90lxrider

might i ask about twin turbos...???a dart block may be in the picture also

FoxGT

This doesn't always apply though. There is no properly sized turbo, it's all on where you want power. Unless you are saying a properly sized turbo for a race setup or low end setup. Most full race setups won't see full boost until after 4000rpm even as they set them up for max high rpm power. Likewise you can get a smaller turbo & see full boost by 2000rpm, but you'll run out of air at higher rpm. It all depends on where the person wants their powerband.

tt460

I would have to disagree... And so do the OE's and every turbo manufacturer out there. Everyone keeps marketing "no lag" etc, but why do the OEs and turbo manufacturers CONTINUE to keep spending so much money to "eliminate" lag if it doesn't exist? Turbo lag exists in EVERY turbo vehicle, and it's very noticeable even in the latest tech vehicles. Why else would the OEs be spending money on bi-turbo, series turbocharging, super turbo (ala VW's "TwinCharged" Golf GTi) if turbo lag wasn't a problem? These are very expensive solutions for a problem that doesn't exist.

I own 1 turbo vehicle, have built 1 twin turbo vehicle, been around and worked on several other twin turbo vehicles, and have driven several of the latest European turbocharged vehicles over the past couple of years. They ALL have lag. And the lag from off idle at a stop is VERY noticeable.

So how do the kit builders/turbo manufacturers show the dyno chart that says their kit has "no lag"? It's VERY easy to run a steady state dyno and show that a turbo has no lag. They apply the brake on the chassis dyno, or load the engine on an engine dyno. This spools the turbos up and they can start recording their data with "no lag". Even though they probably spent several seconds getting the engine loaded properly and the engine RPMs down to a low level where they want to start aquiring their data. This is the equivalent of foot braking your car at the starting line, but who on earth drives their car like that from every stoplight, intersection, supermarket parking lot or driveway that they pull out of?

Postitive displacement superchargers have the upper hand on response time. No matter how you run them, they always have instant boost and always will. This makes them easier to drive and most importantly easier to tune.

So why does all this matter? It really doesn't. But turbo lag DOES exist. And it will continue to exist until the turbo manufacturers employ some very expensive manufacturing techniques to their turbos.

Or, everyone will switch to a positive displacement supercharger like all of the OEs are doing.


- Trever

poobank

go turbo all the way

FoxGT

I think you misunderstood what I said. I was implying from a dead stop revving the engine until you reach full boost then taking off, not from a 1000rpm take off, or perhaps a better example would be a turbo car with a 3500 stall. I've built a twin kit for a car of my own, a few single kits for other cars, & a supercharger kit. I agree with you 100% on lag being an issue at any rpm, but it is a smaller amount the higher the rpm. I'm talking about just while racing. Lag time shouldn't worry you if you aren't racing.
You said "who would want to do the whole foot braking thing from every stop light, intersection, supermarket parking lot or driveway that they pull out of?" I don't know of anyone that leaves all of the above sideways or doing a burnout. Either of the setups (even without foot braking) will provide more than enough power to do so if setup correctly anyway. Who really wants to take off at WOT at every stoplight?

What i'm about to say i'm sure you already know, but for getting my point across. Lag is like a second version of throttle response. From the time you push down the petal till you reach the amount of boost able to be created at that given rpm. You can't measure lag below your boost threshold.
If you go full throttle at say 1000rpm & was under a heavy enough load to where your car wouldn't gain any rpm, lets say going up hill in 5th gear at 1000rpm at full throttle. You can't tell how much lag there is becuase you aren't producing enough exhaust gas to power the turbo(s).
Take my twin turbo v6 probe for example. It reached full boost at around 2700rpm. If I punched it at 2700 & was going up hill then it would take at or around a full second for my gauge to read 12psi. But if i was in 3rd gear going up the same hill, cruising at 4000rpm & I punched it, I may only have about a .2 second lag time.
Suppose I was at the exact same spot at a dead stop. I revved the engine to 4k rpm, dumped the clutch, & stayed at 4000rpm spinning the tires. Then when I get a little speed up & am at 6700rpm, I shift fast to 2nd & go down to 5000rpm & have a lag time of about .1 seconds at 5000rpm, but my throttle is already all the way down as i'm releasing the clutch. It takes people more than .1 seconds to release the clutch.

