If you've not seen it already, this thread has a lot of useful information in it. Please put on it any useful information you find out, particularly on your adapter plate, so that others like me can find the benefit of your work.

Thanks for looking out. Good info!

Ok here we go! Rx8 Compressor came today, got to work. This is a little more intense than I anticipated, but I think it will be workable. The bolt holes end up being close enough that there will likely be no room for two nuts. To make it easy, I will have spacers and nuts welded on opposite sides of the plate to give me the room for the additional hardware. Fear not, I'll post up final measurements.

First three images here are comparing the new billet pulley to the oem fd pulley. I am taking an assumption that they mount up the same because to be frank, they pretty much do. We need this info to find out where the belt is running. As it turns out the billet accessory pulley shown fits the Rx8 ac belt perfectly, but the fd outer pulley does not, meaning we use an rx8 pulley for the ac as intended. I'm not sure why this worked out, but hey lucky me! Anyway long story short we are 1/16" off at this point.

https://cimg9.ibsrv.net/gimg/www.rx8...5e1ef9573d.jpg

https://cimg0.ibsrv.net/gimg/www.rx8...9853c2c6b5.jpg

https://cimg1.ibsrv.net/gimg/www.rx8...76ab1d2d6c.jpg

The next two images show a little more distance. What is happening here is the compromise of this task. If I aligned the pulleys perfectly, no bolt holes match and we get overlapping bolt holes. Yuck. So I aligned the Rx8 Compressor rear lower bolt hole to the rear lower bolt hole on the FD compressor. These were easiest to align and imo yeild the best result. We increase our "offset" by 3/16" more, yielding a total offset of 1/4". That's kind of a bit for a pulley, and I will be unable to comment on how that will work in real world applications for a long time.



https://cimg8.ibsrv.net/gimg/www.rx8...f10a0fe604.jpg

https://cimg9.ibsrv.net/gimg/www.rx8...3d9fd63adf.jpg

Here are some images of my quick measurements. Generally rounded to 1/8" Please note I am mounting the Rx8 compressor to the FD tensioner pulley bracket atm. Have yet to tackle the tensioner pulley issue (it is not grooved like the rx8 one).

https://cimg8.ibsrv.net/gimg/www.rx8...2f5e19f8da.jpg

https://cimg0.ibsrv.net/gimg/www.rx8...8234eece12.jpg

https://cimg1.ibsrv.net/gimg/www.rx8...67f069934a.jpg

https://cimg2.ibsrv.net/gimg/www.rx8...b45f2a4f15.jpg

https://cimg3.ibsrv.net/gimg/www.rx8...174752bf23.jpg

https://cimg4.ibsrv.net/gimg/www.rx8...58c7f447db.jpg

https://cimg5.ibsrv.net/gimg/www.rx8...f66ccb2079.jpg



The top front bolt measurement was a little too far forward. Again, these are for mock up purposes only, if I finish I'll get final dimensions.

https://cimg2.ibsrv.net/gimg/www.rx8...b5a84f11a8.jpg

Combined dimensions


https://cimg3.ibsrv.net/gimg/www.rx8...cc5e50ee83.jpg

Offset over the 31" Rx8 AC belt. May end up with a longer belt, not sure yet. I'll post up with whatever belt I use.


https://cimg4.ibsrv.net/gimg/www.rx8...3306d3a078.jpg

https://cimg5.ibsrv.net/gimg/www.rx8...bb42e0d378.jpg

https://cimg8.ibsrv.net/gimg/www.rx8...acaabcecf7.jpg

Top bolts are quite close.


https://cimg9.ibsrv.net/gimg/www.rx8...cc8063f9b5.jpg

^ Fit to Rx8 compressor.

That's my progress for the day. I am off to find a piece of aluminum that is 5' by 5 1/2" (likely 1/8" but possibly 1/4" thick).

Are you going to run the Gilmer pulley on the water pump?

The kit uses the back side of the gilmer belt for the WP since it spins backwards on the FD.

https://cimg8.ibsrv.net/gimg/www.rx8...e38703fa58.jpg

Also I thought through this a little bit and I decided to not be an idiot. I am going to move the Compressor upwards 1 inch, forward 1/4" to properly align it, and just cut the custom adapter plate to clear the FD bracket. Additionally, I will use new short bolts to put the adapter plate on the bracket. I will tap the new holes for the rx8 compressor to mount to the adapter plate. Clear as mud yet?

See pic below. Bolts are in the OEM FD location, while the open holes are where the Rx8 compressor will mount. https://cimg9.ibsrv.net/gimg/www.rx8...6793e30ee1.jpg

That will be OK...there is an issue with Gilmer pullies and water pumps that cause a lot of stress to the pump bearing.

