I ordered RENNTECH's ECU upgrade for US 451s.

[markitect]

To me this is almost as important as the HP:

Does it make it shift faster?

[tigerwong58]

I do feel it shift faster, it an all around improvement, but I can't justify $800. I am waiting for a turbo/supercharger upgrade.

[WilyB]

Originally Posted by tigerwong58

The Renntech makes a difference, it's more responsive and you can feel the power in the low end.

Good news, thanks!

Originally Posted by tigerwong58

We plan to DYNO the car next week and will let you know the results.

How do you avoid the kickdown when you fully press the accelerator?

[smarticus]

On my cabrio, you can feel the throttle fully open about 1 inch up from max pedal travel and then, with more foot pressure there is a noticable breakover point to reach the kickdown position.

[smarticus]

How much is the alledged output increased by the upgrade?

[Evilution]

Brabus themselves haven't managed to get over 10bhp extra on the N/A 451 so I would be wary of claims any higher than that.

[lowndex]

If Willy finds the added hp is 8 or more, I'll spend $800.00! I'm that deperate for added hp. BUT, I want to know the impact on mpg. I have a heavy foot and never get more than 34 mpg now. So, I am concerned about a ECU change, more hp and dropping my mpg down in the 20's.

[randyzimmer]

Originally Posted by tigerwong58

...it's more responsive and you can feel the power in the low end. We plan to DYNO the car next week and will let you know the results.

With the electronic throttle,
it'd be easy to just have it open more aggressively.
Not unlike the big-bore throttle bodies sold a while back.

Here's a good resource:
How to Read a Dyno Sheet- Car Craft Magazine

[Bigperformance]

"Not unlike the big-bore throttle bodies sold a while back"

What ever you do, do NOT go down this route. All it does it causes MAJOR problems.

[WilyB]

Originally Posted by lowndex

If Willy finds the added hp is 8 or more,

Lowndex, I too would love to see 8 hp, but I expect more like 4 or 5 accross the useful range, or about +10% hp/tq at mid range, tapering down to +5% at higher rpm.

Originally Posted by lowndex

BUT, I want to know the impact on mpg.

There has been some lively debates on the subject, but my experience is that the more efficient the engine, the less fuel you use - as long as you drive at exactly the same speed, rate of acceleration etc.

But we are talking about minute changes here, one or two mpg.

Of course, if you use the new power, then it is most likely that your mileage will decrease...