Did a couple of WOT blasts while data logging this morning, and noticed a few things that surprised me. This is a 7730 $8D speed density setup on a 383 with a SuperRam, LS1 28# injectors, and Holley 52mm TB:

1. I never get to a 100 KPa load setting, never exceeded 95-96. If the throttle blades are opening all the way, does this indicate I need a larger (58mm) throttle body?

2. When you go into PE, I realize the O2 sensor quits adjusting BLM values, but why would I see the TPS reading drop off to zero as well? And in addition to that, the injector DC stopped recording a few records after that. If it makes any difference, this was right at about 100MPH. Anyone ever see this before? FWIW, the speed fuel cutoff is set to 255, and the RPM fuel cut off is set to 6200 RPM, neither one of which was I even close to.

If it makes any difference, I'm using an AXYC base since this is a manual tranny set up (I like the shift light!) in a 91 Formula.

Hope someone can give me some direction or explanation on this....


- Vern

 

Yes a pressure drop after the throttle body indicates a restriction. You can never have too much throttle body when it comes to making horsepower.
I can't help you with number 2.

 

Might want to increase the diameter of your MAP sensor vacuum line or move it closer to the plenum.
Could be getting a pressure drop in the line that is not allowing a full signal output. just a thought.
Number 2 is interesting but don't have any ideas on that.

 

The Air intake tubes prove to be pretty restrictive as well...

As for the other problem, just sound like it lost connection with ecm..

 

1) Never? Not even at low RPMs? What is your altitude? If at say idle, and then floored, you'll see the highest MAP for running, and as the RPMs increase, it'll only go down without a supercharger. Do you have a baro reading displayed - that'll be the max it can ever achieve, and usually won't achieve quite that while running?

You could install a second MAP sensor in front of the TB and datalog it's voltage vs the used one to find out how bad the TB is choking things.

2) Maybe the communications get scrambled at high RPMs with ignition noise, or maybe the ECU doesn't have enough time to communicate and concentrates on fuel injection and ignition (in other words, I have no clue).

 

To get max Map kpa, Just turn on key and see what it is..
For that given time that will be the max you will see.

 

That loosing communications problem could just be a loose connection between the aldl and computer.

I used the pressure drop testing years ago to see if the TBI was air flow limited or fuel flow limited. All that I cam to conclude was that the 2" TBI (50.8mm) was only dropping 4-5 kpa from atmosphere so it wasn't airflow limited. That was on a ~330hp vortec crate motor.
Here's something interesting about the TPI throttle body size, did you know the Ramjet 502 BBC makes 502hp with a stock sized L98 TB. I wonder if anybody has upgraded the TB size and seen measurable results.
Honestly, I wouldn't worry about it too much. If it's a regularly driven vehicle then don't bother, if it's going to see the drag strip then you might want to try out a larger TBI to see if it makes a difference in the trap speed.

 

Is the TPS working 100%,
- turn on ignition
- check outgoing voltage on tps as you turn it by hand to WOT.

/N.

 

Thanks for all the replies and ideas!

I'll verify my TPS voltages, and connector fitting tightly. I'll also check the reading with just the key on via the data log, as well as try to see if I can hit 100KPa at idle with a quick flooring of the accel.

As far as my altitude being a concern, the Dallas TX area is only about 650 feet above sea level. So I doubt that has any bearing on it....

On my SuperRam, my MAP sensor is mounted on the back of the plenum and only has a 3 or 4 inch long vacuum line that is large enough to fit snugly on the sensor.

However, that still doesn't explain the injector duty cycle dropping out on me. I didn't lose connection to the ALDL/ECM because I was still data logging the RPM, vehicle speed, etc.

Any other ideas?

 

Flooring at idle will probably not yield much, you want to be under load at low rpm flooring it..
As for the duty cycle, it was probably just a glitch - -duty cycle was obviously not "0".
Not sure if it has anything to do with it, but my moates freeware will not log over 6200, well it does but rpm will not raise.. Anyone know anyway to fix that?

 

Not the post I was looking for but it will do.
I lost a lot of my scans when my laptop crashed sometime ago but I do not remember seeing the Z ever get to 100 KPA and I know the B4C has not got that high

https://www.thirdgen.org/techbb2/sho...ghlight=100KPa

We still need to meet up so I can give you the money for the T-shirts, maybe next weekend sometime.
We can hookup EASY to your car and see if it's the scanner.
I would think if the tps sensor went to 0 the car would nose over really bad.

 

Vern, 650 ft is high enough to NOT get 100 kpa in WOT.

