Will turbo cause any lag?

[SRV BOY]

I am really thinking of purchasing a turbo, I would like to know if putting on a turbo will cause any lag??

[Polygon]

Of course it will.

It takes time for the exhaust gases to spin the turbine. However, depending on what turbo you go with, this can be greatly reduced. If you don't lower your compression ratio then you won't notice any lag in acceleration.

Speaking of which, what compression ratio are you running at?

[duplox]

NO!!! Puttin on a turbo will not CAUSE any appreciable lag. The only thing the turbo will change at low rpm is maybe a slight bit of an intake and exhaust restriction, but very very slight! If there isnt enough exhaust pressure to spin the turbine, then there really isnt that big of a restriction! Sure it will take time for the turbo to spool up... but if you compare dyno graphs from 1000-3000rpm of a turbo'd and non turbo'd engine(same engine except one is turbo'd), the turbo car may lose a few tq and hp but nothing noticeable(you probably wouldnt notice a loss of 10tq, hp isnt really that applicable at low RPMs... a 4cyl probably has less than 50 hp at 2000rpm. You'll notice a 10tq loss at the track, but as for feeling that ammount just driving the car, you probably wont.) It WILL take time for the turbo to spool up, but your 60ft times at the track will not suffer much at all.

[88_SC_CRX_Si]

It's not only how much time it takes the turbo to spool up, the plumbing has to pressurize too, before the engine will see boost...

[mycivic]

Turbo will lag because exhuast gasses are the ones that spin the turbo like Polygon said. Depending on how you tune your car, lag may be reduced.

But be sure to build up your internals real well if you going to boost high.

[duplox]

You're missing what I'm saying. You will not LOSE a great ammount of low end power if you add a turbo to a nonturbo'd car. Lag is just the time before you make MORE power than a nonturbo car would.

[mycivic]

Originally Posted by duplox

You're missing what I'm saying. You will not LOSE a great ammount of low end power if you add a turbo to a nonturbo'd car. Lag is just the time before you make MORE power than a nonturbo car would.

You wont loose power to a turbo...turbo is free power. You might be reffering to the supercharger where it takes power to create power.

Turbo lag is what it is...lag. You wont loose any power to lag. Its just the time turbo sppols up before it can boost.

[Polygon]

Originally Posted by duplox

You're missing what I'm saying. You will not LOSE a great ammount of low end power if you add a turbo to a nonturbo'd car. Lag is just the time before you make MORE power than a nonturbo car would.

I see what you're saying. I should have stated my post better. You won't notice any lag in initial acceleration if you keep the compression ratio at stock. You will notice a lag of you lower the compression ratio. Then you will notice a lag in the time it takes for the turbo to spool.

Since he is running a 10:1 compression ratio and in another thread I recommended he lower it to 9:1 for the turbo. In his case he will notice some lag.

However, my 89 GTC ran an 8:1 compression ratio @ 13 PSI, and I had no problem what so ever blowing the doors of many cars you wouldn't think it could.

[mycivic]

Originally Posted by Polygon

I see what you're saying. I should have stated my post better. You won't notice any lag in initial acceleration if you keep the compression ratio at stock. You will notice a lag of you lower the compression ratio. Then you will notice a lag in the time it takes for the turbo to spool.

Since he is running a 10:1 compression ratio and in another thread I recommended he lower it to 9:1 for the turbo. In his case he will notice some lag.

However, my 89 GTC ran an 8:1 compression ratio @ 13 PSI, and I had no problem what so ever blowing the doors of many cars you wouldn't think it could.

My thoughts exactly.

OT: Which one would be better? Considering "PROPER TUNING".

High C/R with low boost?

or

Low C/R with high boost?

[duplox]

I'll quote myself from another post:

Compression ratio vs. Boost
If compression by the piston was better than compression by boost, then no one would ever turbocharge! Compressing via boost and via piston do the same exact thing, but using a turbocharger/supercharger has a few distinct advantages. The only difference between the two is the compressor does this before the air enters the engine. This actually increases the displacement of the engine. Consider this: a naturally aspirated engine(no boost) sucks air in by creating vacuum in the cylinder by the motion of the piston down in the bore. It displaces a certain ammount of air, which means it can never fill the entire chamber. It can only take in slightly more than the volume the cylinder displaces when moving from TDC to BDC. N/A engines employ advanced pressure tuning to intake more air than the piston displaces, mainly through intake pressure wave tuning and exhaust wave tuning(also called scavenging). I will not get into the specifics of these, I don't want this post getting too long.
In a forced induction application(turbocharged or supercharged), there are two main advantages:
a) Intercooling. When you compress air, whether by piston or a supercharger/turbocharger, the temperature of the air increases by a large ammount. Cooler air resists detonation and is denser(more oxygen per given volume), allowing more compression. Even though the piston still compresses air and thereby still heats the charge, the final heat of the air from compressing to a total of 20:1 boosted compression(yes boost does affect the *dynamic* compression ratio... I'll talk about that later too) will be much less than a N/A engine with 20:1 dynamic comp ratio.

