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Old 09-20-2010, 09:10 AM
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Comp Cams grind 4-7 swap

ok so my grind number on my comp cams camshaft is xs274s10, from what i looked into this means this cam is a 4-7 firing swap, however when i was setting up the valve lash in order i didnt notice 4-7 being swapped. is it just the firing order on the distributor which is switched? need some help or advice....thanks.
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Old 09-20-2010, 09:59 AM
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That cam number does not indicate a 4-7 swap cam.

Look at the cam catalog part number. A 4-7 swap cam has a special part number.

You only get a 4-7 swap cam if you order it that way.
The Xs274S-10 cam is not offered in a 4/7 swap, unless special custom ordered.

There is nothing to be gained on mild/moderate street motors with a 4/7swap cam. Its not a nascar motor.
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Old 09-20-2010, 10:13 AM
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I wonder if a 4/7 swap would help exhaust scavenging any on motors with dual exhaust but no crossover pipe
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Old 09-20-2010, 11:54 AM
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cool thanks for the info
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Old 09-20-2010, 04:18 PM
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I watched an episode of horsepower TV and they did a 4/7 cam swap on a mild 383 and gained almost 70 hp. I thought that's not bad for a cam only change.
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Old 09-20-2010, 04:29 PM
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Yes and maybe they did...but at what rpm did they see the increase...maybe 6500 on up?
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Old 09-20-2010, 08:03 PM
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Quote:
Originally Posted by Big D's Customs
I watched an episode of horsepower TV and they did a 4/7 cam swap on a mild 383 and gained almost 70 hp. I thought that's not bad for a cam only change.
It is amusing to think you would believe claims like this from a sponsor driven show like Horsepower TV. Even the people that make the cam will not give you such an outlandish claim.

I would bet the cams duration, lift, and lobe seperation was changed on the 4/7 swap cam at the same time.
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Old 09-20-2010, 08:09 PM
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They failed to place the decimal point in front of the 7....
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Old 09-20-2010, 08:29 PM
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Quote:
Originally Posted by techinspector1
They failed to place the decimal point in front of the 7....
I'd even be willing to maybe believe the decimal after the 7 but before the 0 for 7.0hp gained, but even that is starting to push it for two cams of identical specs except for one being a 4/7 swap.

This is another one of those topics that has been beat to death on engine builder and machinist forums, virtually everyone with documentable results found power gains to be in the single digit area, if gains were found at all. Most agree the best attribute to the 4/7 swap is in different bearing loads and the way the altered firing order changes the order heat is put into the different areas of the block, seems to even out water temps around individual cylinders. Can also sometimes be benificial to mixture distribution being more equalized with some manifolds as the different order has intake runners pulling mixture from different areas at different times compared to standard firing order.

Nothing too remarkable about the 4/7 swap, it makes the firing order the same as the old Ford flathead engines and old 50's Cadillac V8.
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Old 09-21-2010, 09:57 AM
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If the two cams were the same price, one 4/7 one normal, why not get the 4/7 swap cam?
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Old 09-21-2010, 12:45 PM
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Quote:
Originally Posted by Big D's Customs
I watched an episode of horsepower TV and they did a 4/7 cam swap on a mild 383 and gained almost 70 hp. I thought that's not bad for a cam only change.
No way no day- if the cams were otherwise identical w/the ONLY change being the firing order.

This is for the rarefied atmosphere where finding a 1/2 HP increase is considered "significant", IMO. Without tuning and possibly intake design work, carb and port work done to take advantage of the change, there will be no difference in output, in all likelihood.

This reminds me of fishing lures and the way they are named, the way they look and the way they are packaged. It is all about catching the FISHERMAN- not the FISH!
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Old 09-22-2010, 04:42 PM
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Quote:
Originally Posted by Dirty Biker
I wonder if a 4/7 swap would help exhaust scavenging any on motors with dual exhaust but no crossover pipe

You always have two consecutive cylinders firing on the same bank with a crossplane V8 regardless of what you do to the cam. Your only choice is which cylinders. There are several different possible firing orders but all have two cylinders firing consecutively on one bank followed by two on the other bank later in the same cycle. That's what stops the exhaust systems being able to pulse tune effectively compared to a flat plane which is basically two straight four cylinder engines arranged side by side.


found the answer here, http://www.pistonheads.com/gassing/t...0&t=611982&d=0
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Old 09-24-2010, 02:11 PM
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Okay 70 horse gain is rediculous if it was to cams with the same specs. I didn't state all the facts and your right about believing something that's sponsored. The cam they took out of that engine wasn't that big. .510 lift with 236 degrees duaration and the 4/7 was much larger .575 lift and 248 degrees duaration. Sorry about that. I will take the heat on that one.
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Old 09-24-2010, 07:32 PM
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It's cool, we all get things mixed up once in a while- some do it on a routine basis. But no problem, in any event.
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Old 09-24-2010, 08:55 PM
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Has anyone on here ever tried it? I was just wondering if the engine ran any smoother and had fewer harmonics.
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