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Go Back   REVscene Automotive Forum > Technical Discussion > Advanced Forced Induction & N/A Engine Tuning

Advanced Forced Induction & N/A Engine Tuning This forum is brought to you by Racing Greed in Port Coquitlam.
Supercharger vs Turbocharger vs NA? Hondata vs Megasquirt? 94oct vs 87oct? Through technical discussion, let's find out what will the best option for you...

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Old 10-02-2009, 01:28 AM   #1
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best tuning option? 88 turbo cavalier

let me start by saying I'm a noob to turbo builds and i don't know anything about tuning

so my friend just "finished" his turbo z24 build
he's using a custom burned chip for the stock ecu but It's probably not the best tune in the world seeing as how it is just a base tune (imo)

and the fact that it was sent half way across the country without the tuner actually ever sitting in the car
maybe im too skeptical..the car does indeed run though


the car has a tendency to die after decelerating when coming to a light
not 100% of the time but enough to make it a nuisance

it also does something else
i'll try my bast to describe it
when you're driving the car and you give it gas it can tend to do nothing
a lot like how my car feels when it's almost out of gas
the car bucks and there is no response for a short while
and it does this throughout the rev range
even a tiny bit under WOT

It doesn't run very smooth under deceleration either kind of bucks a bit

according to the wideband it's not leaning out like crazy or something but it defnitely doesn't feel right to me (keep in mind i've never been in a custom turbo car before though)

are these symptoms of a possibly bad tune or something else??
and what would the best solution be?
try to find someone local who can reburn the chip to a more prescise tune?

switch to a piggy back of some sort

or go for something like megasquirt?
I like the idea of megasquirt but have no idea how to tune the thing
what's the learning curve like?
is it possible to get a base map from someone else with a similar setup then get a local tuner to fine tune it?

the setup:
1988 z24 cavalier 2.8v6
- pretty standard 50 trim turbo .63 ar? or whatever from kinetic
- the manifold is basically the two stock logs connected in a y then going to the turbo
- 38mm tial knockoff with a 6 lb spring although the gauge only ever reads a max of 4psi (there is a very tiny hole in the intercooler though where we can feel air escaping)
- hks sqv blow off
- medium sized intercooler
- 2.5'' exhaust and intercooler piping
- STOCK fuel pump
- 28 lb injectors
- custom burned chip
- 2 bar map sensor
- stock clutch that slips under WOT
I think the eventual goal of the car is to get into the 250hp range on stock internals
hopefully something like a low 14 high 13 car.. the thing only weighs about 2800 pounds with all the turbo goodies and the system

the car makes around 125-130 hp stock? my butt dyno tells me it Might be in the 180-200 range now (not very accurate i know)


another question i have is regarding plugs
I've heard it's good for turbo cars to go to a "colder" plug
at what point is this necessary?
is it okay to run the stock plug for now since it's not making a huge amount of power?

tell me If I'm leaving some critical information out here..

If I'm a moron that worries too much about my friend's car go ahead and tell me

any input is appreciated
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Last edited by Johnrb; 10-02-2009 at 10:52 AM.
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Old 10-03-2009, 06:29 AM   #2
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It's very difficult to tell what could be wrong without seeing the car. It does sound like the tune could be off. First things first get rid of the stock spark plugs and get some cheap plain ngk plugs with a heat range of 6 or 7 and gap them to .030 (don't use platinums)
It also sounds like their could be a problem with the 2bar map calibration or the tps adjustment on the throttle body.
You say the car has a wideband, what are the air/fuel ratios during cruising at light load and what are they during full throttle? What boost is the car running?
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Old 10-03-2009, 08:18 AM   #3
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first and foremost,just scrap that POS and just start over with something other than a junkyard cavalier
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Old 10-03-2009, 01:54 PM   #4
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It's very difficult to tell what could be wrong without seeing the car. It does sound like the tune could be off. First things first get rid of the stock spark plugs and get some cheap plain ngk plugs with a heat range of 6 or 7 and gap them to .030 (don't use platinums)
It also sounds like their could be a problem with the 2bar map calibration or the tps adjustment on the throttle body.
You say the car has a wideband, what are the air/fuel ratios during cruising at light load and what are they during full throttle? What boost is the car running?
under light load the afrs are around 14-15
under full throttle it goes down to 10

the car has a 6 pound spring in the wastegate but the gauge is reading 4 psi tops

I'll get my friend (owner of the car) to chime in here
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Old 10-03-2009, 03:14 PM   #5
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Hi im the owner of that POS (blackedoutaudi) thanks for the post whore.

Anywho, yea the car is bogging as johnrb said, it doesnt always go to 10 AFR under WOT but sometimes does.Anywho it seems that under deceleration it boggs kinda like the tranny is lugging but its not. even if the tun is bad could it be that the vacuum lines come lose or the plugs, can the plugs really casue this to happen.It gives me problems in lower rpms, but once i got on the highway, it would be fine, but once i started to decelerate, it starts bogging again,

Any ideas
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Old 10-03-2009, 03:19 PM   #6
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Hi im the owner of that POS (blackedoutaudi) thanks for the post whore.

