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Applying throttle, roll-in, mash-it....results.

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SHOgoFast

Hard-core CEG'er
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Just curious how other's boosted cars respond to different methods of throttle application.

For example, if I am in 4th, rolling at say 45ish and I mash it, it get a decent amount of stumbleing before it pulls out smooth.

Same situation and if I roll slowly to the floor it is much less pronounced but still not buttery smooth.

The lower gears have the same scenario, but given that the RPMs climb so damn fast at anything below 4th it clears any hic-ups really fast.

I guess I am curious if additional tuning can smooth any of this out or if that will continue to be 'the nature of the beast'.

Also, in any gear my car seems to hate tip-in. It just does not like that first few degrees of open throttle. Probably because of the massive MAF?
 
i have a 75mm MAF and mine seems to have the same problems (not boosted)

i am only posting to say i have those problems with a big MAF. oddly, the bigger TB seemed to help it some. it's not tuned, i think more timing on the bottom end will help your issue. or a little more boost instead. lol.
 
SHOgoFast said:
Just curious how other's boosted cars respond to different methods of throttle application.

For example, if I am in 4th, rolling at say 45ish and I mash it, it get a decent amount of stumbleing before it pulls out smooth.

Same situation and if I roll slowly to the floor it is much less pronounced but still not buttery smooth.

The lower gears have the same scenario, but given that the RPMs climb so damn fast at anything below 4th it clears any hic-ups really fast.

I guess I am curious if additional tuning can smooth any of this out or if that will continue to be 'the nature of the beast'.

Also, in any gear my car seems to hate tip-in. It just does not like that first few degrees of open throttle. Probably because of the massive MAF?
Click to expand...

You're sure you don't have a plug / wire / ignition issue? My 3 liter did the same thing, it would stumble in lower RPM's on tip in, I thought it was a tune thing (granted not boosted)

I changed out the TPS incase it was that... it helped for a quick second. The plugs were good, connections solid, I checked just about everything.

I was going to check the plugs again after it had started doing it pretty frequently and I pulled a plug wire up.... the wire (not the boot or shielding) was coming out, I unraveled the whole damn thing just about. Once I replaced that one wire all was good again.

I don't think you should ever just 'settle' and live with it as it is. To many people on here say things like "ahh yeah, it dies when I come to a stop after thrashing on it so I just brake with my Ebrake and keep pumping the gas" - stupid :censored::censored::censored::censored: like that = LAME.

Check your plugs, wires, etc. then work on the tune, anything can be fixed.

IIRC Livin was stumbling because he was either running out of injector or because he was blowing out spark.
 
Good to know that it is not 'normal'. My plug wire are not very old, but they are just off-the-shelf from NAPA. I know the plugs to be good and at 5 psi I am pretty sure the spark is not being blown out.

When I get into the gas it stumbles between 1 and 3 times before it races to redline. It's not really a pause like the turbo is spooling but the motor actually sounds like it misses before ramping up. It very well could be timing....my last 3L had a VERY sensitive knock sensor and would pull timing under even the mildest load situations.

Also, this tune was done on my small water to air intercooler. Do you think the additional length in the intake track would be a culprit?
 
BAD SVT said:
not likely. i've seen longer ones. howz urs routed?
Click to expand...

When Warmonger orginally tuned my 3L I had the ADC water to air intercooler so the intake was really short, from the top of the turbo to the intercooler that was directly above it into the TB, less than 1.5 feet of length.

Now, with the FMIC installed the distance from turbo outlet to TB is greatly increased. That increase in distance is what I am wondering about. Can\would the tune perfected on a short intake path have effects in performance when the path is lengthened so much?

Basically, there is a much larger volume of metered air in the intake track (after the MAF, before the TB) with the FMIC vs the water-to-air. Is there a tuning adjustment necessary to account for that?
 
SHOgoFast said:
When Warmonger orginally tuned my 3L I had the ADC water to air intercooler so the intake was really short, from the top of the turbo to the intercooler that was directly above it into the TB, less than 1.5 feet of length.

