Head work
- Thread starter karlj
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frank
Club Member
the GA ones are bigger and have the same size stem, but they,re 3mm shorter iirc karl, and SR etc are fatter stems
OP
OP
you going for an N/A screem Karl?
Hopefully
Do you know which valves ebbdude used? (Can't seem to find his thread on my phone)
frank
Club Member
"another jap car" mate, 1.6mm bigger
Hopefully
Do you know which valves ebbdude used? (Can't seem to find his thread on my phone)
I wouldn't worry about not being able to find his blog, you wont find anything helpful there except for them being 1.6mm larger. EBBdude was always vague enough to omit such information despite being questioned, (very Norwegian behavior by the way). Remember though, they were not his perfect choice
I agree with EBBdude though, his valve choices were less than ideal. I don't know why he bothered to go so large on the inlet valves, nor why he increased the size of the exhaust valves. Given the setup and the vast tuning experience, the latter was very surprising to see even though they were free and were in his garage.
As far as the inlet valve sizing goes, any increase in area could be considered compromised by valve shrouding, (there's little room there to work with). The CG series engines weren't blessed with a big bore, so things are pretty tight from the factory. The most I would go would be +1mm and even that's pushing the limits in terms of benefits. The only way to increase things significantly would be to offset guide the head and that's a whole lot of work and was already tossed out as an option by us in our build.
Unless you're going to really push things I'd spend money elsewhere first rather than on the cylinder head. The standard heads are pretty good from the factory and pretty much 100bhp/liter out of a standard head on a pathetic 8:1 DCR engine should support that theory. The NME boys used to say, unless you're looking to push more than 130bhp there's little to find in the head. I am sure Paul Smith will testify to that. There was 5bhp between out setups and that was likely down to the difference between a CG13 and CGA3.
Not trying to put you off though. Whatever floats your boat and all that
OP
OP
It's info like that, that saves money
So I was right in saying that apart from the usual there isn't much point
A 1ml head skim will help a good bit.
and saying im getting rid, gauging interest a lot .dont help the bhp,,,,,,,,,,,,,,,
OP
OP
OP
OP
and saying im getting rid, gauging interest a lot .dont help the bhp,,,,,,,,,,,,,,,
Shh
euro_micra
Matt :)
You could double-up on the spring washers to make the springs more firm, IIRC ebbdude also pointed this out in his blog. But I'm unsure if anyone else has tried and reported back about it. My head has this but it's off the car untested atm.
I'd also go with CR buckets and underbucket shims for a n/a screamer, even if stock cg is fine, I'd do it for peace of mind.
I'd also go with CR buckets and underbucket shims for a n/a screamer, even if stock cg is fine, I'd do it for peace of mind.
Yes, I have seen people do this to gain more seat pressure from an OEM spring. Since EBBdude's philosophy was to use only modified OEM parts, (which he stuck to for most of it), it was a valid option. Also, given the home brew cam grinding which was still tame in terms of lift and duration it wouldn't pose much of an issue and was more than likely done so he could keep things in spec better at higher rpm even though his engine was out of puff beyond 7200rpm. He seemed to want it to rev past 9000rpm to allow him to hold it in gear on sprints to save gear changes.
The standard biscuit shims limit the follower to an effective 28mm diameter due to the shim size. Swapping to a CR lifter for example brings that back out to a true 30mm follower which is much kinder to the valve train, eliminates the possibility of throwing a shim out with an aggressive cam and provides a larger window for cam selection......not to mention the fairly significant weight reduction.
CR buckets are a nice idea and piece of mind for some people is a very strong motivator indeed. I would imagine the approach of modifying a standard bucket would yield similar results as a lower cost option. Frank, (who in my mind had already done and proven the majority of EBBdude's work already), has done this with no issues.
Incidentally EBBdude has sold Maxi Micra, so there will be no more vague updates of any kind.
I meant on his website.
Cool late night, early morning doesn't work in favour of my brain
Does it matter which CR engine?
No, CR's like the CG's share the same head between models.