b) Increased displacement - As I said before, a N/A engine can only intake slightly more than the piston displaces. With forced induction, the boost fills the entire chamber, not just what the cylinder displaces - For example, a 393" V8 I'm building has a volume of 58.80ci in the entire chamber at BDC( (bore/2)(bore/2) x (Stroke + piston to deck clearance) + volume of head gasket + volume of chamber) - the piston itself displaces 49.125 of those cubic inches. That is a 19.7% difference in volume that a turbocharger or supercharger will get you - and this is with the same dynamic compression ratio for both the N/A and FI engines. Boost will allow you to cram more air in there than the chamber is supposed to handle, giving huge cylinder pressures, more than you're normally see with a really high compression N/A engine. Turbocharged and supercharged engines avoid detonation that would normally occur with this ammount of cylinder pressure by retarding the ignition and intercooling.
Turbo and supercharged engine's extremely dense mixtures elongate the burn time of the mixture. This means that even though maximum cylinder pressure only increases 20%, you may see a 100% increase in power.


Another thing I neglected to mention - A turbo or supercharger allows you to cram more oxygen into the chamber, further increasing displacement. Even though this pushes the dynamic compression ratio very high, we can retard the ignition to prevent detonation. Even if you used the piston only(n/a) to compress the mixture to a similar dynamic compression ratio, you arent taking in any more air, just compressing it further. Sure the extra compression will make more power than a lower compression ratio, but no where close to boost power. Think of it like this: you have a cylinder that displaces 100 cubic inches(ci). Put on heads that has a chamber that gives you a compression ratio of 10:1. That would be a 10ci chamber. Now pretend you have a chamber that gives you an 8:1 static compression ratio, or a 12.5ci chamber. Now add a turbocharger to the 8:1 static compression ratio(i'll use SCR for short, DCR for dynamic compression ratio). Set the turbo to run enough boost for an equivilent DCR as the 10:1 N/A motor. that would mean that your turbo would need to take in 125ci of air and cram that into the chamber. 125/12.5 = 10:1. would you rather have a 100ci, 10:1 compression ratio motor or a 125ci, 10:1 compression ratio motor? by the way, that extra 25ci means you're cramming 25% more air into the chamber... .25*14.7(ambient air pressure) = 3.675. That is on less than 4psi boost. Now, pretend you retard the timing of both motors to withstand 15:1 DCR. So for our N/A motor, we now have 100ci at 15:1 DCR, and a 150ci at 15:1 DCR for our turbo motor... We're only at a hair over 7psi boost. Plus with an intercooler, we could increase the timing even further than the N/A motor would get away with, or, even better, run more boost with the same timing. say with an intercooler we can run an extra 5 pounds of boost - we're up to 182ci. Make that an air to cold water intercooler - maybe allowing another 5 for 17psi boost... 215ci. Add some water-alcohol injection gettin us up to 22psi and we get 250ci. PLUS, turbos make the burn time longer, which means they dont mind retarded timing so much! They make a broader, flatter band of power throughout the power stroker of the piston than a N/A engine. So we can knock the timing back a few more degrees and run more boost... there are so many ways with a turbo or supercharger to allow more boost to be run without detonation. Low compression w/ boost beats high compression w/out boost anyday in my humble opinion.

[Polygon]

Originally Posted by mycivic

My thoughts exactly.

OT: Which one would be better? Considering "PROPER TUNING".

High C/R with low boost?

or

Low C/R with high boost?

For the street I would say lower compression ratio. The reason I say that is that you can run more boost safely. The risk of detonation on pump gas is too much for a street driven car to safely run 10:1 or higher. If you're going for a full on race setup, run as high of a compression ratio as you can without detonation. You don't have to worry about fuel sine you're running 110+ octane and the risk of bad gas is very low.

[mycivic]

Originally Posted by Polygon

For the street I would say lower compression ratio. The reason I say that is that you can run more boost safely. The risk of detonation on pump gas is too much for a street driven car to safely run 10:1 or higher. If you're going for a full on race setup, run as high of a compression ratio as you can without detonation. You don't have to worry about fuel sine you're running 110+ octane and the risk of bad gas is very low.

I had that in mind...I just wasnt too sure of the answer. Thanks.

[Polygon]

Sure, no problem.

[Hypsi87]

from an engineering standpoint, it is always better to lower compession to run more boost. It does not matter weather your compression is 8 to 1 or 20 to 1, the air charge mass is the same. Boost, aka turbocharging incresses *sp* air density (mass) not volume. Turbocharging is a density thing, not a flow increase. If you want to run a turbo car with minamal lag, run an automatic. If you where to take two turbo cars that are the exact same, the only difference is one is an auto and the other is a stick. The auto will be faster. You can launch under boost, can't build any boost with the clutch in on a stick. It would just be like launching on your NA four cylender and you don't lose any boost when you shift.

[duplox]

I agree. In order to explain the ammount of O2 the engine intakes N/A vs turbocharged I find it easier to compare the CFM of air passing through the air filter before the turbo. That way pressure is the same, the only thing that is different is volume. I've found it is easier for people to grasp the difference between 100cfm and 200cfm rather than boost differences.