Now, with the FMIC installed the distance from turbo outlet to TB is greatly increased. That increase in distance is what I am wondering about. Can\would the tune perfected on a short intake path have effects in performance when the path is lengthened so much?

Basically, there is a much larger volume of metered air in the intake track (after the MAF, before the TB) with the FMIC vs the water-to-air. Is there a tuning adjustment necessary to account for that?
Click to expand...

good question. but remote mounts(different) also have quite a bit of distance to the TB. havnt heard of them stumbling due to intake length. if this "problem" started after u installed the fmic, then u're probably right. i dont also think theres a tune to account for that, i could be wrong tho. did u ask joey?
 
SHOgoFast said:
Good to know that it is not 'normal'. My plug wire are not very old, but they are just off-the-shelf from NAPA. I know the plugs to be good and at 5 psi I am pretty sure the spark is not being blown out.

When I get into the gas it stumbles between 1 and 3 times before it races to redline. It's not really a pause like the turbo is spooling but the motor actually sounds like it misses before ramping up. It very well could be timing....my last 3L had a VERY sensitive knock sensor and would pull timing under even the mildest load situations.

Also, this tune was done on my small water to air intercooler. Do you think the additional length in the intake track would be a culprit?
Click to expand...

Brand new plugs wires have been known to be 'bad'. Its hit or miss, without a doubt. Read some old threads about stumbling, there were a few posts from fornetti I remember in particular; he bought new plug wires 2 or 3 times and the only set that ended up working worth a damn he grabbed from a junk yard. Try the free stuff first obviously but there is no point tuning it if its a 'hardware' problem... Know what im saying?
 
Yea I dunno about some of the Napa wires. They appear just ok to me. I think as I've always stated the Autolite wires seem to work well. They are the best set I've had.
 
I will see what a set of wires does for me.

I also have this question into Joey via PM.

Thanks for the comments.
 
SHOgoFast said:
Also, in any gear my car seems to hate tip-in. It just does not like that first few degrees of open throttle. Probably because of the massive MAF?
Click to expand...

I blame the big MAF for poor acceleration from a stop, but I don't have any trouble with tip in when I'm rolling. :shrug:
 
SHOgoFast said:
Basically, there is a much larger volume of metered air in the intake track (after the MAF, before the TB) with the FMIC vs the water-to-air. Is there a tuning adjustment necessary to account for that?
Click to expand...

You can calculate the resultant pressure drop, but it shouldn't impact the tuning. It just means the turbo must work harder to feed your engine.
 
There is a tune setting for throttle tip in that will cause a hesitation if not set correctly. I believe the ECU uses a base table for air/fuel for a set amount of time before switching over to the MAF readings. If you cut the time down the hesitation should go away. Of course there are other items that could also cause the hesitation but in my case it was the tune.
 
I've driven a couple of boosted SVTs, I found that on a dead stock SVT motor running Joey's turbo kit; when you mash the gas pedal and slam the gears the motor bogs down a little bit, but if you are a little more relaxed and roll into the gas pedal the amount of power is just CRAZY that you get out of the little 2.5L motor.

in fact, I feel like a stock SVT drives better if you roll into the gas pedal, rather than mashing it.
 
the problem you described sounds like what my car did when I first started to work on the acceleration enrichment. In my case I was getting a stumble from going too rich because my AE was too high. Now that it is tuned out, stepping on the loud pedal lets the smoke out of the tires.

My car/engine/computer are all different, but a stumble on tip-in can potentially be in the tune in the form of either too much or too little accel. enrichment. If it were spark blow-out you would be seeing it in boost not during the initial transition from steady state to accelerating.
 
mine is nice and smooth. mash the pedal on the highway and it just takes the time for the turbo to spool to get going.

I have noticed what feels like a slight miss or stumbling between 2 and 3k rpm but I noticed that before the turbo. so I think it is just due to the ported 3L heads.
 
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