I've got some newby questions about the big cylinders from researching this and related threads.

The only 'big' cylinder I can see on the market NOW is TheBom Racing which is a 725 resleevable kit for $1800. It seems similar to the TVI cylinder ERBE has that was once offered and is the same size as the HPR 730 from calculations, roughly. They also offer the expensive Pami parts, so they seem to corner the market in quality oversize re-sleevable cylinder-kits now.

A resleeved big bore kit from Millinnium is $714, depending on how large you can bore the stock DS650 cylinders.

Questions,
1. Would the max big bore on stock jugs with Millinium just be a couple of piston over-sizes larger (690cc?)?

2. What other considerations are involved with the big cylinder kits concerning beefing up the cylinder welds, or was that just with nitrous burners?

3. Are there any other engine systems that NEED to be upgraded with bigger cylinder kit? $$$


Never considered big bores before, but seems interesting now that I know there are resleevable units available, which makes them more affordable.

Thanks and sorry for dumb questions for you smart racing guys.

 

I think Eric (MR HP) has the 730 kits on sale for $1299 in Jan.

 

<div class="FTQUOTE"><begin quote>Originally posted by: fast69
I think Eric (MR HP) has the 730 kits on sale for $1299 in Jan.</end quote></div>

Thanks, but from what I thought the posts read, was Mr HP said himself, 730 (or 725.5cc) AL sleeves would not fit into the tight cylinder design of 730 cylinder kits. Designed that one a little tight for me, but it may be good for drag racers. I dunno.

I wonder if TheBom will compete with Mr HP and sell his 725 kits for $1300? Sounds fair to me, but I ain't sellin either. I wonder who makes TheBom's 725 kits, Pami? More questions. Shoot fire, my heads spinnin now.

 

<div class="FTQUOTE"><begin quote>Originally posted by: goobds650

<div class="FTQUOTE"><begin quote>Originally posted by: fast69

I think Eric (MR HP) has the 730 kits on sale for $1299 in Jan.</end quote></div>



Thanks, but from what I thought the posts read, was Mr HP said himself, 730 (or 725.5cc) AL sleeves would not fit into the tight cylinder design of 730 cylinder kits. Designed that one a little tight for me, but it may be good for drag racers. I dunno.



I wonder if TheBom will compete with Mr HP and sell his 725 kits for $1300? Sounds fair to me, but I ain't sellin either. I wonder who makes TheBom's 725 kits, Pami? More questions. Shoot fire, my heads spinnin now.</end quote></div>


What was your previous username? I know you are bored but why hide?

 

<div class="FTQUOTE"><begin quote>Originally posted by: goobds650

Questions,

1. Would the max big bore on stock jugs with Millinium just be a couple of piston over-sizes larger (690cc?)?



2. What other considerations are involved with the big cylinder kits concerning beefing up the cylinder welds, or was that just with nitrous burners?



3. Are there any other engine systems that NEED to be upgraded with bigger cylinder kit? $$$

</end quote></div>


OK, think I've got some answers to my own questions after some more diggin.

From looking at TheBom's Pami link, it looks like 102 pistons is other stock size, like a overbore: which don't require engine block reboring like 105.5 pistons with complete new cylinder. Don't know if that's the case with TheBom's 725 kit nor with ERBE's big bore since he don't mention reboring block. 102 piston is 678cc vs 652cc with stock 100 pistons and stock 83 stroke in both, which ain't worth the cost to me unless needs overboring to begin with.

Maybe if TheBom lowers his kit to $1300 some day, I'll reconsider and ask the expert himself, TheBom. It sure sounds nice though, and ERBE's sounds like a load of fun. I envy all you guys with big cylinders.

Anyone bought one of TheBom's 725 kits yet? I haven't heard from any customers of that product yet, although pretty sure it sounds like a quality product. Looks like the TVI 720 with oversize looking cylinder bolts, but that is speculation.

 

When Building a Big Bore use TVI or the Bom studs, whatever you do replace those head studs when doing a sleeved cylinder and use Cometic Head Gasket its multi layered metal gasket.

 

<div class="FTQUOTE"><begin quote>Originally posted by: ERBEDS650

When Building a Big Bore use TVI or the Bom studs, whatever you do replace those head studs when doing a sleeved cylinder and use Cometic Head Gasket its multi layered metal gasket.</end quote></div>

So the TVI or TheBom studs keep you from boring out the block by allowing the head assembly to move up without changing the displacement? Or the heavy duty bolts are elastic and need replacing every assembly? Or both?

So it sounds like these two highly sought after big bore kits both use a unique bolting system which avoids the block reboring (?). And maybe TheBom picked up TVI's cylinder mold vendor, since the initial costs were already paid for (?).

Hmm. Shucks now, that sounds encouraging and more likely for a $1300 price adjustment, ha ha, now that he has the market cornered in ds650 big cylinder kits that are: resleevable AND don't require engline block reboring!

But maybe I'm reading what I want into it. But it does make more sense to use this type big bore cylinder, even over the high dollar Pami cylinders, if you are not racing and cost does matter. A larger reliable stock big bore is all I would want. Nothing more. And then it should last longer since it would not be stressed as much, or so my tiny head thinks.

And if you could ever find one of these jewels used, you would be done and not have to worry about buying another cylinder again. Just resleeve the cylinders instead of buying a new cylinder.

 

Best reason to use them they wont stretch as easy as stockers, keeping a better head gasket seal is all.

 

<div class="FTQUOTE"><begin quote>Originally posted by: ERBEDS650

Best reason to use them they wont stretch as easy as stockers, keeping a better head gasket seal is all.</end quote></div>


Ah so. The stock elastic head bolts require retorqueing each bolt separately, or will snap and/or will warp the head gasket interface. So the larger forces of cylinder pressures may require racing duty bolts for normal wear and tear of head bolts. Shoot, its already getting complicated. You guys must have PhD's in Motors to do this stuff, and work as good at ERBE's and SANDMAN's atvs look!

 

You guys do know that you have to torque head bolts to the point that they do stretch for the necessary clamping force, right?

The heavy duty studs are harder so they simply require more torque to stretch. This means that the harder the stud, the more torque you have to apply to get the same clamping force. The more torque you have to apply to get the proper amount of stretch to provide the necessary clamping force, the more likely you are to distort either the head or the cylinder.

The fastest, most powerful DS motors in the country use OEM studs with proper torque specs with virtually no head gasket trouble.