Board logo

lack of power in 5th gear
deltron63 - 25/6/10 at 08:02 PM

Hi all, iv'e still got a problem with the car.
I can hit the red line in all gears with no problem,a part from 5th. At 80mph i can put my foot down and not a lot happens, It just feels like it's bogging down.
Any ideas?

Paul TigerB6 - 25/6/10 at 08:04 PM

Fit an engine with more than 50bhp??

Sorry - it was either ^^^ or fit a 4spd box and problem solved

[Edited on 25/6/10 by Paul TigerB6]

BenB - 25/6/10 at 08:06 PM

What engine is it? Vacuum is vacuum so if it doesn't bog down at that level in any other gear it does kind of suggest it's just running out of puff....

jacko - 25/6/10 at 08:07 PM

quote:
Originally posted by deltron63
Hi all, iv'e still got a problem with the car.
I can hit the red line in all gears with no problem,a part from 5th. At 80mph i can put my foot down and not a lot happens, It just feels like it's bogging down.
Any ideas?

Have you posted about this before ?
We need more info

deltron63 - 25/6/10 at 08:07 PM

quote:
Originally posted by Paul TigerB6
Fit an engine with more than 50bhp??

Sorry - it was either ^^^ or fit a 4spd box and problem solved

[Edited on 25/6/10 by Paul TigerB6]


i just took the 4 speed out

deltron63 - 25/6/10 at 08:11 PM

1800 zetec, 136 cams, ninja bike carbs, megajolt.
i thought i had found the problem but it wasn't it.
i've replaced the fuel pump and dumped the regulator. still no joy

deltron63 - 25/6/10 at 08:13 PM

quote:
Originally posted by BenB
What engine is it? Vacuum is vacuum so if it doesn't bog down at that level in any other gear it does kind of suggest it's just running out of puff....


i can do over 110 in 4th ( still some to go )

Ivan - 25/6/10 at 08:14 PM

Yep - it's all about power, gearing and aerodynamic drag - if your gears are too long and put you in the wrong spot on the power band to overcome the drag that's growing exponentially at 80 + MPH you will be going nowhere.

What happens when you drop to fourth gear at those speeds - do you regain acceleration - if so then your in the wrong spot on the power curve for your engine in 5th at those speeds.

tomgregory2000 - 25/6/10 at 08:15 PM

do your butterflys open fully under full pedal travel?

paulf - 25/6/10 at 08:16 PM

Have you experimented with the ignition timing? you should have about 24 degrees at full throttle above 3000 revs.
Paul

mcerd1 - 25/6/10 at 08:19 PM

what gearbox and diff have you got ?

deltron63 - 25/6/10 at 08:19 PM

quote:
Originally posted by Ivan
Yep - it's all about power, gearing and aerodynamic drag - if your gears are too long and put you in the wrong spot on the power band to overcome the drag that's growing exponentially at 80 + MPH you will be going nowhere.

What happens when you drop to fourth gear at those speeds - do you regain
acceleration - if so then your in the wrong spot on the power curve for your engine in 5th at those speeds.


i can change down and take off again.

deltron63 - 25/6/10 at 08:20 PM

quote:
Originally posted by mcerd1
what gearbox and diff have you got ?


type 9 from a seirra. escort axle. i dont know the diff ratio

[Edited on 25/6/10 by deltron63]

mcerd1 - 25/6/10 at 08:23 PM

quote:
Originally posted by deltron63
quote:
Originally posted by mcerd1
what gearbox and diff have you got ?


type 9 from a seirra


sierra 4cyl ratios:

1st = 3.65
2nd = 1.97
3rd = 1.37
4th = 1.00
5th = 0.82

thats a 22% increase in the gear ratio when you change from 4th to 5th then

what revs does your engine drop to when you change ?

[Edited on 25/6/2010 by mcerd1]

dinosaurjuice - 25/6/10 at 08:27 PM

need a diesel engine

deltron63 - 25/6/10 at 08:28 PM

it drops to about 4500

deltron63 - 25/6/10 at 08:30 PM

quote:
Originally posted by dinosaurjuice
need a diesel engine


or put the v8 mg back on the road

mcerd1 - 25/6/10 at 08:31 PM

sorry, is that 4500 when you drop into 4th @ 80mph ?

if thats what you ment then it could just be too high a gear

on my focus (stock 1.8 blacktop) the power only starts co come in properly at ~4000rpm
and by my calcs you'd be doing 3750 in 5th which might not be making enough power yet to pull that gear at that speed

how does it perform if you stick in 4th till say 90mph+ then change to 5th ?
(obviously your going to try this off the public roads)

[Edited on 25/6/2010 by mcerd1]

deltron63 - 25/6/10 at 08:42 PM

quote:
Originally posted by mcerd1
sorry, is that 4500 when you drop into 4th @ 80mph ?


no thats in 5th i haven't looked at the revs when i drop down to 4th. i haven't changed up at 110+ .some thing always gets in the way !!

