Low power down low, smoking tire(s) up top, what to do?

I've had a few issues with my truck after doing a conversion from a manual to automatic transmission. My current build is listed in my sig.

My low down power sucks, granted some of that is that I'm running a SXE369 turbo at 5K+ elevation with 25* timing. I do have a 181/210 cam to help spool it + BD diverter valve. I'm pretty sure I'm running 3:54 gears with little tires. I'm sub 2k rpms at 70 MPH with OD on.


I posted a pic to show how little my tires are.

When I'm into the power band since I can't seem to clean my truck up even though I'm running AFC Live since if the turbo isn't smokey it's a dog. Either doggy or smokey no in-between. That may be in part because I'm a novice and just don't know the ins and outs and suck at tuning even with a tuning aid like AFC Live. At half throttle as boost is coming in and over 25lbs I'm smoking one tire, the driver's side tire, I can tell because it is becoming bald. What do I do to remedy that and get both tires to lock up?

I'm getting ready to install traction bars on my truck, will that help at all with getting both tires to lock up or do I need some kind of locker to get that under control?

Would changing my gear ratio to a 4:10 or even a 4:56 help my low down power? Changing tire size? I don't want to go up much in my tire size due to the fact that my truck won't fit in my garage anymore. I do have 5Ks installed so I have some RPMs to work with.

Thanks,

Andrew

I'd recommend rebuilding the LSD in your rear end. You can get kits to replace the clutches. You can even stack an extra clutch/steel in there, but that makes it basically a locker.

I'd also check for boost leaks and keep playing with tuning (tuning to your spool valve too).

And instead of going to lower gears, I'd look into going to a higher stall Torque Converter. Maybe 200rpm higher. I think that with tuning should get you into a very comfortable place with drive-ability.
3.56 gearing rocks. You'll be disappointed at expressway driving if you switch to 4.10's.

Traction bars will not help with a one tire fire. A locker, posi or spool is the only way to cure that. Going to a numerically higher gear would help get your rpms up to a usable range. Adding larger tires would negate or even compound your issue further.

Different stall converter can help lowend smoke. Let you smoke one tire fasterLOL

That's how they run with a large single turbo, I'd bet you'd be alot happier with something like a 62mm. Or best of both worlds, compounds with a 57mm secondary.

Thanks for the response. I just did some research that I could just possibly re-stack my Dana 80's LSD rather than do a rebuild on it and that would likely solve the problem. Pertaining to checking for boost leaks, I've pressurized my system recently to 30lbs and couldn't hear anything that sounded like leaks but I'm no mechanic either. Truck boosts to about 48lbs with no load under full throttle at 60ish mph. My turbo is currently not waste gated. I don't think I have a boost leak but I could be wrong.

Best way to check for a boost leak is pressurized the system again and spray soapy water on all your connections if it bubbles at all you have a leak

bellabulldog said:

I just did some research that I could just possibly re-stack my Dana 80's LSD rather than do a rebuild.

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Right, That's what I meant. I just normally see the kits labeled as rebuild kits.
If you can find just the PN's for the clutches and steels, go that route.
I really don't think you need a locker or a spool for street use.

Spoke with previous owner, apparently he changed axles on the vehicle and it has an open rear differential. Looks like it will be a Detroit TrueTrac locker or something similar. Furthermore I spoke to Lonnie at PDD and he recommended a BW K27 secondary turbo over my 369 in a twin set up. Looks like the big single will be going and going into twins. More money into this black hole lol.

So you have a mystery axle or a D80? You should see if you can find a rear D70/80 in a junk yard (or just the diff). I bet you'd be in less cash than a good locker, and you'd know the axle was great for the platform. I've been on 37's for a while now, I'm at just shy of 300k, and the diff locks and unlocks great. I do actually change my fluid, and that might go a long ways.

higher timing, cam with more overlap, taller gearing, elevation, big single.. yeah low end is gonna suck bad.
Whats your converter stall set at? Youd want a looser converter so the motor is loaded when its closer to its peak efficiency, instead of where its most inefficient.
4.10's not gonna help much. Ive got 4.10s and a smaller turbo. Only way to get decent low end power with the cam was to go with 155* nozzles and stock timing.
If you have a bunch of money to throw at the problem maybe higher compression pistons or a supercharger compound kit.
Small tow twins will work nice, but the low end will still be a little weak with cam and high timing.

I have no idea what my converter is set at. I can tell you this that it is tight enough I can't easily brake boost my turbo. As soon as my foot is off the gas my truck is rolling forward. I suspect I need to get a looser converter. How much I have no idea.

