Monty

bInteresting article in the August issue of Hot Rod.
Take a stroked 327 ci SBF with common aftermarket parts, and compare the performance of the engine with commonly available Centrifugal (Paxton Novi 1200), Turbo (HP Performance T62-1), and Roots (Holley 174) supercharger kits. Boost was limited to 9.5psi, non-intercooled.

--------------------------------Baseline------Centrifugal------Turbo--------Roots
Peak HP---------------------392@6000------617@6000----600@6000--535@6000
Peak TQ---------------------386@5200------561@5200----617@4200--513@4600
Min Boost--------------------------------------1.7@2500-----5.7@2500--4.8@2500
Max Boost-------------------------------------9.5@6000-----9.5@5100--8.0@6000
Ave HP(2500-6000rpm)-------310-------------412------------460---------394
Ave TQ(2500-6000rpm)-------365-------------494------------564---------483
Ave HP(4000-6000rpm)-------352-------------518------------555---------472
Ave TQ(4000-6000rpm)-------371-------------542------------585---------497

TQ@2500-----------------------------------------360------------490---------440
TQ@3000------------------------340-------------405------------500---------450
TQ@3500------------------------355-------------450------------560---------475
TQ@4000------------------------365-------------500------------610---------500
TQ@4500------------------------380-------------525------------610---------505
TQ@5000------------------------375-------------555------------600---------505
TQ@5500------------------------355-------------555------------560---------485
TQ@6000------------------------354-------------540------------530---------475

HP@2500-----------------------------------------170------------235---------210
HP@3000------------------------190-------------235------------290---------250
HP@3500------------------------240-------------300------------375---------325
HP@4000------------------------275-------------375------------455---------375
HP@4500------------------------325-------------450------------525---------445
HP@5000------------------------360-------------525------------575---------485
HP@5500------------------------380-------------575------------600---------510
HP@6000------------------------395-------------617------------600---------535






[Modified by Monty, 5:54 PM 6/28/2003]

PatG

So it looks like the centrifugal wins out on the high end but the turbo seems to have a wider powerband. The roots does not seem to hang with the crowd.

What is the difference between the turbo and centrifugal type?

Twin_Turbo

the centrifugal only wins above 5500 with very little difference, all rpms lower and the turbo is on top.



[Modified by Twin_Turbo, 5:51 PM 6/28/2003]

1979toy

I found it to be an intersting article, but wish that they had given more type to the cost and setup problems with the various systems.
While I would love to have a twin turbo system like Monty's I lack the skills to do the work myself and most vendors are better at beating thier drum than backing those words up with proven systems installed.
The supercharger systems are a bolt on for most vehicles.

Fevre

Is there any way to even out the boost on the super charger? Starting at 1.5 is a real disadvantage. Wonder what the average hp per lbs of boost is.

Fevre

Just noticed that for the numerical figures at rpm levels the sc does not go over 600 hp but in the peak it says 617? :confused:

EDIT

Upon further inspection it seems that hp and tq are reversed for the rpm levels.





[Modified by Fevre, 6:38 PM 6/28/2003]

Monty

Fevre,

Sorry 'bout that, I fixed it. Thanks for catching my error.

Not really. You can change pulleys, etc. but since a supercharger is belt driven, the boost curve is dependant on engine rpm. It can't make as much boost at lower rpms as it can as the rpms increase. That's one advantage that turbos have, they can make boost at low rpms and maintian that boost throughout the rpm range, hence more average torque and horsepower (more area under the curve). This goes against "internet wisdom" that seems prevalent - that turbos are "high rpm only power adders", which is obviously not true.

The turbo made more power and torque compared to the other power adders at every rpm point up to about 5700 rpm, and was only down 17hp at 6000 rpm, where all the engines' curves were heading south.

Boost is not a good indication of power production or potential, since it is merely "stacked up" air in the intake manifold. More efficient intakes and heads will make more power with less boost.


