[Steve Taylor]

Here are the results of back-back simulated acceleration tests for my car.

Firstly with the factory limiter set to 6750; secondly with a limit raised to 7200 rpm.

PS - The unichip Q allows the rev limit to be raised; based on the assumption that an extra 450 rpm won't blow up the KV6 .

The two images show the acceleration from rest to 100 mph.

After 100 mph, the times were as follows:

Standard rev limit

0-110 - 21s
0-120 - 28s
0-130 - 40s
0-140 - 62s

Raised limit

0-110 - 20.5s
0-120 - 25s
0-130 - 36s
0-140 - 59s

The biggest difference here is that with the raised limiter, 4th gear can pull beyond 120 mph (standard 116/117 mph); hence gaining 3 seconds over standard.

Bear in mind these figures reflect the current state of tune of my 180.

This gives a 30-130 time of 33.6 or thereabouts (raised imit) vs 37.6 standard limit.

So the question is; is it safe to raise the limiter to 7.2k?

 

[Steve Taylor]

Is there any point, how often do you need an extra few seconds getting to 50% over the legal speed limit, unless you are on a drag strip?

Not debating whether there is a point to this or not. For road use obviously not!

Purely an illustration to demonstrate the gains that can be had down the 1/4 for example, or for timings on a v-max run.

 

[Steve Taylor]

i ran mine with rev limit raised to 7200 for a long time but i wouldnt bother again without 285 cams.

At what RPM was your car making peak power when you did this?

Are you suggesting the gains (although marginal as illustrated) were not apparent at all? Surely you could cross the line on the 1/4 in 3rd?

 

[Steve Taylor]

it made peak power at about normal revs but then held the power all the way with no drop off.
It made no discernable difference at santa pod as i still needed 4th to cross the line at 98-99 mph.

Interesting; according to the gear ratios at 7120 rpm in 3rd the car would be pulling 102 mph.

Anyway; the whole purpose of the post was to share some theoretical info that may in the real world deliver a small advantage on acceleration tests.

My car makes peak power around 6730 according to my last RR, so I may give this a try at some stage.

 

[Steve Taylor]

Side by side gear/speed comparision with the two rev limits.

The only slight anomaly is 4th gear; Most gear speed calculators I have used (when inputting the factory ratios) claim that a true 120mph can be attained in 4th, whereas in reality I know this is 116/117.

 

[Steve Taylor]

Steve Whats the software you are using?

Interesting stuff there.

Paul - see here for acceleration simulation.

http://forums.xpowerforums.com/showthread.php?t=41684&highlight=cartest

For the gear/speed info I just googled "gear speed calculator" and found a range of different sites offering the same info.

 

[Steve Taylor]

yes i agree in theory it should gain something and thats the very reason i did it.
Standard car max speed in 3rd gear according to the mg brochure is 92 mph, with the raised limit i was changing at about an indicated 93 but that was with 40 profile rubber which alters the speedo reading by 1.5 mph i believe, i cant see you going over a 100mph in 3rd on standard profile rubber imo but you could see possibly 97-98 maybe.

Thanks for the info Dave.

I have a Scanguage and have calibrated the speed display to my GPS. As far as RPM goes, I have hit the limiter on occasions before and the gauge has reported back a max RPM of 6830, some 80RPM over the supposed 6750 factory limit.

When the car is back up and running, I'll try a 3rd gear pull and see what speed is attained at the limiter.