Help getting the car to rev over 6500 rpms

chadtn · Post by **chadtn** » Thu Apr 28, 2005 9:03 am

I've got a 93 5.0L coupe with an A3M ECU. The car has Victor Jr heads, a Victor 5.0 intake, solid roller lifters with good springs and a pretty aggressive cam. I changed the pip filter to 600 and left the half fuel limiters at 8000 and 7500. The car revs up to right at 6500rpms and then hits a wall and dives back down to around 6000.

Does anyone have any ideas about what is going on here?

Thanks!

Chad

kickerscrt · Post by **kickerscrt** » Thu Apr 28, 2005 1:42 pm

did you happen to change the rev limit maximum RPM (no fuel) scalar? I'm sure someone will chime in here with a definite answer...I'm sorta just guessing as I have yet to mess with the rev limiters. Good luck!

chadtn · Post by **chadtn** » Fri Apr 29, 2005 8:07 am

It was already set at 7000 rpms I think...I'll make sure later today. My laptop is still out in the car.

All I did was change the PIP filter to 600...I'm wanting it to turn around 6800-7200, but for right now I'm just trying to get it over 6500.

BTW...I'm getting the 6500 rpms off an Autometer tach..Not the stock one. ; )

Chad

rockin_rick · Post by **rockin_rick** » Fri Apr 29, 2005 11:42 am

While I don't really have a definitive answer, perhaps some of my thoughts will steer you towards a correct answer.

Perhaps your 12Mhz EEC can't go over 6500 RPMs (regardless of allowed PIP and rev limit settings). That's a lot of calculations in a very short time with a slow EEC. There has to be a RPM (and thus window for calculations) limit somewhere. 6500 RPMs = 3250 RPMs per cycle = 54.167 Rev/sec = 18.46ms per cycle.

Perhaps your injectors are maxed out and you are leaning out. What kind of duty cycle are you seeing? What is your A/F at 6500? Your PW's @ 6500 can't be more than 16.61 ms (90% duty cycle) I've heard that the EEC limits the DC to 90% (regardless if a higher duty cycle is needed). This, of course, decreases as RPMs increase.

6800 = 15.88ms max PW (@ 90%)
7200 = 15ms max PW (@ 90%)

Perhaps your valvetrain weight is limiting you. Got titanium/lightweight valves/spring hardware? Are you certain that your setup will handle that RPM?

Perhaps you do have a tuning issue and all this stuff I listed is not your problem.

Good luck,
Rick

Dale McPeters · Post by **Dale McPeters** » Fri Apr 29, 2005 11:53 am

rockin_rick wrote: Perhaps your 12Mhz EEC can't go over 6500 RPMs (regardless of allowed PIP and rev limit settings). That's a lot of calculations in a very short time with a slow EEC. There has to be a RPM (and thus window for calculations) limit somewhere. 6500 RPMs = 3250 RPMs per cycle = 54.167 Rev/sec = 18.46ms per cycle.
Good luck,
Rick

Rick,

Just an FYI the EEC-IV's will rev over 6500 rpm. My 347 will rev to 7500 rpm or better........"BUT" you have to have a light weight valve train if not the lifters get to bouncing around a little even if they are solid lifters....

chadtn · Post by **chadtn** » Fri Apr 29, 2005 1:42 pm

I don't think this set up should have any trouble turning 7000 rpms. It's a 306 cubic inch motor with a 236/247 duration ~.630 lift on a 112 cam. It has titanium retainers, and whatever 2.05/1.60 valves that come with the Victor Jr heads. The springs are matched for a solid roller cam. I've been told on a 302 that the Victor intake will make power up to about 8000 rpms...So I wouldn't think that would be the problem.

I haven't hooked my wideband up yet because I haven't gotten around to welding a bung in the exhaust, but I don't think the injectors are any where close to maxed out. It's a blower car and I'm just trying to get all of the wrinkles worked out before I put the belt back on. Right now I've got 30lb injectors with a C&L 76mm MAF and the correct sample tube. When I can get it turning the rpms I want and get all the little things working right I'll put my Univer, 42lb injectors and blower belt back on. As the car sits I doubt it makes any where near 300rwhp on the motor. Nothing is sized right for a N/A 306...It should turn rpms to the moon and make crappy tq numbers. ; )

Little more info... 1 3/4" long tubes with 3" collectors to straight 3" pipe dumped. 76mm MAF (temporary), 75mm throttle body, ported Victor 5.0 intake, ported Victor Jr. heads /w 2.05/1.60 valves, titanium retainers, springs matched to the cam, and solid roller lifters. I'm not expecting it to make very good power on the motor...I've already got a D-1 Procharger hooked up on the car, but I've got the belt off until I get the wrinkles ironed out.

Thanks!

Chad

chadtn · Post by **chadtn** » Fri Apr 29, 2005 1:47 pm

BTW...When it hits 6500 rpms the car hits a wall and drop downs to about 6000. It doesn't feel like valve float and is nothing like a spark rev limiter that flutters. It slams 6500 and drops like a rock.

