"The Mongoose" - 1 3/4" Headers To 1 7/8" Headers (447 rwhp and 431 rwtq)
04-28-2016, 10:44 PM
#81
TECH Fanatic
I was thinking maybe it was over scavenging. It falls off a lot more than I would think it would regardless. I've read that longer primary length helps low end torque. Made me curious how long the primaries are on the stainless works vs speed engineerings stuff and if they are equal length or not. The 2.5 inch vs 3 inch collectors will make a difference also. I dunno I'm still trying to learn more but there are only so many dyno comparisons of this header vs that header out there.
04-29-2016, 12:57 AM
#82
Not to doubt Brian's advice, but I'd be interested to see how an overscavenging problem could be solved by an intake manifold. No doubt the FAST will benefit like he said, but I would think cutting down either exhaust duration and/or decreasing the amount of overlap would fix it.
Just a little food for thought: If you haven't heard of the Engine Masters Challenge, these guys are building engines and competing for best horsepower and torque per cubic inch in an RPM range of what a typical street engine would see (6-7k RPM). SAM built a 436ci LSX that made 727hp at the flywheel using a 240/252 cam with a 100 LSA.
Just a little food for thought: If you haven't heard of the Engine Masters Challenge, these guys are building engines and competing for best horsepower and torque per cubic inch in an RPM range of what a typical street engine would see (6-7k RPM). SAM built a 436ci LSX that made 727hp at the flywheel using a 240/252 cam with a 100 LSA.
04-29-2016, 04:27 AM
#83
I was thinking maybe it was over scavenging. It falls off a lot more than I would think it would regardless. I've read that longer primary length helps low end torque. Made me curious how long the primaries are on the stainless works vs speed engineerings stuff and if they are equal length or not. The 2.5 inch vs 3 inch collectors will make a difference also. I dunno I'm still trying to learn more but there are only so many dyno comparisons of this header vs that header out there.
04-29-2016, 06:17 AM
#84
Not to doubt Brian's advice, but I'd be interested to see how an overscavenging problem could be solved by an intake manifold. No doubt the FAST will benefit like he said, but I would think cutting down either exhaust duration and/or decreasing the amount of overlap would fix it.
Just a little food for thought: If you haven't heard of the Engine Masters Challenge, these guys are building engines and competing for best horsepower and torque per cubic inch in an RPM range of what a typical street engine would see (6-7k RPM). SAM built a 436ci LSX that made 727hp at the flywheel using a 240/252 cam with a 100 LSA.
Just a little food for thought: If you haven't heard of the Engine Masters Challenge, these guys are building engines and competing for best horsepower and torque per cubic inch in an RPM range of what a typical street engine would see (6-7k RPM). SAM built a 436ci LSX that made 727hp at the flywheel using a 240/252 cam with a 100 LSA.
04-29-2016, 07:41 AM
#85
A lot of it depends on how big the exhaust valves are and how well the exhaust ports flow. When you look at the flow data for these heads, they flow so much more on the exhaust side than most aftermarket CNC ported heads. The only one that's comparable is the AFR heads, and now the Mamo Motorsports heads. Brian said that back when he was at TFS and tested different sized headers on with different head combinations, the bigger headers always made less top end power when paired with the AFR heads.
I picked the car up last night and I sure as hell cannot tell it's lost a damn thing past 6,000 RPM's. The car screams. I do notice the increased torque/power in the mid-range.
I picked the car up last night and I sure as hell cannot tell it's lost a damn thing past 6,000 RPM's. The car screams. I do notice the increased torque/power in the mid-range.
04-29-2016, 08:46 AM
#88
No doubt the car runs its *** off down low and never skips a beat on the big end.
Opinions for 92/92 or go straight to the 102/102?
The car makes so much tq down low will the 102 be better for the head flow or should he go with the 92 set to keep some of the velocity for down low?
Opinions for 92/92 or go straight to the 102/102?