If you power brake like you are spooling up for a boosted launch, at what rpm does your engine quite gaining ? That max rpm you can reach, will be the stall speed for your converter at your power level.

Also I might add, you don't want to hold it like that too long. No point in building a bunch of boost and risking a busted input shaft... you should be able to reach rpm limit fairly quickly.

Way too long. Maybe 30 seconds and the only way I can do it is with AFC on the kill/open position. I don't think I'm revving over 1300 RPM but I haven't tried to do it in awhile.

That's a low stall, stock is 1900-2100.

Stock stall at stock power with new fluid is 1800.
I've seen guys with stock stalls, no spool valve, and S475's in Denver spool up faster than that.

I'd keep looking for something else that's causing this. I wonder if you're just set up with too much fuel.
What's your pump, fuel pressure, DV's, and injectors?
I also think you should spend some time on your AFC tuning and your spool valve tuning. Maybe call Will and ask him about the right way to set up his AFCLive box.

Pump is a 215 benched and balanced by Scheid diesel who also installed 5ks, they set pump at 500cc, running 191 DVs. Injectors are Weston 5x.16 tuned for advanced timing into marine pistons.

Don't know what fuel pressure is, I have a fuel pressure gauge in truck but not hooked up. Will try to get it set up this weekend. Running a FASS 200 that previous owner says was set to 45PSI as well as a restricted TORKTEK OFV to further boost fuel pressure.

I have spoken to Will a few times regarding the AFC Live, he instructed me to first tune boosted fueling to an acceptable level and then tune pre boost to be as responsive as possible. He also mentioned to me that being able to light a turbo like that would require some smoke. I can drive the truck basically smoke free by being gentle on the throttle but it is very unresponsive.

I have contemplated tightening star wheel despite how the AFC Live says to be installed just to slow fueling under boost because as it is right now the fueling feels almost binary, lots or none.

As far as spool valve, I also purchased that used from someone on this forum, took it apart, cleaned it and reassembled, tested under shop air to have it begin opening at 10ish PSI and full open by 20.

Mine had a low stall and it was a smokey and SLOW off the line. Put the stall at 1800 it got better then pulled the trans again to have it restalled back to stock 2000-2200 and it's clean as a whistle will light and burn the tires down.

I also had an open diff so it would spin one tire. I installed a power trax lock rite locker and it solved that problem. Although it's a bit different and you know it's there I like it. The only problem is if it breaks both tires loose your going to be sideways. I call the lockup switch the ditch switch now becaise if you flip it in 2wd that's where your headed.

bellabulldog said:

Pump is a 215 benched and balanced by Scheid diesel who also installed 5ks, they set pump at 500cc, running 191 DVs. Injectors are Weston 5x.16 tuned for advanced timing into marine pistons.

Don't know what fuel pressure is, I have a fuel pressure gauge in truck but not hooked up. Will try to get it set up this weekend. Running a FASS 200 that previous owner says was set to 45PSI as well as a restricted TORKTEK OFV to further boost fuel pressure.

I have spoken to Will a few times regarding the AFC Live, he instructed me to first tune boosted fueling to an acceptable level and then tune pre boost to be as responsive as possible. He also mentioned to me that being able to light a turbo like that would require some smoke. I can drive the truck basically smoke free by being gentle on the throttle but it is very unresponsive.

I have contemplated tightening star wheel despite how the AFC Live says to be installed just to slow fueling under boost because as it is right now the fueling feels almost binary, lots or none.

As far as spool valve, I also purchased that used from someone on this forum, took it apart, cleaned it and reassembled, tested under shop air to have it begin opening at 10ish PSI and full open by 20.

Click to expand...

What spring do you have in your AFC? Call into the shop on Monday and we'll see if we can set you up with a stiffer AFC spring that will be a better match the fueling curve that will work best for a big single at high altitude. You could try adding a couple turns of pre-load to the starwheel if you think the spring tension is definitely too low. The more spring tension, the more resolution you'll have on the tuning knobs, meaning a light spring goes from minimum to maximum in just a 2 turns but a heavier spring might have 6 or 7 full turns on the knobs to go from minimum to maximum, this makes it easier to dial-in the perfect tune... as long as you don't go too heavy on the spring tension.

Also on the AFC LIVE small black throttle response/smoke knob, try turning it in all the way then backing it out 1/2 turn. Watch the AFC LIVE boost pressure gauge and try to see how fast you are feeding boost to the AFC. If it's too smokey, turn the knob in 1/4 turn. If it's too sluggish and really clean, turn the knob out 1/4 turn. There should be enough adjustability to make almost any spring work in tuned mode; in full power mode..... really light AFC springs are a different story.