Serpentine Belt size and Underdrive Pulleys

[pavlos413]

Just so you have some background info, I removed my smog pump but put a LMR offroad pulley on it. I also put on a set of the SVE underdrive pulleys on my car, therefore I did not bypass anything. Well the belt that came with the kit was a 90.3 inch belt. There was too much slack with that belt and I thought my tensioner was bad, so I got a new one. Still didn't fix the tension. So I went to the parts store got 2 smaller belts to try out and the correct size working for me was 88 and 7/8 inches. Hope that helps some of you.

I tried measuring the pulleys with a string and got around 85 inches but knew that was too short....maybe I used the wrong type of string or did it wrong somehow? I don't know, so I tried a 3 inch shorter belt and 2 inches shorter belt than the belt kit and one of them worked perfectly.

Trial and error sometimes does work. I attached the before/after picks so you can see the correct tension now.

 

[Mustang5L5]

Gotta add a couple inches for the tensioner and the extra angle that it adds when it tensions the belt.

I usually measure with the string tight, add 3” and then buy a belt that size plus, 1” above and below that measurement. Test fit, and return what’s not needed or try a different belt if needed.

 

[pavlos413]

And here she is now in all her glory...Future mods to install for me will be 70mm Throtttle body and egr spacer. 3.55 Ford Racing Gears with new speedometer cable and gears. I also just bought a Performance Automatic Street/Strip Automatic Transmisson Shift Kit. Now I have to save up money for installation.

 

[evintho]

Next time anyone needs to measure for a serp belt.....this is the ticket. Tailor's tape. Ask your wife. Any yardage store will carry one. Wrap it around the pulleys and get an exact measurement. Also, what Mustang5L5 said. Buy 3 belts and return the 2 that don't fit. NAPA carries serp belts in 1/2" increments.