Backpressure BS
Senior Member
Joined: Aug 2002
Posts: 208
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From: North Georgia
Originally posted by InS0mNiAc
I'm not sure what they would sound like on an L, but on my gt stang it made it sound like I had a damn big block in it! I love them and was pissed when I heard that they didn't go well with the L's. But who knows now, there was supposedly a whole back pressure issue with them but with this news now, I wonder if it was all just a bunch of bull! Can anyone clear up the flowmaster issue?
I'm not sure what they would sound like on an L, but on my gt stang it made it sound like I had a damn big block in it! I love them and was pissed when I heard that they didn't go well with the L's. But who knows now, there was supposedly a whole back pressure issue with them but with this news now, I wonder if it was all just a bunch of bull! Can anyone clear up the flowmaster issue?
Senior Member
Joined: Aug 2001
Posts: 1,987
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From: MA
Originally posted by air1kdf
. I don't know the diameter of the primaries of the long tube headers, but the larger the better. The same holds true for the rest of the exhaust system. This wouldn't be the case if it weren't SC'd though, and we'd be having a much different discussion.
. I don't know the diameter of the primaries of the long tube headers, but the larger the better. The same holds true for the rest of the exhaust system. This wouldn't be the case if it weren't SC'd though, and we'd be having a much different discussion.
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Joined: Aug 2000
Posts: 379
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From: San Jose, California, U.S.A.
Not sure how wise it is to defend this to the death but its hard to argue real life data.
sixth post down from TimBurnTire.
https://www.f150online.com/forums/sh...threadid=93985
Flatsman after changing his exhaust found he lost HP and TQ. He was running a roots supercharger on a 4.6L at the time.
https://www.f150online.com/forums/sh...atsman+exhaust
He regained it by closing up the flow with exhaust traps
https://www.f150online.com/forums/sh...t=tunable+trap
Now I'm not sure how the cam profile is different on a stock 4.6L vs. a stock profile of an L. But I think that has a lot to do with it. If there is any overlap and you don't have ANY backpressure you're going to be blowing out your air fuel mix along with the exhaust. It may be that the stock L cam's are not the best for a supercharged application. If I'm off base in my thinking let me know and why.
Jes
sixth post down from TimBurnTire.
https://www.f150online.com/forums/sh...threadid=93985
Flatsman after changing his exhaust found he lost HP and TQ. He was running a roots supercharger on a 4.6L at the time.
https://www.f150online.com/forums/sh...atsman+exhaust
He regained it by closing up the flow with exhaust traps
https://www.f150online.com/forums/sh...t=tunable+trap
Now I'm not sure how the cam profile is different on a stock 4.6L vs. a stock profile of an L. But I think that has a lot to do with it. If there is any overlap and you don't have ANY backpressure you're going to be blowing out your air fuel mix along with the exhaust. It may be that the stock L cam's are not the best for a supercharged application. If I'm off base in my thinking let me know and why.
Jes
Senior Member
Joined: Sep 2001
Posts: 1,433
Likes: 3
From: cincinnati, ohio
Originally posted by RedShift
Here is an example for you. 1997 Honda Valkyrie with stock exhaust dynoed and 100 HP and 102 ft/lb of torque. This person put a 6 into 6 exhaust with no baffles in it (way too loud btw) and LOST 10 hp and 10 ft/lb of torque. Some backpressure is required.
Here is an example for you. 1997 Honda Valkyrie with stock exhaust dynoed and 100 HP and 102 ft/lb of torque. This person put a 6 into 6 exhaust with no baffles in it (way too loud btw) and LOST 10 hp and 10 ft/lb of torque. Some backpressure is required.
if you don't, you will start bluing the pipes in less than 50 miles,
i know,
i had a valkyrie with the same 6 into 6
Thread Starter
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Senior Member
Joined: Aug 2002
Posts: 703
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From: Louisville, KY
Whip, I read a post wrong, got flamed real bad, and apologized twice for it. I'm trying to post only positively on this and want others to learn collectively. Also note that almost 1,500 people have read this post and nobody is disagreeing with me, yet read exhaust posts and many say the more plugged the better.
rocketir, as you mentioned the capping on a 4.6 makes a lot of sense because of the difference in the cam profiles. I know nothing about cam profiles on a forced induction system. But I know alot about cam profiles on a naturally aspirated system.
As far as a valkyrie, does that use a forced induction supercharger on it? If not then exhaust theory from this post doesn't apply. Also I can tell you from experience on different bikes that beefcake is right about the jetting.
I would love to see actual data about the different header sizes. The best I got was some theory from David Vizard that I found in How To Build Horsepower. In this book he basically says on forced induction blowers:
1) The bigger the exhaust the better.
2) All other induction will respond 2x better.
3) The entry of the header is just an aiming device.
4) Scavenging from the head is due to boost.
Again this is theory on street engines. Actual testing done on an L engine would be much better than this. Facts are nice, and I would love to see more.
I also thought of this. If overlap was totally removed from our cam profiles, then boost would not drop when long tube headers are put on.
rocketir, as you mentioned the capping on a 4.6 makes a lot of sense because of the difference in the cam profiles. I know nothing about cam profiles on a forced induction system. But I know alot about cam profiles on a naturally aspirated system.
As far as a valkyrie, does that use a forced induction supercharger on it? If not then exhaust theory from this post doesn't apply. Also I can tell you from experience on different bikes that beefcake is right about the jetting.
I would love to see actual data about the different header sizes. The best I got was some theory from David Vizard that I found in How To Build Horsepower. In this book he basically says on forced induction blowers:
1) The bigger the exhaust the better.
2) All other induction will respond 2x better.
3) The entry of the header is just an aiming device.
4) Scavenging from the head is due to boost.
Again this is theory on street engines. Actual testing done on an L engine would be much better than this. Facts are nice, and I would love to see more.
I also thought of this. If overlap was totally removed from our cam profiles, then boost would not drop when long tube headers are put on.