Long rod pistons

No I don't know for sure what's safe on the stock block but I'd guess around 840 or 850. I wonder also if you can just fill that thin area in with a welder and then bore to 880. If you were wondering why mkst guys build 750s not 850s it's because the crank case came cut for 750 sleeves right from the factory. If you want to go bigger than about 81mm pistons the cut out in the case needs to be enlarged.

I don't know what the max stroke you could fit is either but I know machines up around 1000cc have been built. There are a lot of reasons not to go down that road unless you really need to. Craig Weeks has a post on here talking about the things that start to fail if you push the power much over 70 rwhp.
 
My comments about this conversion is the people that raced these 650 motors are still around---it might be worthwhile to try and get any info that you can by chasing them down for info I have been told Kenny is approchable
 
Most 840/880cc sleeves are 91mm O.D, usually it's just the bore size that is different.
Because 880 sleeves are typically 2mm thick, they can get a bit out of shape where the cylinder block breaks through into the air passage.
 
I thought I had better post some pics of my LR combo before assembly etc. There is a long way to go, setting compressions etc. I have parts on order to help complete the motor, but the cases have to be blasted and prepped and I imagine this engine could take the rest of the year as I am looking into having my own flow bench to do some head work/research for this engine., as well as having to complete the bike as well.

Photos below - enjoy (hope the uploads work out).

8 plate clutch pack

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CR500 rods bushed down to 18mm to suit customs Ross pistons.

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Ross LR piston

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Ross LR piston 01

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My LR combo incl PHF36 DellOrto's

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A big shout out has to go to Dave Rayner, as it is his piston design which he kindly gave me the order number for.
Also a big thank-you goes to Mike Mendenhall for helping me get some machining work completed & providing a forwarding address in the US.

I have decided to post the build up of my LR 750cc engine in this thread rather than start another complete thread, hopefully more photos and progress in the coming weeks.:thumbsup:
 
Damn those pistons are "SEXZY":thumbsup: I'm beginning to regret buying those KZ 900 78MM slugs. Do you happen to know the piston weight,what's the compression and would you consider PM'em the jobber #

I'm in the process of porting my L/R head at the moment,when I have the exhaust ports to my likens,I'll post a few shots here for you to drool over,like I'm doing over your pistons:D*
 
bowser said:
What is the advantage of the long rod engine? more torque i'm guessing?
Click to expand...

Has to do with piston speed and where it occurs in the stroke. Also, longer rods increase dwell at TDC. Longer rods generally work better with cylinder heads with poor intake ports. Probably the biggest single advantage is being able to use a piston with a pin that sits higher up, allowing for a (much?) lighter piston.

Or you could do what Smokey Yunick says to do, 'stick the longest rod you can in the engine'.

Usually dirt track car and motorcycle racers argue over rod/stroke ratios. Road racers and drag racers usually just jam in the longest rod they can in.


Nice build!
 
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Component weight below -

Yamaha 75mm 650cc std bore
Piston 268g
LE pin 84g
Ring set 20g
BE pin 268g
Rod 276
Total 916g

Ross 80mm 750cc LR combo
Piston 298g
LE pin 65g
Ring set 21g
BE pin 240g (if hollow cr500 pin used)
Rod 340g
Total 964g

Regards.
 
HD,thanks for the stats. In the beginning when I began fooling with XS heads,they were flowed on 110 and that data was factored over to SF600 and out of curiosity I wanted to see how accurate the conversions where,so I had a gentleman flow a few heads on actual SF600 and in comparison the #s where very close. In the end it's not the #s that are a concern but the gains or negatives is what you're looking for. I don't use any flow services when re-working the XS head now a days cuz I know what areas to address for my needs. On the L/R motor in particular when addressing the E/P's,you want to achieve
big #s in order to obtain a higher flow ratio to some what re-coop the pumping loses that occur from Mid stroke to TCD. I have a recipe thats works and that address a few of the turns,especially the outside turn of the floor from the short-side. There's nothing more gratifying that porting your own head,rather than some else collecting your green back. If you like,I could take you through the steps with dimensional stats or ship me a head with good even flow castings at the exit in the exhaust ports and on the intakes, make sure around the short turn to the seat that the cap isn't protruding,either way is fine with me but the intakes are off the public table.

The pistons you have,won't allow you to take advantage of the squish in Lilly head as it's designed for a different dome shape,this is one area where the Lilly head generates it's power.