I seem to remember Frank saying the CR valve's have longer stems, so one would need to perhaps fiddle somewhere or rob a CR engine of the valves also. Valves in terms of size, (IN 27.5mm & EX 22.5mm), are the same by the way.
The spring rate will remain constant yes, (F = kx), but you can increase the closed seat pressure by increasing the static preload, which will have a corresponding offset in force when fully open, assuming one doesn't go coil-bound >.<
Personally, I scrapped the entire OEM valvetrain and started again but with the lift we wanted to run there was little choice and even then things require fairly extensive modification to work.
frank
Club Member
hmm, so the increase of pressure from 52kg to 65kg is not down to the extra washer then (maybe down to being near coilbound ?).
but the slightly higher static preload while the valve is closed will deter valvebounce a tad maybe ?
I don't understand the context of 52kgs v's 65kgs. However, regarding static preload, that was my thought too. I am sure there will be other things to consider perhaps, such as ramp angle and valvetrain weight as to how effective it is but it sounds like the ASDA approach
frank
Club Member
Ah ok.
From the photos, it looks like he will have set the spring to the corresponding installed height in the head, (left photo), then shimmed it to get the desired increased load at the same installed height, (right photo), to meet his desired spec.
frank
Club Member
but if the springrate always stays the same, then the extra preload will only alter the closed pressure, and the pressure while opening the valve will be the same on both setups.
ie, if he measured the pressures half open, the dial would read the same on both
Actually, now with my eyes turned on, the loads are actually 52 and 65lbs. Given that he used a 1.03mm additional shim thickness, this puts the K11 valve spring rates at approximately 320lb/in.
Remember one spring has been subjected to additional displacement due to the installed shim. This additional displacement is present throughout the springs entire range of displacement relative to valve lift.
but if the springrate always stays the same, then the extra preload will only alter the closed pressure, and the pressure while opening the valve will be the same on both setups.
ie, if he measured the pressures half open, the dial would read the same on both
Remember one spring has been subjected to additional displacement due to the installed shim. This additional displacement is present throughout the springs entire range of displacement relative to valve lift.
frank
Club Member
same number of coils, same spring, therefore same springrate.
surely only the valve closed preload has changed ?.
my conclusion is that the fact that the spring is more coilbound with the extra washer in, its registering more poundage ?
my heads have no washers in at all (so i could run the 260deg/10mm lift cams)
Yes, all identical, so the rate of change relative to displacement, (valve lift from the cam), will indeed remain the same, (F = kx).
Yes, valve closed preload has changed due to adding an additional shim and displacing the spring to give additional poundage.
With the increased preload, the spring has effectively been compressed by valve lift + shim thickness relative to it's free height, so has been compressed further than before, thus giving a higher final load when fully open.
No washers at all, I'm assuming that's to stop the coils binding or the retainer hitting the top of the stem seal rather than a function of spring load?
We upped the spring, went for just over 11mm lift and modified the guide boss area to stop stem seal/guide contact, which is an issue at that level.
pollyp
Club Member
when i first disassembled the spare engine from the turbo kit i won off ebay yrs ago (prob from kristians car) i noticed a lower groove for the collet had been lathed on all the valve stems to induce more preload maybe to reduce valve bounce?
correct me if wrong but I've drawn a force/displacement graph of a coil spring (assuming it behaves roughly linear before coilbound) and plotted the movement of the valves.
now if the cams are the same and so the displacement/lift of the valves are the same distance, by compressing/shortening the coilspring more via lower collet or washer spacers we've moved the min/max range up the graph from red region to the green region which results in a higher force overall.
meaning the moment the cam starts to touch the bucket, the spring/bucket will be pushing harder against the cam throughout the valve travel from fully closed to fully open
correct me if wrong but I've drawn a force/displacement graph of a coil spring (assuming it behaves roughly linear before coilbound) and plotted the movement of the valves.
now if the cams are the same and so the displacement/lift of the valves are the same distance, by compressing/shortening the coilspring more via lower collet or washer spacers we've moved the min/max range up the graph from red region to the green region which results in a higher force overall.
meaning the moment the cam starts to touch the bucket, the spring/bucket will be pushing harder against the cam throughout the valve travel from fully closed to fully open
frank
Club Member
nah, the springrate/load stays the same surely ?, like when you alter the preload on coilovers, it does,nt make the suspension any softer or harder
pollyp
Club Member
the spring rate (angle of the line on the graph) of the coil spring stays the same.
preload is measured between the springs natural length and how much it's compressed when the damper/valve shaft is fully extended under zero load.
preload on coilovers affect how much load it takes before the fully extended damper shaft begins to deflect.
this example is assuming a linear non-progressive spring rate.
