Twin screw vs. Centrifugal - Interesting observations

[Joseph Dell]

Folks -

I'm on a quest to _quantify_ the differences between viper setups out there. So I took a look at about 20 different dyno charts from modified NA cars (Lethal) to ROE SC (a few, including some of his posted early test runs, DLM (biggest sample), and Heffner.

It is also worth mentioning that with the exception of my personal car's DLM level 1 first dyno run (560rwhp and 590rwtq) and one of Sean Roe's test set-ups
prior to the VEC2 (565rwhp and 593rwtq), there were very _few_ dyno graphs that wwere even close for comparison.

As a result, I looked at all the dyno charts NOT for the raw numbers themselves, but for the attributes of a DLM car vs. a ROE care vs. the Lethal car vs. a Heffner car.

- Almost all SC HP and TQ numbers cross at 5300rpm
Treynor's DLM car was closer to 5100rpm, but almost all SC cars, regardless of manufacturer, had this occur.

- about 90% of tq was achieved at 3800RPM on all DLM cars.

- ROE Twin screw cars make about 90% of tq at ~2700 rpm, max at 3500rpm, and begin to gradually drop off TQ at 4200RPM

- DLM cars maintained TQ from 3800 until 5100 on cars w/o head work.

- DLM cars w/ head work have increased tq over 5100rpm.

- Heffner SC cars tends to build tq more gradually with less agressive tq curves. Specifically, 3600rpm to 5100rpm is slightly slower than DLM cars.

- All SC cars w/ head work appear to drop off power higher in
the RPM range (higher than 5100).

I wanted an answer to the "what are some differences" with regards to twin-screw vs. centrifugal... Here they are, right from the dyno sheets.

One note on the Lethal dyno sheet. TQ also began to drop off after 4200 rpm... This car looks like it will respond well to a SC.

I hope this info helps a bit! It certainly explains why my car is slower off the line than some, but faster at the end of the track.

Take care!

Joseph

 

[RedGTS]

Thanks for the review Joseph. BTW, hp and torque should intersect on ALL dyno graphs at 5,250--it's a mathematical function of the way hp is calculated from torque.

 

[Daffy Duck Viper]

Wonderful breakdown, Joseph. Confirms what I had learned from reading other posts on this matter. Nice work. This one will be a good one to keep, and post for anyone that asks about this again, because we ALL know it will get asked again...and again...and again. But, hey, that's what we're here for, right? To learn and share what we have learned.
-Daffy
P.S. I thought this other post of yours was really good, too - which explains the difference between a centrifugal supercharger and a twin-screw/roots supercharger:
DLM Stage 1 vs. Sean Roe
http://vca2.viperclub.org/forums/showflat.php?Cat=&Board=UBB2&Number=249347&page=0&view=collapsed&sb=5&o=7&fpart=1#Post249728

 

[J DAWG]

Jd

Do you have the graph of your stage 1 pull. I have the Roe graph and I would like to compare them with my own eyes. Great info. Thanks1

 

[lleone]

BTW, hp and torque should intersect on ALL dyno graphs at 5,250--it's a mathematical function of the way hp is calculated from torque.

Specifically: HP = (Torque * RPM) / 5252.

Search the archives for the derivations of the formula and more interesting tidbits about the relationship between torque and horsepower.

Lou

 

[Doug Supercharged Vipers]

Hi Joseph!

I'm not certain which dyno graph for our Level I you are utilizing for comparison. Please take into consideration that our older Level I we installed in your beautiful beast over 2 years ago, today would be considered more than obsolete! Two years ago it was an extremely conservative 600 bhp horsepower supercharger package but actually produced 650+ bhp. And remember, it was a special offer back then without all the bells and whistles . Our current Level I's, produce about (if not more) than 775 bhp without any other modifications. I am referring to a "stock" engine, stock exhaust, and yes, cast piston!

Rest assured, I'll be posting more about our Level I in just a short bit but it's Sunday and I have to get back to work .

I'm looking forward to talking with you soon my friend!
Doug

 

[Sean Roe]

To further this professional discussion regarding the differences in power curevs of two different types of compressors, here's a dyno graph I found on of a '99 Viper with a Novi 2000 centrifugal supercharger at 8 to 9 psi, but I don't know what other mods it had. It did not have a charge cooler from what I recall.

You must be registered for see images

This will not be a direct comparison because we don't know what the '99 above had, but here's a run of my own '96 GTS along with a customers '98 GTS. Both cars had the same mods and boost. My car was just a little weaker The mods are listed below the graph.

You must be registered for see images

Since we don't know what the '99 centrifugal car had, I'll qualify a couple of the mods shown on the twin screw cars and the peak HP the mods netted.
- 1.7 rockers, worth 26 rear wheel HP.
- 70 mm throttle bodies, approximately 7 peak rear wheel HP.

