Lunati "4/7" cams
02-18-2004, 09:48 AM
#31
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Originally posted by 96Z28SS
Jim there is no difference in the 2 eDist boxes they are exactly the same only difference is that the LS1 part number comes with the LS1 coil harness mating connectors. I think just recently they list the box as the same part number, but the harness are 2 different part numbers. You can check with FAST on that but I'm pretty sure the boxes are the same you just change the pins on the harness.
Also in the Setup menu or System config menu, (I can't remember) in the FAST system you can change the firing order to anything you want.
Rob
Jim there is no difference in the 2 eDist boxes they are exactly the same only difference is that the LS1 part number comes with the LS1 coil harness mating connectors. I think just recently they list the box as the same part number, but the harness are 2 different part numbers. You can check with FAST on that but I'm pretty sure the boxes are the same you just change the pins on the harness.
Also in the Setup menu or System config menu, (I can't remember) in the FAST system you can change the firing order to anything you want.
Rob
Chuck
02-18-2004, 01:27 PM
#32
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Originally posted by 96Z28SS
Jim there is no difference in the 2 eDist boxes they are exactly the same only difference is that the LS1 part number comes with the LS1 coil harness mating connectors. I think just recently they list the box as the same part number, but the harness are 2 different part numbers. You can check with FAST on that but I'm pretty sure the boxes are the same you just change the pins on the harness.
Jim there is no difference in the 2 eDist boxes they are exactly the same only difference is that the LS1 part number comes with the LS1 coil harness mating connectors. I think just recently they list the box as the same part number, but the harness are 2 different part numbers. You can check with FAST on that but I'm pretty sure the boxes are the same you just change the pins on the harness.
:I'll have to dig out my eDist and check.
Also in the Setup menu or System config menu, (I can't remember) in the FAST system you can change the firing order to anything you want.
02-18-2004, 01:29 PM
#33
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BTW, the FAST SEFI-8LO no longer controls the firing of the coils after the introduction of the eDist, does it? I mean, the eDist doesn't get a signal from the SEFI-8LO, it gets it from the cam sync stub, right? So configuring the firing order in the SEFI-8LO doesn't impact anything and wouldn't unless you had a sequential system anyway, would it?
02-18-2004, 02:14 PM
#34
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Somewhere at the beginning of this thread it was mentioned that you have to use the 4/7 swap cams with some sort of single plane manifold. I believe I know why that was said, but I don't believe it's true. If you run the "altered" firing order (18736542) and check which side of a dual plane intake it's sucking mixture from you'll see that it's still going left, right, left, right evenly.
One thing I haven't seen in this thread is WHY it makes more power. Both firing orders have 2 cyliners in the same bank firing consecutively.
On a standard cam it's 8 & 4, 5 & 7
On the 4/7 swap cam it's 7 & 3, 4 & 2
I can understand perhaps less crank stress from a firing order change but how the heck could this possibly generate more power? It's like stealing from Peter to pay Paul.
One thing I haven't seen in this thread is WHY it makes more power. Both firing orders have 2 cyliners in the same bank firing consecutively.
On a standard cam it's 8 & 4, 5 & 7
On the 4/7 swap cam it's 7 & 3, 4 & 2
I can understand perhaps less crank stress from a firing order change but how the heck could this possibly generate more power? It's like stealing from Peter to pay Paul.
02-18-2004, 02:42 PM
#35
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Originally posted by Damon
Somewhere at the beginning of this thread it was mentioned that you have to use the 4/7 swap cams with some sort of single plane manifold. I believe I know why that was said, but I don't believe it's true. If you run the "altered" firing order (18736542) and check which side of a dual plane intake it's sucking mixture from you'll see that it's still going left, right, left, right evenly.
Good point! On a SBC dual plane (ZZ manifold) 2,3,5,8 on on the "high" plenum and 1,4,6,7 on the "low". 4/7 swap still pulls high/low consecutively as you said.
One thing I haven't seen in this thread is WHY it makes more power. Both firing orders have 2 cyliners in the same bank firing consecutively.
