So Johnny what kind of 175 do I want and why? (ie: what do you run and why please?)
Do you have photo's of each so when shopping on ebay I can see the tell tale signs... what year make and models fit into the class??
Hey...somebody post pics of a slant and vert...it's late and I'm too tired to scan the Honda book.
Ok....here we gooooo..
First of all I think the vert is a marginally better engine. Without a doubt the cylinderhead and cylinder is better (more on that later). The vert crankcase seem to be more rigid despite the fact it's not used as a stressed frame element like the sloper.
The main advantage to the sloper engine is this.....it allows you to use a sloper frame...a whopping 11 pounds lighter than the vert frame. That's easily 1 hp. Next...it's a better looking engine. And...in some clubs it's a more legal engine being first produced in late 1967 (in the 175 version).
The down side to the sloper is that it's getting hard to come buy...they only made a 5 speed sloper 175 for about 18 months. The later models being the best..with a beefier rear mount and an extra case bolt back by the kick start hole to prevent leaks and case splitting by people that engage the kick starter while the engine is running.
I think a stock vert frame handles a bit better than a sloper...I've had substantial on track experience with both. However the sloper chassis can be strengthened with some minor work and the weight advantage is more important. The sloper chassis is more adaptable to various tanks and seats, and is mostly tubular where the vert frame is mostly stamped steel.
The sloper engine will need to have a vert cylinderhead and cylinder installed. The vert head has considerably better port design on both intake and exhaust and more extensive cooling fins. A vert cylinder should be used because it also has more cooling fin area. Basically the ideal engine is a 68-69 CL175 sloper, five speed, with vert head and cylinder, sloper head cover, CB160 bronze bushed cam bearings, SL350 K1 24mm carbs or NEW Keihin PE24 race carbs, 2-1 exhaust, megacycle 122-20 camshaft (or milder), suitable valve springs (sorry can't give away the secret valve spring to use) but RD springs will do for basic race engine. Don't go crazy with porting cause it won't do much without larger valves. As for pistons...well, I'll be honest, unless you are Rossi you aren't going to beat a bike that's using my pistons...not that my pistons are that good...it's just that the other stuff that is out there is total crap. You'd probably be better off with 1mm oversize stock pistons.
You can use vert crankshafts, vert gear clusters (except some of the shift drum and rachet parts). The vert crank is actually a couple oz lighter than the sloper cranks. Stock oil system on the sloper is suitable with some very minor modification and good maintainence. Synthetic is a must...I recommend a ester based synthetic like Redline, or a quality normal synthetic like Royal Purple...it DOES make a difference keeping these engine alive.
Sloper engines are easy to spot, the cylinders are slanted forward at 30 degrees, the left side engine cover has TWO bolts on the front of the starter mount area...the vert has ONE bolt and is more pointy there. The ONLY five speed sloper 175 made was the CL175 in 68-69, actual production started in 67 and official release date was 1/1/68 but I have found examples with 1967 dates.
I run an early production CL175 lower end with vert top end, in a CL160 frame (1965 I think). All sloper 175's will fit into all sloper frames EXCEPT the CA160(CD175?) single carb model that only had a one bolt top engine mount. My wife runs a late CL175 engine in a CB160 frame. The ideal frame is a CL175 sloper frame as these has every so slightly larger frame tubes in a couple of places.
The USCRA 200gp class has an exception that allows any year CB175, including verts up to 1973. I run the sloper because of the weight and in case anyone ever starts bitching about verts being technically non period. I didn't want to invest a ton of time and money, only to start winning and have someone try to say the bike was post period. It's a moot point...as it would be difficult to get a vert down to the weight necessary to make it a class winner.
The upside to the vert is...like I said, it's handling and I think the engine is a bit more durable in design. Also parts are VERY easy to come by for the vert. A clever person could build a custom chassis for a vert and have a quick bike that is very easy to get parts for. I considered that...but after realizing that the sloper frame is already 11 pounds lighter...why build a custom frame when a 21 pound frame is readily available? The sloper is without a doubt the nicer looking of the two bikes.
One warning....if you see a sloper 175 engine on ebay you will probably be bidding against me.... AS OF NOW I CLAIM DIBS ON ALL EBAY SLOPER 175's FROM THIS POINT HENCE TO A POINT 100 YEARS IN THE FUTURE!!!
Actually...I've heard of more than a few sloper 175's at various vintage salvage yards in the northeast. But those bastards usually get about $300 for an engine. I've got one spare at the moment...I'd like about three.
PS. CL175's were made in both sloper and vert models.
CB175's were only made in the vert model.
All CL/CB 175's are five speeds (both sloper and vert).
ALL CB160's are sloper four speeds
ALL CA's were single carb four speeds (both vert and sloper)
There were CD models sold in Europe...not sure of the details on those