timing for 125 hp fogger

[roadrunner451]

whats the ideal setting for the timing on a 125 shot fogger , is it 2 degrees for every 50hp nos reccomends 3or 4 degrees for the 125 , sound right to ya ,,, ty

[John_Heard]

Depends a bit on your engine combo, weight of car, fuel, etc. For example a low compression pump gas engine and race fuel will tolerate far more timing than a real high compression engine. In general a 125 shot is very forgiving as long as the engine is not some super high compression beast. So assuming you're like 12:1 compression or lower and you have race fuel you should be fine with 4-5 degrees of retard and one step colder plugs than you normally run N/A with your 125 shot.

Start out with fresh plugs and read them after making a pass...

http://www.dragstuff.com/techarticles/r ... plugs.html

[roadrunner451]

its a 70 roadrunner with 12.8 to 1 comp,probly weighs 3500, tire size "30" tall. Cam is 267 @ 50 int, 269 @ 50 exsaust installed 4 degrees retared timing is locked out at 38 total 440/1 indy cyl heads. racing fuel 110 octaine.

[John_Heard]

Probably 5 degrees retard would be a good starting point but it's important to look at the plugs to see where you are at after that first pass. It might need more retard, or be happier with less. It all depends on what your particular engine is happy with.

What are you going to do regards to jetting and fuel pressure?

Is this your first time playing with Mr. Frosty?

[roadrunner451]

jetting for the fogger 125 kit , i have 20/20 and the fuel pressure is 5.9lbs @950 bottle pressure,distributor locked out 38 degrees total,magnafuel 500 pump running both ..plugs are autolites 3933 gapped at 25 to 30 ,i also run a window switch set to come on at 5000 and shut off the nos at 6600 i shift at 6900,, the reason i posted this was because last few times i hit it , i swore i heard it spark knock ,just when i first hit it , like 3or 4 slight rattles and it went away, retard was at 4 , i did put it at 5 as of today , just havent treid it yet ... i have an indy clyinder aluminum timing cover because the stamped steel ones dont like the solid roller cams and it has only a boss on it for your timing marks so i used a piston stop to find top dead center and mark it on the cover so i could be off there a degree or 2, im real close thou cause i ran this set up for years before the nos.

[John_Heard]

Square (20/20) at 5.5 will be a touch fat, but not so bad it's going to hurt anything at this level. AR3933 is like a -9 NGK, you're good there. If you're concerned on the timing, you can easily take one more degree or so more retard out of it for 6 total until you get a plug reading.

[roadrunner451]

what about putting in some 24 jets on the nitrous side and leave the fuel pressure at 5.5 psi and take out 5 degrees of timing when i hit it , that will take it to what hp level 150 or so ,what do you think cause i have the jets on hand they came with the kit. thanks for helping,,

[John_Heard]

24/20 at 5.5 psi is gonna be a pretty lean. That is 7.75:1 N/F Ratio, probably not a good starting point. What do you have for a fuel regulator? Can you go up to 8 psi? 24/20 @ 8 psi is 6:1 N/F ratio which might be just a tad rich but not a bad starting point on that size of a hit.

[roadrunner451]

i have the holley , part# 12-803 reg, i was just wondering cause the jetting is 20/20 fuel pressure at 5.5psi and 5 degrees out .... now with 24 on the nos side only is it worth the extra hp do you think , cause now that i lowered fuel pressure a tad should show an improvement, so if nos makes them run rich out of the box then whats the fix lowering fuel pressure at the nos reg ... thats why i came up with this idea to put 24 in , shows what i know.

thanks for the help.

[John_Heard]

A stock 12-803 is at it's upper limits at 8 psi, you probably won't get much more pressure out of it. If i remember correctly about 9 is max on most of them with the stock spring in them. The 24/20 is more ideal tune up with it's 4 jet spread, when you get a chance to look at what the plugs show at 8 psi you can probably start taking some fuel away from it. I'd guess depending on the engine and lots of unknowns you may end up at around 6.5 to 7 psi with a light fuel ring in the plug. Again you have to focus on what the plug tells you to know which way to go on the tune up because each engine is different in what it'll want.

[roadrunner451]

so should i stick with the reg i have 12-803 or change it, and which one ...... ty

[John_Heard]

The one you have is fine as long as you're in the 8 psi or lower range. You get up around 9 psi and it probably won't work so hot.

[roadrunner451]

ok thanks alot .... john....... ill let you know.

[71Hellride]

I'd go with at least four jet spread. With that low of a horsepower running rich will take you a while to hurt it, if ever. I'd also pull more timing than you think it needs, get the tune up clean then add timing back as needed. If you end up taking the pressure down into the 4 psi range i'd add more nitrous jet. Hey John do you have a nitrous program or is the n/f ratios from stuff you flowed? I'm kinda curious what my n/f ratio is. I think it's actually in the 8's but I don't know for sure.

[roadrunner451]

so your saying to set the fuel pressure at 8psi is that because its a fogger , does a plate system require less fuel pressure with staggered jets at 125 -150 hp range,