4 / 7 cam swap

[TruckMuddr]

ok, I've been meaning to ask this for awhile now.

Whats the point of doing the 4/7 cam swap?????

I know it changes the firing order to 1-8-7-3-6-5-4-2 and now number 5 cylinder and 7 won't fire next to each other, but now 2 and 4 are firing next to each other.

I just wanted to know what everyone thought about this???

[fastTa]

It is said to reduce cranshaft deflection due to the changed firing order.

Every internal combustion motor that has a crankshaft, experiences a measurable amount of flex or twisting. This is caused by the spring-like properties of steel or most metals for that matter. When the a/f is compressed and then ignited, it exerts an enormous force on the journal of the crankshaft and consequently distorts the cranshaft. Well the crankshaft naturally attemps to spring itself back into it's orginal shape, but by doing so over corrects.

This happens over and over and over throughout the spinning of the motor. So anytime you can help to elimnate crank deflection, you can free up a little HP.

I have also heard rumors that this has shown to make the motors run slightly cooler as well.

Don't expect much in the way of power increase though. I've heard reports of 3-6 HP and 7-10 lb/ft of TQ.

[N20LT4Bird]

How do you do it?

[Injuneer]

There's also the advantage of separating the #5 and #7 intake events, reducing the impact of the adjacent cylinders pulling from the intake plenum.

LT1 is tricky, because of the sequential fuel injection... along with the "4/7" cam, you need to swap the injector wires, and the plug wires. Then you have the "unknown" issue of having the "banks" of the PCM "mixed".... in closed loop, you are trying to control the A/F ratio for a full "bank" of the engine, and with the 4/7 swap, you have 3 cyls from one bank + 1 cyl from the other bank.

There was a very good thread - long, 75 posts - on the CamaroZ28.com "Advanced Tech" forum:

http://web.camaross.com/forums/showt...hreadid=225034

[TruckMuddr]

So, not really worth the trouble that comes with it?

[Kevin - Blown 95 TA]

There's also been a lot of talk on the LT1 Edit list. Whether it is worth it or not depends on your wallet and the amount of time you have to spend on it. Like Fred said, the closed loop control is affected because there is one O2 sensor per bank, and unless you can hack the program, there might be slight problems with fuel corrections. Open loop wouldn't have that issue.

Probably not worth it to change over an average engine, but the professional racers that are searching for every advantage use these type of enhancements, and some of the newer engines are made that way.