800-840mv is probably not rich enough for WOT operation. When I put my headers on I found that I needed to recal the chip for more fuel. You'll need a WB to do it right. If its not available, see if you can at least get O2 readings in the 1.0+mv range. You can do this by lowering the PE AFR that's commanded by the cal. It won't be very accurate but it'll be less likely to knock. I'd also back off the WOT timing. Drop the PE adder timing. :seeya

 

My guess is that your getting false knock. Before doing anything you must find out if the knock is real. You can do this by disconnecting the ground wire to the knock sensor module. I cut the wire and put a switch in so I could do this. I went throught the same problem you are having and I had false knock from the header resonance. If you find that you do have false knock you could get the lt4 knock sensor set up or wrap your present sensor with teflon tape. The other option is to use the switch when you race. IF YOU CHOOSE THIS OPTION YOU WON'T WANT TO GO TOO AGGRESSIVE ON THE INITIAL TIMING BECAUSE THE ECM WONT RETARD WITH THE WIRE DISCONNECTED IF IT DOES DETONATE. The other thing to check is the gasket match up with the cylinder head exhaust outlet. Beach Bum had a problem with this and it slowed him way down. I also had a similiar problem with my gaskets that came with the headers. My headers are 1-5/8" and the gaskets were under 1-1/2"! This is worth checking into!
Also check the base timing. 89's run at 6 deg BTC with a stock calpak.
Hope this helps!
John

 

Yes if the header primaries are huge, like putting Big Block headers on a small block.

It is not supposed to happen in his case this much.

 

Gaskets are the correct size, they were the Felpro ones made for the D-port heads, they were slightly bigger than the head's exhaust ports. Wrapping the knock sensor sounds pretty easy to do, I guess I could just pop it out, hold the hole closed with my finger while someone else wrapped it, then put it in? I wouldn't loose too much antifreeze that way, or isn't there that much in the block anyway? Also, would upgrading my ESC to the newer design help me also?

One other thing, I'm using the Stage 8 locking header bolts, how they work is there is a washer that slips over the bolt once it is installed, then a C clip goes into a groove on the bolt to lock the washer on. The washers and clips fit a little loose and "jingle" a little when you tap them with you fingers. Would my knock sensor being picking this up, or shouldn't I be worrying about it?

I never had many knock counts before the headers were installed, they mostly occur now under WOT.

 

With only 800-840mV you are running too lean, possibly causing real knock. Increase fuel pressure till you see around 900-940mV at WOT.

If you're still seeing knock retard, try replacing your ESC module with the upgraded P/N sisted on my site (link in my sig. below).

If it's real knock, try running a 160deg stat & fan switch; and check your base timing.

 

with a intake that does not make power past 4200 rpms you will not see big power gains.

Yes, you will lose some minor low end on a stock L98 and pick up a 5 hp or so..

 

I disagree, I know lot people who have picked up atleast 15hp+. Honestly it was the best bolt on mods I have done to my car. I have 1 5/8" headers, and my car seemed to gain low end torque and revs through rpm band a lot quicker. From reading the forum over the years it seems like 1 3/4" header lose a little low end, while 1 5/8's do not.

 

Just a couple of general observations. Headers typically cause an engine to lean out. Back in the days of carbs, if you put on headers, you always had to put in bigger jets. Might have to bump up the fuel pressure a little to compensate.

Also, how much the knock sensor is tightened will have an effect on how much knock it sees. You can "desensitize" a knock sensor by loosening it a little. But I suspect you are getting false knock from the headers.

 

I had my intake, plenum, and runners replaced in the spring (see sig). Two months later, I had the headers installed. Never been to the track or the dyno (yet). I will tell you that the car runs like a raped ape. It pulls hard up to about 5500. My next step is to have 1.6 RR's installed, MSD ignition and wires, re-tune it, and head to the dyno shop. :smash:

 

no, we have proof of a 15hp gain with headers on the L98
Several people have dyno results and ET's

 

I've read on the forum that shorties only give like 5 hp but long tubes give like 10 to 15 hp.

