The combination of the Daily Engineering
dry sump and a remote electric water pump means that I need to completely redesign the serpentine system. The dry sump is located where the A/C compressor usually sits and it replaces the serpentine pulley behind the super damper with a cogged one. This means that the compressor needs to be moved to the other side of the engine. I knew that before I had the engine built.
However, I didn’t realize the impact of removing the mechanical water pump until I pulled the engine and removed the pump. In the picture below the automatic tensioner, idler and water pump (obviously) pulleys are mounted to the water pump. I now understand why there are multiple companies offering direct-replacement electric water pumps. They replace the water pump pulley with an idler with the same OD and maintain all of the mounting holes. This means you can use the same belt and pullies without any engineering or fabrication. That said, I’m glad I went with the remote pump discussed in a previous post
because it’s superior to direct-replacement pumps and it’s extremely easy to service. I’d have to pull the engine to service a direct-replacement pump.
I also learned that unlike the left side of the engine (right side when viewed from the front) which has three M10-1.5mm mounting holes, the right side has none.
Engine as delivered had a dry sump, a mechanical water pump and no provision for accessories
The first step was to figure out the location of mounting holes; three on the block, four on the right head and five on the left head. I spent a lot of time looking for a simple dimensioned drawing to no avail. I found a CAD model of an entire LS3 on GrabCAD
(I have an LS7 block, but the relevant mounting holes seem to be the same). After removing the accessories, the exhaust and the crank pulley, I was able to determine the location of the mounting holes relative to the crank. They seem to be accurate, but if anyone has actual dimensions I’d love to have them.
There will be three layers of belts, from back to front:
- Dry sump: cogged belt
- Supercharger: serpentine belt running on the super damper
- A/C compressor and Alternator: serpentine belt running on a pulley mounted to the front of the super damper
I took a guess and laid everything out in SOLIDWORKS.
Left (supercharger belt in black and accessory belt in orange) and Right (base plate)
I designed three mounting plates:
- Base Plate: spans the majority of the block, supports the other two plates and the rear mounting points for the compressor and alternator
- Center Plate: replaces the mechanical water pump’s mounting points
- Accessory Plate: supports the idler and the front mounting points for the compressor and alternator
I wanted to confirm the locations of the holes in the block and check the locations of the accessories so I laser cut plates from 1/4” plywood and 3D printed spacers in Onyx. Version 1.0 fit fairly well, but I need to tweak the location of the compressor and finalize the exact locations of the idlers and automatic tensioners.
Base and accessory plates; center plate not mocked… pretty naked without the water pump
All three plates installed
Spacers printed in Onyx for mocking purposes
I know that significant engineering goes into designing a proper serpentine system, but I only have a rudimentary understanding — watch the amount of wrap, tensioners on the slack side, etc. — and I haven’t been able to find a resource that discusses serpentine design. If anyone knows of a good book, article, post, consultant, etc. please let me know.
I stumbled into Design IQ
, a downloadable free program from Gates
. The video below provides a quick overview.
As can be seen below, I entered the information for the accessory system into the application. It calculates the Effective Belt Length (top middle of black background) which is useful. It also calculates the wrap angle of each pulley, but I’m not sure if 259.26 degrees is too much for the drive pulley or if 47.93 degrees is too little for the tensioner. I’m also not sure how to orient the tensioner’s arc nor how to determine where to place the mounting holes so that the tensioner applies the correct amount of pretension to the belt while providing the maximum amount of adjustability. If anyone has any pointers, please let me know.
Accessory belt entered into Design IQ