Not the BHP we'd hoped for any ideas?

[The Baron]

Hi,

Just finished rebuilding our GT Turbo. Had a rolling road but we didn't make the BHP we'd hoped for. :dearme::scratch:

Car - standard C1J bottom end.
carb Modified jets - changed and adjusted by rolling road tuner.
T28 with .49
T3 actuator
GT tuning uprated intercooler (NOT FMIC)
2.5 inch down pipe and scorpion exhaust
possible uprated cam (have receipt but not 100% sure it's in the engine!)
possible uprated valve springs
uprated air filter - PIPERCROSS

adjustable bleed valve

new turbo installed and then rolling road str8 after.
was 125bhp, now 157bhp flywheel
was 105 at wheels, now 145 at wheels,
was 120lb/ft now 165lb/ft.

this is on V-Power running 18psi.

to be honest we were expecting more?

one thing that surprised us is that the turbo didn't seem to want to blow anything over 20psi regardless. (although we want to run at 18psi - wondered if this was an indication of a problem?) this was the tuners measure not a crappy boost gauge (although our boost gauge was very similar).

so 3 questions...:rolleyes:

what is the restriction in this set up that is holding us back?
is it maybe the turbo as it wouldn't blow over 20psi no matter what he did?
or are these figures ok for this set up?

it does feal alot quicker and a great drive now but we are still looking for more.

PS: the engine is spot on for compression etc so think its in the fuel or boost circuits?
PS: the tuner is very familiar with turbo carbs and old school motors and is a pro guy not just some have a go hero.

thanks

Team Baron! ;)

[Andrew Cooke]

Where are you measuring boost?

Have you checked the boost circuit for leaks?

[The Baron]

Where are you measuring boost?

Have you checked the boost circuit for leaks?


measured from the carb top

and no obvious leaks.

thanks

Team Baron.

[James5]

measured from the carb top

and no obvious leaks.

thanks

Team Baron.


Most peeps take boost meausrement from carb base aka the AEI vacum line as you loose 4-5 psi through the carb itself and this gives a more accurate reading as to what the engine is actually getting. Check those pipes as Andrew suggest's loose pipes, split's etc,

[Guybrush]

157bhp with a T28 and 18psi.... :scared:
I got more than that in my 1/2 cup with a T2 and 15psi... So i think you were definitely correct in assuming you'd be making more power :(

[BluntyR5GTT]

That is very low fella my car made 178bhp on a hub dyno at 19psi with a poorly carb only.ran to 5k due to.it leaning.out this was.on.a t28/t2 Is the compression.etc all ok

[Matt@CodeRedMotorsports]

Afr's ok?
Duff spark plugs were the cause of clarkys low power on one RR session.

[5teve L]

What were the afr's, what jets did you end up with, do you have a 2" scorpion, actuator opening ok & not loose, does the turbo spool up ok, my old unit would hit full boost around 4k & i'd rev it to 7k
Cam timing ok, tooth out & it will drop power... ?

[DaveMayGTT]

Realistically though were talking 157bhp @ around 14psi, doesn't sound rediculously low really.

Definately check for boost leaks though

[Logg]

I'd say take your boost reading from below the throttle as James says you'll probably find out your only running about a bar of boost.

To check for boost leaks see if you can find something like this or get one made and block the other end of of the boost run and wack the pressure up to 30-40psi and you'll be able to hear any boost leaks. :)

[The Baron]

thanks for all the posts peeps. :agree::agree::agree:

I believe we were at full power just under 4k and keeping it solid up to 6300 maybe higher. spools up fine for the size of the turbo versus the CC.

we took a print out of what the AFR should be from this site as a reference :) and our man new what was what so had these spot on. so think fuelling is OK... glad we took the car for RR actually because it was running lean :eek: when we arrived apparently. fitted a stack gauge and wideband now so we can keep an eye on that.

plugs etc all good.

as the fuelling/engine itself appears to be spot on, my first thoughts were crap intercooler, poor flow, leak or air starvation due to a p!ss poor air filter (even though it is not standard)?

BUT I'm also suspicious of our 2nd hand T3 actuator which is a bit bodged on! :crap:
what actuator do most tuned GTTs run?

The comment about winding it up to mega boost to detect leaks is interesting but we tried unlimited boost and it wouldn't register above 20psi no matter what (taken from the carb base as suggested sorry not the top). If unlimited would we expect that to go a lot higher?
I'm suspicious that this is an indicator of our issue?
but I'm also confused as we were getting our target 18psi regardless yet it does seem not the power that would go with it.

I like the boost leak tester but think it might be a bit out of our league - is there a (cough cough) bodge it and scarper method to find boost leaks?
most of our plumbing is standard but certainly no obvious issues.

once again I really appreciate the comments chaps... great stuff. :agree::agree::agree::)

[Markey Mark (BD)]

If the turbo doesn't want to produce anymore boost than 20psi8 then you could be looking at weal actuator, try removing the vacumn pipe and try throttle for breath moment see if it creeps past 20psi and you'll see if it actuator related.
Was the turbo new when you fitted it?

As for power, if you took the boost measurement on carb top then that 18psi will be about 15psi carb base so 157bhp on a fairly standardish engine isn't too bad.
A look at the AFR graph would be good, no harm in having other peoples opinions on it as there could be something showing up on there.

[Ricardo]

Might not be the problem but worth checking the GT Tuning intercooler, correct me if i'm wrong but weren't they prone to something wearing a hole in the bottom part of the intercooler?

