Nos Tuning question

[quickone2]

Have some questions guys. Dynoed my engine with a Louisiana performance plate out of N.O. La. The engine ran great with the 82/57 jets made 976hp which is supposed to be the 200hp jets it made an extra 260hp. The graph on the dyno was so clean engine sounded great. The highest EGT was 1240. So I decided to put in the 300hp jets 99/72 as per the card to see if we could get 1100 hp.

We brought the engine up to speed on the dyno and purged it once it took it. When we put the engine under the load and I sprayed it. Kaboom! sounded like an a bomb went off in the dyno room. Fortunately I only lost the head gaskets. One guy said It had air in the nitrous line and it caused the backfire. What do you guys think? The pressure was at 1050psi.
Thanks for your help.

[brothern2o]

every nitrous backfire I ever had was due to lean condition. I am guessing bang and fire back up thru carb. Last time I had air in the line I got a stutter/bog but nitrous is a funny animal and I could be in the minority.

[8secgt350]

You were big time lean for whatever reason. Maybe the fuel soleniod did not open or was bouncing due to poor wiring. You get the backfire when you go lean, extra O2 burns more quickly, and when the intake valve opens it ignites the lean mix upstream in the intake. BOOM.

It is probably one reason you made 260 hp on the NOS jet you had in prior. With C16 in the tank I have got away with fuel soleniods not opening altogether and did not blow the inatke off the motor with a 31 jet in the fogger.... It did run very hard though :-)

Something was not right, actually, not even close to being in the ballpark.

BK

[quickone2]

Do you think it could have been to much fuel going through the plate and puddling in the intake? Scared the S*%$ out of me when it back fired. Lot of time and money in it. I put it back together and I am just hopefully be satisfied with the 200 hp jets. Its probably good It didn't take it my rotating assy. isn't billet it is eagle 4340 forged. Thanks guys.

[brothern2o]

nos pressure - 1050 psi : fuel pressure - 4-9 psi , doubt fuel beat nitrous to intake. I had aleaking fuel solenoid everytime system was on it would almost shut down motor not cause it to pop. Remember fuel is added in a nos system to suppress/slow down combustion. Thus to much fuel will lead to a bog to much nos and you get an uncontrolled reaction or sometimes a "pop".

[8secgt350]

Brothern2o is correct is his opinion that puddling is not an issue. FI cars have that problem when fuel seperates from air in low speed situations where the air has to turn. The fuel seperates but the nitrous is able to make the turns, momentary lean condition, intake valve opens, BOOM.

You have an issue somewhere. Even with your 200 horse tune you have an issue of some sort but it is hard to hurt anything with an 82 jet. I am not an expert on plate tune ups, but maybe someone else is. If your jet spread is 82nitrous/57fuel, what are you using for fuel pressure??

This thing had to be dead lean for it to go boom. Again, it is one reason it probably made good power on the 82 jet..

BK

[quickone2]

Fuel pres was set at 8 psi on a holley 500 gph pump. I dunno. I'm just gonna stick with the 200 hp jets the graph was so clean and the plugs looked great. What do you guys think about the rotating assy. It is an Eagle 4340 handling the hp? Thanks.

[8secgt350]

The question is not always the pieces you have which compromise the rotating assembly, it generally comes down to the saavy of the tuner.

I have had 2 engines in my car. One where I fought the nitrous tuneup constantly as I was trying to cut some corners. Lifted ring lands on pistons, crushed ring lands, melted pistons, bent pins, bent a scat crank, and broke a r302 block. This engine did not last 2 years. Car went 9.20's at 145mph.

Next engine I did everything right and paid attention to detail. Have had the same pistons and bearings in the engine when we first put it together in the spring of 2000. Same car, combination has not changed, went 8.06 at 172 this fall.

It is all about the tune. If the engine is happy, it will live longer than most.

Your combo does not sound happy. Step back and take a breath. It will save you money in the short and long run.

[coulterz28]

Your jet spread is way to wide for 8PSI. You have to be way lean.



Jessie Coulter
Marketing/Motorsports Supervisor
Holley Performance Products

[spdracr0]

For what it is worth, I run a 82 square and 5psi with a nos big shot kit, NOS recommends a 10 jet spread but this is where we have gottent eh best performance and air fuel numbers..

[coulterz28]

Yes, Square usually makes for a good tune up. The 10 jet spread with the larger fuel jet is by far not a race tune-up.

Jessie Coulter
Marketing/Motorsports Supervisor
Holley Performance Products