Downtuning the Insight for better low RPM torque?

[predrag]

Hello everybody...

Here's an idea that has been bugging me for a while, but is too big & risky to just go about experimenting with without some educated assesment:

Insight's gas engine is tuned to the torque peak at about 5000 rpm, counting on the electric motor to bail it out at lower rpm's.

Now, I don't really rev the engine much ever, trying to keep the fuel efficiency at max. Moreover, I think that the engine isn't really working at its most comfortable rpm if it is driven mostly at 2000 rpm.

Is there any ways of down tuning the Insight gas engine to lower the peak torque rpm number? Some things I could think of would include adjusting the cam timing or ignition timing - but of course I'm not brave enough to try!!!!!!

Any thoughs? (Much appreciated!)

Thank you...
Predrag

[Insightful Trekker]

Originally Posted by predrag

Insight's gas engine is tuned to the torque peak at about 5000 rpm, counting on the electric motor to bail it out at lower rpm's.

Where'd you find that data The Insight also uses Honda's VTEC system whereby the torque range is extended via a switchable dual profile cam. So "peak" torque would have been at a _much_ lower (or at least narrower) RPM without it. And their are practical limits. In shifting torque down the RPM range you will give up greater available power in the higher RPM ranges. At some point it becomes a driveability issue. And it is a balance with limits of the physical properties involved. You can't peak torque at 2000 RPM's and have sufficient power for the task of a reasonable rate of acceleration or speed too.

Cam lift, timing, and duration is the primary factor in a given displacement engines HP & torque curves. And given how the IMA system is integrated to compliment the ICE's power bands I think your talking some _major_ redesign problems.

And thats not even considering lean burn parameters. Change the cam too much and you will effect it. Maybe even narrow the window

If the Insight was an I4 engine there _might_ have been some cam swaps with a Civic model that could prove interesting. But being an I3 it stands alone. And I doubt you'll be able to get any cam manufacturer interested (at a reasonable cost). There won't be any market for it.

Right now there appears to be only 2 options that have been proven.

1) Turbo power, higher speeds without a significant MPG "hit" with hyper MPG still available when driven as such.

2) MIMA, more IMA assist to better hold the lean burn window or more tire smok'in power at your discretion.

3) (remember there's always a 3rd option) Hopefully waiting in the wings, supplemental IMA batteries. Burn their SoC down at your pleasure. Or extend the hyper MPG lean burn range even farther.

All the above have taken a LOT of engineering effort Your concept of "re-tuning" ICE power bands and the likely consequential need for the same in regard to IMA assist is even a greater challenge (not to mention the costs ).

My 2c.

How much do you want to spend

[predrag]

Thanks for the reply, John!

The torque data was simply lifted off that power/torque graph that is available somewhere on this site too: ICE alone peaks at 5000 rpm, while in combination with EM it peaks at 2000.

Of course this was just a dream. Too big a mod for anybody to try at home - and as you say, changing one thing (like the cams) will immediatelly influence a number of other balances. I was just wondering if anybody more mechanically educated would have any interesting suggestions.

Thanks for the consideration, though!

Predrag

[b1shmu63]

It is my opinion that Honda designed the top gear ratio and cams etc for maximum efficiency at 55 MPH at 70 degrees F. This was in an effort to achieve 70 MPG EPA highway. They could have achieved even higher MPG but at the cost of making the car a real dog for accelleration. As is, they achieved the national average for zero to sixty. The Insight is really stating: If you want to achieve X-mileage,comfort, safety, performance, this is the way you have to do it.

10 years have passed. Could Honda do better today? Certainly! Would it make sense? Probably not from a corporate perspective, as gas is still too cheap. Know this for certain, Honda is applying for patents every couple of days on technologies that will make future ICEs practical.

But to your question. To increase the efficiency of the ICE at normal driving speed (55 to 60) by modifying the cam, would require reducing the power of the engine. At higher speeds efficiency could be increased by disableing the second set of VTEC cams. Again this would reduce performance dramatically, but could probably be easily done.