Torquer

I’d like some thought regarding both of these engines for a Miss Vegas.

O.S. 18 TZ
1.8ps @ 29k
7.8 oz

O.S. 21 RG
1.7 @ 28k.
11.18 oz


It would appear that they both have about the same power output but the 21 weight is 43% heavier.

Would it be safe to assume that the 21 being the larger bore and stroke engine would turn out more torque and would allow for the use of a larger prop? Would the weight difference be a key advantage for the 18? What are some other things to consider?

I understand that power numbers are all relative, but I believe that both engines coming from the same company would share a very similar testing environment and condition.

BB Modss

Here is the real debate, are the numbers true corrected numbers? the .21 will make more torque but less RPM's,the .18 will make more RPM's but less torque,Rotational mass will determine the engines ability to move the drivetrain to a certain point with XX amount of weight being pushed.Truth is the .21 will leave you with more options to run hotter fuel and make more mods to produce more power. So what do you really want out of the engine?

wave waker

what i saw from engine spec. the os .21 rg rated 1.9 @ 30,000....yes, power to wt. ratio matters...i'l still pick the .21.

sleepy306

My Feedback: (1)

I'd pick the 21 over the 18 for performance. But for ease of installation, you can drop an 18 in with no problems and gain a few mphs. If you are going to the tz, keep in mind that the header is longer than the stock aquacraft 18 side exhaust header. I'm using an mac 3.5 airplane muffler I got off ebay for cheap. I had to cut a large amount of it off to get to where I want to be. I could estimate I cut a good, 3 to 4 inches of the front. Using a Tape measure from the glow plug, following the 180 curve of the header, to the widest part of the muffler, is about ~ 7 inches.
I use a m435/3 balanced and sharpened by twisted liquid race. the set up is good for approx high 30's/low 40's. It runs solid through the turns and the straights. Very solid runs. I have an x437/3 balanced by a guy on ebay (dasboata). Without touching a thing from the m435 set up, the 437/3 picks up may be 2 -3 mph, but in turns, it falls off the pipe and takes a good 15yds to get back on the pipe in the straights. I probably need to lengthing the pipe length but ran out of time.
I also just installed a grim turn fin and a sullivans 6 oz tank. Everything else is stock.

I actually ran today and everyone at my local pond was very impressed with this rtr. VERY impressed. These are guys who pilot the 55+mph gas and nitro boats. At the end of my runs, the majority was very interested in seeing the vegas with a 21. Only thing is, for a 21, you'll need to fabricate engine mounts, upgrade the flex shaft to 3/16 also the strut. It is a lot of work relative to the drop in aspect of the os 18.

Just my 2 cents.

Let us know what you decide and post a video. I don't have one. When I bring my camera, I end up being the only one there. When I don't bring my camera, everyone is there. Gotta' luv the law of murphy.

ron

misshydro

Hay sleepy!! get a different.18.I saw some have the higher rpms at 40.000 and there different .21 have 2.5 hp and top out at 40.000 rpms.Why go with the O.S motors?

sleepy306

My Feedback: (1)

Which ones? I picked the os since it had the regular shaft. A lot of others have sg shafts used with clutches. I'm not sure if those will work with the hardware. I'm not to excited about the short thread area on the sg's shaft either. How's your 21 coming along?

Torquer

Good points…

I totally agree that the listed power numbers are not absolute. There’s a dozen factors to consider when producing numbers…fuel, air, temp, carb settings, and so on… Another thought is that both engines in question are from O.S. and would lead me to believe that both engines would probably be tested in similar environments. So it’d be safe to say that these are “ball park figures” which would put both of these engines in the same “ball park” power wise but with different design considerations.

The reason for comparing these two specific engines if the fact that they share common denominators…power, price, popular, and both are sport engines from the same manufacturer. Yes, there are many other engines that are superior to these, but I’m just wondering about the variables between these two very popular and inexpensive engines from the same manufacturer.

I guess a good analogy would be…

Jerry Dunlap tosses in his tuned and proped 18 TZ Miss Vegas into the pond at the same time his twin brother Jerry Dunlap II tosses in his tuned and proped 21 RG Miss Vegas. They’re now going at it. Either have an engine advantage? Why?

Jerry Dunlap

Jerry Dunlap and his twin brother Jerry Dunlap II have built Vegas hydros with a 18 TZ and an O.S. VZM 21(which is a much stronger engine than the 21 RG). So, it's kinda like comparing apples to oranges(what ever that comparison means). JD II's VZM 21 Vegas was noticably faster than JD's 18 TZ Vegas - but that would be expected. However, JDII believes a 21 RG powered Vegas would probably be faster than the 18 TZ Vegas because you could swing a bigger prop.

JD & JDII

BB Modss

BB thinks He needs to build a very special limited edition set of his .26 sportwerks and let the JD's see how they like 4hp on 65% nitro spinning 42k rpm's and easy to tune.

Jerry Dunlap

Unless the .26 would fit the same engine mount at the AquaCraft 18, JD doesn't have a Vegas to to try it in. However, JD does have a Sport 20 that would accept an engine with a 21 mount pattern.

JD

misshydro

Hay dont forget me BBmodSS I will be getting a .26 stort work motor and it will be at your door steps for 4hp and 42.000 rpm mod to do!! I only conserned is how much do it weigh?Rember these boat are very sencitve to add weigh changes!! I'd just won a thundertiger pro.21 for 36 dollars and a erwin .21 tune pipe for 35 dollars on ebay today.Thundertigers have a2.1 hp and rpms at 38.000.Sleepy306 the a VX.18 that has that power that I'd told you about.I'm going to check on other motors too and let you know on other high power.18s. Oh guys get ready,I'll be posting the New Miss Blueangel shortly!!in a day or two!! She looks awsome!! BBmodSS that the boat I need that power house in!!She's alittle heavy,about 5 1/2 pounds with a.21 in it so I need somthing to realy move her!![>:]

BB Modss

Ok e have to stop talking in 3rd person, Misshydro the weight of my engine is so close to that of a OS .21 it wont hurt a bit, though i can say now that we might have a problem, i got my boat on the water today and after 2 fast throttle rips i twisted the 3/16 cable in half....JD the .26 sportwerks will fit in that boat of yours with only a few changes, mount the motor mounts and move the engine back just a hair and run the screws back into the stringers.If you need i have a flat mount ready for the engine.

misshydro

Now that scare me abit! Holy cow that raw power!!!LOL Was that the.26 sportworks in the vegas!!If I put that in my Miss Blueangel I should be all right.Its the stock strait shaft.[8D] I would like to run that in my Miss Bud flex drive hull.But that might/would rip the stock flex cabel that is 5/32.Proboat was tell me that it was 3/32 and I'd told them they better recheck that!!The tech told me that this cabel was the same size that in the shockwave and cat that runs the.32 in them,So the cabel collectrer from the.32 should fit the.21-32 bigblock!!

cwaterhunter

hey you beat my bid on both of them lol... also that guy with the pipe has a mac i was bidding on and he removed it,,,, i hate it when that happens lol

misshydro

Whats your ebay name you go by?Mine is 6217anna! Yes I was going to bid on that pipe to and he'd took that down.I'd won a realy fast computer yesterday.I'd used the libarys computer on the thundertiger and used my nabors computer on the tune pipe.My nabor computer is realy fast and he'd said my new computer is faster then his!!