Thread: Project Sebring GT Spyder

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The last thing I had to do was get the intake sorted. If you’ve been following along for a while you will remember that I’m using a 2x4 Holley EFI setup. I found this for sale on another forum and thought it would look a lot better than the standard LS intake. The squat stock LS front throttle body intakes just don’t look right to me on an older car. I thought this setup looked more like it belonged on a 60’s muscle car.





Even after several searches, I couldn’t find much info on using this thing. The throttle bodies flow 1000 cfm each and are progressive like a standard 4 barrel carb. 2000 cfm is a ludicrous amount of air for a 350 CI engine. The linkage that came with it has both TB opening together. At this point I really don’t want to disconnect the secondaries. I may have to eventually, but I consider getting it to work without that as a challenge.

The only complaint that I read from someone that actually used it said that it had touchy throttle response, sort of like an on/off switch. That stands to reason if they didn’t try to slow down the throttle opening. There’s a 1000 cfm available on the primaries alone. That’s a lot of airflow potential for a small amount of throttle opening. My last reasonably accurate weight I have for the car is about 2700 lbs. With a potential for 450 HP on tap, the last thing I need is an on/off switch for a throttle. I’m going to attack that problem 2 ways.





First, I came up with a throttle linkage that slows down the opening on the initial tip in. It uses a cable wheel/cam that has an offset axle. This changes the ratio as it’s opened. Slower initially and faster at the end. I didn’t build that part. It came off a 90mm FAST LS throttle body that I had laying around. It stands to reason that the larger single bore TB's would be touchy too. Apparently, FAST used this cable wheel to slow their opening rate. You can see the off set compared to a stock GM cable wheel in the bottom picture.



I had to mount the throttle cable on the right side of the engine. There wasn’t a lot of room on the left due to the fuel rails being close to the existing linkage on the TB’s. The FAST cable cam was designed to work on the right side too. I built this mount that transfers the throttle movement to the left side. It’s cut from 6061 aluminum and has a 3/8” stainless shaft. Another nice thing about the FAST cam was that it had it’s own torsion return spring. I transferred that over to the new mount.







This is the linkage I built on the left side. The way the pivot is positioned (close to the centerline of the shaft), it slows the initial opening down even more. It spends much of it’s initial travel moving more vertically than it does moving backwards. After the first 20 or so degrees. It speeds up considerably. I am getting full stroke on the TB’s. So far, the combo seems to be working like I wanted it to. The proof will be in the driving.