underdrive pullies

pxcr_600 · 01-24-2002, 04:14 PM

Hey guys, would adding underdrive pullies to my 85 GT make a big difference? HOw about a good intake? How much would these things cost and how much HP would i gain? Mine is stock and my goal is about 300 HP. Any idea's, exlude the NO2. I will save that for later.

Mustang_289 · 01-24-2002, 05:33 PM

Underdrive pullies is one of the cheapest easiest ways to gain a some horses - I believe somewhere around 8 hp.. Cost is under $100 bucks sometimes you can find sales for about $50 (MAC). Be carefull if you've got a lot of power suckers in your car like a stereo, electric fan etc and you've got the 65amp stock alt you may have some starting problems.

We installed underdrive pullies and put a PA-PERFORMANCE 3G 130 amp alt on as well.

Mr 5 0 · 01-24-2002, 05:57 PM

pxcr_600:

Underdrive pulleys are fairly cheap (as performance mods go) at $100. or less and are worth from a 5 to 10 HP increase.

Your '85 could really benefit from a true duel exhaust system, possibly from a later model. Losing the catalytic converters would help a lot, if emissions aren't a problem in your state. High-flow cats are another option when replacing the exhaust. Cost a lot more but are legal.

Of course a better intake and carb tweaking wouldn't hurt HP a bit.

Your stock engine was rated @ 210 HP in '85 so you need another 90 HP to get there. Not easy.
Subtracting 10 for the pulleys and maybe 15 for the exhaust you still need another 65 HP to reach your goal. Aftermarket heads and intake would get you close but thats fairly expensive, as you know.

I would focus more on et rather than HP numbers.
HP numbers don't mean all that much, it's who wins that counts. From that standpoint I would suggest a 3.73 ratio rear gearset as a great mod to wake up your '85, along with the pulleys, exhaust, intake and carb work.

Unfortunately, your '85 has the weak 7.5" rear so I would think about just replacing the whole rear with one from a later model Mustang and do the ring and pinion, seals, bearings etc. at that time.

If you're really set on having a dyno readout of 300 HP, you'll need better heads, at least, plus the other items mentioned.

pxcr_600 · 01-24-2002, 07:36 PM

So to reach about 300 hp. I should go for a grand. Can i run 12:1 with prem fuel? The heads are so expensive.

Unit 5302 · 01-25-2002, 01:44 AM

12:1 compression is not realistic on iron heads. I would stay below 10.5:1. Even then you'll be pressing the limits.

To get the power you're looking for, the true dual exhaust, an intake, and better carb will come in handy. The heads will need upgrading as well.

01-24-2002, 04:14 PM	#1
pxcr_600 Registered Member Join Date: Nov 2001 Location: Elk River, MN Posts: 44	underdrive pullies Hey guys, would adding underdrive pullies to my 85 GT make a big difference? HOw about a good intake? How much would these things cost and how much HP would i gain? Mine is stock and my goal is about 300 HP. Any idea's, exlude the NO2. I will save that for later. __________________ Balls to the Walls

01-24-2002, 05:57 PM	#3
Mr 5 0 Conservative Individualist Join Date: May 1997 Location: Wherever I need to be Posts: 7,487	300 HP? pxcr_600: Underdrive pulleys are fairly cheap (as performance mods go) at $100. or less and are worth from a 5 to 10 HP increase. Your '85 could really benefit from a true duel exhaust system, possibly from a later model. Losing the catalytic converters would help a lot, if emissions aren't a problem in your state. High-flow cats are another option when replacing the exhaust. Cost a lot more but are legal. Of course a better intake and carb tweaking wouldn't hurt HP a bit. Your stock engine was rated @ 210 HP in '85 so you need another 90 HP to get there. Not easy. Subtracting 10 for the pulleys and maybe 15 for the exhaust you still need another 65 HP to reach your goal. Aftermarket heads and intake would get you close but thats fairly expensive, as you know. I would focus more on et rather than HP numbers. HP numbers don't mean all that much, it's who wins that counts. From that standpoint I would suggest a 3.73 ratio rear gearset as a great mod to wake up your '85, along with the pulleys, exhaust, intake and carb work. Unfortunately, your '85 has the weak 7.5" rear so I would think about just replacing the whole rear with one from a later model Mustang and do the ring and pinion, seals, bearings etc. at that time. If you're really set on having a dyno readout of 300 HP, you'll need better heads, at least, plus the other items mentioned.

01-24-2002, 07:36 PM	#4
pxcr_600 Registered Member Join Date: Nov 2001 Location: Elk River, MN Posts: 44	So, about a grand So to reach about 300 hp. I should go for a grand. Can i run 12:1 with prem fuel? The heads are so expensive. __________________ Balls to the Walls

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01-24-2002, 05:33 PM	#2
Mustang_289 Registered Member Join Date: Sep 2001 Posts: 512	Underdrive pullies is one of the cheapest easiest ways to gain a some horses - I believe somewhere around 8 hp.. Cost is under $100 bucks sometimes you can find sales for about $50 (MAC). Be carefull if you've got a lot of power suckers in your car like a stereo, electric fan etc and you've got the 65amp stock alt you may have some starting problems. We installed underdrive pullies and put a PA-PERFORMANCE 3G 130 amp alt on as well.

01-25-2002, 01:44 AM	#5
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	12:1 compression is not realistic on iron heads. I would stay below 10.5:1. Even then you'll be pressing the limits. To get the power you're looking for, the true dual exhaust, an intake, and better carb will come in handy. The heads will need upgrading as well.