I have heard about the stress on the alternator pullet, but not on the WP yet. Please share if you feel inclined! Here is a CAD drawing, courtesy of my eldest brother, to help those who are unfamiliar with the specific parts.

Rx7 Tensioner Pulley Bracket >> Custom Adapter Plate >> Rx8 AC Compressor


https://cimg9.ibsrv.net/gimg/www.rx8...76cea4422e.jpg

Looks like it will work 😊

The Gilmer issue was something a mechanical engineer from a race team told me. He said that when you decelerate fast the motor slows down and the coolant keeps moving due to the mass. He says it puts suprising large torque on the water pump bearings and flange. He has seen them twist the flange off the pump or take out the bearings in short order.

Not something I had heard before but it makes sense

I can't see how that kit won't slip. Gilmer belts are not supposed to be run super tight, seems like with the proper tension the water pump pulley would just slip all the time.

Why are you so set on using a gilmer belt when you have absolutely zero need for one?

They sound cool 😊

Interesting, I think they sound like shit.

qft.

^ The man has got it. No real performance reason. Why would I "waste" time sanding and polishing the UIM if it doesn't give a performance gain? Same sort of thing. I wasn't going to reuse the crappy rusted stock pulleys so I figured I would upgrade while I was at it. And yes idk if this kit solves the WP slipping issue. Maybe the wider belt will help? Hopefully? Time will tell!

Electric Water Pump ;)

Ordered Rx8 Idle/Tensioner Pulley and 1/4" metal plate. Got the former and was sad to see it doesn't have any of the dimensions I had hoped for. Oh well, more work to do, not a big surprise. I will be using a washer on the back side, a spacer within the pulley, and another washer on the front. My brother suggested I get precise measurements and have them custom made. I am hoping to make this as simple as possible by getting parts from Mc-mastercarr or something similar. Let me know what you guys think is best. Lastly, the nut or the Rx7 FD idle pulley does not clash with the bearing on the new Rx8 pulley, so that is re-usable. Basically the inner diameter of the pulley changed.

https://cimg9.ibsrv.net/gimg/www.rx8...6cfc76c231.jpg

https://cimg0.ibsrv.net/gimg/www.rx8...30fce794e9.jpg

https://cimg3.ibsrv.net/gimg/www.rx8...d877e6c244.jpg

Alright gang! Here are the two custom pieces you will need for this job: adapter plate and pulley spacer. Here's what I got so far. I botched the ac mounting holes, so I will have to redo those. Additionally I ordered the plates prior to deciding to move the ac up, so I have to use two plates. Anyone else could use one plate. A few progress pics:

https://cimg3.ibsrv.net/gimg/www.rx8...46d2109030.jpg

https://cimg6.ibsrv.net/gimg/www.rx8...8d3df35e8f.jpg

https://cimg7.ibsrv.net/gimg/www.rx8...1ad3aa6751.jpg

https://cimg8.ibsrv.net/gimg/www.rx8...d822bff654.jpg

https://cimg9.ibsrv.net/gimg/www.rx8...3ca9ae2287.jpg

Update: AC idle pulley done! Spins like a champ and looks aligned to the eye ball. Just buying a belt and redoing the bracket is all that's left and once I get the holes right I will put out all the part numbers and measurements and we will finally have a documented RX8 AC to FD Front cover write up!

https://cimg2.ibsrv.net/gimg/www.rx8...5dc7b10027.jpg

https://cimg3.ibsrv.net/gimg/www.rx8...c1c8f8bfa7.jpg

How easy do you think this is to do with the engine in the car?

Good work man but you might have clearance issues.
Have you tried it in the car yet? not sure if you gotten that far in your build.

I hope you have enough room to get to a/c compressor in there.
Looks to be sitting further down and sticking out further(meaning closer to the drivers fender).
Also the steering shaft is in that area.
Just something to consider... I hoping it all clears.

#norenesis
.

Just as firecran mentioned I haven't gotten to the point of fitting in the car. At that point, modifications will have to be made to the other items to make it fit. I haven't had a chance to look as my Rx8 is covered up for the winter. If anyone can take pics and mark distances in the Rx8 bay, we can coordinate roughly what the clearance will be, otherwise it will have to wait until next winter when this build actually starts.

Wow that looks like a ton of work to get that all to fit on there, I sure hope it all fits. Good work.

Thanks, it would be a bummer if it didn't fit for sure. Anyway, almost done!

https://cimg6.ibsrv.net/gimg/www.rx8...4cfdb2ec47.jpg

https://cimg7.ibsrv.net/gimg/www.rx8...b2c0e76f68.jpg

https://cimg8.ibsrv.net/gimg/www.rx8...b6ffdb6b2b.jpg

https://cimg0.ibsrv.net/gimg/www.rx8...0a01d6337a.jpg

https://cimg1.ibsrv.net/gimg/www.rx8...9ce7b159e4.jpg