Boost Cut on a JSPEC vr4

[Evil_Mx6]

hey guys, wats the boost cut on a jspec....
i want to boost it to 14psi....
any ideas?

cheers
Barbs

 

[NZVR4]

you will be able to run 15psi safely on a jspec vr4,as long as the engine is reasonably healthy,if you can afford it then it always pays to have A/F's checked to safeguard against problems

the boost cut usually takes effect at about 17psi with a standard computer,it is not safe to run boost past 15psi on a standard computer

 

[Evil_Mx6]

thanx man, even though its auto ???
that helps i wont be goin over 15 anyway....itll be 13-14psi...just under a 1 bar

 

[JAP63]

In my car i was hitting cut around 12 pound.It cut at 12 pound because i had enriched mixtues from an SAFC2,usually cut is around 13-14 on a JDM VR4.(Monte,Super,And R.S are a little higher)
The cut is introduced by the computer,it reads the volume of air present and determines whether or not it is at the level to cut.
I have found my way around it,I dont know if anyone else has done this method yet or knows about it.

What i did was add 510 cc injectors and i already had an SAFC2 in my car,once i added the injectors i pulled the fuel maps down to compensate for their larger size.This meant that instead of having a positive map,(for more fuel) i had a map that had readings in the negative,(a zero map is stock)This meant that the computer thinks its getting less air,so it doesnt bring the fuel cut in,it postpones it.So...I wound the boost to around 15-16 and now i have no cut at all,and im not running lean,because the 510's on a negative map stil flow more than the 450's on a positive map.
Hope this isnt confusing.
But if youve played with an SAFC you'll know what i mean.
Its just an Air Signal interceptor,So if u go positive,it thinks its getting more air,So it adds fuel,go Negative and it thinks its getting less air,so obviously it gives less fuel,but in my case with the 510's its receiving more because the stock computer thinks its firing 450's.
So the end result is more fuel,and the boost cut threshold raised.
I cant see a flaw with it,maybe someone else can
i havent heard of anyone using this method,though it seems to work fine.

As for the standard pump i dont know how close it would be to running out of flow,but my mates vr4 made 180Kw @wheels with the stock pump and had acceptable fuel mixtures.(theres more to that but i wont go into it now)

At the moment my car still pumps Black smoke out under load and this is with a Negative map,so running lean isnt a worying factor.

 

[brisvr4]

The only flaw with using only your safc to compensate for injectors comes into play when you are using large-ish injectors.

I am currently running a 055 maf and 560 cc evo injectors and stock chip.
I have got my high settings set right around -33% or so.

Because of this the computer isn't seeing anywhere near to the correct info and is using the wrong map all the time, this leads to far too much timing high in the rev-range and this in turn leads to knock .

I have sent an email or 2 out to the guys here who apparently write chips but haven't receieved any reply.
I guess I will just have to get one from Keydiver.

 

[NZVR4]

thanx man, even though its auto ???
that helps i wont be goin over 15 anyway....itll be 13-14psi...just under a 1 bar

i didnt realise it was an auto,maybe the boost cut will be a tad lower with the td04 but im pretty sure the fueling for an auto is the same as a manual vr4 so it shouldnt be a problem but im not sure how different an auto factory computer is compared to a manual in relation to the boost/fuel cut

 

[JAP63]

The only flaw with using only your safc to compensate for injectors comes into play when you are using large-ish injectors.

I am currently running a 055 maf and 560 cc evo injectors and stock chip.
I have got my high settings set right around -33% or so.

Because of this the computer isn't seeing anywhere near to the correct info and is using the wrong map all the time, this leads to far too much timing high in the rev-range and this in turn leads to knock .

I have sent an email or 2 out to the guys here who apparently write chips but haven't receieved any reply.
I guess I will just have to get one from Keydiver.

It adds timing up top because it thinks its not getting as much air?
that what you mean?

What sort of fuel figures should i be at for 510's?

 

[brisvr4]

It does add timing up top because it isn't seeing as much airflow and thinks it isn't under as much load as it is.

Well the 510's are around 13% larger than the 450's so you should be running at around -13% or so.
I would set your high settings at -8% and gradually lean it out till you see knock and then back it off a touch

 

[CLuTZ]

thanx man, even though its auto ???
that helps i wont be goin over 15 anyway....itll be 13-14psi...just under a 1 bar

what about leaving it auto n putting a bigger turbo in it? like would that destroy the gearbox or would i have to do sumthing to it?? n what would be a good turbo for a auto like sumthing not to big sumthing that would put out about 15~18psi n what would be an approx cost of it?

and thanx for all the info guys its a big help

ok, think of it this way, here's how long our auto e39a lasted when we upped the boost:

12psi = 3 months
14psi = 2 months
18psi = 17 days.

Each time it was a freshy rebuilt gearbox with $2k of parts thrown into it.

That was on the td04, a td05 would rip the auto apart without even batting an eyelid, keep in mind that the auto gearbox in your car is from a non-turbo galant, mitsu never strengthened it to cope, so even running factory boost, it's right on the edge.

 

[JAP63]

SHIT!!!

 

[Evil_Mx6]

what about leaving it auto n putting a bigger turbo in it? like would that destroy the gearbox or would i have to do sumthing to it?? n what would be a good turbo for a auto like sumthing not to big sumthing that would put out about 15~18psi n what would be an approx cost of it?

and thanx for all the info guys its a big help

ok, think of it this way, here's how long our auto e39a lasted when we upped the boost:

12psi = 3 months
14psi = 2 months
18psi = 17 days.

Each time it was a freshy rebuilt gearbox with $2k of parts thrown into it.

That was on the td04, a td05 would rip the auto apart without even batting an eyelid, keep in mind that the auto gearbox in your car is from a non-turbo galant, mitsu never strengthened it to cope, so even running factory boost, it's right on the edge.

[/quote]

well currently the car is runnin 10psi and seems to be fine, i find it really hard to see that the auto will blow with more boost, obviosly u have to take into account the drivin style....most of the time my drivin only goes up to 5psi-7psi....its only for those special occasions i would like to feel the car boogy

i already have a larger cooler installed so that would of given me more power and wit more boost im guessin the car should be about 180-190 flywheel kw's ???
surely the auto should be good for up to 200 flwheel kw's...

cheers guys
i really appreciate your help on this topic, since the last thing i want to do is blow the auto....with 5 months left till the weddin its the last thing i need!!!!

for curiousitys sake how much would a manual conversion from auto cost ???

 

[VR-4-PLAY]

if ur interested in makin the auto box a bit stronger PM Rockabilly on Galantvr4.org.au , he has been through all this and has it sussed :wink:

 

[Entaran]

You can pm him here too.