General Category > Quadrajet Carb Talk and Tips
Exhaust crossover in intake
Kenth:
Any engine not reached the normal operational temperature is cold.
Thats why engineers uses the crossover channel to heat up the manifold as quick as possible.
And, thats why engineers uses the choke on carburator to add fuel until the engine reaches the normal operating temperature.
All parts of the principles of the internal combustion engines, same today as 120+ years ago.
This has NOTHING to do with ambient temperatures, winter or summer.
tayto:
just for the record, i had no intention of blocking the exhaust cross over completely off. i was more curious as to why the factory would use restrictors, or no restrictors or a combination of both so i could make a decision on what to use.
as for the intake, I found very in little info on the marine intake. it apparently is a copy of the old Z28/LT-1 intake where I didn't find a lot of negative "reviews". However, I like to try things for myself as most information found on the internet isn't always correct.
Saying that, Cliff you haven't steered me wrong. if you think it's a waste of time then i wont bother.
68rs/ss:
I see that you modified your intake at the divider and eliminating the four holes into two sides with a small opening between dividers. I would like to try this on my BBC street engine. Are there other modifications that can be done with a die grinder to made the 68 stock Q-jet cast manifold perform better? Some of the corners going into the runners are sharp. Guessing smoothing these would benefit? The stock cast intake weighs a ton.
Phil
Cliff Ruggles:
My intake underwent a series of "modifications" about 20 years ago, followed by dyno, street and track testing.
Right on the dyno it outran the larger Performer RPM by a solid 6HP with no other changes. A company the CNC ports cylinder heads actually has a CNC scan of it to modify intakes in similar fashion.
Removing the exhaust crossover shaved a lot of weight off of it as well. I would actually still be using the crossover but the aftermarket aluminum heads on my engine have no provisions for exhaust gas flow to the intake.
It's worth the time but be aware that those old cast iron intakes are difficult to grind and machine. I have about 8 hours alone just opening up from four holes to two larger openings.......Cliff
Too Fast:
Cliff I see a 1968-69 iron intake for sale for $145. First place I looked has one. From your testing you say this would be a great intake if I modded it like you did the iron one? I have time this winter to do that. I have a .030 over Pontiac 400/Kauffman 74cc heads/4 tube 2.5" mandrel bent exhaust with X-pipe from Pypes. Currently I have an Offenhauser 360 that you previously said to get rid of. Seems to run fine and easily pulls to 5800 RPM but I am always looking for improvements.
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