[Scoff]

18psi at the carb top is going to be 15psi in the manifold I guess, so 157hp isn't bad with a standard camshaft I would have said. Or has carb tuning come on leaps and bounds in the last few years and I havn't noticed ? :D

Peak power at 4krpm sounds a bit oddball, maybe you could post up the plot, the problem (if there is one) might become more aparant :)

[Slim]

sounds pretty normal to me.... -4 pr 5 psi loss at the carb.. 157 bhp seems fine for 15 psi..

[Logg]

The comment about winding it up to mega boost to detect leaks is interesting but we tried unlimited boost and it wouldn't register above 20psi no matter what (taken from the carb base as suggested sorry not the top). If unlimited would we expect that to go a lot higher?
I'm suspicious that this is an indicator of our issue?
but I'm also confused as we were getting our target 18psi regardless yet it does seem not the power that would go with it.



I'f this was about my comment.

Not boost or even engine running. But if you look at the picture you can see one side of the boost circuit blocked with a compressor take off then block off the side just before the carb and by using a compressor to pressurise the system. you will hear any pressure escaping.

no unlumited boost very bad idea.

and as Ricardo said the GTtuning intercooler was so big that if a cars engine mount had ever gone soft themount would wear a hole into the bottom of the cooler. worth a check.

[Tony Walker]

If the engine steady is worn/missing then the gearbox release bearing arm tends to puncture the intercooler :S

[Jimmy_GTT]

I'm very curious about your results in this BHP hunting as I'm also running on 18psi and I'm also measuring 147bhp @ wheels. And I share your opinion it is a bit low.
I've measured my cam which have been bought from K-tec and it is very similar to a Piper285. And I have peak power around 4500rpm.

I think the 8% loss you are calculating the power @ flywheel is very low. I was told that on a FWD car it is around 15%.

[BluntyR5GTT]

I'm very curious about your results in this BHP hunting as I'm also running on 18psi and I'm also measuring 147bhp @ wheels. And I share your opinion it is a bit low.
I've measured my cam which have been bought from K-tec and it is very similar to a Piper285. And I have peak power around 4500rpm.

I think the 8% loss you are calculating the power @ flywheel is very low. I was told that on a FWD car it is around 15%.

my flywheel to atw loss was 28bhp, 150/178 this was done on a hub dyno as well which i believe are meant to be a tad more accurate

[The Baron]

I'f this was about my comment.

Not boost or even engine running. But if you look at the picture you can see one side of the boost circuit blocked with a compressor take off then block off the side just before the carb and by using a compressor to pressurise the system. you will hear any pressure escaping.

no unlumited boost very bad idea.

and as Ricardo said the GTtuning intercooler was so big that if a cars engine mount had ever gone soft themount would wear a hole into the bottom of the cooler. worth a check.

thanks will check that..
the unlimited boost was just to check the turbo really as the RR chap seemed to think it was a bit odd. we never intended 40 psi even for testing but he just checked to see without limitations if the turbo would boost up correctly.

ALSO:
I can now confirm the measurement was carb top so 18psi carb top, so prob 15 =psi at base.
Maybe it's not that bad afterall?

When people set a limit on a standard engine of say 18psi, I presume that is carb base? So we could safely go a bit higher at the carb top?

Will get a graph up as soon as I can get it scanned in.

Thanks

Team Baron

[The Baron]

here is the bhp & torque graph....

any comments welcome...
sorry this is all I have...

thanks

[Jimmy_GTT]

The 1st measurement is also your car?
Than I can not undersand how the difference between wheels and engine is 20bhp there (nearly 20%) than in the 2nd measurement is is only 14bhp (10%)

[The Baron]

The 1st measurement is also your car?
Than I can not undersand how the difference between wheels and engine is 20bhp there (nearly 20%) than in the 2nd measurement is is only 14bhp (10%)

both my car...

you got me jimmy - why is that?

i have to confess i'm a bit confused by why the ...
max power wheels is @ 5133rpm
yet the
max power flywheel is @ 6204rpm
for the same run? :scratch:

someone smarter than me is hopefully going to explain that? :)

[Markey Mark (BD)]

Clutch slip :confused:

[SCHWARTZ]

surley the dyno operator would have noticed that tho:confused:

[Fordy]

Is your setup ment to be that laggy? looks like full boost after 4000rpm?

How much preload is on the wastegate? i got a feeling it not enough

I'd be tempted to increase the preload which will raise the base boost presure up to 14psi and then use a boost controller to get 18psi

[The Baron]

Is your setup ment to be that laggy? looks like full boost after 4000rpm?

How much preload is on the wastegate? i got a feeling it not enough

I'd be tempted to increase the preload which will raise the base boost presure up to 14psi and then use a boost controller to get 18psi

thanks fordy... :agree: are you thinking early wastegate creep?

preload is probably low as you say.
it isn't designed to boost that laggy - it just is I'm afraid.

PROBLEM: I think we need a new actuator... currently using an old T3 actuator which was a tricky fit and had very little adjustment in it.
the main problem we had was getting the actuator which is tight on the turbine housing in line with the wastegate. very little room to play with.
once we had done that we were nearly at the limit of the actuator arm adjustment.

can anyone recomend an actuator for this set up - someone who has experienced a similar problem?

[Fordy]

only thing the extra preload will do is make the boost come in quicker as the gate may be opening slightly before it should thus loosing boost and making it laggy

And by raising the actuator pressure up your making the boost controller have to do less work which helps to stop spiking when out on the road

Personally i dont go number chasing as it always ends badly and i always use wheel figures rather than flywheel, as flywheel figures are fake (calculation from wheel figure) unless they are from a proper engine dyno

There is a few good pointers on here that might help like where the boost source is taken from etc