Camshaft questions

[gsr778]

Im getting ready to buy some new camshafts for my car but i need to know what the degrees mean. I cant seem to figure out which number is lift and which one is duration. I was also told that for N/A engines that a higher lift is better than a longer duration, is that true? And since i drive an integra with vtec would the degrees be in a different order? Any help would be greatly appreciated.

[DAEDALUS]

Could you give an example of the numbers you're looking at? Lift is usually around 1/2" roughly, and duration is probably 200-300 degrees. I don't know much about Hondas, but for the VTEC it seems you should have 2x as many numbers, since there are 2 sets of lobes if I remember right. But I don't recall if they're on intake, exhaust or both.

[Q45tech]

Peak lift is not as important as the lift area and ramp rate. Valve diameter and lift make the curtain area and above a certain point more lift doesn't do any good.

You must measure the valve to piston distance to make sure the exhaust valve don't hit at extreme rpm/heat.

[gsr778]

Sweet!!:ylsuper Thanks guys that clears up a lot for me. DAEDALUS: There are two sets of number for the vtec cams. The current cams that i am looking at are 250/295 and from what i can gather thats some fairly agressive profiles.

[gsr778]

in case your wondering the cams im looking at are toda racing spec c cams.

[DAEDALUS]

So both intake and exhaust cams are the same variable duration? I'll assume lift is the same in all cases. The VTEC is impressive. A buddy of mine has a (I think) '99 'lude. I rode in it once, and every time he floored it, it was like a switch was flipped and the car just took off like a scalded banshee everytime the RPMs rose above a certain point.

[gsr778]

Well i got the excact specs on the cams, but i cant figure out what the numbers in parenthesis means. Maybe you guys could tell me.

IN 250 (11.0) - 295 (12.5) - 250 (11.0) EX 250 (11.0) - 295 (12.5) - 250 (11.0)

Yeah vtec is really impressive. Its really nice in my car because i have a spoon ecu and it makes the dual intake runners open up at the same time (in vtec). So when i hit vtec the cars intake really signs a high and loud note. Usaully one intake runner open up at 4500 rpms (in most hondas with vtec) then the other one opens up upon vtec.

[DAEDALUS]

Don't know, but I would guess that those numbers are the lift (in mm). 11mm is .433", which sounds right. The 3rd sets of numbers seem redundant, but I don't know what the conventions are for specifying camshfts.

[MrFox]

Vtec cam lobes come in sets of 3 - the 2 low rpm rockers flank the center high rpm rocker.

[gsr778]

250 seems like a good degree but im not really sure. Ive heard people get 270 degree cams and thier car barelly idles. So will 250 idle fairly well or will the car struggle to stay alive?

[Q45tech]

Nissan uses [used before OBD2] 248 degrees on both intake and exhaust as it's perkiest oem cam duration.......Overlap is the key. Much beyond 15-20 degrees at idle is asking for it with 4 valve engines.

The Q VVT had 8 degrees at idle which shifted by oil pressure to 28 degress overlap at 1500 rpm........4600 rpm, then back to 8 degrees till redline... 248/248 ......9.9mm max valve lift on both.

[s13sr20chris]

hey sorry to threadjack but i gotta ask this. does anyone know why vvt retards back again at the very top end? i was wondering if they just wanted the power to drop off or what? by the way i think vtec is cool too, but if any of my honda lovin friends ask i always tell them the vvl is better just to make them mad.

edit: please disregard a retarded comment i made about vtc a few months ago, i was talking out of my bum without checking the fsm. i swear this question is totally legit and not retarded.

[Q45tech]

Once the runner air velocity is high [>4000 rpm] you don't need to open the intake valve early [1500>4000] what you want is the take valve to stay open later so the refelected wave arrives just in time to push the last bit of air in before the valve closes.Function of runner length and diameter and taper to plenum.

[s13sr20chris]

dude your kidding. thats what i really thought it was all along but i thought i would sound crazy or retarded. i swear. thanks!

[fredtoast]

in case your wondering the cams im looking at are toda racing spec c cams.

Toda spec c's are some of the biggest cams you can buy for the honda b18 engine.