The car makes so much tq down low will the 102 be better for the head flow or should he go with the 92 set to keep some of the velocity for down low?
04-29-2016, 08:59 AM
#89
I'm still curious how a more efficient intake is going to solve an overscavenge problem. If it's overscavenging, the exhaust gases are being completely evacuated from the combustion chamber and fresh air is being pulled out into the exhaust as well. That may explain why it needed more fuel as the O2 is reading that as a lean condition. Now in my mind, adding a better intake will just result in even more fresh air to escape out of the exhaust since the intake will now flow more air. More air may make it in towards the end of the intake stroke, resulting in a net gain, but you're still just band aiding the overscavenge problem.
But back to what I said earlier, I personally would be happy with the results. The power in the low and mid RPM range is excellent. The peak numbers alone don't tell the whole story. I would take that 3hp loss at peak to gain what looks like 20-25ft-lbs in the midrange. That's what makes a street car fun to drive. If it were me, I would drive the car around for a while, enjoy it while it's up and running and mull over the next step until the winter when the weather gets crappy again. Once you have a game plan, then tear the car apart again and make some changes.
04-29-2016, 09:52 AM
#90
11 Second Club
Well the LSA does have a lot to do with overlap. How often do you see a cam with a 100 LSA? That's 46 degrees of overlap @ .050". Darth's cam is still only 11 degrees.
I'm still curious how a more efficient intake is going to solve an overscavenge problem. If it's overscavenging, the exhaust gases are being completely evacuated from the combustion chamber and fresh air is being pulled out into the exhaust as well. That may explain why it needed more fuel as the O2 is reading that as a lean condition. Now in my mind, adding a better intake will just result in even more fresh air to escape out of the exhaust since the intake will now flow more air. More air may make it in towards the end of the intake stroke, resulting in a net gain, but you're still just band aiding the overscavenge problem.
But back to what I said earlier, I personally would be happy with the results. The power in the low and mid RPM range is excellent. The peak numbers alone don't tell the whole story. I would take that 3hp loss at peak to gain what looks like 20-25ft-lbs in the midrange. That's what makes a street car fun to drive. If it were me, I would drive the car around for a while, enjoy it while it's up and running and mull over the next step until the winter when the weather gets crappy again. Once you have a game plan, then tear the car apart again and make some changes.
I'm still curious how a more efficient intake is going to solve an overscavenge problem. If it's overscavenging, the exhaust gases are being completely evacuated from the combustion chamber and fresh air is being pulled out into the exhaust as well. That may explain why it needed more fuel as the O2 is reading that as a lean condition. Now in my mind, adding a better intake will just result in even more fresh air to escape out of the exhaust since the intake will now flow more air. More air may make it in towards the end of the intake stroke, resulting in a net gain, but you're still just band aiding the overscavenge problem.
But back to what I said earlier, I personally would be happy with the results. The power in the low and mid RPM range is excellent. The peak numbers alone don't tell the whole story. I would take that 3hp loss at peak to gain what looks like 20-25ft-lbs in the midrange. That's what makes a street car fun to drive. If it were me, I would drive the car around for a while, enjoy it while it's up and running and mull over the next step until the winter when the weather gets crappy again. Once you have a game plan, then tear the car apart again and make some changes.
Another thing with overscavenging. As engine rpm goes up there is less & less time to scavenge. This is why more overlap helps out at higher rpm. Giving it more time to scavenge. So here a cam with more overlap would make less high end power? Doesn't seem to fit right.
Also the power loss. It's only a couple at around 6k. I think it was stated to be almost 25 down by 6500 or so.
The test Brian did with the exhaust valves is interesting. Each different valve size was in a different cylinder head though? Saying a stock size valve, to a TFS head, to an AFR head?
If someone were to ask which would make more power: 1, great scavenging but some of the air/fuel charge was brought into the exhaust. 2, scavenging not so good, some exhaust still left in the cylinder. I would pick #1.
