Why are the exhaust ports "siamesed"?
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Why are the exhaust ports "siamesed"?
Why are the exhaust ports on SBC heads "siamesed" instead of evenly spaced? No contemporary design head is made this way, so obviously there must have been some percieved advantage "way back then" that has since been debunked. Anyone know what it was?
Rich Krause
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'95 Z-28 383 with Vortech, nitrous, etc.
"1FASTZ28"
Rich Krause
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'95 Z-28 383 with Vortech, nitrous, etc.
"1FASTZ28"
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Joined: Sep 1999
Posts: 670
From: Kissimmee/Orlando, FL
I "heard" it was beacuse back in the 50's when the original SBC was on the drawing board they wanted all 8 intake ports as close to the center of the motor as possible. This would help ensure each cylinder gets the same amout of fuel because the carb's of the day did not atomize fuel as well a more modern piece.
Keep in mind this is just theory I heard at one time. I dont know for sure if its right but it does make sense.
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Jason
93 TA, M6
Keep in mind this is just theory I heard at one time. I dont know for sure if its right but it does make sense.
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Jason
93 TA, M6
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Joined: Mar 2000
Posts: 446
From: Texarkana Tx
Thats why I wouldnt mind seeing some of Brodix's IMCA Modified SBC heads on a LT1 car. 
They have the evenly spaced ports just like the LS1 heads. Headers and intake would be a pain to fab up tho. 320cfm out of the box would be worth it. And ppl would be like, is that a Ford in there? Thats the only downside.
Kyle
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Kyle aka Shaggy
Purple 95 Formula
ETFA
12.00@116
They have the evenly spaced ports just like the LS1 heads. Headers and intake would be a pain to fab up tho. 320cfm out of the box would be worth it. And ppl would be like, is that a Ford in there? Thats the only downside. Kyle
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Kyle aka Shaggy
Purple 95 Formula
ETFA
12.00@116
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From: Michigan's left coast
Back in the carb days, the spacing of the intake ports allowed a relatively even path length from the carb to the port. If you do symmetrical ports, it's much more difficult to get a straight shot from the carb to the port with a low-height manifold.
The "mirror-image" SB2 NASCAR head eventually came along 40 years later and addresses this problem. GM had a symmetrical port head for IMSA racing, but they didn't work well with the single 4bbl carb required in stock car racing.
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1996 Impala SS - LT4 396, T56
1996 GMC K2500
1992 Buick Roadmaster Estate Wagon
The "mirror-image" SB2 NASCAR head eventually came along 40 years later and addresses this problem. GM had a symmetrical port head for IMSA racing, but they didn't work well with the single 4bbl carb required in stock car racing.
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1996 Impala SS - LT4 396, T56
1996 GMC K2500
1992 Buick Roadmaster Estate Wagon
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From: 51°N 114°W, 3500' elevation
Could be worse. I saw an old Ford flathead V8 where the 2 center cylinders shared the same exhaust port. A V8 engine with 3 exhaust tubes on each side.
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Stephen's racing page
or check out the race car
87 IROC SuperPro race car
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Best ET on a time slip: 11.589
Best MPH on a time slip: 116
Best corrected ET: 11.079
Altitude corrected rear wheel HP: 468
Best 60 foot: 1.646
Member of the Calgary Drag Racing Association
------------------
Stephen's racing page
or check out the race car
87 IROC SuperPro race car
461 big block
Best ET on a time slip: 11.589
Best MPH on a time slip: 116
Best corrected ET: 11.079
Altitude corrected rear wheel HP: 468
Best 60 foot: 1.646
Member of the Calgary Drag Racing Association
Thread Starter
Moderator
Joined: Dec 1969
Posts: 10,745
From: Buffalo, New York
<font face="Verdana, Arial" size="2">Originally posted by Eric Bryant:
Back in the carb days, the spacing of the intake ports allowed a relatively even path length from the carb to the port. If you do symmetrical ports, it's much more difficult to get a straight shot from the carb to the port with a low-height manifold.
The "mirror-image" SB2 NASCAR head eventually came along 40 years later and addresses this problem. GM had a symmetrical port head for IMSA racing, but they didn't work well with the single 4bbl carb required in stock car racing.
</font>
Back in the carb days, the spacing of the intake ports allowed a relatively even path length from the carb to the port. If you do symmetrical ports, it's much more difficult to get a straight shot from the carb to the port with a low-height manifold.
The "mirror-image" SB2 NASCAR head eventually came along 40 years later and addresses this problem. GM had a symmetrical port head for IMSA racing, but they didn't work well with the single 4bbl carb required in stock car racing.
</font>
Rich Krause
------------------
'95 Z-28 383 with Vortech, nitrous, etc.
"1FASTZ28"
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