Want to change the serpentine belt configuration to include a 25% underdrive crank pulley, alternator (low driverside mount location), ribbed idler, water pump & tensioner. Basically, this will mean an approx. wrap angle of 90 degrees on the crank pulley. All other pulleys will have more wrap angle w/ only the water pump using the flat side (non-v side) of the belt.

Has anyone else used a minimum 90 degree wrap angle w/ a stock belt tensioner? Is it enough tension to maintain grip & 6700 RPM? If not, which sponsor sells a high tension pulley & how much more than stock tension does it create? Thank you


Please no guessers. I appreciate all comments, but only experience w/ a 90 degree minum wrap angle &/or angle to tension calculation will reveal the correct answer. The set up can work as long as the there is enough tension.

 

For the archives, ended up adding another idler pulley & mount between the crank & alternator pullies. This creates a 110+ degree wrap angle @ the crank, of which am sure will work.

 

This sounds a lot like what I'm going to do as well.

 

Do you have any pictures of the belt installed, with the new tensioner? Thanks

Chris

 

Gonna bring this back from the dead. Any updates or pictures?

 

I have changed my pulley/belt setup.





notice no tensioner



that us a modded mezeire street pump with no pulley on it. I've been running it like this for years. Turn it to 7k.

 

That’s a great setup you’re working on—choosing a 25% underdrive crank pulley and aiming for a 90-degree wrap angle on the crank seems like a smart move to reduce parasitic loss while still maintaining accessory performance. I’ve seen similar configurations run reliably at high RPM, as long as the belt tension is properly managed. Stock tensioners can sometimes struggle when the wrap angle is as minimal as you're aiming for, especially at 6700 RPM, so it might be worth considering high-tension options from brands like Gates or Dayco. They offer models with increased preload that could help keep grip even under high-demand conditions.

Interestingly, although I’m an app developer in London, I’ve spent quite a bit of time working on LSX swaps and Miata setups as a hobby—so I really appreciate the attention to detail in your build. You’re absolutely right to look for real-world experience, as figures alone don’t always tell the full story. Do keep us updated on how the setup performs once you've sorted the tension.

 

Tension is fine. Even more so now with the adjustable alt bracket from jegs. It's been ran to 7800 rpm.