Question about Big Bores and their resulting performance

[IchWarriorMkII]

I've asked in the past about big bored 460's and what not, In my hunt for more power as I feel that I need it (Boredom) and then talk myself out of it (Balance the checkbook) and I've heard mixed reviews on the Big Bore saws.

At altitude they seem to work less that ideal. Might be an issue for me...

Without a port job, they don't work all that great.
I would definately send it to a builder to get a port job, mostly aimed at more torque.

Now for the question part, do the big bore jugs add more low end grunt to saws (vs. original displacement) specifically, or is it top end power... or just power all around?

In terms of Stihl, they offer the same displacement as the next size larger of saws (440>460 460>660) and on that scale, do they offer less torque than the next larger size saw, or just less power all around?



Im just curious on the fundamentals of this whole concept... because I don't have near enough money to test myself. If I had... I'd need a 460 ported, 460bb ported and a 660... hmmmm

....If I sell the truck...

 

[ropensaddle]

I don't know on the stihl but a husky 372 the big bore worked
great but I muffler modded and slight porting has power I have
a 28 inch bar and it pulls it fine and when I put 24 inch pulls
also over all I am happy with the change. The saw stock was
great but the extra power in a same size saw is awesome.

 

[sawinredneck]

An unported BB on a 460 is like kissing you're sister, you wont be happy. I have heard that a good port job on a stock saw will outrun a BB. I don't know, but an very happy with my BB 046, I couldn't ask for more from that saw. Doesn't help much I know, but I don't think you will be unhappy with a BB 460.

 

[IchWarriorMkII]

An unported BB on a 460 is like kissing you're sister, you wont be happy. I have heard that a good port job on a stock saw will outrun a BB. I don't know, but an very happy with my BB 046, I couldn't ask for more from that saw. Doesn't help much I know, but I don't think you will be unhappy with a BB 460.

I had you in mind when I was thinking about this!

You post very good reviews for the BB460... running something like a 32" bar with full comp?

What elevation are you? I wonder if you are low enough the BB is making useful gains vs. BB's at altitude.

 

[sawinredneck]

I had you in mind when I was thinking about this!

You post very good reviews for the BB460... running something like a 32" bar with full comp?

What elevation are you? I wonder if you are low enough the BB is making useful gains vs. BB's at altitude.

Yes, I run full comp on a 32" in Hedge with no problems!! Guessing, I am at 1200'elevation. flatlands of KS ya know.

 

[IchWarriorMkII]

Yes, I run full comp on a 32" in Hedge with no problems!! Guessing, I am at 1200'elevation. flatlands of KS ya know.

Dang, I got you by almost a mile.

 

[Four Paws]

On Stihl saws, the BB kits are lackluster - especially at high elevation. You can't get the RPM's out of them that you can out of a stock jug. Stihl saws have a small base volume, and seem to suffer with the increased displacement. If you want more torque, have your stock 460 Stihl jug modified, or better yet, do it yourself.

Josh

 

[drunkenredneck]

Stick with the stocker if it's in good shape.

If your stock jug is in good shape which I bet it is then stick with it. At the high elevations in Colorado you won't gain as much with the BB as with the stock jug like what has already been said. I don't run saws at that high of elevation but I have seen more than one 046 outcut an MS660 with a 32" bar in about 28" doug fir both running brand new stihl full comp chisel chains with 8 pin sprockets. The 046s only had a milled head and domed piston with the transfers opened up the muffler triple ported, the intake widened, the exhaust widened, and some finger ports put in the cylinder.Timing was also advanced and limiter caps removed. The 660 didn't have a dual port cover.

 

[Mad Professor]

Some thoughts.......


If the saw can benifit from improved ports and/or more compression why don't the BB manufacturers do so from the factory?

I know some port jobs/comp ratios are not appropriate for work saws but I'm talking about something equivalent to a woods port job.

Secondly, for saws running high altitude it seems that increased CR would be a way to get over small air volumes somewhat. If you needed to drop CR later just add a base gasket (although this will effect port timing a bit).

Finally, I see lots of people opening up exhaust, how many hot rodded saws are also limited by intake restrictions (e.g. air filtration and/or carb too small)? Probably not as much of a problem for work saws.............

 

[romeo]

I have had the best luck with high elevation saws through transfer port work (widen them allot and raise them a little). They just have to flat be able to pull more atmosphere through them. Also, on the race saws I don't raise the exhaust port near as much as I would a low elevation saw. Exhaust numbers that work on a low elevation saw would need 7 or 8 deg. less opening on one at your elevation. You can go nuts on int/ext port width and higher compression is good.

 

[Lakeside53]

Some thoughts.......


If the saw can benifit from improved ports and/or more compression why don't the BB manufacturers do so from the factory?

