Advice on belt size?

[Frank Dux]

I know there is a ton of info on this and I spent a lot of time cross referencing on CobraBob's website but I am a bit uneasy with my belt choice.
2.76 upper, 4lb lower with the "New" Billetflow 4 piece idler set (3 100s & 1 90mm)
I ordered the 79.75" belt (Gatorback 4080797)
Am I in trouble? Should i be getting a 79"? I have the stock alt pulley on and wasnt planning on swapping that out either.
I wish i could just buy a bunch and try them but I need to special order everything except for the 79.75..
It looks like i should get a 79.5" belt according to the belt guide...

Got the dyno date on Friday so I am cutting it close...

Thanks!

 

[cobradrivr]

Get a 79", I have same setup, But with 3.2 alt pulley, And i use a 79", You might even want a 78.5" so no slip.

 

[Frank Dux]

Thanks....

 

[Jroc]

You might even want a 78.5" so no slip.

I don't agree.

Ultra-tight belt setups on Cobras running no support brace on their lower pulley can = a bad day in many cases.

IMO if you're running an aftermarket lower you shouldn't try to run a very tight belt setup. Just run a belt with good tention, and go with it.

 

[stangaholic280]

I think the recommended belt size for this setup is a 80". I am personally running the same setup as cobradrivr and I will be running a Dayco 79" belt. From what I've read you should also consider a 3.2" alternator pulley. About $50 from LP. Apparently if you don't change your alternator pulley with this setup it will be under spinning and could potentially cause issues. As for the belt though, 79-80" should work with 79 being on the tighter side.

 

[Frank Dux]

I guess that's where the problem is. You dont want to be too tight and if you are too loose you have belt slip issues... I ordered 78.5-79.75" belts. Something is bound to be right...

 

[Frank Dux]

78.5 has perfect tension. Just a little past the center. It seems to be holding boost but then again I didnt get on it too hard at all since I am not tuned. Dyno day is tomorrow...

 

[CobraBob]

The 78.5" wasn't difficult to install?

 

[Frank Dux]

The 78.5" wasn't difficult to install?

No, it was actually pretty easy and it started slipping on the dyno and squealing like a pig...

 

[bubblehead93]

I think the recommended belt size for this setup is a 80". I am personally running the same setup as cobradrivr and I will be running a Dayco 79" belt. From what I've read you should also consider a 3.2" alternator pulley. About $50 from LP. Apparently if you don't change your alternator pulley with this setup it will be under spinning and could potentially cause issues. As for the belt though, 79-80" should work with 79 being on the tighter side.

actually the other way around, if you keep the stock alt pulley you'll be over-spinning the alt relative to stock. school of thought, to which I subscribe, is that the stock alt/crank pulley over-spins the alt - so you are aggravating the situtation with a 4# lower. if you want to know more, several recent threads you can search through related to alt charging issues.

 

[KINGCOBRA86]

how much power did it pu down ?

 

[Frank Dux]

I agree bubblehead and my plan is to put on a larger pulley for sure. I was looking at the stock blower pulley and was wondering if it will fit on the alternator. I'm sure it wont fit on the shaft but need to look closer.

As far as HP.
I put down 492hp and 520ft/lb at the wheels. Restriction was in my exhaust since I have 100% bone stock exhaust. Up to 20hp there. Also, my belt started slipping at you see boost dropoff at 4500RPM.
I really think the car is good for 520/545 but thats just my hunch... After I change the pulley and tighten up the belt I will datalog and check my boost throughout.