LS6 intake w/runners cut back 1.5"
10-22-2011, 02:15 PM
#1
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LS6 intake w/runners cut back 1.5" On a LS 6 intake with an 85mm throttle body ported to match, is it worth cutting the runners back in the plenum @1.5-1.75"? Cam power seems to be 5000-6600 234/236 .596/.605" 114+4LSA. 5.7, 243 heads, 6 speed.
The shorter runner would increase the plenum volume.
Would a the shorter runner put more power in the 5000-7000 rpm range?
With loosing the "dog-leg" on the port inlet hurt anything considering the sides and the top of the port opening are still against the other runners and roof?
May just have to cut one port down and see what a flow bench says....
The shorter runner would increase the plenum volume.
Would a the shorter runner put more power in the 5000-7000 rpm range?
With loosing the "dog-leg" on the port inlet hurt anything considering the sides and the top of the port opening are still against the other runners and roof?
May just have to cut one port down and see what a flow bench says....
10-23-2011, 08:22 AM
#2
In theory...maybe. Would need to know MAP pressure from 5-6.6K in order to know whether or not plenum volume is holding it back. Although, a shorter runner will likely cost low end torque.
10-23-2011, 08:36 AM
#3
To follow that up; the inlet opening size should be increased before enlarging the plenum. There are plenty of threads in here that explain how, either @ home or through TPIS.
Sorry for the double post.
Sorry for the double post.
10-23-2011, 11:17 AM
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Its getting an 85mm ported to match, then resealed. The plenum volume is seperate from flow.
You right about it costing low rpm torque but once the hammer drops, I don't plan on letting it drop below 5200. So its all about average power above 5000. Cutting the runner will change the pulse wave for better filling but lose the bottom part of the radius entry. If the flow bench shows no loss, then may approach cutting them. Would have thought someone attempted this by now but can't find anything anywhere searching so made this post.
You right about it costing low rpm torque but once the hammer drops, I don't plan on letting it drop below 5200. So its all about average power above 5000. Cutting the runner will change the pulse wave for better filling but lose the bottom part of the radius entry. If the flow bench shows no loss, then may approach cutting them. Would have thought someone attempted this by now but can't find anything anywhere searching so made this post.
10-23-2011, 12:37 PM
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It will of course raise the powerband, how much who knows you might try Pipemax to get a guesstimate though. You will need to figure a way to radius/bellmouth the runner openings for sure. I have heard of people doing this on a FAST but never a LS6. I'm sure it's been done before and there are a few out there but they probably won't want to talk about it and it definitely wont be on LS1 tech (clownfest) of all places. 
Last edited by JS01; 10-23-2011 at 12:43 PM.
. You obviously already know too much, lol.
10-23-2011, 06:19 PM
#7
I would not worry about the plenum volume as there is plenty already. A 1.5" reduction in runner length is a lot. I would shorten it 1/2 to 3/4" and see what happens. Then go from there. Also as said above get a nice radius entry. This is the first post I have seen on the subject in the LSX world. By the way I have no experience working on LSX intake manifolds so take my post for what it is worth.
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10-23-2011, 08:46 PM
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The plan was to go @ 1/2 -3/4" after the 90 degree turn in the intake. Which is about 1.5". Its hard to tell whether the 90 degree leg is part of the runner or its the radius for it.
10-30-2011, 12:21 PM
#12
Theoretically by shortening the intake runner you raise the rpm's that in this case the 3rd harmonic wave comes in at. Also along with a nice radius inlet you should be able to raise the horsepower level. The harmonic wave gets stronger the higher the rpm so there is more boost from it. Apparently no one has done this of if they did they are not talking about it.
10-30-2011, 01:44 PM
#13
Try to get in touch with HioSSilver. I know that he had an ls1 intake where the runners were cut shorter. It didn't give more power, just moved it up I think. He may be able to give more details on it or even pictures if he knows where it is.
10-30-2011, 11:26 PM
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For the moment I have widened the runners. Port-matched at the flange and up the runner about 4 inches. Wider by about .100"-.125". Added a 85 mmm throttle body and ported the adapeter and opening as far as possible without breaking thru.
Still on the fence about shortening the runners....
Still on the fence about shortening the runners....
