Who's Running the Super Rat?

I have a little experience with that vendor, and some experience with another Canadian vendor with the same catalog. as far as I knew they only sold Grubee Skyhawk motors, but I guess the top end is probably identical.

the top end in your pics looks identical to the one on my Skyhawk though, same hardware too. My engine doesn't have the fancy ignition though, so I can;t give you any feedback on that (I would also like to hear from anyone with that though, sounds like a good idea too me, if they work)

My motor is really strong but most of the hardware it came with is crap though, needs a decent set of bolts before you can really use it. other than that it ran nice, but runs great with new plug, boot, and carburetor.

That is the high pin piston and its for a 38mm stroke long rod geometry... it'll work on the gt5 engines and the super rat is a gt5 based engine with the main difference being the wider intake bolt spacing and the cdi and ignition coil are built into the magneto coil. This is a very nice design for a really clean looking install but the internal cdi is notorious for failing.
Id like to build up a super rat but would want to have a reliable source for spare cdi units before getting one of these engines. If the cdi unit problems have been resolved then this would be a great engine to base a build on.

allen standley said:

internal cdi is notorious for failing. Thanks Dave! considering a short stroke bottom purchase. Just that this Top end trim and finish looks so nice. For now back in the box.
Anyone else?

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get a 38mm stroke lower from dax and you'll basically have a "Super Rat" main differences being the rat motor use 6203 main bearings and has the internal cdi that cant take the heat from the engine for long.

MZmiami has some pics of a bike with a genuine rat motor that has wide vent slots cut into mag cover and a small flywheel fan, may help add life to the cdi unit by allowing heat out instead on it being trapped under that cover.

But honestly Id just get a dax lower, build it up well and it will probably out perform the "Super Rat"

just my opinion, not claiming the gospel truth on any of this.

allen standley said:

Yup, that's exactly what I'm gonna do with it Map.

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Sounds like a great plan, hope you'll share pics and/or info as you get it together.

I agree... The Super rat is a really nice idea for a really clean looking install, but the CDI located where it's at it really isn't worth it if it goes out all the time.
I was going to build one once I saw I could get spare ignition parts for them but decided against it because of the Texas heat combined with the engine heat, even putting vents to keep things cool wouldn't help much...

Hey Guys the Super Rat is a 40mm engine.

Yes I've got one, I just need to figure out the transmission

Sounds like you will need to make a spacer for the base to raise the jug, this will put the piston back below the deck or at least flush with the deck as well as raise the ports so they'll be a lot more open at BDC... Personally I really don't worry about how far open they are at BDC as much as what crank degree they start to open at... More port duration makes for a screamer of an engine if not done too excessively...

Basically when setting up a jug with a spacer it's best done with a degree wheel so you can record where the ports begin to open and from there you can figure out the exhaust, inlet, and transfer duration so you can set up the engine to make lots of power up top without overdoing it and killing off your low end power. Once this is done you can install the right thickness spacer then measure how far from the deck your piston is if it's below the deck, then shave off just the right amount to set your compression ratio and squish clearance.
Then for porting you shouldn't have to raise the exhaust or transfer roofs, but you can clean up the ports and widen them to fit your setup. The intake floor can be lowered to compensate or the bottom of the skirt on the intake side can be raised which does the same as lowering the intake floor to set your intake duration, which needs to be set on the conservative side if you plan on staying piston port.
There's some good power improvements to be had by raising your jug, but you'll need to take the measurements to know how thick of a spacer to make.

I think you have a GT5A jug. It has a 40mm intake spacing but is 1mm shorter than the GT5SR Super Rats jug. I seem to have read that there is a crank with 115mm rod length, I think it was Dax. My 38mm GT5 type engine has a 114mm rod and uses the high pin piston. If what I am thinking is true a GT5A jug on a Dax 40mm bottom end would having a piston that is 2mm proud of the cylinder. Or I could be totally wrong!!?

Same thing happened to me when I built up mine, I made the mistake of thinking all these kits were the same when I bought my first kit and my bottom end lasted a whopping 90 minutes of run time before I noticed a critical problem that would have destroyed it in short order but I already spent a lot of time porting my jug and getting it just right so instead of starting over I got a Dax f80 bottomnend and my piston stuck out past the deck a little over a milimeter. This was after I milled the deck and base to get everything just right on the old bottom end.
Got a new jug from BGF on ebay and the ports were tiny and slanted... not wanting to deal with a LOT of cutting to make that jug perform I opted to raise the original one by making a .040" thick spacer and sandwiching it between a set of. 025" thick copper base gaskets to set the piston back where it needed to be in the cylinder.
I learned my lesson there and it took a little extra work but I ended up with a great engine and also gained quite a bit more rpm on top since the Dax lower was balanced so well. Found out later on that there are different rod lengths both for the 38 and 40 mm stroke bottom ends and this is why I ran into these problems, but I learned from it and still ended up with a really nice screamer of an engine.
I am planning another engine build really soon and gathering parts so I can get it all put together in the next week or so. I hadn't been paying a lot of attention to some of the latest engine geometries but I'll definitely check up on all this before I buy the top end parts...

cannonball2 said:

Hey Guys the Super Rat is a 40mm engine.

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Nope its a 38mm stroke engine take a look at the chart again, clearly says 47mm bore 38mm stroke.

Are we talking about the intake stud spacing or are we talking about engine stroke?

mapbike said:

Nope its a 38mm stroke engine take a look at the chart again, clearly says 47mm bore 38mm stroke.

Are we talking about the intake stud spacing or are we talking about engine stroke?

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Im a little confused by this statement Map.
The chart on the extreme left lists the Super Rat/Super Mouse as having a stroke of 39.8mm.

Intrepid Wheelwoman said:

Yes I've got one, I just need to figure out the transmission

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I think thats the the Super Mouse, the Super Rat uses a bigger tread mill.

Hers some info folks. I have learned more about engine specs from the Grubee site than anywhere else. I believe I posted a link in the other Grubee thread and encouraged reading through the engine sections.
Heres some more info.
Notice the cranks pic shows what appears to be the ZAF80 rod that would indicate the 40mm crank. Notice how nicely finished it is. the rod also has 23 rollers and deep oiling slots.
Look in the exploded engine pic at the large counter weights. This is similar to a half breed crank. Notice also the low pin piston!
Pic three jug dimensions
Map pic four is for you, another indication of the SR/SM 40mm stroke.

cannonball2 said:

Im a little confused by this statement Map.
The chart on the extreme left lists the Super Rat/Super Mouse as having a stroke of 39.8mm.

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Yep Im the one who screwed up.... You're right, it does say 39.8mm stroke which is basically 40mm, I was looking at the wrong line.....duh!.....sorry about that......got in a hurry and wasnt paying attention.