EFI University

[jspeeduk]

Hi guys,

I've been tuning a number of Evo, STI and Honda Vtec turbo and realised 80% of the time was spent troubleshooting. Wasting Dyno Time on issues that should have been sorted before tuning. Mechanical issues would then become a tuner's issue and i need to learn as much mechanically to help solve these issues quickly.

My experience from tuning at least 200 occassions in the last few years as a free lance tuner has been centered around Honda Vtec drag race engines, NA to Methanol engines. I am confident to say that i'm quite a seasoned tuner for NA engines, ITB, i can get compensation maps, AFR, Timing maps to almost ideal even on knock limited engines etc.

But i've got issues tuning boosted engines. Maybe the few higher HP that i worked on had mechanical issues to start with, or i am just unlucky, but i sometimes wonder if i've missed out some techniques that the top tuners use.

Example: 1

Subaru STI with Mahle pistons, forged rods. GT35R turbo, FMIC with 1200cc injectors. Vipec PNP ecu. I'm using Vipec Knock Amlifier to listen to knock, Innovate LC1 hooked up to Dynapack.

Full boost kicks in between 4800rpm to 5500rpm. Possibly between this 700rpm boost would build from around 0.5bar to 1.8bar. With this 'ramp up' igniton timing around 15degrees i can hear the occassional knock, maybe 3 audible knocks and once its settled on 1.8bar from 5500rpm it goes all the way to 8000rpm with no audible knock, also 15degree timing.

If i take out all knock, say around 13degree or 12degree while boost is building, i will lose 30 to 40hp easily between 4800rpm to 5500rpm.

QUestion: How much knock can i push it for? THat 50hp would make a huge difference in driving.

Now, next big question: THe car was tuned on a dynapack. After tuning, itook it out for a drive and had 4 guys in the car. I will only see 1.3bar max boost from 1st to 3rd gear. Only hitting 1.8bar on 4th. The road load on the engine meant the way the boost build up was different and i heard slight knock during boost up, so i had to reduce timing by about 2degrees but i could imagine how much power loss that would have meant! I tune the engine to 11.4AFR with no audible knock all the way.

Now, after 2weeks, the engine builder is reporting white smoke coming out of the catch can. Have i toasted the piston rings? Melted something? I really dont know how much 'safer' tune i could do for this engine. No knocks, good safe AFR. Whats missing??

Example 2:

When you put the car on the dyno, after warming up the first power pull might show 480hp. Make another pull and power would go maybe 530hp. Keeping the water temp constant, the next pull would most certainly show 480 to 490hp! IAT and ECT constant! So the other variable might be the exhaust temp? I mean, how do you guys make your pulls and ensuring the results are conclusive?

I am almost terrified of tuning these STI engines now. Despite how careful my approach with the tune, it would still melt pistons or fail. What have i missed?

[StantonWarrior]

What fuel are you using?

Is 11.4 afr giving best power whilst helping with knock, or is this a figure you use as a general rule?No detonation is acceptable really, so whether you hear just a few rattles then it settles or not, your doing thr right thing by pulling back timing to resolve it.
Cam timing in my experience will hugely affect detonation, especially on tip-in transient conditions. So maybe double check or alter this.
Do a leak down test to confirm cylinder/piston condition if there are any doubts.
For the road showing more det than the dyno, are the IAT's the same between both. It is always possible to over-cool on a dyno as it is under cool....

As for inconsistencies in initial dyno readings, font forget, that although engine may be up to temp transmission and diff oils won't be til you've done a few runs.

[MrDomino]

STI engines aren't that durable. One guy brought his bone stock STI to an autocross and blew the ring lands while the car was in the staging area. I'm guessing the pistons are probably toast. Maybe the engine was running really lean for some reason.
_________________
I am a Mechanical Engineer.

[stevieturbo]

Ive tuned plenty of them and never destroyed a piston yet through bad tuning.

Obviously you cant expect miracles if using standard cast pistons, but even then, they are pretty strong. I cant even recall seeing one fail on anything Ive tuned.

Standard engines tend to fail pistons because dummies try and run the wrong fuel, do DIY bodge tuning and generally do silly things.
But the pistons are not the problem

You can get odd tinkles of knock during gearchanges and boost rising back up, and need to reduce timing in some strange places to resolve it.
The exact cause could be triggering or ecu related, or just tuning. But if it's knocking, not much else you can do other than pull timing. Doesnt matter if it will make more power with more timing if it's going to blow up lol.
You'll either need better fuel, lower CR etc etc.

But there is certainly nothing fragile about them if built and tuned properly. The only issue they do have, is the big ends. Seems to be little Rhyme or reason as to why they go. Although often poor maintenance or owner abuse are key factors.

If you're only doing mapping, is the rest of the engine/fuel system even capable of safely supporting the power they expect ?
_________________
LS1, V7 YSi

9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0

[jspeeduk]

Fuel system is capable. 2x Bosch 044 pumps with Bosch 1200cc injectors.

As the car was boosting, the catch can does see oil being collected after every run. How much is normal?

[StantonWarrior]

There's no definitive answer to that, all engines pass a bit of oil.

A leak down test or better still a blow by test on a dyno, will show how healthy she is.

[stevieturbo]

Depends on your breather setup, how it is plumbed etc. And of course bore/piston/ring condition

But if you're just talking a couple of dyno pulls with the vehicle not moving. I wouldnt be impressed if it's chucking oil out that easy.

You could even go so far as to say it would be enough cause for concern to stop tuning.
_________________
LS1, V7 YSi

9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0

[baldur]

Keep in mind that there are two completely different cars sold under the name "Impreza STi".
The euro/jap model which is pretty much bulletproof and for the most part had a 2.0 liter engine.
The USDM model which for the most part had a really weak 2.5 engine, much slower than the 2.0 cars and on stock internals it'll bend rods if you turn the boost up just a little bit, even if it isn't knocking.

[MrDomino]

It was a brand new STI and my friend who works at a Subaru dealer said that the STIs were routinely failing engines due to broken ring lands as a result of the stock tune (really lean to meet emissions). I can't verify the accuracy of that information but I'd be willing to assume it's correct.
_________________
I am a Mechanical Engineer.

[stevieturbo]

Some of the latest 2.5 definitely had some serious issues. A dealer ecu reflash was one of the solutions to that.

But that isnt what the OP is talking about
_________________
LS1, V7 YSi

9.85 @ 144.75mph
202mph standing mile
http://www.youtube.com/watch?v=XgWRCDtiTQ0

[MrDomino]

Yeah sorry I kind of sidetracked things a bit. Thanks for bringing up the dealership reflash info. I'll make sure to let any STI friends know about it.

BACK ON TOPIC
_________________
I am a Mechanical Engineer.

[niterydr]