why use a lower crank pulley?

[Rick James]

I have to agree with the "boost is boost" theory here. The torque peaks at a LOWER blower RPM where the blower is still relatively efficient. Peak HP is obviously made at higher RPM where the blower becomes inefficient and falls off. That is why I think TQ increase is greater than HP at those boost levels on the Heaton......

 

[96stanggt]

You're talking night and day! 2.8 to a 2.65 isn't comparing a TQ curve to a 2.75 upper stock lower and a stock upper and 6 pound lower.

Huge huge difference! If it is all about boost then why do underdrive pulleys exist for NA cars?

Because they reduce the rotational mass and free up power. But aftermarket lowers are larger and spin the everything else harder, it's the complete opposite affect. A 2.75 upper/stock lower and stock upper/6# lower should produce the same numbers.

 

[Rick James]

Huge huge difference! If it is all about boost then why do underdrive pulleys exist for NA cars?

Ah, but has anyone really seen much of a difference with U/D pullies on a N/A car? I know I didn't with my 01. :shrug:

 

[CobraBob]

I guess we're still waiting for a definitive and proven answer.

 

[jm@ReischePerf]

If it is all about boost then why do underdrive pulleys exist for NA cars?

For a totally different reason: they spin the accessories slower to reduce drag on the engine. On most modern cars they don't really make much power though, kind of a robbing Peter to pay Paul proposition.

 

[jm@ReischePerf]

Honestly I respect many of you who have posted arguments on here and I know that you most of you are intelligent people but I think maybe this whole debate is sparked by a bit too much imagination and possibly misinterpretation of dyno numbers.

Don't need a physics prof for this equation:

Engine rpm(X) = Blower rpm

X = Final drive ratio - whether this is created by an upper, lower or combo of the two; this is a fixed ratio, not a variable ratio.

With the final drive ratio being equal on two different pulley systems and assuming there is no belt slip on either system, the only difference in engine power should be created by the rotational mass of the pulley(s) being used and the length/elasticity of the belt. However, I'm sure any power/torque differences would be small if even noticeable.

 

[spincobra03]

I would love to see this comparison. As Bob said earlier, this topic has been beat to death (almost as much as what Tranny Fluid is better :rollseyes).

I would like to see the science behind this mystery :read:.

And I am with Almo on this one, a lower only car with the same overall blower RPM as an upper only car will make more torque :burnout:.

Hummm which tranny fluid IS better???? I think im gonna start a new thread.;-)

 

[2004silvercobra]

i had a 2.8 upper and stock lower and did 460/466, than did a 2.8/4lbs and did 467/495. all i have ever seen even with my kenne bell is a huge tq increase not hp..

 

[Almo]

Honestly I respect many of you who have posted arguments on here and I know that you most of you are intelligent people but I think maybe this whole debate is sparked by a bit too much imagination and possibly misinterpretation of dyno numbers.

Don't need a physics prof for this equation:

Engine rpm(X) = Blower rpm

X = Final drive ratio - whether this is created by an upper, lower or combo of the two; this is a fixed ratio, not a variable ratio.

With the final drive ratio being equal on two different pulley systems and assuming there is no belt slip on either system, the only difference in engine power should be created by the rotational mass of the pulley(s) being used and the length/elasticity of the belt. However, I'm sure any power/torque differences would be small if even noticeable.

I for one agree to disagree. If you have an upper (no lower) spinning the blower at a certain RPM as a lower (no upper) spinning the blower at the same RPMs... then the TQ curve will be moved lower in the powerband.

I spoke to Chris at Excessive yesterday and we are going to pull my car with just a 6 pound lower (stock upper) and match it up to my dyno curve when I had the 2.75 upper (stock lower). Of course, the 2.75 upper spins the blower at the same motor RPMs as the 6 pound lower (stock upper) will. Either way, comparisons of the dyno runs will be able to tell for sure if TQ curve is different pending on if a lower or upper is used around the same boost level.

 

[CobraBob]

That will be cool Allen. Finally an actual test that will provide some real conclusions. In case I miss the thread, if you think of it shoot me off a PM when you post the test results.

