Can anyone explain why high lift and long duration cams such as (toda b & c) causes piston to valve clearance issues in a ls/vtec with stock bottom end. Also what can be done to prevent this problem for happening. Thanks in advance.

 

I'll try, and I am sure someone will chime in if I am wrong...or if nothing else you get a bump.

The b series vtec head has 33mm dia valves and the nonvtec head had 31mm dia valves. Therefore, vtec pistons have 33mm valve reliefs and nonvtec pistons have 31mm valve reliefs. So, when you put a vtec head onto a novtec block (with stock pistons) you can see the problem that would arise if you retard/advance the timing too much...the valve could hit the piston, and this is with stock cams.

When you use high lift cams, the are essentially putting the valve farther into the combustion chamber leaving even less, if any, clearence for the valves.

 

You pretty much said it Jeff C, I really wouldn't recommend those cams for a stock bottom end motor.... First of all I hate stock bottom end motors because I really don't see the point of opening the motor up and atleast not tossing in some OE VTEC pistons and ARP rod bolts... That makes the motor a lot more "reliable" then slapping a VTEC head on a nonVTEC block... My friend has an EG with a stock bottom end LSVTEC... and i mean stock, the only thing that was swapped for their VTEC counterparts was the oil pump and water pump... With a GSR head and ITR cams it ran a 13.4@103 on slick which isn't real bad and again is nothing special... Now how much i trust that motor I do not know, he revs it to 8200 but that's a lot for not having rod bolts.... Okay now back to my main point, Toda B/C's, SK2 st 2/3, and JUN3's all are pretty similar with their lift/duration... They generate a lot of overlap which is good for high compression motors anywhere from say ~11.5:1+ I seriously doubt you could make any power with those cams and stock pistons... Rather than spending money on those cams i would buy pistons... OS OE will work fine, If you still wanted to use some cams like that I would go with P30 or PCT 81.25mm slugs.. If you still wanted to get some cams for a setup like that I would stick with B's if you use Toda... C's are probably just going to be more than you need, SK2 st 2's, and JUN3's would probably be cool too.. Before using any of those cams i would also probably recommend getting the head ported... Everything I use goes through Portflow and Tom there does awesome work.... You can see how this starts adding up... You'll probably need injectors ECU, a Hondata system would be good... Also before totally assembling a motor with those cams and pistons I would take the time to clay it... See how far you can advance and retard so you don't tap accidently later... Just have fun and remember that TUNING is everything.... No power without that.. Peace

 

Good suggestion...claying a motor.