10% pulley?

Couple of things to know about. A 10% on stock exhaust is not a good idea. Headgaskets are allready a week point on these cars and the increase in pressure from a 10% pulley just makes them more likely to blow. The other thing is the heat that is generated from spinning the sc that much faster. I forget if it was here or on another site, someone did a little testing. They found that with a stock IC at 3k rpm the knock sensor started pulling timing but that the 5% didn't. Just some food for thought.
 
10% vs. Knock Sensor

93SC said:
A 10% on stock exhaust is not a good idea. Headgaskets are allready a week point on these cars and the increase in pressure from a 10% pulley just makes them more likely to blow.

.......They found that with a stock IC at 3k rpm the knock sensor started pulling timing but that the 5% didn't.
I put a 10% pulley on my '89 XR-7, shortly after I bought it new. It took me about 18 months to blow the HG's. Now I have ALL the intake/exhaust mods, but kept the SIC. Put it on the dyno & found out that the knock sensor started pulling timing at 3K, & kept doing so until redline. That was due to high temp. air flowing into the engine.

Now I have a DIC w/10" fan. Dropped my ET .33 Sec. Haven't put it on the dyno since the DIC & 10" though.

68COUGAR
 
Re: 10% vs. Knock Sensor

68COUGAR said:
I put a 10% pulley on my '89 XR-7, shortly after I bought it new. It took me about 18 months to blow the HG's. Now I have ALL the intake/exhaust mods, but kept the SIC. Put it on the dyno & found out that the knock sensor started pulling timing at 3K, & kept doing so until redline. That was due to high temp. air flowing into the engine.

Now I have a DIC w/10" fan. Dropped my ET .33 Sec. Haven't put it on the dyno since the DIC & 10" though.

68COUGAR
Just out of curiosity what kind of numbers did it make?
 
jre97 said:
Just out of curiosity what kind of numbers did it make?
230 rwhp
330 rwtq

Those numbers are with the following mods:

ENGINE: Coy 1 cam, 70mm MAF w/36 lb tube, 36 lb injectors, 10% pulley, SCCoA headers, Big Dawg Exhaust (2.5" downpipes, no cats, no resonator), Raised Top, Underdrives, K&N panel, Removed Air Silencer. Single IC w/o fan. OEM computer.

DRIVELINE: 3.27 gears, Auburn Cone, RAXLES, Brass Blockers, Poly tranny mount, Poly front diff bushings, RIPPER, 255/50/16 BFG Comp T/A's

NOTE: With the 10% & SIC, the knock sensor was pulling timing out from 3000 rpm to redline. The SIC just couldn't keep up with the 10%

Haven't had it on the dyno since the first time.

MODS Since Then: DIC w/10" fan, SPEC Stage III clutch, Alum. flywheel, Late Model 5-spd w/Brass Blockers {WOW!!!!}, Poly rear diff. mount.

NOTE: When I ran the 14.250 @97.6 {80 mph @ 1/8th mi.} a few weeks ago, it was with the DIC w/8" fan, NOT the 10". Also w/o the poly rear diff mount, which is currently on order. But WAS with the late model 5-spd & SPEC clutch/flywheel & of course, Brass Blockers.

68COUGAR
 
10% pulley

old thread, i know, but good information doesn't expire. i have had one on my car over 100k mi, and it has a little over 130k on it. if you use one, you need to get better exhaust. true duals aren't balanced, but they are a definate improvement, and you should be able to go to any exhaust shop and get 2" true duals until you can get something better. and if you put a cold air induction kit or any maf or throttle body upgrades, you definately need better exhaust. it's restrictive as it is, and it has narrow spots. most importantly about the pulley, if you do use one, you HAVE to use top grade fuel. i was talking to a guy on here who filled his car up with 89 because he was broke, and when he stepped into it, it blew up. the mech said it was early detonantion. you may be able to use el cheapo fuel buy it should only be to go home and get your wallet. i run 18 psi and i have heard mine knock on 90 octane fuel. don't be cheap, it comes back on you like when you leave a crappy tip.

also the heat produced by the supercharger isn't really a big deal. the 94 m90 is rated to spin much faster than it does. don't quote me, but it's rated at around 20k rpms i think. and if i remember they only turn at about 10k or 12k rpms. the older ones are a little slower, but you get the point.
 
belt

oh yeah, i can't find the part number to the belt. there is a smaller belt, but it is to something completely different. in fact the stock supercharger belt is actually a tractor belt the napa carries. if i can find the part number, i'll post here and i'll post a new thread.
 
also the heat produced by the supercharger isn't really a big deal. the 94 m90 is rated to spin much faster than it does. don't quote me, but it's rated at around 20k rpms i think. and if i remember they only turn at about 10k or 12k rpms. the older ones are a little slower, but you get the point.