- if the preload is less or equal to the cars static corner weight, then the suspension behaves as the spring rate is determined. preload ring mainly affecting ride height.
(ie a 6kg body rests on a 6kg/mm spring with zero deflection. when it hits a bump/step, for every 1mm of compression the spring would push up against the chassis at that instance by 6kg. that force will now try to extend the damper between an immovable object (wheel on solid ground) and the 6kg suspended body via basic physics Acc = Force/Mass until the damper has returned back to its equal resting position)
- if preload is more than the cars 6kg corner weight (say 12kg preload), the damper is now fully extended so doesn't affect ride height but for every 1mm of compression the spring would push up against the chassis at that instance by 6kg PLUS the 12kg induced preload = 18kg. that 18kg force will now try to extend the damper (move the 6kg body up) until its back to its resting position in a much quicker time resulting in a higher Acceleration/G = harsh ride
Now on a valve spring, spring rate affects the difference/bias between the highest/lowest force the bucket is pushing against cam during each stroke, while preload affects the overall level of force applied to the bucket/cam.
you'd want the valve/bucket to be in constant touch with the cams profile at all times throughout each stroke. as the cam revs faster, the valves have to be able to accelerate more in order to keep up with the cam lobes profile. their acceleration is Acc = Force/Mass so by increasing force via preload or reducing the valves mass, they're able to keep up at higher revs and prevent the valves from being out of synch potentially smashing into the piston or causing compression leaks.
i wonder if the increased overall force between the buckets & cams will squeeze the oil away from the contacting surfaces and cause increased wear?
preload is measured between the springs natural length and how much it's compressed when the damper/valve shaft is fully extended under zero load.
preload on coilovers affect how much load it takes before the fully extended damper shaft begins to deflect.
this example is assuming a linear non-progressive spring rate.
- if the preload is less or equal to the cars static corner weight, then the suspension behaves as the spring rate is determined. preload ring mainly affecting ride height.
(ie a 6kg body rests on a 6kg/mm spring with zero deflection. when it hits a bump/step, for every 1mm of compression the spring would push up against the chassis at that instance by 6kg. that force will now try to extend the damper between an immovable object (wheel on solid ground) and the 6kg suspended body via basic physics Acc = Force/Mass until the damper has returned back to its equal resting position)
- if preload is more than the cars 6kg corner weight (say 12kg preload), the damper is now fully extended so doesn't affect ride height but for every 1mm of compression the spring would push up against the chassis at that instance by 6kg PLUS the 12kg induced preload = 18kg. that 18kg force will now try to extend the damper (move the 6kg body up) until its back to its resting position in a much quicker time resulting in a higher Acceleration/G = harsh ride
Now on a valve spring, spring rate affects the difference/bias between the highest/lowest force the bucket is pushing against cam during each stroke, while preload affects the overall level of force applied to the bucket/cam.
you'd want the valve/bucket to be in constant touch with the cams profile at all times throughout each stroke. as the cam revs faster, the valves have to be able to accelerate more in order to keep up with the cam lobes profile. their acceleration is Acc = Force/Mass so by increasing force via preload or reducing the valves mass, they're able to keep up at higher revs and prevent the valves from being out of synch potentially smashing into the piston or causing compression leaks.
i wonder if the increased overall force between the buckets & cams will squeeze the oil away from the contacting surfaces and cause increased wear?
