Building up a mean F head

[Sam_Q]

once again thanks heaps Bill. If I did this it would be over the course of a long period of time because such as yourself I have many other commitments. To optimise it for power and economy I would have stock cams or a mild grind depending on what it has standard. Cams arnt really my area but I was thinking something along the lines of 260 degrees and 8.5mm lift.

For the inlet I have orgniased some quad throttles, for which I need to get a block of aluminium and make my own manifold. It would likely be a single peice and have an integral chamber at the bottom for a mini-plenum for brake vacuum.Considering that I am about the start the milling part of my tafe course and I have no experience I would say this is going to take quite a while... oh well I am patient.

with your rods I would really recomend using 4340, first off to ditch that current buisness your dealiing with because they are obviously not worth your time, and secondly for the nature for titanium to fatigue (although open to debate). So if you were to get your rods how long do you think it would take to build your engine? I am guessing 2 years for me.

[abently]

Best advice you will get, is to go for as much lift as physically possible.

That means, check how much Valve - Piston clearance you have @ TDC and that will give you the max ( minus clearance value of 1-1.5mm) allowable lift @ TDC. This affects your ramp rate around this point and the total Area under the curve. The bucket diameter & shim arrangement will also play a part on max lift velocity per each degree, but most professionals like Tighe and Kelfords will sort it out once they know the physical constraints of the Engine.

Duration affects your RPM range, lift only costs you a bit heavier springs, ie a few Hp but the difference in Area (and Hp) between an 8.5mm camshaft and running 12+mm lift is substantial.

[abently]

Forgot to mention, you will most likely need to machine/die-grind the Head around the cam lobes path running that much lift, but it won't be much.

[takai]

1-1.5mm clearance..... thats huge. Heck even my non-built atmo engine is running about 0.5mm.

[abently]

1-1.5mm clearance..... thats huge. Heck even my non-built atmo engine is running about 0.5mm.

Depends on too many things, Kelfords would be the best to ask on how much clearance you can safely get away with.

[oldcorollas]

Depends on too many things, Kelfords would be the best to ask on how much clearance you can safely get away with.

how much rod stretch are you expecting?

given that he is only thinking of relatively stock cams (???) and so valve springs should be easily able to prevent float...

[ed]

why does the universe rotate around kelfords... i dont get it...

anyway, id agree with a 60thou valve-piston clearance
and a 30thou piston-head clearance

based on a generic forged steel rod and a hefty rpm

[abently]

Go to the Kelfords custom Cam design webpage and there are a few hints there which if you understand, tell you they are amongst the top of the game worldwide.

Anyhow, Piston weight affects stretch so up to him if he wishes to use Factory pistons......

Bumping the CR up a point or 2 helps null the negative affects of longer duration camshafts on drive ability.

[Sam_Q]

Best advice you will get, is to go for as much lift as physically possible.

That means, check how much Valve - Piston clearance you have @ TDC and that will give you the max ( minus clearance value of 1-1.5mm) allowable lift @ TDC. This affects your ramp rate around this point and the total Area under the curve. The bucket diameter & shim arrangement will also play a part on max lift velocity per each degree, but most professionals like Tighe and Kelfords will sort it out once they know the physical constraints of the Engine.

Duration affects your RPM range, lift only costs you a bit heavier springs, ie a few Hp but the difference in Area (and Hp) between an 8.5mm camshaft and running 12+mm lift is substantial.

if I was in it just for all out power then yes you would be right, otherwise you are way out. if there wasnt a downside to running a huge cam then they would do it from the factory. I want to still have as good a low down power as what I do now with my silvertop and massive lift as I understand it will make me have a rougher idle, less low end power, worse fuel economy, driveablity, etc...If I do go ahead with this I will have higher compression, which will help.

So whats the verdict on what is a good cold valve to piston clearence? 1mm?

Ed: thats a pretty tight piston to head clearence, thats without the head gasket?

[Billzilla]

once again thanks heaps Bill. If I did this it would be over the course of a long period of time because such as yourself I have many other commitments. To optimise it for power and economy I would have stock cams or a mild grind depending on what it has standard. Cams arnt really my area but I was thinking something along the lines of 260 degrees and 8.5mm lift.

For the inlet I have orgniased some quad throttles, for which I need to get a block of aluminium and make my own manifold. It would likely be a single peice and have an integral chamber at the bottom for a mini-plenum for brake vacuum.Considering that I am about the start the milling part of my tafe course and I have no experience I would say this is going to take quite a while... oh well I am patient.

with your rods I would really recomend using 4340, first off to ditch that current buisness your dealiing with because they are obviously not worth your time, and secondly for the nature for titanium to fatigue (although open to debate). So if you were to get your rods how long do you think it would take to build your engine? I am guessing 2 years for me.

It should only take a couple of months, as I have the crank, can prep the block pretty quickly, the head won't take more than a couple of weeks, and I just have to fabricate up the manifolds. Plus then some of the fiddly stuff.
I'll be running it wet-sump initally then going to dry-sump after a few months.

FWIW the cams I'm going to be running have 0.440" lift.

[abently]

...I understand it will make me have a rougher idle, less low end power, worse fuel economy, driveablity, etc...If I do go ahead with this I will have higher compression, which will help.

Worse Fuel Economy = Product of Overlap.....
Drive ability = (Rpm range....) Product of Overlap.....
Less Low-end Power = Product of Overlap....

The only down-side to High-lift cams, with high-ramp-rates will be a slight idle difference, nothing more or less. The reason it isn't done from Factory is for NVH reasons with Idle and Warranty concerns.

[oldcorollas]

The only down-side to High-lift cams, with high-ramp-rates will be a slight idle difference, nothing more or less.

what about accelerated wear? more friction loses due to heavier springs required for valve control? and.. spitting shims/hitting edge of buckets?

are you sure about that claim?

[takai]

Much heavier springs, which cause much more wear on the valves and valve seats. Most shim over bucket will run the risk of spitting shims over about 8mm of lift and require much more attention to the wear patterns of the shims over time.

[The Real Roadrunner]

Best advice you will get, is to go for as much lift as physically possible.

but most professionals like Tighe will sort it out once they know the physical constraints of the Engine.

*cough* wouldnt use his cams if they were given to me *cough*

[takai]

*cough* wouldnt use his cams if they were given to me *cough*

Good for beating sticks so i hear.