On a standard cam it's 8 & 4, 5 & 7
On the 4/7 swap cam it's 7 & 3, 4 & 2
I can understand perhaps less crank stress from a firing order change but how the heck could this possibly generate more power? It's like stealing from Peter to pay Paul.
How about this? with the 4/7 swap the two fronts AND the two rears fire (and induct air) 90* apart so perhaps the airflow is already biased that way on a single plane. IOW, as #8 intake opens and airflow starts down that runner, 90* later #7 starts opening so the "signal strength" pulling toward the rear of the plenum gets stronger perhaps increasing the amount of air dumping into 8. As 8 closes its intake the strong flow then helps fill 7. With 184365721843... this only occurs in the front 2 cylinders. Just putting forth an idea here. I've not seen any measured airflow data on this. Of course, if it works, and it seems to, explaining it means less than using it.
With a dual plane this effect (if it in fact exists) wouldn't happen.
My $.02
Somewhere at the beginning of this thread it was mentioned that you have to use the 4/7 swap cams with some sort of single plane manifold. I believe I know why that was said, but I don't believe it's true. If you run the "altered" firing order (18736542) and check which side of a dual plane intake it's sucking mixture from you'll see that it's still going left, right, left, right evenly.
Good point! On a SBC dual plane (ZZ manifold) 2,3,5,8 on on the "high" plenum and 1,4,6,7 on the "low". 4/7 swap still pulls high/low consecutively as you said.
One thing I haven't seen in this thread is WHY it makes more power. Both firing orders have 2 cyliners in the same bank firing consecutively.
On a standard cam it's 8 & 4, 5 & 7
On the 4/7 swap cam it's 7 & 3, 4 & 2
I can understand perhaps less crank stress from a firing order change but how the heck could this possibly generate more power? It's like stealing from Peter to pay Paul.
How about this? with the 4/7 swap the two fronts AND the two rears fire (and induct air) 90* apart so perhaps the airflow is already biased that way on a single plane. IOW, as #8 intake opens and airflow starts down that runner, 90* later #7 starts opening so the "signal strength" pulling toward the rear of the plenum gets stronger perhaps increasing the amount of air dumping into 8. As 8 closes its intake the strong flow then helps fill 7. With 184365721843... this only occurs in the front 2 cylinders. Just putting forth an idea here. I've not seen any measured airflow data on this. Of course, if it works, and it seems to, explaining it means less than using it.
With a dual plane this effect (if it in fact exists) wouldn't happen.
My $.02
02-19-2004, 07:29 AM
#37
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Originally posted by PurePonyPounder
Still missing something here, how does switching firing order result in additional horsepower. Can someone simplify the entire equation for us ametuers here. Thanks
Johnny
Still missing something here, how does switching firing order result in additional horsepower. Can someone simplify the entire equation for us ametuers here. Thanks
Johnny
Any takers? naysayers? other opinions?
02-19-2004, 12:43 PM
#38
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Originally posted by OldSStroker
I offered one possible explanation just above, but maybe not too clearly: Better airflow into the two front and two rear cylinders because the are working 90 degrees apart. That could boost the Volumetric Efficiency of those cylinders and produce a little more power. Normal SBC firing order only has front two 90 degrees apart.
Any takers? naysayers? other opinions?
I offered one possible explanation just above, but maybe not too clearly: Better airflow into the two front and two rear cylinders because the are working 90 degrees apart. That could boost the Volumetric Efficiency of those cylinders and produce a little more power. Normal SBC firing order only has front two 90 degrees apart.
Any takers? naysayers? other opinions?
The 4/7 and LS1 firing orders fire cylinder #1 and then immediately fire #8 and #7 in succession, pulling air to the rear of the intake. In the standard SBC/LT1 firing order, #8 is fired after #1, but then the four center cylinders are fired and I suspect that cylinder #7 isn't nearly as efficient as it could be in the alternate 4/7 (or LS1) firing order.
Again, just a guess. I know that people have complained about the LT1/LT4 intakes having trouble filling the rear cylinders. My guess is that switching the firing order solves that problem which is where the extra horsepower comes from.
