Odd surging in high gear? FIXED
 

I only made four passes last year due to a slow as hell engine builder.
My last pass last year ran 147mph at 18psi and I noticed this issue.
Feels like a quick loss in power then comes back and repeats.

The only things I saw in the log last year were what looked like slight tire spin and low control module voltage. It was 12.5v. Fuel pressure also looked to be dropping a couple of psi.

So over the winter I rebuilt the charging system. That's fixed. I picked up a solid 1.5v.
Added a second Holley fuel pump on a hobs at 15psi.
Added new MT 275 Pro drag radials.

So got out last night. First pass of the year.

Left at 11psi and the car hooked for maybe 2 feet.......soft pedaled it and finished the run.

Same thing in high gear.

So today I pulled the plugs. They look new. Gapped at .024"
Ohm'd the wires. One was 80 ohms higher than the others. These are the stock 800 ohm wires that were on the engine when I bought it.
Anyway, that bugs me so I'll replace.

Removed and cleaned the injectors. one of my adapters came off in pieces. I'll get rid of them and add pigtails.

Did a compression test. 180-182 all cylinders.

The log shows flat AFR, reasonably flat boost, smooth mph. The fuel pressure wiggles about .5psi.
The rpm trace is lumpy, and that's what I am feeling.

Looked at the log from a 9.2X pass, 19 psi from two years ago. The boost wiggled pretty good, but the rpm trace was smooth.

So I'm puzzled.

Any ideas beyond what I'm going to do?

Ron

There is no chance in hell a deviation of 0.5psi would be felt.

And fuel pressure deviations are very common given what goes on within the rail etc, even more so with injectors using lots of fuel.

As for rpm trace....without seeing it impossible to say.

It could be interference, slip issues, trigger issues, lots of things really.

Are you sure its not the converter coupling and pulling the engine down some rpm?

Spark blow-out? Maybe tighten them up a bit to before going crazy with anything else.

hey ron, glad you got out with the nice weather!

what plugs are you using? i've been using the tr6 projected tips
but now that I can make way more boost i think i might switch to the br7ef

Screen capture of the data log.
The rpm drops can be seen.
The second screen shot from when it ran 9.2x@149

The only thing I changed before this started was the forged rods and pistons.
I've been running R5724-8 race plugs since I first got this running.

I doubt it would be the converter. But I'll at least check the fluid level.

I dont know Lambda, but could it want more fuel-may not show up in the AFR's, but it just wants more (or lower Lambda)

Are you sure that's not valve float?

Valve float would show changes in wideband readings.

I've run the same AFR for quite awhile. Power didn't change when I leaned it from 11:1, but it eased the duty cycle a tad.

I'll see what happens with new plugs, wires and getting rid of the injector adapters.

I suppose I could throw it on the dyno. But I'd rather race it. I need the seat time.

Do you have calculations setup to figure out converter slip? IE: Engine RPM vs Trans output shaft RPM or even driveshaft speed?

It's a turbo 400 trans, so sadly the built in calculations and measurements in hpt don't function. As you can see I do have mph and it's accurate. I managed to find the th400 speed sensor setup.

What are you thinking?

Ron

Well,

I replaced the plugs (R5724-8), wires (AC Delco stock replacements) and soldered in injector pigtails.

The plugs BTW come pre-gapped at .022".
I use the stock wires because they are 800 ohm resistance and I'm running the non resistor plugs.

Fired it up, took it for a drive and noted the fuel trims changed. So I did something!

I haven't been able to test WOT as it's been raining and I don't do that on the street anyway. Track days have all been rained out.

I'll be racing it this sat at a Woodburn Dragstrip with actual track prep and everything.
It will either fly or be a dud......

Ron

Good luck Ron.

Thanks man!

Ron any reason for running non-resistor plugs?

No. Not really.
The 8 heat range seems fine, and I don't think there is an 8 resistor plug.

Others say extended tip is a no no in a boosted setup. Yet every manufacturer of boosted cars use them. They must know something....,

I have a set of BR7 to try just in case.

There are many many 8 resistor plugs

The two I've used are BCR8ES at the cheap end or more expensive BKR8EIX, or there's TR8IX etc etc

BCR8ES does not show up on the NGK search index

They're common as muck here, seems not in the US for some reason

http://www.ngk-sparkplugs.com/bcr8es-p-1874.html

http://www.sparkplugs.co.uk/ngk-spark-plug-bcr8es

http://www.opieoils.co.uk/p-63532-ng...-ngk-5430.aspx

Some "sort of" cross reference listings. I say sort of as some of the Denso listings they give are regular projected nose, so clearly not the same.

Loads of sellers on ebay too...again at least in the UK.

http://www.sparkplug-crossreference..../NGK_PN/BCR8ES