04-29-2016, 10:03 AM
#91
Correct. Around 6,000 RPM's the car was down 3 HP or so, but after 6,000 RPM's, it drops off fast, loosing something like 20 HP. With the new headers, the combo just flat out does not make more power past 6,000 RPM's. On two independent dyno's, with the old 1 3/4" headers, the car made power to till 6,300 RPM's and then basically flat-lined to 6,500 RPM's. That's not the case with the new headers. It drastically falls off past 6,000 RPM's.
So, KCS, what do you think would yield better results. A cam change and stay with the LS6 intake or leave the cam and go with a FAST 102/92 setup?
So, KCS, what do you think would yield better results. A cam change and stay with the LS6 intake or leave the cam and go with a FAST 102/92 setup?
04-29-2016, 01:00 PM
#92
11 Second Club
For safety this is not against anyone. Just my opinion/thoughts.
I feel overscavenging is maybe an old wives tale. Think of an engine only pumping air. No fuel for now. Even if the scavenge ability, of the header, was the highest of them all. It would still have just as much, as a "perfect" scavenge, or more, air in the cylinder when the exhaust valve closes, to make power. I don't think the ls6 is choking you too much. But more air in, from a fast, =more power. Now let's go to the fuel. The only way I see it being a down side (overscavenging) is if you don't have the fuel charge to make up for whatever could have been lost, in the exhaust, or the extra air pulled in. If you don't have the fuel, made up for, it may run on the lean side. Maybe more power but not safe. Get it all tuned up. I see more scavenge=more power. Not too good for mpg though lol.
I feel overscavenging is maybe an old wives tale. Think of an engine only pumping air. No fuel for now. Even if the scavenge ability, of the header, was the highest of them all. It would still have just as much, as a "perfect" scavenge, or more, air in the cylinder when the exhaust valve closes, to make power. I don't think the ls6 is choking you too much. But more air in, from a fast, =more power. Now let's go to the fuel. The only way I see it being a down side (overscavenging) is if you don't have the fuel charge to make up for whatever could have been lost, in the exhaust, or the extra air pulled in. If you don't have the fuel, made up for, it may run on the lean side. Maybe more power but not safe. Get it all tuned up. I see more scavenge=more power. Not too good for mpg though lol.
04-29-2016, 06:42 PM
#93
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Well the LSA does have a lot to do with overlap. How often do you see a cam with a 100 LSA? That's 46 degrees of overlap @ .050". Darth's cam is still only 11 degrees. I'm still curious how a more efficient intake is going to solve an overscavenge problem. If it's overscavenging, the exhaust gases are being completely evacuated from the combustion chamber and fresh air is being pulled out into the exhaust as well. That may explain why it needed more fuel as the O2 is reading that as a lean condition. Now in my mind, adding a better intake will just result in even more fresh air to escape out of the exhaust since the intake will now flow more air. More air may make it in towards the end of the intake stroke, resulting in a net gain, but you're still just band aiding the overscavenge problem. But back to what I said earlier, I personally would be happy with the results. The power in the low and mid RPM range is excellent. The peak numbers alone don't tell the whole story. I would take that 3hp loss at peak to gain what looks like 20-25ft-lbs in the midrange. That's what makes a street car fun to drive. If it were me, I would drive the car around for a while, enjoy it while it's up and running and mull over the next step until the winter when the weather gets crappy again. Once you have a game plan, then tear the car apart again and make some changes.
I'd like to pose this scenario. If the exhaust scavenging is really good, during overlap, air/fuel can short circuit straight out. Now, if the scavenging gets TOO good, is it possible to create a depression in the intake manifold - say a 10kpa vacuum? If this happens, the map never exceeds say 87, so definitely not getting enough air to reach full atmospheric pressure.
Now, insert fast102. 4" vs 3" opening will flow 1.8x more air, and the bigger plenum will require way more scavenging to get any sort of depression, so now the map reaches 97 kpa and the car makes a lot more power.
