[Otto_Ing]

http://www.hitchcocksmotorcycles.com/news/72321//Long_stroke_crankshaft_for_500535cc_EFI_engine_including_the_GT

Really quality looking crank. They claim 35rwhp with their valve, spring and cam set for the 612cc engine.

Hope they do it with standard stroke as well.

http://www.hitchcocksmotorcycles.com/news/72322/0/Forged_alloy_piston_for_500cc_Efi_

A new piston as well, only for the 500 though.

[ace.cafe]

I hope they make a standard stroke version too.

I have had quite a bit of exposure to the 612 long stroke models, and have participated in several 612 builds for iron barrel Fireballs. In most cases, it turned out to less preferred, and indeed, several users actually took the long stroke crank out and replaced it with a normal stroke HMC crank instead.

In any case, it presents a 22.5% increase in displacement. This creates a similar percentage of demand increase for intake breathing, or else the torque curve and peak rpm points will be commensurately reduced proportionally. In other words, the bike will run out of breath at a lower rpm unless something like porting is done to overcome the issue.

So, the added displacement boosts the torque curve, and makes it peak higher and earlier, which is good. But it runs out of breath earlier, which is not so good. It depends what you want.

An interesting observation is that they get 35 hp out of it, which is in a similar neighborhood as the rest of us are also getting.  Why would that be? I'd wager that the 34mm intake tract is limiting the air intake at a certain amount in all our EFI engines, and that they are all running that 34mm OEM throttle body, and that's why we are seeing what we're seeing.
The 612 will see that 35 hp at a lower rpm than our Fireball 535, and the modded 500 at a higher rpm. All because the intake is thru a fixed 34mm orifice. Of course, there have been examples of up to 38 hp seen on dyno graphs here, but it comes down to the porting increases to help the flow do the best that it can at that 34mm MCSA, and also that the 500 demands a bit less air so it can rev a bit higher when breathing thru the same hole.

To get similar rpm range as a 500, the 612 will need a bigger throttle body and port. Without those things, the 612 will have a lower rpm limit, but with a fatter torque curve down below. We have also observed that the 612 doesn't seem to accelerate as fast up to speed, and it's just a slower revver.

Anyway, it might be just the right ticket for some riders, but not so much for others.

As for the piston, it looks nice quality,  but the stock piston seems to be fine too.

I have ideas to bring the EFI  up to greater heights, but I am afraid that the cost and the changes would not be in a category that the Enfield market would accept. For people who have the Ace head, there is plenty of upward capacity in that head to be ported for a larger throttle body or carb, and put out plenty more power and rpms.

[Otto_Ing]

The fact that MeVo's GT landed at exactly the same hp figure as mine, although I've got higher lift on the valves clearly points in my view that the horse limiting factor is the 34mm throttle body.

I'm currently investigating the cost of a throttle body rebore, if it's turns out too expensive I may give up on the entire EFI and buy a nice carb. That has the additional advantage that I won't need to bother with rev. extend.

Next week I may take apart my spare barrel and see how the sleeve looks and what the biggest bore could be that can be realized.

In my view with a light piston 7 to 7.5krpm could be achieved with the 90mm stroke. That could turn the bike in a small rocket.

[Ice]

 As you know Keihin of Japan makes the EFI. My question would then be what bikes from the big 4 use Keihin EFI with a similar but larger throttle body and where to source one second hand ?

[Otto_Ing]

EFI or Carb. personally if the EFI was not already part of the package I would have taken the carb. The EFI reaches an marginally better fuel efficiency. This is because when you shut the throttle on deceleration the EFI stops injecting fuel completely. At least the GT's EFI does that, not all EFI's do. The carb on the other hand can't be shut off entirely and some fuel will always make it's way inside the barrel. Another advantage of the EFI is that you can have different AFR ratios at different engine speeds. All this said, in reality the difference is marginal, however some people are very particular about fuel consumption. To adapt a different throttle body will definitely be more costly than to rebore it.

[ace.cafe]

If planning to do this, it would be advised to inspect for clearance under the frame and tank, and raise the angle of the intake tract as high as possible. When porting to suit, only grind at the top and sides of the port. Leave the port floor alone. In other words, try to make a raised port arrangement. Even a few mm higher at the port roof can be a big help. This will work with the steeper valve angle in the Ace head to make a more direct air flow into the deeper part of the cylinder, like the modern engines have. The 20° valve angle on the Ace head is very suited to higher port angle. The only reason I didn't do it was because I wanted to match the head to the factory intake system,  so that cost could be contained, and 34mm was okay for our expected street rev limit and power aims.  If you want 7500 rpm, use a 38mm throttle body or carb. It will give away some lower rpm torque, though.

