4 7 cam lobe swap
#21
I was thinking that 7 and 8 next to each other would be worse than the benefit of the 4 next to 2 swap. Never mind that 4, 2 and1 are all in a row. I think the center cylinders (3,5,4,6) are fed the best by the LT1 intake and that is where the adjacent pairings are with the stock firing order.
Last edited by 93Z2871805; 02-28-2011 at 02:56 AM.
#22
I saved these links off of camaroz28.com because I thought about going to a 4-7 cam swap for my next cam. Im running a pro-systems carb with a traditional SBC ignition so easy for me to convert my LT1 over. These are some of the best threads on 4-7 info pertaining to LT1's I could find. People like (Mindgame, jmlab, Injuneer, etc...) all were in deep thought and discussion about this swap so enjoy the read. Its a shame there is not a lot of this type of tech talk on ls1tech about LT1's like there used to be, good for us we have people like you guys that still bring the love on LT1's.
http://www.camaroz28.com/forums/show...t=4-7+cam+swap
http://www.camaroz28.com/forums/show...t=4-7+cam+swap
http://www.camaroz28.com/forums/show...t=4-7+cam+swap
http://www.camaroz28.com/forums/show...t=4-7+cam+swap
http://www.camaroz28.com/forums/show...t=4-7+cam+swap
http://www.camaroz28.com/forums/show...t=4-7+cam+swap
#25
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Here's another link from HOT ROD Magazine, it's on a 492ci BBC, but a 4/7 swap nonetheless.
http://www.hotrod.com/techfaq/113_07...ams/index.html
http://www.hotrod.com/techfaq/113_07...ams/index.html
#26
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you will need some tuning work if you do this. One thing that comes to the top of my head will be the injectors will need to be reassigned to their appropriate banks if the engine is intended to run in closed loop
#28
Very true sir. I included it because of what's involved in the swap and they go a little bit into expert opinions (both good and not so good), theory, and what they saw on their control. I'd doubt the gains they saw on a BBC with aftermarket aluminum heads and a .712 lift cam is going to be anything close to what you might see on SBC, unless it's moving alot of air and/or turning high RPM.
#29
I do, however think the OEMs did the swap based on some kind of testing that showed improved reliability. They had to have some kind of real data (other than just an idea) to make them switch from a firing order that's been standard from 1955-up.
#35
This quoted part seals the deal for me:
The 4/7 swap gets you part of the way there.
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."
#37
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This is a very good read, i have done this on older sbc but never thought of attempting this on a lt1 efi car. Gregrob are you going to do this for sure? i have never heard of anything negitive about the 4/7 swap anywhere.