Hi,

i have a 2007 mustang gt and i have a slight problem with my top speed. I will try to make this as short as possible.

My car is equipped with a 4.10 ford racing ring and pinion. As we all knowwitha 4.10 the top speed decreases to 230-235kph. Earlier,with my 4.10 on 4th gear my car hits the top speed of 230 or 235 kph.

Now i have installed the JLT filter and i ordered a special aggresive tunning from the states. My car is much more powerful now, my rpm is set to 7000 now, but my problem is the now even though the car is more powerful, my 4th gear does not hit the top speed anymore. 4th gear goes max upto 210kph even though my rpm is set to 7000 whichforces meto change to 5th. i loose alot of power when i change to 5th.

in simple words, 0-200kph my car is great, but 200-235kph is horrible and i want my car tohit its top speed on 4th gear.

Please pass your valubleinformation.

 

Cams will help with top end speed

 

larger diameter rear tires

 

Well, first thing is the definition of "a lot more powerful". Might scrape another 20 horses if you're lucky from the CAI/tune.
The other thing is that your speedometer will need recalibrating now you've altered the rear end ratio although in reality the speed should now be over reading, so that's screwed up.

So how are you measuring speed? I guess to realise you don't have the legs you used to, you must be reading something else, GPS?

4.10's are installed to improve acceleration by reducing gear ratio, so this is all part of the game. Sticking a larger diameter wheel/tire combo will only negate the gears.

Finally, 7000rpm ?? WOW

 

You had the 4.10 before the tune? Did you do anything to the computer when you got the ring and pinion? Did the new tune reset your speedo for 4.10? Maybe you really weren't going 235 kph (146 mph) with 4.10 gears in 4th to start with.

 

This makes no sense. I must be missing something here. I have 4.10's. I've had my car to 235 kph (146 mph) and it was still pulling hard. That was in 5th gear of course. (5000 rpm)
Now assuming you have a 27.1" tall tire you can go 138 mph in 4th gear at 7000 rpm, assuming your engine makes power that high up which I highly doubt. I'd question the stock bottom end's ability to withstand 7000 rpm. I wouldn't go over 6500.
Also keep in mind that the computer starts adding an over rich mixture the last 250 rpm. So if you have your rev limit set to 7000 you power will drop off at 6750. This will be more noticable at the higher speeds you are talking about.
This is why many aftermarket tunes will raise the rev limit to 6500 so you can shift at 6250 which is close to where the stock cams and heads are at their limit anyway.
Dunno, that's my 2 cents anyway.

 

This may sound like a stupid question, did you disable the speed limiter? Cause if you didn't and you also did not recalibrate your speedo after the gear change, your top speed would decrease.

 

+1
Explain in more detail

 

I think e meant that his RPM "LIMITER" was set on 7k.

 

he probably still has the speed limiter on