Lag off the line?

For example: If you have a 427 LSx based engine and say a GT55-91mm, and the same exact engine with twin turbo's, making the same boost collectively, what will be the difference in daily driving characteristics. Forget the 1/4 mile. Just romping around on the street with drags or MT street slicks.

I'm wondering how a single turbo will feel off the line if you nail it (of course not all the way to the floor), will you jump off nicely kind-of "on-motor" and than the boost will come in and all of a sudden blow the tires off.

As opposed to a twin set-up that I assume has the boost already there building up so you can roll into the throttle with more control out of the hole, regarding spinning the tires.




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These questions kill me. You guys talk as if a Trans Am with a 436 stroker is a dog off the line and you want more low end torque. Get a grip man. The car will be stupid fast and for the most part undrivable on the street with either twins or a big single.

The fast DSM guys are happy to make any kind of boost by 5000 RPM.

Andrew

 

with a proper sized turbo there wont be lag with a single or twins maybe only a couple hundred RPMs

 

Yes, my ~500 RWHP/500 RWTQ is boring and old now, like my sig says, "Not enough power", my car is no different TO ME than driving my mothers minivan, I'M BORED WITH IT. Sorry.

So, yes, I'm going to get more. And I don't understand why people say that 1,000+ rwhp cars are undrivable on the street, these are obviously people who SUCK at driving. Everyone told me I couldn't drive my 436 powered car in the rain, no way, you're gonna wrapp it around a poll Dorks! It drives no different than a 3 cylinder 50 hp Metroplolitan in the rain.

I have friends with 1,000 RWHP TT Heffner Vipers, Supras, and I know others with the same power levels, they drive them regularly and put the power down when they race people. Even in the rain.

This is a question/thread about LAG, or other distinguishing characteristics of the 2 types of set-ups, thats all. Posted to help me make a decision and to learn a little more. And if you go back and read the post again, I'm interested in ROLL RACES where it's much easier getting the power to the ground compared to an all out launch. I'm just wondering how it'll feel off the line in every day driving or aggressively applying throttle at low speeds.


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I ask this because I would rather go with a single turbo so I can use the "street killer" kit and put the turbo where the battery is and retain A/C

But I hear people talking about the turbo's being better for smoother and more controlled rpm's throughout their range during acceleration.

Andthat a single turbo will kind-of all of a sudden come in and hit you like a ton of bricks.

The S95, will it fit where the battery goes, if you know???


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Anything that can make the power of a 95mm turbo is going to hit you like a sack of bricks falling on your head, be it twin turbos or a single turbo. The lag difference between properly sized twins and a properly sized single is going to be negligible, the only thing about twins is you get more turbine wheel and housing choices (P-trim, Q-trim, GTQ-trim, GTS-trim, GT42, GT40, ETC) vs. the standard thumper turbo F-trim and G-trim wheels.

 

So the turbo's that are used in TT set-ups can't be used as a single by themself?

Do you know who makes the S95, I need the outer dimensions of it.

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Yes the turbos used in TT setups can be used as singles, but for a motor your size you're talking about needing atleast a pair of 61mm turbos, which wouldn't cut it as a single on a 427. There's nothing that expressly differentiates a turbo as being used for a single or twin setup, but obviously you arn't going to run a single TO4E 50-trim on an LS1, nor are you going to run twin PT91's.

Jose @ Forced Inductions is selling S95's, they're a Borg-Warner hybrid IIRC.

 

Jose is the person who mentioned this turbo to me.

Do you think the S95 is good for a 427?


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Do you guys measure horsepower differently to us down here in Aussieland? 1000rwhp, traction in the rain......wtf?

 

He's saying that some of friends have cars making 1000rwhp, and they drive them all the time.

