Longtubes+Blower=?

MiracleMax · 01-13-2001, 05:47 PM

any engine can benefit from a properly designed header. Even a super-charged engine. Until the intake valve opens there is no positive displacement of the exhaust gases. In the case of a header. It needs to be of sufficient cross-section to handle the additional volume of exhaust gas. Say for sh1ts and giggles the engine has a peak VE of 125% on the super-charger and its a 302. Then the engine is equivalent to a 377 cid motor in the volume of gas that needs to be expelled. So lets do a little math here.

First of the SC engine is putting out the same volume of spent exhaust gas as a 377 cid engine, so divide that by 8 = 47.18 cubes a cylinder (VE based)

This is the formula for determining primary pipe size at peak torque (we'll use 3000 rpm)

(CID/8) x Peak Torque RPM/88,200/17724538509 x 2 + the wall thickness of the primary pipe material (x 2) = 1.850 (closest pipe would be an 1-7/8 ). thats at peak torque. Figure peak power is about 1500 rpm higher and plug this in.

(CIDx1900) / (RPM x PPA^2) or

(377 x 1900) / (4500 x 3.7) = 43.02 inches

Okay so on this supercharged 302 with a VE of 125% the engine needs a 1-7/8 x 43 inch primary tube header with a 3-1/2 x 21 inch collector. (using a peak torqe at 3000 rpm and a peak power at 4500 rpm).

This is all just pluging in some numbers and getting in the ballpark. there are more exacting formulas using valve timing events to accurately place the primary pipe length. but it illistruates the point that even a supercharged engine can benefit from a long tube header. IMO before the intake valve opens and the cylinder is blown down via positive displacement of the super-charger.

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01-13-2001, 05:47 PM	#13
MiracleMax Registered Member Join Date: Apr 1999 Location: Hayes, Va, USA Posts: 798	any engine can benefit from a properly designed header. Even a super-charged engine. Until the intake valve opens there is no positive displacement of the exhaust gases. In the case of a header. It needs to be of sufficient cross-section to handle the additional volume of exhaust gas. Say for sh1ts and giggles the engine has a peak VE of 125% on the super-charger and its a 302. Then the engine is equivalent to a 377 cid motor in the volume of gas that needs to be expelled. So lets do a little math here. First of the SC engine is putting out the same volume of spent exhaust gas as a 377 cid engine, so divide that by 8 = 47.18 cubes a cylinder (VE based) This is the formula for determining primary pipe size at peak torque (we'll use 3000 rpm) (CID/8) x Peak Torque RPM/88,200/17724538509 x 2 + the wall thickness of the primary pipe material (x 2) = 1.850 (closest pipe would be an 1-7/8 ). thats at peak torque. Figure peak power is about 1500 rpm higher and plug this in. (CIDx1900) / (RPM x PPA^2) or (377 x 1900) / (4500 x 3.7) = 43.02 inches Okay so on this supercharged 302 with a VE of 125% the engine needs a 1-7/8 x 43 inch primary tube header with a 3-1/2 x 21 inch collector. (using a peak torqe at 3000 rpm and a peak power at 4500 rpm). This is all just pluging in some numbers and getting in the ballpark. there are more exacting formulas using valve timing events to accurately place the primary pipe length. but it illistruates the point that even a supercharged engine can benefit from a long tube header. IMO before the intake valve opens and the cylinder is blown down via positive displacement of the super-charger.