 
Thanks Jack I appreciate your offer & I understand you have done a lot of work with these heads, certain things being "off the table" is cool with me, but I cant help asking.

The Audie flow quick retails at approx $1500 + you have to build your own bench & source a vacumn unit for it. I have been reading some of David Vizard's work & he reccomends them highly though...

At this point I have 4 x options -
1. Clean up the standard head around the bowl & seat area with your stats for the Ex port.
2. Get a F.B. & start experimenting.
3. Pull the trigger on an Lillie head, but as you have hi-lighted this head is better suited to the Venolia piston dome. (I'll have to check the photos I have of a Lillie head to compare)
4. Win the lottery & dicover a lost Axtell ported head.

Regards.


Jack said:
There's nothing more gratifying that porting your own head,rather than some else collecting your green back. If you like,I could take you through the steps with dimensional stats or ship me a head with good even flow castings at the exit in the exhaust ports and on the intakes, make sure around the short turn to the seat that the cap isn't protruding,either way is fine with me but the intakes are off the public table.

The pistons you have,won't allow you to take advantage of the squish in Lilly head as it's designed for a different dome shape,this is one area where the Lilly head generates it's power.
Click to expand...
 
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Now winning the lottery and locating a Axtell or a Branch head all in one day,now that would a spot in the genius books for sure:thumbsup: If you were to invest that amount of money in a flow bench,I'd be looking at adventuring into ideas of an investment return. The most time you'll have in an E/P would be two Hrs max plus the intakes. The keys to the exhaust ports in turning the flow in a manner and early to avoid shoving all that flow at the step lip,which would to the port going turbulent,you can hear it on the bench,another learning tool to optimizing the port into going silent. You have to increase the port volume to achieve certain goals by extensively modifying the roof by completely removing the E/P's guide boss and work the crap out of it till you turn the roof so there's a consistent and evenly flow across the roof from left to right looking from the frontal view,the right side of the port is a dead zone that needs some attention to details in speeding the air up. Just get an head flip it over looking through the bowl and try to vision what I've described by looking straight down the guide boss with almost 90% removed,along the the guide length reduced where it flush with roof. First lesson.:D
 
Thanks Jack, I will have a look in a few days as I am currently in the middle of a 5d x 12hr shift swing, when finished I will get the head out & have a look at what you have suggested.
Regards.

Jack said:
Now winning the lottery and locating a Axtell or a Branch head all in one day,now that would a spot in the genius books for sure:thumbsup: If you were to invest that amount of money in a flow bench,I'd be looking at adventuring into ideas of an investment return. The most time you'll have in an E/P would be two Hrs max plus the intakes. The keys to the exhaust ports in turning the flow in a manner and early to avoid shoving all that flow at the step lip,which would to the port going turbulent,you can hear it on the bench,another learning tool to optimizing the port into going silent. You have to increase the port volume to achieve certain goals by extensively modifying the roof by completely removing the E/P's guide boss and work the crap out of it till you turn the roof so there's a consistent and evenly flow across the roof from left to right looking from the frontal view,the right side of the port is a dead zone that needs some attention to details in speeding the air up. Just get an head flip it over looking through the bowl and try to vision what I've described by looking straight down the guide boss with almost 90% removed,along the the guide length reduced where it flush with roof. First lesson.:D
Click to expand...
 
When I decided to get the Lillie head digitally copied as the basis for a run of CNC'd reproductions, I decided to first see what the difference was between a stock head and the head that Harry had hand ported.

Using a bead-blasted, otherwise stock and unmarred head, the comparison was conducted on a SuperFlow 600 test bench within a half hour. The following table depicts the difference from stock at several lift heights:

LIFT IN EX
.050 0% +12%
.100 0% 4%
.150 +2% 3%
.200 6% 18%
.250 6% 22%
.300 9% 22%
.350 19% 27%
.400 37% 25%
.450 46% 24%
.500 56% 23%

This table enables you to use any flow bench to first run the numbers from the stock head and then compare the results of your porting efforts to the Lillie head. It also highlights the restriction inherent in the EX port, which was the primary reason the OU effort was launched.
 
Craig, thank you for the flow figures for the Lillie head, it is appreciated by me and for others to see.
I do have your performance guide & have read it cover to cover. If I do go with obtaining a bench I could only hope too acheive figures like those.
 

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