flat spot?

[guidos]

Hey guys.

My VL used to have a flatspot from take off until around 3500rpm. Wasnt too bad but if you went up a hill it was so slow but as soon as it hit 3500rpm it would go a lot better.

When i say flatspot i dont mean no power at all, it just didnt make as much power (very slow to rev up) until 3500rpm. At that point it revved up so much quicker you could hear the difference.

I put in an adjustable cam gear and advanced the cam 6 degrees.. and while this has made it a lot better, i still feel it lacks power down low.. now the 'flat spot' ends at 2500 or so rpm and the difference is much less, however, i still notice it going up a hill.

My brothers totally stock VL actually feels slower to drive but the power comes on smoothly and consistantly, unlike mine, and it feels better going up hills.

Hope my explanation makes some sense. Sorry if it seems a little stupid, its hard to explain :confused:
Anyone got any ideas as to whats causing this? is it just the cam being retarded from factory?

BTW, o2 sensor is fine (i get ~400-450kms/tank), starts fine, idles ok, tried different ECU, swapping AFM.. checked TPS and that seems OK too. Ign timing is advanced to 20 degrees also.

[OVL087]

throw a huffer on it. you know u want to

[Sin]

yes, yes he does ;)

[guidos]

hopefully once ive finished tafe and got a job it'll come off the road for a turbo conversion.

just tryin to get it to run as well as i can in the meantime...

[Peter...]

i hear ya man, my falcon is as doughy as all getout until about 2500-3000 rpm then it goes like a bastard.

Any answers anyone has for this man, and I will be listening...

:wtf:

[lad13s]

I had the same problem with my N/a VL

inherent flat spot at 1800rpm. It's purely a case of freeing up the intake and exhaust restrictions ive found.

I have an auto slushbox which made matters worse but in standard trim i found it difficult to rev up to 2500rpm in the auto.

whacked ont he exhaust and i could hit 2500rpm. o2 rush air filter 2800rpm. cold air intake 3500rpm whacked on a hi-flow cat and pod filter with heat sheild 5000rpm

revs to the sh*thouse now in auto form, so much nicer than standard trim and ive toasted a few VR's so the power is up there over the 114kw standard.

So my recomendation:

Cold air intake $30 http://www.autospeed.com/A_0779/page1.html

Exhaust (extractors, 2.75in pipe, straight thru muffler and resonator) approx $800 (prolly cheaper somewhere else)

Hi flow cat $225 www.uniqueautosports.com.au

O2 Rush pod filter $199 <- must enclose with a heat sheild!

Now you have all but totally freed up the intake and exhaust restrictions, although im goin to try for a 3inch exhaust after the extractors and see how that goes because the biggest possible exahust diameter should be used after the tuned length of exhaust (extractors) on a N/A engine.

Exhaust is the best way of eliminating the flatspot thou. Thats just my opinion.

[guidos]

hmm lad13s.... either i'm confused by what you're saying... or you're confused by what im saying!!

its flat up until 3500.. then onwards it hammers...

also its strange that my brothers car (totally stock in every way) doesnt do it.

i just got rid of my loud (catback) exhaust also. sounded really good but was too droney (just one turbo muffler) and it annoyed me. i swapped it with my brother for his stock one. i'm not about to get another exhaust, or do any intake mods, or any mods for that matter, to the n/a, unless they can be 'carried over' with the turbo stuff.

in my opinion its pointless spending lots on an n/a as a stock turbo will still beat it, unless you get serious with head and cam work...

[lad13s]

Sorry, i was lost.

u could always do a 3inch cat back exhaust which will suit a turbo nicely :D

And dont use turbo mufflers, use straight thru!

Peace.

[lad13s]

A flatspot is more of a point where revs halt for a small period of time at a certain spot thou...

or are u just suffering from a lack of power up until 3500rpm?

cauz thats what i had, at 3500rpm i think it is the cam kickin in, but dont quote me on that.

Peace again.

