Seems like Rev limiter @ 3000 RPM

[KevinsZ28]

I am at a Local Dyno shop and me car (94 Z28 LT1) with fast seems to be hitting a brick wall. We have it tuned up till 3000 RMP and then the car seems to hit what best can be described as a Rev Limiter. We are tunning it in open loop mode, would this be some kind of safety feature and we have to be in closed loop over 3000 rpm???? and suggestions would be appricaiated.

Kevin

 

[bobc455]

Are you unable to exceed 3000 RPM or are you just losing power above 3000 RPM?

-Bob Cunningham

 

[KevinsZ28]

Sorry it took so long to respond, I just got back in town last night. We did figure out the problem. The guy was Tuning my car in Open loop and using the Dyno A/F Ratio info to know which way we needed to make adjustments in FAST. What had happened, was we checked the Target A/F Ratio Table and above 3000 rom everything was set to 0, so that was the problem... the funny thing is why in the world would the Computer me looking at the Target A/F Tables when it was set in Open loop mode????

 

[bobc455]

Why wouldn't it look at the A/F tables? That's how it calculates injector PW, and if you tell it to put in no fuel (or infinite fuel) then it might try to do that.

All that "open loop" or "closed loop" do is make fine-tune adjustments (based on the O2 sensor) to bring the actual A/F reading a bit closer to setpoint.

-Bob Cunningham

 

[KevinsZ28]

I guess I assumed that if it was in Open loop mode, it would not be looking for readings off the O-2 Sensor, therefore it wouldn't need to look at the Target A/F Ratio Table.
Another Question I have, is how do you get the Volumetric Efficiency cells above 150 in the Volumetric Efficiency VS RPM and MAP tables. I am only running 4 pounds of boost, and we are at 139 in the Cells at 158 MAP. I plan on running 15 pounds of boost and it seems I will be way over 150. Thanks for your help.
Kevin

 

[Craig Smith]

In speed/density mode the target a/f table is always used. It's part of the equation for the speed/density calculation. The purpose of the VE table is to make it so that your actual a/f ratio is the same as the target a/f ratio. Closed loop mode just makes it so that it corrects automatically if the a/f ratio is off.

If you are getting that high in the VE table it sounds like either your injector flow rate setting is too low or you have no boost reference to the fuel pressure regulator. They can't be set to over 150.

 

[KevinsZ28]

Thanks for the reply Craig. I am using 72# injectors and I do have the Fuel Pressure Regulator plumbed to the Intake Manifold. I don't know what else I could do to change the Injector flow rate.

The thing that really bothers/disappoints me is that when we ran my car N/A it only made 220 RWH and the new CNC LT4 heads flow 300 cfm @ .600 lift, the Intake manifold was CNC ported, the Block us bored .030 over, 3.875" stroke, all good quality parts and everything has been carefully picked out and matched to make some good HP numbers, and all I have is less HP than a stock LT1 motor. Is there a way I could E-mail you my program and have you look at it, something has got to be wrong. I entered all the head flow data, cam specs, header size, etc. into Desktop Dyno and it says I should be running 530HP to the crank. Changed my plugs and did compression checks last night (all cylinders above 150 psi). I have no idea what could be wrong.
Kevin

 

[KevinsZ28]

...and at 4 pds of boost it made 401 HP and 380 ft/lbs of torque, whichs seems backwards to me... every dyno sheet I have seen with a blown car makes more torque than HP.

 

[bobc455]

Send me a copy of your .gct if you'd like...

-Bob Cunningham

 

[KevinsZ28]

I emailed you a file, thanks for your help.

Kevin

 

[Chuck Leeper]

Sumpin wong!

At a map of 158, the boost is 8.2 psi, not 4.
What kind of MAP sensor are you using??

 

[KevinsZ28]

I am using (at least I think I am) a 2 Bar MAP Sensor. I set it up in FAST as a 2 Bar, and the MAP is reading about 86 without the car running. I am at an elevation of 4800 feet above sea level, so that is why it is low, I think.

 

[Chuck Leeper]

MAP??

I would make sure of the sensor value. Your post said you were going to run 15# of boost. If that's the case, you must change to a 3 bar sensor...
Do a search as there was a considerable amt of MAP discussions/ effects at altitude here recently.
Could be some good info there that would help.

 

[Craig Smith]

At 15 psi of boost, especially at high altitude, wouldn't a 2 bar sensor be fine?

 

[KevinsZ28]

Re: Sumpin wong!

Originally posted by Chuck Leeper
At a map of 158, the boost is 8.2 psi, not 4.
What kind of MAP sensor are you using??

So do you think I have something wrong with my MAP Sensor??? What kind of Formula is there to figure out boost based on MAP readings???

 

[Chuck Leeper]

Originally posted by Craig Smith
At 15 psi of boost, especially at high altitude, wouldn't a 2 bar sensor be fine?

I guess so, as long as you didn't ever feel the need to turn up the wick a bit, or come down off the mountain a tad!!!

I think there was a comment that the sensor was not known for sure.. 1 bar??
As for the bar values, here's what I've got.
KPA psi Boost[net psi]
79 11.5 vac.
99 14.7 zero boost
119 17.25 2.5
138 20.0 5.3
177 25.7 11
197 28.6 13.9
216 31.3 16.6
236 34.2 19.5
256 37.1 22.4
275 39.9 25.2
295 42.8 28.1
314 45.5 30.8

HTH,

 

[Rickerbucks]

Yeah, your NA numbers are not right Kevin. I don't know the answer though to the poor result. If the AFR is fine, then probably take out timing.

You have a VERY similar set up to me, and I saw 335 rwhp running NA.

I have a 2 bar MAP and I see about 13 #'s of boost at most on my worked AFR 190 heads and 383 motor. My base MAP reading are about 55 and I'm at sea level and my peak MAP reading are about 190 (going from memory) My base retard is 37 degrees and my WOT is 26 degrees although that MAY be a little high. I need to get to a dyno to finish up on WOT tuning.

 

[Rickerbucks]

Originally posted by KevinsZ28
and we are at 139 in the Cells at 158 MAP. I plan on running 15 pounds of boost and it seems I will be way over 150. Thanks for your help.
Kevin

Are you saying that at the 158 MAP cell you have a number in there that says "139" I would suggest that must be resulting in a way rich condition. What is your AFR at WOT?

My number in that cell is about 82 - 85. At WOT my cell is about 90 - 92

 

[Rickerbucks]

Originally posted by KevinsZ28
I guess I assumed that if it was in Open loop mode, it would not be looking for readings off the O-2 Sensor, therefore it wouldn't need to look at the Target A/F Ratio Table.
Another Question I have, is how do you get the Volumetric Efficiency cells above 150 in the Volumetric Efficiency VS RPM and MAP tables. I am only running 4 pounds of boost, and we are at 139 in the Cells at 158 MAP. I plan on running 15 pounds of boost and it seems I will be way over 150. Thanks for your help.
Kevin

Yeah, something is not right here Kevin.

It seems to me that you are suggesting that the dyno AFR is running lean and you are trying to rishen it up and are having to go to 139 - 150 in the VE tables then the problem is not the tune but a hardware issue. Either you have an injector (s) not working OR a spark problem.

Candidly I had tons of problems getting started and i cannot remember what solution fixed what problem.

Get a noid light and make sure all injectors are firing. I had this problem, the WB sensor said I was running lean but the tune was super rich. After about 20 hours of investigation, I found my problem was that I had not properly connected the harness to the ECU box. What a dumbass. Two injectors were not pulsing as a result, meantime the other six had gobs of fuel.