4/7 swap
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Teching In
Joined: May 2013
Posts: 24
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4/7 swap looking to send heads to either l/e or a/i for full p&p & milling not sure if i sure do a 4/7 cam swap or stay with normal firing order how beneficial would it really be has any1 done this on this swap
TECH Apprentice
Joined: May 2009
Posts: 323
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From: NW AR
There is people that do the 4/7 and the 2/3, cam lobe switch. Many people have ideas about what it does. They say it prevents cylinders from firing next to each othere but all it does is make the 5-7 become 4-2 firing. Another theory i've heard is that it balances out the torque made in the engine so that the mains dont wear as much. I dont believe any of that enough to spend money on it.
Joined: May 2004
Posts: 1,593
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From: Halfway back on the Highway to Hell...again!
I had this discussion with my machine shop guys and they build some badass motors. And just like shbox said, nothing to be gained. According to them, it's only optimal for cars that will spend their entire time above 5500rpm. i.e. drag cars leaving the line at 5500 or dirt track/sprint cars.
There is a little to be gained, but we are talking single digit numbers. Carbureted engines show more due to 5 & 7 pulling fuel so close is the difference there. I have heard 12 for one carved engine. Otherwise, for an EFI engine it's supposed to be easier on cranks, blocks & bearings. I changed my firing order, but it was a new cam so no back-to-back same day, same cam lobes on an engine dyno so can't say it was worth anything. My bearings always looked like new anyway, so can't see a difference there either.
If I were building another one I would do it for a high dollar (those cam core cost more) race engine due to gains seen by pro engine builders that have back-to-backed it. We are looking for every hundredth we can find. I would not spend the time & money to just change that. You would never know the difference in a street car.
If I were building another one I would do it for a high dollar (those cam core cost more) race engine due to gains seen by pro engine builders that have back-to-backed it. We are looking for every hundredth we can find. I would not spend the time & money to just change that. You would never know the difference in a street car.
10 Second Club
Joined: Oct 2007
Posts: 2,630
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It helps with the bearing loads. This is right from a GM engineer:
If there was a case of #5 robbing fuel from #7 in a standard sbc firing order then the 4/7 swap wouldn't do anything because it puts #4 right next to #2 in sequence.
In the realm of OE production engines, the altered firing order is said to increase engine smoothness. In fact, when we questioned Gen III valvetrain engineer Steve Pass, he said the firing order was dictated by the crank guy. That was Bill Compton, who had this to say via e-mail: "Since the G3 engine was a clean-slate project, each group looked at things that they could change to optimize the performance of the small-block. Although we did not have an issue with crankshaft loading on the older V-8s, there was room for improvement in the area of distributing the peak firing loads among the five crankshaft journals. Analysis showed that main 4 had peak loads significantly higher than main 2. By changing the firing order, the peak loading on main 4 was reduced and the peak loading on main 2 went up. Overall, the loading through the mains was much better balanced. By improving the load balance across the crank, we created a better balanced oil film interface across the crank. The valvetrain group simply changed the cam lobe timing to work with the new crank firing order."
Read more: http://www.hotrod.com/techfaq/113_07...#ixzz2hSj3ff9n
Read more: http://www.hotrod.com/techfaq/113_07...#ixzz2hSj3ff9n
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The op asked about the 4-7 swap. The engine builders I talk to tell me with the 4-7 swap only the 2-4 fueling issue isn't as bad as 5-7 was. It isn't that simple. Has to be the manifold. I know the fast Super Stock guys running single plane intakes on SBCs have a LOT of work in them, including altered divider lengths.
I had $3500.00 in the one I tested. My old Hogan was faster, and cylinder-to-cylinder air/fueling needed much larger corrections than my Hogan sheet metal. There are several fast LT1 SS guys running single planes with elbows in SS (we have to run stock TBs) but some may be faster with a Hogan. Your results may vary.
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