Chad

Dale McPeters · Post by **Dale McPeters** » Fri Apr 29, 2005 7:39 pm

Have you checked the speed limiters since you are using the A3M binary? (Edited to proper binary)

Look at what I have pasted in below and tell me if yours is simular to this it is from an A9L

HALF_FUEL_REV_LIMIT_ON 8000 # Turn on half-fuel rev limit
HALF_FUEL_REV_LIMIT_OFF 7500 # Turn off half-fuel rev limit
SECOND_SPEED_LIMITER_ON 127.5 # Turn on 2nd speed limiter (MPH)
SECOND_SPEED_LIMITER_OFF 127.5 # Turn off 2nd speed limiter (MPH)
FIRST_SPEED_LIMITER_ON 127.5 # Turn on 1st speed limiter (MPH)
FIRST_SPEED_LIMITER_OFF 127.5 # Turn off 1st speed limiter (MPH)
NO_FUEL_RPM 7000 # Max RPM (no fuel)

Post by **2Shaker** » Fri Apr 29, 2005 8:56 pm

We had 2 different conditons over the past year in our 347 which felt just like you describe: 1. hit the rev limiter - there was no bouncing around, it just lays down until it hits the rev limiter off value; and 2. we pegged the MAF. This one took a while before we figured it out. When it pegged it was like someone reached over and turned the key off.

chadtn · Post by **chadtn** » Sat Apr 30, 2005 10:16 am

My processor is an A3M...not an X3Z. Did I misunderstand? Are you saying the A3M and X3Z are in the same family? I have the half fuel and max rpm scalars, but nothing with an exact match on the speed limiters. I do have speed limiters A & B though.

PIP Filter is set at 600. Half fuel off is set at 7500 rpms...half fuel on is set at 8000. Max rpm is set at 7000. I guess I'll try raising these and see if it makes a difference, but it seems like it shouldn't be hitting a wall at 6500.

About pegging the MAF meter...I don't think this car is making any where near enough power to be pegging the meter, but I'll datalog the MAF voltage to make sure. It will probably be next week though because it's raining pretty hard outside right now and I think it's supposed to be pretty bad all weekend. : (

Thanks for the input!

Chad

Dale McPeters · Post by **Dale McPeters** » Sat Apr 30, 2005 11:01 am

chadtn wrote:My processor is an A3M...not an X3Z. Did I misunderstand? Are you saying the A3M and X3Z are in the same family? I have the half fuel and max rpm scalars, but nothing with an exact match on the speed limiters. I do have speed limiters A & B though.

Yes the A3M & X3Z are in the same family. I mis typed as I was helping another memeber of the Forum right before my post and had X3Z on the brain....

Even if the speed limiters are named differently you should still have 4 of them and to disable them they all need to be set at 127.5. One reason for this if you hit the speed limiter in 2nd-3rd at 6500 rpm the car will lay down on you just about like hitting the rev limiter.....

chadtn wrote: PIP Filter is set at 600. Half fuel off is set at 7500 rpms...half fuel on is set at 8000. Max rpm is set at 7000. I guess I'll try raising these and see if it makes a difference, but it seems like it shouldn't be hitting a wall at 6500.

What rpm is the cam good for? Also see my reply above.

chadtn wrote: About pegging the MAF meter...I don't think this car is making any where near enough power to be pegging the meter, but I'll datalog the MAF voltage to make sure. It will probably be next week though because it's raining pretty hard outside right now and I think it's supposed to be pretty bad all weekend. : (

Thanks for the input!

Chad

2shaker also has a valid point on the pegging the MAF. I also had this happen on the '91 that I have back now at one time & it is a NA car......It now has been changed to 42lb/hr injectors with the proper sample tube and modified maf curve....

PLohr · Post by **PLohr** » Wed Nov 29, 2006 7:06 am

chadtn,
Would you mind sharing the specs on your solid roller camshaft? And how about the idle, do you have enough vacuum to operate the power assist brakes and power steering? Thanks for any help.

chadtn · Post by **chadtn** » Wed Nov 29, 2006 8:49 am

This thread came back from the dead. heh..I've been broke and haven't messed with that car in a while. Still need to do some more work and figure out what is going on. I just got my other Mustang running this week so I should be able to test the tweecer out and see if I get the same results on it.

I don't recall the exact numbers on the cam off the top of my head...It's something like 236/247 duration ~.630 lift on a 112. Pulls around 8-10lbs of vacuum at idle on my 9.5:1 306. When you first start the car the brakes are a little weak, but after it has run a while they work fine for a couple of hard stops back to back. : )

Chad

Cougar5.0 · Post by **Cougar5.0** » Wed Nov 29, 2006 10:20 am

Hey, we gave you a year-and-a-half to get back to us on that!!

Help getting the car to rev over 6500 rpms

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