Old school apex turbo question

[prairiepowderhead]

I will try not to drag this out, my 08 apex has a stutter in the top end. It has a boo docker type of turbo setup , side mount, 3072 Garrett. It has rods and pistons head studs eagle cams, valve springs and pretty much everything else you can do. 8.5 to 1 pistons. When I first run it when it's cold it rips, then after it gets hot it acts like it drops a cylinder, the boost still comes up but it will only rev 9000 , doesn't matter if I run 12 lbs or 25 lbs, also doesn't matter if i change fuel up or down. One thing I thought of is that I haven't changed spark plugs for probably 3000 miles or more. It also has a knock box but I've ran it unplugged and makes no difference.
It really stutters on the top end at full throttle otherwise sounds fine. Any thoughts please.

 

[Octanee]

I will try not to drag this out, my 08 apex has a stutter in the top end. It has a boo docker type of turbo setup , side mount, 3072 Garrett. It has rods and pistons head studs eagle cams, valve springs and pretty much everything else you can do. 8.5 to 1 pistons. When I first run it when it's cold it rips, then after it gets hot it acts like it drops a cylinder, the boost still comes up but it will only rev 9000 , doesn't matter if I run 12 lbs or 25 lbs, also doesn't matter if i change fuel up or down. One thing I thought of is that I haven't changed spark plugs for probably 3000 miles or more. It also has a knock box but I've ran it unplugged and makes no difference.
It really stutters on the top end at full throttle otherwise sounds fine. Any thoughts please.

not too sure but my best guess would be perhaps try new plugs now. and make sure you have them gapped to 20 thousandths. hell If you run 25# It might even need to be as little as 18thou so I'm not sure.

When I originally bought my apex it had some stuttering happening through out boost and stuff. I checked plugs and sure enough non gapped plugs. Changed plugs and gapped them to 20 thou and my sled ran/runs fine now

 

[BCBOOST]

Look up the specs for the resistance check for the coil assy's in the service manual as well, you could have a bad one/out of spec. Would cause what you are describing.
BC.

 

[julio]

stumble

It sounds like you are on the rev limiter, the tach will show around 9 but you are actually on the limiter.
if you are out riding and let it sit to cool can you open her up without the problem. can you slowly advance the throttle to get it over 10?
Its worth looking at the plugs either way..

 

[prairiepowderhead]

Thanks guys, If i fiddle around at half throttle just cruzin I can get it over 9000 but if i ask for boost after that it just starts falling out, If I let it cool all the way off it will start up and rip for a few minutes. then right back at it. When it rips it will run 25 lbs at 11,000 ish rpms, I am running 108 grams in each weight. I will check plugs for sure, probably just put new ones in it.
Julio, I had similar issues on the sled that I got from Miran that was your old one, but it turned out to be the knock box mal****ion, put a new one on and ran great, so I thought that was this ones issue but it doesnt seem to be.

 

[Octanee]

Thanks guys, If i fiddle around at half throttle just cruzin I can get it over 9000 but if i ask for boost after that it just starts falling out, If I let it cool all the way off it will start up and rip for a few minutes. then right back at it. When it rips it will run 25 lbs at 11,000 ish rpms, I am running 108 grams in each weight. I will check plugs for sure, probably just put new ones in it.
Julio, I had similar issues on the sled that I got from Miran that was your old one, but it turned out to be the knock box mal****ion, put a new one on and ran great, so I thought that was this ones issue but it doesnt seem to be.

hopefully its a easy fix. Could be the plugs going bad. I know these motors can be hard on plugs just from the higher rpm all the time and the boost/bigger BANGS for more power


also on another note. 25# of boost... I want to see a video

 

[prairiepowderhead]

View attachment 225553No video yet. Still tuning. I just installed 2 stages of nos to help keep it cool on the top end and spool up quicker on the bottom. Ill try to get some pics on here for you.

 

[julio]

runner

I have ridden a couple apexs that were running 25-30lbs and it was just silly. Even in powder they spun the paddles off the track.. also hard to climb cause you want to pin it but cant for more than a second or two..

 

[prairiepowderhead]

It's not much fun to ride, but it goes really fast. I'm just trying to win a few races with it is all. Just for kicks. The nitro gets the miles pounded on it. ..... Viper soon !!!!!!!!!

 

[prairiepowderhead]

I'm not real excited bout the rear skid yet. I'm sure it's just setup but too much air no transfer, not enough air falls out on boost and up in the air we go....don't know what to do yet. Got to get it running right first I suppose.

 

[Octanee]

very nice sled. You certainly are going balls to the wall with it lol!

And Yeah I could not imagine that much horse power on an apex. As it is I run mine ~12-15# and with a 174 2.5 it goes pretty damn crazy.... and will pick up a wheelie pretty easy so 25-30# must be very hard to keep the nose down. But as you said its more for races and or just quick spurts lol

 

[mattymac]

check the coils

 

[prairiepowderhead]

Well, coils and plugs replaced and still happens, any other thoughts? Im lost.

 

[up-high]

Maybe a heat issue? The ecu limiting rpm due to a sensor being too close to the turbo and getting hot? Just guessing. You're sure it's not over revving? The tachs have trouble keeping up to the Apex motor boosted. Seem to lag behind. Make it snow and shoot some video so we can hear the stutter.

 

[BigFish BC]

it almost sounds like your fuel lines mite be getting to hot, causing fuel flow issues.is your fuel pump or lines close to your header or fuel lines,i know a bunch of powderlites turbo nytro had this prob.fuel gets hot & bubble making air in the lines.

 

[icr]

Do you have an inline fuel filter or tether?

 

[prairiepowderhead]

I'll have to check the fuel lines for sure . The pump is up out of the way but the lines might be getting hot. Which sensors are close to the header? I could run it out in the field with a helmet cam, might be able to hear the stutter. Might try that tomorrow. Thanks for all the input.

 

[prairiepowderhead]

And I do have a teather

 

[icr]

And I do have a teather

Roll over valve tether?

 

[prairiepowderhead]

No just tether.