I have a 1991 Firebird 383 HSR Dart Pro 1 200cc heads running at 10.4:1 compression, custom '7730 $8D 224/230 Comp Cam, hooker headers, 3" exhaust, hooker aero chamber muffler, and the list goes on...

I found I had the wrong reach plugs in my dart heads and purchased a set from Accel that matches what Dart recommends. I've upgraded to the Accel iginition module and purchased a MSD Blaster coil. I've tuned my timing correctly and am not spark knocking at high RPM's. I've got plenty of fuel as my WBO2 reads decently rich in that area (Same as pulling at 4500 RPM). Now, my car pulls better than ever, but seems to stop RIGHT AT 5500 RPM. What's the magic for this? Do I need to upgrade to another ignition module? Has anybody else ran into this problem? I know this car can pull past 6000 RPM, so what's the deal? Do I need a MSD 6AL? Please help.

 

If you have verified that your rpm limiter in the prom is set higher than 5500, than maybe it is your valve springs?

 

I have the '7730 8D ECM. I do not see a rev limiter in it. But I do know I have valve springs that can handle up to .600 lift.

 

It's in the constants table, called 'fuel cutoff rpm limit' or something like that. There are 2 limits, one for fuel cut-off and another for fuel cut-back on.

 

My "Fuel Cut Off Engine Speed" is set to 7021 RPM. My "Fuel Resume Engine Speed" is set to 6922 RPM.

 

That's not your problem then.

I once had a similar misfire around that rpm that turned out to be the intake bolts being loose(vacuum leak).

What do the 02's look like at that rpm when it happens?

You sure those valve springs are stiff enough for the cam? The springs that come on the heads are usually the worst. The ones on the AFR's I have were crap.

 

I'll try to log some data next time to see what it's doing at those RPM's.

I also have standard 8mm plug wires (Valucraft). I planned on ordering some Spiro Pro plug wires and see if it helps any too.

 

what are you plug gaps set to?

 

.045

 

maybe try bringing that down alittle .040-.035 what is your DCR

 

Basic Question:

Are you using the factory tach or an aftermarket tach?

The factory tach is usually incorrect...

 

Factory Tach.

 

Springs good for .600" lift doesn't really mean much, I think factory ones are good to that, but they'd float at 4500RPM.
Which springs? Part number? Seat and open force?
224/230 is a somewhat mild cam, the xe268 but roller I imagine? So... XR276hr right? On a 383 that should stop making power in the 5500RPM range...

 

It's the XE276, which is supposed to make power from 1800-5800 RPM. When the guy built my heads, I told him that I was wanting springs to support my cam lift with 1.6 rockers .536/.544 at .050. So he built them accordingly. But to fall off that fast, and I mean like I hit a rev limiter shouldn't be because of my cam/head/HSR combo.

 

I would hook an aftermarket tach to verify that your factory tach is accurate. Keep the factory one hooked up too to verify RPM's at different steps. If the factory tach checks out...then go from there.

You should be able to use datalogging software to check the RPM that the ECM sees...that would be a good double check as well.

If the RPMs are accurate...I think that the valvesprings could be the culprit.

HTH...

 

So...

Is there an update to this?

 

I verified that what I'm seeing is not related to my springs or how my engine is set up. Here's what I plan to do. First, I'm going to verify that my plug wires are not faulty. My new Spiro Pro wires should be in today or tomorrow. Second, I've spoke to a buddy of mine who has a VERY similar setup that I have and he's running a MSD 6AL. I'm thinking about hanging up the basic HEI setup and upgrading my ignition. As soon as I determine what is going on exactly, I'll be back to update this thread.

 

Unless you really want/need a rev limiter, I don't think that the MSD box gives any noticeable improvement over a stock HEI with an upgraded coil and module. Your money, your call.

 

More about.490"

 

Hopefully the wires will be in tonight. Can't wait to put an OHM meter on my current wires and compare those to the Spiro Pro's.

 

For all of you who may be interested, here is the specs for the wires. Autozone wires are the Valucrafts

----------------Valucraft------------------
22" -> 7.7k Ohm
22" -> 8.52k Ohm
26" -> 5.76k Ohm
26" -> 8.7k Ohm
28" -> 6.76k Ohm
32" -> 14.4k Ohm
32" -> 13.15k Ohm
40" -> 9.67k Ohm
-------------------------------------------

---------------Spiro Pro------------------
23" -> 651 Ohm
23" -> 648 Ohm
24" -> 644 Ohm
26" -> 702 Ohm
32" -> 867 Ohm
32" -> 864 Ohm
35" -> 947 Ohm
39" -> 1.06k Ohm
-------------------------------------------

I also purchased some boot gaurds for my new plug wires as I do not want them overheating. The wire that had the most resistance is the one that had bubbles in the boot where it got too hot. Once the boots come in and I get them installed, I'll do a test this weekend.

 

I'm running a stock HEI distributor & module, upgraded coil, and Taylor wires on my 350. I have no problem running it to 6000 RPM and still making power.

Like someone said, I suspect the valve springs are too weak and you're starting to feel valve float around 5500. Having springs that "can handle 600 lift" doesn't mean squat. You need specs like closed & open pressures.

Your cam is one above mine (XE270) plus you're running the longer rockers. If you're running anything less than a dual spring, that will be your problem. I'm running the dual springs that CompCam recommended. For you cam they are recommending as a minimum the 986s which are a dual w/ damper spring with 132 lbs @ 1.75" seat height, and 293 lbs @ 1.25". They recommend you run the 26986 which are beehive springs, but double the price than a regular dual spring. But since you're running the 1.6 rockers, I would go with the 987 dual springs which is what they recommend for the cams running lifts in the .540 to .560 range.

The XE roller cams have crazy ramp speeds, and adding the longer rockers makes it even worst. Don't skimp out on cheap springs or you might end up with a bent valve and/or a hole in the piston.

 

I'm running dual springs, but from what I'm hearing they're not enough. I'll go ahead and look into replacing them.

 

What springs are you running?

 

Tomorrow, we plan on pulling one of the springs. I have a friend who has the tools we need to check the pressure of the spring at open installed height and closed plus any more vital information needed. If we find out that my springs are not enough, I'll order some Comp 986 or 987 Springs.