I'm thinking about making some custom underdrive pullies and was wondering what would be some good percents? Also to make them turn slower the pullies need to be bigger right? The only one i am thinking about making a little smaller is the alt. because i am running a decent sound system.

 

To slow down the accessories, the drive pulley needs to be smaller and/or the driven pulley larger.

It would probably take 20-30% to make a noticeable difference.

 

Make them? You have the tooling to get that V-belt sizing and angle correct?
I can think of a pile of things i'd machine if I had my own lathe/milling machine before I'd worry about underdriving certain accessories. That's more of an import thing to do, ie when you've already squeezed every last HP out of the engine, and you're now trying to squeeze HP out of your accessories.
Hint - Squeeze the engine more first. Less downsides vs underdriving stuff.

 

I'm in a engineering/manufacturing class and I was trying to think of somewhat simple stuff that I could make and the only thing I could think of that could add a little HP was underdrive pullies, and it would be kind of cool to have a 1 off part... what else could I make???? I have just about every machine available to me too.

 

Shifter **** is the obvious one.

Strut tower brace (requires a smidge of welding).... A couple of carb spacers. Try a 4 hole, try and open, etc. Buy a block of phenolic/garolite and make those up.
I can't think of any others right now, but be creative.

 

a carb spacer sounds like a good one... is phenolic just more heat resistant than aluminum?

 

Phenolic doesn't transfer heat much at all. Aluminum lets heat move through it very very quickly. Use wood/phenolic/garolite, etc etc. Wood probably isn't ideal since it doesn't tolerate the gasoline very well. Use mcmastercarr to spec some 1/2" thick material. I know they sell garolite there (enjoy the smell of machining it! )

 

alright, i will machine a prototype out of aluminum or something but what is the biggest or ideal thickness for it do you think? Also I was looking at some tapered designs but they seem kind of complicated so i was just going to go with an oped design, how much of a difference do you think it will make?

 

Carb spacers?
Don't bother prototyping it with aluminum. Aluminum is expensive. Proto it with fiberboard (MDF). Or buy the phenolic and just use that.
1/2" you're wasting your time with anything smaller. 1" is too tall to close your hood.

Grab a JY q-jet, and remove the bottom plate. Remove the butterflies. Make a 4 hole to match that, and make an open one. Make the 4 hole one like venturi's, so that they open up more as the fuel goes down. Use a die grinder and a sanding drum to do that. Not crucial, but worth trying.

It can make 5-10HP or so they say.

 

ya, I got some cheap stuff called REN or something which is like that. I might still have the q-jet, i will check.

 

Wait, what's on the car now as far as a carb ? Use a base plate that's similar to get the holes right.
I just assumed it was still a q-jet, so you'd use a q-jet to line up the holes.
If you have a holley squarebore, then you use a square bore.

 

oh, no i got an edelbrock 650. is there any way to do it without the carb? I'm gonna see if i can find some dimensions. the bolt holes are 4x4 right? And am i gonna need longer bolts too?