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Curious why so many of the big guys are sticking w/ the 23degree heads by mullins instead of going to the 18degree stuff. my understanding from reading these forums is that the 18degree stuff is smoother power than the 23degree heads. if thats the case and 18degree is that much easier to make big power why are these guys still using the 23degree stuff? opinions?
IMCA you have to have 23* heads...Stock valve angle...UMP mods I'm sure you are seeing 18* stuff out there..
I've never seen a valve angle rule in IMCA
no valve angle rule that i see. just fear of losing it probably keeps people from getting the 14degree heads.
Now back on track. I am refering to the open USRA and usmts type motors.
USMTS has a weight penalty for different styles of heads
most of the USMTS guys run the SPEC head. not very many are doing anything but that anymore cuz of the 8" spoiler advantage. its pretty hard to beat the 8" blade in the USRA/USMTS stuff. even if you were penalized weight for having the 18deg stuff.
according to mullins the 23deg makes much smoother power at the hit of the throttle so the driveability is a lot better. the 18deg makes better power down the straights but you have to back off coming out of the corner so you are losing your rpm and momentum where the 23deg you can stay right after it with the throttle. like i said this is all what mullins told me directly....
Thanks justin that is exactly what i was looking for. i was under the impression these guys were running his 23 degree castings that he makes at the bigger tracks and then running specs at 1/4-small 3/8 tracks.Quote:
Originally Posted by hobby12
What about w/ the USRA 8k chip rule. Do you think the spec still has an advantage when you throw that in? And are all the USMTS guys running 420+ci in the spec motors?
i think the spec or the ct525 is the best for the USRA deal and the 8k chip. that 8" blade makes a big big difference. last year when you had the 5" spoiler with the open motors and the 6" spoiler with the spec the guys were running the outlaw heads on the big tracks but from what i have seen they are running the spec all the time now! the 3" difference in the spoiler does that this year vs. last year.
the USMTS guys are all over the board on engine size. i know dripps was running a 388 most of the year. i think gustin usually runs those as well but hughes runs the 400-415 stuff? i'd say the most common is 400+ but doesn't really mean anything with those guys. on the USRA stuff i think the 400+ is the way to go since you have the chip rule. might as well have the cubes if you can't turn the rpm's!
You guys are right, there is no valve angle rule for IMCA, but don't you have to run shaft rockers with the 14* iron heads? If you do, they are illegal for IMCA aas it does say in their rules "No shaft or pedestal rocker arms"
ya they do that to try an keep big cams with stiff springs out.
Has anyone checked the angle mill on the usmts spec head and intake then see what the valve angle is.
With the 14* iron heads, you have to run a shaft rocker because of the 60/40 type valve placement, so even though IMCA says nothing about valve angle, the fact of the matter is that most non 23* heads require rocker shaft valve train, so in essence, IMCA is forcing a mod to stay with 23* stuff....
I would like to know the answer on this as well!Quote:
Originally Posted by anissa5