Dear Diary,
The valve spring problem.
So here's the issue, briefly. I am going to be running the KMCams Stage2 cam (more agressive profile, 292°, 10.2mm lift) with KMCams steel rockers; and going to be revving the engine to 6800-7000rpm. I had a gut feeling that the stock B35 springs will not hold, so I contacted Kenneth@KMCams to suggest me some values. After some discussion, we agreed on the following values.
The springs should have a seat pressure of 35-40kgs. He stated that over 40, the rockers may get damaged at it's too much.
So, off I went to find myself some springs. Here are the options.
1. Run the stock B35 dual springs
I measured the dimensions of the B35 springs and I ended up with the following values for springs rates (calculated)
33kg @0mm (72.7lbs)
3.46kg/mm (19.4 lbs/in)
68.3kg @10.2mm (150.5lbs)
Not quite 35-40kgs.
2. Space the stock B35 dual springs
I was recommended this before and it sounds like it *would* work.
Spacing it 1mm would give me the following results:
36.46kg @0mm
71.7kg @10.2mm.
So this is plenty.
But here's the issue. According to my calculations, the main spring bottoms out at roughly 25mm. There's also some measurements of coil bind at 24.41mm (thanks, Luke!).
Based on this... L1 -1 -25 -10.2 = 0.8mm.
I'm not sure if I'm comfortable with this - that's not a lot of gap (and also, more stress on the stock springs).
Does anyone have experience with this? Please let me know.
3. PPF retainers
The same as above expect the PPF retainers do the job instead of getting spacers. I was informed that they space the springs down by 1.0mm, but I'm waiting for confirmation.
UPDATE 1!
Their retainers do not space down the springs.
UPDATE 2:
Even tho PPF says their retainers don't space down the springs, they DO. So watch out for this.
4. PPF stage 1 springs
45kg @0mm.
Kenneth said these will damage the rockers, so unfortunately not an option.
(This is also just stage 1, stage 2 is 68kg??)
UPDATE 1:
AB from PPF just messaged me back.
They state that they have been running KMCams rockers with these springs and had no issues whatsoever.
Secondly, he gave me more specs for their springs.
44kg @37mm
81kg @15.5mm (coilbind)
So their spring rate is 2.38kg/mm ---> less than stock?!
For my engine:
44kg @0mm
68.4kg @10.2mm
Looks like their spring has more inital seat pressure, but less strength later on. This is quite much the same as the OEM B35 springs.
THIS IS VERY WEIRD TO ME.
Does valve float usually appear on these engines at low lift?
UPDATE 4:
These are turbo engine valve springs, that's why it's weird. More valve float protection is not really needed, but the seated pressure is higher to protect against the exhaust pressure opening the exhaust valves.
5. Schrick springs
I've found a set of Schrick springs that state "for M20/M30"
000202090
270N @38.5mm
880N @26.5mm
--> 50.8N/mm
Let's translate this to my engine.
35.3 kg @0mm (stock retainer height of 37.0mm)
88.2kg @10.2mm
The spring is juuust long enough when compressed - 26.8mm, and Schrick states that I need a minimum of 26.5mm.
I think so far, this is my best bet, but I will ask Kenneth (as we only ever talked about installed strength.)
This is a single spring, I need to ask Schrick if it will fit my B35 dual retainers. (ofc, I can measure myself, but I just want to make sure)
For fun, I just wanted to see what would happen if I paired this with the stock small springs.
5kg @0mm
14kg @10.2mm
40.3kg @0mm
128.5kg @10.2mm --> OK, this is overkill.
6. DBilas springs
Literally no info on them whatsoever
I'm hoping to resolve this soon, as I cannot continue due to this issue.
I'll update this soon with my choices and answers from Kenneth, PPF and Schrick
Regards
Dave