A decent oil with a good level of ZDDP will help that.
pollyp
Club Member
ah ok
Yeah thats right1 liter pistons do the same
frank
Club Member
ehh, what are you on about dave ? its the same principle as suspension preloadHa ha very funny. I'm not falling for this prank any longer
we both agree that the springrate stays the same whatever the preload is.
and the cam lobe just compresses the spring (10mm in my case)
so a 1kg/mm spring will need 10kg to open the valve/compress the spring 10mm wont it ( it does,nt matter how many washers you fit, it will always need 10kg to open the valve, and if you remove the 10kg it will close)
so the only thing you are changing with preload, is the pressure of the valve on its seat when its closed (not the force @ full lift, ie, erik,s dial gauge)
Enuo
Glorified Electrician
with preload the spring rate stays the same, however until the cam is exerting the same or more force than is all ready pre loaded, there will be very minimal travel. displacement = force x spring constant. But the spring is already displaced, so you need to match or beat the preload to carry on displacing the spring if that makes sense.
ehh, what are you on about dave ? its the same principle as suspension preload
we both agree that the springrate stays the same whatever the preload is.
and the cam lobe just compresses the spring (10mm in my case)
so a 1kg/mm spring will need 10kg to open the valve/compress the spring 10mm wont it ( it does,nt matter how many washers you fit, it will always need 10kg to open the valve, and if you remove the 10kg it will close)
so the only thing you are changing with preload, is the pressure of the valve on its seat when its closed (not the force @ full lift, ie, erik,s dial gauge)
Compress them both by an additional 10mm, (assuming they wont go coilbound), and tell me what the resultant spring loads are.
frank
Club Member
whats that got to do with it dave ?
i said
which are correct, and you said
which i dont buy
frank
Club Member
yes, and stays at the same 1kg per mm with preload or without preload, just like preload on your suspension wont make it any harder or softer, and will only effect the static height of the car
pollyp
Club Member
ehh, what are you on about dave ? its the same principle as suspension preload
we both agree that the springrate stays the same whatever the preload is.
and the cam lobe just compresses the spring (10mm in my case)
so a 1kg/mm spring will need 10kg to open the valve/compress the spring 10mm wont it ( it does,nt matter how many washers you fit, it will always need 10kg to open the valve, and if you remove the 10kg it will close)
so the only thing you are changing with preload, is the pressure of the valve on its seat when its closed (not the force @ full lift, ie, erik,s dial gauge)
the spring "rate" (force/displacement) generally remains the same value at the temperature it's measured from and is measured From its natural length (zero kg = zero displacement).
the positive incline of the graph dictates the more a spring is displaced from its original natural length, the greater the reactive force the spring applies to the mechanism its pushing against.
the rate of incline of the graph (how steep) dictates the amount of reactive force applied for every unit of displacement.
"pre" load, as the term suggests, is the initial extra force the mechanism applies on the spring by displacing from its natural unloaded length before any external forces (you, road, cam lobe, etc) is applied. the external force must be greater than the preload before the spring displaces further.
on valves we use preload to force the valve against the sealing seat when closed.
ok from a valves perspective:
preload defines how much minimum force the cam has to apply against the spring before the valve seating pressure reaches zero and begins to "move/displace/unseat" from its closed position
while spring rate defines how much additional force the cam has to apply "on top of" the preload before the valves reach their maximum stroke, displacement, lift etc
from a cam lobes perspective:
preload defines how much minimum force the valve bucket is gonna apply against the cam lobe when the valve seating pressure reaches zero and begins to "move/displace/unseat" from its closed position
while spring rate defines how much additional force the bucket is gonna apply "on top of" the preload before the valves reach their maximum stroke, displacement, lift etc
too much preload = higher forces between cam/valve throughout stroke = higher frictional loss = higher energy loss & higher wear if beyond oil film strength
too much spring rate = higher forces between cam/valve towards the peak of the lobe = higher frictional loss = higher energy loss & higher wear if beyond oil film strength near peak valve lift
the extra energy produced from altering the valve preload & rate must out-weigh the increased frictional losses before we gain additional peak power or efficiency
extremely excessive preload = cam can't unseat the valve = cam jams = tries to slow down other engine bits = things begin to break or stall
extremely excessive spring rate = cam can't fully open the valves = cam jams = tries to slow down other engine bits = things begin to break or stall
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