MG MGB and MGB GT Tech Talk
So as most of you know I re-torqued the head and then adjusted my valves. As I did this I noticed that the Exhaust valves are opening a signifigant amount further than the Intake valves. Seemed kind of odd to me and was sure I had found a problem with lobes rounding off till i noticed that it is the same on all exhausts and all intakes.
So this is normal right? A signifigant amount more exhaust lift than intake?
not normal with a stock cam..........should all be the same....
A lot of aftermarket cams have a longer duration exhaust lobe that also happens to have a little more lift, so in that case it would be normal.
If you have some way to test your performance, you can actually play with valve lash slightly to alter the way the engine runs. For instance, loosening the exhaust lash by .003" and tightening the inlet lash by the same amount will sometimes yield a little better performance in situations where the exhaust side works really well.
I just happened to have this cam spec on my hard drive. On this grind, the lift for intake and exhaust are the same.
Derek, that Chambers cam is for sure a race cam, those duration numbers are at .050" not advertized, look at the center line note (103A3), I read that to be 103 center line advance 3 degrees to 100, for sure a race cams, I haven't heard of Chambers cams in a long time. Thats one hot grind, even by racing standards.
Interesting, thanks for sharing.
Oh oh! I'm the proud owner of that cam. Bought it on Ebay several years ago and stuck it on the shelf as a cheap spare. I'd assumed from the duration numbers (265/271) that it was a mild performance cam, like the Piper 270.
Maybe this Piper info will be big enough to read. :)
so.....back to the original post.........Jay has a problem. Lift should all be the same (or so close it wouldn't be easy to spot just by looking). Right guys?
balloonfoot Wrote:
Sorry, I wasn't planning to hijack the thread, rather to illustrate that there's usually little or no difference between inlet and exhaust valve lifts. As can be seen, the only one of the 4 that differs, it's only by 16 thou, not something that you're likely to notice by eye.
a stock cam has .250 lift on all 8 (plus whatever the rocker ratio turns out to be...no matter really). The real point is...they should all be the same, intake and exhaust. Any VISUAL difference means something is wrong...flat cam/cupped lifters probably. Funny that exhaust are all the same but different from intakes on his car.
A question for Jay.
Guys,
thanks for the help. I am planning to get myself set up with a mag base and actually measure the amount of valve travel on each and every one.
Strange thing is that the exhaust are very markedly opening further. Difference is almost the width of the valve spring retainer. and the down angle of the rocker is quite noticeably different from the exhaust valves to the intake valves.
Have some numbers in a couple days
Stating the obvious here. If you find the exhausts are all very close to one another, and the same for the intakes, then I think you'd be safe to assume you have some kind of unusual grind. The intakes would be what I'd scrutinize...if they vary from each other, then it's time to worry!
