Running out of revs

[Winthattt]

My car is a Sigma Roadsport spec, basically 125hp academy car but with ZZS tyres (which are smaller diameter  than academy tyres). On track I regularly hit the rev limiter in 4th but changing up to 5th is slower as the engine cannot pull 5th.  Top speed is therefore about 105mph, 7k revs in 4th.  Is this normal? I believe the 135hp upgrade is a rev limit increase?

 

thanks

 

[ScottR400D]

I wouldn't think that was too bad with 125bhp. Do you have a screen on? That makes a huge difference. 

[Winthattt]

Screen off, sometimes.

[Tom_Arundel]

Is that with 13`` or 14`` wheels and what is the tyre section?      I think rev limiter should be 7200 on a 125.                               135 is a different engine with VCT.        125 upgrades to 140 supersport.   So yes it should go better than that but not much.

Where are you?

[Winthattt]

It is a 2014 car so vct, I think tge Apollo wheels are 13 inch.

I watched some training videos of a 135 at Castle Combe and it looked like max speed was 115mph.  I'm wondering if I'm down on power as it goes slower in 5th than 4th. 

[K7 VCT]

Go for the 310 upgrade, I did and I love it, even after 5 years...

[Neil Allen]

I agree with K7 VCT #6

The 310 upgrade is well worth considering. 

 

 

[K7 VCT]

Sevens and classics do it for less than CC, get a lightweight flywheel to add to the fun

[Tom_Arundel]

Just for fun.....Set car on level road/garage floor.   Put chalk mark on bottom of tyre and floor/road.   Move car until chalk mark comes around to bottom again and mark floor/road again.    Measure distance between marks in feet.   Do sums as follows (assumes 4th gear is direct drive 1:1 and diff is 3.9)

7000/3.9 = 1795      multiply by distance between marks     we will say 6ft.     = 1795 x 6 = 10,769 ft/min     Divide answer by 5280 and multiply by 60 which will give speed for your tyre at 7000 rpm   which is 122 mph.  However....engine power peaks at 6800 and it take time to get there ..... so  6800/7000 = 0.97 x 122 = 118 mph...Enjoy 

Note.  13`` wheels usually have a smaller rolling rad. so less feet per rev. but it looks faster on the standard speedo setting !!

Note 2.     I easily passed a guy, at a track day, who was doing 135mph down the straight on `little wheels` .......I was doing max 120mph....felt good at the time 

[SLR No.77]

Increasing the power is just disguising the problem that basically the gearing is wrong, whether it be the diff or gearbox ratios.

Stu.

[Winthattt]

I was basing my speeds on the vbox gps which is probably more accurate than the speedo.  I have been watching a couple of videos of really fast drivers on the same track and they use 5th in a Roadsport. I don't as it feels like it's slows down  and there are two extra gear changes which costs time. Obviously it's at times when I'm too busy to study the Speedo.  I was on the limiter in 4th at Dony past the exhibition centre, pit straight and Craners. 
 

I know the 310 is really good but I like working the lower powered car and trying, without too much success, to keep momentum in the scary bits.

[heptagon]

The CC ECU flash to 135bhp gives another 500 rpm  (I understand) and is a cheap and simple upgrade

[Tom_Arundel]

If you are actually doing 105mph at 7000 in 4th then you have a 4.4 diff fitted....which is ok for acceleration but not great for speed, should be 3.9

[Tazio]

If that were the case I would have thought he would be able to pull 5th gear.

 

[krisfl]

I'm no expert, but have just recently done my homework on the Sigma's having just bought a Ti-VCT which was moonlighting as an older fixed cam sigma.

so, from my reading, the stock 135BHP sigma sold from 2015 on has a 7000 rpm rev limit with peak power at 6,800. So not really any different to the 125BHP . But the 125 hits peak power lower down c6,100rpm, then drops away. Top speed (officially) for the 125 is only supposedly 112mph too. So 105mph in 4th isn't too shabby??

So the 135 map won't give you more revs, but it will give you 10bhp more at 6800. But it sounds more like something else (gearing?) as others have suggested.

Worth double checking which engine you have though, as UK cars sold from 2006 to 2015 were all "officially" fixed cam sigma's not Ti-VCTs. There was a 115BHP VCT available during that time, but it was sold over seas only, not in the UK.

But!

I've separately been told that towards the end of the 2014 the fixed cam sigma supply dried up from Ford (they were End of life due to Euro 4) and the last 125 Roadsports were switched to the Ti-VCT lump, before the 135 bhp 270 arrived in 2015. So your car (think you said was 2014?) could have either potentially. A quick glance at the top of the engine will tell you. Fixed cam sigma's don't have the wiring harness for the solenoid which flips the cam profile...

If you have the older lump, you can still remap it, but you might need to look into the 140 supersport spec and map, not the VCT 135 (map, light flywheel, revised air intake with side vent in the bonnet - all standard on the later 270, except the flywheel)

My 135 Ti-VCT positively headbuts the rev limiter in all gears and only feels slow when I happen to see a 420/CSR/R400/620 etc etc etc disappearing up the straights!

[heptagon]

Interesting, I thought the Academy cars had a lower rev limit in first and second seasons before going to the 270 spec.

Mine is an ex-Academy with the Ti-VCT but I never drove it before the 135 ECU flash was done. 

[Winthattt]

Thanks for the comments. My car has the Ti-VCT, two ears sticking out of the front of the engine. I knew it was an early model. I'm getting a compression/leak check and checking the diff ratio. I'll let you know what I discover. 

[7 wonders of the world]

may want to check the the cat too...

[Winthattt]

Compression and leak down are all good, I'll check the final drive ratio when I next get to the car, thx for your help.  I'm sure the cat has long since expired! It's only used on track.

 

 

[7 wonders of the world]

If the cat is dead / partially melted this will cause a restriction in the exhaust......

Cat's dont like track work as this involves long periods of WOT which is open loop resulting in meltdown 

[simon_h]

The cats can fail, melt, from wot but usually only if it’s been set up too lean in the first place. They don’t normally melt with a good rich mixture going through to keep them cool. A severe misfire can also make them overheat and melt. If there are excessive pops and bangs on the over run this is more likely to cause one to break up. 

[7 wonders of the world]

Its unburt fuel that melts them which takes the peak temp too high.

[Winthattt]

After a bit more research I have decide I just need to pedal harder.  Compression and leak down are good. I have been studying Ben Clucas laps in a Roadsport at Castle Combe. On the pit straight to quarry corner he runs out of revs at about 106 and shifts to 5 to get to about 109.  Because he entered the straight with more speed than me and brakes much later he gets a 3mph reward over a longer period.  I get no gain as it's hardly any faster and I have two more gear changes.  
 

Thanks for your input everyone, must drive faster (on track).