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bendee
14-08-2007, 17:26
ive just fitted a decat to my hybrid now for some reason it doesnt feel as fast as it once was.
it has a valver manifold, decat, scorpion back box and itg panel filter so maybe needs a chip or something, a remap maybe?
would the decat make it slower somehow?

maybe i was imagining it but just didnt feel like it has in the past.

J o n
14-08-2007, 18:21
valver manifold is no doubt causing this. they are useless on the F7R imo. my friend tried both on the same day and the valver one gave more low end torque and strangled it up the rev range

bendee
14-08-2007, 18:28
yeah ive been told a couple times the valver manifolds better low down i thought maybe with a remap or chip it would help sort it.
also its only since the decats been on its felt a little slower.

AndyFielder
14-08-2007, 18:31
hill power swear by the valver manifold.. i tend to agree, why do the race spec cars not use a Williams manifold?

I have been told the effect to top end is minimal unless you are running 220bhp +

Andy

Laine_16v
14-08-2007, 18:51
Torque wins races, BHP impresses your mates.

Mr.AdamB
14-08-2007, 19:11
i have valver mani and mine is a ripper!

Hulio
14-08-2007, 19:24
The valver mani is bloody heavy though!

MatBrown
14-08-2007, 19:31
Sounds like the decat is losing you back pressure, put the cat back on.


Mat.

Matty86
14-08-2007, 19:38
Torque wins races, BHP impresses your mates.

why is my clio faster round the track than my brothers diesel golf which must have double the torque ;)

Bailey_1260
14-08-2007, 19:43
why is my clio faster round the track than my brothers diesel golf which must have double the torque ;)

Depends where it is in the power band.

Bit of a sweeping previous statement, a balanced graph and well mapped engine is better imo

Laine_16v
14-08-2007, 20:13
Torque wins races, BHP impresses your mates.

why is my clio faster round the track than my brothers diesel golf which must have double the torque ;)

Cos its a lardy golf :lol:

Laine_16v
14-08-2007, 20:14
Sounds like the decat is losing you back pressure, put the cat back on.


Mat.

Stan tells me backpressure isnt needed, the less backpressure the better.

Its so conflicting id really like someone to clear this up.

MAXIBOY
14-08-2007, 20:18
engines don,t need any back pressure just tuned length

Laine_16v
14-08-2007, 20:27
engines don,t need any back pressure just tuned length

By that you mean the length of the exhaust, so it resonates with the engine?

MAXIBOY
14-08-2007, 20:35
the length of the four different exhaust headers so that they cause a suction type effect on the emptying cylinders. also the length to the first box i believe has an effect.

richy
14-08-2007, 20:49
the valver manifold is a ugly heavy peice of shit! lol :lol:

bendee
14-08-2007, 22:45
bloody hell it certainly dont help with different peeple telling me differet things lol.

eternalife
14-08-2007, 23:07
If 'back pressure' as it is currently called on this forum is not needed then I have a question...

Why do race cars use manifolds/headers of some sort on their exit?

As some believe it has no affect on power then an engine with no exhaust/manifold (exit direct into atmosphere) should produce more power? and therefore race cars should adopt this methodology...

Answers much appreciated

MAXIBOY
14-08-2007, 23:15
back pressure is not needed. end of. tuned length manifolds can create a negative pressure at the right time thus drawing air out of the cylinders creating less back pressure.

bendee
14-08-2007, 23:22
thats all well and good lol but what do i do.

eternalife
14-08-2007, 23:25
If exhaust (mass of fluid) are too far forward neg pressure reduces.

back pressure keeps mass of fluid at certain point to create optimum neg pressure. If back pressure is lost - then u will see mass of fluid too far forward to create a 'great' amount of vacuum - This is why decats can knock acceleration but increase top end power as they are do not create the vacuum required at the lower revs but perform at higher revs

Also, known as 'scavenging'.

hence some cars have their exit retarded, to create larger vacuum more power.

MAXIBOY
14-08-2007, 23:25
sure you haven,t knocked the lambda sensor. decat should not make it slower.

seanofnp
15-08-2007, 00:13
My hybrid runs a decat and valver manifold and it rips. Doesnt have any flat spots in the rev range from what i can tell through driving and feels like it has stupid more low down power than my mates williams.

Tommo
15-08-2007, 12:24
My Devil decat killed low down torque and it was so frustrating to drive. I put the cat back on soon after at it was miles better.

bendee
15-08-2007, 16:07
sure you haven,t knocked the lambda sensor. decat should not make it slower.

im sure i did apply pressure to it when tigtening it up i left the spanner on and it pressed against the sensor as i tightend dont think it moved but might be wrong.
what would the problem be if it is the lambda?

VIPERONE
15-08-2007, 22:20
the decat does reduce torque. it does however improve your in gear speeds, you should notice it in 3rd 4th and 5th.

the valver manifold is crap, i had it on my hybrid then ended up getting rid as it starved my car of bhp and torque to the extent that standard williams could out run me. I swapped to a williams manifold and made some other mods and a standard williams is like a valver is to a willy. lol


so
1) fire off the valver manifold
2) if you never speed, then fit the decat for more torque
3) if you enjoy a track day fit a decat.

:-) Gunner

bendee
16-08-2007, 14:52
i think i will try a williams manifold, take it ill need a williams decat aswell so ill try and swap someone.

MatBrown
16-08-2007, 16:55
I have a williams manifold and downpipe for sale, also have a decat.


Mat.