Lamborghini engine in Fiero (Page 6/6)
Will NOV 16, 11:06 AM
No lag = no turbo.

While the basic physics of bigger turbo = more lag can not be sidestepped, the combination of variable cam phasing and direct injection reduces lag and improves the turbo's transient response.

But no, a small 4 with a big turbo will never accelerate uphill from 1000 RPM in top gear like a V8 would. While doing that is cool, I'm not sure it's any more necessary than the ability of a car to parallel park itself.
pmbrunelle NOV 16, 12:25 PM

quote
Originally posted by Will:
While doing that is cool, I'm not sure it's any more necessary than the ability of a car to parallel park itself.



Once you're into the domain of auto modification, presumably your basic transportation needs have already been met.

So auto modification becomes about satisfying one's desires (however arbitrary), more so than one's needs.
Will NOV 16, 02:12 PM
I just meant that someone can drive around a lack of low RPM torque just like someone can drive around the inability of the car to park itself.
Joseph Upson NOV 20, 08:12 AM

quote
Originally posted by Will:

No lag = no turbo...



Yes and no. I've found that theory to have died the death of compression ratio guidelines for boost and fuel grade of 20 yrs ago. Modern engines and modern turbo designs are far more efficient. GM turbo cars are usually sporting 10+ to 1 compression with boost, which would have and has netted insults for anyone attempting such builds not very many years ago.
The same with compression limits and fuel. To my knowledge, the highest stock compression ratio GM has rated for regular unleaded is 11.7:1 (No doubt they can make it an even 12:1 all else the same) in the 3.0L V6, which is basically a smaller displacement 3.6L currently at 11.5:1 on regular. Less than 20 yrs ago some might have argued you could not do that without premium fuel.

The key to lagless boost is proper balance. Sufficient compression for strong off boost response to help eliminate the spool up gap and efficient intake and exhaust arrangement. Direct injection and dual variable camshafts clean up the rest. Of course there are limitations, but since manufacturers are building daily drivers, they're getting better at building turbo cars that respond like naturally aspirated cars and keep in mind they are seldom delivered at peak performance capability, often teased out by aftermarket tunes.

Speaking of the LNF, GM sold an upgrade for it at ~$700 that took the stock 270/270 stock output to about 290/300.
Read it for yourself here: https://www.motorauthority....for-solstice-sky-hhr

All of that from just a stock tune change. I have the same PCM operating system and a remark made in that article supports what I suspected in my HPTuner logs, the PCM can adapt to premium fuel use (based on tune limits as these cars use a torque based program) in cars rated for regular, without a fuel grade sensor, by advancing the spark advance, and monitoring knock feedback, which I noted in my logs upon testing regular unleaded against premium.

A sluggish modern turbo car probably has far more to do with factory tune goals than performance limitations, as noted above in the LNF upgrade. There's about .2 sec difference in 0-60 times between the ATS-V turbo 3.6 and the supercharged CTS-V 6.2L with nearly a 200 hp difference and the better of the two 8 speed trannies. I doubt lag is part of the equation in this fairly balanced comparison.

[This message has been edited by Joseph Upson (edited 11-20-2020).]

BillS NOV 22, 06:17 PM
The stock LNF output was actually 260 bhp/ 260 Tq. The factory GMPP kit changed a couple of sensors and the tune and yielded 290 bhp and 340 Tq, a significant boost. There were other after market tunes that gave around 310 bhp and torque similar to the GMPP tune.

If you also change turbos for a higher volume unit, you will increase turbo lag but you will also increase boost pressure. If you optimize some other stuff at the same time, you can head into the high 400s pretty easily.

I run 375 bhp/375 Tq and there are no disadvantages - the lag is almost imperceptible

.