Before the Shootout recently I thought I may have a problem with overboost despite the AVC-R.

Trundling along in 2nd or 3rd at gentle speeds, say 3000 rpm, then flooring the pedal I got 1.7 - 1.89 bar boost! It's mapped to 1.65 with a bit of a safety margin, but I was concerned I would overboost and do some harm, despite precautionary octane booster!

In actual fact, when spinning the wheels off the line at 6000 rpm start in 1st and quickly shifting into 2nd, 3rd, 4th etc. - I found the AVC-R only registered about 1.47 - 1.53 bar boost. Some where I had lost 0.2 - 0.3 bar boost.
Adjusting settings on the AVC-R made no difference. No leaks were found.

BUT on the return run from the strip if booted from 2500 rpm I got the 1.7 plus bar boost again!


I got some advice at the SSO ( Cheers Simon ) but can anyone explain what was occuring and how I can work around it, to get best boost when dragging?
Actually, tried a fast start ( not spin wheels / 6000 rpm start ) but a foot to floor in first when rolling to red line in 1st, 2nd, 3rd gears ... and same thing happened, reduced peak boost .. and watching boost gauge / tracing boost profile the held boost was also showing at the lower level of around 1.5 bar.

Any explanation welcome, it's confusing me!

Any work around or fix? Apart from new / bigger turbo!


Spec is AFP TD05-20G, Apexi PFC & AVC-R, headers and 2.5" turbo back decat exhaust, FMIC, Forge recirc dump valve, 850 injectors & walbro pump/parallel fuel rails/external FPR, STi IV heads/cams, steel innerds, light flywheel & pullies, etc.

Cheers

Neil

 

bump would like an answer to this aswell

Banny

 

and me, noticed the same today when i went down the strip. made 1.34 bar boost, where on the road it can reach 1.4-1.5 (mapped for 1.5 peek)

 

me too, mapped for 1.5 bar, only makes 1.4 bar peak in gears 1-3 but 1.6 bar peak in 4th when on the 1/4 mile.
I think it has something to do with loading on the turbo, i.e will only make full boost when the engine is under full load.
I would also like to know how to compensate for this on the AVCR and set up 2 settings, one for road and the other for the 1/4 mile. Maybe one of the mappers will come to our rescue.

 

think that is normal to be honest as you are through those gears so quickly the turbo doesnt have enough time to spin up to full pelt

 

Doesn't the AVCR have a setting for a "quick getaway"....is it called "scramble boost" ....or am I having some sort of Radio 2 moment ??

Shaun

 

As above. When you start in a lower rev the turbo has a larger rev range to build up boost and the duty setting will be higher in lower revs, wheras on the strip and through the gears the lowest the revs will fall is probably around 5.5k.
As the duty in higher revs is normally set lower, the peak boost will be also be lower for the remaining 2-2.5k rpm.

 

Also by the time you've finished your 1/4 mile everything is nice and hot (turbo, headers etc) which will improve spool and boost, as opposed to the temps the turbo / headers are at whilst on idle waiting your run.

You should notice this on a drive too, cruise down the motorway so that everything is at operating temp, then nail it and note your max boost. Then nail it 10 times in quick succession and note the max boost on your 11th run - you should see more boost than on the 1st run.

 

The AVC-R also has in gear boost control , a mapper who is informed you use your car for drag racing will set this up for you so that you reach your desired peak in all gears when launching....

 

The problem is simply engine load impedance and engine rev ramp rate, the AVC-R can't work miracles, if the load isn't there with the time for it to react no amount of start duty will equalise boost and ... it requires some optimisation of the boost control pipework to overcome that issue. It also needs the speed and rpm signals to be connected and configured properly, The JDM OE ecu's, new age variety, MY03 on, have built in gear compensation, and mega rom has full boost mapping for all gears with 5th/6th being on a single map. Sti only of course.

Neil if you want some remote help the glad to oblige ... no charge of course (lol). I normally set up one setting for normal road and the second for the drag strip, but it does need some attention to pipework detail.

cheers

bob

 

Evening Bob

Just thought I'd mention my car is running like a dream in the Cumbrian heatwave LOL (mapped by Bob)

Cheers

Shaun

 

Scramble boost is a short increase in allowed boost level for e.g. a quick get away or overtaking manoever, not a magic increase in boost at a given level.

I set my AVCR up to max duty / way too high boost levels on the strip and STILL only got 1. bar! So it's not down to AVCR speed or performance.

 

Makes sense, was what I was seeing.

See the same on strip and on fast 1-2-3-4 run to red line on road, less boost ( now I am looking for it! ) than if just boost it from 3000 rpm in any gar!