:D

[Pete]

Guido,
Has the car got a distributor?
Not familiar with that model so I'm not sure but it may be a sticking advance / retard plate or worn or weak springs in the dizzy not allowing the engine to make full power until the revs get up above 3500.
One other thought has the car been set up on a rolling road type dyne? This may help pinpoint the problem more quickly.
Cheers, Pete.

[guidos]

lad13s tis ok dude :)

yeah its true but to be honest thers no point if its cat back! i dont want the noise, and cat back offers no performance gain.. i just took my 2.5" cat back off a few weeks ago and with the stock peashooter back on its no different power wise (one either car).

yeah its pretty much a lack of power until 3500rpm. its not a slight thing though - as i said i dont notice it on my brothers car. for example, with the hill thing, mine would be a total slug until it hit 3500rpm then it would race up there nicely. my brothers is much better in the lower revs.

i understand there is a point where all cams are operating the most efficient but i honestly feel that the difference in my car is way too much!

as i said, advancing the cam 6 degrees made it much better. i do recall reading that due to variations in deck hight (and a few other things, i cant remember what though?) cams often come retarded from the factory. i meant to use the adjustable pulley to get mine profesionally dialled in but i dont really have the spare cash.. too many other problems have arisen with this stoopid car.

[guidos]

Originally posted by Pete
Guido,
Has the car got a distributor?
Not familiar with that model so I'm not sure but it may be a sticking advance / retard plate or worn or weak springs in the dizzy not allowing the engine to make full power until the revs get up above 3500.
One other thought has the car been set up on a rolling road type dyne? This may help pinpoint the problem more quickly.
Cheers, Pete.

Dude my name is nathan. nickname is guidos and it comes from people not being able to pronounce my surname (Giuliani) properly :)

In answer to your question the car does have a dizzy - but AFAIK the computer controls the advance/retard of the timing.

It has never been on a dyno while i have owned it. Im guessing it was when it had its chip installed but i have nothing to prove that.

I have tried a stock ECU by the way so its not the chip either :)

:confused:

[guidos]

oh and sorry for calling it a flat spot if its not.. from what i understood it was.. but i wasnt too sure so thats why i put a ? in the thread title. thanks for all your help so far..

[Pete]

Guidos,
Sorry for stuffing up the name.
No offence meant..... I just can't type.
Cheers, Pete

[guidos]

Originally posted by Pete
Guidos,
Sorry for stuffing up the name.
No offence meant..... I just can't type.
Cheers, Pete

no worries mate! im not fussed. i just point it out coz theres a guy whos name IS guido and he did an rb25 VL conversion, i get a lot of emails meant for him..

[lad13s]

hmm well with 20 degrees of timing it should fly damn

is it auto or manual?

and have u checked the ECU for diagnostic code errors by any chance?

[guidos]

it actually is reasonably quick for a near stock n/a. im just confused as to why the power delivery isnt as smooth as it should be and why it took stuffing around with the cam timing to get it closer to 'normal'.

its an auto. in fact thats why im asking, my old auto died, and im starting to think the reason i cant seem to get the new one to shift perfectly is that the cam timing has been played with.

[lad13s]

DId u check the ECU error codes?

[guidos]

sorry dude i forgot to answer that one. there are no codes on the ecu, havent had any in quite some time.

i put the cam timing back to stock today, there is a huge difference. doesnt really pull well till 3500-4000rpm. drove my brothers straight after, its MUCH better.

however the auto seems to shift better while the cam timing is stock? :( i'll drive it for a few days like this and see how it goes.

im not happy though, its gutless without that advanced cam timing.

btw the injectors have all been cleaned and checked recently too, and the compression is all spot on as i put a reco head on ~9 months ago. the lack of power existed before the head was done too (the gear went on after that)

im quite confused.

[lad13s]

not sure, but i think there is a vaccum line from manifold to auto tranny

the manifold pressure would be different at different revs based upon cam intake and exhaust duration

check the manifold for leaks or the line to the tranny for cracks

otherwise i am stumped...

Peace.