Is that a plausible scenario?
04-29-2016, 06:55 PM
#94
That's a great point, and I agree with you that I would happily trade 3hp up top for 20-25 in the midrange.
I'd like to pose this scenario. If the exhaust scavenging is really good, during overlap, air/fuel can short circuit straight out. Now, if the scavenging gets TOO good, is it possible to create a depression in the intake manifold - say a 10kpa vacuum? If this happens, the map never exceeds say 87, so definitely not getting enough air to reach full atmospheric pressure.
Now, insert fast102. 4" vs 3" opening will flow 1.8x more air, and the bigger plenum will require way more scavenging to get any sort of depression, so now the map reaches 97 kpa and the car makes a lot more power.
Is that a plausible scenario?
I'd like to pose this scenario. If the exhaust scavenging is really good, during overlap, air/fuel can short circuit straight out. Now, if the scavenging gets TOO good, is it possible to create a depression in the intake manifold - say a 10kpa vacuum? If this happens, the map never exceeds say 87, so definitely not getting enough air to reach full atmospheric pressure.
Now, insert fast102. 4" vs 3" opening will flow 1.8x more air, and the bigger plenum will require way more scavenging to get any sort of depression, so now the map reaches 97 kpa and the car makes a lot more power.
Is that a plausible scenario?
04-29-2016, 07:11 PM
#95
I'd like to point out a couple of things.
1st- KCS and SoFla, you guys both know well enough about LSA being only a number. I've never particularly been a Martin fan, but his thread in the Gen III internal section is excellent. I can make a cam with an LSA of 100 and very little overlap or a cam with 115 and huge overlap, its about valve events and what the combo is.
2nd- KCS your point about a better intake setup is still a bandaid to an over scavenging situation has merit, but short of swapping cams or moving back to 1 3/4 headers a better intake tract seems like a reasonable way to go. I absolutely believe in over scavenging. Your overlap, exhaust port flow, and exhaust setup dictate scavenging. At high RPM, there isn't much time for fresh air to be sucked into the chamber, so if a small amount of air is sucked in due to a weak intake tract, and a significant portion of that is pushed out the exhaust before the valve closes, it makes sense its not going to make the high rpm power it should. By adding a better intake setup, there is more air available at high rpm.
Think about this scenario. Take a really small breath in, and then exhale fully, repeat the sequence and see how many times you can do it before youre tired and need to take a full breath in. Your intake stroke doesnt have the charge you need, but youre exhaling fully everytime as if you did have a full breath in. Darth_V8r has an excellent point, what does the log of map pressure look like throughout the pull?
1st- KCS and SoFla, you guys both know well enough about LSA being only a number. I've never particularly been a Martin fan, but his thread in the Gen III internal section is excellent. I can make a cam with an LSA of 100 and very little overlap or a cam with 115 and huge overlap, its about valve events and what the combo is.
2nd- KCS your point about a better intake setup is still a bandaid to an over scavenging situation has merit, but short of swapping cams or moving back to 1 3/4 headers a better intake tract seems like a reasonable way to go. I absolutely believe in over scavenging. Your overlap, exhaust port flow, and exhaust setup dictate scavenging. At high RPM, there isn't much time for fresh air to be sucked into the chamber, so if a small amount of air is sucked in due to a weak intake tract, and a significant portion of that is pushed out the exhaust before the valve closes, it makes sense its not going to make the high rpm power it should. By adding a better intake setup, there is more air available at high rpm.
Think about this scenario. Take a really small breath in, and then exhale fully, repeat the sequence and see how many times you can do it before youre tired and need to take a full breath in. Your intake stroke doesnt have the charge you need, but youre exhaling fully everytime as if you did have a full breath in. Darth_V8r has an excellent point, what does the log of map pressure look like throughout the pull?
04-30-2016, 03:43 PM
#99
Uh...isn't this your setup in an LQ9???https://ls1tech.com/forums/dynamomet...ick-tuned.html