I don't think that your going ot find a whole lot of people agreeing with you on that one. Heat is huge, and the M90 tends to produce it's fair share.
 
misunderstand

i'm not saying the heat is not important. simply pointing out that the m90 isn't pushed close to it's limit on this car.
 
As with most Roots type blowers, the Eaton M90 has diminishing returns as the RPM increases. Heat is one of the largest factors that play into it.

The faster the blower spins, the more HP it takes to spin it.
The faster the blower spins, the greater the temperature rise due to compression.
The greater the temperature rise of the intake charge, the greater the decrease in volumetric efficiency of the cylinders in the engine.
Thus less power can be generated from the same stroke.
Thus as the Supercharger asks for more power, to compress the air charge more, generating more heat, that sapps power from the cylinders, that are being called on to provide more power.

Eventually you hit a point of limited value. Especially in our cars that are very sensitive to detonation.

Thus, is it a valid bolt on mod? I say yes with the understanding it should be accompanied with a better exhaust system, a better intake system, and a better intercooler.

Personally, I'd rather go with the 10% overdrive Jackshaft pulley rather than the 10% SC pulley simply due to the belt slippage issue. Personally I'm eyeing the development of Super Coupe Innovations 5% jackshaft pulley.
 
i'm not saying the heat is not important. simply pointing out that the m90 isn't pushed close to it's limit on this car.

The speed rating has more to do with longevity of the bearings and efficency. At some point spinning the blower faster consumes more power to turn it than it produces. It's called diminishing returns. That speed will vary with what mods a car has.

I'm spinning mine just about 21,000 rpms at 6,500 engine rpms and making about 17 pounds of boost. I tear the ribs off the jackshaft belt about every three months because it's not big enough to transmit that much horsepower. It's not the high boost I want..it's the greater volume of air. If I spin it any faster it loses top end power. BTW, My blower bearings usually don't last more than a year.

David
 
Dave,

Just curious, did you get a lifetime warranty jackshaft belt? If so, do they hassle you when you bring them in every 3 months for a new one?
Who rebuilds your blowers for you when your bearings need replacement?
 
Dan,

I've never tried turning a belt in for warranty, I just buy them two or three at a time. Right now I've got 3 spares (a kelly springfeild and two gatorbacks).

The first two times ESM did the rebuild and bearing upgrades, this last time I traded my old MP II with ESM titianum shaft and high speed bearings in on a stock (polished) MP II. Charles Warner knows how fast I'm spinning it, and he still warrants the blower.

I've recently installed a less agressive cam (damaged the old one over revving the engine) and won't be racing the car as much, so it will probably last a little longer this time.

David
 
Last edited:
Im a little confused. So, if I got a 10%, I would have to get a shorter belt or bigger tensioner? I also need to upgrade my IC? What size fan do I need; 8 or 10"? I think someone in another thread said that with the 10% you loose hp but gain tq but with the 5% it was opposite of that? :confused: :confused:
 
sonicman1634 said:
Im a little confused. So, if I got a 10%, I would have to get a shorter belt or bigger tensioner? I also need to upgrade my IC? What size fan do I need; 8 or 10"? I think someone in another thread said that with the 10% you loose hp but gain tq but with the 5% it was opposite of that? :confused: :confused:


All those comments above are if you want to optimize the use of the 10% pulley. You can certainly install it without doing anything. But then expect some of the issues if you don't do it.

The absolute necessity is the exhaust. After that the rest is just to give you what you expect from the 10%. Otherwise if you're not going to do something with the IC, something with the intake and other little things, you might as well just do the 5%.

It's all personal opinion, but that's how I see it.

With a 10% pulley you'll want a smaller belt. I think Dave is having belt issues because he is overdriving his SC faster than just a 10% pulley.
 
Yeah,I understand about opening up the exhaust. Im doing that next week. I was just making sure I do everything right. I planned on having the exhaust done, cai, double IC, and IC fan before I put the pulley on.
 
Hey Guys im in the same boat, i have an 90 XR7 with a 10% pulley, i have still have the stock intercooler but have the additional fan, i also switched the exhaust out so the is no more restrictions there. but i have been told i should still be looking at a tune and after reading the thread maby a bigger intercooler also. any thoughts?
 
Back
Top