[Modified by Monty, 6:58 PM 6/28/2003]

Bearcat

Quote:
________________________________________ __________
So it looks like the centrifugal wins out on the high end but the turbo seems to have a wider powerband. The roots does not seem to hang with the crowd.

What is the difference between the turbo and centrifugal type?___________________________________ ______________

How can you say the roots does not seem to hang with the crowd? Look at the area under the torque curve. The roots has more torque than the centrifugal until almost 5000 rpm. On the street, it would be the centrifugal that can't hang with the roots.

The turbo's curve really surprised me. I didn't expect it to have more torque down low than the roots. I knew the power would be the highest of the three, but more importantly, it had the most torque too.

To answer your question, the centrifugal and the turbo have the same impeller design, but while the turbo is exhaust driven, the centrifugal is driven by the crank. There isn't much you can do about a centrifugal having low boost at low rpms. The characteristic of that supercharger is that it has a linear boost response, if you buy that kind you have to live with that. But there are good advantages too. It's no harder to install than an accessory, you can fit it under a stock hood, and you can intercool it.

Another thing they didn't talk about in the article, which is very important, is the size of each. They used a very large centrifugal, a Paxton Novi 2000, but they didn't use the largest roots blower. The reason that's important is because a larger roots supercharger will move more air at less rpm, meaning even greater torque. They may have very nearly had the roots blower come in second place, and first in low end torque, if they had chosen an 8-71. I thought about writing them and asking about that.

Another interesting note is that they left out the screw superchargers. These are supposed to have the low end of the roots, but the peak more like a centrifugal. They "say" that's because there wasn't any available at the time of the article. Huh? They've been selling them for years, how is it that they weren't able to have a screw supercharger available?
:confused:

If it weren't for the height of the roots, that might be the ideal street set up, since you need strong low end torque for good street performance. I'd like to build a 50's Chevy pick up, and my choice would be a 406 small block with a fairly large roots blower, at least a 6-71. That should be good for towing.

Fevre

No problem!

Does it state why the roots blower only reached 8.0 boost? That is a pretty big diff from 9.5 , would be an increase of almost 19%.

Very interesting comparison though. I still want to try a super charger in the vette with a 383, FI and LT1 intake.

turtlevette

i like turbocharging. exhaust gases that would be run through a muffler with a resulting hp loss is used in the turbo. I guess in therory less muffler is needed.

i used to run my Grand National with straight pipes and it wasn't even loud.

Monty

Actually, they used a Novi 1200. In the "Conclusions" section, they questioned if a Novi 2000 would have produced a better curve. They also mentioned they would have probably benefited from a larger Roots blower such as a 250 Powercharger or 6-71. The smaller Roots they used couldn't keep up with the engine and make the 9.5 psi limit even with the smallest pulleys.

As a side note, it was mentioned in the Hot Rod Online section that the Project Anvil Motown-based stroker they've been beating on the last few months with nitrous is now a Twin-Turbo motor. They also mentioned in the Editor's story that more turbo stuff is coming, "It's Turbo Time", so I'm betting there's a future "TT Anvil" story coming soon.


[Modified by Monty, 6:17 PM 6/28/2003]

Bearcat

:iagree:
Okay. I must have misread that. I thought I saw Novi 2000 instead of 1200. And yes, they absolutely would have gotten better results with a bigger roots blower. The smaller blower would have to spin faster to make the same boost as a larger blower. They of all people should know that, being Hot Rod editors. That surprises me a little.

The drag racers running roots blowers every weekend must have some reason why that's the blower of choice.

Monty

In classes where Roots blowers are still used and dominant, the rules don't allow Turbos or Centrifugals

Fevre

Monty

I have always wonder way running the exhaust through the turbos does not create a bottle neck of back pressure, like if you ran it through a smaller pipe? Obviously this does not happen but it seems it would to some extent.

