Jerk On Little Throttle Or Backoff - Do You Jerk Is The Question ;)

[benl1981]

I went the tuner today as I am about to get a tune on the R33

Mods will be enough to get to around 230-240rwkw.

At the moment I am running the new GCG 450hp turbs with the old stock turbo tune.

If you ease into the throttle in say 4th gear at 3000rpm then back off slowly you get a jerk.

The tuner I spoke to today said you can't really tune it out.

He said that on the map tracer when you back off it should jump straight up the vertical axis but it jumps through a few others causing the jerk. This is a problem with AFM cars and this type of turbo. He said all skylines with HKS2530 and GCG etc (that size turbo) do this to some degree.

I mean it isn't that severe but can others try doing this on theres and see if they get the same problem.

I am going to show it to another tuner and get a 2nd opinion

cheers

Edited May 17, 2007 by benl1981

[R31Nismoid]

All of them do it? load of crap

What BOV are you using?

[benl1981]

Stock BOV plumback.

would be interested to hear from others with similar turbos..

Thanks

[R31Nismoid]

Hmm thats odd indeed with the stocker.

Is it working correctly?

I know of 3 GCG cars that have no issue... although... the OLD GCG turbo used to surge, the 500hp one.

There used to be two on the market, now there is just the one.

[Cubes]

Your still running the stock rubber afm to turbo pipe?

I've driven other R32's and R33's *all with stock turbo's* that all do this under a specific driving condition.

Its not exactly easy to get the jerk and I can't always get it to do it easily. You must only just bring it up on boost then quickly back off but with your foot still on the throttle; the car then does a little jerk; almost like it bogs then accelerates normally again.

A larger afm to turbo pipe helps reduce this.

Adjust your driving style.

[benl1981]

Yeah will I didn't notice it with the stock turbo. Maybe it's more exaggerated with the bigger turbo.

Sometimes it seems you can get it at a light constant throttle input, but mostly when backing off but not fully.

Maybe I'm being too fussy on this one.

Will show it to another tuner..

[Cubes]

Backing off but not fully.. Sounds like exactly like the drivability issue I am thinking of.

Try changing your driving style.. Or throw a bigger afm to turbo pipe on it as chances are it will be close to sucking shut anyway.

[benl1981]

The AFM to turbo pipe looks like a hassle to make a new one. At what sort of airflow or power do they become a problem?

Cheers

[rob82]

What your tuner is describing is reversion. On very light throttle you get some back flow (reversion pulse) off the compressor wheel. The only way to fix it is to increase the distance between the AFM and the turbo or introduce a 90deg bend. With the right software it can actually be seen as you back of the MAF voltage gets larger for a second. The majority of AFM's - RX8, any Subaru, some large yank lightening MAFs will NOT run without a bend or a large distance from throttles or turbo chargers etc etc.

[BHDave]

I agree with cubes to a certain degree and Rob

It is reversion, the pressure differential between the front and back of the throttle isn't big enough to lift the bov off it's seat.

I only noticed it after i did the stock bov mod and blocked up the little hole. I never noticed it before that, even with an old stage 2 gcg high flow

Edited May 17, 2007 by BHDave

[benl1981]

Here is the turbo. It's an earlier one but was brand new when I put it on. Loooks like similar exhaust wheel to the one used in the HPI article on the white R34 ..

Stage 2 is the 500hp one isn't it?

This one is a 450hp..

[benl1981]

Ok - I have been checking the map tracer.

At low rpm in 4th or 5th (2000-3000rpm) and around load point 8-11 if you hold a steady throttle input you can see the little black dot jumping around up and down in the same vertical column (i.e. going up hill)...I

It doesn't look normal like what happens in 2nd or 3rd gear.

Sometimes holding this throttle input (around 0-3psi) the load point will jump from 10 to 15 accompanied by a jerk (not sure if jerk is before or after) then back to about load point 5...

I guess this could be a misfire..e.g. the car misses/halts, hence requires less air for a split second since the engine can't take it. This air builds up there and shows a higher load point reading..although this doesn't really hold true unless the car misses which allows more air to flow through..

The air build up wouldn't register a high reading on the AFM

or is the air coming back on itself and the high reading is air flowing backwards..

Anyone had experience with this?

Cheers

[skylinecouple]

I have the GCG hiflow for the last 3 years and have never had this problem.Look at your boost controller,the amount of times I`ve seen people not turn the gain up to maximum is amazing.This creates little tuning problems on it`s own.If you have set gain,turn that up til it starts to spike as well.I did not have your problem exactly but I did have a little hick up on back off in 2,3 and 4th gear and proper tuning of the boost controller fixed it beautifully.Sorry,didn`t think to ask if you have a EBC.My theory is that an EBC is basically a vacume leak,so if gain is to low you may induce a constant boost leak.

[benl1981]

Thanks mate. Although I think the boost controller isn't really doing anything because at 0-3psi it shouldn't even really be opening the wastegate.

[benl1981]

Is there such thing as a 80mm or 3" one way valve that would help this ....hahah

[Dav]

ive got a 2530 and if you back off a certain way it does seem to jolt a tiny bit.

[MANWHORE]

hey ben, I get massive reversion on my car. After the 20th, if you like, we can try and see if we can reproduce it, then i suppose you could then say that it would be reversion.

I've also got a gtr bov spare that's going into my car. I suppose after the 20th, suppose you could try wacking that onto your car to see if the bov is the issue. in addition, maybe blockign the bov off all together, just for testing, to see if it makes it worse.

My car seems to have a small issue atm though. When I put the throttle down in neutral, then let go, my revs drop below normal idle. Only started happening around the time I put the pump in (which was 1 week after I put the turbo in). grrr, doing a few mods at once makes it hard to pinpoint issues.

[RBwhatever]

Isn't it possible to 'tune out' some of the effects of reversion?

I had reversion pretty bad on my stock computer, the had the FC installed and tuned and it is mostly gone. You can still feel it slightly, but you wouldn't know if you weren't told.

[yogi000]

i've got an r32 with a 2530 and gtr bov and a apexi stainless steel intake pipe (longer than stock by about 5cm)

i get that jerk aswell, but the funny thing is you dont get it so much when the car is cold and running rich.

it used to do the same with the stock bov.

I would like to fix the problem if its fixable

[benl1981]

Chris,

Yeah I dont know whether to try diff BOV, AFM or even wack in the stock ecu.

I have checked all hoses but I guess if there is a small vacuum leak it would be hard to see.

Wouldnt this be evident at idle etc though.