bottledgto

iTrader: (1)

Alright guys got my car on the track for the second time now, I noticed the car falls on its face above 6200 along with a nasty backfire...currently running 16lbs not sure what h.p is but it did 640 wheel on 10 #'s ?? Car did pretty good a 6.8 @ 110 in the 1/8th through a 6 speed breaking loose in 2nd ..question is what would cause the missing up top...back pressure, valve springs,fuel press?????? Not sure where to start looking..has new wires and plugs..any input is greatly appreciated..

yenkomike

iTrader: (2)

if your fuel pressure drops you should see that in the wideband. did you log the run. also what plugs and gap are you running. ?

what cam and valve springs.

NoorJ

I would guess valve float or spark blowout, like mike said what plugs/gap and springs you running?

bottledgto

iTrader: (1)

No logging and I don't have a wideband yet ,im gonna pick up a fuel press gauge today so I can monitor ..


..cam "tu1.5" 228/228 571/571 112 LSA lunati dual gold springs good for 650 lift I believe..

Bp7efs gapped at 24 I would get blowout underload at anything higher ..

Fuel : magnafuel 4303 -10 feed -8 return
Aeromotive 1:1 fpr
Fic 1000cc injectors
E85..

Turbo: turbonetics 7875 .96 3" Down pipe dumped ..

My springs had some miles on them before being boosted around 25k ..
Can it be possible that there getting weaker?? Possibly losing pressure??

Maybe bring spark plug gap down a little more?

Bad Apache

With no data it's hard to speculate. But with that said, it's easy enough to tighten the gap and run it again. It also could be a lean misfire as well. So be careful leaning on it too much until you have a wideband and can safely see what it's doing. A valve spring getting weak is always a possibility as well. It also could be a coil getting weak as well, although not common. You can check output with a simple/cheap ST125 type tester.

Good luck!
Lon

NoorJ

I wouldn't do a pull without a wideband

1969x11

iTrader: (36)

^^^^^werd!!!

95bowtie

Valve springs are shot......I had a similar issue with mine. Have a 238/242 .605 cam and patriot doubles. They had prolly 35k+ when I went boosted. Did fine on 10# 600whp for a year. Next year I upped it to 15# or tryed atleast. Anything over 13# and like 4500 rpm it just sounded funny and felt like it was missing.

Swapped plugs for fresh ones, swapped them out for some tr6s as well after that. Did plug wires, changed to truck coil packs too. Also tried going rich and leaner on the tune up and neither helped.

Finally decided to swap springs, used some pacs....they were doubles. Can't remember what part # but I called BTR and he was out of stock of his springs and recommended the PAC springs to me instead.

bottledgto

iTrader: (1)

Just ordered BTR PAC 1905's.. For some reason I have a feeling its my springs ..gonna get them in and drop it off at my tuners ,hopefully he can figure it out possibly turn the boost up I'd like to push this 5.3 to its limits but first have to get it to operate correctly lol...thanks fellas for all the input ,its greatly appreciated ..I'll update as soon as I have the culprit to this madness!! Cheers!!

turbotater1

i had a similar problem that turned out to be a sync issue with the crank sensor. it would not happen every time but always at higher rpm

turboventura

Valve springs usually just quit pulling rpm/making power and level off, not so much backfiring/popping/missing. You can drop the boost and see if it pulls more rpm, if it was a crank sensor I wouldn't think it would care about boost, but doesn't help to eliminate plug gap or coils.

Bad Apache

I have had valve springs cause a misfire/backfire. I had never seen that before in 30 years of building/repairing/racing. Like turboventura said, they usually just lay over at high rpm. It also made the wideband dance full lean just like a spark misfire.

Chucklee

iTrader: (3)

post the data log when you get a chance.

Rob383

Valve springs is what it sounds like. Boost on the back side of the valves will cause the valve to want to open "or not close" which makes you need stronger springs then with n/a motors. If you get valve float your wide band is going to read alot different when it happens. I had an egt probe and it would go from 1400degs to 1800degs. The pistons survived but the spark plugs didn't. Burn ground staps off. Just a suggestion. Could be wrong.