Group Buy - Honda 400cc +1mm pistons -

[racesupplies]

I dont know mate,suppose it depends what else you are doing to it.I want a set of 1mm over,slightly higher dome ones for my 29,my mate is building his RVF with 57mm for a road bike.The 29 should be mid to upper seventies,I have one that made that on RLRs dyno.I want to rebuild a spare for the Manx.

[Drunkn Munky]

Well i have one of ABR's old bikes, engines makes 74bhp currently. As theres quite a bit of interest in these oversized pistons i thought id get the low down on them, if i could get 80+ with the pistons then happy days and id consider putting an order in.

[CMSMJ1]

Howdo all...not been too well this last few days so not been checking my work email.

Got one from them - check out omegapistons.com
I'm not sure how the varying sizes for these will count towards a group buy discount. I guess it depends if people want these for racing or for a bigger bore road motor?

you work it out

Pi x 2.75^2 = cross section of piston
times the stroke 4.2cm
times 4 cylinders

equals 398.9cm^2

So...
56mm = 413.6
57mm = 428.5
57.5mm = 436

If you recall the G force details - they had issues with the liners in the blocks being straight and so went to 57mm - they also had +3mm conrods too...

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

[racesupplies]

If they are like the K4 ones they did for me they will be a lot lighter.Cant remember what the K4 was to start with,but their piston made it 350 from 320 or something.Because they are forged slugs of ally,there was less material,and slipper instead of full skirt.We raised the revs by 2000,and later after we moved on to other things heard others were running even more.Didnt they give you weights? I can get longer rods if you want them,lots of money though.I was reading the other thread about the Carrillos.They work out a bit cheaper,and less if you want to buy several.Arrow are the people that I know,again used them before.

[ScottieDucati]

So with 57mm what becomes of the liners? Would you need new cylinders or bore out, removing the liner, and then go with a coating process?

I can go either way as far as bore, mine is a track day bike and will not see racing... in my mind, the biggest bore that's *safe* is the way to go.. for torque and rideability.

Howdo all...not been too well this last few days so not been checking my work email.

Got one from them - check out omegapistons.com
I'm not sure how the varying sizes for these will count towards a group buy discount. I guess it depends if people want these for racing or for a bigger bore road motor?

you work it out

Pi x 2.75^2 = cross section of piston
times the stroke 4.2cm
times 4 cylinders

equals 398.9cm^2

So...
56mm = 413.6
57mm = 428.5
57.5mm = 436

If you recall the G force details - they had issues with the liners in the blocks being straight and so went to 57mm - they also had +3mm conrods too...

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

[racesupplies]

I dont know how far you can bore it,I dont know much about V4s.Dont forget by increasing the cylinder volume increases the compression ratio as well.Rick told me the liners are thinner at the ends,all I know.

[speedsiren]

Apparently, just found out that 0.1 mm isnt enough for mine either - so may need to exclude me from this initial buy

[racesupplies]

They are available as 55 56 57mm you are on 55mm,or were. 0.1 is about 4 thousandths of an inch,1mm is nearly forty if you are trying to work out what to bore to clear bore damage.A good late 400 engine that comes from a good source would be the easiest by far.

[mlohmeyer]

What are they supplying for rings? They must be a standard off the shelf item because custom rings are really expensive unless you are buying thousands of them. It's surprising to see the price _includes_ rings.

Re: boring out cylinders... Yes, a 58mm bore started to cut into the cylinder walls too much, not leaving enough cylinder sleeve to make us comfortable. It works on some engine cases, but you are depending on how centered the cylinder sleeve is when Honda made the case. If the sleeve is offset too much, you can't safely bore to 58mm. My oldest 450cc engine (using 57mm pistons and 2.5mm longer stroke) has re-sleeved bores because of this, but most our motors have been bored out to 57mm using the original sleeves. A 56mm piston/bore should have no problems with this.

When you bore you cylinders, you have the pistons in hand so they can match the bores with the piston diameter. They aren't going to be exactly 56.000mm. You need the final specs from the piston company, and then give those specs (or the actual pistons) to the company that bores out your cylinders. Piston to cylinder clearance is important to check on custom pistons. Get it wrong, and you'll seize the pistons. The piston company should be able to help you with this because they know their material and it's expansion (due to heat) characteristics.

Be careful "adding a touch more crown" to the piston. This isn't trivial stuff. If the piston company doesn't do their homework, you'll have valves smashing into your pistons. With any custom piston, make sure you clay it to check clearances, even if they are supposedly stock compression.

FYI, 58mm is about 444cc. You can do 58mm, but I would plan on re-sleeving the cylinders.

[racesupplies]

I was going to Clay it to check the squish,have the pockets with same valve clearances as everybody elses but check it with the cam I have as I dont know what the lift is till we dial it.By more crown I meant more material left on the very top of the piston,not overall.Then measure the cc af the chamber at TDC after optimising squish.If the ratio is over 13.5-1 remove from the top,does that make sense? Stop if I am barking up the wrong tree.but I want to get the compression up more than standard RVF crowns will go to.We were going to take a mould of the chamber at TDC with silicone to see where to remove the extra.Would adding it to the top slow the flame path?I havent taken a cast yet,so I am guessing.But I can remove metal if they left some on.