etc. are a larger variable with a centrifugal.
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Re: Carb'd Procharger vs Supercharger...
A draw through carb has the possibility of taking in relatively calm air. A blow through carb likely has a swirling, tumbling hurricane of air trying to get in. What effect that might have on exposed air bleed jets and other vents when the air blows across them, I don’t know, but it might affect the calibration somehow.
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Re: Carb'd Procharger vs Supercharger...
Yes Mike Laws, you should do some reading up on how carburetors work!
ROFL
ROFL
DON'T PANIC
Re: Carb'd Procharger vs Supercharger...
Are the procharged guys intercooled? You're looking at a double whammy of temperature effects if they are.
A roots blown motor will suck in air at whatever density is on the day and as long as timing and fuel remain right your power isn't going to vary that much.
A centrifugal pump is not a fixed volume pump though and will compensate a little for boost changes caused by extra cooling. (Easily confirmed on a compressor map. Lower boost at the same rpm almost always shows higher mass flow, even if efficiency drops)
Also as stated in an above reply but slightly differently, if your torque curve is flat it's going to be largely flat with a roots blower too, and whatever you end up stalling at will deliver much the same torque off the line regardless of slight rpm variances. With a centrifugal blower on the same motor any increase in density will also raise stall rpm slightly as before, but also raising boost and torque, stretching the converter slightly more and compounding the difference.
I'm not sure on the finer details of drag racing but i know on my old centrifugally blown street car the difference between 3000 and 3200 rpm was visible on the boost gauge, so I could see it affecting traction
A roots blown motor will suck in air at whatever density is on the day and as long as timing and fuel remain right your power isn't going to vary that much.
A centrifugal pump is not a fixed volume pump though and will compensate a little for boost changes caused by extra cooling. (Easily confirmed on a compressor map. Lower boost at the same rpm almost always shows higher mass flow, even if efficiency drops)
Also as stated in an above reply but slightly differently, if your torque curve is flat it's going to be largely flat with a roots blower too, and whatever you end up stalling at will deliver much the same torque off the line regardless of slight rpm variances. With a centrifugal blower on the same motor any increase in density will also raise stall rpm slightly as before, but also raising boost and torque, stretching the converter slightly more and compounding the difference.
I'm not sure on the finer details of drag racing but i know on my old centrifugally blown street car the difference between 3000 and 3200 rpm was visible on the boost gauge, so I could see it affecting traction
Re: Carb'd Procharger vs Supercharger...
Thanks for the insight, good info! There is a definite heat difference between the 2 engines. Boost vs RPM is also very different. I'm surprised no one has tried a 2x4 carb setup with the Procharger... I've noticed there is a trend back toward Root style blowers and am told it's for better consistency but have no personal comparison data.
Mike Laws Performance
Re: Carb'd Procharger vs Supercharger...
The 2x4 carb setup has less pumping loss than a single carb blow thru.. Especially with methanol.
The giant sized single carb venturii are not efficient again especially with methanol
The blow thru customers are 2x4 averse.. They want to run what they see at the track. The carb builders comply with ever bigger venturii Single 4bbl carbs.
The giant sized single carb venturii are not efficient again especially with methanol
The blow thru customers are 2x4 averse.. They want to run what they see at the track. The carb builders comply with ever bigger venturii Single 4bbl carbs.