[Edited on 25/6/10 by deltron63]

mcerd1 - 25/6/10 at 08:46 PM

that'd be 5400rpm in 4th then - which seems a bit high too not be in the power band

ever had the car on the rollers ?

[Edited on 25/6/2010 by mcerd1]

deltron63 - 25/6/10 at 08:47 PM

I know i'll put on a 4 speed gear knob, problem solved

deltron63 - 25/6/10 at 08:49 PM

quote:
Originally posted by mcerd1
that'd be 5400rpm in 5th then - which seems a bit high too not be in the power band

ever had the car on the rollers ?


not yet , i'm looking for a rr local

mcerd1 - 25/6/10 at 08:50 PM

btw - I can have a go at working out your diff ratio for you if you tell me what size your rear tyres are

BenB - 25/6/10 at 08:52 PM

quote:
Originally posted by mcerd1
that'd be 5400rpm in 5th then - which seems a bit high too not be in the power band

ever had the car on the rollers ?


Or even 4500 in 5th

deltron63 - 25/6/10 at 08:54 PM

quote:
Originally posted by mcerd1
btw - I can have a go at working out your diff ratio for you if you tell me what size your rear tyres are


185/65/14 i think?

mcerd1 - 25/6/10 at 08:57 PM

quote:
Originally posted by BenB
quote:
Originally posted by mcerd1
that'd be 5400rpm in 5th then - which seems a bit high too not be in the power band

ever had the car on the rollers ?


Or even 4500 in 5th

oh b*****ks, I getting confused already - edited above...

[Edited on 25/6/2010 by mcerd1]

mcerd1 - 25/6/10 at 09:04 PM

quote:
Originally posted by deltron63
quote:
Originally posted by mcerd1
btw - I can have a go at working out your diff ratio for you if you tell me what size your rear tyres are


185/65/14 i think?


well based on the above I recon that either a 4.9 or a 5.1 ratio (I think those are standard english axle ones)
thats a fairly low gear ratio

could be a bit more sure if you had a few more 'rev+gear=speed' figures

[Edited on 25/6/2010 by mcerd1]

deltron63 - 25/6/10 at 09:09 PM

what would be the best ratio?
anyone got a diff

mcerd1 - 25/6/10 at 09:16 PM

download this gear calc program and have a play linky

In general the lower the ratio the better your acceleration, but the faster you run out of gears/revs

most of these programs assume you have unlimited power (this one included) so won't allow for the areodynamics that will limit your top speed in real life

instead its best to look at the speeds you know you can or should be able to achive and see what revs you'll be doing in each gear at a give speed


then compare that to a print out from the rolling road and you might start to see where the problems are.....
(assuming they don't find your problem on the rollers)

[Edited on 25/6/2010 by mcerd1]

deltron63 - 25/6/10 at 09:20 PM

cheers i'll give it a go

paulf - 25/6/10 at 09:21 PM

I have a 3.89 diff in my car and it pulls fifth gear from 30mph up to 120mph although it is a 2 litre.The 1.8 I had in it was not as torquey but still managed 115 to 120mph in top.This is with 185/60/13 tyres.
You will probably benefit from a rolling road session to set the carbs and ignition correctly.
Paul

mcerd1 - 25/6/10 at 09:23 PM

just a though - are you running a 3D map on the megajolt ?

if you are is it off a MAP sensor or a TPS ?

deltron63 - 25/6/10 at 09:56 PM

quote:
Originally posted by mcerd1
just a though - are you running a 3D map on the megajolt ?

if you are is it off a MAP sensor or a TPS ?


3d map with tps

Danozeman - 26/6/10 at 11:19 AM

My 1.8 with bike carbs and megajolt and 3d map. Type 9 and 3.44 cortina diff pulls in 5th from 60 to over 120. No where near aswell as if i drop it to 4th or even third but it does go. You can tell the difference over 90 when the coming wind is like a wall.

If the calc for your diff is right then you need a different one.

deltron63 - 26/6/10 at 06:08 PM

i went out today, i think it must be fuelling.
pulls from 30mph no problem, then plays up at 80.
i hope another jet hasn't fallen out!!

iank - 26/6/10 at 07:57 PM

The engine doesn't know how fast you are going only the rpm it's doing, as the rpm in 4th at 110mph is going to be more than 5th at 80mph it would seem able to rev properly.

Does it struggle in 4th around 65mph? i.e. there's a big dip in the power curve.

deltron63 - 26/6/10 at 08:23 PM

quote:
Originally posted by iank
The engine doesn't know how fast you are going only the rpm it's doing, as the rpm in 4th at 110mph is going to be more than 5th at 80mph it would seem able to rev properly.

Does it struggle in 4th around 65mph? i.e. there's a big dip in the power curve.


nope only in 5th