Boost port hole in piston

MURDER YAMAHA

MURDER YAMAHA

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I have new Bender 835 Viper pistons for my big bore.
They have no hole in them yet.
Stock Viper hole size is 3/8" roughly.
Justin Fuller said to make a 1/2" hole in the stock location.
So, since the new hole is bigger, do I need to worry about keeping
the bottom of the hole no lower than the stock hole ?
Will it mess up port timing ?
 
PM sent! I apologize as all I have at home right now is a mechanics rule so here goes... from the top of piston crown down to the top of the port hole is 7/8". From the top of the piston crown to the bottom of the port hole is 1 3/8". Centre of port hole to edge of piston crown on each piston appears to be 1 5/32". So, yes, the port hole is now 1/2" as opposed to 15/32" of the stock port size. Hope this helps! Keep me posted on your build!
 
Thanks for the measurements !

Mac, are you suggesting making bigger ports in the pistons like you show in the pic ?
Or just a standard hole like the piston in the back left ?
 
yes use a bridgeport milling machine. Make the piston boost hole the exact same size rectangular positioned perfectly as the transfer boost port to maximize flow. Its simple port matching. It makes no sense to create a round hole in front of a square port.
---mac---
 
Had Mr. Viper port my red head, and his boost port is not like that either, More like an up and down cylinder shape, not near that width, but almost up to the piston ring land.
 
I simply posted the rough measurements from the BB 835 piston I have on hand. I'm sure other modifications can be made for even more performance. Mac, are the modifies pistons shown in the pic a representation of a 780 Viper motor?
 
yes for Viper cylinders. The idea should work for any piston boost hole.

Piston boost ports are a great idea for piston cooling and power increase. Works like this. When the piston drops..... the crank case pressure builds. All the transfer ports begin to flow fuel. The pressure charge flows out the piston hole in the back of the piston and up into the chamber. That fuel movement of fuel charge past the underside of the piston crown removes some heat from this area. This Increase of transfer port and and extra flow can help to increase power and reduce heat.

I don't have data to support HP increase. Im just thinking more is better. More fuel flowing more cooling more power.
 
That does make sense, but not something I can do in my garage without fear of wrecking the pistons.
May have to just go with the hole.
 
I agree you cant port the piston with hand tools in your garage. I machinist and a bridgeport milling machine is required. I do think its worth the expense and the extra time to complete because cooling of the pistons is a hugh benefit. The Viper could barely cool itself stock. Then add 50 -70 extra HP and it runs hot. You just cant make HP without creating extra heat. Running hot is the enemy of any aluminum engine. Its a different story with cast iron blocks so please never compare.

Do you run a temp sensor in line measuring coolant from the head?
I was boiling coolant out of my big bore more times than i could count.
Many many pistons. The piston skirts finally collapse several thousandths. The piston rocks in the bore. Failure.
I was breaking the cylinder skirts. Pushing skirts through the block. The fun never ended until radiator install.
I couldn't control heat until i added a go cart radiator. Sled now runs 155 to max 160 ish. I shared my install writeup many years ago here on TY.
---mac---

TY.piston center drilled.jpg
 
yes SRX exchanger. Its one of the first mods to my new sled back then. Could barely cool itself bone stock in 2002. There was lots of discussion about hot Vipers back 17-18 years ago. With your 835 mod - all the expense - and install time - at least put the aluminum tee inline with digital gauge between the head and thermostat and see how your sled responds to the heat. Enjoy.
---mac--

https://youtu.be/UbJFIDckE7U
 
For the boost port hole in the piston to really do anything positively HP wise, it needs to be raised to get the correct timing with the rear boost port on the cylinder. You may have to adjust the height of the rear boost port on the cylinder (I won't say which way) to get it to work properly with the modified boost port hole in the piston, which can be widened as well. If you need someone to machine the boost port holes and modify the rear boost port on the cylinders for you, I can do that. I'm a machinist, so doing the piston mods is no biggie. Done it numerous times before, as well as port cylinders with my cc speciaties tools.
 
Mac, do you have a link to your old post about the go cart radiator?

I’m getting more confused about the hole....
Justin Fuller said to just make a 1/2” hole in the stock viper location.
Others have good points about making bigger holes.
I’m sure a bigger hole would be better, but I don’t know where to put them, or have the tools to do it...
Not sure what to do...
 
I have no idea if the old post would be available. I would think the server has limitations for storage and old stuff may be missing.

Im holding a cylinder in my hand and sliding a piston up and down and thinking about port timing and the piston hole purpose. I'm thinking that hole has more to to with lubrication of the wrist pin and cooling the bottom side of the piston than it has to do with HP. I would think widening the piston hole to match the transfer port width would be beneficial. Raising or lowering the hole port timing.... i don't know. And for the love of Pete don't touch the cylinder transfer port at all.
On disassembly of several overheated motors my wrist pin bearings were blue and may have benefited from extra lube.
PM Mr Viper.
 
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I think Mr. Viper is back to working lots of hours again. No response from emails. Either that or he has had his fill of me already. Lol
I may just do the safe route, and do the 1/2' hole that Justin Fuller recommended, as I know that will wreck nothing.
These pistons are getting to be super rare, so really don't want any trouble.
 
As I stated, that is exactly how all my BB 835 pistons are set up. You will be safe and if you want to try something in the future you can modify accordingly!
 
Cool video Mac !
That radiator is B I G !! lol

northern srx, have you had any heat related failures ?
any BB info you wanna share as far as jetting or clutching goes ?
 
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