[guidos]

this auto went in over the easter long weekend.
the vacuum supply to it is good.
i adjusted the bands myself recently too..

the cam timing did make a difference i think - i need to drive it a bit more to be sure. i'll let yas know.

i dont think there are any manifold leaks but i'll have a closer look soon.

it seems that the hoses that the injector guys put on the injectors are starting to show little vertical splits so i'll prolly pull thew hole IM apart in a few weeks to fix that.. i'll check then.

the car is still driveable its just a slug without those timing changes and the auto is clunky with them :(

[lad13s]

Yeah sorry buddy but im flat out of ideas

gave my atmo vl a fang tonight in the brisk air of sydney and it got up and going a bit

just a quick question for my sake, did u recurve the distributor or apply a variable cam timing set?

how much did it cost and where could i source one?

sorry for hijacking the thread

[guidos]

a dude on the internet made it up for me, cost $100 if i remember right, $50 for his work and $50 for him to source a stock gear. he machines out the inside and makes up a new one thats adjustable.. pics speak better.. look , i took thiswhile installing it...

i just set it to six degrees advance. i was going to have it profesionally dialled in but i'd rather not spend the money right now.

other things (like tyres) are more important with winter approaching

here (http://guidos.8m.com/pulley.jpg)

[lad13s]

Do u remember his contact details cauz im quite interested

did u need a new timing belt?

[tandy ass]

Originally posted by lad13s
Yeah sorry buddy but im flat out of ideas

gave my atmo vl a fang tonight in the brisk air of sydney and it got up and going a bit

just a quick question for my sake, did u recurve the distributor or apply a variable cam timing set?

how much did it cost and where could i source one?

sorry for hijacking the thread

The fuel and ignition timing maps are all computer controlled; the distributor on the 3 litre engine serves two functions - Distributes the spark to the appropriate cylinder and via the crank angle sensor (CAS) it tells the computer what rotational position the engine is in.

As to having the flat spot, I honestly wouldnt know. Cam timing certaintly could cause that but have you checked simple things such as the timing? Whack a timing light on it and see if the timing is 15 deg BTDC. Put the car in drive and get an assistant to put his foot hard on the brakes and accelerate and see what the timing does. The auto trans computer perhaps could be interfering with the engine computer or didn't the VL's use a tranny computer?

Another thing is have you driven it and attempted to tune it be ear; ignoring everything the timing light tells you, crank the advance up a bit and give it some stick and keep doing it till you hear detonation (pinging). If you hear it ping then stop immediately and back the timing off a bit - the RB30E motor is dead easy to hear pinging. Then whack the timing light on and see the base timing....

As to the mention of "just put it at 20 degrees timing" is just plain ridiculous; you will have a blown/smashed/dead motor in seconds.

Cheers

[FastEHHolden]

I tend to find that a stretched timing belt causes most of the flat spot probs in VL's.....you described the groovy adjustable cam drive...but after you adjusted the cam timing did you recheck your ignition timing?...it has moved. If cam and ignition timing check out OK have a quick look at the Throttle Position Sensor.

[vrmmmpshhh]

ok dont know if this wil help, but when e15et owners whack in the vl throttle body some get flat spots while others dont... they fix them by adjusting the TPS next to the TB..

[guidos]

thanks for all your help guys.

i doubt the timing belt could be stretched as it is only just over a year old. 18 months tops.

i still have it running stock cam timing now but the ignition timing is at 20 degrees. i havent driven it much as its quite wet here and my tyers arent the best but i'll get back to you about how it feels..

i know its not as good as it was with the 6 degrees of advance but i think it feels 'normal' now. maybe it was just bad ignition timing all along.. i dunno.

also i remember that i had the ignition timing on 25 degrees once (yes idle speed was right) and it ran that way for ages on std unleaded without pinging. i dont feel like trying it again but i dont know how that works.

by the way after setting the ignition timing yesterday i gave it a few revs with the timing light hooked up and it went over 30 degrees. is that normal? when back to idle it was at 20 again.