Sean

 

[Joseph Dell]

I'm glad Sean found that graph! That car is my 99 RT/10 bone stock with the exception of an old-school DLM level I SC set-up. When Doug ran his "winter special" 2 years ago, I signed up. 6 weeks later I had that car.

Take Sean's graph, overlay it on my graph, and you start to see some of the differences in types of blowers out there.

Of course, then Dan had his car done, and it put my dyno numbers to shame. And the rest is history.

JD

 

[Chuck B 98 GTS]

---To further this professional discussion regarding the differences in power curves---

Sean,
How do you perceive the word professional about that comparison? YOU, yourself said compare apples to apples.
Just look at the dyno dates .

Cheers,
Chuck

 

[Paolo Castellano]

---To further this professional discussion regarding the differences in power curves---

Sean,
How do you perceive the word professional about that comparison? YOU, yourself said compare apples to apples.
Just look at the dyno dates .

Cheers,
Chuck

Chuck, as far as professional goes, Sean is as professional as it gets. Apples to apples==> Dates? You cannot compare dates in the apple-apple format here. Sean has not been developing superchargers near as long as Doug has. Doug has done the most superchargers and for the longest time of all supercharger tuners who have done more than one or two kits. Doug does custom systems, Sean does bolt-on systems. Each type was intended for a different application.

You said to look at the dyno dates..... What does that prove? Who is to say that Sean Roe has currently spent less or more time developing his systems than Doug had two years ago for the OLD dyno sheet Sean posted? I remember being skeptical about Doug's systems at the beginning because he was doing a piggyback fuel system instead of using MoTec like a local Viper supercharger tuner was using. They preached MoTec stand alone was the only way to go and that piggyback was a joke.... Now look at what has happened in the last 3 or so years....... Doug has done more supercharged Vipers than anyone on the planet. Doug has a loyal following of supersatisfied customers who idolize him..... Right? Of course! And that other stand-alone guy has sold one more supercharger kit in this whole time. So I guess piggyback must be OK since Ryan Falconer and John Lingenfelter told me so and convinced me maybe they were right. But I have seen that it must be just fine as Doug's customers cars have been reliable and powerful( Doug's cars have stood the test of time quite well). I would think that the scary part for all previous supercharged customers as well as all other supercharger tuners would be that Jason Heffner seems to be making more and more power with each and every supercharger kit he does. I would venture to guess that they will all shudder to think just how much more power Heffner will be making by the time he has done as many kits as DLM. He uses piggyback, and tunes the fuel management to a level of perfection and smooth power curves not yet seen in the Viper community!

Sean's systems have a different target demographic than Doug's systems period. I am sure Sean's 8 PSI system will make more power than the 5 PSI system. Will it compete with the INSANE supercharger packages? Probably not, maybe it will. I think it all depends on exactly what each customer is looking to do with his car and how far Sean wants to go to make big power. He certainly has the skills and engineering background to do so!

 

[RedGTS]

Our current Level I's, produce about (if not more) than 775 bhp without any other modifications. I am referring to a "stock" engine, stock exhaust, and yes, cast piston!

Doug, so your current Level I is approaching 700 rwhp with stock exhaust, throttle bodies, rockers, etc. on cast piston cars? Now that is interesting. Can you elaborate on the setup any more without revealing any trade secrets? Specifically, how much boost?; is that with an intercooler?; and what kind of fuel system mods and tuning are you using?

 

[Chuck B 98 GTS]

Paolo,
Your missing my point. I have total respect for Roe and his products, that's NOT even a question, I don't need to go further.

You need to go back and read the thread in it's entirety. JD and Doug said that his DLM system was a winter special deal. The system he bought back then was rated at 600 horsepower at the engine. The dyno sheet in comparison I believe is not a comparable one and should be compared to what Doug only asked, compare to a true level 1 by today's standards. I think that's only fair and allows the same respect for both tuners.
As for Heffner's system, I don't doubt he's doing a great job, but this is not about Heffner. The topic was about DLM and Roe.

Peace,
Chuck

 

[Sean Roe]

Hi Chuck,

I think you misunderstood what I meant by "professional discussion". I meant it in the regard that we should post relevant information regarding the differences in how different types of blowers come on and what their overall curves look like. It also meant "please check emotions at the door before posting".

Sean

 

[Chuck B 98 GTS]

Sean,
You still can't compare where the two systems come on. It's like me comparing my car to your car and mine makes well over 700 rear wheel. That's all I'm saying, no hard feelings. Hopefully Doug will post a Level 1 dyno sheet so we can do a fair comparison for both excellent tuners.

