My 750 speed demon came jetted 76 83 from Barry Grant. I tweaked it up to 76 86 last time out and my 60 ft went down on average by .227 but the car picked up on average 2 mph at the end of the track over its 5 runs. Pretty significant. My question is - is there any benefit to squaring the jetting vs staggered jetting . Or with a speed demon can you not do this ? Instead of 76 86 run 81 81 I am running an SP1 single plane intake. My 850 Holley came jetted 80 square out of the box.....J
It likely had a power valve in front, none in back, thus the big difference in front/rear jet sizes. Likely had both front and rear power valves. My BG Silver Claw did, but I run the rear PV blocked and upped the jetting in the rear to compensate. Devon
Devon thats what I thought / heard too..I have heard 8-10 jet sizes with a blocked p.v.......I am at a weird place .....the car picked up an avg of 2 mph over last time out with the fatter jets in back but the average 60 slowed by .227 and the car ran slower ....So I may pull just the primary back 2 jet sizes to 74's to possibly get the 60 happier BUT leave the rears as is at 86 for the mph improvement. Sound reasonable ?
Your experimentation will show you the "sweet spot". You can even experiment with staggering left to right...just don't let it detonate if you're leaning it out. Devon
I have read a few articles online that say keep going up in jet size until mph stops gaining ...so that being said by that rule I am supposed to upjet again BUT what I dont get is the car slowed down - so wheres the gain ? So should I keep going up ? Or tweak as I said before .
I think you're at the point where your combo will be more sensitive than what some rules of thumb will show with regard of what should happen, so you're just going to have to try things. When I experimented with jetting many moons ago, I also re-tweaked total timing to make it even better, although timing had already been optimized for the previous carb tuning. Lots of things going on. Devon
I understand what you are saying -the point I am at .... Regarding jetting advice found on the internet -I guess mph is an indicator of overall power being made -so more power should take up for the "slack"created in the 60 ft eventually guess ...so I guess I will take it up a few more jet sizes and see what happens. Kind of going opposite of my gut though......
I'm with you. I've had my share of "it worked better but wasn't supposed to work like that" which I would have never figured out if I hadn't tried some things that went against common judgement. It's fun and frustrating at the same time. Devon
