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Cam timing on a O/C 1340

4K views 13 replies 7 participants last post by  1216 Bandit 
#1 ·
I just finish building up my first big block gsxr. Its got cam motion cams in it i g21 e g28 and I've degree them to a 110 center line. After lots of research and reading I'm not sure thats the best setting to start with and if I need to change it I'd like to do it while its on the bench. Motors 13.5 to 1 compression, 30/26 valves, ported and 40mm mikuni flatslides.
 
#3 ·
Is this a street bike or a drag bike? Big difference where you would set them if it's a street bike. Also, the exhaust cam #s need to be two bigger. Like if it's a drag race motor you would go 110/112. on a street motor I would go 107/109 as long as you have piston to valve clearance.
Ray.
 
#4 ·
Don't start moving things till you measure P to V where the cams are at.
Closest is 8 degrees BTDC for the exh and 8 degrees ATDC for the intake (IIRC...been a while guys)
IIRC, 2 degrees of cam timing gained/lost .010" P to V..
I made a chart tracing P to V with both intake and exhaust cams and then started moving the cams.
I sold the motor and it was resold, The new owner thought 110-112 was NG and set the cams at 106-108.
Couldn't figure out why the motor slowed down....till he found bent intakes.
.050" P to V on the intakes and .075" P to V on the exhausts minimum...
 
#8 ·
Just to be clear...you checked intake V to P at 8 degrees ATDC and exhaust V to P at 8 degrees BTDC? Reason I asked is that sounds like an awful lot of clearance.
I usually start to check maybe 20 degrees before and go to 20 degrees after, plotting every 5 degrees or so on both cams.
 
#11 ·
Naturally Aspirated? I set to the tightest limit = but you have to have good valve springs and an expert operator - no constant over revving and proper deck height allowing for sling out tolerance for 10K rpm. = P-V int 0.080" exh 0.050" and V-V 0.060" - my tight spots are closer to 11 not 8 degrees. let the LC numbers be whatever your combo allows (static deck height main factor). there is no secret combo. you'll get the most overlap and the best mid to high range power -- Idle will suffer and lope under 1500rpm - cam mfg advertise 108 or 110 equal I&X because nothing will hit each other - and idle is good -- but will create a midrange dip in power. it is a give and take - nothing is gained.
I have been running 103 and 115 in a 9.0 second GS,, my 98 1200 bandit #'s have a little have less spread.

just be careful if you decide to have a tight tolerance engine.
 
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