 

I was warned of heat soak which may lower boost after queueing or many fast runs, but that's not it in this case as immediately after a run, on return to start leg, booted in 2nd or 3rd from 3000 rpm and got full 1.7+ bar boost. Next run 30 seconds later, back to 1.5 bar ... the lanes were empty and I ran with 1 car wait, or even on my own 2 or 3 times out of a set of 6 conescutive runs over 1/4 hour.

 

Not sure how the in gear boost control works, as the boost & duty are set by rev, and start duty, although gear judge is set up to identify gear/speed, but I can't see where individual gear changes for duty/boost are made.
Learn mode is set off.

 

AVC-R was set up by Andy F when he remapped the PFC for the TD05 20G/850 injectors, Z32 MAf etc. He knows I do the odd drag so sets up the B map aggressively ... with appropriate boost!

 

Usually feel guilty asking other tuners for advice .... but I'll PM you for a bit of advice Bob if you don't mind! ( ROFL )

Neil

 

Building boost needs engine load. Load is best at 4-5th gear. Also, air charge load runs engine richer which again helps spool at the heavier ends of the range.
Hard to hit full boost at 1st and 2nd generally unless really loaded up, eg l-f braking...

 

Looks like we are getting somewhere, might be back to see a mapper and get my AVCR set up for drag racing.

 

I did some of the pipework and AVC-R start duty mods Bob R suggested, a little improvement, but still get the high ( too high in some gears! ) boost if gently trundling along and then floor it from say 3000 rpm - 1.7 odd bar ... but if go to red line in 2nd - 3rd then lower boost - approx 1.5 bar boost.

Does seem like engine load issue ( less load in lower gears ) and time to allow turbo to spin up - remember this is a TD05-20G - with the bigger TD06 ?? compressor wheel ) so may be heavier turbo wheel and so need a slight extra time to get spinning?

The boost flies TOO quickly once at 3000 rpm .. very quick accelleration to next gear .. 12.5 second 1/4 and 118 mph at last shootout ... OK not up with Andy F or Zen , but fast on full boost!

V

 

Could it be boost creep and the turbo needs porting on the wastegate penny?

 

Sounds to me like you need an ECU with really good closed loop in gear boost control like the SimTek.....

 

Sounds to me like you need a banner add!

 

lol.....You paying.....?

 

The TD05/06 20G is about a year old ( new then ), and came with all the porting etc. that was known of then, from AndyF. Yes that included wastegate porting and other stuff IIRC.

The increase in boost over the AVC-R set point is still likely to be boost creep I'll agree, it's the loss of boost when booting it through the gears I am at a loss to explain, as it is there before and after a hard run if start from say 2000 rpm to red line in 2nd, 3rd 4th .. full ( over! ) boost of 1.65 - 1.75 bar!
But going hard through the gears can't break 1.52 bar ... as above comment I feel the turbo is either outside it's efficient spin speed / efficiency area on the compressor map or the time to go from the start revs ( maybe 4.5 - 5k revs on gear shift up ) revs after gear change to red line is too short for turbo to get up and go!

 

silly observation but is it simply you are seeing the boost level at the red line rather than the 'peak boost' which will generally at occur at lower revs...........??

 

Probably not as the AVC-R has a peak hold function like most other EBCs so doesn't require watching during the run....

 

As above Alyn, I do watch the ( psi ) boost gauge and can see it only reach 20psi not 25+ psi when booted but use the AVC-R boost hold max value for the recording of max boost pressure.

 

You may have a peak boost of 1.75bar but that is a peak and not held figure... it is from what you have said peaking at 1.75bar max and tailing off and holding 1.5ish... as the peak is where the peak torque is and lower rpm than you are seeing on the strip you won't see higher than the held 1.5ish on the strip..
which is probably at the top of a 20gs efficency and even if you had it holding high boost rather than just peaking higher you are unlikely to gain much..
It is the nature of the setup and situation...
you aren't losing any boost etc...

Simon

 

Cheers Simon

On the strip or fast runs thru the gears, lower peak boost.

Start from slow speed/revs in a gear and get higher boost peak .. which is held for 2000 revs or so.

Not much tailing off ... whether peaks at 1.5 stays more or less there all run, and on the more sedate start runs with 1.7+ boost, again holds frokm 4000 - over 6000, before tailing off a little.


What I am trying to determine is why a fast thru the gears thrash like a drag run gives lower peak & held boost than starting off at 2000 rpm to red line ... in 3rd, 4th, 5th ( at seperate times ).