That's what i'm getting at. If you are any good with a manual transmission & you are racing from a stop why would you worry about lag? That would be something I worry about if I was racing from a roll. Even then, if i was going at 45mph in 3rd gear at 4500rpm it's still only .2 seconds from when I hit it before my intake sees full boost. There it does pose a problem I very small one, but still one none the less.
I don't share your views on them being able to get rid of lag with turbo's though. You have to create enough exhaust gas to spin the exhaust side before your intake see's the pressure. & if they employ another method other than that then it would be more of a hybrid, no longer being 100% driven off of exhaust gasses.
Don't get me wrong, superchargers are fun to mess with, & A WHOLE LOT cheaper to fab a kit for. And I will most likely fab another supercharger kit for a car of my own even, but i'll always prefer the mid & high end power of turbo(s) over the low/mid (& high on twin screws) of a positive displacement supercharger.

tt460

No matter what you do, it's fairly hard to go wrong with boost. Turbos have a hand up in the ability to produce some massive compressors. Positive displacement superchargers have the upper hand in low end response and torque...

But... I think if you were to build two motors running at the same boost level, same displacement, etc. The positive displacement supercharged engine would be easier and more enjoyable to drive (and easier to tune) due to a more linear power transient.

For some reason, those turbo response numbers (i.e. lag) seem to mean alot less on paper than they do to the driver. Even though they appear to be sub second response times, the driver can always tell the difference between a well engineered turbo system and a similarly well built supercharged engine. The power of the supercharged engine is directly proportional to the position of the throttle. Not so in a turbo engine. Both engines will surely have a huge "grin" factor... But, the driver will likely choose the supercharged version over the turbo version due to it's ease of control and the fact that the power feels directly connected to the drivers foot or hand (whatever is working the throttle). It sounds trivial, but it makes a huge difference in what the driver thinks about the driveability of the engine.

This is something that's extremely hard to explain... Unfortunately, very few people in this world will have the opportunity to drive two cars back to back and feel the difference between the two. All one can do is speculate what the power will be like.

Another thing about lag... The bigger the engine, the less turbo lag really becomes an issue. It's really only a "problem" on small low-torque engines. So, the problem won't really become evident until the OEs (or horsepower enthusiasts like us) start downsizing our engines to get more fuel economy and then boosting to get the power levels back up to what the N/A V6s and V8s had before.

Hopefully some day turbos will be lag free and cheaper to build or positive displacement superchargers will achieve higher top-end output. Then we can have everything we've always wanted. I'm sure at least one of them will overcome their problem sometime in the near future.

- Trever

FoxGT

For the fun factor yes I would choose a positive displacement supercharger & it gets the most comments as far as putting you in the seat because of the instant response, the whole "d*** this thing has a sh** load of power" vs "This thing is fast... feels like it has two different power bands, one below 3000rpm & one above."
I've never personally had a car smaller than a v6 with a sc or turbo, but I have built a turbo kit for a 4 cylinder & it was more than enough fun during the time that I was driving it. The smallest size engine I've personally owned was a twin turbo 2.5L v6 & it was already a fun car before the turbo & the f/i just added to the experience. As far as supercharging vs turbocharging on the 2.5L I can say I've driven both & I still prefer the turbo, BUT that was a centrifugal setup, not a positive displacement. That will all come on the mustang.

My friend asked me to build him a supercharger kit for his '86 5.0L mustang, but he doesn't have much money. I told him I would build him a non intercooled roots setup, port the s/c, & do some other work to the unit before putting it on for $500 or intercooled for $700. Then I'll get the feel of a twin turbo 5.0L mustang vs roots 5.0L mustang. Both fox body's, & both are still relatively close to stock, but until then I can't honestly give a review on which one is better on the same setup or close to the same setup running the same psi. & I've not yet experienced a twin screw car, I have driven a roots charged '03 cobra, but it was stock psi & stock supercharger & stock roots superchargers are horrible until they get worked on.

Birdieman4

Pulley size dictates how soon you start making boost on a centri. On my procharged setup, im making positive boost at 2000 rpm. And centris don't lag, not even slightly. You cant confuse 'lag' with punching it at 1200 rpm and seeing no boost. And turbo(s) lag folks. It's a part of life. Yes, a properly sized turbo tuned well helps eliminate a little of this, but there will always be some lag. And any1 who belives that screw blowers are good for low and mid power only probably haven't ever driven a well tuned screw car. Folks, we need not confuse people with roots characteristics when discussing screw blowers. Screws pull EVERYWHERE in their range, unlike turbos and centri's. And roots, for that matter.

grabbem88

so should i get screwed then?...i just want blood curdling power from start to finish!...oh and make 530 rwhp.

Birdieman4

The short answer is 'yes'.