secondarries

[XfireZ51]

Hib,

I wonder how much of the "stock motor needs secondaries" conventional wisdom is a result of removal but not addressing the tuning properly. Anecdotally, the problem should be exacerbated by top end porting of an otherwise stock motor.
More air by increasing volume should negatively affect flow velocity on the low end. And that should demonstrate itself as a loss of low end torque.
Perhaps the addition of freer flowing exhaust (re: headers) which tend to accompany other mods, may mitigate the effect of greater volume. How much of the "loss of low end" is SOTP instead of data driven? My own personal experience has been that porting the top end, and having secondaries come on just after idle has increased torque throughout the rpm range and I could post dyno sheets showing that. Most tuners will tune for WOT, but the process of tuning for part throttle is much more time consuming and involved than WOT.
Which is why it's not done. Having looked at calibrations from other tuners, I can tell you that the stock calibration is hardly modified if at all. And in fact, it needs to be modified quite a bit.
So my point is that we can't be sure how much of the low end loss is due to improper tune rather than strictly a result of removing secondaries. Maybe we'll never know.

[grahambehan]

At the time of the project ending announcement Roy Midgely made a presentation to the LT5 team at Lotus which included a page and a half of A4 bullet points on the technology transfer from the LT5 programme to what would become the LS engine family, guess I need to dig that out.

Meanwhile, fuel to the secondary debate

[Paul Workman]

Originally Posted by grahambehan

At the time of the project ending announcement Roy Midgely made a presentation to the LT5 team at Lotus which included a page and a half of A4 bullet points on the technology transfer from the LT5 programme to what would become the LS engine family, guess I need to dig that out.

Meanwhile, fuel to the secondary debate

Thanks, Graham! Thanks for the graph (and hope to see the bullet points soon), and most especially, thanks for the LT5!!

P.

[grahambehan]

Originally Posted by Paul Workman

Thanks, Graham! Thanks for the graph (and hope to see the bullet points soon), and most especially, thanks for the LT5!!

P.

No problem Paul, I was just lucky enough to be part of the team, family really, that made the LT5 what it is.

Graham.

[XfireZ51]

Graham,

First of all, welcome! Super to have your one of a kind perspective.
Looking at the curves, was anyone ever able to explain that sag in the torque curve between 4-5Krpm that seems so characteristic of the LT-5.
I know Marc H. can show you graphs of variously modded LT-5 but that sag shows up on each one of them. Just curious.
BTW, how about a thread on the 2nd Gen LT-5 build?

Cheers.

[Tyler Townsley]

Originally Posted by XfireZ51

Graham,

First of all, welcome! Super to have your one of a kind perspective.
Looking at the curves, was anyone ever able to explain that sag in the torque curve between 4-5Krpm that seems so characteristic of the LT-5.
I know Marc H. can show you graphs of variously modded LT-5 but that sag shows up on each one of them. Just curious.
BTW, how about a thread on the 2nd Gen LT-5 build?

Cheers.

Talked to Geoff today and he confirmed what I always thought. The dip you see is a combination of the 1 injector going into saturation and the 'turning on' of the 2 injector mode. I would be interested in seeing a run with the 2 injector graph right behind a all in graph on the same motor. Apparently the crossover point causes the motor to run a little lean in that part of the calibration.

Tyler

[tf95ZR1]

Originally Posted by grahambehan

Meanwhile, fuel to the secondary debate

OK, I'll be the dope. What are we looking at on these dyno curves?
I see pt open vrs closed and 2 sets of pulls, but..........

[Hog]

Originally Posted by grahambehan

At the time of the project ending announcement Roy Midgely made a presentation to the LT5 team at Lotus which included a page and a half of A4 bullet points on the technology transfer from the LT5 programme to what would become the LS engine family, guess I need to dig that out.

Meanwhile, fuel to the secondary debate

Thanks for posting that dyno graph Graham I have never seen a Secondary open vs. Secondary Closed dynograph overlayed before.

As expected extra airflow adds power and torque, and also raises the rpm at which peak power and torque occurs.

Looks like having the plenum throttles open costs about 30 lb/ft of torque at 2500rpm, I assume that if we exrapolated that graph to lower rpm, we would see even more torque loss with the Plenum throttles closed..

Both PT open and PT Closed both make the same 290 horsepower at 3900rpm.

Thanks again Graham.

peace
Hog

[grahambehan]

Tyler,
OK we have already confirmed that the LT5 goes into 16 injector at WOT, so lets think about that? There are many phenomina that influence the characteristics of an engine, ie the fundamental shape of the curve, P/T switching is not one of them, in this instance

Graham.

[Tyler Townsley]

Originally Posted by grahambehan

Tyler,
OK we have already confirmed that the LT5 goes into 16 injector at WOT, so lets think about that? There are many phenomina that influence the characteristics of an engine, ie the fundamental shape of the curve, P/T switching is not one of them, in this instance

Graham.

OK Todd has a calibration mod that can be used in a stock motor that can be used to test that. It pulls the secondary throttle blades open and goes 16 injectors on startup. It changes nothing else in the calibration, run that back to back vs a stock calibration and see what happens.
In the stock configuration going WOT does not enable an instant 16 injector secondary's open mode there are a series of check points that have to be met before going to the next calibration configuration and into the final PE table.

If not that then its cam design? Ie the lower rpm profiles are such that its engineered for a leaner mixture and it gets more aggressive as the rpms elevate with a transition point where the motor is slightly under fueled.

Its got to be in the fueling, calibration or cams.

Tyler