Jump to content


Sign in to follow this  
senna_T

Overboost

Recommended Posts

OK - This is my opinion based on my experience with turbo cars, feel free to discuss, disagree or deny!

Alot of people get warned off buying and fitting intercooler kits and under battery pipes and plenum for fear of over boost.

On my car personally I have gone from stock cooler to wog style cooler, wog style cooler with around battery pipe, to full air intake and 3" piping to the throttle body. Not once did any of these changes create over boost at any time and any rpm!

I have experienced over boost once - after I got rid of the cat...

I beleive any intake mods available for our cars will not cause overboost while running a standard cat in a std exhaust - even with a bigger cat back system.

Even when I went to my current cooler and piping setup (similar to RAPIDs gear) and still no cat the boost stayed bsaically the same (1psi difference in fact) and my AFR's did not change at all. This is even without the UBP boost sensor hooked up! (I don't have a UBP anymore)

Good proof of this is in exarsixturbo's thread about his 800hp Plazmaman Kit install.

Again, if anyone thinks this is too big a call, please let me know about a time when your car has overboosted in a similar situation.

Cheers,

Pat

Edited by senna_T

Share this post


Link to post
Share on other sites

yeh I take it you are meaning when you have the car edited, all you have said you done will over boost stock, without edit, once edited, the main over boost is not the main isue, it is leanout, from not having big enough injectors, or the fuel pump not keeping up, so it is a gamble if you did not check it. but if your fuel pump is up to the job, and your injectors are big enough, and the tune was suited your car well before, well most intake mods will be ok, (this does not mean you would not check them though.

the other thing that can happen to the 4 speed auto is the extra power can slip the clutches,

so there is a bit you have to look out for, that can cost a lot more then getting a custom tune to suit.

David

Share this post


Link to post
Share on other sites

no, stock tune with a cooler and UBP - no overboost. exarsixturbo's car is running stock tune also - no overboost, and AFR's within factory margins

Share this post


Link to post
Share on other sites

Sorry Dave, I didn't really understand that first part.

My car was stock. On the weekend I changed the cooler, ALL the piping and the plenum. To be honest I didn't know what it would do. I’m running the standard cat and exhaust (minus the mufflers) and NO EDIT WHAT SO EVER.

I put it on the dyno to make sure it wasn't over boosting or leaning out. It did neither.

The boost stayed at exactly 5psi the entire rev range and the AFR's were a little all over the place, but stayed in the 13-11 range.

When I get a custom tune I will be putting valve springs and injectors in there too, and a custom exhaust and cat will follow along with another tune.

I'm with Pat. I have seen lots of intake upgrades not change anything, but as soon as a big cat goes on there, that is what stuffs them up. But again, feel free to tear that apart because I am certainly not an expert in this field.

Share this post


Link to post
Share on other sites

Agree with Pat to, I cant see how fitting a cooler or intake can really change anything, makes it more free flowing but the car still has factory parameters in the tune which back boost off if it does creep to high. I had PWR Cooler cat back exhaust, changed intake pipes and nothing at all, doesnt over boost wats so ever. even if I loaded up hard in 5th on a cold night I might have seen 4.5psi for bout 2 secs then it dropped back to 4psi that seriosusly wont do anything. there has to be some tolerance in the factory tune as I seen this in my previous auto dead stock and the auto loaded up seen 5psi.

Cause the boost is still standard controlled to back off once it goes past the tolerance set by the factory tune then how can it over boost. Once an edit is placed on the car ive seen 12psi when I load it up in 3rd on a cold night but even then it drops back to 10psi in a matter of second and the car has had more fuel put in up top to combat this.

Share this post


Link to post
Share on other sites

Interesting guys...

So a cooler at the larger end of the spectrum such as RAPIDS would work out all ok? - with factory tune?

What about the battery relocation aswell with a cai under the right wheel arch?

Share this post


Link to post
Share on other sites

Simple

You all are putting on larger inlet gear . The engine can breath on the inlet side ....

But the exhaust side has not been opened to suit . Car is chokeing on the exhaust side . Efficiency is down . Air can come in freely , but cant exit as efficiently .

One of our company vehicles runs purely a bolt on 800 hp kit , std exhaust and everything else stock OEM . Picked up aprox 20 - 25 odd Kws on std boost due to cooler and air intake swap . Tune can be tidyed up a bit on the fuel side , but safe to drive . It has although hit boost cut once or twice , this was on real cold nights when ambient air density was up .

As soon as a turbo back exhaust goes on , no way in the world can you stop overboost without a tune and wastegate mod .

But saying all that - Plazmaman highly recommends that all vehicles fitted with our competition gear be tuned by a reputable tuner so that you DONT grenade your engines .

exarsixturbo , interestingly how much power did you vehicle pick up over std ??

Share this post


Link to post
Share on other sites

I am in total agreeance with plazmaman on this subject. Having made my own hot and cold side pipework and a straight through system dump pipe back, I agree it is hard to stop overboost. I picked up 4 pound on each map.

Share this post


Link to post
Share on other sites

Yeah Plaz is right there.

Another thing that's happening is the turbo no longer has to spool up the extra 6 or so psi to over come the factory piping/IC's restrictions.. so the turbo is working less and thus producing less heat.

But, free up the exhaust side with a bigger dump,cat, pipes ect and the turbo is able to spool alot easier due to the increased airflow and reduction of back pressure on the exhaust turbine.

