I am in need of some help with my car i took it down to duncan at surrey rolling road.
All was going well but at around 420bhp the car started to have the issue were the more boost he was giving the car the more the power would actually drop.
I asked duncan what he thought it could be and he said it seemed like the exhaust had a bung in the end or that the silencer on the centre section had collapsed so the gases was not getting out quick enough.so basiclly reached the limit of flow from exhaust. Its fitted with a kakimoto race exhaust system 3” and a 3” centre section with a resenator. I dont have a bung fitted and once i got the car home i removed the exhaust and the resonator hadnt collapsed. However it does narrow down inside to around 2” inside the resonator and also in the back box as pictured. Is this normal and could that cause the car not to allow the gases to get out quick enough if it is then ill have to buy another exhaust system or i could replace the centre section with a 3” straight through but though i would ask opinions on here as im unsure at this point any advise would be great thanks in advance

 

Yes fit a 3" center for better flow.

 

How about the back box tho as the middle picture is of the back box could that restrict the flow aswell ?

 

I don't know how well that system flows tbh.
If Duncan says it's the cause of the restricted power then did he suggest a system?
What turbo and other mods are you running,what's your expected power goal?

 

ej257 2.5 cdb done by alyn
bored honed and block faces skimmed to 99.75mm bore
14mm headstud conversion (rcm)
mahle 2618 forged pistons
rcm arrow rods
acl race series main and big end bearings
rcm oil pump
rcm mls 1.1mm headgaskets
all new seal ect

the heads are the 2.0 avcs heads reworked for the 2.5 block
heads skimmed
valves cleaned and lapped in
new stem seals
new cam seals
valve clearance adjusted
new cambelt
the engine was build by Williams competition engine

rcm headers
rcm uppipe
kakimoto straight thought exhaust
6 speed box
twin plate exedy clutch
fmic
walbro intank pump
swirl pot setup with bosch 044 external pump and fuel lab fpr, with braided lines.
850cc injectors
rcm cone filter
Spec c inlet manifold
forced performance red turbo with perrin intake pipe
simtek ecu
defi gauges oil pressure, fuel pressure,boost. oil temp.
ks2 knock sensor

There wasnt a goal i was aiming for close to 500 as possible there is
Another guy on here running simular spec and turbo and over 530bhp

Duncan never suggested a exhaust system im just trying to get to the bottom of thw issue so that i can get it back up and on the rollers. He said engine side of things its perfect the issue is the gasses coming out

 

Very nice spec altho you didn't say which turbo.
What exhaust is the 530bhp car running?

What torque figure did you hit?
I would imagine 450+ with that engine and 420bhp

 

Same turbo unsure on the exhaust.

The car got to 433bhp but then more boost that was added it actually dropped to 417 there was plenty more to come but for some reason the engine would give more but for some reason the car wouldnt put out the gases quick enough well that was what he though and i have no reason to doubt what duncan says as he knows what he is talking about

Give me a few mins and ill post the graphs up

 

 

Hmmm interesting.
You got a torque graph?

 

No they was the only 3 graphs that came printed of, i cant remember of my head what the torque was as it was a bit up and down as duncan was trying diffrent things. so hopefully i can sort the issue and get it back up to him so he can remap it again as there is alot more to come from the car

 

Just had to double take,looks like your torque is well down for that engine,very laggy,not hitting peak boost and torque until 5300rpm.
Defiantly something not right there,look to go lean on spool but I think some mappers do this.
Hope you get things as they should be

 

Definitly something not right but to be fair once its on high boost the sound of the car does completly change and sounds like its struggling to get the gases out, i could just try a 3” centre section but not sure on the back box think of i can get that sorted then the car will be completly diffrent

 

Yes get a better flowing exhaust if the one you have isn't,see how you get on with that.

 

What turbo is this.

 

looks seriously laggy as well :s

 

forced peformance red according to his spec list. they come with a gt35r wheel i believe.

 

Is the inlet pipe new?

 

is the dump valve blanked on your set-up?
Trev

 

Journal Bearing style too

I think

 

Its a fp red and does have a gt35 wheel domino on here is running the same turbo with similar spec at 530 the dv is blocked of and i bough the rp red intake pipe aswell at the same time so both new

 

The mapping was cut early as he could get the boost in but the more he added the car would actually drop power. As he said it seemed the car couldnt get the gasses out. Measure inside of the exhaust and inside the silencer and back back it actually drops from 3” to just under 2” so obviously thats not helping as surely it will cause huge back pressure