Anywho, yea the car is bogging as johnrb said, it doesnt always go to 10 AFR under WOT but sometimes does.Anywho it seems that under deceleration it boggs kinda like the tranny is lugging but its not. even if the tun is bad could it be that the vacuum lines come lose or the plugs, can the plugs really casue this to happen.It gives me problems in lower rpms, but once i got on the highway, it would be fine, but once i started to decelerate, it starts bogging again,

Any ideas
the fuccin hole in ur intercooler doesnt help either pal...i suggest u just get someone to weld it
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Old 10-03-2009, 04:56 PM   #7
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10:1 at WOT?

As for the symptoms, it sounds like it could be a possible fuel issue, either not enough going through due to a clogged fuel filter, or too much is going through and it's blowing out the spark on the plugs... especially on one cylinder. It's been years since I worked on a Z24 (brother turbo'ed his '93 many years ago), so I forget what the vacuum system is like on 'em.
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Old 10-03-2009, 06:09 PM   #8
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10:1 at WOT?

As for the symptoms, it sounds like it could be a possible fuel issue, either not enough going through due to a clogged fuel filter, or too much is going through and it's blowing out the spark on the plugs... especially on one cylinder. It's been years since I worked on a Z24 (brother turbo'ed his '93 many years ago), so I forget what the vacuum system is like on 'em.
I've seen the afr dip into the 9s under wot sometimes.but only for a split second

I thought excess fuel would just run through the exhaust so it's better to be a bit rich as opposed to lean

maybe 10 is a little more than a bit though huh

93 eh? i kind of like those series two cavs with the slanted headlights a little more..

and to the audi guy
It's not a POS but to each his own
some people prefer to drive a car that's a little unique as opposed to a
civic or something else a million other people drive
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Old 10-03-2009, 06:49 PM   #9
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first and foremost,just scrap that POS and just start over with something other than a junkyard cavalier
tnx for the infraction
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Old 10-04-2009, 11:21 AM   #10
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I've seen the afr dip into the 9s under wot sometimes.but only for a split second

I thought excess fuel would just run through the exhaust so it's better to be a bit rich as opposed to lean

maybe 10 is a little more than a bit though huh

93 eh? i kind of like those series two cavs with the slanted headlights a little more..

and to the audi guy
It's not a POS but to each his own
some people prefer to drive a car that's a little unique as opposed to a
civic or something else a million other people drive
The car is definately running too rich during wot, and it sounds like the deceleration fuel cut may not be functioning properly. Hard to say though without seeing the car. Give us a call if you want us to check it out for you.
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Old 10-04-2009, 04:23 PM   #11
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The car is definately running too rich during wot, and it sounds like the deceleration fuel cut may not be functioning properly.
What he said. At normal cruising speed, I usually go for an AFR of between 14.5:1 and 15:1, just to keep it safe. At WOT, especially on a turbo'ed car, I aim for around 11.5:1 to 12:1, depending on the throttle position and how much boost is being pushed in a particular spot of the graph. If you have it too rich, you run the risk of pushing too much fuel into the cylinder and blowing out the spark from the plugs.

As for the deceleration, I'm not sure what program/chip you're running but as Muskys SS said, it sounds like the decel fuel cut is incorrectly programed, especially if you're pushing much more fuel into the engine than it's designed to work with.
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Old 10-04-2009, 10:54 PM   #12
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what do you mean, could it be a bad TPS or too hot of plugs, the tune is decent, overs used the same thing but they told me to check those first. What do you guys think?
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Old 10-05-2009, 09:51 AM   #13
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It does sound like the accel and decel settings are both off.

Well, either the settings are off, or as has been said it's possible the tps is either misadjusted, or broken, or noisy, etc.

Generic tunes being horrendously rich under full load like this one is (unfortunately) extremely common. This is a function partially of the "tuner" taking a "one size fits all" approach, and partially do to him being inclined to make a "safe" tune. Unfortunately power drops like a stone as a result. While still not ideal, low-mid 11's is still plenty safe, easier for the plugs to ignite, and will make way more power.

Why these guys set chips up to have afrs in the mid 10's or worse is beyond me...
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Old 10-07-2009, 12:43 AM   #14
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Old 10-30-2009, 11:35 PM   #15
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Okay so this is going to sound like a very noobie question but it doesn't hurt to ask..

Is it possible that a horrible tune would contribute to lowering the lifespan of a timing chain? (or am i just being crazy now because this tune sucks)

I would think a chain should be designed well enough to be able to take the sudden jolts and whatnot but i guess the added power from the turbo doesnt help either..

anyways the chain snapped like last week i think? bent most of the valves..
it had an original 200k on it though
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Old 10-31-2009, 12:38 AM   #16
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In regards to the car dying after decelerating, does this car have an AFM? If so, I hope you are re-routing back into the intake stream as I see you have the HKS SSQV. If you vent to atmosphere, the AFM is going to tell the ECU to use "x" units of fuel to compensate for the "metered air." When it doesn't see this air, it'll stall.
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Old 10-31-2009, 01:05 AM   #17
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It is probably due to the uneven delivery of power, caused by the car constantly dying. I won't say it is directly caused by the tune. It sounds like the engine had underlying problems before you stick things on it.

I hope you guys learn something from the process... good thing parts etc for the car are cheap.

With everything, if you want things to last long, do proper engineering from ground up, ie blueprint, test and verify.. make sure everything is understood and running before you move on to the next step in the bolt on process.

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Is it possible that a horrible tune would contribute to lowering the lifespan of a timing chain? (or am i just being crazy now because this tune sucks)
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