Group Buy - Honda 400cc +1mm pistons -

[mlohmeyer]

Ya, you have the right idea, especially about claying it _after_ you have set your adjustable cams because adjusting the angle of the cam can put the valve right into the piston. Also, yes, it's easier to remove material to set the compression ratio. I just wanted to remind people that anytime you do something custom like a piston, don't assume anything - measure and check everything.

[racesupplies]

Thanks,I havent done such a small bore 4 valve engine before.I want them to leave a bit on the top,but put the valve cutouts like eveyone else.I have just been talking to them,I sort of started this,but handed it over to you lot to organise your group purchase.We have had their stuff before,they did my classic racer pistons.And a friend of mine imports GM speedway engines and uses their stuff.They need to know everyones requirments,I have been speaking to them this afternoon.Sarah said could the people she has emailed please get back to her with what they want.Mark is sorting all this,I was having some done so thought it might be of interest to you lot.Cheers Carl.

[CMSMJ1]

I'm crafting a mail to them as we speak and wanted to confirm the details in this thread before Ia asked some questons.

The main things I think we need to be aware of (and I'll be making 100% sure) is that all the talk of some 56s a few 57s and maybe a 57.5s is going to be invalid as a group buy.

Also - the additional material on the crowns - it will probably have to be all of them or none. I expect they want to knock out as many sets of the same exact piston as we can get the money for.

I'll ask about expansion etc for the compatibility with the boring process. In fact, I'll ask if they have any facility onsite or nearby to offer to do the work.

Personally - I want these for my road bike so 57mm RVF pistons for me.

[racesupplies]

Nice one Mark,I will keep my big nose out.

[mlohmeyer]

Again, I'm curious - does this pricing include rings? You said so, but are you sure? What are the rings? Are they making custom rings, or using something off the shelf. I ask because with all the crazy custom expensive stuff we've done, we've never been able to afford custom rings. We always had to make the piston fit some ring from another bike. --Thanks.

[racesupplies]

They include rings,they have them sorted.Mark will keep you up to date.Cheers Carl.

[CMSMJ1]

I'll ask them for specs etc.

[CMSMJ1]

1: The thermal expansion of the pistons – relating to the person who will bore these motors for us – is there a spec sheet with the pistons to confirm the material properties?

2: The rings – are these customer rings or off the shelf parts? Can they be bought separately if required?

3: Specifics of crown etc - I know Carl is after some higher compression pistons and has asked for a tall crown with the same valve cut outs. – if some wanted these and some didn’t – does this affect the group purchase?

4: related to 3 – if some people wanted 56mm and some 57mm or maybe 57.5mm – does this affect the group buy?

5: What is the expected piston weight with pin and rings for 56mm, 57mm and 57.5mm?

6: Do you have any facility, or associated companies that might complete the boring of engine blocks to match these pistons? Do you recommend anyone?

7: Are they 2 ring or 3 ring designs?

8: Do you have a picture from one of the previous sets that have been produced? I think a visual idea of what we will get will help any people who are undecided at present.

[g-force performance]

I'm also curious from the V4 guys, what a max *safe* overbore would be.

I don't have racing displacement requirements to deal with, and would like to use stock rods (cryo treated), but will balance everything.... so for an NC-30 what could I run, +2mm, +3mm ?

Hi Scottie:

You called me about this yesterday, sorry I wasn't able to talk (I am an Engineer for Kawi - it would be bad business to talk about Honda stuff at work )

We have been boring +2mm for the last several years. We have, on very rare occasion, seen the cast-in liner from HOnda bored off-center. This causes an extremely thin wall on one side. Just look at your liners and see that the thickness is fairly consistant around (it won't ever be perfect).

When we started this adventure to 450cc land, we picked up a bike that had the 444cc JE kit in it. The cylinders had punched through the sides of a couple of liners, so we decided that +2mm was the max we could safely go without requiring a re-sleeve. If you want to go with a re-sleeve (ouch, it was expensive) the guys at Millennium Technologies did a great job. For those of you in Europe, Perfect Bore would probably be the equivallent supplier of sleeves.

Mike Norman
G-Force Engine Development

[g-force performance]

I'd be happy with 57mm personally but want to know the weights of the pistons as more weight = lower revs...and lower reliability at the end of the day

The weight is the killer. I had the JE pistons which were anchors and they caused several rod failures. We have never seen a stock rod fail under any other circumstance in racing or street applications (unless it was from a spun rod bearig due to low oil).

If Omega can give you a weight estimate, you want something lighter than 97g for just the pistons and lighter than 133g for the whole assembly (piston, pin, rings & circlips) for each cylinder. For comparison sakes, here's the total assembly weights for all of the pistons we have worked with so far:

JE 444cc: 147.6g
OE VFR: 133.4g
OE RVF: 133.3g
REC 57mm: 127.6g
CP 57mm: 119.5g
Cosworth: 118.0g
HRC 55mm: 117.2g

Mike Norman
G-Force Engine Development