I'm a bit curious about the knock sensor, do any one of you guys know if the knock sensor would act up a bit less on a set of shorties instead of long tubes?
It seems like more and more I read about headers.. more problems people have when installing them.
Leaks, kock sensor problem, fitment on the car, possible low end torque loss (with 1 3/4 inch), gas pressure ajustments.

I'm really starting to think that headers are a bunch of trouble to install, its making me a bit worried because I really wanted to bolt some on one day.

 

:withstupid: I run around 950mv at WOT. Increase your fuel pressure with an AFPR. I think I'm running around 52psi. (I also have the 160* thermo)

 

I'm going to try putting a quarter in the AFPR to see what it does for me, it will only be a temp thing until I get a real AFPR, but it should be a quick and easy test I'd think. I've been watching one on eBay for a while now, if I don't get it, I'll order one from Summit next week. The Holley is the best, right?

 

It would take less time to disconnect the brown wire on the knock module and listen for detonation than it will to remove the plenum and put a quarter in the fp regulator. Besides this may be too much fuel then or you risk damaging the regulator diaphram. You say 5-6 knock counts during 0-60mph set at a base of 6 deg. Thats really not alot. Are the knocks throughout the run or can you pin point the rpm range? Dont ignore the false knock theory because I raised the f.p. and raised it some more. Still had it. Then I put in bigger injectors and still had it.
Then I put in a walbro pump and still had it. Then I raised the pressure so much that after a few months carbon built up on the tops of my pistons and spark plugs! I still had it! I took the 24# FMS injectors out and put the stockers back in.
If you didn't detonate prior to the headers then I doubt your running lean with them. The MAF sensor would compensate for the increase in air flow through the motor. I agree with the theory that putting headers on a carbed car would require a jet change but this is a computer controlled MAF system.
It will correct for mild mods!
I would not tune your car at wot with a 1 wire stock oxygen sensor. They are not accurate at all. I'll probably get flack for that but anyway best thing would be to tune for best mph at the track or a chasis dyno.
If you are running headers with no cats and duals you are getting false knock.
There is no doubt in my mind. As far as leaning out I run 12.70's with stock 89 injectors set at 48 psi.

Just trying to help you avoid years of b.s.. Yes years. It took me two years and a lot of troubleshooting to find out what was actually wrong.

Well anyway good luck finding your problem.
John

 

"You say 5-6 knock counts during 0-60mph set at a base of 6 deg. Thats really not alot."

As John89 states here, the determining factor is not as much the number of knock counts but the RATE at which the knock counts occurs. That's partly how the ECM differentiates real from false knock. I get knock counts when I downshift sometimes or take the 4+3 out of OD. So you really need to investigate if the knock counts are registering during acceleration or at other times.

 

Just another observation point, I have a 91 L98 when I installed hooker 2149's with their Y-pipe the car seems to have gained all around. In my case it seemed to make a big difference. The car was so-so fast before, lil spin off line, after installing the headers it seems very fast, sorry no track times.
:seeya

 

Not doing the quarter thing now, thought the bolts were allen head, turns out they are the tamperproof torx kind.

Here's my knock counts, pretty steady gain in them under WOT

Time(sec) Speed RPM Knocks(total)
0.0------------13-----1718----0
0.5------------17-----2087----1
1.0------------22-----3140----2
1.5------------26-----3709----3
2.0------------32-----4636----4
2.5------------38-----5256----5
3.0------------43-----3255----5
3.5------------48-----3561----5
4.0------------53-----3916----5
4.5------------58-----4113----5
5.0------------62-----4488----6

On another run it recorded 3 counts between 2500 and 3400rpm as soon as I stepped on it, with a similar gain as above.

Will disconnecting the brown wire hurt anything for testing? What am I actually looking for if I do this?

 

Try increasing the pump shot for AE and make the slope of the spark curve a little less aggressive (ie have the spark advance come in later). Also do you have a spark slope in your ECM Constants Table?

 

Wish I could do that, but I don't have the ability or equipment to tune my own chips. Hope to be able to someday. The chip that is in it now is a Hypertech thermomaster. (Been in the car ever since I've had it)Should I put the stock chip back in, it is light blue and says Delco ARAP 4194 on it.

 

:lurk:

This is cool! I don't understand anything.. but its very interesting