I know some port jobs/comp ratios are not appropriate for work saws but I'm talking about something equivalent to a woods port job.

.

Yes, it would be a smart idea, but... Most BB I have seen are just bored-out small bores - exact copies of the orginal castings and no thought put into making it work. Makes you wonder if they've ever used or even seen the saw it runs on.

 

[romeo]

Makes you wonder if they've ever used or even seen the saw it runs on.

Probably not, I'm sure that the locally built poulans cut through the bamboo just fine without big bore kits.

 

[Lakeside53]

All they'd have to do would be to buy a "conservatively" ported BB cylinder and copy that.

 

[bcorradi]

How is the plating on the big bore cylinders? Has anyone done any machining to dome the pistons included with the big bores?

 

[Grande Dog]

Howdy,
We hear ya. When we started doing these we had long laundry list of things we would like to do. The things that became a priority were price, dependability, durability, and added torque. We took a real pounding on these originally because of some crappy piston pin clips. We replaced pile of kits on our dime. Goes to show you that the most insignificant part price-wise can end up costing you the most. The next generation that we have in the works will be adding to our dependability, durability, and hopefully a little performance also. The BB 044, and BB 046 will be the first to transition. The new kits will be nikasil coated cylinders, MsO2 coated pistons, and a brand new style of ductile v-groove piston ring. I agree that if you have a OEM top end in good shape and modded it. It would out perform the stock BB kit and you didn't have to buy materials. If you're having to purchase a new top end, I think our kits are a viable alternative to OEM. Our original goal was to get a product that was half the price of OEM, as dependable, as durable, and better bolt on power. If you were to spend the same amount of time, or money modding one of our kits compared to OEM. There is no comparison.
Gregg

 

[Goat]

MsO2????

 

[oldsaw]

Howdy,
We hear ya. When we started doing these we had long laundry list of things we would like to do. The things that became a priority were price, dependability, durability, and added torque. We took a real pounding on these originally because of some crappy piston pin clips. We replaced pile of kits on our dime. Goes to show you that the most insignificant part price-wise can end up costing you the most. The next generation that we have in the works will be adding to our dependability, durability, and hopefully a little performance also. The BB 044, and BB 046 will be the first to transition. The new kits will be nikasil coated cylinders, MsO2 coated pistons, and a brand new style of ductile v-groove piston ring. I agree that if you have a OEM top end in good shape and modded it. It would out perform the stock BB kit and you didn't have to buy materials. If you're having to purchase a new top end, I think our kits are a viable alternative to OEM. Our original goal was to get a product that was half the price of OEM, as dependable, as durable, and better bolt on power. If you were to spend the same amount of time, or money modding one of our kits compared to OEM. There is no comparison.
Gregg

Very well stated. This is the beginning of a project with some learning curve (fair assessment?), and we look forward to this next generation. This shows that you guys are the real thing. Customer service is #1. Keep up the good work.

Mark

 

[timberwolf]

I am working on a cut off head piped 372bb right now, going to be interesting to see how it does. I am thinking it will be able to smoke a ported piped 066 when its done.

 

[1953greg]

as seen from the laundry list i have a 460, 460bb, and 460 whsII. both the 460 and 460bb were modded by me to the same degree. ie, raised exhaust .020", widened exhaust and intake ports, squish .020", dual port muff. i am not good enough to alter the transfer ports so i left them alone. the only thing negative about the 460bb is i just could not get the compression up to where it ought to be. 165-170 while the oem is 185-190. physics dictate that if everything else is equal and bore is increased then compression is also increased. conclusion: cylinder has more dome in it. perhaps a wrong one but the only one i can conjure.

as for performance: the 460oem and the 460bb are neck n neck w/ the oem having a very slightly faster accleration (maybe 10%) and the bb just a little more torque (maybe 10%). as for timed cuts (18-22" oaks), times are a wash w/ each coming out on top sometimes. perhaps someone w/ more talent could produce a difference but i cannot.

as compared to the 460whsII: it will smoke either of the others by 20% maybe 25. the downfall to it is it uses 30% more fuel. compression is 200-210.

all run a 24" bar full comp chain.

bottom line: the 460bb is a viable and money saving alternative if the cylinder needs to be replaced. if oem cylinder is good then i do not hesitate sticking w/ oem.

obtw: the 385 falls bout half way between the whsII and the other two.
as for which one i use most? the oem460. why? it has half wrap handle and cost me less (bout $350) so i dont cringe as badly when something goes amiss!!!

 

[Grande Dog]

MsO2 is molybdenum di-sulfide. It's a coating that is applied to the piston to decrease friction and retain lubrication. It's used mostly in the racing industry.
Gregg