magn1t wrote:
Just wondering if anyone has actually done this.
I know several people have either aftermarket cams or camgears or both.
Low cam
In opens 27 btdc
in closes 60 abdc
ex opens 60 bbdc
ex closes 24 atdc
So that gives an overlap of 51 deg
in duration 267 deg
ex duration 264 deg
High cam.
in opens 54 btdc
in closes 102 abdc
ex opens 85 bbdc
ex closes 39 atdc
So that gives an overlap of 93 deg
In duration 336 deg
ex duration 304 deg
Should be correct to +- 2 deg apart from error with tapet clearance.
Steve
Just bringing this back up from the dead.
I've been thinking for ages that the best way to do this is with a standard unmolested engine that's never been pulled to bits.
So that's now what I've done .....numbers to follow.
So what I've actually done.......Diamante 30M engine, I've had it sitting complete for a few years, got the spun bigend mod. I've stripped it down to the cambelt, removed covers and brackets.....roughly confirmed that the tappet clearances are correct then measured several points with a dial gauge. I'm using the same flywheel and pointer setup at TDC and 3.076 deg per tooth.
Starting with the original numbers above of (IO,IC,EO,EC) 27, 60, 60 ,24.
Those numbers changed later with tappet clearance and modified camgears.
Ended up with 33, 56, 52, 18,for the small cams and 51,94,77,30, for the big cams.
I still wasn't happy with the numbers.That was all back in 2009.
The new numbers are for a proper 30M engine
Now we have, small cams 18.5(21.5), 67.5(63), 72(72), 38.5(38.5), the numbers in brackets are for cylinder no 4.
The big lobes 33.8(33.8 ), 93.8(96.9), 94(94), 57(54).
So adding up numbers the int duration is 266(264.5), ex 290(290) and int dur big cam 307.6(310.7), ex 307.6(310.7).
The overlap is 56 deg on the small lobes and 89 deg on the big ones.
The intake cam lift is, 3.6mm, valve lift 6.8mm small cam.
big int cam lift 5.8mm, valve lift 9.5mm.
Small ex cam lift 4.2mm, valve lift 7.5mm.
Big ex cam lift 5.6mm, valve lift 9.5mm.
Peak lift small int 103 BTDC, centreline 110 BTDC.
Peak lift small ex 106 ABDC, centreline 107.5 ABDC.
Peak lift big int ummmm, centreline 119 BTDC
peak lift big ex 109 ABDC, centreline 106.75.
So next step is to re adjust the tappets.
More measurements.
Going back to the original post on this subject. I don't know whether I mentioned it but I got my numbers to change when I modified the camgears. I'm not interested in adjustable camgears but I modified the originals by shifting the locating slots sideways....because I can.
edit, measured, adjusted tappets.......re measured valve opening/closing, changed the numbers.
A difference of .15mm valve lash can make a difference of 6 degrees at each end of the cycle.
The exhausts were at .25mm lash measured with the dial gauge, one intake was OK ish at .15 but the other was at .20. The proper spec is .10 intake and .20 exhaust.
Steve