Does adding a larger FMIC and CP add to lag?

[JPuehl]

Over the Winter I upgraded from OEM to a 7" FMIC and was thinking that I was adding volume to the charge side of the turbo and last weekend I upgraded the charge pipe from OEM and realized the new CP had a larger diameter and so was also adding to the volume on the charge side of the turbo as well; would this be adding lag since the turbo now has more volume to pressurize? Or is the PSI not as important as the turbo delivering the same (or more) volume of air?

I realize the benefits of both the upgrades but would rather not add lag if possible.

Also I see mention of upgrading the "inlets" and "outlets" of the turbo, is that just the piping lead into and out of the turbo? Are there dynos technical info about the benefits to doing this?

[Soterios]

I think from a totally technical standpoint, it does add lag, because the system has a larger volume to pressurize. That said, I just installed a stepped 5" intercooler (60% volume increase for the intercooler) and can't tell a damn difference. While the intercooler volume is going up drastically, the overall volume of air that is being compressed is less significant. (turbo pipe, intercooler, chargepipe, manifold)

I haven't seen too many guys with the 7" intercoolers complain about lag increases. Usually they're eaten up by the new tunes anyways.

[1and1]

You could probably see the difference if you had comparable logs before and after the IC install. Difference is likely only a few hundred RPM at most, tough to feel during a WOT run unless you're really tuned in to the granular details, but seen in logs if consistent.

You're balancing the extra volume against the reduced pressure drop. Stock IC is a restrictive sonofagun...

[JPuehl]

Originally Posted by 1and1

You're balancing the extra volume against the reduced pressure drop. Stock IC is a restrictive sonofagun...

Good point.

[Ginger_Extract]

In short, yes.

Every intercooler is different in terms of core size, pressure deltas/drops (difference between inlet and outlet pressure) and efficiency. In general, massive intercoolers do experience a greater pressure drop than smaller ones. However, with this platform, which has a relatively large engine, and, thus, quick spool, it's largely a non-issue.

For my car, N54, FBO including ER intercooler and CP, I did notice a slight increase in lag, though, as pointed out above, we're talking several hundred RPM, max. The trade-offs are, of course, worth it, simply because the OEM cooler is completely inadequate for a performance application.

[JPuehl]

My wife and I auto-cross my car so adding lag seems to be the opposite of what I'd want, but the added cooling of the FMIC is beneficial.

I think I need to Google the pressure drops encountered with a IC because it seems to me that the more efficient an IC is, the more the pressure would drop because cooler air is more dense and spaces up less space.

I'm probably just over-thinking this.

[BimmerAg]

I think you're talking about a different type of pressure drop than Ginger_Extract . Yes, according to the ideal gas law, the pressure in a closed system (which and engine is not!) will decrease as the temperature decreases, but in my experience I have not seen much pressure drop due to cooling. For example, on a large diesel engine I have seen the following values:
IC In Temp: 286 °F
IC In Press: 18.8 psi
IC Out Temp: 83 °F
IC Out Press: 18.4 psi
For the same inlet pressure and temperatures, the ideal gas law would predict an outlet pressure of only 9.7 psi!!!

The important pressure drop through an intercooler is the pressure loss due to the flow restriction. This is important because it allows the turbo to work more efficiently to achieve the same target boost pressure. Let's say that your tune is targeting 15psi in the intake manifold. With the stock IC, the pressure drop may be around 2 psi, so the compressor outlet pressure has to be 17 psi. To get this pressure, the pressure in the exhaust manifold driving the turbine will probably have to be about 25% higher, or 21.25 psi. Now, for the same target boost pressure (15 psi), let's assume a large aftermarket intercooler has a pressure drop of only 1 psi. Now, the compressor outlet pressure only has to be 16 psi, and the exhaust manifold pressure is only 20 psi. For the exact same pressure in the intake manifold, we've reduced the exhaust manifold pressure by 1.25 psi! Every time the piston comes up during the exhaust stroke, it has to push against this pressure and that takes away from some of the power that the engine could be generating, so minimizing this pumping work makes more power. That also doesn't take into account the effects of how changing these pressures moves the turbo to a slightly different point on it's efficiency map...