Cheers,
Chuck

 

[J DAWG]

The comparison for me is how each setup delivers boost and when. To me it is not about the amount of hp, but rather when the hp is produced and the curve it creates.

We all know the "base" DLM makes 8-9 pounds and is normally intercooled where as the ROE (for this discussion) is at 5 pounds and is not.

This is not meant to be a "who can make the most hp" discussion, but rather "how and when does each s/c make hp."

Thanks Joseph and others for the knowledge you have shared.

John

 

[MichaelP]

---To further this professional discussion regarding the differences in power curves---

Sean,
How do you perceive the word professional about that comparison? YOU, yourself said compare apples to apples.
Just look at the dyno dates .

Cheers,
Chuck

IMO that is a cheap shot at a guy who really does not deserve it and doesn't help any of us.

 

[Chuck B 98 GTS]

MichaelP,
I stand firm on my comment. I meant NO insult whatsoever. I just feel a "professional" comparison should be agreed upon by both parties DLM and Roe Racing. Both are professionals, both should agree. I think that's fair.
I will continue to promote Roe or Levin products to everyone in the viper club.

Peace,
Chuck

 

[Sean Roe]

Here's a link that you may find interesting. Has several pages of questions and answers.

http://www.kennebell.net/faq/faq1.htm

Sean

 

[RedGTS]

Sean, that is a great resource--I just wish it addressed whether Viper heads can handle as much massflow from an Autorotor as a GM truck.

 

[GONABITE]

Chuck,

Why do you say you can't compare a 700 hp car vs a 600 hp car? Look at the whole picture(dyno) peak numbers are great, but compare those two graphs and there is a much more usable,consistent,smooth power curve on the twin screw unit, and no one here can deny that. And as you say look at the dyno dates. Well why hasn't anyone including Doug posted an updated dyno sheet of a level 1 kit?

 

[Joseph Dell]

I sure as heck wasn't planning on starting THIS battle when I started this little research.

If you forget the DYNO NUMBERS for one minute, and look at the trends in the CURVES, you will see what _I_ am most interested in analying.

Whether DLM, Heffner, Vortech, Paxton, or OTHER, and whether on a VIPER or a MUSTANG or a VETTE, the dyno graphs tell a story. Imagine REMOVING all the numbers on the X axis and the Y axis...

Now overlay the graphs and notice 2 things...

1 - Twin screw SCs pull more rwtq sooner.
2 - Centrifugal SCs take a _little_ more time to get up there, but once they do, they maintain it longer. In fact, it even increases.

That's all I was trying to prove!

Sorry that y'all turned it into a DLM vs. ROE discussion. It isn't, because there are NO TWO VIPERS WITH THE EXACT SAME SETUP. The only two that were _close_ at one time were Dan Black's DLM and my DLM. And that was when they were both winter special Level I's and one was completed right before the other!

JD

 

[Dr Roof]

Joseph Your a trouble maker

You just had to do an analize everything!

Just kidding

 

[Gerald]

haha u said anal

 

[Joseph Dell]

Hey Roof - Check your PM... RE: drag racing dates.

I'm not _usually_ the anal one... Looks like today I might be...

JD

 

[Bugeater]

Chuck,

Where in the **** does Sean state any tuner in his comparison of dyno graphs? Its only in later posts is it revealed that it was an old DLM setup. And HE didnt specify that fact. Let the data be posted, take it for what its worth (you decide whats an apple and whats a snowball) and dont worry about hidden agendas.

 

[Vipermed 97.01]

oops wrong thread....forwarded to roe vs DLM stg1

 

[Torquemonster]

Not to be a trouble maker - but there is one type of centrifugal blower that offers explosive bottom end power if sized right, and keeps it all the way up to the cam's top rpm. It can go from zero boost to full boost in a heartbeat and is capable of making more power than any of the other blower systems. It's called a turbocharger!



I'll go away now

just couldn't resist that one... hehe

 

[Joseph Dell]

Torquemonster -

You got a valid point. If I could find a few samples of turbo set-ups, I could analyze those graphs against centrifugal graphs as well as against twin screws...

JD

 

[Chuck B 98 GTS]

Chuck,

Where in the **** does Sean state any tuner in his comparison of dyno graphs? Its only in later posts is it revealed that it was an old DLM setup. And HE didnt specify that fact. Let the data be posted, take it for what its worth (you decide whats an apple and whats a snowball) and dont worry about hidden agendas.

Bugeater,
I don't dispute posted information on this forum that helps educate us, BUT I don't agree with inaccurate information claimed to be "professional."


Cheers,
Chuck

 

[Martin D]

Yeah, when are all you slow pokes going to wake up and realize that NITROUS is the way to go??????




Regards,