[Otto_Ing]

I don't care much what comes below 3000rpm as I almost never ride there and I'm not one of those environmentalists to be concerned about a microgram of fuel consumption.

Space is there to rise the port somewhat for the efi, probably the abx can be adjusted too. Carb could be difficult.

The biggest issue will be to get pistons, 89 or 90.

Of course the ACE head is an awesome asset in that regard.   

[ace.cafe]

My piston company can make anything, as long as we order 4 or more. I have heard that Egli is doing 89mm. Preserving at least 4mm of cylinder wall thickness is preferred,  even if you have to sleeve to get it. You can step the sleeve to fit the hole in the engine case, if necessary.  There is no real pressure in the cylinder down near the bottom. If you have the engine apart, you can open up the case mouth to suit the sleeve O.D.
 

[Otto_Ing]

As for the piston, it looks nice quality,  but the stock piston seems to be fine too.

I'm not getting why they made the dish on it.

Than I don't get why always "forged" piston. Isn't there some casting somewhere that could be adjusted? Ok, if you make a small quantity of pistons the cost of the forging tool is probably lot less than of a pressure die cast tool and you reach break even quicker. Somehow I would think that a piston specialist company already has lot of casting's they could use and machine them to suit.

[ace.cafe]

I'm not getting why they made the dish on it.

Than I don't get why always "forged" piston. Isn't there some casting somewhere that could be adjusted? Ok, if you make a small quantity of pistons the cost of the forging tool is probably lot less than of a pressure die cast tool and you reach break even quicker. Somehow I would think that a piston specialist company already has lot of casting's they could use and machine them to suit.

I know that they have a series of forgings in incremental sizes which allows machining them down to most sizes in between. Since the forgings are denser and stronger than castings, this may be the reason why we always see that type. Not certain, but that's my guess.

Regarding the dish, I don't know why they would keep that. My design philosophy is often not similar to HMC, so I can't really imagine their thinking on this piston dish.

Anyway, it's an option for those who have some application for it.

It would be nice to have a flat top with some valve reliefs for high lift, instead of a dish. I guess we'll have to make what we want....again.

Perhaps it might be a good idea to research some automotive pistons in the bore size and pin height you have in mind, and sleeve it for that?

[Bullet Whisperer]

I had a big bore / long stroke UCE engine project in for assembly recently, but the long stroke crank was so badly made and running out so bad, the owner got a refund after I showed him how bad it was and the project stalled, but what may be of interest here is he was using forged Wiseco pistons for some sort of Harley, if that is of any use?
 B.W.

[Otto_Ing]

I had a big bore / long stroke UCE engine project in for assembly recently, but the long stroke crank was so badly made and running out so bad, the owner got a refund after I showed him how bad it was and the project stalled, but what may be of interest here is he was using forged Wiseco pistons for some sort of Harley, if that is of any use?
 B.W.

I remember seeing that clip. HD pistons will probably weigh a ton. In theory if I want to go from 6000 to 7000 rpm without increasing the load on that poor crank I will need a 24% lighter piston than what I have today. That of curse is utopia, but somewhat lighter piston would do good. Let's see, it's just a wishful thinking at present but a long winter is coming and riding season is finished.

[Bullet Whisperer]

The pistons were quite light, with a short skirt. Here is one of them - the crown height had been skimmed down by approx 1mm, apparently.
 I was asked to take that clip about the crank off youtube, by the way 
 B.W.

[Otto_Ing]

My piston company can make anything, as long as we order 4 or more. I have heard that Egli is doing 89mm. Preserving at least 4mm of cylinder wall thickness is preferred,  even if you have to sleeve to get it. You can step the sleeve to fit the hole in the engine case, if necessary.  There is no real pressure in the cylinder down near the bottom. If you have the engine apart, you can open up the case mouth to suit the sleeve O.D.

89mm can be realized in the existing sleeve and is probably the smarter choice. Regarding the piston, the valves are bit off centre on the ace head if I remember correctly, if I have that info than I can paint up the piston and we can see with some companies, I doubt that we find anything out of the shelf which is perfect fit.

The HD piston still looks heavy to me, I would estimate that we can save appx. 10% weight on the stock GT piston, that could be worth something.

[ace.cafe]

Just be advised that this 89mm piston will increase displacement by about 4.5% to 560cc,  and thus breathing demand, so it will slightly reduce the rpm at which max hp and max torque are reached. But tq will be stronger.
When you increase breathing for the bigger displacement,  then the rpm and hp should go higher.