 

[SicStang03]

I understand what everyone is saying and I can see both sides of the argument. What I don't understand is why everyone keeps talking about tq. Why not include hp? If you have a 2.8 upper and do a pull and then add a 2 or 4lb lower and do a pull, your tq will go up drastically and your hp will only creep, if that. I have seen plenty of dyno sheets and peoples numbers.

If boost is boost, why doesn't hp change drastically like the tq when using an upper/lower?

I am curious to see the graph Almo..

 

[jgheels2003]

I understand what everyone is saying and I can see both sides of the argument. What I don't understand is why everyone keeps talking about tq. Why not include hp? If you have a 2.8 upper and do a pull and then add a 2 or 4lb lower and do a pull, your tq will go up drastically and your hp will only creep, if that. I have seen plenty of dyno sheets and peoples numbers.

If boost is boost, why doesn't hp change drastically like the tq when using an upper/lower?

I am curious to see the graph Almo..

Increasing the boost past a certain level without porting the supercharger is exactly the reason why the hp won't change drastically. You need a blower that is more efficient with higher levels of boost.

This is why you port. Superchargers/turbos have an efficiency range. If you just keeping upping the boost passed this range you are creating more heat without increasing flow further in the powerband. You'll make the power a little quicker, inc. torque, but you'll be more prone to heatsoak, timing etc etc.

 

[Sniperdog]

And since the heaton can only flow so much and then looses boost in higher rpm, that higher rpm # (hp) may not go up bt the mid rpm # (tq) will go up, cause there is more boost at that rpm,., so tq goes up when hp may not :thumbsup:

 

[DieselNuts]

A 2.75 upper/stock lower and stock upper/6# lower should produce the same numbers.

I am a complete rookie to this subject and thats why I am reading this thread, but as far as what this chart says, a 2.76 upper/stock lower spins 17,899rpms making 15.2#of boost, while the stock upper/6# lower spins 16,205rpms and creates 13.5# of boost. So, if boost is boost, these combos will not make the same numbers...

 

[Rick James]

Double Post!!:fm:

 

[SicStang03]

OK.. Because of my setup I only see 13# max... If I through a 2lb on there I will see around 15#. But because my boost is lower, is the blower rpm down too? I will still make the same power with less boost/heat ect... Obviously more efficient because of this but how do the blower RPMs compare to this?

 

[Rick James]

I understand what everyone is saying and I can see both sides of the argument. What I don't understand is why everyone keeps talking about tq. Why not include hp? If you have a 2.8 upper and do a pull and then add a 2 or 4lb lower and do a pull, your tq will go up drastically and your hp will only creep, if that. I have seen plenty of dyno sheets and peoples numbers.

If boost is boost, why doesn't hp change drastically like the tq when using an upper/lower?

I am curious to see the graph Almo..

Didn't I explain this on page 2?

I have to agree with the "boost is boost" theory here. The torque peaks at a LOWER blower RPM where the blower is still relatively efficient. Peak HP is obviously made at higher RPM where the blower becomes inefficient and falls off. That is why I think TQ increase is greater than HP at those boost levels on the Heaton......

I for one agree to disagree. If you have an upper (no lower) spinning the blower at a certain RPM as a lower (no upper) spinning the blower at the same RPMs... then the TQ curve will be moved lower in the powerband.

I spoke to Chris at Excessive yesterday and we are going to pull my car with just a 6 pound lower (stock upper) and match it up to my dyno curve when I had the 2.75 upper (stock lower). Of course, the 2.75 upper spins the blower at the same motor RPMs as the 6 pound lower (stock upper) will. Either way, comparisons of the dyno runs will be able to tell for sure if TQ curve is different pending on if a lower or upper is used around the same boost level.

Should be interesting. It would also be interesting to see a 2.76/4lb combo compared to a 10lb lower only to see the differences in the higher boost ranges. Let me know when you do the test, I may swing by. :beer:

 

[SicStang03]

Didn't I explain this on page 2?

Totally missed that post.:beer:.. I should have known that too... considering I just ported and gained over 40 RWHP:rockon:

 

[Almo]

Even with boost down a bit on the 6 pound lower (stock upper) it will still show the difference in TQ at peak and throughout the curve compared to the 2.75 upper (stock lower).

 

[SicStang03]

Even with boost down a bit on the 6 pound lower (stock upper) it will still show the difference in TQ at peak and throughout the curve compared to the 2.75 upper (stock lower).

I agree...