Monty

It does create back pressure, as a matter of fact it is common for the backpressure between the exhaust valve and the turbine to be 2 times greater than the boost pressure. In other words, in some systems making 10psi of boost, there might be as much as 20 psi of backpressure in the headers. Obviously, this does diminish power production somewhat, but it is substantially less than the parasitic power loss associated with belt driven superchargers.

Of course, better header and turbine designs lessen the back pressure, and well designed systems will have backpressures relatively equal to the boost pressure. In relative terms, this would equate to the intake/exhaust pressure balance typical of a naturally aspirated engine, so the back pressure is no longer a liability.

One thing alot of people don't realiize is that as a turbo gets larger it's efficiency increases. If you study the compressor and turbine maps you can see this. A larger compressor will make boost at lower compressor speeds than a smaller one will. This is basically similar to Bearcat's statements above about larger Centrifugal Superchargers. The same goes for the turbine side, the larger turbines result in less backpressure, but at the expense of lag.

Speaking of lag, most people blow this out of proportion and don't really understand it. Unfrotunately, most people's impressions of turbos are based on small displacement, or old turbo systems that are not optimized compared to current standards. As you can see from the results of the Hot Rod comparison, modern turbo's have no problem spooling up and providing boost throughout the rpm range when properly sized and applied. In any regard, the fact is that turbo lag is measured in milliseconds and the turbo is still providing boost well ahead of a belt driven supercharger.

evilsmf

I'm Happy :hurray: with my 509 and 8-71 :rofl:





[Modified by evilsmf, 8:54 PM 6/28/2003]

Bearcat

Well ...actually...
:leaving:

The Subaru WRX has quite severe turbo lag. If you catch one with his pants down, it'll take up to 2 full seconds for his turbo to spool up and start pulling hard. But if he's ready for ya, he can keep that lag insignificant with the proper throttle technique.

The A/R ratio tends to affect turbo lag. (This is far more of a problem with lower torque 4-bangers than it is with a V8). The higher the A/R ratio, the more air it can pump, but the longer it takes to spool up (lag). This can be minimized, as you say, with some careful matching of the turbines and the compressors. Some hybrid turbos minimize lag while maximizing "boost".

Some of this changes when you introduce extremely light ceramics, but then durability is an issue.

Monty

Exactly, it's a 4-banger with 2.0L of displacement (2.5 for the STI). That was my point, most people's impressions of turbos are based on these small displacement imports. V8's are a totally different story. The WRX and the like isn't even in the same league.





[Modified by Monty, 7:10 PM 6/28/2003]

Bearcat

Monty, I've got a question for ya. I know you probably built your engine to the nines. But for a guy just wanting to twin turbocharge and intercool a stout V8, with the forged crank/rods/pistons and aluminum heads, how much extra would you say twin turbocharging would cost, roughly?

I went with a 427 big block instead of a twin turbocharged 377 small block thinking I'd get more bang for the buck, but once I did the conversion to the big block, suspension, radiator, exhaust, etc., I'm not so sure. One thing's for certain, the twin turbo 377 could have been driven somewhat economically to work on occaision, and the gas mileage of the big block is so bad that it isn't economically wise to drive it to work, even on occaision.

Monty

As with everything else, there's a wide range in terms of what you can spend. I know guys that have less than $2000 in their turbo systems and are making huge power, and then there's guys that have spent ten's of thousands to make huge power. Browse the forced induction forums over on Thirdgen.orf or Camaro Z28.com and there's guys with $2000 setups making 800 hp using salvage yard turbos and intercoolers along with log style headers. There's a guy here in Chicago that I am familiar with that's making 1000+ hp in a daily driver 5.0 Mustang with less than $3000 into it. He's using cast-iron weld el manifolds. I'm currently helping a college student build a budget turbo setup and he's got less than $1500 into it and he'll make 600-800hp.

The thing with turbo's is that the engine is mild and economical when driven normally. I get 20-22 mpg.