At sea level, I can read 102-103 kpa (depending on the Baro for the day) and get 99-100 kpa in WOT. But, for about every 300 ft/100 meters of elevation, I notice a drop of 1 kpa.

Based on your elevation, your kpa should read 100 kpa with the igntion on but engine off and somewhere around 97-98 kpa in WOT.

BTW, I have never seen a perfect match between key on/engine off and WOT. There is usually at least a 1 kpa difference. But the bigger the difference, the bigger there is a restriction in the intake.

 

And simple fluid dynamics says that the air wouldn't even flow if there wasn't at least a slight pressure drop! There's a balance of throttle response/drivability (to much torque change with slight change of throttle - and trying to get it fueled correctly) and WOT performance.

 

Just to second that, My car has never recorded more than 96 KPA at low RPM and 93 when into the revs.
Though I think my 58 is still a little to small yet.

 

What was your baro with those readings?

 

I don't know off hand - but I live at 1800 ft altitude.. Baro is usually high 28's low 29's. Don't get me wrong, there have been really good days 31+ but I don't know that I have ever scanned during them or mostly even cared about KPA @ WOT during those times. Honestly It really does not matter to me - especially because I am not ready to splurge a horrible amount of money for a Mono Blade.
But I am thinking about knife edging my SHAFT and blades.

 

WOT MAP K/Pa, is only part of the picture. It's cylinder filling that makes HP (in reguards to airflow). Tuning to get baro in the plenum, is like tuning to a *spec* AFR. There's no universally perfect WOT AFR, as well as no universally perfect WOT MAP K/Pa to Baro relationship, as far as I've seen.

 

All else being equal a higher plenum pressure will result in more cylinder filling. With that being a truth then the closer you are to baro the more horsepower you'll make. Obviously this is for n/a engines but higher pressure in a system will always result in a higher specific output. Boosted applications (negating everything outside of the intake sub system) also benifits from higher pressure, it's why more psi generally = more torque, again, temperature being equal and what not.
Obviously in the real world nothing is free and so the system is rather complex depending on how accurate you want to be.
The simple fact is this; n/a engines at higher altitudes have less pressure and are down on horsepower compared to sea-level engines.
I'm trying to think of one instance where having a higher plenum pressure would hurt an engines specific output. Pressure isn't velocity so you couldn't say the intake manifold air flow distribution would be better... so where would a lower WOT Kpa actually help? I'm curious.

 

Hmmm... nice technical discussion gents! But you're starting to lose me. I understand the cylinder filling being the real critical factor, and it seems some vacuum remaining indicates that is happening (or possible). In fact, taking that thought to the next level (at least in my feeble senior mind), makes me think if you really have 100KPa readings in the plenum, then the cylinder is not filling any more. Now whether that says the intake valve is closed, or the cylinder is full, I don't know that we can tell. Does this make sense at all?

I still haven't figured out why the TPS and duty cycle readings went to zero while everything else was still reporting though...

WIll do the MAP testing probably tomorrow evening that was recommended in earlier posts and report back my findings...

Apreciate all the replies on this!!!


- Vern

 

If the engine is not properly tuned for the higher MAP value you could end up with less HP. In the good old days of carbs, I had a motorcycle that I purchased from a city with a high altitude. When I drove it back to sea level (where I lived), the bike had to be rejetted before it would run right. It was running too lean and needed to be richened up before it would perform correctly.

 

Yeah, but that's poor tuning, not where a higher MAP would result in less horsepower or "cylinder filling".

 

IF properly tuned, more air will ALWAYS result in more power.

I was just answering your question of "an instance where a higher MAP value would result in less HP"; so I gave one.

 

My choice of words comes from my engineering dictionary, what can I say.

 

I prefer Websters.

 

Well, here's an update for ya. Got to messing around with it last night, and decided to check my TPS voltages (my previous datalog never got over about 88-90% TPS). Voltage only went to a little under 4V. Could not adjust the TPS sensor any more to get it higher, though the Holley 52mm throttle body blades appeared to be wide open (horizontal/flat).

Since I had an almost new 58mm BBK TB on the shelf, I put in on using the same TPS sensor. With idle set at .62v, it's reading over 4.6v at WOT. ECM now reports 100% TPS readings, too. Did a couple of short WOT blasts from a low RPM cruise this morning on the way to work and got MAP readings of 99KPa during both runs. So it looks like the MAP question has been resolved.

Now I've "just" got to go back to my VE tables again due to the 52 to 58 TB change.....

Still don't understand the glitch with the TPS and DC readings, but will have to wait and see if I can reproduce them I guess.

Again, Thanks for all the replies!!!