Serp Belt size question

[1FAST85]

Doing a 351w swap, going to be putting the motor in the car in the coming week, since I know I'm probably not the only one who has done this I'm hoping you all can help me out...

I need to know what size Serpentine Belt I need? I'm running 302 pullies, no A/C, with an air pump eliminator pulley.

Thanks in advance for the help!!
-Chris

[wraithracing]

Chris, I can't give you an exact answer as I ran A/C with my 351. Here is a diagram to show the belt routing options and the most common sizes on a 302. Yours should be a bit longer due to the increased deck height of the 351, but that should get you a good starting point. I would guess the 84.5" would be closest to your combo if you are running the air pump, but as you can see there are a couple of options on how to run the belt on a Mustang. The other option is to use a string to measure around your pullies and then try a belt in that size.





Good Luck!

Trey

[1FAST85]

Thanks for the info Trey!!! I really like the set up of the bottom left on the bottom picture. I'd rather not run my smog eliminator pulley if I don't have to. Thanks again!!

[cb650]

I tried the routing and found troubles. First had to get a 69" belt and then the tensioner pushed the belt so it almost touched itself. I guess there is a way to clock or move the tensioner up. I just ran my smog eliminator pulley.

[ZephyrEFI]

It's funny to me that someone would want to eliminate power steering, but not A/C.

[1FAST85]

I tried the routing and found troubles. First had to get a 69" belt and then the tensioner pushed the belt so it almost touched itself. I guess there is a way to clock or move the tensioner up. I just ran my smog eliminator pulley.

Yeah I've heard of this problem...think I'll just run the eliminator pulley just to be safe. What size are you running now with the eliminator pulley?

[Travis T]

I don't run a smog pump, or at least didn't for 20k miles and never had any issues. All stock pulleys.

[Travis T]

It's funny to me that someone would want to eliminate power steering, but not A/C.

I think the idea there is just to run it at the drag strip. If the air is off, it's just an idler pulley, but the power steering pump takes about seven horsepower to run.

[bwguardian]

For those of you having clearance issues when bypassing the smog pump and/or a few other scenarios. Look at the schematic drawings closely. The factory stock setup starts the belt around the crank pulley on the drivers side. Most the other scenarios (mainly smog delete) starts the belt around the crank pulley on the passengers side. I have a short belt to bypass the smog and have absolutely no clearance issues and the belt is not even close to touching.

[cb650]

I tried the purple route. Which is stock routing with out air and just bypassing the air pump. now just running the stock belt w/o air around the smog eliminator pulley.

[mustangxtreme]

There may be a possibility for the water pump pulley on the 70.5" and 73" belts to slip due to not as much wrap. I know a lot of people have run them that way including myself but, it's still there.

[Go0fY]

If you are doing a 351w swap then the belt diagram is incorrect for the length of the belt, the block of the 351w is about 1.5" taller/wider than the 302w.
Will you running a reverse rotation or standard rotation water pump?

[1FAST85]

If you are doing a 351w swap then the belt diagram is incorrect for the length of the belt, the block of the 351w is about 1.5" taller/wider than the 302w.
Will you running a reverse rotation or standard rotation water pump?

I'm running the 302 pump...which ever that is..haha. I know about the deck height, how much should I add to the belt to compensate?

[1FAST85]

This is the diagram on my rad support, running this water style pump.

[82stang]

the schematic is for under drive pulleys right? so if stock pulleys the lengths are wrong right?

[wraithracing]

I believe the diagrams are designed for stock pulleys, but I might be wrong.

As for the 351W, the deck is 3/4" taller per side to 1.5" wider overall than a 302. IIRC, when I ran my 351 my belt sized increased @ 1-2" compared to the OEM 32 size. So there is a difference, but not much.

Trey

[bwguardian]

The right hand side of the diagram states the belt sizes are for 5.0 engines with under drive pulleys and sizes may vary. It is also good to keep in mind the various differences from year to year relative to pulleys and belt lengths. For example, a stock 85 5.0 only needs the crank pulley for the under drive set because the other pulleys were changed in size from previous years.

[1FAST85]

So since I can't find an exact answer anywhere, I guess I'm going to do the measuring tape/string trick...but now my question is where/in what position should I have the tensioner when measuring? so I can get the right size for the right tension

[bwguardian]

So since I can't find an exact answer anywhere, I guess I'm going to do the measuring tape/string trick...but now my question is where/in what position should I have the tensioner when measuring? so I can get the right size for the right tension

The easiest thing to do is go to your local parts store and try a couple different belt lengths in the parking lot while there. The tensioner should fall in the 4 to 5 o'clock position.

[1FAST85]

Well after a few trips to the parts store I think I finally got the right size belt. So if anyone is wondering...I have a 351w with 302 pullies, no a/c, and using a smog pump eliminator pulley, the size that seems to work best for me is 88.5", part # I used is 885K6.


Thanks for everyone's help and input! Hope this will help someone else out in the future!!

[at_the_junkyard]

Hi guys,

I have been reviewing the diagrams posted with all the different routing for 5.0 serpentine belts. The pictorial notes say that the crank always rotates CW and the water pump always rotates CCW.

When I retrofitted the 302 in my 1980 cobra years ago I had to scavenge for pulleys and brackets for alt and PS, as the motor I got did not have anything etc. The belt/pulley setup I came up with back then (and still have) has everything turning CW with the crank pulley including water pump...so am I crazy or has my water pump been turning backwards all this time ?

It has not give me any problems but got me to wondering after I read the info posted on this thread.

Comments anyone ?

[grabbergreen84]

When I retrofitted the 302 in my 1980 cobra years ago I had to scavenge for pulleys and brackets for alt and PS, as the motor I got did not have anything etc. The belt/pulley setup I came up with back then (and still have) has everything turning CW with the crank pulley including water pump...so am I crazy or has my water pump been turning backwards all this time ?

What year 302 did you use?

[Jerry peachuer]

There's a forward rotation and counter clockwise rotation you will know if you have it wrong very quickly
Rotational differences are in the interior of the pump and it's all in the fin or propeller design
depending on belt routing will determine which pump you need
Smooth pulley is for the backside of a ribbed serpentine belt
You could eliminate all non needed pulleys and do a alternator forward rotation water pump and crank and belt will be very short with a adjustable heim

Easy low cost tip for belt sizing is a piece of nylon rope wrapped around pulleys routed the way you want loop it like its a one piece belt trim it then in loop it and measure it in a straight line and this will narrow your search for sizing purposes

[at_the_junkyard]

It is a 1980 vintage 302 I believe as it has 80 casted on the bottom of the block if I remember correctly. Definitely a 51oz balance so makes sense. It was pieced together by a backyard mechanic buddy of mine back then...so really cant tell you what it come out of.

I suspect the pump is correct rotation for the belts I am using (one for the PS and waterpump and one for the alternator etc) . I noticed that the fans are pitched opposite for different rotation on the serpentine belt motors.

...or maybe I just got lucky with the combo I used ?

Would be nice to know if in fact there is a difference in pumps as I thought all would be the same.

Cheers

[redse]

Well finally got cooling system all redone and went to put the serpentine belt on per the diagrams here, thought I needed the 73 inch way to big used the diagramsnot sure what size? Eliminator ac, no smog pump used the ford ac eliminator kit. Someone here must know size and proper routing thanks!