02-19-2004, 02:29 PM
#39
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Ive done alotta research in this as i run a solid roller with 4/7 swap in my 383, basically the LS1 firing order can be done in an LT1 without a different crank, but the only hp benefit came from a 4/7 swap, the other half of the LS1 order change actually ends up causing a loss for most people and is intended for a smoother engine.
02-19-2004, 02:46 PM
#40
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Originally posted by Nitromethane
Ive done alotta research in this as i run a solid roller with 4/7 swap in my 383, basically the LS1 firing order can be done in an LT1 without a different crank, but the only hp benefit came from a 4/7 swap, the other half of the LS1 order change actually ends up causing a loss for most people and is intended for a smoother engine.
Ive done alotta research in this as i run a solid roller with 4/7 swap in my 383, basically the LS1 firing order can be done in an LT1 without a different crank, but the only hp benefit came from a 4/7 swap, the other half of the LS1 order change actually ends up causing a loss for most people and is intended for a smoother engine.
For example, I'll be changing duration at the same time I change firing order, so who can say what power gain (or loss) is attributable to just the change in firing order? Would a cam with the same profile and a standard firing order make the same power? More? Less? How about an LS1 firing order? We'll never know, because I don't have any interest in buying or playing with two or three cams to find out.
Obviously, that makes it difficult to attribute gains and losses solely to a change in firing order. However, I suspect that GM did their homework and the LS1 ended up with more than just a 4/7 swap for more than just smoother operation. Of course, "just because GM did it" doesn't always mean it's the right thing to copy either.
02-19-2004, 05:17 PM
#41
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I've read that it stresses the crank less, which results in less twist, which results in more accurate valve and ignition timing events.
Wall-2-Wall Engines did some dyno testing and found around 15 hp with the 4/7 swap in a 670 hp, 7,500 rpm SUPR dirt track engine.
Mike
Wall-2-Wall Engines did some dyno testing and found around 15 hp with the 4/7 swap in a 670 hp, 7,500 rpm SUPR dirt track engine.
Mike
02-19-2004, 07:38 PM
#42
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I think the O2 thing could be an issue but if you keep everything in proper working order it should be OK. One thing I think should be addressed is the cylinder balance, I believe LT1 Edit has tables for this and since we are talking improving the VE of a few cylinders the cylinder offsets should be redone. This would mean dyno time with 8 EGT probes in your headers, but would help squeeze every last bit of power out of it while insuring safety.
02-20-2004, 02:07 PM
#44
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Engineermike,
I think that you're on the right track with your theory. I've got several friends at Comp Cams and I've asked a couple of the more knowledgeable ones about the benefits of the 4-7 swap. One told me that the swap results in slightly less monkey motion (harmonics) and that there may be some benefits in valvetrain stability because of this reduction.
Another one told me that there is a slight reduction in cylinder head temperature in cylinder 7 since the firing events are no longer consecutive. This could be the case, but since there are still the same number of combustion cycles per rev, it would seem that the head temp would end up at the same point regardless of firing order.
FWIW, one of them told me that they typically saw power increases of 0-5 hp.
Kevin
I think that you're on the right track with your theory. I've got several friends at Comp Cams and I've asked a couple of the more knowledgeable ones about the benefits of the 4-7 swap. One told me that the swap results in slightly less monkey motion (harmonics) and that there may be some benefits in valvetrain stability because of this reduction.
Another one told me that there is a slight reduction in cylinder head temperature in cylinder 7 since the firing events are no longer consecutive. This could be the case, but since there are still the same number of combustion cycles per rev, it would seem that the head temp would end up at the same point regardless of firing order.
FWIW, one of them told me that they typically saw power increases of 0-5 hp.
Kevin
02-21-2004, 01:47 PM
#45
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Originally posted by engineermike
I've read that it stresses the crank less, which results in less twist, which results in more accurate valve and ignition timing events.
I've read that it stresses the crank less, which results in less twist, which results in more accurate valve and ignition timing events.