[amg6975]

The MAP sensor is post IC though, so you will probably get more pressure pre IC, not less pressure post IC if you cool the air more efficiently. That's just an educated guess though.

Edit: BimmerAg has a good explanation of what's really important though in regards to flow restriction vs. the minor effect of the air cooling/compressing.

[studio54]

I felt a bit of extra lag right after my Forge FMIC was installed.

[iminhell1]

I'm on the big intercooler, stock turbo.
Yes there is lag, more than stock. But as mentioned, through a tune it's mitigated and becomes virtually nonexistent or same as stock.

The major benefit is the 80*F drop in IAT's. Seriously. If you're pushing a stock cooler hard at 18+ psi you'll come close to 180*F IATs.
I was cracking 140*F on a 5" stepped.
With the 7.5" race I can't manage to break 115*F.

The major downside is the weight. It's heavy, 40#, and all ahead of the front wheels.

[The Wind Breezes]

Yes, but the tradeoff is worthwhile because the lag increase will be minimal but you'll make much more consistent power and more of it with the right tune.

A more important issue is tube and fin vs bar & plate ICs. Stock is tube and fin which is good it's just undersized. Bar and plate is a lot heavier and while a given capacity heat soaks slower it also recovers slower. Tube and fin is the way to go in the real world, unless the car is a dyno queen. Wagner EVO II is one good choice.

[1and1]

While I appreciate build quality, and factor in the Made In The USA stuff, and performance all as much as the next guy....

~$1000 shipped is too damn much money for an IC.

[kivyee]

Originally Posted by BimmerAg

I think you're talking about a different type of pressure drop than Ginger_Extract . Yes, according to the ideal gas law, the pressure in a closed system (which and engine is not!) will decrease as the temperature decreases, but in my experience I have not seen much pressure drop due to cooling. For example, on a large diesel engine I have seen the following values:
IC In Temp: 286 °F
IC In Press: 18.8 psi
IC Out Temp: 83 °F
IC Out Press: 18.4 psi
For the same inlet pressure and temperatures, the ideal gas law would predict an outlet pressure of only 9.7 psi!!!

The ideal gas law doesn't apply in this case - you need to use the bernoulli equation to figure out pressure change due to velocity changes in addition to the "ideal gas" changes to P, V and T.

To the OP's original question, this is how I could look at it. A 3L 4 stroke engine will move about 1500L of compressed air per minute at 1000RPM (ignoring flow effects from throttle etc). Depending on how much your intercooler increases in volume - stock intercooler is around 7.5L - Even if you double the volume to 15L, that's a change of .5% relative to the airflow. Now add the effect of more effective charge air cooling and lower pressure drop, I doubt it's a measureable difference in lag.

[ShocknAwe]

It will until you adequately account for the extra post turbo radius and volume in the tune. If vanos can account for a big slow old school single scroll ST, it can account for a tiny increase in volume from a larger FMIC and CP.

[JPuehl]

Thanks for the responses. I think I answered my own question when I said "I'm probably just over-thinking this"; yes, yes I am.

[Jeff@TopGearSolutions]

The lag is negligible on the platform.

[Blu3RSX]

The 135i is the first turbocharged car I've ever owned so this is all very interesting.

I only know that adding a performance intercooler in Gran Turismo is good for more horsepower but is that also the case in real life? ^_^

My only other mod is an aFe drop-in air filter and, maybe later, would like to add Maddad midpipes (or some other comparable brand). I'm not looking to make it too much louder so that would be the extent of any exhaust modifications I'd do.