 

The reason you are getting the non-answers is because there aren't any. A common thing you will hear someone with a mild understanding of turbos say is that a twin setup will spool faster... but you get those comments out of the same idiots who go "It puts out 15 psi out of EACH turbo" as if that is special. They are just nonsensical arguments. You can easily make a twin setup that is laggy and a single setup that spools immediately. The bigger issue is matching the turbo(s) to your engine and your intended goals. If you are uncomfortable doing that, there are many people that can help you, and your best bet is using those resources. What people are saying about the engine size issue is that lag is not an issue on even a stock displacement V8, never mind a 4xx c.i. engine. The problem with lag is on 2.0 liter engines that are making 500 HP… off boost, you are just driving a low compression 2.0 liter engine, so if you don’t make boost until 5k rpms, then the car feels pretty weak, then pulls like mad. If you are running a big V8, then quick spool just blows the tires off quicker, which as cool as it is… a lot of people use a larger turbo because the quick spool isn’t nearly as necessary… you are better off with the more efficient power up top where you can actually use it. As for the what turbos you use for single and twin setups… there are a ton of turbo options out there. A turbo that would be a great unit for a single setup on one car wouldn’t be nearly enough to be used as a twin in another, so it’s not really easy to make broad based statements. You have to be pretty specific. So, to answer you initial questions:

1) No, the difference between single turbos and twin turbos has nothing to do with lag… it has to do with packaging.
2) Your comment about “making the same psi” is irrelevant… Flow rate is important. PSI is a byproduct.
3) As for your comment about how fast the car “feels”… turbos have a very different feel than an NA setup. Torque is what makes the car “feel” fast, and turbos give GREAT “Area under the curve”… (as a general broad based statement).. so if it’s just that “feel” of being fast… turbos will definitely make it happen for you… way better than an NA setup (or centrifugal supercharger for that matter)

Hope I helped…

 

You can set-up both to effectively qualify their lag as "negligible." However, of the dynographs I've seen, it's seemed a bit easier to pull more powerband in the lower rpm's with twins, though like many have said... It's not like the single turbo's powerband will have any significantly low areas, either.

As far as PURE efficiency is concerned, there is somthing to be said about two turbos being fed equally by the same amount of cylinders. This may come into play at really high levels for MAYBE some slightly added consistency, i.e. tuning, exhaust pressure, etc. I dunno...

Two SLIGHTLY different approaches, both of them well equipped to accomplish the same job... On LSX's, of course.

 

Strictly from a physics standpoint, it is always going to be possible to make twins boost earlier than a single at the same peak flow and efficiency ratings. The difference, however, isn't nearly as important as the compromises you have to make in packaging. In some cases, you have room for a big single on one side of the motor, and other times you have room for two small turbos. The technology has risen to the level where packaging should be the deciding factor, not the # of turbos you use. And of course cost could be an issue, in which case you should give up on forced induction anyway.

 

I only see a few differences between singles and twins...

space taken up by the turbo systems which is a very big deal to remain aware of...

twins usually mean double the moving parts, double the moving parts means more initial cost and more upkeep cost (more moving parts means more chances for failure)

I also think that twins are harder to troubleshoot then singles because there are more parts to fail....


now take this post with a grain of salt, I do NOT own a turboe vehicle so this is only an opinion as I have seen over the past few years of research in planning out my turbo path.... (only reason I don't have a turbo is because I have the self restraint to pay off my car and other debts so I can afford to fix my car if.... when I break it...)

 

Thank you for clarifying my point in a much more tacktful manner.

Andrew

 

With all the air coming out of a 400ci + engine, lag will not be as big of an issue as it would be a 348ci setup.

 

well said

 

In the realm of 1000whp cars on the street, horsepower to traction is the limiting factor...I don't care if it is 80 mph+ roll-ons, you have to control the power and keep the tires planted...with the electronics and boost controllers offered today, especially with turbos, power level can be controlled to maintain traction. There may be a 1400hp tt heffner viper beside you, but if you get a jump on him and hook your power to the ground and he is wasting away spinning, you win....how do you think the drag-radial cars go so fast...look at there et to mph...it makes no sense....8.20's at 180 mph....they just keep adding power all the way down the track...tires just on the verge of spinning.

Twins or a big single....it don't matter
Sound like you need a pair of gt47-88 or a g-trim 106....To run with the big boys...especially where you are

 

nice name Turbocuda, i hope you got one