$16 98.3mm LS7 intake manifold upgrade
01-30-2009, 06:35 PM
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$16 98.3mm LS7 intake manifold upgrade Long time lurker, first time poster.
For those who say it hasn’t been done yet, I recently increased the throat of my plastic LS7 intake manifold to 98.3 mm the following way for $16.
I originally bored my Nick Williams 90mm throttle body on a lathe to 96mm and made a new throttle plate to match. I was going to make a wooden ball mill with screw spikes on the parameter and a hand drill to open the LS7 manifold’s throat to 96mm to match (I previously opened the throat of an LS6 manifold this way to 77.5mm). On closer inspection, it was obvious the LS7 manifold’s flange could be opened up but the throat could only be opened to perhaps 94mm before breaking through the plastic wall. Undaunted, I decided to attempt sleeving the throat instead.
I bought a hole saw set from Northern Tool which included the 4” hole saw I wanted for $12. Rotating my bench top drill press' base 180 degrees from the head, I swung the head of the drill press out over the bench and mounted the manifold vertically below it with the manifold’s throat on axis with the drill press. The 4” hole saw cut all of the bottom and sides of the throat completely away but the top of the throat retained enough plastic to hold the throttle body flange rigidly in place.
I used a 3” long section of 4” exhaust pipe as the sleeve (4.0” OD and 98.3mm ID). Surprising, it was a nice tight slip fit into the 4” cut hole. I ground the bottom of the sleeve until it matched the manifold’s irregular shape. I left two tabs on the bottom of the sleeve so I could mechanically lock it in place with eight 8-32 allen cap screws (four on the body side of the sleeve and four on the flange side). I epoxied the sleeve in place for a good seal. I ultimately used all $4 of a J-B Weld kit.
I filled in the throttle body o-ring groove with epoxy and used a flat plate with coarse sandpaper to flatten the flange surface. A thin film of RTV seals the throttle body to the manifold. I also slightly under matched the manifold's portsto the LS7 head ports to complete the manifold. Now, having a 98.3mm throat, I remachined the bore of my Nick Williams throttle body to 98.2mm (nothing like doing the same job twice). 98.2mm is all the room NW gave between the throttle shaft bearings to open the bore.
About three weeks ago I installed the manifold, throttle body and set of newly hand ported LS7 heads on my 438” LS7 in my 99 Z28. After setting the IAC to about 35 counts at idle, I found that my SD tune hadn’t changed. I drove the car in 40F temperatures 35 miles. The next day it snowed and hasn’t warmed up since so I can’t comment on any performance improvement.
FYI, for those who have their hearts set on a 100mm ID throat, there is enough room for a throat cut to a little over 4” by bending the hole saw teeth out and machining a thin wall aluminum tube for a sleeve with a 100mm ID to match.
For those who say it hasn’t been done yet, I recently increased the throat of my plastic LS7 intake manifold to 98.3 mm the following way for $16.
I originally bored my Nick Williams 90mm throttle body on a lathe to 96mm and made a new throttle plate to match. I was going to make a wooden ball mill with screw spikes on the parameter and a hand drill to open the LS7 manifold’s throat to 96mm to match (I previously opened the throat of an LS6 manifold this way to 77.5mm). On closer inspection, it was obvious the LS7 manifold’s flange could be opened up but the throat could only be opened to perhaps 94mm before breaking through the plastic wall. Undaunted, I decided to attempt sleeving the throat instead.
I bought a hole saw set from Northern Tool which included the 4” hole saw I wanted for $12. Rotating my bench top drill press' base 180 degrees from the head, I swung the head of the drill press out over the bench and mounted the manifold vertically below it with the manifold’s throat on axis with the drill press. The 4” hole saw cut all of the bottom and sides of the throat completely away but the top of the throat retained enough plastic to hold the throttle body flange rigidly in place.
I used a 3” long section of 4” exhaust pipe as the sleeve (4.0” OD and 98.3mm ID). Surprising, it was a nice tight slip fit into the 4” cut hole. I ground the bottom of the sleeve until it matched the manifold’s irregular shape. I left two tabs on the bottom of the sleeve so I could mechanically lock it in place with eight 8-32 allen cap screws (four on the body side of the sleeve and four on the flange side). I epoxied the sleeve in place for a good seal. I ultimately used all $4 of a J-B Weld kit.
I filled in the throttle body o-ring groove with epoxy and used a flat plate with coarse sandpaper to flatten the flange surface. A thin film of RTV seals the throttle body to the manifold. I also slightly under matched the manifold's portsto the LS7 head ports to complete the manifold. Now, having a 98.3mm throat, I remachined the bore of my Nick Williams throttle body to 98.2mm (nothing like doing the same job twice). 98.2mm is all the room NW gave between the throttle shaft bearings to open the bore.
About three weeks ago I installed the manifold, throttle body and set of newly hand ported LS7 heads on my 438” LS7 in my 99 Z28. After setting the IAC to about 35 counts at idle, I found that my SD tune hadn’t changed. I drove the car in 40F temperatures 35 miles. The next day it snowed and hasn’t warmed up since so I can’t comment on any performance improvement.
FYI, for those who have their hearts set on a 100mm ID throat, there is enough room for a throat cut to a little over 4” by bending the hole saw teeth out and machining a thin wall aluminum tube for a sleeve with a 100mm ID to match.
01-30-2009, 06:52 PM
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I didn't bother to take pictures while working on the manifold because I didn't know if it was going to work. It's 20F in my garage now so presently I have no enthusiasm to crawl around the car.
Come On just put a heater in the garage LOL 