[Jeff@TopGearSolutions]

Originally Posted by Blu3RSX

The 135i is the first turbocharged car I've ever owned so this is all very interesting.

I only know that adding a performance intercooler in Gran Turismo is good for more horsepower but is that also the case in real life? ^_^

My only other mod is an aFe drop-in air filter and, maybe later, would like to add Maddad midpipes (or some other comparable brand). I'm not looking to make it too much louder so that would be the extent of any exhaust modifications I'd do.

Intercoolers reduce Intake Air Temperatures, this alone adds more power because cooler air has more oxygen per molecule. More oxygen, more fuel, more power.

The lower intake air temperatures also allow for higher ignition timing when tuned, which tuned correctly can produce even more power.

Intercoolers are effiiciency modifications, they bring back power lost from heat soak. They should be one of the first mods on a tuned vehicle and one especially in hotter climates.

[Blu3RSX]

Originally Posted by Jeff@TopGearSolutions

Intercoolers reduce Intake Air Temperatures, this alone adds more power because cooler air has more oxygen per molecule. More oxygen, more fuel, more power.

The lower intake air temperatures also allow for higher ignition timing when tuned, which tuned correctly can produce even more power.

Intercoolers are effiiciency modifications, they bring back power lost from heat soak. They should be one of the first mods on a tuned vehicle and one especially in hotter climates.

Thanks! And from what I've researched, it looks like a relatively easy install. This may have to be a tax refund present ^_^

[Jeff@TopGearSolutions]

Originally Posted by Blu3RSX

Thanks! And from what I've researched, it looks like a relatively easy install. This may have to be a tax refund present ^_^

Yes, they are pretty easy. Few clamps and couplers. 1-2 hour install on avg.

[Freon]

I'd be amazed if you can tell the difference in lag. There is more volume to compress, but without doing math, I'd guess you're looking at a few engine revs worth of extra volume, like counting on one hand number of engine revs at 1.5L per rev with an intercooler that might be a 2-3L larger in inner volume vs. factory. And it only needs to be compressed one time every time the pressure is reset, i.e. on shift. On shift at high rev it's definitely not going to be notable.

Originally Posted by Jeff@TopGearSolutions

cooler air has more oxygen per molecule

Ehhh... no.

[studio54]

Originally Posted by Freon

I'd be amazed if you can tell the difference in lag. There is more volume to compress, but without doing math, I'd guess you're looking at a few engine revs worth of extra volume, like counting on one hand number of engine revs at 1.5L per rev with an intercooler that might be a 2-3L larger in inner volume vs. factory. And it only needs to be compressed one time every time the pressure is reset, i.e. on shift. On shift at high rev it's definitely not going to be notable.



Ehhh... no.

Hmm, yes when engine is spooled, and mostly from 3500rpm to redline, there isn't any lag. I would say, in my case, it is laggier with the FMIC than without when pushing from 2500 and lower. By lag i mean the delay it takes to reach full boost from 2500rpm for example.

I can explain it for two reasons/possibilities :

-Most people installs DP+FMIC at the same time, so you can't make a real difference in terms of lag, according to my MHD logs (from ~2500rpm) :

Stage 1+ to reach 13psi (close to full boost) : without fmic, without DP it took 550rpms
Stage 2+ to reach 13psi (which isn't full boost) : with FMIC, with DP, it took 550rpms too

So the spooling rpm remain the same, but isn't the DP supposed to make the spooling quicker ? that means that my FMIC adds a bit of lag on my setup.

The thing is that i installed my DPs some weeks before installing the FMIC, get used to and the spool was really quicker than stock spooling. When i installed the FMIC i immediatly felt a bit of lag. Too bad i have no log with DP only.

- Another possibility could be that the drop pressure on the Forge FMIC (using stock couplers) is really bad (double checked install) and the flow may be not top notch.

DPs are wagner, and anyway overall i am satisfied with IAT temps with this FMIC, but i think i would chose another FMIC if i could.