There are some combinations that poeple have stumbled across that can work out very well...

Example One- Big IC, Intake and piping, stock dump, Hiflow cat, stock ex system, untouched turbo,wgate... if the accuator is still strong, boost can be held to 12psi to get a healthy low 300wkws without too big of a boost spike- 2ish psi

Example Two- Stock IC, Intake and piping, big dump, cat, full exhaust system... hard to tune a stable 15psi, large spikes ect... the fix, stronger accuator, ported wgate & larger flapper and boost is more stable but power struggles at the top end... valve springs are having issues working under the high pressure now and need upgrading.

Example Three- Big IC, Intake, plenum, full big flowing exhaust... huge lack of restriction resulting in the turbo wanting to spool and hit 18+psi as soon as it can... boost control can be helped to a degree with bigger flapper, ported wgate, but generally wont go less than 15psi with a spike of a few psi.

These are just examples off the top of my head, there's a thousand different combos with varying results, but generally all will have these boost issues.

We are also very lucky that our factory computer can roughly adjust for increased airflow, but this is dependant on the fuel systems supply... so you can fit a bigger IC & intake system to a car that already has bigger injectors fitted and tuned to, and drive it... but dont boot it and boost it up without checking boost levels and AFRs on a dyno.

A good example is Plazmamans XR6T which happily ran around with the 800hp kit and nothing else... dead stock

Share this post


Link to post
Share on other sites

I totally agree

one question thought senna u said it overboosted when u got rid of the cat...

will the car overboost if you gut out the cat?

Share this post


Link to post
Share on other sites

hey I only just caught up on this thread!

Azid Rush, yes it will overboost with a gutted cat, this is the same as deleting it all together

Share this post


Link to post
Share on other sites

on my car I had a plazmaman stage 1 kit with the stock zorst, it ran 211.5 rwkw on the factory tune and having 4.8 psi. cv dyno.

this kit has the underbattery pipe and all the xover removed and replaced with big pipes.

as soon as I started modding the exhaust I found that on the stock tune it would hit 8 psi and cut out.

running my custom tune it hit 18 psi spike. up from 14. after zorst mods.

Share this post


Link to post
Share on other sites

to add more.

I can now, with a high flowed cat and plaz 800 kit , run 14 psi with no spike or fall off but if I add more boost it spikes and falls away to 14 again.

I now need to mod my wgate and actuator to get a solid 15 psi.

Edited by BFHOON

Share this post


Link to post
Share on other sites
what are the fines with gutted cats??

and how are they checked??

the fines for a gutted cat are about 10k, checking them is not easy if the cat is simply gutted epa could tell but your average joe blo policeman would be hard pressed to tell the difference

Share this post


Link to post
Share on other sites

I wouldn't be too sure, you can feel strong smell of petrol. and if mr policeman knows what it means he will call in someone who can tell.

But even though I'm against this mod I have to say that I haven't heard of anyone being caught.

Share this post


Link to post
Share on other sites

Well, in the earlier BA days cars started to develop a problem of boost cutting when accelerating hard. Most people found this out when trying to overtake.

My old ute when 100% stock did this fairly frequently.

When I added a CAI then did it everytime the accelerator was nailed.

Ford revised the PCM calibration and eventually got it right after a few attempts.

It's possible that people who experience this still don't have the latest calibrations.

Share this post


Link to post
Share on other sites

interesting read. heres what I have found.

big cooler relocated fillter to r/h spotlight 3inch pipe from turbo to t/b stock exaust no gutted cat nothing.

and 8psi generic holds 8psi perfect no overboost no other mods. cant see how intake mods would make a diff if any,could someone shed a bit more light on this.

however I can understand exhaust mods creating overboost.

Edited by bda12pleaseu

Share this post


Link to post
Share on other sites

yer I read in a mag if you free the exhaust up to much it pushes straight past the acculator in the waste gate coz there is no bak pressure so you can upgrade the acculator and the flapper spring and have the free flowin exhaust or have a cat with a bit of restriction

Share this post


Link to post
Share on other sites

I am really sorry to bring up an old thread but I have a problem.

I have an FG XR6T ute stock with CAI.

I took the car to a track day on Saturday and experienced the boost cutting in and out. It was quite a hot day.

Could someone explain to me please the 'overboost' and 'boost cut' for me?

I rang Ford and the guy was useless, he just said he didn't know and to ask around.

Share this post


Link to post
Share on other sites

You may find on the track you were experiencing "Fuel Surge". This happens when the fuel sloshes around in the tank and moves away from the fuel pump pick-up. Not as bad onutes as it is on sedans, however with a low fuel level this can happen.

How much fuel did you have in your car when you were at the track?

Share this post


Link to post
Share on other sites

I had about 3/4 of a tank.

It was making the noise like the boost was being blown off and then the power would kick in again.

It was very annoying as I was getting to half way down the straight and it wouldnt go any faster.

Share this post


Link to post
Share on other sites

yeah 1 day I put in normal premium fuel cause the servo didnt have vpower or optimax and as soon as I booted it the engine light came on puttin the engine safe mode with only 5 psi....

so I went to ford and they checked it out and said it was over boost by the computers history ????

so I was like wtf how can it over boost with less octane fuel ?????

but never done it again ......

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Recently Browsing   0 members

    No registered users viewing this page.

  • Donation Box

    Please donate to support the community.
    We appreciate all donations!


FordXR6Turbo.com Powered by Invision Community

×