MG & Rover - XPower Forums banner
1 - 14 of 14 Posts

·
Registered
Joined
·
829 Posts
Discussion Starter · #1 · (Edited)
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?
 

Attachments

  • Like
Reactions: Christina

·
Registered
Joined
·
3,492 Posts
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?
 

·
Front wheels steer, rear wheels drive.
Joined
·
12,325 Posts
i ran mine with rev limit raised to 7200 for a long time but i wouldnt bother again without 285 cams.
 

·
Registered
Joined
·
829 Posts
Discussion Starter · #4 ·
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.
 

·
Registered
Joined
·
829 Posts
Discussion Starter · #5 ·
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?
 

·
Front wheels steer, rear wheels drive.
Joined
·
12,325 Posts
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.
 

·
Registered
Joined
·
829 Posts
Discussion Starter · #7 ·
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.
 

·
Registered
Joined
·
829 Posts
Discussion Starter · #8 ·
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.

 

Attachments

·
R.I.P [The Red Zed] MG ZS 180
Joined
·
19,410 Posts
Steve Whats the software you are using?

Interesting stuff there.
 

·
Front wheels steer, rear wheels drive.
Joined
·
12,325 Posts
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.
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.
 

·
Registered
Joined
·
829 Posts
Discussion Starter · #11 ·

·
Registered
Joined
·
829 Posts
Discussion Starter · #12 ·
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.
 

·
R.I.P [The Red Zed] MG ZS 180
Joined
·
19,410 Posts

·
Registered
Joined
·
2 Posts
First off I know it’s night and day but hope you petrol heads can advice.

previously owned Mercedes’ cclass auto but drive manual Merc Sprinterfor work, I hVe always been told my transport office that gear change optimum is about 2500rpm.

Recently purchased MG ZS Manual 5 speed, it’s just meant to be a A-B car .

before selecting 2nd gear take off is like 3000rpm. 2gear car can run upto 30mph happy within 2500rpm, 3rd gear cars running 35-40 happy, 4th gear car drops down to 2000rpm at 40mph and doesn’t know if it wants To keep going or get you to change lower gear, 5th gear 50-70mph happy.

when I don’t look at rpm counter for optimal gear change I’m quite happy with the smooth running but fear revs might be running high at some gears and killing the 1.5l engine.

can gear ratio be fine tuned by a garage for smoother running
 
1 - 14 of 14 Posts
Top