Port/header interference
Thread Starter
Teching In
Joined: Feb 2005
Posts: 11
Likes: 0
From: near Sears Point Raceway CA
Port/header interference My GM Fast Burn crate motor has "D" shaped exhaust ports, requiring "LT1/LT4-type exhaust header flanges".
Only Edelbrock makes air-tube equipped headers this car needs to pass emissions tests. The header tubes alternate between 1-5/8" & 1-3/4" OD to maximize scavenging effects. He said the 1-3/4" pipes will clear the D ports, but the 1-5/8" pipes will slightly block the ports. Two tubes per V-bank will clear the ports, two tubes per bank will have partially blocked ports.
The tech continued, saying that because the performance is generated upstream in the head, the four partially blocked ports won't decrease power. He said air leaks are the only risk, & that a tight seal would result using Fel Pro gasket #1407 (may need minor trimming).
Do you folks agree with the Edelbrock tech, or do you believe the blocked ports will impede performance? If so, how much hp might be lost? I want this motor, but with all 385 hp, & without the high cost of custom headers.
(I only repeated this post from another forum because there were no replies.)
Only Edelbrock makes air-tube equipped headers this car needs to pass emissions tests. The header tubes alternate between 1-5/8" & 1-3/4" OD to maximize scavenging effects. He said the 1-3/4" pipes will clear the D ports, but the 1-5/8" pipes will slightly block the ports. Two tubes per V-bank will clear the ports, two tubes per bank will have partially blocked ports.
The tech continued, saying that because the performance is generated upstream in the head, the four partially blocked ports won't decrease power. He said air leaks are the only risk, & that a tight seal would result using Fel Pro gasket #1407 (may need minor trimming).
Do you folks agree with the Edelbrock tech, or do you believe the blocked ports will impede performance? If so, how much hp might be lost? I want this motor, but with all 385 hp, & without the high cost of custom headers.
(I only repeated this post from another forum because there were no replies.)
Teching In
Joined: Oct 2004
Posts: 49
Likes: 0
Though it's true that exhaust flow travels considerabily more through the top portion of the port, I wouldn't install a header that masks the ports at all. At higher engine speeds, impeding exhaust port flow can and will have a negative effect on overall performance. Of course how much it's affected is relative. When we designed our flanges for LT1's these issues were addressed. We gave ample room for stock and even highly modified port outlets. Nick "Kook's Headers"
