jet change for nitro

[wideopen231]

  Spud,

Running FI with 6.7 gpm DSR pump..036(4 outer cylindernozzles ).038( four inner cyliders)normally around 125 to 135 bypass. Looking at adding some fun juice after combo is tuned out. Max laod 30% and more like 20% if keep tuner under control.Seeing as thats me I know thats not easy.
How much jet change for 20 and 30% loads.Also timing adjustment suggestion running msd mag 20 and if need have dual drive and two mags,doubtful but do have them.34 to 38 with alky.

Oh yea 526 tfx HEMI 12,5:1. OLD ALKY COMBO WITH CAM CHANGE.

[Spud Miller]

 I assume you're naturally aspirated, not supercharged?

 For 20-30%, the main pill would be the same. Only after 33% is there a need for a smaller pill.

 Just for the heck of it, I'd richen it one step and knock back the timing about 4 degrees for the first pass or two. If things look ok, lean it back to where you were on the pill. If things still look ok, put some of the timing back in. Unless your compression ration is crazy high (14:1+) I'd guess you'll end up back at your original tuneup for methanol but be going quicker. You'll have higher system pressure from the nitro too.

No need for two mags.

Have fun!
Spud

[wideopen231]

Thanks Spud. Yes NA motor. Will start with 25% and .010 rich and step up from there. Not going to be running full time,just need game plan for those need to be bit quicker times .

[Spud Miller]

 You might find .010 rich will cancel out any gains from the nitro. That's a 15% difference in area.  Be ready to lean it down to go quicker. If you can do some testing before race day, you'll know exactly what to do and what it likes...and how much you'll gain.

 Good luck!
 Spud

[wideopen231]

Teating with this to have raceday info is idea. Going to start out little rich step up 1 change at a time to get data as to which change has what effect and record for referance at later date. Mainly looking for good starting point and from what you have said basic tuneup should be real close can tweak from there. Thanks

[alkyal]

I realize this is a Fuel Injection thread. I have read most of Spuds articles on the change over from Straight Methanol to a lower % of nitro ie 10/15%. The point being, no main jet or high speed change is suggested. The Question is with a Carb. When running a Methanol Carb that is well tuned [I know-why run a carb] and then adding the same low % of nitro,Why is a JET Change required? ie larger jet for more fuel delivery?

[bigaldart]

With regard to a carburetor requiring a jet change you need to remember the sheer weight of Nitro compared to alky. Your fuel is fed into the engine by a pressure differential between the booster and atmospheric pressure, this does not change because the fuel changes therefore you need to increase jet size to get the correct volume of fuel. All that fuel has inertia and Nitro has more inertia than methanol is another way of looking at it.

Alan

[wideopen231]

What are the carb things you fellas speak of?

[ricardo1967]

My dr. says carbs are bad!!