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Vfr848Rr Anyone ?


Mohawk

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I was not referring to the guys who know what they are talking about. Phil is probably right about better flow with the wider bore.

That site is great forthe base info, but yu have to check the valve lift for degree measurements, as they vary a lot, so some valves with long duration are much shorter, when measured at 1mm lift rather than 0.3mm etc.

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So our Vfr has steel 29mm intake and 24.5mm exhaust valves. The 2010 zx10r has 24.5mm exhaust valves, and the 2008 gsxr750 has 29mm intake valves, both of which are of the correct 4.5mm valve stem and are made titanium. Hmmmmmm anyone have a clue what the correct valve lengths are?? I believe you can have the valve seats coated and run titanium valves. This would allow us to run big cams and high RPMs while needing less valve spring to do so. I want to look into this.

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So our Vfr has steel 29mm intake and 24.5mm exhaust valves. The 2010 zx10r has 24.5mm exhaust valves, and the 2008 gsxr750 has 29mm intake valves, both of which are of the correct 4.5mm valve stem and are made titanium. Hmmmmmm anyone have a clue what the correct valve lengths are?? I believe you can have the valve seats coated and run titanium valves. This would allow us to run big cams and high RPMs while needing less valve spring to do so. I want to look into this.

I'm pretty sure APE installs valve seat inserts if you switch to Ti valves... don't know about coatings
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As far as I am aware, you only need to change the valve seat for Ti valves to add to the cooling effect on the valve itself.

It has nothing to do with wear and Beryllium copper was the material of choice in racing engines with Ti valves.

If the motor is not being raced, then I'd have to ask the questions

1. Are Ti valves really necessary?

2. If Ti valves are used, what is the expected operational cycle for the engine? Is it going to be revved flat out for extended periods of time.

If the answer to 2 above is no, then you may as well not worry about the seat situation.

when I built my VF750 based superbike in the 80's, I ran Ti valves on the standard seats to 13k RPM with out issue.

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These guys here specialise in Ti components for WSBK and other forms of motorsport.

http://www.titanium-valve.com/

They will make valves and seats/guide to whatever you want.

Speaking of guides.

Ti valves should be run in bronze guides to help dissipate the heat.

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  • 10 months later...

Hi Guys

The following shot is of my Gen5 head and the enlarged head gasket (74mm dia) to suit my 929 bore.

The standard valve head diameters are:

Inlet 29mm

Exhaust 24.5mm

Even with the 2mm bigger bore the valves are pretty close to being shrouded by the bores.

I think it will flow more with the 74mm bores than the 72mm as there is less interference.

attachicon.gif20140831_162643.jpg

Cheers

Phil

That's a great shot.

It does beg the question. Since the heads are off the cases, so that they cylinders can be enlarged, why not have the edges of the combustion chamber "laid back" to meet the new cylinder bore?

It would help the head's flow characteristics and add a few cc's to the chambers volume to help with the compression ratio...

Just some rough calculations.. Using the stock bore & stroke, the stock CR and calculating the compression volume.

Removing 1cc worth of metal from the chamber would drop the CR to 11.1

Does anyone know how the head gasket is??

Another thought,

While the heads are off, has anyone considered o-ringing the cylinders? Or are we all thinking of using the MLS gaskets from Cometic?

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Yes, I did open the chambers up to match the new bores. Best not to shroud the valves if at all possible.

The opened up head gasket is 3.44cc in volume. (per cylinder)

My measured chamber volumes etc. have given a CR of 12.36 and with my cams a dynamic Cr of 11.04

Cheers

Phil

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Yes, I did open the chambers up to match the new bores. Best not to shroud the valves if at all possible.

The opened up head gasket is 3.44cc in volume. (per cylinder)

My measured chamber volumes etc. have given a CR of 12.36 and with my cams a dynamic Cr of 11.04

Cheers

Phil

Phil, I'm try to vet my calculations, how thick was the head gasket after compression??

I'm coming up with .799 mm and a negligible cc gain in the Head's chamber...

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I would say your calculation on thickness is correct.

The volume difference is based on going from 72mm to 74mm

Standard it is about 3.26cc with 3.44cc for the 74mm bore

I do not believe there is a need to go with bigger valves as even the HRC RC45's ran 29mm inlets and 24.5mm exhausts, same as stock VFR800

My calcs show that these sizes can pass enough gas to be able to support 170-180 HP

Phil

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I would say your calculation on thickness is correct.

The volume difference is based on going from 72mm to 74mm

Standard it is about 3.26cc with 3.44cc for the 74mm bore

I do not believe there is a need to go with bigger valves as even the HRC RC45's ran 29mm inlets and 24.5mm exhausts, same as stock VFR800

My calcs show that these sizes can pass enough gas to be able to support 170-180 HP

Phil

Okay,

Did you cc the head to see how much your blending back the chamber periphery might have added?

It wouldn't take much to add a couple of cc's and they will drop the CR pretty fast.

I'd even bet a good de-shrouding and matching to the new bore would keep some of the bigger bore jobs from breaking 12:1.

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You would be suprised as to how little the blending added to the chambers as the radius in the chamber is quite shallow.

I volumed all the chambers and piston crowns and ended up with the following.

Chamber = 14.4cc

Piston crown @ 3mm = 13.2cc

Gasket = 3.44cc

This ended up with a Working chamber volume of 18.14cc to 18.20cc across all 4 chambers

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  • 7 months later...

Check this out. While this would be totally unnecessary over kill on a stock vfr800, it would be a great idea for those wanting to do major over bores like 74 or 75mm. You could support the cylinders and then bore to 75mm, then oring the deck. This would allow for a huge overbore, while not compromising cylinder strength or head gasket sealing.

http://www.cylindersupportsystem.com/

http://www.b20vtec.com/forums/threads/808207-Proven-alternative-to-sleeves-CSS(cylinder-support-system)!!!

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Check this out. While this would be totally unnecessary over kill on a stock vfr800, it would be a great idea for those wanting to do major over bores like 74 or 75mm. You could support the cylinders and then bore to 75mm, then oring the deck. This would allow for a huge overbore, while not compromising cylinder strength or head gasket sealing.

http://www.cylindersupportsystem.com/

http://www.b20vtec.com/forums/threads/808207-Proven-alternative-to-sleeves-CSS(cylinder-support-system)!!!

Interesting... looks like he is familiar with Honda cars; someone would need to work with them to develop a VFR800 CNC file for our block. I think MrCarver was thinking big bore...

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